Process for preparing secondary amides by carbonylation of a corresponding tertiary amine
View Patent ↗The present invention relates to a process for preparing secondary amides with good selectivity by carbonylating a corresponding tertiary amine with carbon monoxide in a reaction mixture in the presence of a metal catalyst and in the presence of a halogen containing promoter. The metal catalyst comprises palladium. A same or even a much better catalytic activity can be obtained with palladium than with the much more expensive rhodium, especially when the palladium is used in a low concentration. Moreover, also a good selectivity can be achieved.
1. A process for preparing a secondary amide with the following formula
wherein
R 1 is an aromatic group or a straight or branched aliphatic carbon chain which comprises at least one carbon atom and which may be substituted or not;
R 2 and R 3 are, independent from one another, an aromatic group or a further straight or branched aliphatic carbon chain which comprises at least one carbon atom and which may be substituted or not, or R 2 and R 3 form a cycle containing the amide nitrogen,
which process comprises the step of carbonylating a tertiary amine of formula
with carbon monoxide in a reaction mixture in the presence of a catalyst which comprises palladium and in the presence of a halogen containing promoter, the reaction mixture comprising less than 750 ppm of palladium.
2. A process according to claim 1 , wherein said halogen containing promoter comprises a halide of formula R 1 X wherein X is I, Br or Cl.
3. A process according to claim 1 , wherein the halogen containing promoter is introduced in the reaction mixture by adding one or more compounds from the group consisting of halides of formula R 1 X, halides of formula R 4 1 N + X − , phosphonium halide salts of formula R 4 1 P + X − , X 2 , metal halide salts, and acid halides of formula R 1 COX to the reaction mixture, the halogen being chlorine, bromine or iodine.
4. A process according to claim 3 , wherein the halogen containing promoter is introduced in the reaction mixture by adding the halide of formula R 1 X to the reaction mixture.
5. A process according to claim 1 , wherein R 1 , R 2 and R 3 are independently a straight or branched aliphatic carbon chain containing 1 to 23 carbon atoms.
6. A process according to claim 5 , wherein the carbon chains are not substituted.
7. A process according to claim 5 , wherein at least the carbon chain of the R 1 group is substituted with an aromatic group.
8. A process according to claim 1 , wherein R 1 is a straight or branched aliphatic carbon chain containing 1 to 23 carbon atoms and R 2 and R 3 form an azacycle together with the amide nitrogen atom.
9. A process according to claim 1 , wherein R 1 is a straight or branched aliphatic carbon chain containing 1 to 23 carbon atoms and R 2 and R 3 form a heterocycle together with the amine nitrogen atom, which heterocycle contains at least one additional heteroatom.
10. A process according to claim 1 , wherein said catalyst comprises Pd(II).
11. A process according to claim 1 , wherein said catalyst comprises Pd(0).
12. A process according to claim 1 , wherein the halogen containing promoter is present in said reaction mixture in a molar ratio of greater than 0.1 with respect to the catalyst metal.
13. A process according to claim 1 , wherein the carbonylation step is carried out at a temperature lower than 285° C.
14. A process according to claim 1 , wherein the carbonylation step is carried out at a pressure higher than 20 bars.
15. A process according to claim 1 , wherein R 1 , R 2 and R 3 are methyl groups.
16. A process according to claim 10 , wherein said palladium is added to said reaction mixture as an inorganic salt selected from the group consisting of PdCl 2 , PdBr 2 , PdI 2 , Pd(OAc) 2 , PdSO 4 , (NH 4 ) 2 [PdCl 6 ], (NH 4 ) 2 [PdCl 4 ], Pd(acac) 2 and PdC 2 O 4 .
17. A process according to claim 11 , wherein said palladium is added to said reaction mixture as a complex and/or as a metal deposited on a support.
18. A process according to claim 1 , wherein the carbonylation step is carried out at a temperature higher than 120° C.
19. A process according to claim 18 , wherein the carbonylation step is carried out at a temperature higher than 180° C.
20. A process according to claim 14 , wherein the carbonylation step is carried out at a pressure higher than 50 bars.
21. A process according to claim 1 , wherein R 1 is a saturated straight or branched aliphatic carbon chain containing from 1 to 23 carbon atoms.