OP ARTS AND SCIENCES. 121 



Oxidation of Cur cumin. 



Our experiments on this subject can be divided into two classes, 

 those in wiiich we made a complete oxidation of the substance, aud 

 those in whicli a partial oxidation was obtained by using au insufficient 

 amount of the oxi(lizin<f airent, or one less ener<i;etic. 



CumpU'te Oxidation. — As Ivanow-Gajewsky states that he obtained 

 terephthulic acid by the action of jjotassic dichromate and sulphuric acid 

 on cnrcuinin, we turned our attention first to this experiment. Un- 

 fortunately only an abstract of his paper is accessible to us, so that we 

 ciitild not liud the exact conditions ol" his oxidation ; we have tliere- 

 fure varied the conditions in several ways, but always with the same 

 result. It will be sufficient to describe a single experiment. Half a 

 gramme of curcumin was mixed with sulpliuric acid previously diluted 

 with its own volume of water, and solid potassic dichromate added ; 

 the action was extremely violent, accomj^anied by great evolution of 

 heat and strong- effervescence ; the gas given off was carbonic dioxide. 

 At the end of the process there was no 'insoluble substance in the 

 licpiid, which was therefore distilled until it was reduced to a small 

 volume. The strongly acid distillate, treated with argentic oxide, after 

 filtering and concentration deposited long flattened needles, which 

 looked exactly like argentic acetate, and were proved to consist of this 

 substance by the following silver determination : — 



0.1812 gr. of salt dried at 100° gave 0.1559 gr. of AgCl. 



Calculated for AgCoH^Oo Found. 



Silver G4.68 ' " 64.76 



There was no other volatile acid in the distillate, and no organic 

 matter could be found in residue from the distillation. If the action 

 was moderated by using more dilute sulphuric acid, the phenomena 

 were the same, except that it was necessary to start the reaction by the 

 aid of heat. In none of the products of the oxidation of curcumin 

 with potassic dichromate could any terephthalic acid be found, they 

 consisted only of acetic acid and carbonic dioxide. 



If curcumin is dropped into fuming nitric acid it dissolves with a 

 hissing noise and formation of nitrous fumes and hydrocyanic acid. 

 The red liquid thus obtained gave no precipitate with water; on evap- 

 oration it deposited brownish crystals, principally oxalic acid, but it 

 was not further examined. In this respect we confirm the resuhs of 

 Daube, who also obtained oxalic acid from curcumin and nitric acid. 



