NOVELTY - Preparation (P1) of prazole compounds (I) involves reacting substituted 2-hydroxymethyl pyridine or its hydrochloride with thionyl chloride in organic solvent followed by isolating substituted chloromethyl pyridine or its hydrochloride as aqueous phase; condensing substituted 2-mercapto benzimidazole with substituted chloromethyl pyridine or its hydrochloride in aqueous medium at 0-100 degrees C followed by heating reaction mass to maintain temperature in range of 30-100 degrees C; and oxidizing obtained prazole sulfide in-situ using oxidizing agent in presence of organic solvent.    USE - For preparation of prazole compounds such as omeprazole, lansoprazole, pantoprazole, rabeprazole, ilaprazole and tenatoprazole (claimed) useful as proton pump inhibitors.    ADVANTAGE - The process produces prazole compounds free of dialkylated impurity i.e. less than 0.2% of impurity and also obviates or avoids the need for isolation of 2-chloromethyl pyridine hydrochloride, and the corresponding sulfide. The process is improved, robust and ecological or environmental friendly in-situ process; and results in the formation of sulfide compounds free of dialkylated benzimidazole impurity. The process avoids the isolation of precursor sulfide compounds which results in lower handing losses and higher yields of above 98%. The sulfide is oxidized in-situ to give prazoles in good yield and quantity.    DETAILED DESCRIPTION - An in-situ process (P1) for preparation of prazole compounds of formula (I) involves: a) reacting substituted 2-hydroxymethyl pyridine or its hydrochloride with thionyl chloride optionally in organic solvent followed optionally by isolating substituted chloromethyl pyridine or its hydrochloride as aqueous phase; b) condensing substituted 2-mercapto benzimidazole with the substituted chloromethyl pyridine or its hydrochloride in aqueous medium at 0-100 degrees C followed by heating reaction mass to maintain temperature in range of 30-100 degrees C to obtain corresponding prazole sulfide; and c) oxidizing the prazole sulfide in-situ using oxidizing agent in presence of organic solvent (s2) to obtain the corresponding prazole compound.    R1=-CH3 or -OCH3;    R2=-OCH3, -OCH2CF3, -O-(CH2)3-O-CH3, -Cl or -NO2;    R3=-CH3 or H;    R=-OCH3, H, -OCHF2 or 1H-pyrrole;    X=CH or N.