Determination of Isocyanic Acid by Back Titration of Excess Alkali

Abstract

Isocyanic acid can be fixed quantitatively with an excess methanol solution of sodium methoxide or sodium hydroxide as sodium cyanate. Solubility of sodium cyanate in methanol-diethyl ether was measured. When volume ratio of methanol to diethyl ether was below 1/3, sodium cyanate was sparingly insoluble in the mixed solvent. Thus, sodium cyanate can be precipitated sufficiently adding three times volume of diethyl ether to that of methanol. After filtration of sodium cyanate, excess sodium methoxide or sodium hydroxide is titrated with O.1 mol⋅dm^-3 hydrochloric acid. The content of HNCO in the purified isocyanic acid was 99.4% or more by this method.