The Typical Cellulose and the Cellulose Group 35 



(3) Some of the methods of acetylation certainly involve a 

 change of molecular weight, and we have no criterion of the 

 relation, in this respect, of the acetate to the original 

 cellulose. 



It must be understood, therefore, that the cellulose acetates 

 about to be described are of undetermined molecular weight, 

 and afford only an empirical expression of the number of OH 

 groups in the undetermined unit .(C 6 H 10 O 5 ), which itself 

 may vary under acetylation. 



These considerations affect the value of deductions to be drawn 

 from the composition of the acetates, as to the number of reactive 

 OH groups in the unit molecule of cellulose. 



On a priori grounds we should expect a maximum of 4OH in 

 the unit C 6 H 10 O 5 . For a long time, however, the ' triacetate' was 

 considered to represent the highest degree of acetylation. This 

 acetate, however, was obtained at an elevated temperature (180) at 

 which a variety of molecular complications are possible. 



Acetates have been obtained by the following methods : 

 (a) Interactions of cellulose and acetic anhydride. On 

 boiling cotton with acetic anhydride and sodium acetate, no 

 reaction occurs. Heated at 180 in a sealed tube, in the 

 proportion by weight of i of cellulose to 6 of the anhydride, 

 the cellulose is converted into the triacetate (Schutzenberger). 

 With the reagents in the proportion of i : 2, a mixture of 

 lower acetates is formed. The latter are insoluble in glacial 

 acetic acid ; the triacetate, on the other hand, is freely soluble. 

 The solution is highly viscous, and passes with extreme 

 slowness through filter paper. Filtration, however, is greatly 

 facilitated by addition of benzene to the solution. The acetate 

 also dissolves when heated with nitrobenzene, the solution 

 gelatinising on cooling, even when highly dilute. 



The cellulose acetates are easily saponified by dilute 

 solutions of the alkaline hydrates, more rapidly in presence of 

 alcohol (50 p.ct. vol.). 



D& 



