CS200427B1 - Process for the purification of-mercaptobenzothiazole - Google Patents

Description

(54) Purification of crude 2-mercaptobenzthiazole

The invention relates to a process for purifying 2-mercaptobenzthiazole. 2-Mercaptobenzthiazole (2-benzothlazolthiol) of the formula

SH is produced in a known manner, mainly by condensation of aniline with carbon disulfide and sulfur at higher temperatures and pressures (art. No. 122 789). Crude condensation product contains only 80-88% mercaptobenzthiazole · Crude 2-mercaptobenzthiazole contains rather unreacted sulfur (eca 7%) as major impurities and benzthiazole (ca. 2.5%), anilinobezthiazole and others besides 1.2% besides reaction by-products resin fractions (DOS 2,822,569). In this quality for use in the rubber industry or as a starting material for further syntheses, it is necessary to purify it,

The methods known to date for purifying crude 2-mercaptobenzthiazole have several directions. Leaving aside the technologically insignificant method of cryptalization from organic solvents (No. 122,790) and the technically demanding method by vacuum distillation (DOS 2,822,569), the crude 2-mercaptobenzthiazole is purified by precipitation and various separation of ballasts. Volatile fractions are separated by steam at 210 ° C (US Pat. 2 730 528), resin fractions and other neutral substances are separated by converting mercaptobenzthiazel to alka200 427

The insoluble matter is removed by filtration, preferably with simultaneous sorpoe, onto the appropriate substrate, or the insoluble matter is extracted from the aqueous solution of the alkali salt of 2-mercaptobenzothiazole by xylene or another solvent. It is also used in the opposite way that the crude 2-mercaptobenzthiazole is dissolved in xylene and 2-mercaptobenzthiazole is extracted from the sodium hydroxide aqueous solution as a sodium salt (DOS 1 941 379). with a pereulphate or another oxidizing agent. Free 2-mercaptobenzthiazole is obtained from acid-purified salt solutions by acid precipitation. In particular, the sodium and calcium salts of 2-mercaptobenzothiazole, to a lesser extent ammonium salts, are used for purification. Conversion to calcium clay has the advantage of easier dosing, since excess lime is not a reaction to the defect, on the contrary it absorbs oily insoluble fractions (ref. No. 102 400). However, due to the low solubility of the calcium salt of 2-mercaptobenzothiazole, it is necessary to prone in a large dilution (eca 2%), which is disadvantageous for capacity reasons. Also the ammonium salt has a low solubility. The sodium salt in which it is converted with an aqueous sodium hydroxide solution is preferable for higher solubility. Excess NaOH, especially at higher temperatures, partially cleaves the benzthlazole ring (DOS 1941 379) and other impurities pass into solution, which are then excreted after acidification together with 2-mercaptobenzthiazole. an excess of strong mineral acids.

It is clear from the overview that the purification of the crude 2-mercaptobensthiazole is quite complicated, laborious and always too effective. The process of purifying crude 2-mercaptobenzothiazole by the process of the invention is simpler and more efficient.

The essence of this is that 2-mercaptobenzthiazole is converted by boiling with a solution of sodium carbonate or sodium carbonate into sodium salt, releasing carbon dioxide. · Due to the milder alkallta (pH oa 12.3) compared to alkallzaol with sodium or calcium hydroxide, mercaptobenzthiazole undissolved under these conditions. The undissolved oily fraction from the sodium salt solution was removed by filtration with carborafine or other sorbent or by extraction with xylene or other non-polar organic solvent. Of the clear solution of the sodium salt precipitates after cooling a free 2-ylsulfanyl thiazol uviděním carbon dioxide to form sodium blkarbonátu / oca pH 8 / .Filtrací to give yellowish-2 merkaptobenzthlazol of mp 178-181 ⁰ C, according to analysis 96.1 99 6% in 96-98% yield.

In order to carry out the purification at a high concentration of 2-mercaptobenzthiazole and due to the relatively low solubility of the sodium salt of 2-mercaptobenzthiazole in view, the carbon dioxide feed should be counted at 50 ^° C and gradually reduced to 30 to 20 ^° C. 2-morcaptobenzthlasol was not contaminated with sodium salt. For more efficient uptake of the carbon dioxide in the sodium salt solution of 2-mercaptobenzothiazole, it is preferable to carry out the autoclaving of the carbon dioxide under pressure. Since the mother liquors still contain 2-4% of the solubilized 2-mercaptobenzothiazole resulted in a small amount of other soluble substances, it is economically suitable for further purification of the crude 2-mercaptobenzothiazole. Even after using the mother liquors ten times, the quality of purified 2-mercaptobenzthiazole did not deteriorate and the olan bllanol

200,427 achieved almost a qualitative yield. Also, from an economic point of view, this method of purification is advantageous since it does not consume any excipients. Carbon dioxide released from sodium carbonate or bicarbonate upon heating can be used to precipitate 2-mercaptebenzthiazole from a solution of its cooled salt. Instead of sodium carbonate or sodium bicarbonate, sodium hydroxide can also be used to dissolve the crude 2-mercaptobenzothiazole. In this case, the excess is converted to sodium carbonate by boiling carbon dioxide, eliminating impurities solubilized at higher alkalinity. The cleaning process according to the invention can also be used to squeeze inferior commercial products, since not only the remainder of the insoluble byproducts but also any calcium salts present are removed. The purification according to the invention can also be carried out as a continuous prooes, wherein the insoluble fractions are removed from the hot aqueous suspension by a suitable flow separator centrifuge or a suitable filter. To further reduce losses, the 2-mercaptobenzthiazole retained can be recovered from the filtered insolubles by repeated axtraction of the mother liquor at boiling. Liquidation of the mother liquors is carried out after its multiple rocyclalation by precipitation with a strong mineral acid to pH 3-4, whereby the precipitated 2-morcaptobenzothlazole can be purified in the same way as the crude product. The examples given show, but are not limited to, the scope of the invention.

Example 1

A 1000 ml flask equipped with a stirrer was charged with 450 ml of water, 18 g of anhydrous sodium carbonate and 50 g of crude 2-mercaptobenzothiazole (about 87%). The suspension is heated it reflux, After dissolving 2-mercaptobenzothiazole with 1.5 g karboraflnu and filtered warm, the filtrate of the initial temperature of 50 ⁰ C OOA was converted into the autoclave and allowed to operate it at the carbon dioxide at a pressure of 2-3 MPa for 1 hour. The precipitated pure 2-mercaptobenzthiazole (40.25 g), 96.7%, mp 178 ^° C, was filtered off and washed with pure water. The mother liquors, without the addition of further NagCO3, are used for other cycles of purification, which can be repeated many times without deteriorating the quality of the product obtained.

Example 2

Dissolution of the crude 2-mercaptobenzthiazole oo was carried out as in Example 1 except that 14.3 g of sodium bicarbonate was used instead of sodium carbonate. Separation of pure 2-mercaptobenzthiazole is then carried out in a similar manner to Example 1. A pale yellow product (40.25 g) is obtained, containing 96.1% of 2-mercaptobenzthiazole and m.p. 178 * C. Example 3

In a 1000 ml flask equipped with a stirrer and a sc delivery tube was added 450 [mu] l of water, 6.8 g of sodium hydroxide and 50 g of crude 2-mercaptobenzothiazole. The suspension is heated to boiling and after dissolution of the 2-mercaptobenzothiazole, carbon dioxide is introduced for 30 min. The resulting insoluble matter was filtered off after addition of 1.5 g of carborafine. Exclusion of pure 2-mercaptobenzthiazole is carried out as in Example 1.

Example 4

Dissolution of the crude 2-mercaptobenzthlazole was carried out as in Example 1, after which the mixture was extracted with 100 [mu] l xylene. After separation of the xylene layer, the deposition was carried out as in Example 4227 du 1. 39.5 g of 94% 2-mercaptobenzthiazole, m.p. 175 ° C.

Example 5

In the mother liquors of the last loop, the resinous residues are placed together with carboraffin and the suspension is heated to boiling. After hot filtration, pure 2-ascaptobenzothiazole is obtained in a similar manner to Example 1. This yields the 2-mercaptobenzthiazole fraction retained on the carburaffin together with the resin fractions. The filtrate is acidified with hydrochloric acid to pH 3-4 after separation of the pure 2-mercaptobenzothiazole and filtered into the channel after filtration. This 2nd crop can be added to the crude 2-mercaptobenzothiazole for purification according to Example 1.

Claims (2)

SUBJECT OF THE INVENTION Process for purification of crude 2-mercaptobenzothiazole prepared by condensation of aniline with carbon disulphide and sulfur, characterized in that the crude product is dissolved by boiling in an aqueous solution of sodium carbonate or sodium bicarbonate in a ratio of 1.0-2.0 alkali equivalent per mole 2-mercaptobenzothiazole to produce soda salt of 2-mercaptobenzothiazole and release of carbon dioxide from the mixture was collected insolubles impurities by filtration with addition of activated charcoal aebo different sorbent or by extraction with a water immiscible rozpustldlem and sodium 2-mercaptobenzothiazole with gradual cooling to 50-10 ⁰ The 2-mercaptobenzthiazole is released by carbon dioxide introduction and the pure 2-mercaptobenzothiazole is separated by filtration from sodium bicarbonate solution. 2. A process according to claim 1 wherein the mother liquor is used to dissolve the crude 2-mercaptobenzthiazole after filtration of the pure 2-mercaptobenzthiazole from the previous purge.