Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic halides
Reexamination Certificate
2002-03-12
2004-04-27
Killos, Paul J. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic halides
C562S866000
Reexamination Certificate
active
06727384
ABSTRACT:
The present invention relates to a process for the purification of carbonyl chlorides which originate from the reaction of the corresponding carboxylic acids with phosgene or thionyl chloride, which leads to carbonyl chlorides with an improved 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 purification of carbonyl chlorides which for the most part originate from the reaction of carboxylic acids with phosgene or thionyl chloride, which no longer has the known disadvantages and leads to carbonyl chlorides having an improved color number.
Surprisingly, we have found that this object is achieved by the development of a process for the purification of carbonyl chlorides which have been prepared by reacting carboxylic acids with phosgene or thionyl chloride in the presence of a catalyst adduct, which comprises treating the carbonyl chlorides with a hydrohalide of carboxamides of the formula (I)
in which R
1
is hydrogen or a C
1
- to C
3
-alkyl; R
2
and R
3
independently of one another are C
1
- to C
4
-alkyl, or R
2
and R
3
together are a C
4
- or C
5
-alkylene chain, and isolating the carbonyl chloride purified in this way by separation from the carboxamide hydrohalide phase.
Contaminated carbonyl chlorides which originate from the reaction of carboxylic acids with phosgene or thionyl chloride can be worked up by extraction in high yield and with improved color number by the process according to the invention. The term “improved color number” is, in the case of the first treatment of the crude solutions, a reduction in the APHA color number to less than 50% of the original value for saturated carbonyl chlorides, and a reduction in the iodine color number to less than 75% of the original value for unsaturated carbonyl chlorides. The determinations of the APHA color number and of the iodine color number are described in the standard DIN EN 1557 (March 1997).
The treatment of the crude carbonyl chloride solution can be both spatially and also temporally separate from the synthesis of the crude solution. The treatment with a hydrohalide of carboxamides of the formula (I) can thus also be carried out in a different apparatus from the synthesis of the carbonyl chloride. Although synthesis and treatment of the crude carbonyl chloride solution can take place directly following one another in terms of time, it is also possible that they are temporally separated by hours, days, months or years, meaning that interim storage or transportation of the crude solution is also included.
For treatment of the crude carbonyl chloride solution by the process according to the invention, the solution is a
Busch Ralph
Henkelmann Jochem
Kneuper Heinz-Josef
Müller Winfried
Stamm Armin
BASF - Aktiengesellschaft
Keil & Weinkauf
Killos Paul J.
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