Benzhydryl chlorides, nucleophilic reactions

Benzhydrylamine Derivatives Attachment of piperazine nitrogen directly to a benzhydryl carbon leads to a pair of compounds which show vasodilator activity, and which should be useful in disease states marked by impaired blood circulation. Reaction of piperonyl chloride (18) with a mixture of piperazine and piperazine dihydrochloride leads to the monoalkylation product (19). (It may be supposed that the mixture of free base and salt equilibrates to the monobasic salt, thus making the second amine less nucleophilic.) Alkylation of 19 by means of benzhydryl chloride then... 

Rate constants and products have been reported for solvolysis of benzhydryl chloride and /7-methoxybenzyl chloride in 2,2,2-trifluoroethanol (TFE)-water and-ethanol, along with additional kinetic data for solvolysis of r-butyl and other alkyl halides in 97% TFE and 97% hexafluoropropan-2-ol. The results are discussed in terms of solvent ionizing power Y and nucleophilicity N, and contributions from other solvation effects are considered. Comparisons with other 3 nI reactions show that the solvolyses of benzhydryl chloride in TFE mixtures are unexpectedly fast an additional solvation effect influences solvolysis leading to delocalized cations. 

Kinetic studies also provide other evidence for the SnI mechanism. If this mechanism operates essentially as shown on p. 298, the rate should be the same for a given substrate under a given set of conditions, regardless of the identity of the nucleophile or its concentration. In one experiment that demonstrates this, benzhydryl chloride (Ph2CHCl) was treated in S02 with the nucleophiles fluoride ion, pyridine, and triethylamine at several concentrations of each nucleophile.23 In each case the initial rate of the reaction was approximately the same when corrections were made for the salt effect. The same type of behavior has been shown in a number of other cases, even when the reagents are as different in their nucleo-philicities (see p. 348) as H20 and OH. ... 

Fig. 7 Plots of log k against pitR for nucleophilic reactions of water, azide ions and chloride ions (A) with benzhydryl and trityl cations.

The situation is different in experiment 3 of Figure 2.12. There, both SN1 reactions are carried out as competitive reactions benzhydryl chloride heterolyzes (just as fast as before) in the presence of equal amounts of both amines. The benzhydryl cation is now intercepted faster by the more nucleophihc pyridine than by the less nucleophilic triethylamine. The major product will be determined by the relative rates of the reaction of each nucleophile with the benzhydryl cation. The major product in this case is the pyridinium salt. 

In the case of triphenylsilane and trityl chloride, this reaction is first order in both reactants in benzene (233). The reaction rate for modified substrates indicates that with respect to R3CX, rate is a function of proclivity to ionize, trityl halides being more rapid than benzhydryl or allyl or tcr/-butyl halides. Indeed the latter required the presence of BBr3 as a catalyst. Within a given series. Cl > Br > I, phenylsilanes react more rapidly than alkyl silanes. A mechanism involving simultaneous nucleophilic attack of halide on silicon, and electrophilic attack on hydrogen by the carbonium ion is reasonable,... 

A very interesting paper80 reported studies of the reactions of several substituted benzhydryl carbenium ions, generated by laser flash photolysis, with halide ions in several solvents. This work provided the nucleophilicity N of chloride and bromide ions in several solvents. These data, along with the ionization rate constants and the solvolysis rate constants for the reactions of substituted benzyhdryl halides, was used to construct quantitative energy surfaces for the. S N 1 reactions of substituted benzhydryl halides in several solvents. 

If a carbocation will react with two nucleophiles to give the corresponding adducts, we would expect the adducts to be formed in the same ratios however the carbocation is formed. Although the decomposition of benzhydryl bromide (bromodiphenylmethane, 7) in 90% aqueous acetone at 50 °C in the presence of 0.1 M sodium azide is 335 times faster than the decomposition of the corresponding chloride 8, the proportion of alcohol 9 to azide 10 remains constant, pointing to a common intermediate, the carbocation 11, in both solvolyses (reactions 5.14). 

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