FIELD: chemical industry. SUBSTANCE: described is improved method of preparing magnesium salt of substituted sulfinyl-heterocyclic compound containing imidazole group of formula I: 
wherein Ar is (a) or (b); Z is (c) and (d), and X is (e) or (f) wherein N is inside of benzene ring of benzimidazole group and denotes that one of carbon atoms substituted by radicals R7-R10, is optionally substituted by nitrogen atom without any substituents; R1, R2 and R3, are the same or different and are selected from hydrogen, alkyl, alkylthio, alkoxy, optionally substituted by fluorine, alkoxy-alkoxy, dialkylamino, piperidino, morpholino, halogen, phenylalkyl and phenylalkoxy wherein alkyl and alkoxy groups are branched or linear and contain cyalic alkyl groups such as cycloalkylalkoxy groups; R4 and R5 are the same or different, and are selected from hydrogen, alkyl, and aralkyl; R6 is hydrogen, halogen, trifluoromethyl, alkyl and alkoxy; R7-R10 are the same or different and are selected from hydrogen, alkyl, alkoxy, halogen, halogen-alkoxy, alkylcarbonyl, alkoxycarbonyl, oxazolyl, trifluoroalkyl or adjacent groups R7-R10 form ring structures which are optionally substituted; R11 is hydrogen or forms alkylene chain together with R3,, and R12 and R13 are the same or different and are selected from hydrogen, halogen, alkyl or alkoxy groups in which alkoxy group are branched or linear C1-C9 chains, and alkyl and alkoxy groups contain cyclic alkyl groups e. g. cycloalkylalkyl wherein substituted sulfinyl heterocycle of formula I is mixed with weak base selected from group consisting of organic amines and ammonia, and magnesium source selected from group consisting of magnesium acetate, magnesium nitrate, magnesium sulfate, magnesium carbonates and magnesium chloride. Method gives high yield by volume, uses less equipment, less time consumption, is advantageous for environment and more economical. EFFECT: more efficient preparation method. 5 cl, 10 ex
