174 PREPARATION OF METHYLATED SUGARS 



(A) Mannitol monoacetone : 



Crystallises in prisms melting at 85. 

 Specific rotation in alcohol +26'4 (c=2 - 7). 



(B) Tetramethyl mannitol monoacetone : 



Liquid boiling at 137-140/11 mm. 

 Specific rotation in alcohol + 39'0 (c=2*8). 



(C) Tetramethyl mannitol : 



Liquid boiling at 167-169/13 mm. 

 Obtained crystalline on standing. 

 Specific rotation in alcohol 12'5. 



The experimental evidence bearing on the constitution of 

 mannitol diacetone is in the meantime somewhat incomplete. 

 Alkylation of the compound gave dimethyl mannitol diacetone 

 (b.p. 140-141/13 mm.), and, on hydrolysis, a crystalline 

 dimethyl mannitol was obtained (m.p. 93; [a] D 8'8 in 

 alcohol). The position of the methyl groups in the latter 

 compound has not yet been determined, but there can be 

 little doubt that they occupy positions 3 and 4 in the carbon 

 chain. Inspection of the above results will show that the 

 behaviour of mannitol triacetone on hydrolysis may also be 

 explained to some extent by the assumption that the com- 

 pound exists in two, hitherto unrecognised, isomeric forms, 

 the arrangement of the substituent groups A 19 A 2 , and A 3 

 being respectively cis, trans, cis, and trans, trans, cis. Until 

 further work has been done on the constitution of dimethyl 

 mannitol, it is perhaps premature to speculate too freely on 

 the validity of this assumption, which certainly adds a new 

 feature of complexity to the condensation reactions of opti- 

 cally active compounds, but our unsuccessful attempts to 

 isolate a second form of mannitol triacetone render this 

 alternative unlikely, and the existence of a monoacetone 

 derivative is also opposed to it. 



In the meantime, therefore, the bulk of the evidence 

 points to the idea that the terminal alcoholic groups in 



