Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic halides
Reexamination Certificate
2002-03-12
2004-08-03
Killos, Paul J. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic halides
Reexamination Certificate
active
06770783
ABSTRACT:
The present invention relates to a process for the preparation of carbonyl chlorides by reacting the corresponding carboxylic acids with phosgene or thionyl chloride in the presence of a catalyst adduct with the simultaneous and/or subsequent introduction of hydrogen chloride, which leads to carbonyl chlorides which have a low color number.
Carbonyl chlorides are important intermediates in the synthesis of a large number of chemical products, in particular pharmaceuticals, cosmetics, surfactants and paper auxiliaries. They can be prepared by reacting carboxylic acids with chlorinating agents, such as PCl
3
, POCl
3
, SOCl
2
, SO
2
Cl
2
or COCl
2
. Of industrial importance are, in particular, the reactions with thionyl chloride, phosphorus trichloride and phosgene.
As a rule, in the synthesis via phosphorus trichloride, one reactant (carboxylic acid or phosphorus trichloride) is initially introduced, and the other reactant (phosphorus trichloride or carboxylic acid) is slowly added. Where appropriate, the synthesis is carried out in a solution diluted with a reaction-inert solvent (e.g. toluene). After removal of the phosphorous acid formed, the carbonyl chloride is as a rule purified by distillation. The addition of a catalyst is not required.
EP-A-0 296 404 describes the purification of crude carbonyl chlorides which originate from the chlorination using phosphorus trichloride, in which the reaction products are treated with carboxamide hydrohalides. The crude carbonyl chloride solutions from the phosphorus trichloride route differ in composition from those obtainable by the phosgene or thionyl chloride route. For example, the latter have:
(i) a considerably higher content of undesired minor components.
(ii) a varying composition of the minor components, which is influenced by the choice of chlorinating agent.
(iii) supplementary to the varying composition of the minor components, also the presence of degradation and/or secondary products from the catalyst adducts used.
The use of phosgene or thionyl chloride instead of phosphorus trichloride generally leads to a higher conversion and better selectivity. Both chlorinating agents additionally have the advantage over phosphorus trichloride that only gaseous byproducts are formed, which either escape in the form of gas during the synthesis or can be completely expelled by stripping with an inert gas when the reaction is complete. Furthermore, phosgene, in particular, is a very good value chlorinating agent.
Thionyl chloride and, in particular, phosgene are less reactive as chlorinating agents compared with phosphorus trichloride. The preparation of carbonyl chlorides by reacting carboxylic acids with thionyl chloride is therefore preferably carried out in the presence of a catalyst to increase the reaction rate. In the preparation by reaction with phosgene, a catalyst is always used. Catalyst precursors which are suitable for both chlorinating agents are N,N-disubstituted formamides and hydrochlorides thereof, and also pyridine or urea. Overviews relating to the chlorination by means of thionyl chloride are given in M. F. Ansell in S. Patai, “The Chemistry of Acyl Halides”, John Wiley and Sons, New York 1972, 35-69 and H. H. Bosshard et al., Helv. Chem. Acta 62 (1959) 1653-1658 and S. S. Pizey, Synthetic Reagents, Vol. 1, John Wiley and Sons, New York 1974, ISBN 853120056, 321-557, in particular 333-335. Both by the phosgene route and also by the thionyl chloride route preference is given to using N,N-disubstituted formamides. These react with said chlorinating agents to give the Vilsmeier salts.
The Vilsmeier salt, the actual reactive chlorinating reagent, reacts with the carboxylic acid or the carboxylic anhydride to give the acid chloride. In the process, formamide-hydrochloride is reformed, which can in turn react with phosgene or thionyl chloride to give the Vilsmeier salt and passes through further catalyst circuits. The N,N-disubstituted formamide-hydrochlorides or vilsmeier salts thereof are not, however, very thermally stable, meaning that it is possible for secondary reactions to take place above 80 to 90° C.
The preferred use of N,N-disubstituted formamides as catalyst precursor for the phosgenation of carboxylic acids also emerges from EP-A-0 367 050, EP-A-0 452 806, DE-A-4 337 785, EP-A-0 475 137 and EP-A-0 635 473.
As regards the color number, in the chlorination of carboxylic acids using phosgene or thionyl chloride, the use of catalysts has an adverse effect. Although these catalysts are separated off by phase separation following the chlorination, they can, however, remain in the product in small amounts and lead either themselves or as degradation or secondary products to yellow colorations of the carbonyl chlorides. For this reason, the carbonyl chlorides prepared via phosgene or thionyl chloride are generally purified by distillation to give largely colorless products. Such a distillation is not only an energy- and time-consuming operation, but also harbors a number of further disadvantages. Many longer-chain carbonyl chlorides cannot be distilled without partial decomposition. Furthermore, it is known that the distilled products can become contaminated as a result of decomposition of the catalyst still present in the distillation bottoms. Relatively large amounts of accumulated catalyst residue also represent a safety risk during the distillation since at elevated temperature there is the risk of spontaneous decomposition.
A further method of purifying the crude carbonyl chlorides is the treatment with activated carbons. However, these absorptive purification steps are industrially complex and, moreover, are not always successful. In addition, a contaminated solid forms, which has to be subsequently disposed of in the correct manner.
It is an object of the invention to develop a process for the preparation of carbonyl chlorides by reacting the corresponding carboxylic acids with phosgene or thionyl chloride which no longer has the known disadvantages and leads to carbonyl chlorides which have a low color number.
We have found that this object is achieved by the development of a process for the preparation of carbonyl chlorides by reacting carboxylic acids with phosgene or thionyl chloride in the presence of a catalyst adduct of an N,N-disubstituted formamide of the formula (I)
in which R
1
and R
2
independently of one another are C
1
- to C
4
-alkyl, or R
1
and R
2
together are a C
4
- or C
5
-alkylene chain, and phosgene or thionyl chloride, which comprises introducing hydrogen chloride during and/or after the reaction.
By the process according to the invention, it is possible to prepare carbonyl chlorides by reacting the corresponding carboxylic acids with phosgene or thionyl chloride in high yield and with low color number. A low color number here means a color number which is at most 50% of the APHA color number, or in the case of unsaturated carbonyl chlorides, at most 75% of the iodine color number which is achieved using the process of the prior art, i.e. without the inventive measure. The determinations of the APHA color number and of the iodine color number are described in the standard DIN EN 1557 (March 1997).
The inventive introduction of the hydrogen chloride can be carried out in a variety of ways. For example, the hydrogen chloride can be introduced, with regard to the introduction of the chlorinating agent phosgene or thionyl chloride, exclusively during its addition, during and after its addition or exclusively after its addition. Preference is given to metering in the hydrogen chloride at the same time as the chlorinating agent is added. In the three variants mentioned, the hydrogen chloride can be introduced continuously, i.e. without interruption, or with one or more interruptions, to a pulse-like metered addition. In addition, the rate of addition of the hydrogen chloride within an addition interval can remain constant or can decrease or increase. Within the meaning of a constant working of the reaction, it is advantageous to introduce the hydrogen chloride continuously, where an
Busch Ralph
Henkelmann Jochem
Kneuper Heinz-Josef
Müller Winfried
Stamm Armin
BASF - Aktiengesellschaft
Keil & Weinkauf
Killos Paul J.
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