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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 23, Number 8
BKCSDE 23(8)
August 20, 2002 

 
Title
Marked Difference in Solvation Effects and Mechanism between Solvolyses of Substituted Acetylchloride with Alkyl Groups and with Aromatic Rings in Aqueous Fluorinated Alcohol and in 2,2,2-Trifluoroethanol-Ethanol Solvent Systems
Author
Yunghee Oh, Gyeong Gu Jang, Gui Taek Lim, Zoon Ha Ryu
Keywords
Solvolysis, Aqueous fluorinated alcohol
Abstract
Solvolyses rate constants of trimethylacetyl chloride (2), isobutyryl chloride (3), diphenylacetyl chloride (4) and p-methoxyphenylacetyl chloride (5) in 2,2,2-trifluoroethanol (TFE)-water, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)-water and TFE-ethanol solvent systems at 10℃ are determined by a conductimetric method. Kinetic solvent isotope effects (KSIE) are reported from additional kinetic data for methanolyses of various substituted acetylchlorides in methanol According to the results of those reactions analyzed in terms of rate-rate profiles,extended Grunwald-Winstein type correlations, application of a third order reaction model based a general base catalyzed (GBC) and KSIE values. Regardless of the kind of neighboring groups (CH3- or Ph-groups) of reaction center, for aqueous fluorinated alcohol systems, solvolyses of 2, 3, 4, and 5 were exposed to the reaction with the same mechanism (a loose SN2 type mechanism by electrophilic solvation) controlled by a similarity of solvation of the transition sate (TS). Whereas, for TFE-ethanol solvent systems, the reactivity depended on whether substituted acetyl chloride have aromatic rings (Ph-) or alkyl groups (CH3-); the solvations by the predominant stoichiometric effect (third order reaction mechanism by GBC and/or by push-pull type) for Ph- groups (4 and 5) and the same solvation effects as those shown in TFE-water solvent systems for CH3- groups (2 and 3) were exhibited Such phenomena can be interpreted as having relevance to the inductive effect ( σI) of substituted groups; the plot of log (KSIE) vs. σI parameter give an acceptable the linear correlation with r = 0.970 (slope = 0.44 ± 0.06, n = 5).
Page
1089 - 1096
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