Ethanol → 3,4-dihydro-2H-1-benzothiopyran-8-ol

40 Grams of 8-hydroxy-thiochroman-4-one were added portion-wise to a mixture of 53.5 ml of hydrazine hydrate and 220 ml of ethanol. The reaction mixture was refluxed for 1 hour and then evaporated to dryness in vacuo. The residue was taken up in 250 ml of ethyleneglycol, and then 22.1 g of sodium hydroxide were added in pellet form. The whole was heated to refluxing, while the water of reaction was distilled off as it formed. The mixture was then heated for 4 hours at 200° C., allowed to cool and the bulk of glycol was expelled under vacuum. The residue was diluted with water and then acidified. The liberated phenol was extracted with chloroform. The chloroform extract was dried and evaporated and the residue distilled under vacuum, to yield 20.1 g of 8-hydroxy-thiochroman, boiling at 105°-110° C. under 0.08 mm Hg pressure, in a yield of 55%. After recrystallization from cyclohexane it melted at 86°-88° C.