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Vinylic Cations from Solvolysis. XXI.1 1 2 Solvent Effects on the External Ion Return and the Internal Return in Several
 

Summary: 836
Vinylic Cations from Solvolysis. XXI.1 1 2 Solvent Effects on
the External Ion Return and the Internal Return in Several
Vinylic Solvolyses
Zvi RapPoport* and Yitzhak Apeloig
Contribution from the Department of Organic Chemistry, The Hebrew University,Jerusalem,
Israel. Received January 17, I974
Abstract: The solvolyses of cis- and trans-1,2-dianisyl-2-phenylvinylbromides (5-Br and 6-Br), the cis chloride (5-CI), and
the cis and trans mesylates (5-OMS and &OMS)in 80%EtOH gave the ethers 5-OEt and 6-OEt and the ketone 25. Solvoly-
sis of 5-Br and 6-Br in 1:l AcOH-HCOOH gave the acetates 5-OAc and 6-OAc and the vinyl formates which decomposed
to 25, while solvolysis of 5-Br in 1:l AcOH-AczO gave 5-OAc and 6-OAc. Cis-trans isomerization of the vinyl halides was
observed in all the solvents, and strong common ion rate depression was observed in the RCOOH media. Both phenomena
were used to show the appearance of both the free ion 7 and the ion pair 8 during the solvolysis-isomerization, to calculate
the ionization rate constant (kjon)and to evaluate the extent of the external ion return and the internal return. The solvent
effects on kion (1:l AcOH-HCOOH > 80% EtOH > AcOH > 1:l AcOH-AczO), on the internal return (AcOH -1:l
AcOH-HCOOH > 80% EtOH -1:l AcOH-AC~O),and on the external ion return (1:l AcOH-Ac2O > AcOH > 1:l
AcOH-HCOOH > 80% EtOH) are discussed in terms of the ionizing power, dissociating power, and nucleophilicity of the
solvents. The use of the titrimetric rate'constant(k,) as a model for k,,, is discussed in relation to several kinetic parameters.
The intermediacy of ion pairs in the solvolysis of saturat-
ed compounds was extensively ~ t u d i e d . ~In vinylic solvoly-

  

Source: Apeloig, Yitzhak - Department of Chemistry, Technion, Israel Institute of Technology

 

Collections: Chemistry