_Chemistry._--In its chemical properties glucose is a typical oxyaldehyde or aldose. The aldehyde group reacts with hydrocyanic acid to produce two stereo-isomeric cyanhydrins; this isomerism is due to the conversion of an originally non-asymmetric carbon atom into an asymmetric one. The cyanhydrin is hydrolysable to an acid, the lactone of which may be reduced by sodium amalgam to a glucoheptose, a non-fermentable sugar containing seven carbon atoms. By repeating the process a non-fermentable gluco-octose and a fermentable glucononose may be prepared. The aldehyde group also reacts with phenyl hydrazine to form two phenylhydrazones; under certain conditions a hydroxyl group adjacent to the aldehyde group is oxidized and glucosazone is produced; this glucosazone is decomposed by hydrochloric acid into phenyl hydrazine and the keto-aldehyde glucosone. These transformations are fully discussed in the article SUGAR. On reduction glucose appears to yield the hexahydric alcohol _d_-sorbite, and on oxidation _d_-gluconic and _d_-saccharic acids. Alkalis partially convert it into _d_-mannose and _d_-fructose. Baryta and lime yield saccharates, e.g. C6H12O6·BaO, precipitable by alcohol.
CH2OH CH2OH . . CH·OH CH·OH . . CH CH / / O< O< \ . \ . (CH·OH)2 (CH·OH2 . . HC·OH HO·CH
The constitution of glucose was established by H. Kiliani in 1885-1887, who showed it to be CH2OH·(CH·OH)4·CHO. The subject was taken up by Emil Fischer, who succeeded in synthesizing glucose, and also several of its stereo-isomers, there being 16 according to the Le Bel-van't Hoff theory (see Stereo-Isomerism and Sugar). This open chain structure is challenged in the views put forward by T. M. Lowry and E. F. Armstrong. In 1895 C. Tanret showed that glucose existed in more than one form, and he isolated [alpha], [beta] and [gamma] varieties with specific rotations of 105°, 52.5° and 22°. It is now agreed that the [beta] variety is a mixture of the [alpha] and [gamma]. This discovery explained the mutarotation of glucose. In a fresh solution [alpha]-glucose only exists, but on standing it is slowly transformed into [gamma]-glucose, equilibrium being reached when the [alpha] and [gamma] forms are present in the ratio 0.368:0.632 (Tanret, _Zeit. physikal. Chem._, 1905, 53, p. 692). It is convenient to refer to these two forms as [alpha] and [beta]. Lowry and Armstrong represent these compounds by the following spatial formulae which postulate a [gamma]-oxidic structure, and 5 asymmetric carbon atoms, i.e. one more than in the Fischer formulae. These formulae are supported by many considerations, especially by the selective action of enzymes, which follows similar lines with the [alpha]- and [beta]-glucosides, i.e. the compounds formed by the interaction of glucose with substances generally containing hydroxyl groups (see GLUCOSIDE).