Org. Synth. 1966, 46, 72
DOI: 10.15227/orgsyn.046.0072
1-METHYLCYCLOHEXANECARBOXYLIC ACID
[Cyclohexanecarboxylic acid, 1-methyl-]
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 12N 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
1.
Three moles of 99–100% sulfuric acid may be used in place of the
96% sulfuric acid.
2.
With slow stirring there is a higher concentration of
carbon monoxide and hence less rearrangement. For example,
cyclohexanol in a slowly stirred reaction mixture gave
75% cyclohexanecarboxylic acid and
14% 1-methylcyclopentanecarboxylic acid; with rapid stirring the corresponding yields were
8% and
61%.
23.
Technical grade 85% formic acid can be substituted for
98–100% formic acid if the decrease in
sulfuric acid concentration that would result is compensated for by a suitable increase in the amount of
sulfuric acid charged.
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
1-Methylcyclohexanecarboxylic acid can be prepared by carbonation of the Grignard reagent from
1-chloro-1-methylcyclohexane3 or by Friedel-Crafts condensation of
1-chloro-1-methylcyclohexane with
methyl 2-furancarboxylate followed by saponification and oxidation.
4 It can also be prepared by successive hydrogenation and saponification of the Diels-Alder adduct from
butadiene and
methyl methacrylate,
5 by oxidation of
1-methyl-1-acetylcyclohexane with
nitric acid6 or
sodium hypobromite,
7 and by the present method of synthesis.
8
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.
|
In a related reaction, saturated hydrocarbons with a tertiary hydrogen are carboxylated by a mixture of
formic acid,
t-butyl alcohol, and
sulfuric acid.
10,11This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
3- or 4-Methylcyclohexanol
1- or 2-Butanol
1- or 2-Pentanol
sulfuric acid (7664-93-9)
hydrochloric acid (7647-01-0)
Benzene (71-43-2)
carbon monoxide (630-08-0)
nitric acid (7697-37-2)
Cyclohexanol (108-93-0)
formic acid (64-18-6)
potassium hydroxide (1310-58-3)
2-Methylbutyric acid (600-07-7)
Cyclohexanecarboxylic acid (98-89-5)
Trimethylacetic acid (75-98-9)
sodium hypobromite
magnesium sulfate (7487-88-9)
butadiene (106-99-0)
cyclopentanol (96-41-3)
2-Methyl-2-butanol (75-85-4)
hexane (110-54-3)
2-methylcyclohexanol (583-59-5)
t-butyl alcohol (75-65-0)
cyclopentanecarboxylic acid (3400-45-1)
1-Adamantanecarboxylic acid (828-51-3)
1-Hydroxyadamantane (768-95-6)
2,2-Dimethylbutyric acid (595-37-9)
1-Methylcyclohexanecarboxylic acid,
Cyclohexanecarboxylic acid, 1-methyl- (1123-25-7)
1-methylcyclopentanecarboxylic acid (5217-05-0)
1-chloro-1-methylcyclohexane (931-78-2)
methyl 2-furancarboxylate (611-13-2)
methyl methacrylate (80-62-6)
1-methyl-1-acetylcyclohexane
2,2,3,3-Tetramethylbutyric acid
2,2-Dimethyl-1-propanol (75-84-3)
Cycloheptanol (502-41-0)
2-Decalol (825-51-4)
cis-9-Decalincarboxylic acid
trans-9-Decalincarboxylic acid
2,3,3-Trimethyl-2-butanol
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