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 only 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 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. 



