Triphenylmethyl chloride, absorption

Initiation of tetrahydrofuran polymerisation by Ph C SbClg has been studied speetrophotometrieally by Ledwith and co-workers (20). Decay of the characteristic triphenylmethyl cation absorption, in methylene chloride was represented by the expression... 

Probably the first isolation of a triphenylmethyl carbocation salt was by Gomberg and Cone (68) who successfully prepared the perchlorate from the corresponding chloride. A direct synthesis from the carbinol was achieved at about the same time (69), and more recently the preparation of the perchlorate and tetrafluoroborate have been much improved (70). Anderson (7/) succeeded in recording the characteristic visible absorption spectrum of the ion in concentrated acids, and Fairbrother and Wright (72) observed the same absorption when triphenylmethyl bromide was ionised in benzene in the presence of stannic bromide. 

Led with and his co-workers [50] have also studied the mechanism of initiation by triphenylmethyl salts in some detail, by following the decay of the characteristic visible absorption maximum of the initiating cation. The kinetic equation which has been established for both methylene chloride and THF solvents is... 

Protonation of the olefin, or protonation and subsequent dehydration of the parent alcohol, gives cations which are then subjected to laser excitation or steady-state irradiation. Cations generated in this way were identified by their characteristic absorption spectra, which also indicated cation stability over the time scale of the individual experiments by the lack of change in their absorption spectra. Among the numerous cations generated in acidified solution for photochemical studies are the xanthyl and thioxanthyl [7-15], dibenzosuberenyl [10], triphenylmethyl [10,15], a,co-diphenylpolyenyl [16], and 1,1-diarylethyl [17] cations. Media included acetonitrile acidified with trifluoroacetic acid (TFA-ACN) or aqueous sulfuric acid [7-9,11,14,15], TEA in 2,2,2-trifluoro-ethanol (TFA-TFE) [10,12,13], n-heptane acidified with TFA [9], and BFj-etherate in methylene chloride [16]. The absorption spectral data for several cations have been previously reviewed [6]. Characterization of the cation excited states will be discussed in Section III. 

---