Document Detail


Mechanisms of acid decomposition of dithiocarbamates. 5. Piperidyl dithiocarbamate and analogues.
MedLine Citation:
PMID:  18722406     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
In this work, the acid cleavage at 25 degrees C in 20% v/v aqueous ethanol of a series of analogues of piperidine dithiocarbamate X(C2H4)2NCS2(-) (X = CH2, CHCH3, NH, NCH3, S, O) was studied. The pH-rate profiles were obtained in the range of H(o)-5 and pH 5. They all presented a dumbell shaped curve with a plateau from which the pH-independent first-order rate constant k(o) (or the specific acid catalysis k(H)) was calculated, in addition to the acid dissociation constant of the free (pKa) and conjugate acid (pK(+)) species of the DTC. LFERs of the kinetically determined pKa and pK(+) versus pKN (pKa of parent amine) were used to characterize the reactive species and the structure of the transition state of the rate-determining step. For X = CH2, CH3CH the values of k(H) agree with those of alkDTCs in the strong base region of the Brønsted plot of log k(H) versus pKN where the transition state is close to a zwitterion formed by intramolecular water-catalyzed S-to-N proton transfer of the dithiocarbamic acid. However, when X = NH, CH 3N, O, S, the reactive species is the DTC anion, which is as reactive as an arylDTC, and similarly, the pK(+) values correspond to a parent amine that is about 3-4 pK units more basic. The solvent isotope effect indicated that the acid decomposition of these dithiocarbamate anions is specifically catalyzed by a Hydron anchimerically assisted by the heteroatom through a boat conformation.
Authors:
Eduardo Humeres; Byung Sun Lee; Nito Angelo Debacher
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2008-08-22
Journal Detail:
Title:  The Journal of organic chemistry     Volume:  73     ISSN:  1520-6904     ISO Abbreviation:  J. Org. Chem.     Publication Date:  2008 Sep 
Date Detail:
Created Date:  2008-09-15     Completed Date:  2008-11-14     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  2985193R     Medline TA:  J Org Chem     Country:  United States    
Other Details:
Languages:  eng     Pagination:  7189-96     Citation Subset:  IM    
Affiliation:
Department of Chemistry, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil. humeres@mbox1.ufsc.br
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MeSH Terms
Descriptor/Qualifier:
Acids / chemistry*
Hydrogen-Ion Concentration
Kinetics
Molecular Conformation
Piperidines / chemistry*
Solvents / chemistry
Stereoisomerism
Thiocarbamates / chemistry*
Chemical
Reg. No./Substance:
0/Acids; 0/Piperidines; 0/Solvents; 0/Thiocarbamates; 0/piperidyl dithiocarbamate

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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