Mr Fenton, Oxidation in Presence of Iron. 
363 
is glycollic acid. From these and other considerations it is shewn 
that the substance produced is glycollic aldehyde. This aldehyde 
which is of special interest as being the first representative of the 
(aldose) sugars had hitherto onty been obtained in aqueous 
solution and mixed with other substances, but by the present 
method it is easily isolated in the pure state and in the crystalline 
form. In the decomposition mentioned above a small quantity of 
an acid (apparently glyoxylic) is formed at the same time and, in 
order to obtain the pure aldehyde, the mixture is neutralized with 
chalk and the calcium salt removed by treatment with alcohol. 
On evaporation of the alcoholic solution in a vacuum desiccator 
and heating to 40°, the aldehyde is left in a pure state in form of 
a wax-like solid. 
The molecular weight of this product as ascertained by the 
freezing-point method corresponds to the double formula C 4 H 8 0 4 , 
but its aqueous solution still gives the same osazone as before 
with phenylhydrazine. 
If the amorphous aldehyde be heated to about 100° in a vacuum 
the greater part undergoes polymerization in the manner to be 
described below, but during this operation crystals usually appear 
in the upper part of the apparatus. These crystals were subse- 
quently further examined [Fenton and Jackson, Trans. Chem. Soc. 
1899. 575] and found to be the pure aldehyde. In this case also 
the molecular weight determined by the freezing-point method 
initially indicates the doubled formula but, after the aqueous 
solution has remained standing for several hours, the number 
obtained exactly corresponds to the single formula. This point is 
of much interest in view of the fact that crystalline glyceraldehyde 
which had just previously been isolated by Wohl, and is the 
second representative of the aldose sugars, shews an exactly 
similar behaviour [Wohl, Ber. 1898, 31. 2394]. 
Glycollic aldehyde crystallizes in colourless transparent oblique 
plates melting at 95 — 97°. It has a sweet taste, is fairly easily 
soluble in water and may to a considerable extent be vaporized 
unchanged. 
In order to prepare the crystalline aldehyde the initial puri- 
fication above described is not necessary ; dioxymaleic acid is 
decomposed by warming with water, and the resulting solution 
fractionally distilled under reduced pressure ; the aldehyde passes 
over at 90 — 100° under a pressure of about 20 mm. as a syrupy 
liquid which crystallizes on standing. 
