No abstract

The reaction of ethyl 2,4,6-trinitrophenyl ether with aniline in dimethyl sulfoxide containing Dabco occurs in two stages. The first gives 5, the σ -adduct intermediate on the substitution pathway, which has been identified spectroscopically. The second yields 2,4,6-trinitrodiphenylamine, the substitution product. Kinetic studies show that proton transfer is rate limiting both in the formation of the intermediate and in its subsequent acid-catalysed decomposition. Phenoxide is a considerably better leaving group than ethoxide and the substitution reactions of phenyl 2,4,6-trinitrophenyl ethers and phenyl 2,4-dinitronaphthyl ether with aniline in DMSO occur without the accumulation of intermediates. The kinetics indicate both uncatalysed and base-catalysed pathways. The kinetic and equilibrium data for reaction of the ethyl and phenyl ethers are compared with data for σ -adduct formation from 1,3,5-trinitrobenzene and aniline.Key words: nucleophilic substitution, proton transfer, base catalysis, σ -adducts

A kinetic study is reported of the exchange reactions of substituted phenoxide ions with some ring-substituted 2,4,6-trinitrophenyl ethers in water. The βrønsted diagrams formed by plotting log k, where k is the second-order rate constant for reaction, versus pK a show a distinct change in slope when ΔpK a = 0 (ΔpK a being the difference in pK a values of the leaving group and nucleophile). This is consistent with a two-step process involving a discrete σ-adduct intermediate rather than a concerted process. From the measured β values for forward and reverse processes, the overall effective charge map has been constructed.

No abstract

Reactions of morpholine in dimethyl sulphoxide at unsubstituted ring positions of 1,3,5-trinitrobenzene, and phenyl 2,4,64rinitrophenyl ether, yield anionic a-adducts via zwitterionic intermediates. Reactions at the 1-position of phenyl 2,4,64rinitrophenyl ether, phenyl 2,4-dinitronaphthyl ether, and phenyl 2,4-dinitrophenyl ether result in substitution of the phenoxy groups. In both these reaction types proton-transfer is rate-limiting. Comparison of kinetic and equilibrium data with those for corresponding reactions of piperidine shows that rate constants for proton transfer are similar for the two amines, but equilibrium constants for zwitterion formation have lower values for morpholine, the less basic amine. Implications for base catalysis are discussed.