ISSN:
0894-3230
Keywords:
Organic Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Direct 1H, 13C and 19F NMR spectroscopic analysis was carried out on the carbocationic intermediate generated in the interaction of tin(IV) chloride (SnCl4) with the adduct [4, CH3CH(OiBu)OCOCF3] of isobutyl vinyl ether (IBVE) and trifluoroacetic acid (CF3CO2H), either in the presence or in the absence of tetrabutylammonium chloride. The reactions were to mimic the living cationic polymerization of IBVE by the 4-SnCl4 initiating system (with added nBu4NCl) that was also found in this study. In CD2Cl2 solvent at -78°C, the 1H and 13C NMR analysis revealed the formation of a carbocationic intermediate [CH3C+H(OiBu)] that is in a rapid exchange equilibrium with the covalent counterpart 4. For the first time, the cation formation was further supported by 19F NMR analysis on the counteranionic part (CF3COO-) in 4, where, with SnCl4, the CF3 group gave a broadened signal that appeared clearly downfield relative to that in the covalent form. These and other results, which are in close correlation with the corresponding polymerizations, demonstrated the following: (i) the SnCl4-assisted generation of carbocationic species from the covalent ester 4; (ii) a rapid exchange between the cation and its covalent precursor 4; (iii) the relatively high cationic concentration in the salt-free system, where no living polymerization occurs; and (iv) the effective suppression of the cationic species in the presence of the salt, which proved to be the prime key factor for living polymerization.
Additional Material:
9 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/poc.610080411