No abstract

Perbenzoic and peracetic acids have been used for some time to determine the degree of unsaturation and the rate of oxidation of olefinic compounds.2 Of particular interest in our investigations is the work of Bóeseken and Blumberger on the three isomeric phenylbutenes, 1,2-C6H6-CH=CH-CH2-CH3; A2'3-C6H6-CH2-CH=CH-CH3; 3,4-C6H5-CH2-CH2-CH=CH2; and also on cinnamic acid and its methyl

In the course of an investigation on the addition reactions of conjugated systems we had occasion to study the preparation and properties of phenylbutadiene. In our early work with this hydrocarbon1 we encountered considerable difficulty in obtaining consistent results. The yields of phenylbutadiene were at times very good, while again, with the same procedure and under apparently identical conditions, we failed to obtain any of the desired product. A search of the literature revealed that other investigators had encountered similar difficulties.2 We therefore undertook a thorough study of the preparation of this hydrocarbon with the result that we were able to isolate the geometric isomers of both methylstyrylcarbinol and of phenylbutadiene and have determined the conditions under which to obtain either.Phenylbutadiene was first prepared by Liebermann3 by distilling allocinnamylidene-acetic acid under diminished pressure. He obtained a very low yield of this hydrocarbon, which distilled at 86°under 11 mm. pressure, and which absorbed two moles of bromine to give a tetrabromide. In a later paper he reported an improved method for the preparation of the same compound by heating cinnamylidene-malonic acid with quinoline.4 A phenylbutadiene with the same properties was then prepared by Klages,6 who treated cinnamic aldehyde with methylmagnesium iodide and dehydrated the methylstyrylcarbinol that was formed. Doebner6 prepared a different phenylbutadiene by the dry distillation of cinnamyl-acrylic acid with barium hydroxide. This phenylbutadiene distilled at 120°under 10 mm. pressure and crystallized to a solid, m. p. 22°. It did not react with bromine, and this led Doebner to assign to it a cyclic structure to indicate its saturated nature.

I may be decomposed directly with a saturated solution of sulfurous acid and thus avoid the preliminary treatment with dilute acid. After all of the iodine had been removed the ethereal solution was washed with water until neutral. A large number of washings were required to remove all of the sulfurous acid. The ethereal solution was dried over sodium sulfate and the ether removed by vaporization. When subjected to distillation under reduced pressure, the residual oil distilled over almost completely at 117°under 4 mm. pressure. It was identical with the trans carbinol described above.The Preparation of Cis Methylstyrylcarbinol.-The above preparation was repeated except that the ethereal solution of the carbinol was washed only twice with water before distillation, thus leaving some of the sulfurous acid in solution. On distilling the residual oil, the cis methylstyrylcarbinol was obtained, b. p. 144°under 21 mm. pressure. It was identified by its characteristic tendency to lose water.