Process for preparing 4-aminodiphenylamine

1. A complex base catalyst comprising a tetraalkyl ammonium hydroxide, a tetraalkyl ammonium salt, and an alkali metal hydroxide or oxide, wherein molar ratio of the tetraalkyl ammonium hydroxide to the alkali metal hydroxide or oxide to the tetraalkyl ammonium salt is selected from the group consisting of 1:0.5:1, 1:1:1, 5:2:2, 0.5:0.5:2, 3:2:2, 2:2:2, and 1:1:2, and the tetraalkyl ammonium salt is represented by a formula of

[(R 1 )(R 2 )(R 3 )(R 4 )N] + n X n-

wherein R 1 , R 2 , R 3 , and R 4 , identical or different, respectively, is an alkyl having from 1 to 4 carbon atoms and said alkyl being optionally substituted by a hydrophilic substitute,

wherein X n- is selected from the group consisting of halide ion, sulfate radical, carbonate radical, phosphate radical, bicarbonate radical, bisulfate radical, C1-C2-alkyl carbonate radical, and C1-C2-alkyl sulfate radical; n is a value of from 1 to 2.

2. The complex base catalyst according to claim 1 , wherein an amount of total concentration of tetraalkyl ammonium hydroxide, alkali metal hydroxide or oxide, and tetraalkyl ammonium salt in a reaction mixture is from 10 to 100 percent by weight.

3. The complex base catalyst according to claim 2 , wherein the amount of total concentration of tetraalkyl ammonium hydroxide, alkali metal hydroxide or oxide, and tetraalkyl ammonium salt in a reaction mixture is from 25 to 38 percent by weight.

4. The complex base catalyst according to claim 1 , wherein the catalyst is prepared by stirring tetraalkyl ammonium hydroxide, alkali metal hydroxide or oxide, and tetraalkyl ammonium salt in a solid or aqueous solution form in water at a temperature of from 0 to 90° C. until being homogeneous to form an aqueous form of the catalyst.

5. The complex base catalyst according to claim 4 , wherein the aqueous form of the catalyst is treated through azeotropic process by adding benzene to completely remove water and form an anhydrous form of the catalysts.

6. The complex base catalyst according to claim 1 , wherein at least one of R1, R2, R3 and R4 is substituted by a hydrophilic substitute selected from the group consisting of hydroxy, methoxy, polyether, cationic polyamide, polyester, polyethylene polyamine, and highly water-soluble quaternary ammonium salt-containing radical.

7. The complex base catalyst according to claim 1 , wherein the tetraalkyl ammonium salt is a hydrophilic substitute-carrying tetraalkyl ammonium salt selected from the group consisting of poly-methylated triethylene tetraamine sulfate, poly-methylated diethylene triamine carbonate, N,N-dimethyl-N,N-bis(methoxyethyl) ammonium carbonate, N-methyl-N,N,N-tri(methoxyethyl) ammonium carbonate, N,N,N-trimethyl-N-hydroxyethyl ammonium carbonate, trimethyl hydroxyethyl ammonium chloride, N,N,N-trimethyl-N-ethoxylated (1-4 moles of ethylene oxide) ethyl ammonium carbonate, N,N,N-trimethyl-N-ethoxylated (1-4 moles of ethylene oxide) propyl ammonium carbonate, N,N,N-trimethyl-N-ethoxylated (1-4 moles of ethylene oxide) propyl ammonium chloride, and N,N-dimethyl-N,N-bis(ethoxylated (1-4 moles of ethylene oxide) propyl) ammonium carbonate.

8. The complex base catalyst according to claim 1 , wherein the tetraalkyl ammonium salt is selected from the group consisting of tetramethyl ammonium carbonate, tetramethyl ammonium methyl-carbonate, tetraethyl ammonium carbonate, tetraethyl ammonium ethyl-carbonate, tetramethyl ammonium sulfate, tetramethyl ammonium methyl-sulfate, tetraethyl ammonium sulfate, and tetraethyl ammonium ethyl-sulfate.

9. The complex base catalyst according to claim 1 , wherein the tetraalkyl ammonium salt is prepared by reacting trialkyl amine with di(C 1 -C 2 )alkyl carbonate or di(C 1 -C 2 )alkyl sulfate in a polar solvent.

10. The complex base catalyst according to claim 9 , wherein the reaction is carried out under a reaction pressure of from 0.1 to 3.0 MPa, a reaction temperature of from 50-200° C., reaction time ranges from 1.5 to 6 hours.

11. The complex base catalyst according to claim 10 , wherein the reaction is carried out under the reaction pressure of from 0.4 to 2.0 MPa.

12. The complex base catalyst according to claim 10 , wherein the reaction is carried out under the reaction temperature of from 60-150° C.

13. The complex base catalyst according to claim 9 , wherein a molar ratio of trialkyl amine to di(C 1 -C 2 )alkyl carbonate or di(C 1 -C 2 )alkyl sulfate of from 2:1 to 1:2.

14. The complex base catalyst according to claim 9 , wherein the polar solvent is in an amount of from 1 to 10 times of weight of the trialkyl amine.

15. The complex base catalyst according to claim 1 , wherein the tetraalkyl ammonium hydroxide has a formula of

R′ 4 N + OH − ,

wherein R′ is independently an alkyl having one or two carbon atoms.

16. The complex base catalyst according to claim 15 , wherein the tetraalkyl ammonium hydroxide is prepared from corresponding tetraalkyl ammonium salt and a base in a polar solvent.

17. The complex base catalyst according to claim 1 , wherein the catalyst is in an aqueous solution.

18. The complex base catalyst according to claim 1 , wherein the catalyst is anhydrous.

19. A process for preparing 4-aminodiphenylamine comprising the steps of

reacting nitrobenzene and aniline in presence of the complex base catalyst as described in claim 1 to form a reaction mixture, and

hydrogenating the reaction mixture to obtain 4-aminodiphenylamine.

20. The process according to claim 19 , wherein a molar ratio of nitrobenzene to aniline is in a range of from 1:1 to 1:15.

21. The process according to claim 19 , wherein a molar ratio of hydroxide ion in the complex base catalyst to nitrobenzene is in a range of from 1:4 to 4:1.

22. A process for using the complex base catalyst of claim 1 , comprising the step of

reacting nitrobenzene and aniline in presence of the complex base catalyst as described in claim 3 to form a reaction mixture having 4-nitrodiphenylamine and 4-nitrosodiphenylamine.

23. The process according to claim 22 , wherein molar ratio of nitrobenzene to aniline is in a range of from 1:1 to 1:15.

24. The process according to claim 22 , wherein molar ratio of hydroxide ion in the complex base catalyst to nitrobenzene is in a range of from 1:4 to 4:1.

25. The process according to claim 22 , further comprising

hydrogenating the reaction mixture having 4-nitrodiphenylamine and 4-nitrosodiphenylamine to make 4-aminodiphenylamine.

26. The process according to claim 25 , further comprising

reductively alkylating the 4-aminodiphenylamine to produce alkylated derivatives of 4-aminodiphenylamine.