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Preparation of Pure Montanic Acid.
Although the method of fractional precipitation did not yield montanic acid in a state of purity, yet by fractional distillation of the ethyl ester of the crude acid under diminished pressure purity was at last attained. 100 grams of crude montanic acid were dissolved in 2,300 c.c. of 95-per-cent. alcohol, to which had been added 60 c.c. strong sulphuric acid. The whole was kept hot on the water bath for forty-four hours. It was found that equilibrium was attained within thirty hours, but if 95-per-cent. alcohol is used there still remains 6 per cent. of acid unconverted to ester. The crude ester was therefore reheated with absolute alcohol and a little sulphuric acid in order to complete the esterification, and now gave, after removal of mineral acid, only the slightest trace of free organic acid.
The ester obtained by the above process was carefully washed free from sulphuric acid, then dried in a vacuum over sulphuric acid, and distilled under reduced pressure. The apparatus employed for this purpose was novel, in that the neck of the distilling-flask was electrically heated, and in that a special type of fractionator was used. Three fractions were always collected from each distillation. The following diagram shows at a glance the method of procedure and the number of distillations performed:—
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The following table is a comparison of the physical constants of the five final fractions obtained by repeated distillation:—
| No. | Boiling-point. | Melting-point, Ester. | Melting-point, Acid. | Per Cent. Weight of Fraction. | Molecular Weight. | Apparent Formula |
|---|---|---|---|---|---|---|
| A6 | -292°/15 mm. | 60°5–61°5° | 78°7–79°7° | 11 | 385 | C25H50O2 |
| A9 | -302°/15 mm. | 61–62° | 81–82° | 27 | 413 | C27H54O2 |
| B11 | -312°/15 mm. | 66°5–67°5° | 83° | 32 | 426 | C28H55O2 |
| C9 | Residues | 12 |
Fractions C8 and C9 were obviously impure, being mixtures of montanic acid and melissic acid, together with some ketone. The free acid derived from these two fractions did not crystallize in plates, and gave titration values much above that required for montanic acid. From the residues, after saponification, a single fractional precipitation gave a regenerated acid, melting at 88°5°, which corresponds with the melting-point of melissic acid.
The acid obtained from the saponification of B11 is to be regarded as pure montanic acid,* for further fractional distillation of the ester did not alter the melting-point of the ester or of the acid obtained from the ester nor did it affect the titration value of the acid thus obtained within the limits of experimental error. Thus, acid from B11: 1°0785 grams reqd.
25°60 c.c. N/10 KOH = M.W. = 421.
Acid from B11 twice redistilled: 1°845 grams reqd.
43°70 c.c. N/10 KOH = M.W. = 427.
The titration values approach very closely to that required for a formula C28H56O2, thus placing montanic acid among the even members of the higher fatty acid series. The montanic acid purified by this process crystallized in plates, and was readily soluble in hot ethyl acetate or motor spirit, and fairly soluble in hot alcohol and acetic acid.
In concluding this section on the acid constituents the writer wishes to summarize the following results:—
(a.) Crude montanic acid is a mixture of cerotic, montanic, and melissic acids.
(b.) Pure montanic acid crystallizes in plates, melts at 83°, and has a molecular weight corresponding to the formula C28H56O2. (Previous experimenters have described it as crystallizing in needles, which is correct so long as the substance is impure.)
(c.) Cerotic acid has also been obtained for the first time in nacreous crystalline plates.
[Footnote] * The acid crystallized in pearly scales, which also is an indication of purity.