Process for continuously producing 3-isothiazolinone derivatives and intermediate products thereof

A process for producing 3-isothiazolinone derivatives, comprising continuously carrying out the following four steps:

• (1) continuously adding a compound of formula I, sulfur and H2S to a first reaction device to obtain a first reaction solution comprising a compound of formula II and a compound of formula III by way of a first reaction:
• wherein the first reaction is carried out in an aqueous solution of ammonium sulfide;
• (2) continuously adding the first reaction solution and an aqueous solution of sodium sulfite to a second reaction device to obtain a second reaction solution comprising a compound of formula II by way of a second reaction:
• wherein step (2) comprises i) continuously adding a mixture of a compound of formula II and a compound of formula III and an aqueous solution of sodium sulfite to a first counter-current extraction column;
• and
• ii) continuously adding the organic phase obtained from step i) and water to a second counter-current extraction column to obtain the compound of formula II;
• (3) continuously adding the second reaction solution and a primary amine of formula IV to a third reaction device to obtain a compound of formula V by way of a third reaction:
• wherein R represents C1-C18 alkyl or C3-C18 cycloalkyl;
• and
• (4) continuously adding the compound of formula V and chlorine to a fourth reaction device to obtain a compound of formula VI by way of a fourth reaction:
• R represents C1-C18 alkyl or C3-C18 cycloalkyl, and R1 and R2 independently represent H or chlorine, and
• the fourth reaction is carried out in the presence of an ester.