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Substituent effects on enol nitrosation of 1,3‐diketones
Author(s) -
Iglesias Emilia
Publication year - 2012
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20710
Subject(s) - chemistry , enol , tautomer , nitrosation , aqueous solution , reaction rate constant , pentane , keto–enol tautomerism , ketone , medicinal chemistry , photochemistry , kinetics , organic chemistry , catalysis , physics , quantum mechanics
The keto–enol tautomerism of 3‐chloro‐pentane‐2,4‐dione (ClPD) was studied in aqueous micellar solutions of cationic, anionic, and nonionic surfactants. The enol of ClPD tautomerizes rapidly in water to the equilibrium proportions of the keto form, K E =0.55; whereas the keto–enol conversion of 3‐ethyl‐pentane‐2,4‐dione (EPD) is a much slower reaction than the enol nitrosation. Kinetics of enol –nitrosation of both ClPD and EPD in aqueous acid medium using nitrous acid shows first‐order dependence upon [ketone] and linear or curve relationships of the observed rate constant, k o , as a function of [nitrite] or [H + ]; the observed behavior depends on the molecular structure of diketone and varies with the experimental conditions. The reaction is strongly catalyzed by Cl − , Br − , or SCN − , and the observed rate constant shows a curve dependence on [Br − ] or [SCN − ], which is more pronounced at high acidity. The results are consistent with a reaction mechanism in which the nitrosation occurs initially on the enol–oxygen and releasing a proton to form a chelate–nitrosyl complex intermediate in steady state. Fine differences on the mechanistic spectrum of enols nitrosation are considered on the basis of the molecular structure of the diketone. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 668–679, 2012