KILIANI'S REDUCTION OF GLUCOSE AND FRUCTOSE CYANOHYDRINS TO THE CORRESPONDING HEPTANOIC ACIDS AND LACTONES

Abstract

Kiliani's classic reduction of α-glucoheptonic (D-gluco-D-guloheptonic) lactone led to small, variable yields of n-heptanoic acid and varying amounts of the lactone of a hydroxy-n-heptanoic acid. A repetition of this work showed that the combined yields of these two products reached a maximum near 70% of theory when the reduction with constant-boiling hydriodic acid (b.p. 127 °C) and phosphorus was limited to two hours. Under these conditions up to 9/10ths of the product consisted of the lactone. After purification through the hydrazide, m.p. 89 °C, the fragrant smelling lactone boiled at 61° to 62 °C at 10 mm. pressure, had a density of 0.9948, and a refractive index of nD, 1.4405, both at 20 °C. The supposition that this lactone referred to 4-hydroxy-n-heptanoic acid was confirmed by preparing it from the known 4-keto-n-heptanoic acid, which in turn was synthesized by an improved method.The optimum time for reducing an uncrystallized mixture of α- and β-fructoheptonic acids under similar conditions was three to four hours, and the optimum yield of product was again near 70% of theory. This product consisted almost exclusively of the lactone of 2-methyl-4-hydroxyhexanoic acid. After purification through the crystalline hydrazide, m.p. 122 °C., the lactone was recovered as a fragrant oil boiling at 48° to 49 °C at 2 mm. pressure, with density 0.9806 and refractive index nD1.4332 at 25 °C. The structure of this lactone was not in doubt.These lactones, prepared in good yield and with well defined hydrazides, were more readily characterized than the fully reduced heptanoic acids upon which Kiliani relied.