Continuous Method For Producing Amides Of Low Aliphatic Carboxylic Acids
The invention relates to a continuous method for producing amides, according to which at least one carboxylic acid of formula (I) R 3 —COON (I) wherein R 3 is hydrogen or an optionally substituted alkyl group comprising between 1 and 4 carbon atoms, is reacted with at least one amine of formula (II) HNR 1 R 2 (II) wherein R 1 and R 2 are independently hydrogen or a hydrocarbon group comprising between 1 and 100 C atoms, to form an ammonium salt, and said ammonium salt is then reacted to form a carboxylic acid amide, under microwave irradiation in a reaction pipe, the longitudinal axis of the pipe being oriented in the direction of propagation of the microwaves of a monomode microwave applicator.
1 . A continuous process for preparing an amide comprising the steps of reacting at least one carboxylic acid of the formula I
R 3 —COON (I)
wherein R 3 is hydrogen or a substituted or unsubstituted alkyl group having 1 to 4 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 fatty acid amide 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 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 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 is an alkyl group which has 1 to 4 carbon atoms and least one substituent selected from the group consisting of C 1 -C 5 -alkoxy, ester, amide, carboxyl, cyano, nitrile, nitro and C 5 -C 20 -aryl groups.
9 . A process as claimed in claim 8 , where the C 5 -C 20 -aryl groups have substituents 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, carboxyl, cyano, nitrile and nitro groups.
10 . 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.
11 . 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.
12 . A process as claimed in claim 1 , wherein R 1 or R 2 or both have substituents selected from the group consisting of hydroxyl, C 1 -C 5 -alkoxy, cyano, nitrile, nitro and C 5 -C 20 -aryl groups.
13 . A process as claimed in claim 1 , wherein R 1 or R 2 or both have C 5 -C 20 -aryl groups, and the C 5 -C 20 -aryl groups have at least one substituent selected from the group consisting of halogen atoms, C 1 -C 20 -alkyl, C 2 -C 20 -alkenyl, hydroxyl, C 1 -C 5 -alkoxy, alkoxyalkyl, ester, amide, cyano, nitrile and nitro-substituted phenyl radicals.
14 . 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.
15 . 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 hydrogen or 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 hydrogen, 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.
16 . 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 and q and p are each independently 1 to 50, and
m is from 1 to 20.
17 . A process as claimed in claim 1 , wherein the microwave irradiation is performed at temperatures between 150 and 500° C.
18 . A process as claimed in claim 1 , wherein the microwave irradiation is performed at pressures above atmospheric pressure.
19 . A process as claimed in claim 1 , wherein R 1 or R 2 or both substituents are independently an aliphatic radical having 1 to 24 carbon atoms.
20 . A process as claimed in claim 15 , wherein R 10 and R 11 are each independently an aliphatic radical having 2 to 18 carbon atoms.
21 . A process as claimed in claim 16 , wherein m is from 2 to 10.