Esters vs. Thioesters

Electrostatic potential map for 2-mercaptoethanol reveals most acidic sites as positively-charged regions (in blue). 

Benzoyl chloride reacts with 2-mercaptoethanol in base to give an ester. When the reaction is monitored carefully, the rapid buildup of an intermediate, X , of molecular formula C9H10O2S, is observed. This is slowly transformed into the ester of the same molecular formula. Although ester formation is known to be a multi-step process, X does not correspond to any of the usual intermediates in ester formation. What is going on here  

The base may control some of this chemistry by selectively converting 2-mercaptoethanol into a stronger nucleophile. Display an electrostatic potential map for 2-mercaptoethanol. Which proton, that attached to oxygen or sulfur, is more acidic, that is, more likely to be removed by strong base Rationalize your result. 

The ultimate reaction product, the ester , is an isomer of X. Logically, the ester must be more stable than X. Examine the various esters, and identify the most stable molecule. Is it more stable than X Is it an ester  

It is not at all obvious why esters should have lower energies than thioesters. It is generally observed that SH bonds are about. 03 au (20 kcal/mol) weaker than OH bonds. Given this, which bond must be stronger, S-CO or O-CO Estimate the difference in bond energies between the two  

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Because of their previous findings that a,/l-unsaturated thioesters were more reactive than their ester counterparts in Diels-Alder reactions85, Hart and coworkers86 performed a systematic study of the cycloaddition reactions of a,/l-unsaturated thioesters and a,ft-unsaturated selenoesters with several dienes. Thermal reactions were compared with Lewis acid catalyzed reactions at room temperature (equation 28 and Table 2). The results clearly demonstrated that use of a Lewis acid enhanced the regioselectivity (entries 1 vs 2, 3 vs 4, 5 vs 6 and 7 vs 8) as well as the endo (with respect to the thioester or selenoester group) selectivity (entries 5 vs 6 and 7 vs 8). 

How similar are the two classes of proteinases How do the structural differences affect the activity of CP Are the relative rates for acylation and deacylation similar in CP and SP How does the more polarizable and less electronegative sulfur compare to oxygen along the formation of the TI, and during hydrolysis of a thioester vs. an ester ... 

The C(0)-0 bond length in esters is significantly shorter than the C(sp )-0 bond of aryl or vinyl ethers. In a study of the geometry of thioesters in crystal structures by Zacharias et al. [27] it was found that the bond length does not differ from that of the corresponding bond in aryl and vinyl monosulfides (O 1.336 [21] vs. 1.367 A S 1.767 vs. 1.763 A [27]). This suggests that there is more electron delocal-... 

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