The sulfur trioxide mechanism for acyclic esters

In contrast, the acid-catalyzed hydrolysis of alkyl selenates is A-2158. The actual species which undergoes decomposition to alcohol and sulfur trioxide is probably the zwitterion as in the case of phosphate monoester monoanions. Evidence for sulfur trioxide as the reactive initial product of the A-1 solvolysis is obtained from the product compositions arising with mixed alcohol-water solvents. The product distribution is identical to that found for sulfur trioxide solvolysis, with the latter exhibiting a three-fold selectivity for methanol. Although the above entropies of activation and solvent deuterium isotope effects do not distinguish between the conventional A-l mechanism and one involving rate-limiting proton transfer, a simple calculation, based on the pKa of the sulfate moiety and the fact that its deprotonation is diffusion controlled. 

The spontaneous reaction of aryl sulfates is particularly detectable when the aryl moiety bears strongly electron withdrawing substituents. A logarithmic plot of rate against pKa of the corresponding phenol is linear with a slope of 

Comparison of the various mechanistic facets of the above sulfate reactions to those of the acid-catalyzed hydrolysis of the Bunte salts (RSS03 ) suggests that the mechanisms are identical, i.e. A-1163 

In (65) only electrophilic catalysis of the scission of the S-S bond is involved, a situation also encountered in the acid-catalyzed hydrolysis in weekly nucleophilic media (acetic acid-1% water) of certain aryl sulfinyl sulfones substituted with electron-donating substituents (66)164, viz. 

Heterolytic scission of the -S-S- bond in which only electrophilic assistance is involved is the exception rather than the rule in reactions involving bond fission of this type. Kice et a/.165,166 have demonstrated that a variety of S-S bond cleavages involve concomitant electrophilic and nucleophilic catalysis including (a) the formation of aryl thiolsulfones from aryl thiolsulfinates and aryl sulfinic acids and (b) the hydrolysis (acetic acid—1% water and 60% 

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