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Volume 44, 1911
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Crude Montanic Acid.

Crude montanic acid was extracted from montan wax by the following process: 500 grams of montan wax were digested five times with hot alcohol, about 3 litres for each extraction. This hot alcoholic solution, containing practically the whole of the free acids, was siphoned off, neutralized with ammonia, and the acids were then precipitated as calcium salts by means of alcoholic calcium-chloride solution. The calcium salts were then filtered off by means of a hot funnel.

The crude calcium salts thus obtained were dried on the water bath, and then pulverized and boiled out six times with alcohol. Motor spirit, although a very good solvent of unsaponifiable matter, could not be employed for the purification of the calcium salts, by reason of the almost unfiltrable paste produced in this case.

The calcium salts were now decomposed by glacial acetic acid, and the crude acid thus obtained melted at 81°5°. Crystallization from motor spirit raised the melting-point to 82°5°, but further crystallization from alcohol, motor spirit, and acetic acid did not further raise the melting-point. The acid crystallized from acetic acid in granules.

The titration of the acid thus obtained, although the greatest care was taken in the standardization of the decinormal solutions employed, gave a molecular weight of 432—i.e., almost the mean of the molecular weights required for the formulae C29H58O2 and C28H56O2.

It thus appeared that either the montanic acid contained some inert compounds such as hydrocarbons or ketones, or that it was admixed with a higher acid. To test the first of these suppositions the acid was purified by potash-lime saponification with an excess of lime, and then extraction with hot motor spirit in which high-molecular-weight hydrocarbons and ketones are readily soluble. The molecular weight of the purified acid, however, remained unchanged (430).

That the acid, although its melting-point was unaltered by further crystallization, was not a single compound was demonstrated by submitting 10 grams of the acid to fractional precipitation with magnesium acetate, for the regenerated acids from the different fractions had the following melting-points:—

Melting-point.
Fraction I (weight 1/10 of original acid taken) 85°5°
" II " 3/10 " 83–84°
" III " 4/10 " 81–82°
" IV " 1/10 " 74°5°

Fractional precipitation was therefore undertaken on a large scale. 50 grams of crude montanic acid were dissolved in 800 c.c. of alcohol, the solution rendered alkaline with ammonia, and then precipitated with 20 c.c. of a solution of magnesium acetate (equivalent to 10 grams montanic acid). Four fractions were thus precipitated, and a fifth fraction was obtained from the alcoholic filtrate on cooling. The regenerated acids from these fractions had the following melting-points:—

Melting-point.
Fraction 1 83°5–84°
" 2 83–84°
" 3 82–83°
" 4 81–82°
" 5 74–76°
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This practically agrees with Eisenreich's experience. He obtained the first four fractions melting at 83°. It seems strange that he did not proceed with further fractional precipitation.

Fractions 1 and 2 were each fractionally precipitated again, and it was found that the regenerated acids from the first two precipitates had risen 3° in melting-point.

Fractions which melted within 1° were mixed before the next precipitation was proceeded with. After four consecutive precipitations of the highest melting fraction in each case, there resulted an acid melting at 88°5°. This fraction was not altered in melting-point by a series of further fractional precipitations, and must be regarded as pure melissic acid, which, according to Brodie* and to Schwalb,† melts at 88–89°. It is, however, to be noted that the melissic acid from the oxidation of canaüba wax is stated by Maskelyne‡ to melt at 91°.

The following is a scheme of precipitations employed in the isolation of melissic acid. The melting-points given are those of the regenerated acids:—

Repeated fractional precipitation failed to yield an acid melting at about 83° which could be considered pure, but from fraction 5 precipitation yielded lower fractions, which when repeatedly crystallized melted at

[Footnote] * Phil. Trans. Roy Soc, 1848.

[Footnote] † Annalen, 235, p. 135.

[Footnote] ‡ Journ. Chem. Soc., 1869, vol. 22, p. 87.

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78–78°5°, and were absolutely identical with the cerotic acid of beeswax. This identity was proved as follows:—

(a.) Both acids had the same melting-point, and a mixture of the two acids melted within 0°5° of the original acid.

(b.) The ketone prepared from each, by means of the catalytic action of metallic iron, melted at 92°5–93°.

(c.) The ethyl esters of each acid had the same boiling-point, 285°, at 14 mm.

(d.) Both acids crystallized in pearly scales.

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.

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