Some aspects of chromium(II) reduction of organic compounds.

Abstract

2-Bromoethanol and 2-bromoethylamine hydrobromide have been shown to behave analogously to annotinine cholorohydrin on reduction with chromium(II) chloride. 2-Bromoethanol yielded 20% ethylene and was shown to undergo considerable hydrolysis under the reaction conditions. 2-Bromoethylamine hydrobromide yielded both ethylene and ethylamine. 2-Chloroethanol was not reduced under the conditions used. Phenacyl acetate yielded 96% acetophenone separated as the 2-4-dinitrophenylhydrazone. A number of compounds have been reduced and the chromium(III) products of reduction identified spectroscopically as well as separated on an ion exchange resin. Phenacyl acetate, 2-nitropropane, alpha-chloroacetophenone, alpha-bromoacetophenone and trans 1-2-dibromocyclohexane yielded mainly Cr(H2O)6+++. Carbon tetracholoride, p-toluenesulfonyl chloride and tetra-bromoethane yielded CrX(H 2O)5++. There is therefore an anomaly in the behavior of trans 1-2-dibromocyclohexane and tetrabromoethane. The chromium(II) perchlorate reduction of benzyl chloride has been shown to involve formation of an intermediate organo-chromium compound of a type previously unknown. This compound has been named benzylpentaaquochromium(III) perchlorate. Countercurrent distribution has been used to demonstrate the presence of only one chromium organic compound and to obtain a pure solution of perchlorate. Separation was carried out at 5°C. with the solvent system 0.01M. perchloric acid-butanol and gave after seventy transfers a separation of the chromium organic compound (partition coefficient 0.35) from Cr(H 2O)6+++ and Cr(H2O)5Cl ++. Solutions of the benzylchromium(III) perchlorate varied from yellow to reddish brown depending on the concentration. The compound has a molar extinction coefficient of 1,830 at 358 mmu. and 49 at 54 mmu. Decomposition of the complex in the absence of oxygen yielded bibenzyl, in the presence of oxygen, benzaldehyde. Catalytic hydrogenation yielded toluene. Solutions of the complex reacted very quickly with aqueous mercuric chloride with no change in the pH of the solution to give benzylmercuric chloride and Cr(H 2O)6+++ in equimolar amounts. On this basis the compound has been designated as a chromium(III) complex with one benzyl group per chromium atom and two positive charges. The six coordinate positions normal for chromium(III) are completed by five molecules of water and a normal octahedral structure is proposed.