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Introduction.
Montan wax is a hard yellowish material which, on account of its high melting-point, is used for raising the melting-point of stearine candles, and, on account of its low price, has also found some use as an adulterant of beeswax. The wax was first manufactured from the brown coal of Saxony and Thuringia, and more recently has been prepared from Irish lignites.
In the manufacture of montan wax, pyropissite is either extracted with light petroleum and the soluble bitumen, obtained from the extract, then distilled in superheated steam, the distillation being repeated until a nearly colourless product is obtained, or the brown coal is itself distilled with superheated steam.
The method of manufacture was first patented by E. von Boyen (German patent 101373, 1st July, 1897). In the original patent E. von Boyen* described the wax as consisting of two well-characterized substances—an acid and an unsaturated hydrocarbon. C. Hell† assigned the formula C29H58O2 to the above-mentioned acid, now called “montanic acid.”
E. von Boyen‡ adopted the formula C29H58O2 for the acid, but now stated that the other constituent is an alcohol melting at 60°, which is readily attacked by sulphuric and nitric acids. He regarded the original bitumen as an ester of montanic acid which is decomposed during distillation.
K. Eisenreich§ purified montanic acid by fractional precipitation with magnesium acetate. He adopted the same formula for the acid as von Boyen and Hell. He noted that the last portions of the acid to be precipitated melted several degrees lower than the earlier fractions, but no attempts were made to obtain acids of lower molecular weight from these fractions.
To the non-acid constituent of the wax, melting at 63°5°, he assigned the formula C42H86O, and supported the formula by an ebullioscopic molecular-weight determination, but could not find any evidence that the substance was an alcohol.∥
[Footnote] * Chem. Central Blatt, 1899, vol. 1, p. 864.
[Footnote] † Zeit. f. Angew. Chem., 1900, p. 556.
[Footnote] ‡ Chem. Central Blatt, 1901, vol. 2, p. 1285.
[Footnote] § Journ. Soc. Chem. Ind., 1909, p. 991.
[Footnote] ∥ Such a formula, CnH2n+2O, can only represent an alcohol or an ether derived from a higher alcohol; but the low melting-point of the substance (63°5°) makes it extremely improbable that the compound is anything else than a hydrocarbon.
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Ryan and Dillon* gave the formula for montanic acid as C28H56O2. The non-saponifiable portion they found to melt at 58–59°, and the analysis gave 2°5 per cent. of oxygen, which agrees approximately with the formula C42H86O of Eisenreich. They also stated that no primary or secondary alcoholic group is present in the substance.
The work of previous observers may therefore be summed up as follows: (a.) Three investigators have assigned to montanic acid the formula C29H58O2, while one investigator has assigned the formula C28H56O2, to the same acid; (b.) von Boyen first stated that the non-acid constituent was an unsaturated hydrocarbon, afterwards that it was an alcohol. Eisenreich and also Ryan and Dillon state that the non-acid constituent is not alcoholic in nature, but regard it as an oxygenated compound.
In the present paper it is shown that: (1) the “montanic acid” occurring in the wax is in reality a mixture of three acids—cerotic (C26H52O2), montanic (C28H56O2), and melissic (C30H60O2) acids; (2) the non-saponifiable portion is an olefinic hydrocarbon, probably C28H56 or C26H52, both of which, being olefines, would have, of course, the same percentage composition.
Cerotic and melissic acids were described by Brodie† as constituents of beeswax, but have not hitherto been found in any mineral substance. The separation of these acids was tedious, involving a series of over forty fractional precipitations by magnesium acetate, whereby the cerotic and melissic acids were obtained in a state of purity.
Montanic acid, the acid of intermediate molecular weight, was isolated by conversion of the crude acid into its ethyl salt, and subsequent distillation under reduced pressure. Some fifteen fractionations were needed before the substance could be considered pure.
After purification, the cerotic and montanic acids both crystallized in pearly scales. Hitherto cerotic and montanic acids have been described as crystallizing in needles; and the crude acids certainly do so, but the pure acids crystallize in scales, and in so doing resemble all the lower members of the higher fatty acids which have been obtained in a state of purity.
There can be little doubt that cerotic, montanic, and melissic acids belong to the homologous series of the higher fatty acids, and that these acids are all normal fatty acids. A comparison of the physical properties of a number of their derivatives supports this (Tables I-III, p. 285). In the case of montanic acid it has been possible to show that the substance is undoubtedly normal heptacosane carboxylic acid.
The occurrence of montan wax as the principal product of steam distillation of bituminous coal is of great interest. Krämer and Spilker‡ have shown that fats and waxes, if distilled under pressure, yield mixtures of hydrocarbons not unlike many natural petroleums, and they have suggested that some petroleums at least owe their origin to the decomposition of wax derived from algae.
At first it appears difficult to imagine such supplies of wax in nature as, by decomposition, would give rise to the immense quantities of oil present in the large oilfields. Brown coal is, however, even more widely distributed
[Footnote] * Sci. Proc. Roy. Dub. Soc., vol. 12, p. 20, 1909.
[Footnote] † Phil. Trans. Roy. Soc., 1848.
[Footnote] ‡ Berichte, vol. 32, 1899, and vol. 35, 1902
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than petroleum, so that the suggestion of these authors gains in probability, in that it is known that large quantities of wax, almost certainly derived from micro-organisms, are present in this lignite.
Krämer and Spilker's hypothesis would appear, in this light, much more probable than that of Mendeleef, Moissan, and others, who suggest that the natural petroleums are due to the action of water upon metallic carbides, substances which have never been found in nature in large quantity.
If we assume with von Boyen that the bitumen derived from pyropissite is an ester of montanic acid, then the fact that the inert constituent of the wax derived from the bitumen is an olefinic hydrocarbon, probably C28H56, suggests that the reaction during steam distillation of the wax is represented by the equation
C27H55CO2C28H57 = C27H55CO2H + C28H56
Montanyl montanate = Montanic acid Montanene,*
just as during the distillation of Chinese wax we have—
C25H51CO2C26H53 = C25H51CO2H + C26H52
Ceryl cerotate = Cerotic acid Cerotene.
It is to be hoped that the time is not far distant when a systematic examination of the brown coals and oil-shales of New Zealand will be made, with the object of elucidating the chemical nature of their constituents. It is a regrettable and remarkable fact that, notwithstanding the enormous annual consumption of coal in all countries of the world, we are still practically in ignorance as to the chemical nature of this fuel.
[Footnote] * The fact that the proportion of hydrocarbon in commercial montan wax is much less than that of the free acids is not surprising, for the physical properties of the hydrocarbon are such as to lead to loss during the commercial process of recrystallization from benzene.