6971-38-6Relevant articles and documents
A novel CAN-SiO2-mediated one-pot oxidation of 1-keto-1,2,3,4-tetrahydrocarbazoles to carbazoloquinones: Efficient syntheses of murrayaquinone A and koeniginequinone A
Chakraborty, Suchandra,Chattopadhyay, Gautam,Saha, Chandan
experimental part, p. 331 - 338 (2011/06/19)
One-pot oxidations of substituted 1-keto-1,2,3,4-tetrahydrocarbazoles (1) to carbazole-1,4-quinones (2) are efficiently carried out by CAN-SiO 2-mediated reaction. This generalized protocol was successfully extended to the synthesis of two naturally occurring carbazoloquinones: murrayaquinone A (2b) and koeniginequinone A (2g). A plausible mechanism for this novel reaction involves formation of a 9-hydroxy-2,3,4,9-tetrahydro-1H- carbazole-1-one followed by rearrangement to 1-hydroxycarbazole derivatives, which are further oxidized by cerium (IV) to carbazoloquinones.
Nitrosation of phenolic compounds: Effects of alkyl substituents and solvent
Gonzalez-Mancebo, Samuel,Lacadena, Javier,Garcia-Alonso, Yolanda,Hernandez-Benito, Jesus,Calle, Emilio,Casado, Julio
, p. 157 - 166 (2007/10/03)
Nitrosation reactions of phenol, o-cresol, 2,6-dimethylphenol, o-tert-butylphenol, 2-hydroxyacetophenone, and 2-allylphenol in water and water/acetonitrile were studied. Kinetic monitoring of the reactions was accomplished by spectrophotometric analysis of the nitrosated products at 345 nm. The dominant reaction was C-nitrosation via a mechanism consisting of an attack on the nitrosatable substrate by NO+/NO2H2+ followed by a slow proton transfer. The values of the rate constants of phenolic C-nitrosation were increased by electron donating substituents, and a good Hammett correlation was observed with ρ=-6.1. The results also revealed the strong effect of pH and the permitivity of the reaction medium on the rate constant, whose maximum values were observed for pH≈3, decreasing strongly for higher pH values. The study in water/acetonitrile with up to 25% acetonitrile showed that it is possible to inhibit the reaction strongly by increasing the percentage of the organic component. The conclusions drawn show that (i) it is possible to predict the rate of nitrosation of phenolics as a function of the meta-substituents on the phenol ring and (ii) the nitrosation of phenolics can be strongly inhibited by increasing the pH of the reaction medium as well as by lowering its dielectric constant.
Nitrosation kinetics of phenolic components of foods and beverages
Paz Ferna?ndez-Liencres,Calle, Emilio,Gonza?lez-Mancebo, Samuel,Casado?, Julio,Quintero, Bartolome?
, p. 119 - 125 (2007/10/03)
The kinetics of the reactions between sodium nitrite and phenol or m-, o-, or p-cresol in potassium hydrogen phthalate buffers of pH 2.5-5.7 were determined by integration of the monitored absorbance of the C-nitroso reaction products. At pH > 3, the dominant reaction was C-nitrosation through a mechanism that appears to consist of a diffusion-controlled attack on the nitrosatable substrate by NO+/NO2H2+ ions followed by a slow proton transfer step; the latter step is supported by the observation of basic catalysis by the buffer which does not form alternative nitrosating agents as nitrosyl compounds. The catalytic coefficients of both anionic forms of the buffer have been determined. The observed order of substrate reactivities (o-cresol ≈ m-cresol > phenol ? p-cresol) is explained by the hyperconjugative effect of the methyl group in o- and m-cresol, and by its blocking the para position in p-cresol. Analysis of a plot of ΔH# against ΔS# shows that the reaction with p-cresol differs from those with o- and m-cresol as regards the formation and decomposition of the transition state. The genotoxicity of nitrosatable phenols is compared with their reactivity with NO+/NO2H2+.
