The fraction of a midcontinent pctroleum boiling between 90° and 92° C, from which thc aromatic hydrocarbons previously had been removed, was substantially resolved into its constituent hydrocarbons. Alternation of atmospheric distillation and azeotropic distillation with methyl alcohol separated the material boiling between 90° and 91.2° C into a paraffinic concentrate, containing approximately 75 percent of 2-methylhexane, and a naphthenic concentrate. From the naphthenic concentrate,

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... 3-dimethylcyclopentane was isolated by crystallization from liquid ethane. A similar procedure separated the material boiling between 91.2° and 92° C into a naphthenic and a paraffinic concentrate. From the naphthenic concentrate, trans-l,2-dimethylcyclopentane was isolated by crystallization from liquid propane plus methane. From the paraffinic concentrate, 3-methylhexane was obtained in the residue from distillations at reduced pressure (215 mm Hg). The boiling point, refractive index, freezing point, density, carbon-hydrogen ratio, and critical solution temperature in aniline were determIned for the three hydrocarbons. Referred to the content of n-heptane as unity, the relative amounts of the three hydrocarbons in this petroleum were estimated to be as follows: trans-l,3-dimethylcyclopentane, 0.21; 3-methylhexane, 0.25; trans-l,2dimethylcyclopentane, 0.31. one has actually separated the material into any of its constituent hydrocarbons. Most previous workers [4 to 11] have considered the "isoheptane" fraction to be 2-methylhexane or have reported that although the isoheptanes were present in considerable quantity, their separation by physical means was difficult or impossible. The "dimethylcyclopentane" fraction has been regarded as 1 ,3-dimethylcyclopentane, or the identification has been left incomplete. Bruun and Hicks-Bruun [1], workin~ with the "isoheptane" fraction of petroleum in this laboratory, Isolated 2-methylhexane from the distillate boiling between 90° and 91 ° C. On treating the distillate boiling at 91.8° C, with chlorosulfonic acid, they obtainea some hydrocarbon material that boiled at 91.9° C and had a refractive index of 1.3912 at 20° C [2]. From a comparison of the constants of this material with those of pure compounds, Bruun and Hicks-Bruun [2] concluded that the paraffin in the distillate at 91.8° 0 was most probably 3-methylhexane rather than a mixture of 2-methylhexane and 3-ethylpentane, which combination was next most probable. In 1896, Zelinsky and Rudsky [12] synthesized 1,3-dimethylcyclopentane and reported the following properties: bp76o, 91 ° to 93° 0; d 2 f, 0.7543. Markownikoff [13] believed that some material which he isolated from Oaucasian petroleum was identical with the 1,3dimethylcyclopentane synthesized by Zelinsky and Rudsky [12] . His material boiled normally between 91 ° and 93° 0 and had a specific gravity, d 2 f, 0.7321. Ma, bery and Sieplein [14] found they could substitute one atom of bromine in a petroleum fraction boiling at 98° to 100° 0 (which contained methylcyclohexane) and two atoms of bromine in the fraction 96° to 98° O. From the fractiop so treated, they obtained a compound with the formula 07H12Br2, which they believed to have been formed from dimethylcyclopentane. Balbiano and Zeppa [15] oxidized with nitric acid a petroleum fraction which distilled between 87° and 92° 0, and obtained a mixture of 1,4-p-nitrobenzoic acid, nitrobenzene, adipic acid, succinic acid, and acetic acid. The 1,4-p-nitrobenzoic acid was assumed to be proof of the presence of 1,3-dimethylcyclopentane in the petroleum. By' distilling cracked distillates of petroleum with aniline, Brame and Hunter [11] isolated some naphthenic material which had the constants: bp76o, 93° to 94° 0; d2f, 0.7648; n~, 1.4110. This material was identified as a dimethylcyclopentane because its properties agreed with those of a synthetic dimethylcyclopentane, the constants of which were: bpno, 93° 0; d!O, vO.7530; n~, 1.4130. The present paper reports the completion of the work begun by Bruun and Hicks-Bruun [1, 2] on the resolution of that fraction of petroleum normally boiling between 87° and 98° O. There are described here the isolation and identification of 3-methylhexane, trans-1,2-dimethylcyclopentane, and trans-l ,3-dimethylcyclopentane from the fraction normally boiling between 90° and 92° O. II. TREATMENT OF THE MATERIAL PRIOR TO THE PRESENT INVESTIGATION In the work by Bruun and Hicks-Brmill [1 , 2, 3] on the fraction of petroleum normally boiling between 87° and 98° 0, the material was subjected to several processes of fractionation. The toluene was