US7999112: Reusable transition metal complex catalyst useful for the preparation of high pure quality 3,3'-diaminobenzidine and its analogues and a process thereof

The invention provides a reusable transition metal complex catalyst useful for the preparation of high pure quality 3,3'-diaminobenzidine and its analogues. The invention also provides a process for the preparation of a reusable transition metal complex catalyst. The invention further provides a process for the preparation of 3,3'-diaminobenzidine (DAB) or 3,3',4,4'tetraminobiphenyl (TAB) using reusable transition metal complex catalyst. The high quality 3,3'-diaminobenzedine (DAB) and its analogues are prepared by coupling 4-halo-2-nitroaniline to 3,3'-dinitrobenzidine (DNB) using transition metals as catalysts followed by reduction of 3,3'-dinitrobenzidine to the corresponding substituted 3,3'-diaminobenzidine of formula 1 in high yields.