Aromatic activated nucleophilic substitution. Catalysis by phenols and by salts of piperidinodefluorination in benzene

Abstract

Investigation of the dependence of reaction rate of piperidine with 1-fluoro-2,4-dinitrobenzene in benzene on the concentration of added phenols gives the rate law (A). ‘Salt’ stands for piperidinium phenoxides. Rate//_{[ArF][PIP]free}=k₀+k_PIP[PIP]_free+k_ArOH[ArOH]_free+k_Salt[Salt](A). Catalytic coefficients for the phenols are, within experimental error, independent of the acid strength of the catalyst. This reaction is also powerfully accelerated by tetra-n-butylammonium chloride whereas tetra-n-butylammonium perchlorate has no rate effect. In sharp contrast, the rate of the corresponding reaction of 1-chloro-2,4-dinitrobenzene in benzene is neither accelerated by phenols nor by tetra-n-butylammonium chloride. These findings are discussed in terms of catalysis of the reaction of the fluoro-compound by phenols or by salts of basic anions (bifunctional for the former) of the decomposition of the addition intermediate into products.