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This article mainly explains the traditional 1,2-Benzisothiazol-3-one synthesis process and operation points. If you want to get the details of the reaction formula in the production process, please click here.

1. Main raw material 2,2′-dithiodibenzoic acid production process and control points


Slowly add the prepared and cooled to 0~5℃ sodium nitrite solution in the diazotization kettle for diazotization reaction (0~5℃, 20~30min, starch a potassium iodide test paper turns blue for the end).

The generated diazide solution is added to the disulfide reaction kettle at a certain speed, and the disulfide reaction is carried out (0~5℃, 30min, and the diazide is gradually warmed up to room temperature for 1.5~2h), then the sodium dibasic solution is generated.

The sodium dibasic solution was then acidified, dehydrogenated (80-90°C, 1h), and ammonia solubilized (endpoint pH 8-9). Then placed in the bottom filter of the kettle (the end point is pH 6~7 of the filtrate). The waste residue is filtered off. The liquid is sucked back into the disulfide reactor by vacuum. Neutralized by hydrochloric acid (the end point is the discoloration of Congo red paper) into diacid. Send to centrifuge for dewatering. The filter cake is sent to the drying room (baking temperature 100±10℃, diacid moisture content ≤0.5%). Crushed (fineness 40 mesh through) for the synthesis of 1,2-Benzisothiazol-3-one section.

Control point.

Strictly control the feeding ratio. When the input o-aminobenzoic acid content and other raw material content change, the proportion should be adjusted accordingly.

In the diazotization reaction, the reaction should be strictly controlled within 0~5℃. When the temperature is as high as 5℃, the addition of sodium nitrite should be suspended. If necessary, crushed ice can be thrown in to lower the temperature. When the temperature drops to below 5℃, add sodium nitrite again. Reaction time is controlled within 0.5h.

The amount of sodium nitrite added to starch – potassium iodide test paper becomes blue at the end. If the prepared sodium nitrite solution has been used up, the test paper has not yet changed color, you can add the appropriate amount of sodium nitrite solution. If the test paper becomes blue and sodium nitrite has not been added, you can stop adding. Discard the remaining solution. Sodium nitrite is very easy to oxidation, must be used with the preparation, not allowed to prepare every other shift.

Strictly control the reaction temperature of disulfide in the range of 0~5℃. Pay close attention to the situation in the pot during diazotization feeding. If there is a rise in the pot, the addition of diazotization salt can be suspended.

2. Traditional 1,2-Benzisothiazol-3-one preparation process and operation points.

Chloroforming reaction.

a. Feeding: diacid, sulfoxide chloride, benzene, and catalyst;
b. Reaction temperature: material boiling reflux;
c. End point of reaction: The liquid phase of the material is clear, solid particles settle rapidly, and less hydrogen chloride and sulfur dioxide escape.


Benzene flows from the high-level metering tank into the BIT reactor. Add “diacid” and catalyst to the kettle. After adding sulfoxide chloride from the sulfoxide chloride dosing tank, the material is heated for the chlorination reaction. After the reaction, cool down to room temperature. Add an appropriate amount of bromine to carry out the bromination reaction. Then the ammonia is added to the high-level tank to carry out the cyclization reaction.

After the reaction is finished, the solvent is evaporated, and the liquid becomes salt and is filtered through a thermal filter, and put into a crystallization drum. The product is neutralized with hydrochloric acid to become slightly acidic, cooled, crystallized, and filtered to obtain the 1,2-Benzisothiazol-3-one product.

During the chlorination reaction, the mixture of hydrogen chloride and sulfur dioxide escaping from the reaction is exported to the water flushing pump system for absorption via a cold suspect. The resulting absorption solution is neutralized by lye and discharged.

Bromination reaction.

a. Feeding: bromine;
b. Reaction temperature: room temperature (< 20℃);
c. Reaction time: 10~15min.

Cyclization reaction.

a. Feeding: ammonia;
b. Reaction temperature: 60~70℃;
c. Reaction time: 30min;
d. Material pH: always ≥ 8.

Steaming benzene.

a. Temperature: 75~85℃;
b. Time: about 1h;
c. End of distillation material pH ≥ 8.

When distilling off benzene, the mixture of benzene and water is condensed by the cold suspect, and then the benzene layer is initially stratified by the separator into the acid wash tank and water wash tank in turn for washing, settling and separation operation. Benzene is neutral or slightly alkaline after washing. The benzene dehydration is required to be clear and transparent. The recovered benzene is dried in the benzene storage tank by calcium chloride and then reused.

Salt formation.

a. Feeding: liquid alkali;
b. Reaction time: 10min;
c. Neutralization: add hydrochloric acid to pH 4~5.

Drying of finished product: (1) temperature: 80, 90℃, water content: <1%.

Operation points.

a. Ensure the feeding ratio of “diacid” to sulfoxide chloride and catalyst. Insufficient sulfoxide chloride will make the reaction incomplete; too much will increase the side reaction and increase the consumption of ammonia. If the amount of “diacid” is changed, the dosage of sulfoxide chloride and catalyst should be changed accordingly.

b. Acylation reaction time: the standard is to reach the end of the reaction, which takes about 1h under the above feeding ratio.

c. Ensure the pH value during the cyclization reaction. If pH< 8 is found, ammonia can be added.

d. Prevent the loss of benzene. Because benzene is a flammable and toxic chemical, its loss may bring the danger of fire, so it is not allowed to be lost when operating the delivery. When distilling benzene, all should be distilled cleanly, and when washing, it should be settled sufficiently and separated carefully so as not to bring benzene into the waste water and threaten safety.

e. Ensure the quality of benzene dehydration. Chloroforming reaction should be applied to anhydrous operating system, so the recovered benzene should be basically anhydrous otherwise it will affect the effect of chloroforming. For this reason, the washing, settling and separation operation of benzene should be carried out in aqueous phase at the restaurant corner as much as possible.

f. The raw material bromine and sulfoxide chloride must be handled and added with great care, not to break or leak, and empty bottles are not allowed to be placed anywhere, but should be stored centrally.


1,2-Benzisothiazol-3-one Synthesis Process and Operation Guidelines