Reaction of 4,4′-dimethoxydiphenylmethanimine with carbon disulfide

Abstract

The reaction of 4,4′-dimethoxydiphenylmethanimine with carbon disulfide in bromoform was studied at temperatures of 40°, 50°, and 60° in sealed tubes. The products from this reaction are 4,4′-dimethoxythiobenzophenone and 4,4′-dimethoxydiphenylmethaniminium thiocyanate. The proposed mechanism postulates primary attack on the carbon atom of carbon disulfide by the imine nitrogen leading to a resonance stabilized intermediate followed by ring closure with formation of a 4-membered ring, ▪ which is unstable and decomposes to form thioketone and isothoicyanic acid. Supporting evidence for the proposed mechanism was drawn from kinetic studies, NMR studies, the effect of copper on the reaction system and the reaction of the benzyl substituted imine N-benzyl-4,4′-dimethoxydiphenylmethanimine (Schonberg's Reagent) with carbon disulfide at 43°. The formation of benzyl isothiocyanate in the system was inferred from the presence of N,N-dibenzylthiourea. The presence of benzyl isothiocyanate in the substituted imine—CS 2 system suggests that the initial decomposition product from the four membered ring intermediate in the imine—CS 2 system is HNCS. The work suggests that dithiocarbamic acids in oxidizing metallic copper may not react through a dithiocarboxyl group in a classical sense but through a zwitterionic form of the molecule where the hydrogen is attached to the nitrogen stom.