Binary Systems Containing Isoamyl Alcohol or Active Amyl Alcohol.

Abstract

I S O M E R I C amyl alcohols, active amyl alcohol [ (-1-2methylbutanol] and isoamyl alcohol (3-methylbutanol) are the principal compounds in fusel oil (25) . A by-product of normal alcoholic fermentation, fusel oil is produced to the extent of 0.1 to 0.7 per cent of the ethyl alcohol yield (16). The mixed amyl alcohols are used as solvents and extractives in large amounts in many industrial processes where a five-carbon branched-chain primary alcohol is needed. The purified active amyl alcohol might be used as a starting material for the synthesis of compounds having optical activity. Le Bel (30) tried to purify the optically active isomer by chlorination, because isoamyl alcohol is more rapidly chlorinated. Pasteur (33) separated the amyl sulfates by their different solubilities. Isom and Hunt (27) found only a very slight separation of the alcohols on passing a mixture through a 50-foot column packed with activated carbon a t 91 C., and Blessin, Kretschmer, and Wiebe (5 ) reported that separation of normal alcohols by thermal diffusion was virtually impossible. Isoamyl and active amyl alcohols are difficult to separate by fractional distillation, as their boiling points are 132.0 and 128.7 C. ( 2 , 6), respectively, a t atmospheric pressure. Whitmore and Olewine (37) reported tha t several fractionations on a 101-plate column were necessary to obtain 95T pure active amyl alcohol. Brauns reported (6) that fractional distillation seemed the only practicable method. Separating the two branched-chain primary amyl alcohols by fractional distillation after addition of a third component which would azeotrope with one or both alcohols has never been investigated. Horsley (23) records several azeotropes involving isoamyl alcohol, but only one study of systems containing active amyl alcohol ( 4 ) . The azeotroping agent should ideally form a low boiling azeotrope with active amyl and none with isoamyl, or a high boiling azeotrope with isoamyl and none with active amyl alcohol. Or, if it azeotropes with both alcohols, the boiling points should differ by considerably more than 3.3O C. To determine whether or not an azeotrope had formed in the distillation fractions of binary mixtures containing either isoamyl or active amyl alcohol and another component, the physical properties of such mixtures had to be evaluated. Possible azeotroping agents, chosen with consideration of the principles developed by Ewell, Harrison, and Berg (II), were mixed with pure isoamyl and active amyl alcohols to make known solutions for determinations of refractive indices, densities and, for active amyl solutions, optical activities. In nearly every case nine mixtures of each binary combination were prepared, successive samples differing by approximately 10 weight % in azeotroping agent content. The amyl alcohols were obtained from grape brandy fusel oil by repeated fractional distillations. The active amyl alcohol was distilled until the optical rotation agreed with the values of Markwald and McKenzie (32), who used fractional crystallization of the 1-amyl-3-nitrophthalate acid esters to separate the last traces of isoamyl from the active amyl derivative. After saponification, distillation, drying, and redistillation, the physical constants of the active amyl alcohol were measured. The possibi.!ity of some (+) isomer of active amyl alcohol being present was not considered in the research reported. Cohen, Marshall, and Woodman (8) attempted resolution of the 3-nitrophthalic acid 2-monoester of active amyl alcohol by conversion to the brucine salts, bu t obtained active amyl alcohol of decreased optical activity. This they attributed to racemization by the hot base during hydrolysis of the ester-salt which seems unlikely, as the center of optical activity is not involved directly in the hydrolysis reaction. I t was desirable, therefore, to attempt resolution of the active amyl nitrophthalate monoester using other optically active bases, to be certain tha t Markwald and McKenzie's value was that of the single pure optical isomer.