Aromatic nucleophilic substitution in nucleophilic surfactants. Comparison with alkoxide reactions

Abstract

The reactions of 2,4-dinitrochloro- and fluorobenzene (DNC and DNF) with the alkoxide ions of choline, propargyl alcohol, and 2,2,2-trifluoroethanol give ether intermediates which react readily with hydroxide ion. The nucleophilicities of the alkoxides toward DNC and DNF (in parentheses) are: Me3N+CH2CH20- 19 (27), HC=CCH20~ 63 (132), CF3CH20-11 (10), relative to OH- in water at 25.0 °C. The second-order rate constants (104¿OH, 1. mol-1 s-1) for reaction of DNF, DNC, or the ethers toward OH- are: DNF, 1200; DNC, 1.42; -OCH2CF3,9.1; -OCH2C=CH, 3.7; -CH2CH2N+Me3,9.1. Micelles of hexadecyl(2-hydroxyethyl)dimethylammonium bromide (h-Ci6H33N+Me2CFl2CH2OH Br-, la) are effective reagents toward DNC and DNF at high pH and for ionization of the hydroxy group pA"a ~12.3, estimated kinetically for reactions of DNF and DNC in la and up to 0.15 M OH-. In 0.01 OH- the reactivity of the 2,4-dinitrophenyl ether of la in micelles of la is 260 times that of the corresponding ether of choline in water, and the overall rates of nucleophilic attack on DN F and DNC in micelles of la are 6000 and 14 000, respectively, relative to reaction in water