CH681722A5 - - Google Patents

Description

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CH 681 722 A5

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description

The present invention relates to an improved process for the preparation of 4-chlorobenzenesulfinic acid sodium salt, in which a particularly pure product is obtained in good yield.

For example, 4-chlorophenyl alkyl sulfones can be prepared from 4-chlorobenzenesulfinic acid sodium salt, which are valuable intermediates for the preparation of and dyes (see DE-OS 3 302 647).

It is known to produce 4-chlorobenzenesulfinic acid sodium salt by adding 4-chlorobenzenesulfochloride to an aqueous sodium sulfite solution over a period of several hours at 65 to 70 ° C. and at the same time adding sodium hydroxide solution in order to keep the reaction medium alkaline (FIAT Final Report 949, pp. 23 to 24). In another process, 4-chlorobenzene sulphochloride and sodium hydroxide solution are simultaneously added to a mixture of sodium bisulfite, sodium hydroxide solution, phosphoric acid and water over the course of 2 hours at 60 ° C. (DE-OS 3 302 647, Example 17).

A disadvantage of these processes is that the 4-chlorobenzenesulfinic acid sodium salt produced in this way is obtained in a yield of approximately 80% and always contains 4 to 6% by weight of the 4-chlorobenzenesulfonic acid sodium salt which is formed in a side reaction by hydrolysis of 4-chlorobenzenesulfonyl chloride .

The content of 4-chlorobenzenesulfonic acid sodium salt is undesirable because on the one hand it reduces the yield of 4-chlorobenzenesulfinic acid sodium salt and on the other hand it accumulates in the waste water during the further processing of 4-chlorobenzenesulfinic acid sodium salt. The wastewater is contaminated with COD (chemical oxygen demand) and AOX (adsorbable organically bound halogen) which are difficult to degrade.

A process has now been found for the preparation of 4-chlorobenzenesulfinic acid sodium salt from 4-chlorobenzenesulfonic acid chloride and alkali sulfite, which is characterized in that 4-chlorobenzenesulfonic acid chloride is introduced into an aqueous alkali sulfite solution which has a temperature of 0 to 30 ° C. and a pH 6 to 10, then sodium hydroxide solution is metered in such a way that during at least 80% of the reaction there is a pH in the range from 4 to 8 and the temperature is 10 to 40 ° C., then the pH to 10 to 12 and the temperature is increased to 50 to 95 ° C., then between 25 and 100% by volume of water (based on the reaction mixture) is added, the solid constituents of the mixture are filtered off at 70 to 95 ° C. and finally the 4-chlorobenzenesulfinic acid Sodium salt precipitates by adding sodium chloride and cooling to a temperature below 45 ° C and isolated.

The 4-chlorobenzenesulfonic acid chloride required for the process according to the invention can be prepared in any known manner (see, for example, FIAT Final Report No. 949, page 23). It can be used in the process according to the invention in pure, distilled form, but also as a water-moist material with e.g. 20 to 40 wt .-% water content can be used.

Examples of suitable aqueous alkali sulfite solutions are 15 to 40% by weight solutions of an alkali sulfite or alkali hydrogen sulfite. Solutions of sodium sulfite or sodium hydrogen sulfite are preferred. For example, 3 to 10 parts by weight of the alkali sulfite solution can be used per part by weight of 4-chlorobenzenesulfonic acid chloride. In order to set a pH in the range from 6 to 10, it may be necessary to add an alkali (e.g. sodium hydroxide solution) or an acid (e.g. hydrochloric acid). When using hydrogen sulfites, alkali additives are generally required. The alkali sulfite solution preferably has a temperature of 10 to 20 ° C. and a pH of 7 to 9 before the addition of 4-chlorobenzenesulfonic acid chloride.

It is an essential feature of the present invention that metering in of the sodium hydroxide solution does not begin until the addition of 4-chlorobenzenesulfonic acid chloride has ended. Preferably, all of the 4-chlorobenzenesulfonic acid chloride required for one batch is added at once.

The sodium hydroxide solution can, for example, have a concentration of 30 to 60% by weight. Sodium hydroxide solution with a concentration of 45 to 50% by weight is preferred. The sodium hydroxide solution is preferably metered in such that the pH is in the range from 4 to 8, preferably 5 to 7, during at least 90% of the reaction (ie until 90% by weight of the 4-chlorobenzenesulfonic acid chloride used has reacted) . To keep the temperature in the range of 10 to 40 ° C, cooling is generally required. The temperature is preferably maintained at 25 to 35 ° C.

After at least 80%, preferably after at least 90% of the reaction, the sodium hydroxide solution is metered in so that a pH of 10 to 12, preferably 10.5 to 11.5 is obtained and the reaction mixture is heated to 50 to 95 ° C. preferably first to 40 to 60 ° C and after the addition of water, preferably from 30 to 80 vol .-% water (based on the reaction mixture) to 70 to 90 ° C.

Then solid constituents present, e.g. in the production of 4-chlorobenzenesulfonic acid chloride, 4,4'-dichlorodiphenylsulfone formed as a by-product, at 70 to 95 ° C. and the 4-chlorobenzenesulfinic acid sodium salt formed precipitates out by adding sodium chloride, preferably in the form of rock salt, and cooling a temperature below 45 ° C, preferably to a temperature in the range 30 to 40 ° C. Based on 1 part by weight of 4-chlorobenzenesulfonic acid chloride used, 0.8 to 1.2 parts by weight of sodium chloride can be used, for example.

The isolation of the 4-chlorobenzenesulfinic acid sodium salt thus prepared can e.g. by filtration and, if necessary, subsequent drying.

4-Chlorobenzenesulfinic acid sodium salt prepared in accordance with the invention generally contains less than 0.5% by weight of 4-chlorobenzenesulfonic acid and is generally obtained in a yield of well over 85%. According to the invention

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a purer 4-chlorobenzenesulfinic acid sodium salt is thus obtained in a higher yield than in the processes of the prior art.

This is extremely surprising, because, according to the invention, the reaction of 4-chlorobenzenesulfonic acid chloride takes place under less controlled conditions (for example in terms of metering rate, temperature and pH) than in the prior art, where the acid chloride and the sodium hydroxide solution are controlled and added at the same time will. Otherwise, less controlled reaction conditions generally result in a less uniform product. Surprisingly, this is not the case here.

Examples

example 1

400 l of 50% strength by weight sodium hydroxide solution were added to a solution of 920 kg of sodium bisulfite in 3600 l of water, a pH of 8.5 being established. The mixture was then cooled to 12 ° C. and 4-chlorobenzenesulfonic acid chloride in water-moist form (water content 30% by weight, 1610 kg of 4-chlorobenzenesulfonic acid chloride 100%) was added all at once. Thereafter, 650 l of 50% strength by weight sodium hydroxide solution were run in such that the temperature could be kept in the range from 25 to 35 ° C. by cooling. The pH was initially 5 and gradually increased to 7. A pH of 11.5 was then set with sodium hydroxide solution and the mixture was stirred at 30 to 35 ° C. for 30 minutes. The mixture was then heated to 50 ° C. and stirred for a further 30 minutes. During the subsequent stirring, the pH was kept in the range from 11 to 11.5 by adding a further 300 l of 50% strength by weight sodium hydroxide solution. Finally, enough water was added until the entire reaction mixture had a volume of 11,000 liters, heated to 80 ° C. and filtered. Finally, 1500 kg of rock salt were added, the mixture was cooled to 35 ° C. and 4-chlorobenzenesulfinic acid sodium salt was isolated by filtration. The 4-chlorobenzenesulfinic acid sodium salt was obtained in a yield of 88% and with a 4-chlorobenzenesulfonic acid content of 0.3% by weight in the form of a water-moist filter cake (water content 40% by weight).

Example 2

(Comparative example)

In a sodium sulfite solution, which had been prepared as described in Example 1, 1610 kg of 4-chlorobenzenesulfonic acid chloride in water-moist form (water content 30% by weight) and at the same time 1250 I 50% by weight were added at 65 ° C. in the course of 4 hours. Sodium hydroxide solution entered, the pH was continuously about 11.5. The mixture was stirred for a further 30 minutes and then worked up as described in Example 1.

4-Chlorobenzenesulfinic acid sodium salt was obtained in a yield of 82% and with a 4-chlorobenzenesulfonic acid content of 4.5% by weight.

Claims (2)

Claims 1. A process for the preparation of 4-chlorobenzenesulfinic acid sodium salt from 4-chlorobenzenesulfonic acid chloride and alkali sulfite, characterized in that 4-chlorobenzenesulfonic acid chloride is introduced into an aqueous alkali sulfite solution which has a temperature of 0 to 30 ° C. and a pH Has a value of 6 to 10, then sodium hydroxide solution is metered in such a way that during at least 80% of the reaction there is a pH in the range from 4 to 8 and the temperature is 10 to 40 ° C., then the pH to 10 to 12 and increasing the temperature to 50 to 95 ° C, then adding between 25 and 100 vol .-% water, based on the reaction mixture, filtering off the solid constituents of the mixture present at 70 to 95 ° C and finally the 4-chlorobenzenesulfinic acid sodium salt by adding sodium chloride and cooling to a temperature below 45 ° C and isolated. 2. The method according to claim 1, characterized in that the entire 4-chlorobenzenesulfonyl chloride required for one batch is added at once. 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65