An Improved Preparation of o-Phenylenedi-Isothiocyanate

Abstract

In 1887, Billeter and Steiner¹, during the course of a study of thiophosgene on aromatic diamines found that o-phenylenediamine gave benzimidazoline-2-thione and a by-product, o-phenylenedi-isothiocyanate (1) which they obtained in about 10% yield. Although the meta or especially the para di-isothiocyanates are well documented no further work appears to have been done on the ortho isomer. In 2 the course of our studies of thiophosgene on heterocyclic bases² it was observed that benzimidazole reacted, under ice-cooling, with 2 molecular proportions of thiophosgene to give o-phenylenedi-isothiocyanate in about 50% yield. The process has not been optimised. The residual extracts on treatment with dimethyl-formamide gave the pentacyclic compound (6) previously prepared by Haugwitz and Narayan from 2-thiocyanatobenzimidazole and carbon