Nitrosation of 2-acetylcyclohexanone. 2. Reaction in water in the absence and presence of cyclodextrins.
The kinetic study of the nitrosation of the enol of 2-acetylcyclohexanone (ACHE) has been performed in aqueous acid media in the absence and presence of alpha- and beta-cyclodextrin. The reaction is first-order with respect to both reactants concentration: [nitrite] and [ACHE]; but, unexpectly, the dependence of both [H(+)] or [X(-)] (X(-) = Cl(-), Br(-), or SCN(-)) is not simple first-order. The experimental findings have been explained on the basis of a reaction mechanism that considers the formation of a chelate-nitrosyl complex intermediate in steady-state. Addition of both alpha-cyclodextrin (alpha-CD) or beta-cyclodextrin (beta-CD) diminishs strongly the observed rate constant, k(o), measured either for enol-nitrosation or for enol-ketonization reactions. In the case of beta-CD, the inhibition effect is explained through the formation of nonproductive inclusion complexes between the enol (EH) and beta-CD of 1:1 stoichiometry. Nevertheless, the quantitative interpretation of k(o)-[alpha-CD] profiles requires the assumption that the inclusion complexes formation of both 1:1 (EH/alpha-CD) and 1:2 (EH/alpha-CD(2)) stoichiometries. In the case of enol-ketonization, the EH/alpha-CD complex is nearly as reactive as the uncomplexed enol.
Iglesias
Emilia
E
Departamento de Química Física e E. Q. I. Facultad de Ciencias, Universidad de La Coruña, 15071-La Coruña, Spain. afemilia@udc.es
D000465:Algorithms; D003505:Cyclodextrins / Q000737:chemistry*; D003512:Cyclohexanones / Q000737:chemistry*; D007202:Indicators and Reagents; D007700:Kinetics; D015394:Molecular Structure; D015538:Nitrosation; D012995:Solubility; D013237:Stereoisomerism; D014867:Water / Q000737:chemistry
D003505:Cyclodextrins; D003512:Cyclohexanones; D007202:Indicators and Reagents; D014867:Water; C477259:2-acetylcyclohexanone