Kinetic and equilibrium studies of anilinoalkanesulfonate formation.

(1)H NMR studies of the reactions of some hydroxyalkanesulfonates, 1, with aniline derivatives, 2, show the formation at equilibrium of anilinoalkanesulfonates, 3. Kinetic studies in water are consistent with a mechanism involving dissociation of 1 to give the parent aldehyde, which reacts with 2 to give a carbinolamine. Acid-catalysed dehydration of the carbinolamine yields an iminium ion which reacts rapidly with sulfite to give the product 3. Study of the variation with pH of the rate constants of the reaction indicates a change in the nature of the rate-determining step from carbinolamine formation to carbinolamine dehydration as the pH is increased. Variations in values of rate and equilibrium constants with the nature of 1 and 2 are discussed in terms of electronic and steric effects.

Carbanion reactivity, kinetic and equilibrium studies of sigma-adduct formation and elimination in the reactions of 4-nitrobenzofurazan derivatives with nitroalkane anions.

1H NMR studies are reported of the reactions in [2H(6)]-DMSO of 4-nitrobenzofurazan, 2a, and its 7-chloro- and 7-methoxy-derivatives, 2b and 2c respectively, with anions derived from nitromethane, 3, nitroethane, 4, and 2-nitropropane, 5. The initial reactions result in sigma-adduct formation by carbanion attack at the 5-position of 2a-c and in the case of reaction of 2a with 5 the adduct at the 7-position is also observed. These reactions may be followed by base catalysed elimination of nitrous acid to yield anionic alkene derivatives. Kinetic and equilibrium measurements of these reactions were made spectrophotometrically in methanol. The carbon nucleophilicities of the carbanions decrease in the order 3> 4> 5, as also found in their reactions with benzhydrylium cations, and are much lower than the nucleophilicities of some cyano-substituted carbanions. Comparison with corresponding sigma-adduct forming reactions of 1,3,5-trinitrobenzene, TNB, show that here 2 and TNB have similar electrophilicity, although the value of the intrinsic rate coefficient k(o) = 0.05, for reaction of 2 is rather lower than that, k(o) = 0.20, for the TNB reactions. Literature data suggest that for reaction with a variety of nucleophiles 2 and TNB show similar electrophilicities. Measurements of the rates of elimination of nitrous acid from some 5-adducts in methanol catalysed by methoxide ions are reported. Values of rate constants may be influenced both by steric requirements at the reaction centre and by the electronic effects of the 7-substituent.

Rate-limiting proton-transfer in the sigma-adduct forming reactions of 1,3,5-trinitrobenzene and 4-nitrobenzofuroxan with substituted anilines in dimethyl sulfoxide.

Kinetic and equilibrium results are compared for the reactions in dimethyl sulfoxide of 1,3,5-trinitrobenzene, 1, and 4-nitrobenzofuroxan, 4, with a series of substituted anilines in the presence of Dabco or in, some cases, quinuclidine. pKa values for the corresponding anilinium ions are reported. The reactions of 1and 4 are likely to proceed through nucleophilic attack by the aniline to yield zwitterionic intermediates which may transfer an acidic proton to the bases present to yield the anionic adducts 9 or 12 respectively. In the formation of 9 from 1 the proton transfer step is rate-limiting; however, the slower interconversion of 4 and its zwitterion leads to only partial rate-limiting proton transfer in the formation of 12. Results with substituted anilines including 2-substituted and N-methyl aniline indicate that steric effects are not a major factor in determining rates of proton-transfer in these systems. Contrary to previous reports no evidence was found for a strong interaction between 1 and Dabco in DMSO.

The Strecker reaction: kinetic and equilibrium studies of cyanide addition to iminium ions.

Kinetics studies are reported of the reactions of benzylidene benzylamine 4a, and of benzylidene allylamine 4b, with cyanide in aqueous buffers to give the corresponding [small alpha]-aminonitriles. The results allow the calculation of values of rate and equilibrium constants for reaction of the iminium ions formed from 4a and 4b with cyanide ions. These values are compared with those, obtained from the hydrolysis reactions, for reaction of the iminium ions with hydroxide ions and with water. Comparison with some other iminium ions reveals that those formed from 4a and 4b are relatively unreactive due to the possibilities of charge delocalisation.

Sigma-adduct formation and oxidative substitution in the reactions of 4-nitrobenzofurazan and some derivatives with hydroxide ions in water.

The reactions of hydroxide ions with 4-nitrobenzofurazan, 1a, 4-nitrobenzofuroxan, 1b, and with three 4-nitro-7-substituted benzofurazans have been examined using 1H NMR and UV-visible spectroscopies. In each case initial reaction is at the 5-position to give an anionic sigma-adduct. Kinetic and equilibrium results are reported. NMR spectra show that in the case of 1a oxidation of the anionic adduct yields 4-nitro-5-hydroxybenzofurazan. In the case of 1b rearrangement of the 5-hydroxy adduct to the thermodynamically more stable 7-hydroxy adduct, possibly by a Boulton-Katritzky mechanism, precedes oxidation. When the 7-substituent in the 4-nitrobenzofurazan is Cl, OMe or OPh the eventual product is 7-hydroxy-4-nitrobenzofurazan produced by nucleophilic displacement of the substituent.

Kinetic and equilibrium studies of sigma-adduct formation and nucleophilic substitution in the reactions of 2-phenoxy-3,5-dinitropyridine and 2-ethoxy-3,5-dinitropyridine with aliphatic amines in dipolar aprotic solvents.

The reactions of aliphatic amines with 2-phenoxy-3,5-dinitropyridine, 4, and 2-ethoxy-3,5-dinitropyridine, 5, in DMSO result in the rapid reversible formation of anionic sigma-adducts at the 6-position. Kinetic studies show that proton transfer from the initially formed zwitterions to base may be rate-limiting. Slower reactions result, except in the case of 5 and piperidine, in displacement of the 2-substitutent via intermediates which have lower thermodynamic stabilities than their 6-isomers. Base catalysis of the substitution process is attributed in the case of 4 to rate-limiting proton transfer from zwitterionic intermediates, but in 5 to acid catalysis of ethoxide departure (SB-GA mechanism). X-Ray crystallography of 5 shows a planar non-strained structure although the structure of 2-piperidino-3,5-dinitropyridine, 10c, shows distortion resulting from steric interactions of the 2- and 3-substituents. Kinetic and equilibrium results are compared with those for related reactions of the more sterically strained 2,4,6-trinitrobenzene derivatives. Results for the reactions of 4 and 5 with pyrrolidine in three dipolar aprotic solvents are compared. Values of equilibrium constants for sigma-adduct formation decrease in the order DMSO > DMF >> Acetonitrile, while values of rate constants for proton transfer are in the reverse order.