Continuous Method For Producing Amides Of Aromatic Carboxylic Acids
The invention relates to a continuous method for producing amides of aromatic carboxylic acids by reacting at least one carbonic acid ester of formula (I) R 3 —OOOR 4 , wherein R 3 represents an optionally substituted aromatic hydrocarbon group with 5 to 100 carbon atoms and R 4 represents a hydrocarbon group with 1 to 30 carbon atoms, with at least one amine of formula (II) HNR 1 R 2 , wherein R 1 and R 2 independently represent hydrogen or a hydrocarbon group with 1 to 100 C atoms, in a reaction tube the longitudinal axis of which extends in the direction of propagation of the microwaves of a monomode microwave applicator, under microwave irradiation to form carboxamide.
1 . A continuous process for preparing an amide of an aromatic carboxylic acid, in which at least one carboxylic ester of the formula (I)
R 3 —COOR 4 (I)
in which
R 3 is an optionally substituted aromatic hydrocarbyl radical having 5 to 100 carbon atoms and
R 4 is an optionally substituted hydrocarbyl radical having 1 to 30 carbon atoms is reacted with at least one amine of the formula (II)
HNR 1 R 2 (II)
in which R 1 and R 2 are each independently hydrogen or an optionally substituted hydrocarbyl radical having 1 to 100 carbon atoms, and where R 1 and R 2 together with the nitrogen atom to which they are bonded may form a ring,
under microwave irradiation of the reaction mixture in a substantially microwave-transparent reaction tube within a hollow conductor which is connected via wave-guides to a microwave generator and whose longitudinal axis is in the direction of propagation of the microwaves of a monomode microwave applicator to give the carboxamide.
2 . A process as claimed in claim 1 , in which the microwave applicator is configured as a cavity resonator.
3 . A process as claimed in claim 1 , in which the microwave applicator is configured as a cavity resonator of the reflection type.
4 . A process as claimed in claim 1 , in which the reaction tube is aligned axially with a central axis of symmetry of the hollow conductor.
5 . A process as claimed in claim 2 , in which the reaction mixture is irradiated in a cavity resonator with a coaxial transition of the microwaves.
6 . A process as claimed in claim 2 , in which the cavity resonator is operated in E 01n mode where n is an integer from 1 to 200.
7 . A process as claimed in claim 2 , in which a standing wave forms in the cavity resonator.
8 . A process as claimed in claim 1 , in which the reaction mixture is heated by the microwave irradiation to temperatures between 120 and 500° C.
9 . A process as claimed in claim 1 , in which the microwave irradiation is effected at pressures above atmospheric pressure.
10 . A process as claimed in claim 1 , in which R 3 is an optionally substituted cyclic through-conjugated system having (4n+2) π electrons where n is 1, 2, 3, 4 or 5.
11 . A process as claimed in claim 1 , in which R 3 bears at least one further ester group —COOR 4 in which R 4 is an optionally substituted hydrocarbyl radical having 1 to 30 carbon atoms.
12 . A process as claimed in claim 1 , in which R 4 comprises 2 to 24 carbon atoms.
13 . A process as claimed in claim 1 , in which R 4 has at least one further hydroxyl group.
14 . A process as claimed in claim 1 , in which the compound of the formula (I) is an ester of an aromatic carboxylic acid with a monoalcohol having 1 to 4 carbon atoms.
15 . A The process as claimed in claim 1 , in which R 1 and/or R 2 are each independently optionally substituted aliphatic radicals having 2 to 24 carbon atoms.
16 . A process as claimed in claim 1 , in which R 1 and R 2 together with the nitrogen atom to which they are bonded form a ring having 4 or more ring members.
17 . A process as claimed in claim 1 , in which R 1 and/or R 2 are each independently an optionally substituted C 6 -C 12 -aryl group or an optionally substituted heteroaromatic group having 5 to 12 ring members.
18 . A process as claimed in claim 1 , in which R 1 and/or R 2 are each independently radicals of the formula (V)
—(R 7 O) n —R 8 (V)
in which
R 7 is an alkylene group having 2 to 6 carbon atoms or mixtures thereof,
R 8 is hydrogen, a hydrocarbyl radical having 1 to 24 carbon atoms or a group of the formula —R 7 —NR 11 R 12 ,
n is a number from 2 to 50, and
R 11 , R 12 are each independently an aliphatic radical having 1 to 24 carbon atoms, an aryl 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 11 and R 12 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 , in which R 1 and/or R 2 are each independently radicals of the formula (VI)
—[R 9 —N(R 10 )] m —(R 10 ) (VI)
in which
R 9 is an alkylene group having 2 to 6 carbon atoms or mixtures thereof,
each R 10 is independently hydrogen, an alkyl or hydroxyalkyl radical having up to 24 carbon atoms, a polyoxyalkylene radical —(R 7 —O)—R 8 or a polyiminoalkylene radical —[R 9 —N(R 10 )] q —(R 10 ),
R 7 is an alkylene group having 2 to 6 carbon atoms or mixtures thereof,
R 8 is hydrogen, a hydrocarbyl radical having 1 to 24 carbon atoms or a group of the formula —R 7 —NR 11 R 12 ,
R 11 , R 12 are each independently an aliphatic radical having 1 to 24 carbon atoms, an aryl 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 11 and R 12 together with the nitrogen atom to which they are bonded form a ring having 4, 5, 6 or more ring members, and q and p are each independently from 1 to 50 and
m is a number from 1 to 20.
20 . A process as claimed in claim 1 , in which the amine of the formula (II) is a primary amine.
21 . A process as claimed in claim 1 , in which the amine of the formula (II) is a secondary amine.