JOURNAL OF CATALYSIS 114, 246-258 (1988) Oxidative Carbonylation of Aniline over Pd/C Catalyst: Effect of Promoters, Solvents, and Reaction Conditions’ SUNIL P. GUPTE AND RAGHUNATH V. CHAUDHAR? Chemical Engineering Division, National Chemical Laboratory, Pune 411 008, India Received January 19, 1988; revised May 26, 1988 Oxidative carbonylation of aniline to N,N’-diphenylurea over 5% Pd/C-NaI catalyst has been reported. The effects of promoters, solvents, reaction conditions, and pretreatment of catalyst with reactants have been investigated. Pretreatment of 5% Pd/C catalyst with 02, CO, and aniline resulted initially in a decrease in the activity of the catalyst. Activity-versus-NaI concentration and activity-versus-O2 pressure curves passed through maxima, indicating inhibition of rates at higher concentrations. CO pressure showed a linear dependence below 35 atm pressure, but zero-order behavior at higher pressures. The variation in activity was 1.6th order with respect to aniline concentration. Higher activity is obtained in polar solvents. Process parameters had a strong influence on the activity of the catalyst, but the selectivity for N,N’-diphenylurea was unaf- fected. 0 1988 Academic press, Inc. INTRODUCTION Oxidative carbonylation of amines is im- portant in the synthesis of carbamates, which have applications in insecticides and the polymer industry. This nonphosgene route has led to the development of a new process for methylene diphenyl diisocya- nate (MDI) (I, 2). Oxidative carbonylation of aniline is an important step, which gives phenylurethane when the reaction is car- ried out in the presence of alcohol. The stoichiometric reaction is R-NH2 + CO + $02 2 RNH COOR’ + H20. (1) Oxidative carbonylation of aromatic amines is reported to be effectively carried out using a variety of supported noble metal catalysts (viz., Pd, Pt, Rh, Ir, Ru etc.) (3,4) and in the presence of alkali metal or alkyl iodide promoters. However, metallic Pd or Pd/C with NaI promoter has been found to be highly active and selective for this reac- tion (3) and a phenylurethane yield of 90- ’ NCL Communication No. 4371. z To whom correspondence should be addressed. 95% from aniline has been reported. Most of the literature on this subject is patented V-8), and recent papers (3, 4) describe mainly the activity of different catalyst sys- tems. There is no report of a detailed inves- tigation of the role of iodide promoters, the effect of reaction conditions, product dis- tribution, and catalyst reusability. This prompted us to undertake the present work in which we study the effect of process con- ditions, solvents, and promoters on the ac- tivity and the selectivity of oxidative car- bonylation of aniline with the Pd/C-NaI catalyst system. It is believed that the ox- idative carbonylation of aniline proceeds through diphenylurea as an intermediate. Therefore, this step has been separately in- vestigated in the absence of alcohol. Fur- ther, the effects of catalyst pretreatment and catalyst reusability have also been studied. Such a study seems most useful in view of the potential importance of this re- action in a new nonphosgene process for MDI. EXPERIMENTAL The catalyst, consisting of 5% Pd/C, was prepared according to the procedure de- scribed by Mozingo (9). The specifications 246 0021-9517188 $3.00 Copyright 0 1988 by Academic Press. Inc. AU tights of reproduction in any form reserved.