THE ROLE OF ALCOHOL IN THE CATALYTIC REDUCTIVE CARBONYLATION OF NITROBENZENES TO CARBAMATES IN THE PRESENCE OF RH(CO)4- OR RU3(CO)12

The selectivity of N-phenylcarbamate from the reductive carbonylation of nitrobenzene using Rh(CO)4- or Ru3(CO)12-Et4N+ Cl- as the catalyst is much higher in t-butyl alcohol than in primary or secondary alcohols; the latter two alcohols are readily involved in the reduction of nitrobenzene to aniline leading to lower selectivity of the corresponding carbamates. For example, when 2-butanol was used as the solvent for the reductive carbonylation of nitrobenzene, 2-butanone and aniline were observed in a molar ratio of 1:1. Similarly, the reductive carbonylation of p-nitrotoluene to give the corresponding carbamate in t-butyl alcohol is also higher in yield than in 2-butanol or in butanol. However, for dinitroarenes the selectivity of carbamates is low using either (t)BuOH or other primary and secondary alcohols.