Alkyl chlorides anchimeric assistance

There is much additional evidence to support the postulate that the effect of neighboring sulfur is due to anchimeric assistance. Cyclohexyl chloride undergoes solvolysis in ethanol-water to yield a mixture of alcohol and ether. As usual for secondary alkyl substrates, reaction is SnI with nucleophilic assistance from the solvent (see Sec. 14.17). A C5H5S— group on the adjacent carbon can speed... 

Thionyl chloride Is highly electrophilic, and converts the alcohol to the corresponding alkyl chloride via an addition-elimination process (with neighbouring group or anchimeric assistance of the SMe group). 

The nucleophilic hydroxyl oxygen of the carboxylic anion, generated by deprotonatlon of the carboxylic acid, undergoes a nucleophilic substitution reaction with the alkyl chloride formed In the previous step (with anchimeric assistance of the SMe group) to give the ester product. 

The kinetic data in Table 1 demonstrates that S-4 anchimeric assistance is not important in the hydrolysis of acyclic alkyl chlorides [e.g., n-hexyl chloride solvolyzes 1.8 times faster than PhS(CH2)3Cl in 20 mole % aqueous dioxane at 100°C ]. Some data on cyclic systems will be presented here to demonstrate that proximity effects can drastically affect S-4 participation. The formation of (35) and (36) from treatment of 3j -methanesul-fonyloxy-5-a-methylthiocholestane (34) with tetrapropylammonium acetate was rationalized in terms of S-4 participation as shown. Ireland and Smith found that the rates of solvolysis of (37) and (38) were slower [/Crei(77°C) = 0.46 and 0.21, respectively] than the rate for trans-4-t-huty ... 

The reaction occurs much more rapidly than a regular 5 2 process on a primary alkyl chloride because the sulfur atom assists in ejecting chloride as a leaving group. The role that sulfur plays in this reaction is called anchimeric assistance. 

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