Mandelo-nitrile Glucose
glucoside CN

(_c_) C_{6}H_{5}.CHOH.CN + H_{2}O = C_{6}H_{5}.CHO + HCN
Mandelo-nitrile Benzaldehyde Hydrocyanic
acid

GENERAL PROPERTIES OF GLUCOSIDES

As a rule, glucosides are easily soluble in water. They are generally
extracted from plant tissues by digestion with water or alcohol. In most
cases, the enzyme which is present in other cells of the same tissue must
be killed by heating the material, in a moist condition, to the temperature
of boiling water, before the extraction is begun, as otherwise the
glucoside will be hydrolyzed as rapidly as it is extracted from its parent
cell. Maceration or otherwise bruising the tissue, after the enzyme has
been destroyed, facilitates the extraction. The glucosides, after
extraction and purification by recrystallization, are generally colorless,
crystalline solids, having a bitter taste and levorotatory optical
activity. This latter property is remarkable, as most of them are compounds
of the strongly dextrorotatory _d_-glucose.

Many of the natural glucosides have marked therapeutic properties and are
largely used as medicines; others are the mother-substances for brilliant
dyes; for example, indican, from which indigo is obtained, and the alizarin
glucosides.

Several hundred different glucosides have been isolated from plant tissues,
and their properties described, and this number is being added to
constantly, as the methods of isolation and study are improved. They may be
classified into groups, according to the nature of the organic compound
other than sugars which they yield when hydrolyzed. The following
descriptions of the occurrence, constitution, products of hydrolysis, and
special properties of typical members of each of the several different
classes of glucosides will serve to illustrate their general relationship
to plant growth.

THE PHENOL GLUCOSIDES

=Arbutin=, C_{12}H_{16}O_{7}, is obtained from the leaves of the bear berry
(_Arctostaphylos uva-ursi_), a small evergreen shrub. When hydrolyzed by
mineral acids or emulsin, it yields glucose and hydroquinone.

C_{12}H_{16}O_{7}+H_{2}O = C_{6}H_{12}O_{6}+C_{6}H_{4}(OH)_{2}.

Hydroquinone has strongly antiseptic properties. Arbutin is both an
antiseptic and a diuretic, and is used in medicine.

=Phloridzin=, C_{21}H_{24}O_{