A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMFOUNDS. . 197
and glyoxylic acid). To obtain the pure acid the solution of the
calcium salt is precipitated with oxalic acid, filtered, and the filtrate
neutralized with lead carbonate. The lead salt thus obtained is crystallized,
and the pure salt dissolved in water. Sulphuric acid is then
added, but not sufficient to decompose all the lead glycollate, the
solution evaporated to dryness, and the residue exhausted with ether.
On evaporating the ether, glycollic acid crystallizes out, forming,
when quite pure, laTge regular crystals which are very soluble in
water, deliquesce in moist air, and melt at 79°. Glycollic acid exists
in the juice of unripe grapes, and in the green leaves of the Virginiacreeper
(Ampelopsis hederacea).
Calcium Glycollate (C«HsOs)2Ca is sparingly soluble in cold water,
and crystallizes from a hot saturated solution in colourless needles
usually grouped in stars. By adding silver nitrate to its solution a
white crystalline precipitate of silver glycollate is formed. Copper
glycollate is a greenish-blue crystalline powder, which is obtained by
mixing a solution of copper sulphate with a hot concentrated solution
of the calcium salt.
Olycollyl Chloride C^H2OC12 is obtained by the action of phosphorus
pentachloride on the acid; it is identical with monochlorace'tyl chloride,
and yields with water monochloracetio acid. The formation of the
chloride is explained by the equation :—
CH2.OH CH,C1
+ 2PCL =I + 2POG1
CO.OH C0C1
GLYCOLLJO ETHEKS,
Ethylglycollic Acid CH^O^^CO.OH is produced by the action
of sodium ethylate upon sodium monochloracetate. To prepare the
free acid the copper-salt is decomposed by hydrogen sulphide. It is
a thick, colourless liquid, boiling at about 200°, and having a very
sour taste like glycollic acid.
Ethyl Glycollate CHgfOHJCO.OOjiHg, a neutral liquid, soluble in
•water, is obtained, together with glycollic anhydride, by heating
ethyl mouoohloracetate with sodium glycollate:—
CH,C1 CE..0H CH.. CH..OH ^
| " + | " =| | + | | ">O + NaCl
CO.OC2H6 CO.ONa CO. CO.OC^ CO '
Methyl Glycollate CH^OCjH^CO.OCgHj is conveniently prepared
by dissolving sodium in absolute alcohol, and mixing this solution
gradually with ethyl monochloracetate; the mixture ia heated for
some time, and the ether separated from the alcohol by fractional
distillation. It is a colourless liquid, boiling at 155°, and possessing
a sweetish taste.