JPS5879985A - Preparation of saccharin - Google Patents

Abstract

PURPOSE:To obtain saccharin as a sweetening agent, medicine and intermediate for agricultural chemicals industrially advantageously, by oxidizing o-toluenesulfonamide with a gas containing molecular oxygen in place of dichromic acid in acetic acid solvent in the presence of a catalyst. CONSTITUTION:o-Toluenesulfonamide is catalytically oxidized with a gas containing molecular oxygen, e.g. air, in acetic acid solvent in an amount of preferably 2-10 times that of the o-toluenesulfonamide in the presence of a catalyst constituted of cobalt and/or manganese preferably in 0.04-2wt% total Co and Mn concentration based on the acetic acid solvent and a bromine compound, preferably cobalt bromide or manganese bromide, at 110-180 deg.C and 5-30atm. The reaction mixture is then cooled to crystallize the aimed saccharin. The mother liquor after the separation of the crystal can be repeatedly circulated through the reaction system.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing saccharin (0-sulfobenzoic acid imide), which is useful as a food additive (sugar substitute sweetener), medicine, agricultural chemical intermediate, etc.

Conventionally, saccharin has been produced by oxidizing o-toluenesulfonamide with dichromic acid in sulfuric acid (for example, Japanese Patent Publication No. 49-40232).
Not only is a large-scale electrolyzer required to recover and reuse the by-product chromium sulfate, but also a large amount of waste acid and chromium-containing wastewater must be treated, making it an industrially preferred method. There wasn't.

Therefore, the present inventors conducted extensive research on a method for producing saccharin from 〇-toluenesulfonamide by using molecular oxygen-containing scum as an oxidizing agent, which does not require recovery and is easy to handle, instead of dichromic acid. We have arrived at the present invention.

That is, the present invention is characterized in that 0-l-luenosulfonamide is brought into contact with a molecular oxygen-containing gas in the presence of a catalyst composed of cobalt and/or manogano and bromine in an acetic acid solvent. This is a method for producing saccharin.

The method of the present invention will be specifically explained below.

In the present invention, 0-toluenesulfonamide obtained by a method of reacting 0-toluenesulfochloride obtained by chlorosulfonating toluene and separating the p-isomer with ammonia is used as a raw material. Then, acetic acid of about 2 to 10 times the weight of 0-toluenesulfonamide is used as a solvent. There is no particular problem even if less than 10% by weight of water is present in this acetic acid.

As an oxidation catalyst, a catalyst system consisting of cobalt and/or manganese and bromine is used, and these catalyst components are added in the form of the compounds shown below.

That is, cobalt compounds and manganese compounds can be used as long as they are soluble in acetic acid, but acetates, carbonates, hydroxides, bromides, etc. are particularly preferred.

As the bromine compound, inorganic bromine compounds such as bromine, hydrogen bromide, ammonium bromide, alkali metal bromides, cobalt bromide, and manganese bromide, and organic bromine compounds such as tetrabromoethano and bromoacetic acid can be used. Particularly preferred are cobalt bromide, manogan bromide, thorium bromide, and the like.

The amount of cobalt compound and manganese compound to be used is preferably such that the total concentration of cobalt and manganese as metals is in the range of 0.04 to 2 wt% based on the acetic acid solvent. In this case, preferable results are often obtained when cobalt or manganese is used in combination, and cobalt is used in excess of manganese, rather than when cobalt or manganese is used alone.

On the other hand, the amount of the bromine compound to be used is preferably adjusted such that the gram atomic weight of the bromine atom used is approximately 1 to 6 times the total gram atomic weight of cobalt and manganese.

Although pure oxygen or industrial exhaust gas can be used as the molecular oxygen-containing gas used as the oxidizing agent, normal air is most suitable from an industrial standpoint.

The reaction temperature is preferably in the range of 80-230°C, particularly 110-180°C. The reaction pressure is set so as to maintain the solvent acetic acid in a liquid phase at this temperature, and is suitably in the range of 5 to 30 atmospheres.

From the standpoint of safety, it is desirable to adjust the rate at which molecular oxygen-containing gas (usually air) is blown into the reactor so that the oxygen concentration in the waste from the reactor is in the range of 1-8% by volume.

31 The reactor used in the present invention is preferably of a forced mixing type rather than a simple bubble column type. In other words, in order to achieve good gas-liquid mixing of the molecular oxygen-containing gas and the reaction liquid, to promote the dissolution of molecular oxygen into the reaction liquid, and to ensure smooth contact between the reactants in the reactor. ,
It is preferable to use a reactor equipped with a gas inlet consisting of a large number of pores in the lower part of the reactor, and in which forcible stirring by a rotating stirring blade or forced circulation by a circulation pot outside the reactor is performed.

A reflux condenser is installed in the upper part of the reactor, and the exhaust gas is discharged through the reflux condenser, and the solvent acetic acid contained in the exhaust gas is condensed and circulated to the reaction system.

The reaction method is a batch method in which the entire amount of the raw material mixture consisting of the oxidized substance, solvent, and catalyst is charged into the reactor in advance, and molecular oxygen-containing scum is introduced without taking out the reaction product until the reaction is completed. A mixture or a substance to be oxidized dissolved in a solvent is continuously supplied to the reactor until the reaction is completed. 4- Semi-continuous method in which the reaction product is not taken out, and 1) a raw material mixture is continuously supplied to the reactor. At the same time, any continuous method in which the reaction product is continuously taken out can be adopted.

In the second part of the present invention, the oxidation reaction is carried out under the above-mentioned conditions for several hours until most of the raw material is consumed, and the resulting product is cooled to around room temperature, and in some cases further concentrated. Then, the crystallized saccharin and the mother liquor are separated into solid and liquid. The isolated saccharin is purified to a desired purity by washing with a solvent and, in some cases, recrystallization, to produce a product.

On the other hand, the mother liquor from which Sunocarino is separated contains useful substances such as saccharin, intermediates, unreacted raw materials, and catalysts. It can be applied and recycled to the reaction system for repeated use.

From the method of the present invention described in detail below, saccharin of good quality can be produced economically by using an inexpensive and easy-to-handle molecular oxygen-containing gas as an oxidizing agent instead of dichromic acid, which is expensive and difficult to handle. It became possible to manufacture

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example In a pressure-resistant titanium reactor equipped with a reflux condenser and a rotating blade stirrer, 70 parts by weight of O-l-ruenosulfonamide, 200 parts of acetic acid, and 3.3 parts of cobalt bromide (cobalt to acetic acid) were placed. 0.3% by weight), 0.27 parts of manoganoacetate (cobalt 1
To this, 10% by weight of manganese was charged, and the reaction pressure was 20%.
At a reaction temperature of 140° C., air was blown into the reactor from the bottom of the reactor at a flow rate such that the oxygen concentration in the exhaust gas was 6% or less, and the reactor was brought into contact with air for 3 hours.

The reaction product was concentrated and cooled to around room temperature, and the cake obtained by solid-liquid separation was washed with aqueous acetic acid and dried to obtain white crystals.
Got 5 copies. The infrared absorption spectra of this product matched that of saccharin, and the purity determined by high performance liquid chromatography was over 97%.

Patent applicant Higashi Shikikai Co., Ltd.

Claims (1)

[Claims] 1. A method for producing saccharin, which comprises contacting 0-toluenesulfonamide with a molecular oxygen-containing gas in an acetic acid solvent in the presence of a catalyst consisting of cobalt and/or manokat and bromine.