360 Mr Fenton, Oxidation in Presence of Iron. 



DlOXYFUMARIC ACID. 



OH.C.COOH 



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.] 



DlOXYTARTARIC 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 6 . 2H 2 + Br 2 = C 4 H 6 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. 



