NOVELTY - 2-Chloromethyl pyridine derivatives (III) are prepared by mixing 2,3-dimethylpyridine with glacial acetic acid catalyst and 2-4 pts. wt. concentrated sulfuric acid having a concentration of 3-5 mass%, heating while stirring at 80-110 degrees C, adding 1.25-1.75 pts. wt. hydrogen peroxide having a concentration of 30 plus minus 2 mass%, adding reducing agent, decompressing, distilling, adding concentrated sulfuric acid, heating while stirring at 80-90 degrees C, and dripping slowly 98 wt.% concentrated sulfuric acid and 63-67 wt.% nitric acid having a ratio of 28-3.3:1.    USE - Method of preparing N-chloromethyl pyridine derivatives (claimed) used as lansoprazole intermediate.    ADVANTAGE - The method is simple, low cost and environment-friendly, and has high efficiency, high yield and high solvent recovery.    DETAILED DESCRIPTION - 2-chloromethyl pyridine derivatives of formula (III) are prepared by:    (A) mixing 2,3-dimethylpyridine with glacial acetic acid and 2-4 pts. wt. concentrated sulfuric acid catalyst having a concentration of 3-5 mass%, heating while stirring at 80-110 degrees C, adding 1.25-1.75 pts. wt. hydrogen peroxide having a concentration of 30 plus minus 2 mass%, adding reducing agent, decompressing and distilling to give 2,3-dimethyl-pyridine-N-oxide;    (B) adding concentrated sulfuric acid to the 2,3-dimethyl-pyridine-N-oxide, heating while stirring at 80-90 degrees C, dripping slowly 98 wt.% concentrated sulfuric acid and 63-67 wt.% nitric acid having a ratio of 28-3.3:1, adding sodium carbonate to adjust pH value to 8-10, filtering, adding chloroform, extracting, filtering, spin drying, and washing with ethanol to give 2,3-dimethyl-4-nitropyridine-N-oxide;    (C) mixing the 2,3-dimethyl-4-nitropyridine-N-oxide with alcohol, acetonitrile, water, potassium carbonate and phase transfer catalyst, heating, adding washed product, stirring, reflux heating for 6-8 hours, cooling to - 2 degrees C to 5 degrees C, filtering to remove inorganic salt, concentrating obtained filtrate, adding water and concentrated toluene, extracting, adding anhydrous sodium sulfate, and evaporating to give a 2,3-dimethyl-4-hydroxy-pyridine-N-oxide compound of formula (I), adding ethanol solution to the evaporation residue of compound (I), dripping slowly phase transfer catalyst, heating to 60-80 degrees C for 2.5-3.5 hours, cooling to - 2 degrees C to 5 degrees C, filtering, adding methylene dichloride or ethyl acetate, extracting, filtering the extract, adding anhydrous sodium sulfate and evaporating;    (D) adding acetic anhydride and concentrated sulfuric acid to compound (I), distilling at 90-105 degrees C, adding ethanol anhydride and sodium hydroxide solution, stirring, adding 10-15 mass% sodium hydroxide, heating at 60 plus minus 2 degrees C, hydrolyzing, adding ethyl acetate, extracting, concentrating, subjecting to low temperature re-crystallization, filtering, and washing the filter cake with petroleum ether to give 4-hydroxy-2-hydroxymethyl-3-methyl-pyridine-N-oxide compound of formula (II); and    (E) adding methylene dichloride, dripping thionyl dichloride, reacting at - 10 to 10 degrees C for 3-5 hours, decompressing and concentrating, cooling to room temperature, adding slowly ethyl acetate, filtering, and drying the filter cake to give a compound (III).    R=Me or CH2CF3.    The phase transfer catalyst is tetrabutyl ammonium bromide, benzyl triethyl ammonium chloride, tetrabutyl ammonium chloride, tetrabutyl ammonium bisulfate, methyl trioctyl ammonium chloride, or quat. ammonium salt selected from tetrabutyl ammonium bromide or benzyl triethyl ammonium chloride.