Methyl Pentamethylene

Further light has been thrown on the problem by the researches of Markownikoff,1 of Zelinsky,2 and of

1 Markownikoff, " On Methyl Cyclo-Pentane from different Sources and some of its Derivatives," Berl. Berichte, 1897, 30, 1222. .

2 Zelinsky, " Researches in the Hexamethylene Group," ibid., 1897, 305 387.

Methyl Pentamethylene 366

Aschan1 on Russian petroleum, which has been found to contain large quantities of hexamethylene (b.p. 80.85°; sp. gr. 0.7968 at 0°/4°) 2 and methyl pentamethylene (b.p. about 72°; sp. gr. about 0.766 at 074°), both of which substances have also been prepared synthetically. The two hydrocarbons differ widely in their behaviour with fuming nitric acid, for hexamethylene is only attacked slowly even when heated, a large amount of adipic acid being formed, whereas methyl pentamethy-lene is acted on rapidly at the ordinary temperature, with evolution of much heat, and acetic acid is the chief product of oxidation.

Now the fractions for the first three or four degrees above 69° are attacked in the cold by fuming nitric acid, much heat being evolved and a large amount of acetic acid formed, and it may therefore be concluded that the substance present in American and Galician petroleum with a boiling point not far above that of normal hexane is methyl penta-methylene.

Preparation Of Pure Normal Hexane

Not only methyl penta-methylene, but also the isohexanes and other hydrocarbons which contain a > CH - group may be removed by heating with fuming nitric acid, and it was found that when the fractions from Galician petroleum which came over between 66° and 69.2° were subjected to prolonged heating with the fuming acid, and were afterwards distilled two or three times, almost pure normal hexane was obtained ; indeed from the fractions between 66° and 68.95° the normal paraffin appeared to be perfectly pure.

Summary Of Results

It has thus been shown that in the distillation of this portion of American or Galician petroleum, the liquid which at first seems to be a single substance boiling at about 66° proves to be a mixture of four substances, two isomeric hexanes boiling at nearly the same temperature, 61°, and normal hexane and methyl pentamethylene with the boiling points 68.95° and (about) 72° respectively. The first pair of substances are very closely related to each other, the second pair are not.

Amyl Alcohols In Fusel Oil

As another example of a pair of very closely related liquids which are frequently met with, the isomeric amyl alcohols which are present in fusel oil may be mentioned. Distilled through an ordinary still-head, long continued fractionation would be necessary even to indicate the presence of two isomeric amyl alcohols, and the boiling points are so close together that even with an exceedingly efficient still-head the separation is very difficult.

Hexamethylene And A Volatile Heptane

Another example of the presence, in a complex mixture, of two substances which boil at nearly the same temperature is afforded by the distillation of the portion of

1 Aschan, " On the Presence of Methyl Pentamethylene in Caucasian Petroleum Ether," Berl. Berichte, 1898, 31, 1803.

2 Prepared synthetically by hydrogenation of benzene by Sabatier and Mailhe who give the b.p. 81° under 755 mm. pressure and sp. gr. 0.7843 at 13.5° (=0.7970 at 0°), Compt. rend., 1903, 137, 240.

American or Galician petroleum that comes over between 75° and 80°. It was found possible to separate a liquid of quite constant boiling point and, as derivatives of hexamethylene could be prepared from it,1 it was concluded that that substance had been separated in a pure state. Later on, however, it was found that the liquid could be partially but not completely frozen in an ordinary freezing mixture, and eventually, by fractional crystallisation, nearly pure hexamethylene was obtained with practically the same boiling point as before but with a definite melting point, and of notably higher specific gravity.2 It was evident that the substance separated by fractional distillation only was a mixture of two hydrocarbons, hexamethylene and a heptane, of which the former was present in much the larger quantity, and that either the boiling points are almost identical, or else the two substances form a mixture of constant boiling point almost identical with that of hexa-methylene.

Pentamethylene And Trimethyl-Ethyl-Methane

Such difficulties as have been described are of common occurrence in the distillation of petroleum. For example, American, Galician, and Russian petroleum all contain a certain amount of pentamethylene which boils at about 50° ; but there is also present a hexane, trimethyl-ethyl-methane, boiling at nearly the same temperature, and it appears to be impossible to separate these hydrocarbons by fractional distillation.

Lecat finds that n-heptane and methyl-hexamethylene form an azeotropic mixture very rich in heptane, boiling at a temperature slightly lower than the boiling point of the pure heptane. It is therefore quite probable that azeotropic mixtures may be formed in the two cases just described, and also with n-hexane and methyl pentamethylene.

b. One or more Components Present in Small Quantity. -If one or more components of a complex mixture are present in relatively very small amount, they are apt to be altogether overlooked, and it is only by keeping a careful record of the weights and temverature ranges of the fractions, and by calculating the values of Pentamethylene And Trimethyl Ethyl Methane 367 or mapping the total weights of distillate against the temperatures that the existence of these components can be detected.

The manner in which the presence of a relatively very small quantity of hexamethylene was recognised in American petroleum has been described in Chap. VII. (p. 114).