360 
Mr Fenton , Oxidation in Presence of Iron. 
Dioxyfumaric Acid. 
OH.C.COOH 
ii 
COOH.C.OH. 
When dioxymaleic acid is treated with a concentrated solution 
of hydrobromic acid it undergoes a remarkable change in crystal- 
line form without change of composition, the resulting product 
consisting of long hair-like needles. From the mode of formation 
of this modification and from the fact that its acid aniline salt 
appears to be more stable than that of the previously described 
modification, there seems little doubt that it is the fumaroid 
form. 
Both dioxymaleic and dioxyfumaric acids are fairly strong 
acids, their affinity-constants approaching that of oxalic acid. 
[Skinner, Trans. Chem. Soc. 1898. 483.] 
Dioxytartaric Acid. 
C(OH) 2 .COOH 
i 
C(OH) 2 .COOH. 
[Trans. Chem. Soc. 1895. 48 ; 1898. 71, 167 and 472.] 
When dioxymaleic acid is covered with glacial acetic acid and 
treated with rather more than the calculated quantity of bromine, 
at the ordinary temperature, it is oxidized almost quantitatively 
to dioxytartaric acid 
C 4 H 4 0 6 . 2H 2 0 + Br 2 = C 4 H G 0 8 + 2HBr. 
In this reaction the presence of water is essential, and it is 
shewn that the change is a reversible one, since dioxytartaric acid 
when heated with excess of hydrogen bromide yields dioxymaleic 
acid and free bromine. 
In this manner large quantities of pure dioxytartaric acid may 
be prepared in a very short time as a white crystalline powder 
melting at 114 — 115°. Previously this acid had only been 
obtained in relatively minute quantities from the sodium salt by 
the action of hydrogen chloride in ether, the product so prepared 
melting at 98°. 
Dioxytartaric acid is very easily soluble in water and is easily 
recognised by its sparingly soluble sodium salt and its charac- 
teristic osazone. It may be reduced to dioxymaleic acid either 
by hydrogen bromide as above mentioned, or by zinc and sulphuric 
acid. 
