Method for preparing primary diamines by Kolbe electrolysis coupling reaction

1. A method for preparing a primary diamine of the general formula (II) from an amino acid compound of the general formula (I)

H 2 N-T-COOX  (I)

H 2 N-T-T-NH 2   (II)

by a Kolbe electrolysis coupling reaction in a reaction medium comprising:

a solvent,

an electrolyte, and

the amino acid compound of the general formula (I),

wherein

T represents a linear or branched C1-C 10 alkylene group,

X represents H + or alkali metal cation,

the reaction is performed under a current density of less than 400 mA/cm 2 .

2. The method according to claim 1 , wherein T represents a linear or branched C 1 -C 6 alkylene group.

3. The method according to claim 1 , wherein the primary diamine is selected from the group consisting of 1,10-decanediamine, 1,8-octanediamine, 1,6-hexanediamine, 1,4-butanediamine and 1,2-ethylenediamine.

4. The method according to claim 1 , wherein the amino acid compound is selected from the group consisting of 6-aminohexanoic acid, 5-aminopentanoic acid, 4-aminobutanoic acid, 3-aminopropanoic acid and aminoacetic acid.

5. The method according to claim 1 , wherein the concentration of the amino acid compound in the reaction medium is from 0.05 to 2 mol/L.

6. The method according to claim 1 , wherein the solvent is selected from the group consisting of methanol, ethanol, propanol, acetone, acetonitrile, THF (tetrahydrofuran), DMF (N,N-dimethylformamide), DMSO (dimethylsulfoxide), NMP (N-Methyl-2-pyrrolidone), DMC (dimethyl carbonate), NM (nitromethane), PC (propylene carbonate), EC (ethylene carbonate), toluene, xylene, dimethylformamide, hexane, pentane, heptane, octane, nonane, decane, undecane, dodecane and ionic liquids.

7. The method according to claim 6 , wherein the solvent is methanol or ethanol.

8. The method according to claim 1 , wherein the electrolyte is a base electrolyte.

9. The method according to claim 8 , wherein the electrolyte is an alkoxide.

10. The method according to claim 9 , wherein the electrolyte is selected from the group consisting of sodium methoxide, potassium methoxide, sodium ethoxide and potassium ethoxide.

11. The method according to claim 1 , wherein the reaction medium is free or substantially free of water.

12. The method according to claim 1 , wherein the molar ratio of the amino acid compound to the electrolyte is in a range of 2:1 to 1:5.

13. The method according to claim 1 , wherein the Kolbe electrolysis coupling is carried out under direct current.

14. The method according to claim 1 , wherein the current density is from 100 to 200 mA/cm 2 .

15. The method according to claim 1 , wherein the reaction time is from 2 to 6 hours.

16. The method according to claim 1 , wherein the reaction temperature is from 20-50° C.

17. The method according to claim 1 , wherein the method further comprises the following steps before the Kolbe electrolysis coupling reaction:

(a) hydrolyzing of a lactam to provide the Compound (I),

(b) optionally dehydrating the Compound (I) obtained at step (a).