Organic Syntheses, CV 5, 739
Checked by D. M. Gale and B. C. McKusick.
1. Procedure
Caution! Because
carbon monoxide is evolved, the reaction should be carried out in a good
hood.
Two hundred seventy milliliters
(497 g., 4.86 moles) of 96% sulfuric acid (Note
1) is poured into a
1-l. three-necked flask equipped with a
paddle stirrer driven by a powerful motor, a
dropping funnel with a gas by-pass, and a
thermometer that dips into the acid. The reaction mixture is stirred
vigorously (Note
2) and maintained at 15–20° by means of a
cooling bath as
3 ml. of 98–100% formic acid (Note
3) is added dropwise. Under the same conditions, a solution of
28.5 g. (0.25 mole) of 2-methylcyclohexanol (Note
4) in
46 g. (1.00 mole) of 98–100% formic acid is added in the course of 1 hour. The reaction mixture foams during the additions. The mixture, which is a very light cream color, is stirred for 1 hour at 15–20° and then is poured with stirring onto 1 kg. of crushed ice in a
4-l. beaker. The carboxylic acid separates as a white solid.
The acid is taken up in
200 ml. of hexane (Note
5), the
hexane layer is separated, and the aqueous layer is extracted with two
150-ml. portions of hexane. The combined
hexane solutions are extracted twice with a mixture of
175 ml. of 1.4N potassium hydroxide solution and 50 g. of crushed ice. The two alkaline solutions are combined and extracted with
100 ml. of hexane to remove traces of neutral oil, and then acidified to pH 2 with 12
N hydrochloric acid (about 35 ml.). The liberated carboxylic acid is taken up in
150 ml. of hexane. The aqueous layer is extracted with
100 ml. of hexane, and the combined
hexane layers are washed with 75 ml. of water and dried over
3 g. of anhydrous magnesium sulfate. The
hexane is evaporated by warming the solution at 30–60° (15–30 mm.) overnight. The residue is
33–36 g. (
93–101%) of colorless
1-methylcyclohexanecarboxylic acid, m.p.
34–36°, that is pure enough for most purposes. Distillation from a
100-ml. Claisen flask (Note
6) gives
31.5–33.5 g. (
89–94%) of the acid, b.p.
132–140° (19 mm.),
79–81° (0.5 mm.); m.p.
38–39°.
2. Notes
4. The checkers used
"o-Methylcyclohexanol," available from K & K Laboratories, Jamaica, New York. They redistilled it before use; b.p.
70–80° (20 mm.),
n25D 1.4617.
3- or 4-Methylcyclohexanol can be used in place of
2-methylcyclohexanol, or mixtures of the three can be used.
5. Normal
hexane, commercial grade, from the Phillips Petroleum Co., Bartlesville, Oklahoma, was used. Other organic solvents, such as
benzene, are satisfactory.
6. The checkers used a
30-cm. spinning-band column for the distillation.
3. Discussion
4. Merits of the Preparation
Carboxylation by
formic acid is a rapid and simple method of preparing many tertiary carboxylic acids.
8 It can be applied to primary, secondary, and tertiary alcohols as well as to olefins and other compounds equivalent to the alcohols under the reaction conditions. The reaction often proceeds with rearrangement of the carbon skeleton. The scope of the reaction is indicated by Table I, which lists 13 alcohols to which the reaction has been applied.
TABLE I CARBONYLATION OF ALCOHOLS TO ACIDS
|
Alcohol |
|
Acids Formeda |
Yield of RCO2H, %b |
|
1- or 2-Butanol |
100 |
2-Methylbutyric acid |
36 or 43 |
t-Butyl alcohol |
95 |
Trimethylacetic acid |
75 |
1- or 2-Pentanol |
80 |
2,2-Dimethylbutyric acid |
76 or 81 |
|
20 |
C11 acids |
|
2-Methyl-2-butanol |
10 |
Trimethylacetic acid |
73 |
|
42 |
2,2-Dimethylbutyric acid |
|
|
12 |
C7 acids |
|
|
36 |
C11 acids |
|
2,3,3-Trimethyl-2-butanol |
100 |
2,2,3,3-Tetramethylbutyric acid |
88 |
2,2-Dimethyl-1-propanol |
100 |
2,2-Dimethylbutyric acid |
83 |
Cyclopentanol |
63 |
Cyclopentanecarboxylic acid |
26 |
|
37 |
cis-9-Decalincarboxylic acid |
|
Cyclohexanol |
80 |
1-Methylcyclopentanecarboxylic acid |
78 |
|
9 |
Cyclohexanecarboxylic acid |
|
|
11 |
C13 acids |
|
Cycloheptanol |
100 |
1-Methylcyclohexanecarboxylic acid |
91 |
2-Decalol |
80 |
cis-9-Decalincarboxylic acid |
95 |
|
20 |
trans-9-Decalincarboxylic acid |
|
1-Hydroxyadamantane |
100 |
1-Adamantanecarboxylic acid11,9
|
95 |
|
a The number before each acid is its volume percent in the mixture of carboxylic acids formed.
|
b Total yield of all carboxylic acids formed.
|
This preparation is referenced from:
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