Method for producing biphenylamines from azobenzenes by ruthenium catalysis

1. Method for preparing a biphenylamine of formula (I)

in which

R 1 is hydrogen, hydroxyl, fluorine, chlorine, C 1 -C 4 -alkyl, C 1 -C 4 -alkoxy, C 1 -C 4 -alkylthio or C 1 -C 4 -haloalkyl,

X 1 is hydrogen, alkoxy, alkanoyl, alkyl carboxylate, fluorine or chlorine,

X 2 is hydrogen, alkoxy, alkanoyl, alkyl carboxylate, fluorine or chlorine,

X 3 is hydrogen, alkoxy, alkanoyl, alkyl carboxylate, fluorine or chlorine,

comprising: (I) reacting one or more azobenzenes of formula (II)

in which

R 1 is as defined above,

with an aromatic compound of formula (III)

in which

X 1 , X 2 and X 3 are each as defined above,

and

Hal is iodine, bromine or chlorine

in the presence of a catalyst system consisting of a ruthenium catalyst, an activator, and a base, and (2) the azobenzenes of the formula (IV) thus obtained

in which R 1 , X 1 , X 2 and X 3 are as defined above,

are hydrogenated to give the biphenylamines of the formula (I).

2. Method according to claim 1 , wherein the solvent comprises ketones, nitriles, ethers, hydrocarbons and halogenated hydrocarbons and branched alcohols and/or a mixture thereof.

3. Method according to claim 1 , wherein the solvent comprises 1,4-dioxane, toluene, ortho-xylene, meta-xylene, para-xylene and/or a mixture thereof.

4. Method according to claim 1 , wherein the catalyst is [{RuCl 2 (p-cymene)} 2 ].

5. Method according to claim 1 , wherein the activator is an acid, optionally a carboxylic acid.

6. Method according to claim 1 , wherein the activator is a carboxylic acid selected from the group consisting of: formic acid, acetic acid, propionic acid, pivalic acid, benzoic acid, 2-methylbenzoic acid, 3-methylbenzoic acid, 4-methylbenzoic acid, 2,3-dimethylbenzoic acid, 2,4-dimethylbenzoic acid, 2,5-dimethylbenzoic acid, 2,6-dimethylbenzoic acid, 3,4-dimethylbenzoic acid, 3,5-dimethylbenzoic acid, 2,4,6-trimethylbenzoic acid, 2,3,4-trimethylbenzoic acid, 3,4,5-trimethylbenzoic acid, 2,3,5-trimethylbenzoic acid, 2,3,6-trimethylbenzoic acid, phenylacetic acid, 2-methylphenylacetic acid, 3-methylphenylacetic acid, 4-methylphenylacetic acid, 2,5-dimethylphenylacetic acid, 2,3,6-trimethylphenylacetic acid, 2,3,5,6-tetramethylphenylacetic acid, 2,3,4,6-tetramethylphenylacetic acid, 2-chlorophenylacetic acid, 3-chlorophenylacetic acid, 4-chlorophenylacetic acid and 2,4-dichlorophenylacetic acid.

7. Method according to claim 1 , wherein the activator is 2,4,6-trimethylbenzoic acid.

8. Method according to claim 1 , wherein the base is an inorganic base.

9. Method according to claim 1 , wherein the base is selected from the group consisting of: lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, calcium carbonate and magnesium carbonate.

10. Method according to claim 1 , wherein the base is potassium carbonate.

11. Method according to claim 1 , wherein the activator is used in an amount of 0.1 to 100 mole percent, based on the aromatic compound of the formula (III).

12. Method according to claim 1 , wherein the ruthenium catalyst is used in an amount of 1 to 20 mole percent, based on the aromatic compound of the formula (III).

13. Method according to claim 1 , wherein the molar ratio of azobenzene of the formula (II) to haloaromatic compound of the formula (III) is 1:0.4 to 1.

14. Method according to claim 1 , wherein the molar ratio of azobenzene of the formula (II) to haloaromatic compound of the formula (III) is 1:0.45 to 0.9.

15. Method according to claim 1 , wherein the solvent is 1,4-dioxane, the activator is 2,4,6-trimethylbenzoic acid, the aromatic compound of the formula (III) is a brominated aromatic compound, the base is potassium carbonate and the catalyst is [{RuCl 2 (p-cymene)} 2 ].