Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic halides
Reexamination Certificate
2001-04-25
2002-08-13
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic halides
Reexamination Certificate
active
06433224
ABSTRACT:
The present invention relates to a process for the preparation of carbonyl chlorides from carboxylic acids, carboxylic anhydrides, cyclic carboxylic esters (lactones) or sulfonic acids.
Carbonyl chlorides are important reactive intermediates in the preparation of fibers, films and in pharmaceutical chemistry and agrochemistry. Thus, a number of preparation processes for the synthesis of carbonyl chlorides from carboxylic acids or carboxylic anhydrides is known. In the industrial preparation, it is possible to differentiate between three methods for the preparation of carbonyl chlorides:
1. the chlorination of carboxylic acids or carboxylic anhydrides with phosphorus trichloride,
2. the chlorination of carboxylic acids or carboxylic anhydrides with thionyl chloride,
3. the chlorination of carboxylic acids or carboxylic anhydrides with phosgene.
The chlorination with phosgene is advantageous as compared with the other processes since only gaseous by-products form, which can be removed easily by expulsion with, for example, nitrogen. In contrast to thionyl chloride, toxic SO
2
is not formed, but rather nontoxic CO
2
. Furthermore, phosgene is a low-cost chlorinating agent. The chlorination with phosgene is therefore a very economical route for the preparation of carbonyl chloride.
Since phosgene on its own is too unreactive at suitable reaction temperatures and pressures, the use of a catalyst is necessary.
The literature describes a number of processes in which N,N-disubstituted formamides or their hydrochlorides are used as phosgenation catalysts. These react with phosgene to give so-called Vilsmeier salts. The Vilsmeier salt, the actual reactive chlorinating reagent, reacts with a carboxylic acid or a carboxylic anhydride to give the acid chloride. In the reaction, formamide hydrochloride is reformed, which in turn can react with phosgene to give the Vilsmeier salt, and passes through further catalyst cycles. The N,N-disubstituted formamide hydrochlorides or their Vilsmeier salts are, however, not entirely thermally stable, meaning that temperatures above from 80 to 90° C. can lead to secondary reactions.
EP-A 0 213 976 describes the use of hexaalkylguanidinium salts as catalysts. These need only be added to the reaction mixture in small amounts to achieve adequate selectivity. A disadvantage of this class of compound is, however, its complex preparation.
U.S. Pat. No. 3,547,960 discloses the use of certain catalysts which have C—N or N—N double bonds. Inter alia, cyclic amidines are disclosed as catalysts. Preferred catalysts are imidazoles or hydrochloride salts thereof and triazoles.
It is an object of the present invention to provide catalysts for the reaction of carboxylic acids, carboxylic anhydrides, cyclic carboxylic esters (lactones) or sulfonic acids with phosgene to give carbonyl chlorides which can be prepared more readily than known catalysts and can be used for a large number of compounds. Furthermore, the catalysts should permit shorter reaction times than the catalysts known hitherto and very good conversions.
We have found that this object is achieved by a process for the preparation of acid chlorides by reaction of carboxylic acids, carboxylic anhydrides, cyclic carboxylic esters(lactones) or sulfonic acids with phosgene in the presence of a catalytic amount of a compound from the group consisting of N,N,N′,N′-tetrasubstituted amidinium halides (I), N,N,N′-trisubstituted amidinium hydrohalides (II) and N,N,N′-trisubstituted amidines (III) of the formula
in which R
1
, R
2
and R
4
are linear or branched alkyl chains having a length of from 1 to 20 carbon atoms or cycloaliphatic radicals having a ring size of from 5 to 8 carbon atoms, where the rings can be interrupted by heteroatoms, or R
1
and R
2
are unsubstituted or substituted aromatic radicals or together form a chain of four or five methylene groups;
R
3
is a hydrogen atom or a branched or unbranched alkyl radical or a cycloalkyl radical having a length of from 1 to 6 carbon atoms; and
R5 in compound I is a branched or unbranched C
1
to C
6
-alkyl chain, and X
−
is a halide.
Thus, R
1
, R
2
and R
4
, and also R
5
, can, for example, independently of one another be alkyl radicals such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl or linear or branched pentyl radicals. The radicals R
1
, R
2
and R
4
can also be cycloalkyl radicals, such as cyclopentyl and cyclohexyl radicals, and R
1
and R
2
can be aromatic radicals, substituted or unsubstituted, such as phenyl and tolyl radicals.
R
3
can, for example, be the same alkyl radicals as listed for R
1
, R
2
, R
4
and R
5
. Preferably, however, R
3
is hydrogen. X
−
is preferably bromide or chloride, very particularly preferably chloride.
Particularly preferably, the radicals R
1
, R
2
, R
4
and R
5
are methyl or ethyl radicals, and R
3
is hydrogen. Particular preference is given to N,N,N′-trimethy-formamidine (R
1
=R
2
=R
4
=methyl, R
3
=H), N,N,N′-trimethylformamidine hydrochloride (R
1
=R
2
=R
4
=methyl, R
3
=H),N,N,N′,N′tetramethylformamidinium chloride (R
1
=R
2
=R
4
=R
5
=methyl, R
3
=H) and N,N-diethyl-N′,N′-dimethylformamidinium hydrochloride (R
1
=R
2
=methyl, R
4
=R
5
=ethyl, R
3
=H).
The catalysts used in the process according to the invention are also obtainable on a larger scale by simple reaction. They permit reaction in very good yields and short reaction times.
The N,N,N′,N′-tetrasubstituted formamidinium salts (I) (R
3
=H) are obtainable via a single-stage reaction from formamides with N,N-disubstituted dialkylcarbamoyl halides. A synthesis of the compounds is described in Coll. Czech. Chem. Comm. 24 (1959), 760 to 765. N,N,N′-Trisubstituted amidinium hydrohalides (II) can be prepared by reaction of N-monosubstituted amides with N,N-dialkylcarbamoyl halides in a single-stage synthesis in accordance with Kantlehner et al., Synthesis 1983. The free amidines (III) can be liberated by neutralization of the resulting amidine hydrohalides using an inorganic base.
Since the preparation of the free amidines (III) requires an additional reaction step, namely the neutralization of the hydrohalides (II), in the process according to the invention preference is given to using the amidinium hydrohalides of the formula II.
In a further preferred embodiment, N,N,N′,N′-tetrasubstituted amidinium halides (I), particularly preferably formamidinium halides, are used, which are likewise obtainable via a single-stage reaction, as already described.
The catalytic action of the amidinium salts I and II in the process according to the invention is surprising since they have hitherto been considered to be reaction-inhibiting. For example, U.S. Pat. No. 3,547,960 states that a disadvantage of processes in which carboxamides are used as catalysts is that tarry, catalytically inactive products are formed during this reaction as a result of the decomposition of the carboxamide catalysts. From the literature, however, it is known that formamidinium halides form as decomposition product of the carboxamide DMF (dimethylformamide).
The reactions in which amidines, amidinium hydrohalides and amidinium halides are used are more successful the more substituents the two nitrogen atoms have. The reaction does not proceed to completion if substituents are not present (Comparative Examples 5 and 6). With two substituents on the nitrogen atoms, the reaction proceeds slowly and relatively large amounts of the carboxylic anhydride are formed (Comparative Example 7).
The carboxylic acids which can be used in the process according to the invention are not restricted. In general, use is made of aliphatic carboxylic acids having from 2 to 22 carbon atoms or mixtures of C
8
-C
22
carboxylic acids, the radicals of which can be branched or linear, saturated or unsaturated and optionally substituted by, for example, halog
Henkelmann Jochem
Stamm Armin
BASF - Aktiengesellschaft
Keil & Weinkauf
Killos Paul J.
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