Abstract
The suitability of three routes to primary (1°) and secondary (2°) N-chloroamines for carbonylation to carbamoyl chlorides and isocyanates using palladium catalysts is explored. Free nitrogen bases inactivate the catalyst, which at 65 atm CO pressure and ambient temperature achieves up to 75% conversion of 2°-chloroamines to product, but only 30–45% for 1°-chloroamines. Triphenylphosphine enhances the yield and rate of CO uptake at an optimum Pd: PPh 3 ratio of 1 : 2. N, N-Dichloroamines do not carbonylate under the same conditions and have no influence on the carbonylation of N-chloroamines. Chloroamines having long alkyl chains (C 12–C 18), which need to be prepared using the HOCI route, give good yields of 2°-carbamoyl chlorides but lower yields of the 1°-compounds because of the detrimental effect of HCl generated in the formation of isocyanates. Attempts to isolate an intermediate complex by reacting (PPh 3) 3Pd(CO) with Me 2NCl give (PPh 3) 2PdC 2. A high-pressure IR study of the reactions using Pd, PdCl 2, and (PPh 3) 2PdCI 2 shows [(PPh 3) 2Pd(CO)Cl] + as the only identifiable carbonyl complex detected in solution.
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