- Kinetic and equilibrium studies of σ-adduct formation and substitution in the reactions of sulphite ions with some alkyl and aryl ethers and thioethers
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Kinetic and equilibrium results are reported for the reactions of sulphite with the ethyl and phenyl ethers of 2,4,6-trinitrophenol and 2,4,6-trinitrothiophenol in 80/20 (v/v) water/DMSO. In each case 1:1 and 1:2 adducts are observed by reaction of sulphite at one or two unsubstituted ring positions respectively. In the case of the ethyl derivatives these adducts are long-lived; however, the phenyl derivatives rapidly yield 2,4,6-trinitrobenzene-sulphonate, the substitution product. This difference is attributed to a change in the nature of the rate-determining step, from nucleophilic attack with the phenyl derivatives to leaving group departure with the alkyl derivatives.
- Crampton, Michael R.,Holmes, Anthony J.
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p. 787 - 792
(2007/10/03)
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- Kinetic and Equilibrium Studies of ?-Adduct Formation and Nucleophilic Substitution in the Reactions of Hydroxide Ions with 2,4,6-Trinitrophenyl Sulfides and Ethers
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Kinetic and equlibrium data are reported for reaction of hydroxide ions in 20/80 DMSO/water (v/v) with a series of 4'-substituted phenyl 2,4,6-trinitrophenyl sulfides, 1, and with ethyl thiopicrate, 2, ethyl picrate, 3, phenyl picrate, 4, and 1,3,5-trinitrobenzene, 5.In each case a rapid reaction is observed involving reversible hydroxide addition at an unsubstituted ring-position.In the case of 1-4 this is followed by slower, irreversible attack at the 1-position leading to the formation of picric acid.The Hammett ρ value for equilibrium addition of hydroxide to the 3-position of 1 is 0.98, and the ρ value for rate constants for attack at the 1-position is 0.62.The results are discussed in terms of the electronic and steric effects of the 1-substituents.Comparison of 1-5 indicates that changing from an OR to SR group introduces additional steric crowding.However for the reactions studied changing from R = Et to R = Ph has little steric consequence.
- Chamberlin, Rachel,Crampton, Michael R.,Knight, Roland L.
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p. 2986 - 2998
(2007/10/02)
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- Kinetic and Equilibrium Studies of ?-Adduct Formation and Nucleophilic Substitution in the Reactions of Ethyl Thiopicrate with Aliphatic Amines in Dimethyl Sulfoxide
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Kinetic and equilibrium results are reported for the reaction of ethyl thiopicrate with butylamine, pyrrolidine and piperidine in dimethyl sulfoxide.The most rapid reaction involves attack at the unsubstituted 3-position to give anionic ?-adducts.The rate-limiting step in this process changes from nucleophilic attack by amine with butylamine to proton transfer from the zwitterionic intermediate with piperidine; pyrrolidine shows intermediate behaviour.Attack by amine at the 1-position results in displacement of the ethylthio group, although intermediates are notobserved during this process.It is suggested that base catalysis observed in the reaction with pyrrolidine may result from rate-limiting proton transfer from the zwitterionic intermediate. 1H NMR measurements using 0.1 mol dm-3 solutions of substrate show that the displaced ethanethiolate ion may attack ring-carbon atoms of either unreacted substrate or substitution products.
- Chamberlin, Rachel,Crampton, Michael R.
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