172 PREPARATION OF METHYLATED SUGARS 



Presumably then a difference in stability is to be expected 

 in the three acetone residues in mannitol triacetone in virtue of 

 the different effect of cis and trans grouping on the molecular 

 balance. A further difference in stability might also be 

 expected to arise from the fact that one acetone residue (A 2 ) 

 substitutes the hydrogen atoms of two secondary hydroxyl 

 groups, while the linkage of the remaining ketonic residues 

 (A l and A 3 ) involves one primary alcohol group in each case. 

 This factor, although no doubt present, does not seem to 

 exercise any marked effect on the stability of the different 

 groups as glucose diacetone, a compound in which the same 

 conditions prevail, undergoes hydrolysis in one stage only. 

 This at once points to the fact that the stability of the acetone 

 residues is controlled by their stereochemical arrangement. 



It is of course inadmissible to claim that results obtained 

 with ring structures such as glucose and fructose must find 

 exact analogies in the case of an open chain compound such 

 as mannitol, but a close parallel has nevertheless been estab- 

 lished in that carefully regulated hydrolysis of mannitol 

 triacetone removes the ketonic residues simultaneously but 

 at different rates. It is thus possible to isolate the inter- 

 mediate compounds indicated in the following scheme : 



Mannitol triacetone > mannitol diacetone > 

 mannitol monoacetone > mannitol. 



The reaction is naturally a troublesome one to control, but 

 was effected by heating a 2*5 per cent, solution of the triace- 

 tone compound in 70 per cent, alcohol, containing O'l per cent, 

 of hydrogen chloride, to 40 for about three hours. A con- 

 tinuous polarimetric record of the optical changes gave figures 

 which, when plotted in a curve, showed two indefinite maxima 

 followed by a regular fall to a constant value. On stopping 

 the reaction at intermediate stages, it was found that, in the 

 neighbourhood of the first maximum, the main product was 

 a mannitol diacetone mixed with varying amounts of mannitol 



