Carbonylation of Dinitrotoluene to Dimethyl Toluenedicarbamate; High Efficiency of Phosphorus Acids as Promoters for the Palladium-Phenanthroline Catalytic System

Abstract

Phosphorus acids are excellent promoters for the palladium-phenanthroline catalyzed carbonylation of 2,4-dinitrotoluene to 2,4-toluenedicarbamate. For the first time, all intermediate nitrocarbamates and aminocarbamates have been independently synthesized and their amount after every catalytic reaction precisely quantified. An extensive optimization of all experimental variables has been carried out. The best acids are phenylphosphonic and 4-tolylphosphonic acids. The addition of 2,2-dimethoxypropane as an internal drying agent is highly beneficial. The addition of an amine derived from the starting dinitroarene increases both rate and selectivity of the carbonylation reaction. have been prepared for the first time. The latter displays a markedly higher solubility than all other [Pd(Phen) 2 ] 2 þ complexes. The effect of several possible promoters has also been investigated. Under the optimized experimental conditions, a 77.6% selectivity in dicarbamate was obtained when working at a molar ratio dinitrotoluene/Pd ¼ 2920. At the end of the reaction, the dicarbamate spontaneously precipitates out of the solution in high yields upon cooling, with no inclusion of the acid promoter or of phenanthroline. 2,6-Dinitrotoluene can also be efficiently carbonylated to the corresponding dicarbamate.

Fluoride effect on the palladium–phenanthroline catalyzed carbonylation of nitroarenes to carbamates

“…Previous studies on catalyst deactivation during the carbonylation of dinitrotoluene had led to the conclusion that the most likely explanation for the observed deactivation is that some organic compounds are formed during the reaction which interact with the palladium catalyst and decrease its reactivity. 48 If fluoride does not alter the selectivity of the reaction, it probably also does not prevent the formation of the inactivating byproducts.…”

“…Nitrotoluidine 4b had been earlier found to be the most efficient and the conditions employed for the reported reactions (Table 2) are identical to those previously optimized for these substrates. 48 Note that dinitrotoluene reacts at a much faster rate than the intermediate nitrocarbamates 2. Thus dinitrotoluene will be almost completely consumed before dicarbamate 1 is formed in appreciable amounts.…”

“…We had previously solved the problem of the independent quantification of all compounds shown in Scheme 3, 48 although ureas and azo derivatives could not be quantified. In this case, several amines can be added as promoters.…”

“…For dinitrotoluene reactions, the products were analyzed by HPLC (RP 18 column, methanol-water 55 : 45 as eluent, benzophenone as the internal standard; for 2,4-dinitrotoluene, 1, 2a, b,and 3a, b) and gas chromatography (PS 255 column, naphthalene as the internal standard; for 4a, b and 5). Response factors for both GC and HPLC analyses had been determined in previous works 47,48 by injection of known amounts of the pure compounds.…”

Zinc Carboxylate Functionalized Mesoporous SBA-15 Catalyst for Selective Synthesis of Methyl-4,4′-di(phenylcarbamate)

“…To avoid using phosgene, several alternative methods for producing MDI have been proposed [3]. Among these methods, thermal decomposition of methylene-4,4 0 -di(phenylcarbamate) (MDC) to obtain MDI is very attractive [4], because MDC can be efficiently synthesized by non-phosgene methods like reductive carbonylation of aromatic nitro compounds [5], oxidative carbonylation of amines [6], methoxycarboxylation of 4,4 0 -methylenedianiline (MDA) with dimethyl carbonate (DMC) [7,8]. The last method employs environmentally benign materials and mild reaction conditions and then has attracted many attentions in recent years.…”