CHE 311
Syllabus
Instructor:
Dr. J. L. Lyle
Office:
NSM D-323
Phone:
(310)243-3388;243-3376
Office Hours: Will be announced in class; open door policy
email: jlyle@csudh.edu
webpage: http://chemistry.csudh.edu
Texts, etc.
Introduction to Organic Laboratory Techniques Pavia, Kriz, Lampman & Engel (required)
CRC Handbook of Chemistry and Physics (highly recommended)
Lab notebook (required)
Safety goggles (required)
1. Grading: Traditional letter grades will be assigned on the same basis as in CHE-310.
Lab reports
50%
Notebook
10%
Final Exam
25%
Evaluation
15%
2. Lab reports. A typed lab report will be required for each experiment. The report is due one
week after the scheduled completion of the lab. These reports are due at the scheduled start time
for the lab. Late reports will be penalized one letter grade for the first 24 hours. Lab reports that
are submitted more than 24 hours late will not be accepted!
Please note that lab reports are not written in the lab notebook, but are separate requirements.
You will be given explicit instructions about what each lab report is to contain. Lab reports
are to be your own work and not plagiarised from some other student or lab report. Academic
dishonesty will not be tolerated!
3. Notebook. A written record of what you are doing in the lab will be kept in your notebook.
You are expected to have your notebook with you in the lab. Failure to do so can affect your
grade. The notebook entries will be written in ink. The carbon copies that you make will be
submitted with your lab reports.
4. Final Exam. A written final exam will be given at the end of the semester. Date and location
will be announced later.
5. Evaluation. Part of your grade will be an evaluation of your lab technique, preparedness,
punctuality, etc. by the instructor.
6. Safety. You must wear approved eye protection at all times in the lab. Failure to do so will
result in expulsion from the lab.
7. Prerequisite. You must have completed both semesters of general chemistry. Corequisite is
enrolment in CHE-310.
8. Attendance. You are expected to attend all laboratory sessions. Make ups will only be
allowed if arrangements are made prior to the missed lab and for good reason. You must be
punctual in coming to the laboratory. Students who arrive late and miss the pre-lab lecture will
not be allowed to begin the experiment.
9. Course goals, objectives, and requirements are covered elsewhere in this syllabus.
CHE 311
Organic Chemistry Laboratory I
Week:
1.
Check in/ Orientation to lab
2.
Simple distillation
P. 706-713
3.
Fractional distillation
p. 733-744
4.
Extraction
p. 685-693, p.696-699
5.
Steam distillation
p.753-761
6.
Recrystallization
p. 648-663
7.
8.
9.
10.
11.
12.
"
& melting point
p. 666-674
Chromatography
p. 792-806, p.761-770
"
p. 808-823
Alkyl Halide Syntheses
p. 204-211
"
Dehydration of 4-methylcylcohexanol
p. 248-252
13.
Nitration of a halobenzene
14.
"
15.
Check out
16.
TBA
see sylabus
Final Exam
CHEM 311 ORGANIC CHEMISTRY
NOTEBOOK
Your notebook is to be with you at all times in the laboratory. This is where you record what
you have done and all of the data and obsevations that you take. Note that the lab notebook is
not the lab report. Lab reports are written separately and the carbons from your notebook are
attached to the end of the report.
Please use the following format for your lab notebook entries:
Title of experiment (be specific)
Name
Date
Unk # (if any)
A step by step description of what you did (it must contain sufficient detail so that the
experiment could be repeated by anyone reading your notes). One technique is to write in the
steps you propose to do before you get to the lab and then add additional comments and
observations as you actually do the lab.
All significant observations and measurements must be recorded directly into the notebook. Do
not record data on other sheets of paper for later transcription into the notebook!
The original (white) sheets remain attached in the notebook, the carbon copies (blue or yellow)
will be attached to your lab report.
EXPERIMENT: Simple Distillation and Determination of the Boiling Range of an unknown
organic liquid
Read p. 706-713 in your lab text!
The principal purposes of this exercise are to familiarize you with the mechanics of the
distillation technique and to permit you to observe the behavior of a single substance when it is
distilled. You may regard this to be the situation in which a new compound whose actual boiling
point is not known has just been made. You are in effect carrying out the last step of the
preparative procedure - distilling the compound to purify it and at the same time measuring its
boiling range.
You have an “unknown” organic liquid at your desk; record its number in your notebook.
Procedure
All glassware must be dry! (water is a volatile compound!)
Do not wash the glassware that is to be used for the distillation, unless it is obviously
dirty. If you do wash them, all glass parts must be thoroughly dried before the apparatus is
assembled.
Three ring stands are necessary to construct the distillation assembly described below.
Be sure that the ring stand bases face forward (toward you) and are parallel with one another.
Three clamps and one iron ring are needed. If they are available, 3-prong clamps should be used
to support the condenser and the receiver; a burette clamp is best for the still pot.
1.
Select a distilling flask of appropriate size (the still pot should be about half-full initially).
The receiver for this distillation is a graduated cylinder large enough to contain the
volume of sample you are given. Ordinarily, an Erlenmeyer or round-bottom flask, or
even the bottle in which the product is to be packaged, is used as the receiver. You use a
graduated cylinder here because you are to obtain a record of distillate volume vs. vapor
temperature.
2.
Set up the apparatus as shown on page 711 of your lab text and in the sample assembly in
the laboratory. Pay particular attention to the following points:
a.
b.
c.
Build the apparatus from the "bottom up." Begin by clamping the receiver (a
graduated cylinder) to a ring stand.
If you are using standard-taper ground-glass-joint glassware, be sure to put a thin
film of lubricant on the joint surfaces.
Arrange the assembly so that the receiver is as close to the end of the condenser as
possible. To ensure that the flow of distillate from the condenser to the receiver is
true, a bent adapter may be attached to the end of the condenser. The lower end
of the adapter should protrude into the cylinder, but should not be "jammed" into
the opening. The junction is not meant to be airtight.
d.
e.
f.
g.
h.
i.
Should you find that the receiver is too far from the end of the condenser (with or
without an adapter), raise the receiver by clamping it to the ring stand. Do not use
books, sponges, inverted beakers, etc., to support any part of the apparatus.
Make sure that the space between the flask bottom and the ring stand base below
it is sufficient to allow easy placement and removal of the heating device.
The thermometer must be perfectly vertical. If it is not, make whatever
adjustments are necessary in the angle of the condenser. If you experience any
difficulty ask your instructor for help.
The top of the thermometer bulb must be level with the bottom of the sidearm
opening of the still head.
Make certain that there are no kinks or restrictions in the rubber tubing through
which the cooling water flows to and from the condenser. The tubing must be
long enough to reach from the water source to the inlet tube of the condenser, and
from the condenser to the drain. If only short pieces are available, they may be
joined with short lengths of fire polished glass tubing or special plastic connecting
tubes.
Turn on the cooling water cautiously! If the valve if opened too quickly, the
pressure may force the rubber tubing from the condenser connection, and you and
your neighbors may get an early shower.
3.
If a heating mantle is to be used, observe the following precautions:
a.
The mantle must be of the proper size to fit exactly around the flask (unless the
heating unit is of the type that may be used for several flask sizes). The size is
usually specified on a tag attached to the mantle or the cord.
b.
The heat input is controlled by means of a variable transformer, to which the
mantle cord should be connected. Do not plug the cord directly into the line
outlet unless the mantle has a built-in variable control.
c.
The mantle should be supported by an iron ring or other suitable device (not
books!) so that it is at least several inches above the bench top and can be lowered
away from the flask when necessary. Do not rest the mantle directly on the bench
surface.
5.
Pour the liquid sample into the still pot. Use a funnel with a stem long enough to reach
past the sidearm opening.
6.
Add three or four boiling chips to the still pot.
7.
Make certain that water is flowing in the proper direction through the condenser jacket.
8.
Heat the liquid until boiling commences. Adjust the flame or transformer setting so that
gentle boiling is maintained. Apply aluminum foil insulation unless you are directed not
to do so by your instructor.
9.
Distill the liquid and follow the procedure as below.
Note the temperature when the first drop of distillate is collected. Record the temperature
when the first volume measurement in the graduated cylinder is feasible, and at intervals
of 1 or 2 mL of distillate collected thereafter.
Do not distill the liquid to dryness. Stop the distillation when a few drops remain in the
still pot.
10.
Stop the distillation by turning off the flame or the transformer. If a heating mantle was
used, lower it away from the still pot. Allow the flask to cool for a few minutes before
disassembling the apparatus.
11.
Pour the distillate and any residue in the still pot back into the bottle in which the sample
was received. Return the bottle to the place designated by your instructor.
Interpretation of Results and the Report
In addition to learning the technique of performing a distillation, you have had the
opportunity to observe at first hand the behavior of a reasonably pure compound in the
distillation process. You also measured quantities (temperatures) whose magnitudes you did not
know before-hand.
Your report (see next page) should include the following:
1.
A brief introductory discussion, in your own words, of the physical principles
involved in the distillation of a liquid.
2.
The Experimental section, in which you describe in your own words the
procedure you have carried out. A tabulation of the volume and temperature measurements must
be presented. The atmospheric pressure at the time of the distillation, if known, should be noted
as well.
3.
A brief Discussion of Results, excluding details of experimental procedures.
This part provides the interpretation of the accumulated data and other pertinent observations. A
graph of vapor temperature vs. distillate volume would be most helpful in presenting the
conclusions to be drawn from the experimental results. An indication of the relative amount of
forerun, if any, and the corresponding temperature range over which it was collected should be
cited.
The boiling range of the distillate collected in a single container must be
reported. As an example, consider the following distillation in which no forerun was collected
separately. The temperature at which the first drop was collected was 110oC. The distillation
was stopped when the still-head temperature registered 122oC. The boiling range of the
distillate in that case was therefore 110-122oC. (Note that the boiling range has a beginning
o
o
value and an end value. Thus, the range in the example is not 122 , but is 110-122 C.) If 5 mL
of forerun were collected first, and the main body of distillate (32mL) then collected from 120122oC, the 120-122oC range is the boiling range of the major portion of the liquid.
Some comment on the appearance of the liquid before and after distillation is in
order, as is any other significant observation.
Note: It is not considered good form to use the first person pronouns I or we in chemistry
reports. Instead of “I added 30 mL” , write instead “Thirty mL was added.” (Use passive voice)
CHE 311
Lab Report for Simple Distillation
Your lab report for the first experiment should follow the format and consist of the following:
Title(be specific)
name
date
section number
Unknown #
Introduction
(give a brief statement about what a simple distillation is, what it is used for and an
explanation of how it works to separate compounds. Then state concisely what is to be
done in this experiment. Do not draw the apparatus! Do not state a "purpose".)
Data
(a table of the data collected, suitably labeled)
(a graph of the data. Use mm graph paper and make the
graph professional. Do not use pages from the lab
notebook!)
Results
(a paragraph describing any observations or conclusions.)
(See previous page)
Exercises
1. In a short paragraph, describe how simple distillation separates two compounds with
different boiling points.
2. If the thermometer is placed above the outlet to the condenser, will the temperature
measured be correct? If not, will it be higher or lower than the actual vapor temperature?
3. What are boiling stones and why are they added?
4. Describe the observations that one would make during the simple distillation of an
"impure" substance.
5. What happens to the still head temperature during the simple distillation of a pure
substance.
6. At 30oC, the vapor pressures (in torr) for methanol and ethanol are 350 and 180,
respectively. Given a mixture at 30 degrees that contains 0.3 mole of methanol and 0.1 mole of
ethanol, compute the partial pressures of each liquid and the total pressure.
7. In a simple distillation, you measure a boiling range that is 110-121 degrees; How
pure do you think the liquid sample is? Explain
8. You have just completed a simple distillation and have made observations of the
temperature as the distillate is collected. How would you know whether your distillation was
successful and that the distillate is reasonably pure?
Answer the questions on Page 716 of your lab text.
Attach the carbon copies from your notebook.
EXPERIMENT: Fractional Distillation of a Two-Component Mixture
Read 733-745 in your lab text!
This exercise is intended to demonstrate the behavior of a pair of miscible liquids in a
simple distillation, and to familiarize you with the technique of fractional distillation with a
column. You will first carry out and observe the characteristics of a simple distillation of a
mixture. Then the same mixture will be distilled through a fractionating column. Please note
that the fractional distillation may not be completely effective - the column may not be efficient
enough because of the kind and amount of packing used, or because of insufficient length, and
heat losses due to inadequate insulation may contribute to less than perfect results. Since the
distillation is to be conducted using continuous takeoff (near-zero reflux ratio), the best possible
conditions for fractionation cannot be realized.
Bear in mind that the purposes of the experiment are to demonstrate the distillation
behavior of a mixture of miscible liquids and to acquaint you with the basic technique of
fractional distillation. Your goal is not to determine the boiling point of either component, nor is
it to achieve a perfect separation.
Procedure
A.
Simple Distillation of the Mixture
All glassware must be dry!
1.
2.
B.
Set up a simple distillation apparatus. Use a 250-mL flask as the still pot. A 50-mL
graduated cylinder serves as the receiver. Be sure to add boiling chips to the flask.
Distill the unknown mixture as in the previous experiment
1.
Note the still-head temperature when the first drops of distillate appear, and
record the vapor temperature at intervals of 1 or 2 mL of distillate thereafter.
2.
Continue the distillation and collection until the still pot is almost dry.
Fractional Distillation of the Mixture
1. Set up a fractional distillation apparatus by inserting a fractionating column packed
with steel wool between the still pot and the still head adapter.
2. Add a couple of fresh boiling chips to the still pot and using the liquid funnel, add the
mixture that you distilled in the simple distillation.
3. Distill the unknown mixture as in the previous experiment, noting the still-head
temperature at the first drop and every 1 or 2 mL of distillate thereafter. Continue the distillation
until the still pot is almost dry.
4.
Allow the still pot to cool. Pour the distillate and the distillation residue back
into the sample bottle. Return the bottle to the designated place in the laboratory.
5.
Disassemble the apparatus. If your fractionating column is packed with stainless
steel sponge, do not wash it with water.
Interpretation of Results and the Report
Follow the same format that was used in writing the report for the exercise on simple
distillation of a single liquid.
Of particular importance in the interpretation of your observations is a comparison of the
simple distillation of the mixture with the distillation of the same mixture through a fractionating
column. A tabulation of temperature-volume data for each distillation serves as the basis for the
construction of two graphs, one for the simple and one for the fractional distillation.
Some comment on the efficacy of the distillation using the column should be offered.
For example, the data you obtained may have indicated that the fractions collected were
mixtures, although of different composition than the original. Thus an ideal separation may not
have been achieved because of deficiencies in the apparatus (or your technique?). Some
recommendations about improvement of the fractionation assembly and conduct of the
distillation are then in order. The primary purpose of the experiment was not a determination of
the boiling points of the components, so do not dwell on the aspect of it.
Remember, too, that it is not necessary to go into great detail in either the preliminary
discussion or the Experimental section about the simple distillation procedure used in this
experiment. It is sufficient to state that the mixture was subjected to a simple distillation and to
give the results of that operation. A full account of the fractional distillation, including details of
the apparatus used, should be given since it is being reported by you for the first time.
CHE 311
Report for fractional distillation
1. As before: title (specific)
name
date
CHE 311-0x
unknown #
2. In your own words, explain how fractional distillation works to separate volatile liquids.
3. In one or two sentences, summarize what you did in this experiment.
4. Make a table of the data you collected.
5. Attach a graph (neat and professional on mm graph paper) of the still head temp. vs. volume
collected for the simple distillation. On the same graph, plot the data for the fractional
distillation in a different color.
6. Describe the results you obtained from the simple and fractional distillation. See if you can
put into words the data that you collected and the resultant graph.
7. What conclusions can you make from the results of your experiment? Compare the two
methods for efficacy. If you have an opinion, back it up with data. See previous page.
8. Answer the following questions:
a. What is Raoult’s Law?
b. What is Dalton’s Law?
c. Describe how Raoult’s and Dalton’s Laws relate to fractional distillation as a separation
technique.
d. What’s the difference between a packed column and an unpacked column a fractional
distillation?
e. What is a theoretical plate?
f. On page 735 of your lab text is a temperature composition diagram for mixtures of two
compounds, A & B.
(1) From the graph, what are the boiling points of pure A & pure B?
(2) For a mixture that contains 50 mole% A and 50 mole% B, what is the boiling point? what is
the composition of the first distillate and if this distillate were to be condensed, what at
temperature would it boil? what is the composition of the vapor at this temperature?
(3) For a boiling mixture at 60oC, what is the composition of the vapor and the composition of
the liquid?
g. At what point do you change receivers during a fractional distillation if you are trying to
separate the components?
h. What observations during a simple distillation would cause you to redo the distillation using a
fractionating column?
Answer questions 1, 4 on Page 752 of your lab text.
9. Attach notebook carbon copies.
EXTRACTION
Read p. 685-693, 696-699 in your lab text.
Extraction is a separation technique based on differences in solubilaiies of substances in
two immiscible solvents (usually water and a water insoluble organic solvent).
solubility in solvent 1
Kc = partition coefficient = ------------------------solubility in solvent 2
example: Given compound A, Kc (ether:water) = 4.0, how much of A can be extracted from a
solution of 10.0 g of A in 100 mL of water with a single portion of 100 mL of ether?
X / 100 mL ether
Kc = 4.0 = -------------------(10.0 - X) / 100 mL water
X = 8.0 grams of A extracted into the ether
-same as above, but extract two times with 50 mL of ether each time.
X / 50 mL ether
first extraction:
Kc = 4.0 =
------------------(10.0 - X) / 100 mL water
X = 6.67 grams of A extracted
second extraction: Kc = 4.0 =
Y / 50 mL ether
-----------------(3.33 - Y) / 100 mL water
Y = 2.22 grams of A extracted
total extracted = X + Y = 6.67 + 2.22 = 8.89 grams
==> multiple extractions with smaller amounts of solvent are more efficient than a single
extraction with the same total amount of solvent.
DRYING: an organic liquid that has been in contact with water is "wet" (contains some water).
To "dry" it, use an inorganic drying agent. See Table 2.1 in your lab text.
"WASHING": extraction to remove an unwanted compound.
Today's experiment:
HCl
+
CH3CH2CO2 Na ------> CH3CH2CO2H
sodium propionate
(solid)
propionic acid
(liquid)
Your unknown contains an unknown % of sodium propionate. It is not necessary to weigh the
unknown before you begin the experiment, assume that it weighs 30.0 grams. You will convert
the solid sodium propionate into propionic acid by reacting it with hydrochloric acid. Propionic
acid is both water and ether soluble, has a bp of 141 oC, and forms an azeotrope with water. To
remove the propionic acid from the aqueous solution, you will extract with three 40 mL portions
of diethyl ether. Do not throw anything away until you are absolutely certain you have kept the
right layers. After combining the three ether extracts, dry them over anhydrous magnesium
sulfate. Fractionally distill off the diethyl ether (<100oC). Then set up for simple distillation
and simple distill the propionic acid, collecting as your final product all material boiling above
135oC. Package your product and label the bottle according to instructions below. You will turn
it in with your report next week.
Note: Propionic acid is a “common” name. The IUPAC name for this compound is propanoic
acid. It will be found in the CRC handbook under its IUPAC name.
“Salting Out” The addition of NaCl to an aqueous solution containing an organic compound will
decrease the solubility of that compound in the aqueous solution. This is called “salting out.”
Apparently, the salt increases the ionic strength of the solution, making it more polar and the
weakly polar or non-polar organic compound is less soluble.
EXPERIMENT: Formation of a Water-Soluble Liquid Organic Acid and Its Extraction
from an Aqueous Solution
In this experiment, a simple reaction followed by an extraction to separate the desired
product from solution will illustrate a typical application of extraction.
Some liquid organic acids are very soluble in water. The sodium salts of these acids are
ionic solids that are also very soluble in water. If an aqueous solution of one such salt is
acidified with a strong mineral acid (e.g., hydrochloric or sulfuric acid) the weaker organic acid
is produced, as is shown in the following representative equation:
Na+ + CH3CH2CO2- + H3O+ + Cl- ---> CH3CH2CO2H + Na+ + Cl- + H2O
sodium propionate hydrochloric acid propionic acid
(AKA propanoic acid)
The organic acid is largely unionized in the water solution.
No apparent change will be observed when the reaction is carried out because the
solutions of the starting materials are colorless and the resulting solution containing the indicated
products is also colorless. The acid is completely soluble in water and, thus, does not separate.
Although propionic acid has a boiling point of 141oC, it cannot be separated from the water by
fractional distillation because the two liquids form an azeotrope (bp 99.9oC; 17.7% propionic
acid, 82.3% water). Therefore, it is necessary to resort to extraction with an organic solvent in
which the organic acid is quite soluble. After drying the organic solution, the organic solvent
may be removed by fractional distillation and the residual propionic acid purified by a simple
distillation.
You will receive about 30 g of an unknown mixture of solid salts which contains 50-90%
sodium propionate, the remainder being an inert inorganic salt.
Procedure
1.
2.
3.
4.
5.
Place all of the unknown containing sodium propionate in a 250 mL beacker.
Add 100 mL of distilled water to the beaker and stir the mixture with a glass rod.
Pour 60 mL of 6 M hydrochloric acid into the sodium salt solution, while stirring with a
glass rod.
Transfer the aqueous solution to a 250-mL separatory funnel. (Be sure that the stopcock
is closed and that a beaker is placed beneath the funnel.)
The aqueous solution is to be extracted with three 40 mL portions of diethyl ether as
follows:
a.
Add 40 mL of the solvent to the solution in the funnel. Perform the extraction.
b.
Drain the lower aqueous layer into the beaker, and pour the ether solution through
the top of the funnel into a 250-mL Erlenmeyer flask.
c.
Repeat the extraction twice more with 40 mL of diethyl ether each time.
DO NOT DISCARD ANY OF THE SOLUTIONS UNTIL YOU HAVE REACHED STEP 9.
6.
Add just enough anhydrous magnesium sulfate to the combined ether extracts to just cover
the bottom of the flask. Seal the flask with a cork stopper that does not extend more than
half its length into the flask neck. (Note: If the magnesium sulfate dissolves, you goofed!
Go back through your procedure to see where you made the error.) Swirl the contents of the
flask gently and allow the mixture to stand for at least 30 minutes. If necessary, you may let
the flask stand until the next laboratory period.
7.
Set up a fractional distillation apparatus, using a 250-mL round-bottom flask as the still pot.
The receiver is a 250-mL Erlenmeyer or round-bottom flask. Surround the receiver with a
small plastic bowl containing a mixture of ice and water.
8.
Remove the still pot from the assembly and support it on a cork ring. Place a narrow-stem
funnel in the flask neck, and insert a small plug of absorbent cotton at the top of the funnel
stem.
9.
Carefully decant the ether solution from the drying agent through the funnel into the flask.
Rinse the Erlenmeyer flask containing residual drying agent with about 10 mL of ether and
add the rinsings to the still pot. (Note: None of the drying agent should have entered the
still pot. If some did, empty the still pot into the Erlenmeyer flask, and refilter the mixture
into the round-bottom flask.)
10.
Add three or four boiling chips to the still pot and reattach the flask to the fractionating
column.
11.
Slowly distill the ether from the solution. When distillate collection slows markedly or
stops, or if the still-head temperature reaches 100C, discontinue the distillation. Do not
attempt to distill the propionic acid through the fractionating column.
12.
Allow the still pot to cool for several minutes. Then remove the fractionating column and
receiver from the assembly. Pour the ether from the receiver into the special container
labeled Recovered Ether from Extraction or Waste Organic Solvent.
Transfer the residual liquid in the still pot to a 50-mL round-bottom flask and incorporate
the smaller flask in a simple distillation assembly.
Place two or three fresh boiling chips in the still pot and start the simple distillation.
Collect as forerun any distillate obtained up to a still-head temperature of 135oC. Then
13.
14.
15.
16.
17.
18.
carefully change receivers, placing a preweighed narrow-mouth bottle in position to collect
the propionic acid.
Continue distilling the product, measuring the boiling range simultaneously. Do not distill
the liquid to dryness, but leave a very small amount in the still pot.
Reweigh the receiver plus contents to obtain the weight of the distilled propionic acid.
Label the bottle in the manner shown below.
PROPIONIC ACID
oC
wt.:
g br
Your name
Date
The Report
In addition to a discussion of the principles of simple extraction and the function of drying
agents, the Introductory section should include a statement of the problem - what you were to do.
In the Experimental section, be sure to specify the quantities of materials, as well as the
weight and boiling range of the final product. The following is an example of how this information
may be presented: "Unknown No. 12 (30.4 g) was dissolved in 100 mL of distilled water. To the
salt solution was added 30 mL of 6 M HCL, and no apparent change was observed... . A total of
13.2 g of propionic acid, br 136 - 142oC (lit., 141oC) was obtained."
In the Discussion of Results, offer a comment on the purity of the distilled acid, based on
your experimental observations. You may also calculate an approximation of the composition of
the unknown mixture. The calculation is based on the balanced equation, which indicates that 1
mole of propionic acid is obtained from 1 mole of sodium propionate.
Calculation of Approximate Composition of Unknown
The balanced equation shows that one mole of sodium propionate yields one mole of propionic
acid. From the weight of the propionic acid that you have collected, you must first calculate how
many moles of propionic acid you have. That number of moles is the number of moles of sodium
propionate that you must have started with. Convert the number of moles of sodium proionate to
grams of sodium propionate. That number, divided by the weight of the unkown, times 100% is the
approximate percent of the unknown that was sodium propionate. This number is, of course,
approximate as (a) not all of the propionic acid was necessarily extracted; (b) mechanical losses of
propionic acid were suffered during the distillation; and (c) the propionic acid obtained is not 100%
pure, and the weight of the product includes the impurity.
CHE 311
Report for Extraction; Drying Methods
1. As before:
name
date
CHE 311-0x
unknown #
2. State in a few sentences what you did in this experiment.
3. Include a table containing the following:
Weight of unknown
30.0
g
Weight of propionic acid
obtained
g
Moles of propionic acid
moles
obtained
Moles of unknown
moles
as sodium propionate
o
Boiling range of propionic acid
C
Literature value for the boiling point of
o
propionic acid
C
% sodium propionate in the original sample as
calculated based on the amount of acid
recovered
%
(note the calculation is based on the balanced
equation that indicates that 1 mole of
propionic acid is produced from 1 mole of
sodium propionate.)
4. Answer the following questions:
A. Explain the purpose of reacting the unknown with hydrochloric acid before the extractions?
B. A student made a mistake and did a single extraction with 120 ml of ether instead of three
separate extractions with 40 mL of ether each time. How will his results be affected?
C. A student added anhydrous magnesium sulfate to his combined extracts and the magnesium
sulfate dissolved. What error did the student make in the experiment? What should he do now?
D. During the second extraction, a student added ether to the layer in the separatory funnel and it
did not separate. What mistake did the student make? What should he do now?
E. How pure do you think the propionic acid is that you recovered and how do you know?
F. If, in an extraction, you were uncertain about which layer was the aqueous layer and which layer
was the organic layer, how could you quickly settle the issue?
G. Given 200 mL of an aqueous solution containing 10 g of compound A, from which it is desired
to separate A, how many grams of A could be removed in a single extraction with 200 mL of
diethyl ether? (The distribution coefficient, diethyl ether: water is 6.0).
H. How many total grams of A could be removed if two successive extractions with 100 mL each
were used in G?
Attach carbons
EXPERIMENT: Steam Distillation
Separation of a Volatile Component from a Mixture
Read p. 753-760 in your lab text!
In certain reactions, it is not feasible to remove the desired compound (or unreacted starting
material) from the mixture by simple or fractional distillation, or by other physical methods. Steam
distillation very often successfully effects the separation, and does so at a temperature considerably
below the boiling point of the compound being removed. Steam distillation is also quite useful in
the isolation of natural products.
An artificial mixture is to be steam distilled to recover one of the components. To add an
element of mystery, the sample you receive is an "unknown" in that the quantity of the recovered
compound is to be determined and reported.
The mixture to be separated is typical of that obtained in one of the methods of preparation
of compounds called haloarenes. One byproduct of the reactions is a group of compounds called
phenols. (Some other highly colored substances are present as nonvolatile contaminants.)
Separation of the product haloarene from the phenol contaminant by fractional distillation is
somewhat difficult because of the high boiling points of these compounds. Steam distillation is a
more convenient way of isolating the desired product, but a pretreatment of the reaction mixture is
necessary because the phenol is somewhat volatile and would also codistill with steam.
Fortunately, the phenol is a weak acid and the haloarene is not. Treatment of the mixture with a
solution of sodium hydroxide converts the phenol into a water-soluble, nonvolatile ionic salt, as is
shown in the following illustrative equation.
C6H5OH + Na+ + OH- ---> C6H5O- + Na+ + HOH
phenol
(acid)
base
sodium phenoxide
(salt)
The steam distillation is to be carried out using internal steam generation. The experimental
procedure involves both the separation of haloarene and an attempted verification of the principles
of steam distillation. The latter objective is effected by keeping a record of the vapor temperature
during the codistillation process.
The mixture you will receive is
Phenol (C H OH), bp=182oC + Chlorobenzene (C H Cl), bp=132oC
6 5
6 5
Procedure
1.
2.
3.
Set up a simple distillation apparatus with a 500-mL flask as the still pot and a 50-mL
graduated cylinder as the receiver.
Weigh the unknown. Place the sample in the flask using your liquid funnel, then add about
100 mL of tap water, 40 mL of 6 M NaOH, and two or three boiling chips.
Heat the contents of the flask to a vigorous boil. when distillation begins, make a record of
the vapor temperature vs. distillate volume.
4.
5.
6.
7.
Continue the distillation as long as oily material is collected. If droplets of the oil remain in
the condenser and cling to the walls they may be flushed out by the following procedure:
a.
Turn off the flow of cooling water through the condenser jacket.
b.
Remove the rubber tube from the water tap and allow the water to drain from the
condenser jacket.
c.
Reconnect the tube to the water outlet, but do not turn on the water yet. when steam
begins to issue from the lower end of the condenser, turn on the cooling water again.
If it is not apparent from the vapor-temperature readings that no more organic material is
distilling, the following test may be performed. Remove the receiver and collect a few
milliliters of the distillate in a small test tube, then replace the receiver. Examine the liquid
in the test tube for the presence of oily drops. If none appear (distillate is water only), the
distillation may be stopped.
Read the volume of organic material in the graduated cylinder as best you can and enter the
value in your notebook.
Transfer the distillate to a separatory funnel and add about 50 mL of water. Do not shake!
Allow the layers to separate, and then draw off the organic liquid and weigh it. Return the
wet organic compound to your instructor in the same container in which the unknown was
received.
The Report
A brief discussion of the basic principles of steam distillation should be followed by an
account of your observations and measurements. The Experimental section should, of course,
contain full details of the method by which you carried out the steam distillation as well as all
relevant data. The Discussion of Results should include some comment on the observed vapor
temperatures and their significance.
CHE-311
Report for Steam Distillation
1. Include the normal heading.
2. Discuss the basic principles of steam distillation.
3. State what you did in this experiment in one or two sentences; be explicit.
4. Tabulate all relevant data. Include the weight percent chlorobenzene in the unknown.
5. Discuss your data and observations. See previous page.
6. Questions:
a) What properties must a compound have in order to be steam distillable?
b) What properties do non-steam distillable compounds have?
c) What was the purpose of adding sodium hydroxide to the still pot?
d) When would you use a steam distillation as a method of separation and purification?
f) define Dalton’s Law and discuss how Dalton's Law is relevant to steam distillation.
Answer questions 1, 2, 3 on pages 760-761 of your lab text.
EXPERIMENT: Recrystallization
Read p. 648-674 in your lab text!
This experiment offers a taste of organic preparative work which includes a recrystallization
as the final step. While you have no prior experience and certainly would not, at this stage, be
expected to understand the chemistry involved in the reaction, you can carry out the preparation if
you follow directions.
The type of compound to be made is called an amide, which is formed by the reaction of an
amine with an acid anhydride (one of several ways by which an amide may be prepared). The
reaction is represented by the following general equation:
RNH + (CH CO) O ----> CH CONHR + CH CO H
2
3
2
3
3 2
amine acetic
amide
acetic
anhydride
(substituted acid
acetamide)
In the formula for the amide, the R represents any organic group and NH2 is the amine
group. The specific amide you are to prepare is a derivative of the compound acetamide
(CH3CONH2), which is but one of the many compounds in the general class of amides. Different
amides can be obtained by using different anhydrides or related reagents.
You will receive a sample of an "unknown" amine which is to be converted to the
corresponding amide following the general procedure outlined below. The product of the reaction
is then to be purified by recrystallization. Identification of the purified amide will be made by
means of the melting point and mixture-melting-point determinations.
Procedure
Note: The type of amine to be used in this experiment has a tendency to undergo oxidative
changes in storage, resulting in the formation of colored impurities. Most of the latter will be
removed during the reaction, and the final purification of the product by recrystallization should
eliminate any residual impurity.
The reaction is a relatively simple one; it requires no special apparatus and takes a relatively
short time. The acetic anhydride is added to the amine salt solution. However, the anhydride will
react only with the amine, and not with the salt that was formed by dissolving the amine in the
hydrochloric acid solution. The acidic salt must therefore be neutralized to free the amine, and this
is accomplished by adding the sodium acetate solution:
RNH2 + H3O+ + Cl- ---> RNH3+
base
acid
acid
+ Cl- + H2O
base
+
+
RNH3 + Cl + Na + C2H3O2 ------> RNH2 + HC2H3O2 + Na + Cl
acid
base
base
acid
A.
Reaction
Before carrying out the reaction, it is necessary to make up a solution that will be needed in
a later step. Dissolve 8 g of sodium acetate trihydrate (NaC2H3O2  3 H2O) in 25 mL of
water in a small beaker and set aside.
1.
2.
3.
4.
5.
6.
7.
Prepare a solution of 5 mL concentrated hydrochloric acid in 125 mL water in a 250-mL
beaker.
Weigh about 6 g of the liquid or solid amine into a 50-mL beaker. It is not necessary to
measure out exactly 6.00 g, but the actual weight used should be recorded in your notebook.
If the amine is liquid, a clean medicine dropper pipet may be used to transfer the compound
from the vial to the beaker.
Transfer the amine to a 500-mL Erlenmeyer flask. Rinse the 50-mL beaker with small
portions of the dilute hydrochloric acid you prepared, and add the rinsings to the flask. Pour
any remaining hydrochloric acid solution into the flask. Swirl the flask carefully to dissolve
the amine. Gentle warming may be necessary, and some insoluble matter may remain.
Carefully warm the solution of the amine in hydrochloric acid on a hot plate or steam bath.
Place a thermometer in the solution, and when the temperature reaches 50-55oC, remove
the flask from the heat source.
Caution: In this step you are to add the reagent acetic anhydride, which is both a
lachrymator (induces the flow of tears) and corrosive. The reagent must be handled
carefully. Should any of the liquid come into contact with your skin or clothing, wash the
affected area immediately with large quantities of water.
Measure out 6 mL of acetic anhydride in a dry graduated cylinder and carefully add the
reagent to the warm acid solution of the amine. Swirl the mixture gently until the anhydride
is completely dissolved.
Immediately add the sodium acetate solution you previously made and set aside, and
thoroughly mix the reactants by swirling the flask. Allow the flask to stand for about 5
minutes, while occasionally stirring the contents.
Place the flask in an ice-water bath and stir the mixture vigorously with a glass rod. Within
a few minutes a solid should separate from the solution. In some cases the product initially
appears as an oil, but this should be no cause for concern at this stage. Allow the flask to
remain in the cooling bath for 15 minutes.
B.
Isolation and Preliminary Purification of Crude Product
1.
While the reaction mixture is cooling, arrange a suction filtration apparatus. Be sure to
clamp the flask to a ring stand or other support. Place a disk of filter paper in the funnel and
moisten the paper with water.
Filter the crude product through the Buchner funnel. Rinse the Erlenmeyer flask with small
quantities of ice-cold water to remove any solid that sticks to the walls.
2.
3.
C.
Note: If the product separated as an oil and did not solidify after standing in the ice-water
bath, carefully decant as much of the supernatant liquid as possible. Add a few grams of
crushed ice to the oil in the flask and stir the mixture vigorously while cooling the flask in
the ice-water bath. If the oil does not solidify, add about 20 mL of water, shake the mixture,
and let it stand for a minute or two. Carefully decant the upper aqueous layer and repeat the
treatment with ice, with somewhat longer cooling periods in the ice-water bath, until
solidification occurs.
Leave the crude solid in the Buchner funnel and wash the filter cake with 50 mL of ice-cold
water. Resume the suction for about 5 minutes.
Purification
The amides may be recrystallizable from a number of different solvents, including water.
Unless you are instructed otherwise, the solvent selection in this situation is restricted to water,
methanol, and ethanol. Some of the amides that were prepared can be crystallized from one of
these solvents, while others may require a mixed system (water plus either methanol or ethanol).
If it is known that a crude product is to be recrystallized from water or a water-miscible
organic solvent, then it is not necessary that the solid be absolutely dry before carrying out the
purification. Such is the case in this preparation. (On the other hand, if there is a possibility that a
solvent which is not itself soluble in water will be needed, then steps must be taken to remove the
residual water from the crude product.)
1.
2.
Selection of the solvent: try water first, followed by methanol and then ethanol,
using fresh samples of crude in each case. If it is found that the solid is not
sufficiently soluble in water, but too soluble in both of the alcohols, then it is
necessary to try the mixed solvent approach.
Recrystallize the crude product following the general directions given below:
Recrystallization.
1. Select the appropriate solvent for recrystallization. Sometimes you can find data on solubility
for your compound or related compounds in the CRC Handbook or in the chemical literature. Test
one or more possible solvents using small amounts in test tubes. The compound you are trying to
recrystallize should be insoluble in the cold solvent, dissolve in the solvent when heated, and
recrystallize when the solvent is cooled. A mixed solvent may be required.
2. On a hot plate, heat some of the solvent you have selected in an erlenmeyer flask. Put the
impure, solid compound in a beaker. Placing the beaker on the hot plate, quickly add a small
amount of the hot solvent. If the compound does not completely dissolve, add additional small
amounts of the solvent until complete dissolution is achieved. You want to use a minimum of the
hot solvent to dissolve the compound. Do not needlessly boil off the solvent; if the compound is
going to dissolve it will do so in a few seconds.
3. Once the impure compound is totally dissolved you must decide whether to decolorize or not. If
necessary, add a small amount of decolorizing carbon to the hot solution. Place your stemless glass
funnel in the top of a beaker. Fold a fluted filter paper (page 46 of your lab text) and place it in the
stemless funnel. Add a few mL of the pure solvent to the beaker. Put the hot filtration assembly on
the hot plate and add the hot, decolorized solution of your compound to the filter. The purpose of
the stemless funnel, beaker, and hot plate is to keep the compound to be purified in solution while
you filter out the carbon.
4. Let the hot solution cool to room temperature on the bench top. Then use an ice-water bath to
cool the solution even more. If crystallization does not begin, try scratching the wall of the beaker
with your glass rod.
5. Vacuum filter the cooled solution to recover the recrystallized solid. You may want to wash the
compound with a small amount of cold solvent if the compound is not too soluble in the cold
solvent.
6. After air drying for a couple of days you can weigh and take the melting point of the purified
compound before packaging it.
D.
Identification
When the product is completely dry, you are to determine the melting range. Positive
identification can be made by means of the mixture-melting-range determination. Until this can be
done, put your dry purified product in a clean, dry, wide mouth bottle or vial of appropriate size
(the bottle should be at least half full), which has been weighed while empty. Reweigh the bottle
plus contents to obtain the net weight of product, and record this information in your notebook.
After you have determined what the compound is, label the package as indicated below, or as
directed by your instructor.
Your name
Name of compound
Observed melting range
Net weight
Date
You will turn in the product with your lab report.
Interpretation of Results and the Report
The experiment involved both the preparation and purification of an organic compound.
The primary objective was the purification of the product by recrystallization, and so very little
need by said about the chemistry of the preparative reaction. Greater emphasis should be placed on
the determination of the best solvent system and the results of the purification process in terms of
percentage recovery. Because identification of the compound by the mixture-melting-point
technique is required, the actual writing of the report must be deferred until that operation is
completed. A qualitative statement about the degree of purity as estimated from the observed
melting range and comparison with the literature value is also in order. The Experimental section
should, of course, provide complete details on the method that you actually followed.
Purified Substituted Amide
In the experiment, you prepared a substituted amide from an "unknown" amine. The melting range
determination will indicate how pure your product is, and the identity of the compound may be
verified by the mixed-melting-point method.
1.
Determine the melting range of your product.
2.
Refer to table on the next page, which lists the melting points of a number of amides,
including the compound you have made. Select those which have melting points close to
the range you determined for your product. Use a mixture-melting-point determination,
employing authentic samples of the amides that may be identical to your compound, to find
out which amide you prepared (Notes 1 and 2).
Notes
1.
2.
Even if you find that the first mixture tested shows no depression of the melting point, you
still must carry out the mixture-melting-point determinations with the other possibilities in
order to eliminate them with certainty.
The actual melting points of the authentic samples may not coincide with the literature
values because the samples may not be 100% pure. The samples may nevertheless be
utilized for the purpose intended. Do not measure the melting range of any of the standards,
but accept the literature values given in the tables or listed on the container labels.
Melting Points
of Some N-Substituted Acetamides
Amide (CH3CONHR)
m-chloroacetanilide
o-ethoxyacetanilide
o-methoxyacetanilide
o-chloroacetanilide
o-methylacetanilide
o-ethylacetanilide
acetanilide
2,4-dimethylacetanilide
p-methoxyacetanilide
2,3-dimethylacetanilide
p-ethoxyacetanilide
2,5-dimethylacetanilide
p-methylacetanilide
m-nitroacetanilide
mp (oC)
78
78
58
87
110
111
114
130
130
135
137
139
153
155
Interpretation of Results and the Report
The results of the mixture-melting-point determinations should be presented in tabular form.
List all of the possibilities tested and the corresponding measurements in such a way that your
conclusions are obvious from your experimental results.
CHE 311
Report for recrytallization/mp determination
1. As before: name
date
CHE 311-0x
unknown #
2. In your own words, explain what recrystallization is and how it works to separate solid
compounds. Describe how the appropriate solvent is selected for recrystallization.
3. In a few sentences, summarize what you did in this experiment, be specific.
4. Write balanced equations for the reactions.
5. Make a table:
weight of the unknown
g
weight of product
g
observed melting range of unknown amide
list of possible compounds and their literature
mp's, and the observed mixed mp's with your product.
6. Conclusion as to the identity of the product amide and unknown amine? Justify your answer.
7. How pure do you think the product is? Explain?
8. Answer the following questions:
a) For the following reported melting points, comment on the purity of the sample:
i) 78-79 oC
ii) 299-301 oC
iii) 178 oC decomposes
iv) 137-149 oC
b) If, in any recrystallization, an "oil" (liquid phase) comes out of solution rather than a
solid, why did this happen? What can you do about it?
c) What happens in this experiment if more than the minimum of hot solvent is used in the
recrystallization?
d) Based on the structure of the now known amine and amide, calculate the % yield of your
product. If you can’t figure it out, ask the instructor for the formulas of the reactant and product.
Note: % yield = (actual yield / theoretical yield) * 100%
You will have to convert to moles and use the balanced equation to calculate theoretical yield!
e) What was the purpose of the hot filtration? Why didn’t you use gravity or suction
filtration at this point?
f) Questions on page 664 of your lab text: 1, 2, 3, 4.
g) In the CRC Handbook, look up 1-bromo-2-nitrobenzene (look under benzene) and list
the mp, crystal form, and the solvent used in the recrystallization of this compound.
9. Attach the blue carbons from your notebook.
10. Package, label and turn in your product. name, date, contents, weight, mp or bp, %yield.
CHE-311
Chromatography
chromatography ("colored writing")
separations based on differences in absorption on a stationary phase and differences
in solubility in a moving phase.
I. Thin Layer Chromatography (tlc)
stationary phase = thin layer of solid silica gel, alumina,
etc.
moving phase = liquid solvent (capillary action)
-----------------------+---------+
¦ +---------+ ¦
¦
¦
¦ ¦
¦ ¦
¦
¦
¦ ¦
¦ ¦
¦
¦
¦ +---------¦ ¦
¦
¦
¦ ¦ o ¦ ¦
¦
¦
¦ ¦
¦ ¦
¦
¦
¦ ¦ o ¦ ¦
¦
¦
¦ ¦ o ¦ ¦
mark--> + o ¦ initial ¦ +
¦ ¦
¦
¦ spot +----+---------+---¦ solvent
+---------+
+------------------+
+---------+
mark--> +---------¦
¦ o ¦
- ¦
¦
¦
¦ ¦
¦ o ¦
- ¦ ¦
¦ o ¦ - ¦ ¦ ¦
¦
¦ x1¦ x2¦ x3¦ y¦
¦
¦ ¦ ¦ ¦ ¦
+
¦ -----------------¦
¦
+---------+
distance component traveled
Rf = retention factor = ----------------------------distance traveled by solvent front
Rf1 = x1/y; Rf2 = x2/y; etc.
application:
a) analysis of mixture : number of components
(solids & non volatile liquids)
b) separation of mg amounts
c) identification (Rf's or direct comparison)
II. Column Chromatography
stationary phase = column of solid silica gel, alumina,
etc.
moving phase = liquid solvent
¦ ¦
column preparation
¦ ¦
loading the mixture
solvent->¦ ¦
development
¦ ¦
collection of fractions
+---¦
analysis of fractions
¦ ¦
(tlc)
absorbent->¦ ¦
¦ ¦
¦ ¦
+---¦
+---+
+---+
¦
fractions +----¦ +----¦ ¦ ¦ ¦ ¦
¦ ¦ ¦ ¦ +----¦ ¦ ¦
+----+ +----+ +----+ +----+
applications:
a) analysis of mixture
(solids and liquids)
b) separations of 0.1 gram quantities
III. Gas Liquid Chromatography (glc)
stationary phase = column of non volatile liquid (carbowax,
DNP, SE-30, etc.) on solid support.
moving phase = gas
Oven
Recorder
+------------------------+
+----------+
¦
¦ +-------¦
¦
+---¦ +-+ +-+ +-+ +-+ +---+ ¦
¦
injection¦ +--+ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ +---¦ + ¦ +------+ ¦
+---¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ +---+ +-¦ +-+
¦ ¦ +-+ +-+ +-+ +-+ +-+ ¦ detector ¦ ¦
¦¦
¦
¦ ¦
¦¦
¦
¦ ¦
¦¦
¦
+------+
¦ +------------------------+
¦
Gas
Gas Chromatograph:
+----------------------------------------------+
¦
¦
¦
¦
¦
¦
¦
¦
¦
¦
¦
¦
+----------------------------------------------+
distance after injection
retention time = --------------------------chart speed
area A
%A = ------------------------------ X 100%
area A + area B + area C + etc.
area A = height X width (at half height)
applications:
a) analysis of mixture, # of components
(volatile liquids or gases)
b) separation of mg samples
c) identification (retention time)
d) per cent composition
IV. Today's experiments:
1. tlc
do tlc on your unknown on both silica gel and alumina.
use each of the two solvent systems.
2. glc
glc on known 50/50 mixture of alcohol and ketone
glc on pure alcohol
glc on your unknown mixture of alcohol and ketone
EXPERIMENT: Thin-Layer and Column Chromatography
Read 792-807 in your lab text!
The following experiments include both thin-layer and column chromatographies that are
based solely on the adsorption process. The main intent is to familiarize you with the techniques.
Once you have learned the basic idea and procedure, you will be in a position to utilize one or both
of these methods if you occasion arises during your later experiences with the preparative
experiments.
You will obtain an "unknown" mixture consisting of a minimum of two solid compounds;
one or more of the components may be colorless. a sample is to be subjected to thin-layer
chromatography to determine the number of components and their Rf.
(The same mixture could then be chromatographed in a column in an effort to separate and recover
the individual compounds. Progress of the column chromatography could to be determined by
thin-layer chromatography of each eluate fraction. You might also evaporate each eluate that is
known to contain dissolved solid and determine the melting range of the residue; a comparison with
the melting range of the original mixture would then be done.) It is quite possible that you will not
achieve a complete separation by column chromatography because (a) the solvent system that is
specified is not the best, (b) an insufficient number of eluate fractions are collected, (c) the
adsorbent is not the optimum choice, or (d) the column is not long enough. Nevertheless, exposure
to the method will provide experience in carrying out the chromatography and may well point up
some of the difficulties that can be faced. If there were enough time, it is very probable that you
could work out the optimum conditions for separation of your sample.
A.
Thin-Layer Chromatography of the Original Mixture
The effectiveness of two different adsorbents, silica gel and alumina, will be compared
using two solvent systems.
Procedure
1.
2.
3.
4.
Obtain a 5- or 10-mL beaker or a vial of similar capacity, two TLC strips coated with
aluminum oxide, and two TLC strips coated with silica gel. Use a sharp pencil to carefully
mark the top of each strip (e.g., A and S, respectively) so that they can be distinguished.
Place about 10 mg (estimated; do not weigh!) of the solid mixture in the small container and
add about 1 mL of acetone to dissolve the sample.
Spot the solution on each of the strips. Mark the top of one alumina strip 1:1 and the other
1:3; do the same to the silica gel strips.
Develop the silica gel chromatograms using ethyl acetate-cyclohexane (1:1) for one and
25% ethyl acetate-75% cyclohexane (1:3) for the other. Develop the alumina strips in the
same way. Note: Ethyl acetate alone is too polar and cyclohexane too nonpolar. One or
both of the specified solvent mixtures may prove to be satisfactory, or neither may be the
most desirable solvent system. A different single solvent or combination of solvents may
be superior, but for expediency you are restricted to the two solutions indicated above.
5.
Follow the instructions given. (Note that the solvent moves more slowly through the
alumina then it does through silica gel.)
Calculate Rf values for all observed spots.
The Report
The introductory section should include the usual background discussion of the theoretical
principles underlying the procedures, as well as a statement of the problem. Be sure to include all
observations and measurements (Rf values) in the Experimental section. All thin-layer strips
should be taped or stapled to a sheet of paper and attached to the report.
The discussion of results should provide a comparison of the thin-layer chromatographies on
alumina and on silica gel and the two solvent systems. In the event that you did not obtain a
complete separation of components, offer some possible reasons therefore and some suggestions as
to how separation could be done more effectively if you were to repeat the attempt.
Che 311
Chromatography reports
You will submit two reports for the chromatography experiments, one for tlc/column and one for
glc. Both of these reports will be due two weeks from today.
Thin Layer and Column Chromatography.
1. Include the regular heading.
2. Explain in your own words what chromatography is and how it works; with emphasis on tlc and
column.
3. In a few sentences state what you did in this experiment; be specific.
4. Make a table showing the Rf values for each component for each adsorbent and each solvent
system you used in the tlc.
5. Which adsorbent would you select for a column chromatography separation of your unknown
and why? Which component would elude from the column last?
6. Discuss the results of your experiment.
7. Staple or tape all of the tlc strips to a piece of paper and label each one. This will be included as
part of your report.
8. Answer questions:
a) Two components, A and B, were separated by tlc. When the solvent front had moved 10.0 cm
above the level of the original spot, the spot corresponding to A was 3.5 cm and that of B was 4.1
cm above the original spot. What are the retention factors for A and B? Which component would
elude first from a column chromatography using the same absorbant and solvent?
b) Describe how thin layer chromatography could be used to analyze a urine sample for the
presence of cocaine if you had a known sample in the lab.
c) Why is it important that the sample to be analzed by tlc be dry?
d) Why must the solvent level be below the original spot on the tlc plate?
e) Why must the cap be in place on the bottle during the tlc separation?
Answer questions 1, 2, 3, 4 on page 807 of your lab text.
9. Attach the carbons from your notebook.
Gas-Liquid Chromatography
EXPERIMENT: Analysis of Alcohol-Ketone Mixtures
Read p. 808-823 in your lab text!
A ketone is a type of organic compound that is represented by the general formula I; it is
related to another kind of compound, a secondary alcohol (II).
I.
R-C=O
|
II.
R-C-OH
|
R’
R’
A ketone can be made from the corresponding alcohol by oxidation; conversely, reduction of a
ketone results in the formation of the secondary alcohol. (You need not be overly concerned with
the chemistry of these substances now. The relationships just described will be amplified at the
appropriate point later in the course.)
When a ketone is prepared from the alcohol, or vice versa, it is possible that not all of the
starting material is converted to the end product. The final product may therefore be contaminated
with some of the starting material. The difference between the boiling points of the alcohol and the
ketone becomes smaller as their molecular weights increase, making it more difficult to separate
them by conventional distillation procedures. Analysis by GLC, however, readily indicates the
presence of the contaminant.
You will receive a mixture of a ketone and the corresponding secondary alcohol. Carry out
a GLC analysis following the general instructions given and whatever special instructions are
provided for the instrument available in your laboratory. You will also need to measure the chart
speed (inches/minute or cm/min).
If your sample was given to you as an "unknown," compute the approximate percentage
composition by measuring the areas of the peaks. If authentic samples of the various
possibilities are available, attempt an identification of the components of your mixture. In
this case, you need use either an authentic ketone or alcohol, but not both.
Gas Chromatography Report
1. Include the regular heading.
2. Explain in your own words the physical basis for gas chromatography and how it works to
separate and purify compounds.
3. State in a few sentences what you did. Be sure to give information about the column(s) used
and the temperature(s).
4. Make a table:
stationary phase: carbowax
column temperature:
carrier gas: air
detector: TDC
4-methyl-2-pentanol retention time =
Known:
retention height width-1/2h area calculated
time (sec) (units) (units) (units) weight %
4-methyl2-pentanol
4-methyl2-pentanone
Unknown:
retention height width-1/2h area calculated
time (sec) (units) (units) (units) weight %
4-methyl2-pentanol
4-methyl2-pentanone
5. Discuss the results of your experiment.
6. Attach the chromatograms that you ran, suitably labeled.
(show your calculations!)
7. Attach the notebook carbons.
8. Answer the following questions:
In a glc three peaks are observed and their areas are calculated as follows: A, 13.5 mm2; B,
20.2 mm2; C, 4.6 mm2. What is the % composition of each component in this mixture?
Describe how the identity of each of the components could be determined if known samples of two
of the compounds were available.
In the known 50%/50% mixture of alcohol and ketone, why are the areas of the two peaks not
equal?
Page 823 of your lab text: problems 1, 2, 4.
CHE 311
Preparative reaction pre-labs
For all preparative reaction lab experiments you will have to submit a pre-lab writeup as well as the
usual post-lab report. The pre-lab is due at least 24 hours before the lab. Failure to submit the prelab will result in your not being allowed to begin the synthesis in lab.
For the first preparative experiment, prepare the pre-lab in your notebook (the carbons should be
submitted prior to the lab; turn them into my mailbox in the Chem. Office, NSM B-202).
The pre-lab should include the following:
1. A balanced equation for the reaction as you are going to carry it out.
2. A table of the physical properties (see lab handout) of the reactants/solvents and products. (a
copy of the CRC is in the reserve book room and there is one in the lab)
3. A step by step procedure for the reaction as you are going to carry it out.
CHE-311
Syntheses of Alyl Halides
In this experiment you will synthesize two alkyl halides, a primary bromide (1-bromobutane) and a
tertiary chloride (2-chloro-2-methyl-butane). You will have two weeks to complete both syntheses.
The first lab period you will begin the synthesis of 1-bromobutane; once the reaction mixture is
refluxing, you will start the synthesis of 2-chloro-2-methylbutane. Both syntheses will be finished
during the second lab period.
Note: you must submit prelabs for both syntheses prior to the start of the lab!
See pages 204-211 in your text.
TABLE OF PHYSICAL PROPERTIES (This table must be completed before coming to lab!)
Reactants and
solvents
fw
sodium bromide
water
Moles
(g)
103
18
weight
(mL)
volume
(g/mL)
0.17
density
17.0
bp
mp
solubility
--
--
1390 755
0
0.94
17
17
1.00
100
74
0.109 8.1
10
0.81
117 -89
sw,sal
14
1.84
338 10
sw,d al
1-butanol
sulfuric acid
98
0.26
(HBr)
81
(0.17) (13.8)
calcium chloride 183 -(anhyd.)
25.8
---
--
sw, sls al
--
-67 -88.5 sw,sal
--
--
--
568 I ace; s eth
Product(s)
1-bromobutane
137 (0.109) (14.9) (11.7)
NaHSO4
120 (0.109) (13.1) --
water
18
(0.109) (2.0)
(2.0)
1.28
1.00
100
iw,sal
--
>315 sw,sls al
0
102 -112
d
--
(theoretical)
CH3CH2CH2CH2-OH + NaBr + H2SO4 ---> CH3CH2CH2CH2-Br + NaHSO4 + H2O
TABLE OF PHYSICAL PROPERTIES (This table must be completed before coming to lab!)
Reactants and
solvents
Product(s)
fw
Moles
(g)
weight
(mL)
volume
(g/mL)
density
bp
mp
solubility
Report for syntheses of 1-bromobutane name
1. Balanced equation for reaction as you carried it out:
2. Step-wise mechanism for the reaction. Use curved arrow formalism and label the RDS. Show
how each product is formed if more than one product is possible. Use additional paper if
necessary. Give the name of the mechanism.
3. weight of the starting alcohol
moles of alcohol
weight of the product halide
moles of product
% yield
boiling point (range) of the product
literature values for the bp of the
expected product(s)
4. Discussion of results.
5. a) Why did you wash the crude product with NaHCO3?
b) Why did you then wash it with water?
c) Why was the 1-bromobutane treated with anydydrous calcium chloride?
d) State two purposes of the simple distillation of the product?
e) Was the product produced by an Sn1 or an Sn2 mechanism? How could you verify this?
f) What role did the sulfuric acid play in this experment? Explain! equations!
Answer questions 1, 2, 3, 5, 6 on p. 210-211 of your lab text.
6. Attach the carbons from your notebook, the pre-lab carbons, and table of physical properties.
Label and turn in your product.
Report for syntheses of 2-chloro-2-methylbutane
name
1. Balanced equation for reaction as you carried it out:
2. Step-wise mechanism for the reaction. Use curved arrow formalism and label the RDS. Name
the mechanism! Show how each product is formed if more than one product is possible. Use
additional paper if necessary.
3. weight of the starting alcohol
moles of alcohol
weight of the product halide
moles of product
% yield
boiling point (range) of the product
literature values for the bp of the
expected product
4. Discussion of results. Be sure to compare the synthesis of 1-bromobutane with that of 2-chloro2-methylbutane.
Include a table showing the following for the syntheses of n-butyl bromide and for tert-butyl
choloride:
time of reaction
temperature of reaction
catalyst
%yield
class of alcohol
mechanism
5. a) Draw all of the isomeric butanols. Number them in order of decreasing reactivity with conc.
HCl.
b) Why did you wash the crude product in this experiment with aqueous sodium
bicarbonate?
c) Why didn't you wash it with aqueous NaOH?
d) Why were you able to wash the crude 1-bromobutane with saturated NaHCO3 while 5%
NaHCO3 was used in the washing of 2-chloro-2-methylbutane?
e) What is one major disadvantage of washing with sodium bicarbonate?
f) Neopentyl alcohol reacts with conc. HCl to produce tert-pentyl chloride. Outline all steps
in the mechanism to show how this product is formed.
g) Why does 1-pentanol produce only 1-bromopentane and not 2-bromopentane when
reacted with HBr?
h) Solid sodium hydroxide is a drying agent. Why did we not use it in place of calcium
chloride when drying the crude product?
i) What were the two purposes for the simple distillation at the end of this synthesis?
Answer questions 2, 3, 4, 5 on page 211 of your lab text.
6. Attach the carbons from your notebook, the pre-lab carbons,and table of physical properties.
Label and turn in your product.
TABLE OF PHYSICAL PROPERTIES (This table must be completed before coming to lab!)
Reactants and
solvents
Product(s)
fw
Moles
(g)
weight
(mL)
volume
(g/mL)
density
bp
mp
solubility
name
Report for dehydration of 4-methylcyclohexanol
1. Balanced equations for the reactions as you carried them out:
2. Step-wise mechanism for the reaction. Use curved arrow formalism and label the RDS. Name
of the mechanism?
3. weight of the limiting reagent
moles of limiting reagent
weight of the product
moles of product
% yield
boiling range of the product
literature value for the bp of the
expected product(s)
4. How pure is your product? How do you know?
5. Discuss your results.
6. a) Predict the product(s) for the dehydration of 3-methyl-2-butanol.
b) Predict the product(s) of the dehydration of each of the following alcohols: 1-butanol,
cyclohexanol, 1-methylcyclohexanol, 2-methylcylcohexanol, neopentyl alcohol, 4-methyl-1pentanol.
7. Attach the carbons from your notebook, the pre-lab carbons. Don't forget to label and turn in
your product.
TABLE OF PHYSICAL PROPERTIES (This table must be completed before coming to lab!)
Reactants and
solvents
Product(s)
fw
Moles
(g)
weight
(mL)
volume
(g/mL)
density
bp
mp
solubility
CHE 311
Nitration of a halobenzene
This will be your third preparative experiment. Remember that the pre-lab writeup is due
24 hours before the lab.
Notes:
1. Use your largest Erlenmeyer flask as the reaction vessel.
2. Include a magnetic stirrer in the apparatus. Leave roon between the bottom of
the flask and the top of the stirrer base for insertion of a plastic bowl (water bath).
3. Wear rubber gloves to protect your hands, not only against the concentrated
acids, but also the product which is a skin irritant.
4. If two or more products are expected (e.g. as from chlorobenzene), calculate
the theoretical yield of the mixture as if it were a single substance. Calculate the percent
yield of the actual product as if it were exclusively formed.
You will use 0.1 mole of the following halobenzene as the starting material:
desk number
1,10,20,4 bromobenzene
6,16,11 chlorobenzene
2,12,22,9 1,4-dichlorobenzene
7,17,21 1,4-dibromobenzene
3,13,23,19 1,3-dichlorobenzene
8,18,14 1,2-dichlorobenzene
5,15,24 1-bromo-4-chlorobenzene
Nitration of a Haloarene: Experimental Procedure
The starting haloarenes for this synthesis are either liquid or solid, but the desired
product in each case is a solid. For some, only one possible product may be formed;
some may react to form a mixture of two products, one of which predominates. The
remaining compounds may theoretically be converted to a mixture of two or more
products. Included in your assignment is the isolation and determination of the identity
of the major product.
A.Apparatus
The standard-taper assembly described below could be used for this preparation.
However, it is also possible to carry out the procedure in an Erlenmeyer flask (which you
will do) but it is necessary to carry out the reaction in a fume hood.
1.
A 500-mL Erlenmeyer flask will serve as the reaction vessel. The thermometer is
placed in the flask, with its bulb resting on the bottom. When you must stir or
shake the reaction mixture, hold the thermometer in place by grasping the neck of
the flask and the thermometer simultaneously with one hand.
[alternatively:
a.
Fit a 250-mL two-neck flask with a Claisen adapter or use a 500-mL three-neck
flask. If you are provided with a magnetic stirrer, place a magnetic stirring bar in
the flask.
b.
Place a thermometer in the angled side neck of the flask and position the bulb so
that it will be immersed in the reaction mixture. Attach a reflux condenser to the
other side neck and connect the top opening of the condenser to a gas trop (oxides
of nitrogen may be evolved).
c.
Attach a dropping funnel to the center neck if the compound to be nitrated is a
liquid. If your starting material is a solid, the center neck is to be plugged with a
glass stopper.]
2.
Surround the flask with a plastic bowl containing some tap water. Obtain some
crushed ice in a separate container and keep it handy for cooling the reaction
mixture as needed.
B.
Reaction
3.
Begin the preparation of the nitrating agent by pouring 20 mL (28.5 g; 0.32 mole)
of concentrated nitric acid through a narrow-stem funnel into the flask. Do not
use the addition funnel, if one is included in your assembly. Carefully add in
small portions of 20 mL (37 g; 0.36 mole) of concentrated sulfuric acid. Stir the
mixture mechanically or swirl the flask by hand while you are adding the sulfuric
acid. When all of the sulfuric acid has been added, cool the mixture to 25-30oC
by adding some ice to the water bath, if necessary. Do not cool the solution
below 25oC.
If the temperature of the nitrating agent is allowed to fall much below 25oC it is possible
that insufficient energy will be available to initiate the reaction. Continued addition of
the substance to be nitrated will permit the concentration of unreacted starting material to
build up. when the reaction does begin, and heat is evolved, all of the aromatic
compound present may interact with the nitrating agent and the reaction may get out of
control because of the excessive evolution of heat.
4.
Measure out a quantity equivalent to 0.1 mole of the starting material you were
assigned. Add the aryl halide to the nitrating agent as directed below. Stir or
swirl the reaction mixture to mix the reactants thoroughly. Use the cooling bath
to control the temperature so that it does not rise above 60oC, but do not allow the
temperature to fall below 30oC. If the temperature does get too low, remove the
cooling bath temporarily and allow the reaction mixture to warm up before
continuing the addition.
5.
6.
Continue to add the starting material in the manner described above until all of it
is consumed.
When the temperature of the reaction mixture no longer rises spontaneously, heat
the mixture on a steam bath or hot water bath for 30 minutes. A heating mantle
may also be used, but be certain to wipe the outside of the flask first to remove
any adhering water. Heat the mixture to a temperature between 60 and 100oC.
7.
Remove the flask from the heat source and allow the mixture to cool to room
temperature. You may help it along by using a cooling bath.
C.
Isolation and Preliminary Purification
8.
Put a mixture of 150 mL of water and enough crushed ice to bring the volume to
200 mL into a 400- or 600-mL beaker. Carefully pour the contents of the flask
into the cold water while stirring the mixture with a glass rod. Rinse the reaction
flask with a small amount of ice water and add the rinsings to the beaker.
The crude product should separate as a solid. If it does so, it can be isolated by
suction filtration. If the crude product separates from the aqueous phase as an oil,
the following measures may be taken.
a.
Carefully decent as much of the aqueous phase as possible, leaving the
oily material behind. Add some crushed ice and vigorously stir the
mixture with a glass rod. If this treatment does not effect solidification of
the material, see step b (below).
b.
Dissolve the crude oily product in about 50 mL of diethyl ether or
dichloromethane by adding the solvent directly to the beaker that contains
the product-water mixture. Transfer the contents of the beaker to a
separatory funnel and separate and discard the aqueous phase. After
completing step 11, continue with step 12b.
9.
10.
The reaction mixture contained a strongly acidic solution, some of which will
remain admixed with the crude product. The product must therefore be washed
thoroughly with water. A solid may be washed while it is in the Buchner funnel;
a product in solution should be washed in a separatory funnel.
D.
Purification
11.a.
The product is a solid, so a recrystallization is in order. Select a recrystallizing
solvent from among those available to you in the laboratory.
If the crude product was dissolved in an organic solvent, that solvent must be
removed at this point. A rotary evaporator would be best for this purpose,
but any other suitable means may be employed. If the residue is still
liquid, it may still be subjected to a crystallization procedure, just as if it
were solid.
b.
E.
Verification of Identity and Purity
12.
13.
Determine the melting range of your product.
The product will be analyzed by thin-layer chromatography on silica gel, with the
eluting solvent 9:1 (v:v) hexane:chloroform. Pure samples of most of the possible
reaction products are available, you should attempt an identification by
comparison of Rf values for the authentic material(s) run alongside the reaction
14.
product on the same TLC strip.
Package the product and turn it in.
The Report
The Introductory section of the report should include a discussion of the reaction
mechanism. A description of the intent of the experimental work, naming the specific
compound to be nitrated, and a description of the anticipated outcome should precede the
Experimental section and the Discussion of Results. In the latter, be sure to interpret the
experimental results (including spectra) and to state conclusions about such steric and
inductive effects as are applicable.
Report for nitration of a halobenzene name
1. Balanced equation for the reaction as you carried it out:
2. Step-wise mechanism for the reaction. Use curved arrow formalism and label the
RDS. Name of the mechanism? Show how each product is formed if more than one
product is possible. Use additional paper if necessary.
3. weight of the limiting reagent
moles of limiting reagent
weigt of the product
moles of product
% yield
melting point (range) of the product
literature values for the mps of the
expected products
(name of each!)
tlc:
substrate
solvent
identity (if possible for each spot)
rf for each spot
4. What products did you expect this reaction to form? Explain the effect that the
group(s) present in the starting material have on reactivity and orientation in this reaction
and why. How many were actually formed? What evidence do you have for this? How
did you identify them? If the number formed is different from the number expected,
explain.
5. How pure is your product? How do you know?
6. Discuss your results further.
7. a)In the nitration of bromobenzene, the product after purification by recrystallization
contains mostly the para-bromonitrobenzene and little of the ortho-isomer. Explain.
b) Bromo is a deactivating group in EAS but an ortho/para director. Use
resonance structures to explain why no detectable amounts of the meta isomer are
obtained.
8. Attach the carbons from your notebook, the pre-lab carbons, and the tlc. Don't forget
to label and turn in your product.
CHE-311
Information for Final Exam
This exam is 20 questions long and consists of short essays and a few calculations
(bring your calculator).
To study for this exam, go over each of the techniques that you have learned for
separating and purifying organic compounds. You are expected to know the terminology
and basic physical principles behind each method and technique. Know which methods
you should use under which circumstances. You should also look at each of the
preparatory experiments and know why you did each of the operations that you did.
Calculations that you should be capable of doing include:
partition coefficient in extractions
Rf
retention times
% in gas chromatography
% yield