Kinetics and mechanism of the addition of triphenylphosphoniocyclopentadienide to tetrachloro-p-benzoquinone

Autor:	Juan Palou, Rosa Valero, C. Dennis Hall, Peter Speers, Francisco Pérez Pla
Rok vydání:	1991
Předmět:	chemistry.chemical_classification Acid catalysis chemistry.chemical_compound Cyclopentadiene Chemistry Ylide Stereochemistry Yield (chemistry) Chloranil Entropy of activation Rate-determining step Benzoquinone Medicinal chemistry
Zdroj:	J. Chem. Soc., Perkin Trans. 2. :1925-1932
ISSN:	1364-5471 0300-9580
DOI:	10.1039/p29910001925
Popis:	The kinetics and mechanism of the reaction of triphenylphosphoniocyclopentadienide 1 with tetrachloro-p-benzoquinone (chloranil 2a) to yield 2,3,5-trichloro-6-(3-triphenylphosphoranylidene-cyclopenta-1,4-dienyl)-p-benzoquinone 3 in dichloromethane solution are reported. The rate limiting step was found to be electrophilic attack of tetrachloro-p-benzoquinone on the aromatic cyclopentadiene ring of the ylide. A thermochemical study of the system showed a small enthalpy and a large negative entropy of activation in agreement with the existence of a highly polar betaine as ah intermediate in the reaction. The proposed mechanism involves bimolecular transfer of a proton to a molecule of ylide. No evidence was found either for the formation of a π-complex or for acid catalysis of the reaction.
Databáze:	OpenAIRE
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