JPH038346B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is applicable to food additives (sugar substitute sweeteners), pharmaceuticals,
The present invention relates to a method for producing saccharin (o-sulfobenzoic acid imide), which is useful as an agricultural chemical intermediate.

Conventionally, saccharin has been produced by a method of oxidizing o-toluenesulfonamide with dichromic acid in sulfuric acid (for example, Japanese Patent Publication No. 49-40232).
However, in addition to requiring a large-scale electrolyzer to recover and reuse the by-product chromium sulfate, it is also necessary to treat a large amount of waste acid and waste liquid containing chromium. This was not an industrially preferred method.

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

That is, the present invention provides a method for producing saccharin by oxidizing o-toluenesulfonamide in an acetic acid solvent with a molecular oxygen-containing gas in the presence of a catalyst composed of cobalt, manganese, and bromine. This is a method for producing saccharin, which is characterized in that it is made to exist in the presence of saccharin.

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

In the present invention, toluene is chlorosulfonated,
O-toluenesulfonamide obtained by a method of reacting o-toluenesulfochloride obtained by separating the p-isomer with ammonia is used as a raw material. Then, acetic acid is used as a solvent in an amount of about 2 to 20 times the weight of o-toluenesulfonamide.
Although there is no particular problem even if water is present in the acetic acid in an amount of about 5% by weight or less, it is preferable that the water content in the acetic acid is as small as possible.

A catalyst system composed of cobalt, manganese and bromine is used as an oxidation catalyst, and a zirconium compound is also present in the reaction system. These catalyst components are then added in the form of the compounds shown below.

In other words, cobalt compounds and manganese compounds are
If it is soluble in acetic acid, it can be used, but
Particularly preferred are acetates, carbonates, hydroxides, bromides, and the like.

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 tetrabromoethane and bromoacetic acid can be used. Particularly preferred are cobalt bromide, manganese bromide, sodium bromide, and the like.

The amount of cobalt compound used is preferably such that the amount of cobalt metal used is in the range of 0.04 to 2% by weight based on the acetic acid solvent. If the amount of the cobalt compound used is less than 0.04% by weight, a sufficient reaction rate cannot be obtained, and if it exceeds 2% by weight, separation of the catalyst and the product becomes laborious and the cost of the catalyst increases.

The amount of manganese compound used is 0.01 to 50% by weight of cobalt metal as manganese metal.
A range of 0.1 to 10% by weight is particularly suitable.
If the amount of manganese compound used is less than 0.01% by weight, sufficient catalytic activity will not be obtained, while if it exceeds 50% by weight, the catalytic activity will tend to decrease, and the burden of separation from the product and catalyst cost will increase. increases.

The appropriate amount of the bromine compound to be used is 0.01 to 5 times the weight of cobalt metal, particularly 0.05 to 3 times the weight of cobalt metal. If the amount of the bromine compound used is less than 0.01 times by weight, sufficient catalytic activity cannot be obtained, and if it exceeds 5 times by weight, the contamination of the product by bromine and the burden of catalyst costs will become significant, which is not preferable.

In the present invention, it has become possible to further increase the reaction rate by coexisting a zirconium compound in the reaction system in addition to the catalyst components cobalt, manganese, and bromine.

As the zirconium compound used for this purpose, +4-valent zirconium compounds, such as zirconium bromide, zirconyl acetate, and zirconium acetate, which are soluble in acetic acid and do not contain counterions that interfere with the reaction, are suitable. The appropriate amount of the zirconium compound to be used is 0.001 to 2 times, particularly 0.005 to 1 times by weight, the amount of zirconium metal relative to the cobalt metal used as a catalyst component. When the amount of the zirconium compound used is less than this range, sufficient catalytic activity cannot be obtained, and when it is more than this range, separation from the product takes time.

Pure oxygen and industrial exhaust gas can also be used as the molecular oxygen-containing gas used as an oxidizing agent, but
For industrial purposes, normal air is optimal.

The reaction temperature is preferably in the range of 80 to 200°C, particularly 100 to 160°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 a safety standpoint, 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 of the exhaust gas from the reactor is in the range of 1 to 8% by volume.

The reactor used in the present invention is preferably of a forced mixing type rather than a simple bubble column type. That is, in order to achieve good gas-liquid mixing of the molecular oxygen-containing gas and the reaction liquid, to promote 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 forced stirring by a rotating stirring blade or forced circulation by a circulation pump 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 and the like contained in the exhaust gas are condensed and circulated to the reaction system.

As for the reaction method, the entire amount of the raw material mixture consisting of the oxidized substance, solvent, and catalyst is charged into the reactor in advance, and the reaction product is not taken out until the reaction is completed.
A batch method in which a molecular oxygen-containing gas is introduced, a semi-continuous method in which a raw material mixture or the oxidized substance dissolved in a solvent is continuously supplied to the reactor but the reaction product is not taken out until the reaction is completed, and a semi-continuous method in which a raw material mixture is introduced. Any continuous method can be adopted in which the reaction product is continuously supplied to the reactor and the reaction product is continuously taken out.

When the oxidation reaction is carried out for several hours under the above-mentioned conditions until the raw material is almost completely consumed, the target substance sacculin and the main by-product are o-sulfobenzoic acid monoammonium produced by hydrolysis of sacculin. , this is monoammonium cobalt o-sulfobenzoate and an oxidation intermediate produced by salt formation with cobalt ions of the oxidation catalyst.
- Formylbenzenesulfonamide or a compound presumed to be a Schiff base resulting from intramolecular dehydration and ring closure is produced.

The reaction product and acetic acid can be separated by cooling the reaction product liquid as it is, by concentrating it and then cooling it, crystallizing the reaction product, and separating the acetic acid from solid-liquid, or by completely removing the acetic acid in the reaction product liquid. A suitable method is to obtain a reaction product containing an oxidation catalyst as a residue by distilling off the oxidation catalyst.

The reaction product from which acetic acid has been removed is washed with water that is approximately 1 to 10 times the weight of the reaction product, recrystallized using water that is approximately 10 to 30 times the weight of the reaction product, or dissolved in an aqueous alkaline solution. The metal catalyst and by-products are separated and removed from saccharin through treatments such as removing impurities and acid-fractionation. In order to further improve the purity and color tone of saccharin, it is also a preferred embodiment to carry out these treatments together, or to carry out activated carbon treatment at the time of recrystallization.

In addition, the metal catalyst dissolved in the washing solution or recrystallization mother liquor can be precipitated as a carbonate by adding sodium carbonate, or concentrated and left in the coexistence of saccharin to precipitate as a saccharin salt, which can then be recovered and recycled as an oxidation catalyst. It is also possible to do so.

The mother liquor (acetic acid solution) obtained when the reaction product is crystallized and separated from the reaction product solution contains saccharin, intermediates, by-products, oxidation catalysts, etc., so that the by-product water is separated by distillation. After that, it can be recycled to the reaction system as it is or after an appropriate purification treatment.

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

The present invention will be specifically explained below with reference to Examples.

Example 1 O-Toluenesulfonamide 40
parts, 400 parts of acetic acid, 3.81 parts of cobalt acetate tetrahydrate, 0.11 parts of manganese acetate tetrahydrate, cobalt bromide hexahydrate
1.67 parts, 0.30 parts of zirconyl acetate, (0.3% by weight of cobalt metal to acetic acid, 2% by weight of manganese metal to cobalt metal, 68% by weight of bromine atoms to cobalt metal, 10% by weight of zirconium metal to cobalt metal) weight%) and the reaction pressure was 18
At a pressure gauge and a reaction temperature of 120°C, the reactor was brought into contact with air blown from the bottom of the reactor at a flow rate such that the oxygen concentration in the exhaust gas was 8% or less for 2.5 hours.

A cake obtained by concentrating the reaction product and separating it into solid and liquid (dry weight 40.0 parts, composition of the dry product is saccharin)
72.3% by weight, monoammonium cobalt o-sulfobenzoate 20.7% by weight, o-formylbenzenesulfonamide or its dehydrated closed ring product 5.0% by weight)
was washed twice with 50 parts of water at room temperature and dried to obtain 23.3 parts of white crystals (saccharin). The purity of this product determined by high performance liquid chromatography was 99% or higher.

Comparative Example 1 Contact with air was carried out under the same conditions as in Example 1 except that zirconyl acetate was used at a reaction temperature of 12.degree. C. for 5 hours.

Cake obtained by concentrating the reaction product and separating solid and liquid
The composition of 20.4 parts was 62.3% by weight of saccharin, 2.2% by weight of monoammonium o-sulfobenzoate, and the remainder was an intermediate such as o-formylbenzenesulfonamide or its dehydrated ring product.

Claims (1)

[Claims] 1. When producing saccharin by oxidizing o-toluenesulfonamide with a molecular oxygen-containing gas in the presence of a catalyst consisting of cobalt, manganese and bromine in an acetic acid solvent, it is necessary to include a zirconium compound in the reaction system. Characteristic manufacturing method of saccharin.