Catalytic oxidation reactions of aromatic diamines by transition metal complexes

The catalytic reactions of M(TPP)Cl (M = Fe (1), Mn (2)), Fe(TMP)Cl (3), and Fe(TDCPP)Cl (4) (H2TPP = 5,10,15,20-tetraphenylporphyrin; H(2)TMP = 5,10,15,20-tetramesitylporphyrin; H2TDCPP = 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin) with 2,4-diaminotoluene (5) and p-phenylenediamine (6) were carried out using t-BuOOH (3 M isooctane solution) as oxidant. With the former substrate, the nitro derivatives 2-amino-4-nitrotoluene (5a) and 2,4-dinitrotoluene (5b) (total yield of 5a + 5b ranges between 27-55%) were obtained with low yields and their amounts depend on the catalyst used. An other oxidation product of 5 was 3-amino-4(tert-butyldioxy)-4-methyl-2,5-cyclohexadien-1-mine hydrochloride (5c) (20%). In the oxidation reaction of 6,4-nitroaniline (6a) (11%) was obtained only with catalyst 1, being an unidentified black solid (6b) the major oxidation product. 6b was always the main product with all the studied catalysts (1-3), while the yields and nature of the recovered azobenzenes depend on the metalloporphyrin used: the highest yield of 4,4-dinitroazobenzene (6c) (37%) was obtained with 3 in the presence of acetic acid, 4,4'-diaminoazobenzene (6d) (19%) was obtained with 4, and 4-amino,4'-nitroazobenzene (6e) (17%) with 3. The catalytic reactions of Mo(O)(O-2)(2)(H2O)(HMPA) (7) (HMPA = hexamethylphosphotriamide), with 5, 6, and 4-aminodiphenylamine (8), in the presence of H2O2 (35% w/w water solution) as oxidant, were studied. The corresponding mononitro derivatives, 5a, 6a, and 4-nitrodiphenylamine (8a) were obtained with fair selectivity (35, 70, and 60%, respectively).