PRODUCTION OF TETRAHYDRO-4H-PYRAN-4-ONE

PURPOSE:To produce the subject compound by reacting a 1,5-dihalopentan--3-one in the presence of a phosphoric acid salt, a carboxylic acid and water while reducing formation of insoluble substances complicating the after-treatment of the reaction solution. CONSTITUTION:This method for production of the compound of formula II is carried out by reacting a compound of formula I (X is a halogen) in the presence of a phosphoric acid salt (e.g. sodium dihydrogen phosphate), a carboxylic acid or its salt (e.g. salicylic acid) and water at 90 to 105 deg.C. The phosphate is used in an amount of 4 to 1.8 time mole the compound of formula I and the carboxylic acid or its salt is used in an amount of 0.1 to 500mol%. Water is used in an amount of 1 to 20ml. The compound of formula II is useful as a raw material for synthesis of fine chemicals such as medicines. This production method enables production of the compound of formula II while inhibiting formation of insoluble materials adhering to the wall of a reactor, insoluble in various kinds of organic solvents and having difficulty in removal.