Benzyl chloride, neutral hydrolysis

Neutral Hydrolysis Studies. Investigations of neutral (pH-independent) hydrolysis kinetics in sediment/water systems were conducted for three organophosphorothioate insecticides (chlorpyrifos, diazinon and Ronnel), 4-(p-chlorophenoxy)butyl bromide, benzyl chloride, and hexachlorocyclopentadiene. 

Benzyl chloride hydrolysis proceeds via a third mechanism (Sj.1). Results of studies of benzyl chloride hydrolysis ( 1) in distilled water and EPA-13 and EPA-2 sediment/water systems are summarized in Table V. Results for this compound include only overall first-order disappearance rate constants, but the data clearly show that the hydrolysis rate is independent of the fraction sorbed to sediment. Thus, the conclusion is again made that neutral hydrolysis proceeds via similar rate constants in both the aqueous and sediment-sorbed phases. 

In the hydrolysis of benzyl chloride, the leaving group is chloride anion. When benzyl fluoride is hydrolyzed in alkaline or neutral media, the leaving group is fluoride anion, which is a worse leaving group than chloride anion because the carbon-fluorine bond is much stronger than the carbon-chlorine bond 443 kJ (106 kcal/mol) vs. 328 kJ (78 kcal/ mol), respectively. 

The balance between the S l and 8 2 reactions can be altered by changes in the solvent or by suitable substituents. Thus we have already seen (Table 5.2) that polar solvents accelerate reactions of neutral alkyl derivatives RX but retard their S 2 reactions with anionic nucleophiles. In such cases, an increase in solvent polarity favors the S l reaction, and a decrease favors the S 2. This is seen nicely in the case of borderline reactions such as that of benzyl chloride. In aqueous alcohol, hydrolysis is of an intermediate character, hydroxide ion accelerating the reaction, which, however, is not of first order in HO. In the more ionizing solvent, formic acid, for-molyis is of zeroth order in formate ion, the reaction being S l. In acetone, on the other hand, a poor ionizing solvent, benzyl chloride readily undergoes normal 5 2 reactions. Thus ... 

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