Process for preparing nitriles and isonitriles by dehydration reactions with propanephosphonic anhydrides
The invention concerns a method for producing: a) nitriles of formula (II) and b) isonitriles of formula (III) by reacting: a) carboxylic acid amides (RCO—NH2), ammonium salts of carboxylic acids (RCOO—NH4+) or carboxylic acids in the presence of ammonia or ammonium salts (RCOOH+NH3, RCOOH+NH4+) or b) formamides (H—CO—NHR) or mixtures of amines with formic acid, with cyclic phosphonic acid anhydrides while eliminating water at a temperature ranging from −30 to +120° C., in which R represents an arbitrarily substituted linear or branched C 1 -C 8 alkyl radical, a C 3 -C 10 cycloalkyl radical, alkenyl radical, alkynyl radical or an aryl radical or heteroaryl radical. As a cyclic phosphonic acid anhydride, a 2,4,6,-substituted 1,3,5,2,4,6 -trioxatriphosphinane-2,4,6-trioxide of formula (I) is advantageously used, in which: x=3, 4 or 5; R′, independent of one another, represents open-chain or branched, saturated or unsaturated, straight-chain C 1 to C 16 alkyl radicals or cyclic C 3 to C 16 alkyl radicals or aryl or heteroaryl.
1 . A process for preparing a) nitrites of the formula (II) and
b) isonitriles of the formula (III)
R—C≡N (II)
R—N≡C (III)
said process comprising reacting
a) carboxamides (RCO—NH2), ammonium salts of carboxylic acids (RCOO—NH4+) or carboxylic acids in the presence of ammonia or ammonium salts (RCOOH+NH3, RCOOH+NH4+) or
b) formamides (H—CO—NHR) or mixtures of amines with formic acid, with cyclic phosphonic anhydrides with elimination of water at a temperature in the range from −30 to +120° C.,
where R may have any substitution and is a linear or branched C 1 -C 8 -alkyl radical, a C 3 -C 10 -cycloalkyl, alkenyl, alkynyl or an aryl or heteroaryl radical.
2 . The process as claimed in claim 1 , wherein the cyclic phosphonic anhydride is a 2,4,6-substituted 1,3,5,2,4,6-trioxatriphosphinane 2,4,6-trioxide of the formula (I)
where x=3, 4 or 5 and
R′ are each independently open-chain or branched, saturated or unsaturated, straight-chain C 1 to C 16 -alkyl radicals or cyclic C 3 to C 16 -alkyl radicals, or aryl or heteroaryl.
3 . The process as claimed in claim 2 , wherein R′ is a methyl, ethyl, n-propyl, isopropyl, n-butyl, 2-butyl, isobutyl, pentyl, and/or hexyl, radical.
4 . The process as claimed in claim 2 , wherein the cyclic phosphonic anhydride is propanephosphonic anhydride.
5 . The process as claimed in claim 1 , wherein the cyclic phosphonic anhydride is either a melt or dissolved in a solvent.
6 . The process as claimed in claim 5 , wherein the cyclic phosphonic anhydride is in an aprotic solvent.
7 . The process as claimed in claim 1 , wherein said process further comprises
(i) forming a reaction solution comprising carboxamides; ammonium salts of carboxylic acids; carboxylic acids in the presence of ammonia or ammonium salts; formamide; or mixtures of amines with formic acid;
(ii) adding cyclic phosphonic anhydride to the reaction solution; and
(iii) heating the reaction solution to reaction temperature,
wherein the reaction solution is heated to the reaction temperature after addition of the phosphonic anhydride.
8 . The process as claimed in claim 1 , wherein nitriles are prepared and an ammonium salt together with a carboxylic acid (R—COOH) is reacted with the phosphonic anhydride in the presence of a base.
9 . The process as claimed in claim 8 , wherein the base is triethylamine, tripropylamine, benzyldimethylamine, N,N-dimethylaniline or pyridine.
10 . The process as claimed in claim 2 , wherein R′ is an ethyl, propyl, and/or butyl radical.
11 . The process as claimed in claim 6 , wherein the cyclic phosphonic anhydride and aprotic solvent are in a ratio of from 1:1 to 1:2.