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Laevulose Fructose

1911 Encyclopedia Britannica

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LAEVULOSE, or Fruit-Sugar, a carbohydrate of the formula C6H1206. It is closely related to ordinary d- glucose, with which it occurs in many fruits, starches and also in honey. It is a hydrolytic product of inulin, from which it may be prepared; but it is more usual to obtain it from "invert sugar," the mixture obtained by hydrolysing cane sugar with sulphuric acid. Cane sugar then yields a syrupy mixture of glucose and fructose, which, having been freed from the acid and concentrated, is mixed with water, cooled in ice and calcium hydroxide added. The fructose is precipitated as a saccharate, which is filtered, suspended in water and decomposed by carbon dioxide. The liquid is filtered, the filtrate concentrated, and the syrup so obtained washed with cold alcohol. On cooling the fructose separates. It may be obtained as a syrup, as fine, silky needles, a white crystalline powder, or as a granular crystalline, somewhat hygroscopic mass. When anhydrous it melts at about 95° C. It is readily soluble in water and in dilute alcohol, but insoluble in absolute alcohol. It is sweeter than cane sugar and is more easily assimilated. It has been employed under the name diabetin as a sweetening agent for diabetics, since it does not increase the sugar-content of the urine; other medicinal applications are in phthisis (mixed with quassia or other bitter), and for children suffering from tuberculosis or scrofula in place of cane sugar or milk-sugar.

Chemically, fructose is an oxyketone or ketose, its structural formula being CH 2 OH

(CH

OH) 3

CO

CH 2 OH; this result followed from its conversion by H. Kiliani into methylbutylacetic acid. The form described above is laevo-rotatory, but it is termed d-fructose, since it is related to d-glucose. Solutions exhibit mutarotation, fresh solutions having a specific rotation of - 104

o, which gradually diminishes to - 92°. It was synthesized by Emil Fischer, who found the synthetic sugar which he named a-acrose to be (d+/)-fructose, and by splitting this mixture he obtained both the d and 1 forms. Fructose resembles d-glucose in being fermentable by yeast (it is the one ketose which exhibits this property), and also in its power of reducing alkaline copper and silver solutions; this latter property is assigned to the readiness with which hydroxyl and ketone groups in close proximity suffer oxidation. For the structural (stereochemical) relations of fructose see Sugar.