Carbonylation of o-Phenylenediamine and o-Aminophenol with Dimethyl Carbonate Using Lead Compounds as Catalysts

Lead compounds are active catalysts for carbonylation and carbonylation/methylation of o-phenylenediamine and o-aminophenol with dimethyl carbonate (DMC). 2-Benzimidazolone was obtained in 84% yield by the reaction of o-phenylenediamine with DMC for 1 h at 443 K in the presence of Pb(NO3)2. In the presence of Pb(OAc)2, the reaction quantitatively gave 1,3-dimethyl-2-benzimidazolone, which was formed by methylation of the primary product, 2-benzimidazolone, at 473 K. The effects of reaction variables on the yields of 2-benzimidazolone and 1,3-dimethyl-2-benzimidazolone were examined. The reaction of o-aminophenol with DMC selectively gave a carbonylation product, 2-benzoxazolone, or a carbonylation/methylation product, 3-methyl-2-benzoxazolone, depending on the reaction conditions in the presence of Pb(OAc)2.