Chemistry Laboratory for
Chemical Engineer 2 (AE285)
Department of Chemical Engineering
Faculty of Engineering
Thammasat University
Academic Year 2007
AE285 Chemistry Laboratory for Chemical Engineer 2
Lecturer: Dr. Supitcha Rungrodnimitchai
Dr. Pongtorn Dhupatemeeya
Course Type
Compulsory Level
Credits
Department
Course
Description
Prerequisite
Course objective
Week 1
Week 2
Week 3
Week 4
Week 5
Week 6
Week 7
Elementary for chemical engineering course student
Compulsory Course
1 (Laboratory)
AE
Introduction to Organic Chemistry Laboratory, Safely rules,
Basic techniques for separation (extraction, crystallization,
distillation), Fundamental organic experiments and
characterization techniques. Application in industry.
None
To formulate the skills in Organic chemistry laboratory
To understand the principles and practical use of organic
chemical reactions
Introduction to organic chemistry laboratory
Lab 1. Basic skills for laboratory (determination of boiling
point, melting point, glass blowing)
Lab 2. Separation of aniline, benzoic acid and naphthalene
(extraction)
Lab 3. Separation of aniline, benzoic acid and naphthalene
(distillation, crystallization)
Lab 4. SN2 Reaction
Lab 5. Biosynthesis of alcohol I
Lab 6. Biosynthesis of alcohol II
Midterm Examination
Week 8
Lab 7. Synthesis of polymers
Week 9
Week 10
Lab 8. Synthesis of ester
Lab 9. Synthesis of sulfanilic acid
Week 11
Lab 10 Synthesis of Orange II
Final Examination
Week 12
Evaluation: Laboratory note
Report
Attendance
Final Examination
Preserved for make up class
20%
40%
20%
20%
Textbook: Organic experiments (7th edition, Louis F. Fieser and Kenneth L. Williamson,
D.C. Health and Company
Safety Practices in Chemistry Laboratory
General: Never work in the laboratory alone. Perform no unauthorized experiments. Do
not use mouth suction to fill pipettes. Confine long hair and loose clothes while working
in the laboratory. Wear shoes. Learn the location of and correct use of the nearest fire
extinguisher. Learn the location of the safety shower and first aid kit and be prepared to
give help to others.
Safety Glasses: Safety glasses should be worn at all times while in the laboratory.,
whether you actively engage in experimental work or not. Contact lenses should never
be worn in the laboratory because they cannot be removed rapidly enough if reagents
accidently splash in the eye.
Fire: Avoid unnecessary flames. Check the area near you for volatile solvents before
lighting a burner. Check the area near you for flames if you are about to begin working
with a volatile solvent. Be particularly careful of the volatile solvents diethyl ether,
petroleum ether (ligroine), benzene, methanol, ethanol, and acetone.
Chemicals: Handle every chemical with care. Avoid contact with skin and clothing. Wipe
up spills immediately, especially near the balances and reagent shelf. Replace caps on
bottles as soon as possible. Do not use an organic solvent to wash a chemical from the
skin as this may actually increase the rate of absorption of the chemical through the
skin. Avoid inhalation of organic vapors, particularly aromatic solvents and chlorinated
solvents. Use care in smelling chemicals and do not taste them unless instructed to do
so. Drinking, eating, or smoking in the laboratory is forbidden.
Disposal of Chemicals: Dispose of chemicals as directed in each experiment. In
general, small quantities of water-soluble substances can be flushed down to the drain
with a large quantity of water. Water-insoluble solids and liquids should be placed in the
waste containers provided. Chromium ion in the +6 oxidation state (orange) should be
reduced to the + 3 state (green) with a mild reducing agent such as bisulfite before
disposal.
Caution: It has been determined that several chemicals that are widely used in the
organic laboratory (e.g., benzene and chloroform) cause cancer in test animals when
administered in large doses. Where possible, the use of these chemicals is avoided in
this book. In the few cases where suspected carcinogens are used, the precautions
noted should be followed carefully. A case in point is chromium in the +6 oxidation
stage. The dust of solid Cr+6 salts is carcinogenic. The hazards have been pointed out
and safe handling procedures are given.
In Case of Accident
In case of accident notify the laboratory instructors immediately.
Fire
Burning Clothing. Prevent the person from running and fanning the flames.
Rolling the person on the floor will help extinguish the flames and prevent
inhalation of the flames. If a safety shower is nearby, hold the person under
the shower until flames are extinguished and chemicals washed away. Do not
use a fire blanket if a shower is nearby. Remove contaminated clothing. Wrap
the person in a blanket to avoid shock. Get prompt medical attention.
Do not, under any circumstances, use a carbon tetrachloride (toxic) fire
extinguisher and be very careful using a CO2 extinguisher (the person may
smother).
Burning Reagents. Extinguish all nearby burners and remove combustible
material and solvents. Small fires in flasks and beakers can be extinguished
by covering the container with an asbestos-wire gauze square, a big beaker,
or a watch glass. Use a dry chemical or carbon dioxide fire extinguisher
directed at the base of the flames. Do not use water.
Burns, either Thermal or Chemical. Flush the burned area with cold water
for at least 15 min. Resume if pain returns. Wash off chemicals with a mild
detergent and water. Current practice recommends that no neutralizing
chemicals, unguents, creams, lotions, or salves be applied. If chemicals are
spilled on a person over a large area, quickly remove the contaminated
clothing while under the safety shower. Seconds count and time should not be
wasted because of modesty. Get prompt medical attention.
Chemicals in the Eye. Flush the eye with copious amounts of water for 15
min using an eye-wash fountain or bottle, or by placing the injured person
face up on the floor and pouring water in the open eye. Hold the eye open to
wash behind the eyelids. After 15 min of washing obtain prompt medical
attention, regardless of the severity of the injury.
Cuts: Minor cuts. This type of cut is most common in the organic laboratory
and usually arises from broken glass. Wash the cut, remove any pieces of
glass, and apply pressure to stop the bleeding. Get medical attention.
Major cuts. If blood is spurting, place a pad directly on the wound, apply
firm pressure, wrap the injured to avoid shock, and get immediate medical
attention. Never use a tourniquet.
General rules
1. Dress sensibly in the laboratory.
A white robe is necessary for every laboratory. Wear shoes or
sneakers, not sandals. Confine long hare and loose clothes. Don't wear
shorts. Don’t use mouth suction to fill a pipette and wash your hands before
leaving the laboratory. Don’t use a solvent to remove chemicals from skin.
This will only hasten the absorption of the chemical through the skin.
Lab room will be closed at 16:30. You must finish your experiments,
clean up
your working space and have your lab note checked by then.
The chemical engineering department asks you to deposit 300 bath
with the department during the academic year. This money is for
compensating the loss from broken stuff and instruments. The department
will refund this money to you after subtracting value of broken stuff at the end
of this class. A student is responsible for what that he/she brake during single
operation lab, and a group of students are responsible for what that any
member in the group brake. However, if this money is not enough for
compensate the loss, a student have to pay in addition before deadline (the
first day of final examination), otherwise you may receive ‘F’ in this subject.
2. Not be late!!
To attend every class is the minimum requirement for passing this
subject. Inform the lecturer in advance at least on Friday before the class.
Each experiment in the lab is set for finishing in 3 hours. Students who come
later than 20 minute will not be allowed to join the class.
4. How to write a laboratory notebook?
Bring note lab with you every time. You must prepare for the
laboratory by reading the direction of the experiment prior the beginning of the
class. Write what you have to do in the lab and values that you calculated in
your lab note. Lab note will be checked 2 times, before and after the class
(20% for a complete lab note).
A complete, accurate record is an essential part of laboratory work.
Failure to
keep such a record means laboratory labor lost. An adequate record includes
the procedure (what was done), observation (what happened), and
conclusions (what the results mean).
Use a lined, paperbound, A4 note book and record all data in ink.
Allow the space at the front for a table of contents, number the pages
throughout, and date each page as you use it. Reserve the left –hand
page for calculations and numerical data, and use the right-hand page for
notes. Never record anything on scraps of paper to be recorded later in
the notebook. Do not erase, remove, or obliterate note; simply draw a
single line through incorrect entries.
The notebook should contain a statement or title for each experiment
followed by balanced equations for all principal and side reactions, and,
where relevant, mechanisms of the reactions. Consult your text book for
supplementary information on the class of compounds or type of reaction
involved. Give a reference to the procedure used; do not copy verbatim the
procedure in the laboratory manual.
Before coming to the lab to do preparative experiments, prepare a
table of reagents (in your notebook) to be used and the products expected
with their physical properties. From your table, use the molar ratios of
reactants and determine the limiting reagent and calculate the theoretical
yield (in grams) of the desired product. Enter all data in your note book.
Include an outline of the procedure an method of purification of the
product in flow sheet, which lists all possible products, by products, unused
reagents, solvents, etc. that appear in the crude reaction mixture. On the
flow sheet indicate how each of this is removed-for example, by extraction,
various washing procedures, distillation or crystallization. With this
information entered in the notebook before coming to the laboratory, you
will be ready to carry out the experiments with the utmost efficiency. Plan
you time before the laboratory period. Often two or three experiments can
be run simultaneously.
When working in the laboratory, record everything you do and you
observe as it happens. The recorded observation constitutes the most
important part of the laboratory record, as they for the basis for the
conclusions you will draw at the end of each experiment. Record the
physical properties of the product, the yield in grams, and the percentage
yield. Analyze your results. When things do not turn out as expected,
explain why. When your record of an experiment id complete, another
chemist should be able to understand your account and determine what
you did, how you did it, and what conclusion you reached. In other word,
from the information in you notebook a chemist should be able to repeat
your work.
Report Writing
Chemical engineering students are required to submit a report after every
experiment. A report should contain each of the sections listed below and
arranged orderly.
1.
Title
Experiment title should be clearly and concisely written.
2.
Contents
List the sections and/or subsections together with their respected page
numbers.
3.
Abstract
It is a short paragraph explaining the whole content of the experiment
including title, procedure, result, and conclusion. The length of abstract
should not exceed 1 page.
4.
Objectives
State the purposes of the experiment in this section.
5.
Introduction and Theory
State the problem(s) and fundamental theory related to the experiment.
Reveal how the experiment will solve the problems or support the theory.
6.
Material and Apparatus
List any material, chemical and apparatus used in the experiment.
Quantity, makers, and size of material and apparatus should be clearly
written. Inclusion of the apparatus configuration is recommended when
sophisticated system is applied so that the reader will understand the
principle of the apparatus with brief explanation.
7.
Experiment
Detail of actual procedure should be written in order. List the
experimental procedure step by step. Be reminded that your explanation
should enable the reader to repeat the experiment without any difficulty
in the future. Students should not copy the experimental procedure from
the laboratory manual because there might be some discrepancies
between the manual and the actual experiment.
8.
Result
Raw data from the experiment should be tabulated. Processed data can
be presented in tables, graphs, or diagrams. Titles of tables, graphs and
diagrams should be addressed properly. Correct scale must be used in
graph plotting; i.e. plot graph only on scaled paper or using computer
program). Titles of x-axis and y-axis should be clearly written. Human
errors and instrumental errors observed during the experiment for later
discussion may be mentioned in this section.
9.
Discussion
Analyze the experimental results and compare them with previous study
or refer to the fundamental theory. Investigate the possible causes of
discrepancies if any. Creative comment and suggestion can be written at
the end of this section for future development.
10. Conclusion
State the outcomes of the experiment without re-elaborate the analysis
and discussion. The conclusion should compliment objective of the
experiment mentioned earlier.
11. Appendix
Collection of reference data used for analysis such as calculation sheet,
property table, etc, should be included in the appendix. Inserting such
information in other sections (result or discussion) might disturb the
importance of the main context and so must be avoided.
.
12. References
List the description of book, article, or any published documents referred
to in the main context of a report consequently. The description should at
least consist of author(s), title, and published year.
Examples of reference description for a research paper and a book are
as follows.
[1] J. van der Geer, J.A.J. Hanraads, R.A. Lupton, “The art of writing a
scientific article,” J. Sci. Commun. 163 (2000) 51-59.
[2] W. Strunk Jr., E.B. White, The Elements of Style, third ed., Macmillan,
New York, 1979.
Lab 1 Making of glass tools, Measuring of boiling point and melting of
compounds
Aim Make glass tools and use them in evaluation of physical properties of
compounds
Apparatus
1. Glass rod
2. Burner
3. Glass tube x 4
4. Thermometer x 1
5. Beaker 100 – 200 ml x 2
6. Unknown x 2 for boiling point, x 2 melting point
7. Watch glass
8. Heater
Experiments
1)
Making of capillary
1.1 Capillary is a small glass rod. We use it for sucking solution in
chromatrography, measuring melting point and boiling point.
1. Keep 2 ends of the glass rod.
2. Heat the rod until it changes into red.
3. Take the rod out of fire and pull it rapidly.
4 . Break into short pieces.
red
Flame
glass rod
pull
1.2 boiling stone :Boiling stone prevent overheating of solution in the
reaction
1. Keep two ends of the rods. Burn them into red and fused.
2. Attach two ends together.
3. Twist the glass in fire to introduce bubbles in glass.
4. Take boiling stone out of from the glass rod. (5 pieces/ group)
Flame
Flame
glass rod
glass rod
Flame
glass rod
glass rod
2)
3)
Measuring of melting point
1. Introduce crystals of unknown into the capillary
2. Bind the sealed capillary to thermometer.
3. Add water to a beaker (1/2) and put thermometer and capillary.
4. Heat water with the rate of 2-3oC/min. Record the temperature that all of
crystals melt in liquid.
Measuring of boiling point
1. Add unknown into small glass tube.
2. Put the sealed capillary to the glass tube in 1.
3. Bind glass tube with thermometer and heat by hot water in a beaker.
4. Heat until generation of bubbles. Stop heating, wait until liquid flows
into capillary. Record the temperature.
sample
sample
oil
oil
heater
melting point
heater
boiling point
In your report
1. What are the unknown samples?
2. Explain the principle in measuring of melting point. Use unknown
samples as examples and explain the relation between melting point
and interaction between molecules.
3. Explain the principle in measuring of boiling point. Use unknown
samples as examples and explain the relation between boiling point and
interaction between molecules.
Lab 2-3 Acid-base extraction and purification
Aim
1. Learn the method of acid-base extraction
2. Learn the method for purifying organic compounds
Theory
Acid/Base Extraction
Acid/base extraction, involves carrying out simple acid/base reactions
in order to separate strong organic acids, weak organic acids, neutral organic
compounds, and basic organic substances. . The chemistry involved is given
in the equations that follow, using benzoic acid, phenol, naphthalene, and
aniline as examples of the four types of compounds.
Here is the strategy: the four organic compounds are dissolved in ether.
The ether solution is shaken with a saturated aqueous solution of sodium
bicarbonate, a weak base. This will react only with the strong acid, benzoic
acid, to form the ionic salt, sodium benzoate, which dissolves in the aqueous
layer and is removed. The ether solution now contains just phenol,
naphthalene, and aniline. A 10% aqueous solution of sodium hydroxide is
added and the mixture shaken. The hydroxide, a strong base, will react only
with the phenol, a weak acid, to form sodium phenoxide, an ionic compound
that dissolves in the aqueous layer and is removed. The ether now contains
only naphthalene and aniline. Shaking it with dilute hydrochloric acid removes
the aniline, a base, as the ionic anilinium chloride. The aqueous layer is
removed. Evaporation of the ether now leaves naphthalene, the neutral
compound. The other three compounds are recovered by adding acid to the
sodium benzoate and sodium phenolate and base to the anilinium chloride to
regenerate the covalent compounds benzoic acid, phenol, and aniline. These
operations are conveniently represented in a flow diagram (Fig. 2).
The ability to separate strong from weak acids depends on the acidity
constants of the acids and the basicity constants ofthe bases as follows. In
the first equation consider the ionization of benzoic acid, which has an
equilibrium constant, Ka, of 6.8 x 10-5. The conversion of benzoic acid to the
benzoate anion in Eq. 4 is governed by the equilibrium constant, K (Eq. 5),
obtained by combining the third and fourth equations.
then from Eq. 5 the hydroxide ion concentration would need to be 3.2 x 10-7
M. Because saturated NaHCO3 has [OH-] = 3 x 10-4 M, the hydroxide ion
concentration is high enough to convert benzoic acid completely to sodium
benzoate.
For phenol with a Ka of 10-10 the minimum hydroxide ion concentration that
will produce the phenoxide anion in 99% conversion is 10-2 M. le
concentration of hydroxide in 10% sodium hydroxide solution is -1 M and so
phenol in strong base is entirely converted to the water soluble salt.
Liquid/liquid extraction and acid/base extraction are employed in the
majority of organic reactions because it is unusual to have the product
crystallize from the reaction mixture or to be able to distill the reaction product
directly from the reaction mixture.
Apparatus and Chemicals
1. Tool box
2. Benzoic acid
3. Aniline
4. Naphalene
5. Ether
6. 0.1 N HCl solution
7. 0.1 N NaOH solution
Related Chemical Reaction
ΗΟΟC
in ether phase
NH2
benzoic acid
aniline
naphtalene
extracted with 0.1 N NaOH
Week 1
ether phase
extracted with 0.1 N HCl
aqueous phase
A
aqueous phase
+ 0.1 N HCl
ether phase
B
C
D
E
ether phase
+ 0.1 N NaOH
ether phase
week 2
Recrystralization
Vacuum distillation
Recrystalization
Week 1 Procedures
1. Dissolve benzoic acid 2 g, Naphalene 2 g and aniline 5 g in 50 mL
ether.
2. Transfer the prepared solution into separatory funnel. Add 0.1 N NaOH
(50 mL) and shake well. Separate aqueous phase and shake ether
phase with 0.1 N NaOH (50 mLx2). Collect aqueous phase to give
solution A
3. Shake ether phase in 2. with 0.1 N HCl (50 mL x 2). Collect aqueous
phase to give solution B and collect ether phase to give solution C.
4. Add 0.1 N HCl (50 mL) to solution A in a beaker. Mix until compound D
is precipitated. Filter and wash the precipitation with water. Keep the
precipitation for next week.
5. In separatory funnel, add 0.1 N NaOH (25 mL) and ether (25 mL) into
solution B. Shake well and separate ether phase. Shake ether phase
with new ether (50mL x2). Collect ether phase to give solution E.
Week 2 Procedure
Purification of compound D
1. Dissolve compound D wit ethanol (100 mL). Heat the solution and add
small amount of activated carbon. Stir for 5 min.
2. Filter hot solution by filter paper. Wash filter paper with small amount
of hot ethanol.
3. Cool down the obtained solution in ice water. The crystal of
compound D will be formed. Collect crystals with filter paper. Weight
dry crystal and record the value.
Purification of compound C
4. Evaporate ether out of solution C (Omit this procedure if there is only
small amount of ether is left.).
5. Repeat procedure 1-3, except changing compound D to compound C.
Purification of compound E
6. Fabricate a vacuum distillation set.
7. Remove ether out of the solution by distillation (temp < 40oC).
8. Distill pure compound E out of the crude solution, accept the
compound by new round flask (Weight the flask before use.)
9. Weight the obtained liquid and record the value.
In your report
1. Complete A-E in the table and explain about reactions used in acidbase extraction.
2. Calculate yield of recovery for each compound. (yield (%) = weight of
obtained comound/ weight of starting compound x 100)
3. Show the way to calculate the concentration of OH- that is necessary
in convert 99% of benzoic acid into benzoate ion.
Lab 4: The SN2 Reaction: 1-Bromobutane
Aim: To learn method for synthesis of n-butyl bromide by SN2 Reaction and
purification of the product
Prelab Exercise: Prepare a detailed flow sheet for the isolation and
purification of n-butyl bromide. Indicate how each reaction by-product is
removed and which layer is expected to contain the product in each
separation step.
Apparatus, Chemicals: 1. Tool box
2. n-butyl alcohol
3. Sodium bromide
4. conc. H2SO4
5. 10% NaOH solution
Theory
A primary alkyl bromide can be prepared by heating the corresponding
alcohol with (a) constant-boiling hydrobromic acid (47% HBr); (b) an aqueous
solution of sodium bromide and excess sulfuric acid, which is an equilibrium
mixture containing hydrobromic acid; or (c) with a solution of hydrobromic acid
produced by bubbling sulfur dioxide into a suspension of bromine in water.
Reagents (b) and (c) contain sulfuric acid at a concentration high enough to
dehydrate secondary and tertiary alcohols to undesirable by-products
(alkenes and ethers) and hence the HBr method (a) is preferred for
preparation of halides of the types R2CHBr and R3CBr. Primary alcohols are
more resistant to dehydration and can be converted efficiently to the bromides
by the more economical methods (b) and (c), unless they are of such high
molecular weight as to lack adequate solubility in the aqueous mixtures. The
NaBr-H2S04 method is preferred to the Br2-SO2 method because of the
unpleasant, choking property of sulfur dioxide. The overall equation is given
above, along with key properties of the starting material and principal product.
.
The procedure that follows specifies a certain proportion of 1-butanol, sodium
bromide, sulfuric acid, and water; defines the reaction temperature and time;
and describes operations to be performed in working up the reaction mixture.
The prescription of quantities is based upon considerations of stoichiometry
as modified by the results of experimentation. Before undertaking a
preparative experiment you should analyze the procedure and calculate the
molecular proportions of the reagents. Construction of tables (see table
below) of properties of starting material, reagents, products, and by-products
provides guidance in regulation of temperature and in separation and
purification of the product and should be entered in the laboratory notebook.
One mole of 1-butanol theoretically requires one mole each of sodium
bromide and sulfuric acid, but the procedure calls for use of a slight excess of
bromide and twice the theoretical amount of acid. Excess acid is used to shift
the equilibrium in favor of a high concentration of hydrobromic acid. The
amount of sodium bromide taken, arbitrarily set at 1.2 times the theory as an
insurance measure, is calculated as follows:
8 (g of C4H9OH)
x 102.91 (MW of NaBr) x 1.2 = 13.3 g of NaBr
74.12 (MW of C4H9OH)
The theoretical yield is 0.11 mole of product, corresponding to the 0.11 mole
of butyl alcohol taken; the maximal weight of product is calculated thus:
0.ll (mole of alcohol) x 137.03 (MW of product) = 14.8 g 1-bromobutane
The probability-products are 1-butene, dibutyl ether, and the starting alcohol.
The alkene is easily separable by distillation, but the other substances an, in
the same boiling point range as the product. However, three possibly byproducts can be eliminated by extraction with concentrated sulfuric acid.
Experiments
I. Synthesis of 1-Bromobutane
Put 13.3 g of sodium bromide, 15 mL of water, and 10 mL of n-buty lalcohol in
a 100-mL round-bottomed flask, cool the mixture in an ice-water bath, and
slowly add 11.5 mL of concentrated sulfuric acid with swirling and cooling.
Place the flask in an oil bath, clamp it securely, and fit it with a short
condenser for reflux condensation (Fig. 1). Heat to the boiling point, note the
time, and adjust the heat for brisk, steady refluxing. The upper layer that soon
separates is the alkyl bromide, since the aqueous solution of inorganic salts
has a greater density. Reflux for 45 min, remove the heat, and let the
condenser drain for a few minutes (extension of the reaction period to 1 h
increases the yield by only 1-2%).
Remove the condenser, mount a still head in the flask, and set the condenser
for downward distillation (see Fig.2) into a 50-mL Erlenmeyer. Distill the
mixture, make frequent readings of the temperature, and distill until no more
water-insoluble droplets come over, by which time the temperature should
have reached 115°C (collect a few drops of distillate in a test tube and see if it
is water soluble.). The increasing boiling point is due to azeotropic distillation
of n-butyl bromide with water containing increasing amounts of sulfuric acid,
which raises the boiling point.
II. Purification of 1-Bromobutane
Pour the distillate into a clean and dry the separatory funnel. Then cool 10
mL of concentrated sulfuric acid thoroughly in an ice bath and add the acid to
the funnel, shake well, and allow 5 min for separation of the layers. (Use care
in handling concentrated sulfuric acid. Check to see that the stopcock and
stopper don't leak. The relative densities given in the tables presented in, the
introduction of this experiment identify the two layers; an empirical method of
telling the layers apart is to draw off a few drops of the lower layer into a test
tube and see whether the material is soluble in water (H2SO4) or insoluble in
water (bromobutane).)
Separate the layers. Then wash the 1-bromobutane with 10 mL of 10%
sodium hydroxide (den. 1.11) solution to remove traces
Fig. 1 Refluxing a reaction mixture.
Fig.2 Distillation set.
of acid, separate, and be careful to save the proper layer.
Dry the cloudy 1-bromobutane by adding 1 g of anhydrous calcium chloride
with swirling until the liquid clears. Further drying can be effected by
transferring the liquid to another flask and adding anhydrous sodium sulfate
until the prying agent no longer clumps together.
After 5 min decant the dried liquid into a 25-mL flask or filter it through a fluted
filter paper.
Weight the product and calculate yield of the reaction. Pure sample into the
container provided after having it checked by the instructor.
Cleaning Up: Carefully dilute all non-organic material with water (the
reaction pot residue, the sulfuric acid wash, and the sodium hydroxide wash),
and combine and neutralize with sodium carbonate before flushing down the
drain with excess water. The residue from the distillation
1-bromobutane goes in the container for halogenated organic solvents. The
drying agent, after the solvent is allowed to evaporate from it in the hood goes
in the non-hazardous solid waste container.
Questions
1. What experimental method would you recommend for the preparation of tButyl bromide?
2. How does each of these impurities react with sulfuric acid when the crude
1-bromobutane is shaken with this reagent?
3. How should the reaction conditions in the present experiment be changed
to try to produce l -chlorobutane?
4. What is the purpose of refluxing the reaction mixture for 45 min? Write
reaction mechanisms showing how 1-bromobutane, 1-butene and di-n-butyl
ether are formed.
Lab. 5-6 Biosynthesis of Ethanol
Aim To know about properties of enzymatic reaction.
Table 1. Reaction conditions
Reaction
Sugar
Weight of
sugar (g)
A. Standard
Sucrose
51.5 g
Yeas
t
(g)
2
Na2HPO
B. Effect of O2
Sucrose
51.5 g
2
0.35
C. Effect of
concentration
D. Effect of
temperature
Sucrose
102.0 g
2
0.35
Sucrose
51.5 g
2
0.35
4
(g)
0.35
condit
ion
anaer
obic
aerob
ic
anaer
obic
anaer
obic
o
C
Sugar
concentration
(%)
35
35
35
Low
temp.
Procedures
Week 1
1. Mix 2.0 g of yeast in 50 mL of water.
2. Dilute sugar (and Na2HPO4) to give 150 mL solution.
3. Measure the % of sugar in solution by reflective index (Brix).
4. Mix solution in No. 1 and solution in No, 2 in the given container.
5. Make gas outlet to Ca(OH)2 in glass tube .
6. Ferment the above solution at 35oC or at low temperature.
Week 2
1. Filter yeast out of the fermented solution by celite (5 g). Wash celite with
small amount of water.
2. Adjust the final solution by addition of water to be 300 mL.
3. Measure % of sugar in the obtained solution by reflective index (Brix).
4. Measure % of ethanol in the obtained solution by the following steps.
A. Distillation
1. Take 100 mL of sample in measuring flask.
2. Transfer sample to distillation set. Wash measuring flask with 30 mL of
water. Add washing water to the sample to give 130 mL of sample.
3. Distill to collect about 70 mL of distillate.
4. Transfer into well washed 100 mL measuring flask again. Add water to
give 100 mL of solution.
B. Titration (Oxidation titration)
1. Potassium dichromate K2Cr2O7 (Fw.294.2)
Dilute 33.816 g in water to give 1 L solution. (This solution is prepared by
staff.)
2. 85% phosphoric acid
3. Barium diphenylamine sulfonate
Dilute 0.5 g in water to give 100 mL. Use the clear upper layer. (This
solution is prepared by staff.)
4. Ferrous ammonium sulfate FeSO4(NH4)2SO4.6H2O, (FW. 392)
Dilute 135.1 g in conc. H2SO4, add water to give 1 L of solution. (This
solution is prepared by staff.)
5. Take 10 mL of K2Cr2O7 solution to 200 mL flask. Add 5 mL of conc.
H2SO4 and 5 mL of distillate sample from section A. Mix well, close the
flask and leave for 15 min.
6. Add 165 mL of water, 18 mL of phosphoric acid and 0.5 mL of indicator.
Titrate with FeSO4(NH4)2SO4.6H2O solution until color of solution change
from blue to green. The volume of consumed FeSO4(NH4)2SO4.6H2O is
given as n mL.
7. Do step 5-6 again but use 5 mL water instead of distillate sample. The
volume of consumed FeSO4(NH4)2SO4.6H2O is given as N mL.
8. Percentage of alcohol is calculated by this formula.
Alcohol(%) =
2 x (1- n/N) x (volume of all distillate (mL)/volume of sample used in
distillation (100 mL))
Table 2. Results
Reaction
Sugar before
fermentation
(wt %)
A. Standard
B. Effect of
O2
C. Effect of
concentration
D. Effect of
temperature
Sugar
after fermentation
(wt %)
EtOH
(wt %)
In results and discussions
1. What is the white precipitation in Ca(OH)2 solution?
2. Is there any relation between mol of consumed sugar and mol of the
obtained ethanol?
3. What is the effect of oxygen in this reaction?
4. What is the effect of concentration of sugar in this reaction?
5. What is the effect of temperature in this reaction?
6. Explain the characters of enzymatic reaction. Give 2 examples of
enzymatic reactions.
7. Explain the formula for calculating percentage of alcohol.
Lab 7: Synthesis of Polymer (6,6-nilon & Polyurea)
Aim: To learn method for interfacial synthesis of 6,6-nilon and condensation
synthesis of polyurea
Apparatus: 1. Glass tube 2. 50 mL-beaker 3. tweeter 4. aluminium cup 5.
glass rod
Chemicals: 1. Adipic acid dichloride (ClCO(CH2)4COCl) 2. hexane 3. 1,6diaminohexane (NH2(CH2)4NH2)
4. Acetone 5. 1 M NaOH solution 6. urea (NH2CONH2) 7.
formaldehyde 8. 6 M HCl
Theory
Polymers are ubiquitous. Natural polymers such as proteins (polyamino
acids), DNA (polynucleotides), and cellulose (polyglucose) are the basic
building blocks of plant and animal life. Synthetic organic polymers, or plastics,
are now among our most common structural materials. In the United States
we make and use more synthetic polymers than we do steel, aluminum, and
copper combined-in 1984,46 billion pounds, worth $18 billion dollars.
.
Polymers, from the Greek meaning "many parts," are high-molecular
weight molecules made up of repeating units of smaller molecules. Most
polymers consist of long chains held together by hydrogen bonds, van der
Waals forces, and the tangling of the long chains. When heated, the covalent
bonds of some polymers, which are thermoplastic, do not break, but the
chains slide over one another to adopt new shapes. These shapes can be
films, sheets, extrusions, or molded parts in a myriad of forms.
The first man-made plastic was nitrocellulose, made in 1862 by nitrating
the natural polymer, cellulose. Nitrocellulose, when mixed with a plasticizer
such as camphor to make it more workable, was originally used as a
replacement for ivory in billiard balls and piano keys and to make Celluloid
collars. This material, from which the first movie film was made, is notoriously flammable.
Cellulose acetate, made by treating cellulose with acetic acid and acetic
anhydride, was originally used as a waterproof varnish to coat the fabric of
airplanes during World War I. It later became important as a photographic film
base and as acetate rayon.
One of the most important polymers is nylon, a name so ingrained into
English language that it has lost trademark status. It was developed by
Wallace Carothers, director of organic chemicals research at DuPont, and
was the outgrowth of his fundamental research into polymer chemistry.
Introduced in 1938, it was the first totally synthetic fiber. The most common
form of nylon is the polyamide formed by the condensation of hexamethylene
diamine and adipic acid (Figure 1).
Figure 1. Condensation Formation of nylon6.6
The reactants are mixed together to form a salt that melts at 180oC. This
is concerted into the polyamide by heating to 280oC under pressure, which
eliminate water. Nylon 6.6 is used to make textiles, while nylon 6.10, from the
Figure 2. Interfacial polymerization of nylon 6.10
10-carbon diacid, is used for bristles and high impact sports equipment.
Nylon can also be made by interfacial and by ring-opening polymerization.
Figure 3. Ring opening polymerization of nylon 6.6.
As a diamide, urea is capable of forming polymers, it reacts with
formaldehyde to form the urea-formaldehyde resins, highly important in
molded plastics. In the resin, a space-net work polymer is formed (Figure 4).
Figure 4. Formation of polyurea.
Experiments
I. Synthesis of 6.6 nilon by interfacial polymerization
1. Dilute 0.5 mL of adipic acid dichloride in 20 mL of hexane.
2. In 50 mL- beaker dilute 0.8 g of 1,6-diaminohexane in 20 mL of 1 M
NaOH solution.
3. Carefully pour adipic acid dichloride solution onto the top of 1,6diaminohexane.
4. Pick up the polymer film at the center with a tweeter and lead it over
the outer surface of beaker as it is remove. Remove as much of the
polymer as possible, wash it thoroughly in water, and press it as dry as
possible.
5. Attach a piece of the polymer to your laboratory report.
II. Synthesis of polyurea resin
1. In an aluminium cup, mix 1 g of urea with 2 mL of formaldehyde.
2. Add 6 M HCl 0.5 mL to the mixture and use glass rod mix them
quickly. White precipitation will be formed.
3. Attach a piece of the polymer to your laboratory report.
Questions
1. Discuss about the reaction mechanism in Figure 1, the reaction of
interfacial polymerization and ring-opening polymerization of nylon.
2. Write a balance equation for the reaction of adipic acid dichloride and water.
3. Discuss about the reaction, which happened in synthesis of polyurea resin.
4. Explain the difference between mechanism of condensation polymerization
and free-radical polymerization.
Lab 8: Synthesis of Ester
Aim: To know the characters of ester and method for preparing ester.
Examples of esters in daily life
1. Oils and Fats are esters of higher carboxylic acid and glycerin.
2. Wax is ester of higher carboxylic acids and higher alcohols.
3. Ester is the chief ingredient in fragrance of fruits
4. Ester of salicylic acid and acetic acid is aspirin (acetylsalicylate)
5. Ester of salicylic acid methanol is salomethyl (methylsalicylate)
Theory: The ester group
is an important functional group that can be synthesized in a number of
different ways. The low molecular weight esters have very pleasant odors and
indeed are the major components of the flavor and odor components of a
number of fruits. Although the natural flavor may contain nearly a hundred
different compounds, single esters approximate the natural odors and are
often used in the food industry for artificial flavors and fragrances. (Table 1).
Esters can be prepared by the reaction of a carboxylic acid with an alcohol
in the presence of a catalyst such as concentrated sulfuric acid, hydrogen
chloride, p-toluenesulfonic acid, or the acid form of an ion exchange resin:
This Fischer esterification reaction reaches equilibrium after a few hours of
refluxing. The position of the equilibrium can be shifted by adding more of the
acid or of the alcohol, depending on cost or availability. The mechanism of the
reaction involves initial protonation of the carboxyl group, attack by the
nucleophilic hydroxyl, a proton transfer, and loss of water followed by loss of
the catalyzing proton to give the ester. Because each of these steps is
completely reversible, this process is also, in reverse, the mechanism for the
hydrolysis of an ester:
Other methods are available for the synthesis of esters, most of them
more expensive but readily carried out on a small scale. For example,
alcohols react with anhydrides and with acid chlorides:
In the latter reaction an organic base such as pyridine is usually added to
react with the hydrogen chloride.
A number of other methods can be used to synthesize the ester group.
Among these are the addition of2-methylpropene to an acid to form t-butyl
esters, the addition of ketene to make acetates, and the reaction of a silver
salt with an alkyl halide:
As noted above, Fischer esterification is an equilibrium process. Consider
the reaction of acetic acid with 1-butanol to give n-butyl acetate:
The equilibrium constant is:
Keq = [n-BuOAc][H2O]
[n-BuOH][HOAc]
For primary alcohols reacting with unhindered carboxylic acids, Keq = 4. If
equal quantities of 1-butanol and acetic acid are allowed to react, at
equilibrium the theoretical yield of ester is only 67%. To upset the equilibrium
we can, by Le Chatelier's principle, increase the concentration of either the
alcohol or acid, as noted above. If either one is doubled the theoretical yield
increases to 85%. When one is tripled it goes to 90%. But note that in the
example cited the boiling point of the relatively non polar ester is only about
8oC higher than the boiling points of the polar acetic acid and 1-butanol, so a
difficult separation problem exists if either starting material is increased in
concentration and the product isolated by distillation.
Another way to upset the equilibrium is to remove water. This can be done
by adding to the reaction mixture molecular sieves (an artificial zeolite), which
preferentially adsorb water. Most other drying agents, such as anhydrous
sodium sulfate, will not remove water at the temperature used to make esters.
A third way to upset the equilibrium is to preferentially remove the water as an
azeotrope (a constant-boiling mixture of water and an organic liquid).
Apparatus:
1.glass tube x 3-4
2. pipet(x 2) + ลูกยาง
3. rubber cork
4. beakers (500 mL x 1) (200 mL x 1)
5. heater
6. glass rod
7. glass watch (x 2)
8. Measuring cylinder (10 mL x 1)
Chemicals: con. H2SO4, ether, NaHCO3
carboxylic acid
D
alcohol
D (g/cc)
(g/cc)
formic acid HCOOH
1.22 CH3OH
0.79
acetic acid CH3COOH
1.05 C2H5OH
0.79
propionic acid
0.99 n0.80
CH3CH2COOH
0.96 C3H5OH
0.786
butyric acid
iso0.81
CH3CH2CH2COOH
C3H5OH
0.81
benzoic acid C6H5COOH
n0.81
C4H9OH
salicylic acid
0.81
HOC6H4COOH
0.82
isoC4H9OH
0.83
nC5H11OH
isoC5H11OH
nC7H15OH
nC8H17OH
salicylic
acid
Experiment 1: Synthesis of fragance (Choose 2 combinations of acids and
alcoholsin the table.)
* Smell alcohols and carboxylic acids before and after the reaction
1. Heat 100 mL of water in 500 mL-beaker to 70-80oC.
2. Pour 2 mL of carboxylic acid and 2 mL of alcohol to a glass tube.
3. Slowly add 1 mL of concentrated sulfuric acid to the mixture. Heat
the mixture in hot water for 3-10 min. (Do not warm if your ester has
low molecular weight, or use rubber cork to prevent evaporation
during heating.)
4. If the smell changes from the starting mixture, it means the
occurrence of the reaction. Cool glass tube in water and add 10 mL
of water and 1 mL of ether. Mix the solution and let it separate into
2 layers.
5. Take ether phase out of the glass tube by pipet and transfer ether
phase to glass watch (Do not contain any aqueous phase. Leave it
until all of ether evaporates.
6. Weight the ester and calculate the yield. Write the structures and
names of the obtained ester, and smell the orders.
Experiment 2: Synthesis of Drugs (Choose 1 reaction.)
O
C
O
C
H2SO4
OCH3
OH
CH3OH
OH
H2SO4
CH3COOH
OH
salicylic acid
methyl salicylate
O
C
H3C
O
C
OH
O
acetyl salicylate
Synthesis of methylsalicylate
1. Add 2 g of salicylic acid and 5 mL of methanol in glass tube. Heat the
tube in hot water and stir until all of salicylic acid is dissolved.
2. Add 4-5 drops of con. Sulfuric acid and put the rubber cork on the tube.
3. Heat the solution in hot water for 15-20 min. Stir all the time.
4. After cooling down the tube, transfer the mixture to separatory funnel
and add 10 mL of n-pentane and 20 mL of water. Dispose aqueous
phase.
5. Add the solution of NaHCO3 0.1 g in 20 mL of water to organic phase.
Shake well and dispose the aqueous phase.
6. Let the solvent evaporate out of the product.
7. Smell the obtained ester. Weight the sample and calculate the yield.
Synthesis of aspirin
1. Mix 4 mL of acetic acid and 2 g of salicylic acid in the glass tube. Add
4-5 drops of con. Sulfuric acid and heat in hot water for 10 min.
2. Add 10 mL of water. Cool the glass tube in cold water. Scratch the
inner surface of glass tube by glass rod (to induct the formation of
crystals).
3. When white precipitation is formed, filter the precipitation by suction
filtration.
4. Weight the sample and calculate the yield.
Questions
1. Write and explain the mechanism of each reaction in the experiment.
2. Why the addition of sulfuric acid is necessary in the reaction?
3. List other methods for preparing ester and explain why the reaction
between carboxylic acid and alcohol is still the most useful method.
Ester
methyl acetate
Formula
Ethyl acetate
O
CH3COC2H5
Orange, lemon
n-amyl acetate
O
CH3COC5H11
banana
Benzyl acetate
O
CH3COCH2C6H5
Jasmine
Methyl propionate
O
C3H7COCH3
pineapple
Isoamyl butyrate
O
CH3COC2H4CH(CH3)2
pear
Ethyl hexanoate
O
C6H13COC2H5
Peach, strawberry
n-amyl pentanoate
O
CH3COCH3
O
C4H9COC5H11
Fragrance
pineapple
apple
Lab 9. Synthesis of Sulfanilic Acid
Aim: 1. To know the Electrophilic aromatic substitution reaction via
synthesis of Sulfanilic acid
2. To know the purification of compound by recrystallization
apparatus: 1. Tool box 2. Heater 3. Thermometer
Chemical: 1. Aniline 2. Conc. H2SO4
Theory
Sulfonation of aromatic amines: Dipolar ions
Aniline is usually sulfonated by "baking" the salt, anilinium hydrogen
sulfate, at 180-200 oC; the chief product is the para isomer. In this case we
cannot discuss orientation on our usual basis of which isomer is formed
faster. Sulfonation is known to be reversible, and the para isomer is known to
be the most stable isomer; it may well be that the product obtained, the para
isomer, is determined by the position of an equilibrium and not by relative
rates of formation. It also seems likely that, in some cases at least, sulfonation
of amines proceeds by a mechanism that is entirely different from ordinary
aromatic substitution.
Whatever the mechanism by which it is formed, the chief product of this
reaction is p-aminobenzenesulfonic acid, known as sulfanilic acid; it is an
important and interesting compound.
First of all, its properties are not those we would expect of a compound
containing an amino group and a sulfonic acid group. Both aromatic amines
and aromatic sulfonic acids have low melting points; benzenesulfonic acid, for
example, melts at 66°C, and aniline at -6 oC. Yet sulfanilic acid has such a
high melting point that on being heated it decomposes (at 280-300 °c) before
its melting point can be reached. Sulfonic acids are generally very soluble in
water; indeed, we have seen that the sulfonic acid group is often introduced
into a molecule to make it water-soluble. Yet sulfanilic acid is not only
insoluble in organic solvents, but also nearly insoluble in water. Amines
dissolve in aqueous mineral acids because of their conversion into watersoluble salts. Sulfanilic acid is soluble in aqueous bases but insoluble in
aqueous acids.
These properties of sulfanilic acid are understandable when we realize
that sulfanilic acid actually has the structure I which contains the -NH3+ and S03- groups. Sulfanilic acid is a salt, but of a rather special kind, called a
dipolar ion (sometimes called a zwitterion, from the German, Zwitter,
hermaphrodite). It is the product of reaction between an acidic group and a
basic group that are part of the same molecule. The hydrogen ion is attached
to nitrogen rather than oxygen simply because the -NH2 group is a stronger
base than the -S03- group. A high melting point and insolubility in organic
solvents are properties we would expect of a salt. Insolubility in water is not
surprising, since many salts are insoluble in water. In alkaline solution, the
strongly basic hydroxide ion pulls hydrogen ion away from the weakly basic NH2 group to yield the p-aminobenzenesulfonate ion (II), which, like most
sodium salts, is soluble in water. In aqueous acid, however, the sulfanilic acid
structure is not changed, and therefore the compound remains insoluble;
sulfonic acids are strong acids and their anions (very weak bases) show little
tendency to accept hydrogen ion from H3O+ .
We can expect to encounter dipolar ions whenever we have a molecule
containing both an amino group and an acid group, providing the amine is
more basic than the anion of the acid.
Experiment
Synthesis of sulfanilic acid
1. Set the apparatus as shown in Figure
1. (Put a boiling chip instead of stirrer
chip.)
2. Add 5 g of aniline to the three-neck
flask and add 16.5 g(9.5 mL) of
concentrated sulfuric acid to the drop
wise apparatus (separatory funnel).
3. Drop sulfuric acid to aniline slowly.
Mix the mixture by shaking the flask.
4. Heat the mixture at 180-200oC for 1.5
hour (or untill all of aniline is
consumed).
5. After the reaction, slowly add 100 mL
Experiment setting.
of cold water to the mixture and
mix with glass rod. The crystals of sulfanilic acid will be formed.
Recrystallization
6. Filter the crystals in 5 by suction filtration. Wash the crystals with small
amount of water.
7. Dissolute the obtained crystals with hot water if the solution is not clear,
add small amount of activated carbon.
8. Quickly filter hot solution with fold filter paper.
9. Cool the solution from filtration with ice water. The white precipitation will
be formed.
10. Filter the white precipitation of by suction filtration.
Question
1. Discuss about the reaction mechanism.
2. Why it is said that the reaction yields only para isomer?
3. Calculate yield of the reaction.
4. Why is sulfanilic acid not dissolved in water?
Lab 10: Synthesis of β−Naphthol orange (Orange II)
Aim: 1. To learn about the Diazo coupling reaction
2. To learn about the multi-step reaction
3. To know the principle of dyeing
Apparatus: 1. Apparatus in tool box 2. Heater 3.Elenmyer flask 300 mL x 2 4.
Elenmyer flask 100 mL x 1 5. Elenmyer flask 50 mL x 2 6. Beaker 100 mL x 2
Chemicals: Sulfanilic acid 2. NaOH aq.(2 M) 3. NaNO2 4. Conc. H2SO4 5. βNaphthol 6. NaCl aq (saturated)
Related reactions:
Theory:
Diazonium salts
When a primary aromatic amine, dissolved or suspended in cold
aqueous mineral acid, is treated with sodium nitrite, there is a formed a
diazonium salt. Since diazonium salts slowly decompose even at ice-bath
temperature, the solution is used immediately after preparation.
Replacement of the diazonium group is the best general way of
introducing F, Cl, Br, I, CN, OH, and H into an aromatic ring. Diazonium salts
are valuable in synthesis not only because they react to form so many classes
of compounds, but also because they can be prepared from nearly all primary
aromatic amines. There are few groups whose presence in the molecule
interferes with diazotization; in this respect, diazonium salts are quite different
from Grignard reagents. The amines from which diazonium compounds are
prepared are readily obtained from the corresponding nitro compounds, which
are prepared by direct nitration. Diazonium salts are thus the most important
link in the sequence shown below. In addition to the atoms and groups listed,
there are dozens of other groups that can be attached to an aromatic ring by
replacement of the diazonium nitrogen, as, for example, -Ar, -NO2, -OR, -SH, -
SR, -NCS, -NCO, -PO3H2, -AsO3H2, -SbO3H2; the best way to introduce most
of these groups is via diazotization.
The coupling of diazoniumsalts with aromatic phenols and amines yields
azo compounds, which are of tremendous importance to the dye industry.
Coupling of diazonium salts. Synthesis of azo compounds
Under the proper conditions, diazonium salts react with certain
aromatic compounds to yield products of the general formula Ar-N=N-Ar',
called azo compounds; In this reaction, known as coupling, the nitrogen of
the diazonium group is retained in the product, in contrast to the replacement
reactions we have studied up to this point, in which nitrogen is lost.
ArN2 + + Ar'H
Ar-N=N-Ar' + H+
An azo compound
The aromatic ring (Ar'H) undergoing attack by the diazonium ion must, in
general, contain a powerfully eleotron-releasing group, generally -OH, -NR2, NHR, or -NH2. Substitution usually occurs para to the activating group.
Typically, coupling with phenols is carried out in mildly alkaline solution, and
with amines in mildly acidic solution.
.
Activation by electron-releasing groups, as well as the evidence of kinetics
studies, indicates that coupling is electrophilic aromatic substitution in which
the diazonium ion is the attacking reagent:
It is significant that the aromatic compounds which undergo coupling are also
the ones which undergo nitrosation. Like the nitrosonium ion, +NO, the
diazonium ion, ArN2+, is evidently very weakly electrophilic, and is capable of
attacking only very reactive rings.
In the laboratory we find that coupling involves more than merely
mixing together a diazonium salt and a phenol or amine. Competing with any
other reaction of diazonium salts is the reaction with water to yield a phenol. If
coupling proceeds slowly because of unfavorable conditions, phenol formation
may very well become the major reaction. Furthermore, the phenol formed
from the diazonium salt can itself undergo coupling; even a relatively small
amount of this undesired coupling product could contaminate the desired
material-usually a dye whose color should be as pure as possible-to such an
extent that the product would be worthless. Conditions under which coupling
proceeds as rapidly as possible must therefore be selected.
It is most important that the coupling medium be adjusted to the right
degree of acidity or alkalinity. This is accomplished by addition of the proper
amount of hydroxide or salts like sodium acetate or sodium carbonate. It will
be well to examine this matter in some detail, since it illustrates a problem that
it frequently encountered in organic chemical practice.
The electrophilic reagent is the diazonium ion, ArN2 +. In the presence of
hydroxide ion, the diazonium ion exists in equilibrium with an un-ionized compound, Ar-N=N-OH, and salts (Ar-N=N-O-Na+) derived from it:
For our purpose we need only know that hydroxide tends to convert
diazonium ion, which couples, into compounds which do not couple. In so far
as the electrophilic reagent is concerned, then, coupling will be favored by a
low concentration of hydroxide ion, that is, by high acidity.
But what is the effect of high acidity on the amine or phenol with which the
diazonium salt is reacting? Acid converts an amine
into its ion, which, because of the positive charge, is
relatively unreactive toward electrophilic aromatic
substitution: much too unreactive to be attacked by
the weakly electrophilic diazonium ion. The higher
the acidity, the higher the proportion of amine that
exists as its ion, and the lower the rate of coupling.
An analogous situation exists for a phenol. A
Phenol is appreciably acid; in aqueous solutions it
exists in equilibrium with the phenoxide ion:
The fully developed negative charge makes -O- much more powerfully
electronreleasing than -OH; the phenoxide ion
is therefore much more reactive than the un-ionized phenol toward
electrophilic aromatic substitution. The higher the acidity of the medium, the
higher the proportion of phenol that is un-ionized, and the lower the rate of
coupling. In so far as the amine or phenol is concerried, then, coupling is
favored by low acidity.
The conditions under which coupling proceeds most rapidly are the result
of a compromise. The solution must not be so alkaline that the concentration
of diazonium ion is too low; it must not be so acidic that the concentration of
free amine or phenoxide or phenoxide ion is too low. It turns out that amines
couple fastest in mildly acidic solutions, and phenols couple fastest- in mildly
alkaline solutions.
Azo compound are the compounds that as a class are strongly colored.
They can be intensely yellow, orange, red, blue or even green, depending
upon the exact structure of the molecule. Because of their color, the azo
compounds are of tremendous importance as dyes; about half of the dyes in
industrial use today are azo dyes. Some of the acid-base indicators with
which we are already familiar are azo compounds.
Dyes and Dyeing
In this experiment azo dyes will be used to dye a representative group of
natural and man-made fibers. You will receive several pieces of fabric
samples.
Below the black thread at the top, the fibers are acetate rayon (cellulose
di- or triacetate, cotton, Creslan (polyacrylonitrile), Dacron 54 and 64
(polyester without and with a brightener), silk (polyamide),
Acetate rayon is cellulose (from any source) in which about two of the
hydroxyl groups in each unit have been acetylated. This renders the polymer
soluble in acetone from which it can be spun into fiber. The smaller number of
hydroxyl groups in acetate rayon compared to cotton makes direct dyeing of
rayon more difficult than of cotton.
Cotton is pure cellulose. Nylon is a polyamide and made by polymerizing
adipic acid and hexamethylenediamine. The nylon polymer chain can be
prepared with one acid and one amine group at the termini, or with both acids
or both amines. Except for these terminal groups, there are no polar centers
in nylon and consequently it is difficult to dye. Similarly Dacron, a polyester
made by polymerizing ethylene glycol and terephthalic acid, has few polar
centers within the polymer and consequently is difficult to dye. Even more
difficult to dye is Orlon, a polymer of acrylonitrile. Wool and silk are
polypeptides crosslinked with disulfide bridges. The acidic and basic amino
acids (e.g., glutamic acid and lysine) provide many polar groups in wool and
silk to which a dye can bind, making these fabrics easy to dye. In this
experiment note the marked differences in shade produced by the same dye
on different fibers.
Experiment
I Synthesis of β-Naphthol orange
1. Mix sulfanilic acid 1.6 g with NaOH (2M) 4.2 mL in a 300 mL-Elenmyer.
2. Make NaNO2 solution by NaNO2 0.6 g and water 5 mL, and add to the
solution in 1.
3. Cool the solution in 2. in ice water bath. Add the mixture of sulfuric acid
1.5 mL and water 7.5 mL. Mix the mixture for 20 min, the precipitation of
diazosulfanilic acid will be formed.
4. Prepare the mixture of -Naphthol 1.2g, NaOH (2M) 4 mL and water 12.5
mL. Add the mixture into the mixture in 3. Red crystals of -Naphthol
orange will be formed.
Purification of β−Naphthol orange
5. Warm the mixture in 4. The crystals will be dissolute with the generation of
gas.
6. Filter hot solution with a fold filter paper.
7. Cool down the obtained filtrate. Add 35 mL of saturation NaCl solution.
8. Filter and weight the obtained crystals. Calculate yield of the reaction.
II. Dyeing by β-Naphthol orange
1. Make the solution of 1 g of β-naphthol orange in 50 mL of water. Add 1-2
drops of sulfuric acid to make the pH to be 2-3.
2. Heat the solution at about 60oC. Add three kinds of fabric samples to the
solution (polyester, cotton, silk)
3. Raise temperature and boil the solution for 20-30 min.
4. Wash the fabric samples with water and let them dried.
5. Attach the samples in your report.
III. Decolorization of β-Naphthol orange (Do this experiment during the
dying of sample in the hood. You can join other groups.)
1. Heat the aqueous solution of β-Naphthol orange at 40-50oC.
2. Slowly add powder of Na2S2O4 to the solution. The red color will be
disappeared as the generation of bubble and yellow precipitation of
amino naphtol. Drain the upper clear solution and dispose the yellow
in trash box.
Questions
2 Calculate the yield of the reaction.
3 Explain every reaction in the formation of -Naphthol orange.
4 Why the solution of sulfanilic acid must be adjusted to basic before the
reaction with NaNO2
5 Discuss about the difference among the fabric samples on dying. (Base on
properties of β-Naphthol orange and molecular structures of the fabric
samples.)