18720-46-2Relevant academic research and scientific papers
Substituent effects upon rates of deamination and base strengths of substituted N-tritylamines
Canle,Demirtas,Maskill
, p. 1748 - 1752 (2007/10/03)
Substituted N-tritylamines undergo deamination in aqueous acidic solution containing organic cosolvents, and follow a pseudo first-order specific acid-catalysis rate law (kobs = k0 + kH[H3O+]); the products are the corresponding trityl alcohols in equilibrium with the trityl carbenium ions, and ammonium ions. The change from 4,4′-dimethoxy-to 4,4′,4″-trimethoxy-tritylamine increases reactivity by a factor of about 30 in both k0 and kH, but N-alkyl and N-aryl groups have much greater effects (ca. 106 for both k0 and kH for 4,4′-dimethoxytritylamine) which are largely independent of the nature of the N-alkyl and N-aryl groups. The anions of the catalytic strong acids (perchlorate, chloride, bromide, and nitrate) have only small effects as also does the concentration of acetonitrile as cosolvent; ethanoic acid as cosolvent is mildly rate-enhancing. Substituents in the aniline residue of N-(4,4′-dimethoxytrityl)-anilines have virtually no effect upon either k0 or kH (ρ = 0 for both). The results are interpreted by a mechanism involving a pre-equilibrium heterolysis of the (substituted) tritylammonium ion to give an ion-molecule pair which may undergo diffusional or acid-catalysed dissociation before the (substituted) trityl cation undergoes equilibrium nucleophilic capture by water. Base strengths of some substituted N-tritylamines have been measured; the substituted N-trityl group causes all amines (aliphatic and aromatic) to be comparably strongly basic (pKBH- ca. 9).
Hydrolysis of Aryl and Alkyl Isothiocyanates in Aqueous Perchloric Acid
Joseph, V. Bernadette,Satchell, Derek P. N.,Satchell, Rosemary S.,Wassef, Wasfy N.
, p. 339 - 342 (2007/10/02)
The slow hydrolysis of aromatic and aliphatic isothiocyanates in water is promoted by added perchloric acid.The hydrolysis leads first to the thiocarbamic acid, but this species decomposes rapidly to the (protonated) amine, and is not normally detected.Convenient rates of hydrolysis are obtained at 50 deg C when >/= 6.0 mol dm-3.The effects of substituents, temperature, and acid concentration on the observed rate constants have been studied.Aliphatic isothiocyanates are somewhat more reactive than aromatic derivatives, but the effect of substituent changes is generally small, with electron release favouring reaction.Substit uents close to the nitrogen atom hinder reaction.The value of ΔS(excit.) is typically -120 to -220 J K-1 mol-1, and analysis of the acidity dependence by the excess acidity approach shows m(excit.) ca. 0.8.Addition of water to the isothiocyanate N=C double bond via a mechanism involving simultaneously proton transfer to nitrogen and nucleophilic attack by water at carbon with a cyclic transition state is proposed.The carbamic acids formed by the aliphatic isothiocyanates are sufficiently basic for them to be increasingly trapped as their protonated forms when > 9.0 mol dm-3.
