6533b82bfe1ef96bd128e03f

RESEARCH PRODUCT

Role of solvent and base in the silanization reaction of silicas for reversed-phase high-performance liquid chromatography

subject

description

Reversed-phase packings were synthesized by reaction of n-alkyldimethylchloro- and trifluoroacetoxysilanes with silicas of 15 and 25 nm pore size, employing tetrahydrofuran, N,N-dimethylformamide, benzene, diethyl ether, dichloromethane and acetonitrile as solvents and triethylamine, pyridine, triazole, quinuclidine, 2,4- and 2,6-lutidine and imidazole as bases. With dichloromethane as solvent and 2,6- lutidine as base, n-alkyldimethyltrifluoroacetoxysilanes did not yield n-alkyl ligand densities higher than those obtained with n-alkyldimethylchlorosilanes under identical conditions. With a given base and given n-alkyldimethylchlorosilane the solvent type was found to exert a noticeable influence on the kinetics of the silanization reaction, which can be interpreted in terms of three cooperative ettects. The reactivity of solvents increased in the sequence tetrahydrofuran < benzene < diethyl ether < acetonitrile < dichloromethane < N,N-dimethylformamide. Basic catalysts are known to accelerate the kinetics of the silanization reaction (owing to their acid-binding capacity) when n-alkylchlorosilanes are employed as reagents. Of the tertiary amines studied, imidazole was found to be much more reactive, which can be explained by the formation of reactive imidazolide intermediates via nucleophilic attack on the silane.