Studies in the phenoxarsine series

Abstract

0-Phenoxyphenydichloroarsine has been shown to decompose when distilled under reduced pressure to form 5-chlorophenoxarsine with the liberation of hydrogen chloride (Turner and Sheppard, J,, 1925 544). It was decided to prepare a number of substituted dichloro-arsines and to test the effect of the various substituents on the velocity of ring-closure for a comparison of the rate of ring-closure of o-phenoxyphenyldichloroarsine with its ortho-, meta- and para-chloro derivatives. This method consisted in heating the dichiororrsines in a thermostat at 200 for six hours in a stream of carbon dioxide and determining volumetrically by Volhard's method the quantity of hydrogen chloride evolved per unit of time. The effect of a single methyl group as substituent was first investigated. o -Phenoxyphenyldichloroarsine (I) and its ortho-(II), meta- (III) and para- (IV) methyl derivatives were prepared, and the relative rates of conversion into chlorophenoxarsines determined at 180 and 160. It was found that the velocities of ring-closure were in the order III > IV > II > I, showing clearly the activating effect of the methyl group, particularly when the ring-closure takes place at a position ortho- or para- to the methyl group as in compound III, Three dimethyl derivatives, 2-phenoxy-3:5-dimethyl- (V),2-phenoxy-2:5-dimethyl- (VI) and 2-phenoxy-2:4-dimethylphenyl-dichloroarsine (VII) were also prepared and experiments on ring-closure carried out at 180 and 160. On theoretical grounds the velocity of ring-closure should he in the order V >VI >VII, and this was found to be the case. Attempts were also made to prepare and carry out ring-closure experiments on the p-fluoro-, p-chloro- and p-bromo-derivatives of o-phenoxyphenyldichloroarsine, and also on the p-methoxy derivative.