36 Cellulose 



(b) Cellulose and acetic anhydride in presence of zint 

 chloride. In presence of a relatively minute proportion of 

 zinc chloride, cellulose and acetic anhydride react at 110-120. 

 The product, according to Franchimont, is the triacetate 

 described above. According to later investigations, however, 

 the acetylation proceeds further under these conditions, the 

 numbers obtained indicating the formation of a tetracetate, and 

 sometimes still higher numbers have been obtained. The 

 following numbers show the quantitative relationship of the 

 higher acetylated derivatives of a compound C 6 Hi O 5 : 



Yields on saponi- 



fication 



C H Acetic acid Cellulose 



Triacetate . . C 12 H 16 O 8 288 50-0 5-5 62-1 56-2 

 Tetracetate . . C U H 18 O 9 330 50-9 5-6 727 49-1 

 Pentacetate. . C 16 H 20 Oi 372 51 6 5-3 80-6 



In dealing with the evidence as to the composition of these 

 products, however, we must further remember that the formula 

 C 6 H 10 O 5 has only a statistical value, i.e. that the molecule 

 of cellulose is a complex aggregate ; and if the molecule is 

 partially resolved during acetylation, this may occur by way of 

 hydrolysis or addition of OH groups. It is more than 

 probable that, in presence of ZnCl 2 , the acetylation is com- 

 plicated in this way. It is always to be observed that, on 

 pouring the product of the reaction into water, a fluorescent 

 solution is obtained ; and, further, that the cellulose regene- 

 rated from acetates prepared by this method is oxidised by 

 cupric oxide in alkaline solution (Fehling's solution). These 

 reactions indicate the liberation of the CO groups of the 

 original cellulose during acetylation, and the reaction is not of 

 such simplicity that we can draw any certain conclusions from 

 the products as to the problematical O atom or atoms in the 

 unit C 6 H 10 O 5 . 



(c) Cellulose and acetic anhydride in presence of iodine. 



