Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2003-05-08
2004-11-23
Desai, Rita (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C562S056000
Reexamination Certificate
active
06822113
ABSTRACT:
The invention relates to a process for preparing acyloxybenzenesulfonates starting from carboxylic acid derivatives and low water content salts of a phenolsulfonic acid.
Acyloxybenzenesulfoninc acids and their salts are long-established compounds. Depending on the chain length of the acyl group they may find use as surfactants, as bleach activators, or in other applications.
DE 666 626 describes their surfactant properties and their general use in laundry detergents, while compounds having from 6 to 12 carbon atoms in the alkyl chain, in combination with persalts, are claimed as bleaches by EP 98 129, EP 105 672, EP 105 673 and EP 125 641.
For the preparation of acyloxybenzenesulfonic acids and their salts a multiplicity of methods have been described. They can be obtained by heating a mixture of trifluoroacetic anhydride, sodium phenolsulfonate (SPS), and a (C
6
-C
19
) alkane-carboxylic acid. According to U.S. Pat. No. 4,587,054 this reaction can also be carried out in two stages: first, the alkanecarboxylic acid is converted into the anhydride in the presence of an excess of acetic anhydride, and then the isolated anhydride is reacted with dry phenolsulfonate. This reaction takes place at temperatures from 180 to 220° C. under base catalysis. The acid catalyzed reaction of a relatively long-chain alkanoic anhydride with SPS in an aprotic solvent is claimed in U.S. Pat. No. 4,588,532; the acid catalysis (toluenesulfonic acid and related compounds) allows a reaction regime at just 120° C.
Also known from the literature is the transesterification of (C
2
-C
3
)acyloxy-benzenesulfonate with a (C
6
-C
8
)alkanecarboxylic acid accompanied by removal of the short-chain alkanecarboxylic acid formed. It is also possible to react alkali metal or alkaline earth metal phenolsulfonates with a C
2
-C
31
-alkanephenyl ester at from 200 to 350° C.
A further preparation variant is the reaction of aliphatic or aromatic carbonyl halides with salts of phenolsulfonic acid. The reaction can be carried out under Schotten-Baumann conditions in an aqueous system (U.S. Pat. No. 5,523,434), but in that case leads only to moderate conversions. More advantageous is the reaction of anhydrous salts of phenolsulfonic acids in water-free media. Organic solvents such as methylene chloride (U.S. Pat. No. 3,503,888), high-boiling hydrocarbons (EP 220 826), xylene or toluene (EP 164 786), and trifluoroacetic acid (WO 01/19 771) serve as the reaction medium. According to U.S. Pat. No. 5,069,828 this reaction is conducted in an aprotic organic solvent in the presence of a phase transfer catalyst. According to U.S. patent application Ser. No. 20 020 058 824 this reaction can also be conducted solventlessly if an excess of acid chloride is employed.
With all of the known industrially useful processes the problem arises that it is necessary to use virtually anhydrous SPS for the reaction since otherwise the carboxylic acid derivative (halide or anhydride) and the finished ester undergo hydrolysis in the presence of traces of water, leading to considerable losses of yield. Virtually anhydrous means, in this case, water contents <0.5% by weight, preferably <0.2% by weight.
SPS is available commercially as the dihydrate, with a water fraction of approximately 15% by weight. By conventional drying the water content can be lowered to about 2% by weight. According to U.S. Pat. No. 5,069,828 it is possible to remove the residual water by azeotropic distillation in the presence of an azeotrope former such as xylene. Because of the massive amount of time required, however, this is not very rational on the industrial scale or in plants which operate continuously.
As is known from U.S. Pat. No. 4,666,636, the water content can be reduced to less than 0.5% by weight by means of special drying in corresponding apparatus. For this purpose, however, it is necessary to stick rigidly to defined drying conditions (170 to 200° C., inert gas, vacuum, fluidized bed drier, thorough mixing). If these conditions are not observed precisely, SPS enters into a number of secondary reactions, as a result of which the product is irreversibly damaged. The consequence of this is that both the degree of conversion in the following acylation and the color of the end product are significantly adversely affected. Incorrect drying, i.e., excessively long residence times or excessively high temperatures, lead to overdrying of the SPS, which in the acylation reaction leads to degrees of conversion of less than 50%. Nor is it possible to improve this by using the acylating component in a superstoichiometric amount. In the industrial operation of SPS drying, however, these specific physical parameters are difficult to observe precisely. It would be useful to find ways of suppressing the disruptive secondary reactions during drying, in order to free the quality of the SPS product from its dependency on drying time, drying temperature, and other physical parameters.
It is an object of the present invention, therefore, to develop a process which can be carried out both industrially and continuously and which allows optimal drying of the SPS, even outside of the reaction conditions specified in U.S. Pat. No. 4,666,636, without tolerating loss of reactivity of the SPS in the downstream acylation stage. The process should at the same time be independent of the physical drying parameters of the sodium phenolsulfonate employed.
It has surprisingly now been found that starting from anhydrous SPS it is possible to prepare acyloxybenzenesulfonates, irrespective of the thermal pretreatment of the SPS employed, if the anhydrous SPS, after its preparation and isolation but before reaction with the carboxylic acid derivative, is contacted with at least one substance having basic properties. Irrespective of physical drying parameters, this SPS then reacts with acylating agents in excellent yields to give acyloxybenzenesulfonates of outstanding quality.
The invention provides a process for preparing acyloxybenzenesulfonates by reacting anhydrous phenolsulfonates with carboxylic acid derivatives, which comprises contacting the salt of a phenolsulfonic acid, after its isolation but before the acylation, with at least one substance having basic properties.
The phenolsulfonate starting compounds used are preferably compounds of the formula
where X is hydrogen, halogen or C
1
-C
4
-alkyl and M is an alkali metal or alkaline earth metal ion. Preference is given to sodium ortho- or para-phenolsulfonates, especially sodium para-phenolsulfonate (SPS), which as a result of its preparation process may contain isomeric byproducts (up to 10%) or other impurities in small amounts.
SPS is prepared by sulfonating phenol and then neutralizing the product. Since Na p-phenolsulfonate is of low solubility in water, it can be isolated from the reaction medium by filtration, centrifugation or similar operations. The crude SPS is then washed and after isolation has a high purity and a water content of from 15 to 30%. For the reaction according to the invention with a carboxylic acid derivative it is necessary to dry the phenolsulfonate to a residual moisture content of <0.5%, preferably <0.2%, by weight. This operation can be carried out continuously or in stages via the dihydrate (water content approximately 15% by weight) and quarter-hydrate (water content approximately 2% by weight). Drying can take place in accordance with conventional methods which are known per se, in a disk drier or fluid-bed drier, for example, which allows drying to a residual moisture content of less than 0.1% by weight. In the course of drying it is advantageous to operate under a stream of inert gas. Drying can be operated under reduced pressure or with the same result under atmospheric pressure as well.
Depending on the equipment used the drying times can be between 1 min and 18 h, the temperatures between 80 and 250° C. For the process of the invention the thermal pretreatment of the dried SPS has no effect on the yield of the acylation reaction and it is possible on average to obtain conversions of
Lerch Alexander
Mueller Wolf-Dieter
Naumann Peter
Reinhardt Gerd
Sadanani Narayan D.
Clariant GmbH
Desai Rita
Shiao Robert
Silverman Richard P.
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