Process for preparing aromatic carbamates
The invention is directed to a process for preparing aromatic carbamates which comprises the reaction of an aromatic amine with an organic carbonate in the presence of a catalyst characterized in that Zn 4 O(OAc) 6 is used as catalyst.
1. A process for preparing aromatic carbamates which comprises reacting an aromatic amine with an organic carbonate in the presence of a catalyst, wherein the catalyst comprises Zn 4 O(OAc) 6 .
2. The process according to claim 1 , wherein the aromatic amine is selected from the group consisting of aromatic amines represented by the general formulas (I), (II), (III), (IV) and (V):
wherein:
R, R1, R2, R3 represents, independently of one another, hydrogen or a hydrocarbyl or hydrocarbyloxy group comprising up to 8 carbon atoms,
A represents a divalent hydrocarbon group having from 1 to 10 carbon atoms,
n is zero or 1, and when n is zero both aromatic rings are fused, and
m is zero or any integer greater than or equal to 1.
3. The process according to claim 2 , wherein R, R1, R2, R3 represents, independently of one another, hydrogen or a hydrocarbyl or hydrocarbyloxy group comprising up to 4 carbon atoms.
4. The process according to claim 2 , wherein A represents a divalent hydrocarbon group having from 1 to 6 carbon atoms.
5. The process according to claim 2 , wherein the aromatic amine is selected from the group consisting of aniline, o-toluidine, m-toluidine, p-toluidine, 2,4-xylidine, 3,4-xylidine, 2,5-xylidine, 4-ethylaniline, 3-propylaniline, 1,2-diaminobenzene, 1,3-diaminobenzene, 1,4-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, technical mixtures of 2,4-diaminotoluene and 2,6-diaminotoluene, 4,4′-diaminodiphenylmethane, 2,4′-diaminodiphenylmethane, 2,2′-diaminodiphenylmethane, amines of the diphenylmethane series obtained by acid catalyzed condensation and/or rearrangement reaction of aniline and formaldehyde and containing mixtures of 4,4′-diaminodiphenylmethane, its isomers and higher homologues, 1,5-diaminonaphtalene, o-anisidine, m-anisidine, p-anisidine and mixtures thereof.
6. The process according to claim 5 , wherein the aromatic amine is selected from the group consisting of 2,4-diaminotoluene, 2,6-diaminotoluene, technical mixtures of 2,4-diaminotoluene and 2,6-diaminotoluene, 4,4′-diaminodiphenylmethane, 2,4′-diaminodiphenylmethane, 2,2′-diaminodiphenylmethane, amines of the diphenylmethane series obtained by acid catalyzed condensation and/or rearrangement reaction of aniline and formaldehyde and containing mixtures of 4,4′- diaminodiphenylmethane, its isomers and higher homologues, and 1,5-diaminonaphthalene.
7. The process according to claim 1 , wherein the organic carbonate is selected form the group consisting of ethylene carbonate, propylene carbonate, styrene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, dihexyl carbonate, methyl ethyl carbonate, methyl butyl carbonate, diphenyl carbonate, methyl phenyl carbonate, and mixtures thereof.
8. The process according to claim 7 , wherein the organic carbonate is selected from the group consisting of dimethyl carbonate and diethyl carbonate.
9. The process according to claim 8 , wherein the organic carbonate is dimethyl carbonate.
10. The process according to claim 1 , wherein the reaction is conducted at a temperature of from 80° C. to 250° C.
11. The process according to claim 1 , wherein the reaction time is less than or equal to 12 hours.
12. The process according to claim 1 , wherein the absolute process pressure is about 1-50 bar.
13. The process according to claim 1 , wherein the molar ratio of organic carbonate to primary amino groups originating from the aromatic amine is 1:1-50.
14. The process according to claim 1 , wherein the quantity of the catalyst is 0.001-10 mol zinc per 100 mols of primary amino groups.
15. A process for the production of isocyanates wherein in a first step aromatic carbamates are produced by reaction of an aromatic amine with an organic carbonate in the presence of Zn4O(OAc)6 as catalyst, and wherein in a second step the carbamate obtained in the first step is then subjected to thermal treatment.
16. The process according to claim 15 , wherein the thermal treatment comprises exposure of the carbamate in the second step to a temperature of 50° C. to 300° C. for at least 1 min to 3 h.