Abstract: A process for preparing trioxane from methanol includes: step 1: subjecting a mixture of methanol and methylal to a reaction to obtain formaldehyde, and absorbing the formaldehyde with water to obtain a concentrated formaldehyde aqueous solution; step 2: subjecting the concentrated formaldehyde aqueous solution to cyclization to obtain a mixture containing trioxane, and passing the mixture through a trioxane concentration tower to obtain a crude trioxane product; step 3: converting a by-product and unreacted formaldehyde in the crude trioxane product into methanol, conducting dehydration through a membrane dehydration process, and subjecting a retentate to dealcoholization to obtain purified trioxane; and step 4: subjecting the remaining streams to reactive distillation to obtain a mixture of methanol and methylal at a top-and water at a bottom of the reactive distillation tower; returning the mixture of methanol and methylal to step 1; and returning or discharging the water.

Abstract: The present invention disclosed a preparation method of Clopidogrel (X=2?Cl) and its analogues of methyl tetrahydrothienopyridine acetate (I) by using halogen phenyl acetonitrile (VIII) as starting material and tetrahydrothienopyridine acetonitrile (IV), tetrahydrothienopyridine acetate (V) as key intermediates, and further using kinetic resolution to prepare the optical active Clopidogrel and compounds of methyl tetrahydrothenopridine acetate of formula (XII). The Clopidogrel of present invention is a novel high effective and safety drug for inhibition of platelet aggregation. This invention applied systematic technique of racemization of unwanted optical active enantiomer, recover recycle and reuse of resolution agent etc., with greater economic advantages and suitable for commercial scale industrial production. Wherein: X represents atoms of hydrogen, fluorine, chlorine, bromine or iodine, M represents an alkali metal ion.