HCOONa + HCl = HCOOH + NaCl
Sodium formate is very soluble in formic acid. Formic acid boils at about 101 ° C and forms azeotrope with water boiling at about 107 ° C. Addition of approximately 3 moles of sodium formate to 1 kilogram of formic acid, after deducting its consumption to neutralize hydroxylamine hydrochloride, increase the boiling point of the reaction mixture (see ebullioscopic constant of formic acid) above the boiling point of the azeotrope. In this way, we can remove water from the reaction environment by shifting the equilibrium towards ester formation - oxime formate, which at this temperature decomposes thermally to the nitrile.