Continuous Method For Producing Amides Of Aliphatic Hydroxycarboxylic Acids

1 . A continuous process for preparing a hydroxycarboxamide comprising the steps of reacting at least one hydroxycarboxylic acid of the formula I

HO—R 3 —COON  (I)

wherein R 3 is a substituted or an unsubstituted aliphatic hydrocarbon radical having 1 to 100 carbon atoms with at least one amine of the formula II

HNR 1 R 2   (II)

wherein R 1 and R 2 are each independently hydrogen or a hydrocarbon radical having 1 to 100 carbon atoms forming an ammonium salt and subsequently converting this ammonium salt to the hydroxycarboxamide under microwave irradiation in a reaction tube whose longitudinal axis is in the direction of propagation of the microwaves from a monomode microwave applicator.

2 . A process as claimed in claim 1 , wherein the ammonium salt is irradiated with microwaves in a substantially microwave-transparent reaction tube within a hollow conductor connected via waveguides to a microwave generator.

3 . A process as claimed in claim 1 , wherein the microwave applicator is configured as a cavity resonator.

4 . A process as claimed in claim 1 , wherein the microwave applicator is configured as a cavity resonator of the reflection type.

5 . A process as claimed in claim 1 , wherein the reaction tube is aligned axially with a central axis of symmetry of the hollow conductor.

6 . A process as claimed in claim 1 , wherein the ammonium salt is irradiated in a cavity resonator with a coaxial transition of the microwaves.

7 . A process as claimed in claim 1 , wherein the cavity resonator is operated in E 01n mode where n is an integer from 1 to 200.

8 . A process as claimed in claim 1 , wherein R 3 contains 1 to 30 carbon atoms.

9 . A process as claimed in claim 1 , wherein R 3 contains at least one —OH group bonded to a secondary carbon atom.

10 . A process as claimed in claim 1 , wherein R 3 contains a hydroxyl group in the α position to the carboxyl group.

11 . A process as claimed in claim 1 , wherein R 3 contains at least one double bond.

12 . A process as claimed in claim 1 , wherein R 3 has at least one substituent selected from the group consisting of halogen atoms, halogenated alkyl radicals, C 1 -C 5 -alkoxy, poly(C 1 -C 5 -alkoxy), poly(C 1 -C 5 -alkoxy)alkyl, carboxyl, hydroxyl, ester, amide, cyano, nitrile, nitro and aryl groups having 5 to 20 carbon atoms, where the C 5 -C 20 -aryl groups may be substituted by radicals selected from the group consisting of halogen atoms, C 1 -C 20-alkyl, C 2 -C 20 -alkenyl, C 1 -C 5 -alkoxy, ester, amide, hydroxyl, cyano, nitrile and nitro groups.

13 . A process as claimed in claim 1 , wherein R 1 and R 2 are each independently a hydrocarbon radical having 1 to 100 carbon atoms.

14 . A process as claimed in claim 1 , wherein R 1 is a hydrocarbon radical having 1 to 100 carbon atoms and R 2 is hydrogen.

15 . A process as claimed in claim 1 , wherein R 1 or R 2 or both radicals may be substituted by one or more substituents selected from the group consisting of C 1 -C 5 -alkoxy, cyano, nitrile, nitro and C 5 -C 20 -aryl groups.

16 . A process as claimed in claim 1 , wherein R 1 or R 2 or both radicals are substituted by at least one C 5 -C 20 -aryl group, wherein the C 5 -C 20 -aryl group is substituted by one or more substituents selected from the group consisting of halogen atoms, halogenated alkyl radicals, C 1 -C 20 -alkyl, C 2 -C 20 -alkenyl, C 1 -C 5 -alkoxy, hydroxyl, ester, amide, cyano, nitrile and nitro groups.

17 . A process as claimed in claim 1 , wherein R 1 and R 2 together with the nitrogen atom to which they are bonded form a ring.

18 . A process as claimed in claim 1 , wherein R 1 and R 2 are each independently a radical of the formula III

—(R 4 —O) n —R 5   (III)

wherein

R 4 is an alkylene group having 2 to 6 carbon atoms,

R 5 is a hydrocarbon radical having 1 to 24 carbon atoms or a group of the formula NR 10 R 11 ,

n is an integer from 2 to 50 and

R 10 ,R 11 are each independently an aliphatic radical having 1 to 24 carbon atoms an aryl group or heteroaryl group having 5 to 12 ring members, a poly(oxyalkylene) group having 1 to 50 poly(oxyalkylene) units, where the poly(oxyalkylene) units derive from alkylene oxide units having 2 to 6 carbon atoms, or R 10 and R 11 together with the nitrogen atom to which they are bonded form a ring having 4, 5, 6 or more ring members.

19 . A process as claimed in claim 1 , wherein R 1 and R 2 are each independently a radical of the formula IV

—[R 6 —N(R 7 )] m —(R 7 )  (IV)

wherein

R 6 is an alkylene group having 2 to 6 carbon atoms or mixtures thereof,

each R 7 is independently hydrogen, an alkyl or hydroxyalkyl radical having up to 24 carbon atoms, a polyoxyalkylene radical —(R 4 —O) p —R 5 , or a polyiminoalkylene radical —[R 6 —N(R 7 )] q —(R 7 ), where R 4 , R 5 , R 6 and R 7 are each as defined above q and p are each independently 1 to 50, and

m is from 1 to 20.

20 . A process as claimed in claim 1 , in which the microwave irradiation is performed at temperatures between 150 and 500° C.

21 . A process as claimed in claim 1 , wherein the microwave irradiation is performed at pressures above atmospheric pressure.

22 . A process as claimed in claim 1 , wherein R 1 or R 2 or both are independently an aliphatic radical having 1 to 24 carbon atoms.

23 . A process as claimed in claim 18 , wherein R 10 and R 11 are each independently an aliphatic radical having 2 to 18 carbon atoms.

23 . A process as claimed in claim 19 , wherein m is from 2 to 10.