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Notes 1543 Table I. The X-ray crystallography of the trans diacetate has been reported by T. N. White.6 Experimental Cyclohexanediol6 (471 g.), prepared by the catalytic hydrogenation of hydroquinone, was acetylated with 8.12 equivalents of acetic anhydride by refluxing two hours. The acetylation mixture was allowed to stand at room temperature several days. The volatile material was distilled off at 10 mm. on the steam-bath. The distillate weighed 620 g. The residue crystallized on cooling. The diacetate crystals were filtered at 38°, washed twice with a small amount of alcohol and dried in vacuo, m. p. 102.5-103.5°.The mother liquors were poured into water, extracted with ether, dried with anhydrous potassium carbonate, the ether removed and the residue crystallized from about 300 cc.of alcohol. The first crop weighed 280 g. This material was crystallized from petroleum ether (b. r. 30-60°) (Skellysolve "F")• Two forms of crystals were obtained. The trans form crystallized as fragile needles, while the cis form came down as massive prisms or as resets. By vigorously shaking the dried product the trans crystals were broken up and the cis form was easily picked out. The crude cis form thus obtained melted at 35-37°. This was dissolved in petroleum ether, and when cold seeded with a well-formed cis crystal. The cis form crystallized at once. By carefully watching the course of the crystallization it was easy to observe the formation of the first needles of the trans diacetate. At this point the liquid was decanted from the cis crystals. One or two more crystallizations from petroleum ether sufficed to remove impurities and to yield a cis form with a freezing point of 41.25°. Coops, et al., give 39°as the melting point of this isomer. Typical crystals are shown in Fig. 2. The refractive index of the pure cis form (supercooled liquid) was w25d 1.4508 and jz22-2d 1.4518. The b. p. at 760 mm. was 251 °.

The 2,4-dinitrophenylhydrazone prepared in the usual manner from the product obtained by acid hydrolysis of 2-ethoxytetrahydropyrane melted at 109°and gave no depression in a mixed melting point determination with the 2,4-dinitrophenylhydrazone prepared from 5-hydroxy-pentanalU 2,4-Pentadienal (VII).-To a solution of 40 ml. of 85% phosphoric acid in 200 ml. of water was added with stirring 40 g. cf 2-ethoxy-A:,-dihydropyrane. Within a few minutes the solution became homogeneous. This solution was added drop wise to a solution of 50 ml. of 85% phosphoric acid in 200 ml. of water which was already undergo!):g steam (listillation.Steam distillation was continued until the distillate no longer had the characteristic' odor of pentadienal. The steam distillate was itself steam distilled to concentrate the aldehyde. After the addition of potassium chloride, the pentadienal was extracted with ether and dried over sodium sulfate. After removal of the ether under reduced pressure, the aldehyde was distilled; yield 14 g. (55%), , n2i d 1.5163.