Carbonylation of dinitrotoluene to dimethyl toluenedicarbamate; high efficiency of phosphorus acids as promoters for the palladium-phenanthroline catalytic system

Article abstract of DOI:10.1002/adsc.200404151

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. The complexes [Pd(Phen)₂] [SbF₆] and [Pd(Phen) ₂][BAr^F₄] [Ar^F = 3,5-(CF ₃)₂C₆H₃] have been prepared for the first time. The latter displays a markedly higher solubility than all other [Pd(Phen)₂]²⁺ 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 = 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.