Org Chem II Laboratory (Non-Majors)
The Properties of Alcohols
I.
Kelly
INTRODUCTION
Alcohols are classed into three categories: primary (1˚), secondary (2˚) and tertiary (3˚);
the classification is based on the type of carbon to which the hydroxyl group is attached.
If the carbon is attached to only one other carbon, it is a primary carbon. If the carbon is
attached to two other carbons, it is a secondary carbon and the alcohol is a secondary
alcohol and so on.
H
R C OH
H
H
R C OH
R'
1˚
R''
R C OH
R'
2˚
3˚
Alcohols have a much higher boiling point than ethers or alkanes of similar molecular
weight. This is due to the association of alcohols in the liquid phase through hydrogen
bonding. For example, the boiling point of butyl alcohol is 118˚C whereas the boiling
point of the isomeric diethyl ether is 36˚C.
Hydrogen Bonds
R
-∂
O
+∂ H
II.
H +∂
O
-∂
R
Procedure
Before the advent of modern spectroscopic methods, the determination of chemical
properties was of paramount importance for the identification, characterization and
determination of structure of pure substances. Many reagents or conditions were found to
be specific with substances that contained certain functional groups. Thus these reactions
can be used to confirm or deny the presence of a specific functional group. The following
experiment is designed to acquaint you with the chemical properties of alcohols and to
determine the structure of an unknown that you will receive. You will examine the
chemical and physical properties of various alcohols. From this data you will arrive at
conclusions as to the Structure-Chemical Activity relationship of alcohols. You will then
draw on these conclusions to deduce the structure of an unknown alcohol sample.
I.
Solubility of Alcohols
Because of the hydrogen bonding possible between the polar hydroxyl group of an alcohol
and water, many alcohols are soluble in water. However as the carbon content of an
alcohol goes up, the solubility decreases. This is often described as the 5-Carbon Rule, since
the point at which an alcohol is no longer soluble in water is often (but not always) reached
when it contains 5 or more carbons. However, alcohol structure (either 1˚, 2˚ or 3˚) also
has an effect on solubility.
PROCEDURE
1. Add each of the following alcohols drop wise to 1 mL of water. Count the
number of drops needed to cause a phase separation, but do not use more than 10
drops. If you have added 10 drops of alcohol, and no phase separation has been
observed, the alcohol should be classified as completely miscible in water.
Record your observations as very soluble (6-9 drops), soluble (2-5 drops), or
insoluble (1-drop)
1. absolute ethyl alcohol
2. n-butyl alcohol
3. sec-butyl alcohol
4. tert-butyl alcohol
5. cyclohexanol
6. Unknown
II.
Alcohols as a source of protons
This is a test for reactive hydrogens that is hydrogens that are sufficiently acidic that they
will react with sodium metal. Note that many compounds will give a reaction with sodium
metal even if that compound does not have a reactive hydrogen such as alcohols do. This
is often do to small amounts of water in the sample.
CAUTION SODIUM IS VERY REACTIVE AND MUST BE HANDELED WITH
CARE. USE ONLY SMALL PIECES AND HANDLE IT WITH FORCEPTS.
SODIUM REACTS VIOLENTLY WITH WATER! CARRY OUT ALL REACTIONS IN
A HOOD. IT IS NORMALLY STORED UNDER VISCOUS OIL THAT MUST BE
CAREFULLY BLOTTED OFF WITH PAPER TOWELS.
PROCEDURE (in the Hood)
1. Cut a small piece of sodium metal about half the size of a pea and add to a
beaker containing about 50 mL of water. Do this in a hood! Record you
observations on this reaction. After the reaction is complete, add 1-2 drops of
phenolphthalein indicator to the aqueous solution. Write an equation for the
reaction of sodium with water.
2. Cut small pieces of sodium metal about half the size of a pea and add, in the
hood, to 3 mL of each of the alcohols, below, in a 6-inch test tube. Devise a
method to describe the rate of the reaction (such as the rate of gas bubbles
evolved over time). Test the resulting solution with phenolphthalein. Write an
equation for the reaction of the alcohol with sodium. If all of the sodium
doesn’t react in any one of the alcohols, transfer this remaining sodium to the
alcohol that reacts fastest. DO NOT POUR THE ALCOHOL DOWN THE
DRAIN UNTIL YOU ARE SURE NO SODIUM REMAINS.
1. absolute ethyl alcohol
2. n-butyl alcohol
3. sec-butyl alcohol
4. tert-butyl alcohol
5. cyclohexanol
6. Unknown
III.
Alcohols in Substitution Reactions (Lucas Test)
This test relies on the fact that the ease of formation of carbocations from the
corresponding alcohols is highly dependent on the structural features in the molecule.
Treatment of the alcohol with a solution of zinc chloride in hydrochloric acid can serve as
a means of distinguishing between those alcohols that are quickly and easily converted to
the corresponding alkyl chlorides (via the carbocation) and those that are not.
Coordination of the zinc chloride with the hydroxyl function results in the production of a
sufficiently good leaving group the carbon-oxygen cleavage can now occur…if a
reasonable stable carbocation can form.
RO
H
ZnCl2, HCl
RO ZnCl2
H
R + Zn(OH)CL2
Cl
R Cl
If R is tertiary, the reaction takes place almost immediately, whereas secondary alcohols
require several minutes to undergo reaction and primary alcohols do not react over a
period of 15-20 min. The test depends on the observing the formation of an insoluble
liquid, alkyl chloride as a cloudy suspension that later separates into a distinct upper layer.
This test requires the alcohols to be soluble in the test solvent (namely water) and is thus
restricted to simple alcohols below hexyl (6 carbons).
PROCEDURE
1. Add 5-7 drops of each of the following alcohols to each of 6-inch test tubes
and add to each test tube 2-3 mL of Lucas Reagent prepared by dissolving 16 g of
test to be valid, the alcohol must be initially soluble in the Lucas Reagent. The
formation of a milky or opaque solution is evidence for formation of the
insoluble alkyl chloride. Note the time required for the mixture to become
cloudy or to separate into two layers. Place test tubes that have not reacted after
10 minutes in a beaker of boiling water for 15 minutes. Observe any changes.
Write an equation to describe the reaction, if any.
1.
2.
3.
4.
IV.
n-butyl alcohol
sec-butyl alcohol
tert-butyl alcohol
Unknown
Oxidation of Alcohols
Primary and secondary alcohols are oxidized rapidly to acids and ketones, respectively, by
Cr+6 oxidizing agents. Oxidation is readily detected by the loss of the red-orange color of
Cr+6 and the appearance of green color due to the reduced Cr+3 ion. Tertiary alcohols are
not easily oxidized, (however, over time in an acidic environment, they are dehydrated to
alkenes). This is the chemical test that is used in the common Breathalyzer Test used to
detect alcohol on the breath of drunken drivers,
PROCEDURE
1. Prepare the Jones Reagent by adding 2 grams of sodium dichromate to 10 mL
of water. Then add, slowly, with stirring, 2 mL of Conc. sulfuric acid. Pour 2
mL each of this solution into four 6-inch test tubes and add 2 mL of the following
alcohols to different test tubes.
1. n-butyl alcohol
2. sec-butyl alcohol
3. tert-butyl alcohol
4. Unknown
2. Stir each tube and note any rise in temperature (use you hand as a guide) or
change in color. Report your observations. In an acidic solution, the dichromate
ion, which is usually an orange-red color, is oxidized to the Cr+3 ion. This ion is
usually a dark green color but may form a dark precipitate with the carboxylate
group.
V.
Iodoform Test for Methyl Carbinols
A methyl carbinol is a 2˚ alcohol in which at least one of the R groups attached to the 2˚
carbon is a methyl group. A methyl carbinol can be easily oxidized to a methyl ketone
that is then able to undergo a process known as the iodoform reaction.
OH
R C CH3
H
O
R C CH3
O
R C CH2I
O
R C CHI2
O
R C CI3
I2 as
oxidising
agent
-
OH / I2
-
OH / I2
-
OH / I2
-
OH
O
R C CH3 + 2 HI Oxidation to methyl ketone
O
R C CH2I
O
R C CHI2
O
R C CI3
Successive iodination leading
to triiodomethyl substituent
O
R C O + CHI3 Formation of iodoform
PROCEDURE
Add 4 drops of isopropyl alcohol to 5 mL of dioxane in a test tube and shake until all the
sample has gone into solution. You may need to stopper the test tube to get adequate
shaking. Add 1 mL of 10% sodium hydroxide solution, and then iodine-potassium iodide
solution, with shaking, until a slight excess yields a definite dark color of iodine. If less
than 2 mL of the iodine solution is decolorized, place the test tube in a water bath
maintained at a temperature of 60°. If the slight excess of iodine already present is
decolorized, continue the addition of iodine solution with shaking until a slight excess of
iodine solution again yields a definite dark color. The addition of iodine is continued until
the dark color is not discharged by 2 minutes’ heating at 60°. This excess of iodine is
removed by the addition of a few drops of 10% sodium hydroxide solution with shaking.
Now fill the test tube with water and allow to stand for 15 minutes. Observe the results.
Iodoform is a light yellow solid.
Carry out the same reaction with your unknown alcohol.
The iodine-potassium iodide solution has been prepared by adding 200!g of potassium
iodide with 100 g of iodine to 800 mL of distilled water and stirring until solution is
complete.
Reaction with Carboxylic Acids (Esterification)
Acid catalyzed esterification is an equilibrium in which water is a bi-product (see
reaction a). If we use a concentrated acid to tie up the water produced (through heat of
solvation) and add an excess of carboxylic acid, we can drive the equilibrium toward the
right. After a few minutes of reaction we can convert all the excess acid to its non-volatile
salt (reaction b) and the only volatile material left will be the ester. We will use this
technique to form some common flavor components.
RCH2OH + R'CO2 H
R'CO2H + NaOH
H+
RCH2OCOR' + H2 O
R'CO2-Na+ + H 2O
(a)
(b)
Procedure (IN THE HOOD)
1...Place 1 mL (≈5 drops) of acetic acid in one test tube, 1 mL of butyric acid
in a second, and about 0.5 g of salicylic acid in a third. Note the different odors.
2. Add 5 drops of amyl alcohol to the acetic acid, 5 drops of ethyl alcohol to the
butyric acid and 20 drops of methyl alcohol to the salicylic acid.
3. Add 2 drops of concentrated sulfuric acid to the first and second tubes and
5 drops to the third tube.
4. Place all three tubes in a beaker of water warmed to 60° and let stand for 10
minutes.
5. At the end of this time remove the tubes from the water and add 5 mL of
10% NaOH to each tube, stopper and shake.
6. The ester should float on the water solution as an insoluble oil. Note the odor in
each tube. After you have recorded your results, pour the contents of each tube
down the drain IN THE HOOD. Rinse all glassware well in the hood before
taking anything back to your desk.
ORG II LABORATORY (NONMAJORS)
NAME_________________________
PROPERTIES OF ALCOHOLS
DATA SHEETS
Include these Data Sheets in with your report
I.
SOLUBILITY TESTS
Alcohol
ethyl alcohol
n-butyl alcohol
sec-butyl alcohol
tert-butyl alcohol
Cyclohexanol
Unknown
A.
Drops of H2O
Account for the differences in solubility of the different alcohols.
II.
ALCOHOLS AS A SOURCE OF PROTONS
Alcohol
ethyl alcohol
n-butyl alcohol
sec-butyl alcohol
tert-butyl alcohol
cyclohexanol
Unknown
Rate of reaction with Sodium
A.
Show below the general reactions of the sodium with water and the various
alcohols (except the unknown).
B.
Explain why the order of reactivity is as you observed.
III.
ALCOHOLS IN SUBSTITUTION REACTIONS
Alcohol
n-butyl alcohol
sec-butyl alcohol
tert-butyl alcohol
Unknown
Rate of Reaction with HCl
A.
Show, below, the complete mechanism for the reaction of Lucas Reagent with the
various alcohols (except the unknown).
B.
Offer an explanation of the relative rate of reaction for each of the alcohols.
IV.
OXIDATION OF ALCOHOLS
Alcohol
n-butyl alcohol
sec-butyl alcohol
tert-butyl alcohol
Unknown
A.
Rate of Reaction with Jones Reagent
Show a balanced equation for the reaction of the Jones Reagent with each of the
alcohols.
V.
IODOFORM TEST
A.
Show a balanced equation for the reaction of isopropyl alcohol with iodine in a
base solution.
VI.
FORMATION OF ESTERS
ACID
Acetic acid
Butyric acid
Salicylic acid
A.
ALCOHOL
amyl alcohol
ethyl alcohol
methyl alcohol
SMELL
Show the reactions for the formation of ester for each of the following.
a. Acetic acid + amyl alcohol
b. Butyric acid + ethyl alcohol
c. Salicylic acid and methyl alcohol
VI.
CONCLUSION
What type of alcohol is your unknown? Give a detailed explanation.