ABSTRACT
Experimental Details . . . . . . . . . . . . . . . . . . . . . . . . 277
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
Untreated Silica . . . . . . . . . . . . . . . . . . . . . . . . . . 278
Chemical and H-D Exchange Probes for 1508C Activated Silica . . . . . . . . . . . . . . . . . . . . . . . . . 279
Relative Rates of Reaction of Various
Silanol Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
The accessibility of surface silanols toward hydrogen-sequestering agents with steric dimensions that
increase in the order ZnMe2, BCl3, TiCl4, AlMe3, and Me3SiNHSiMe3 (HMDS) were compared spectro-
scopically and gravimetrically for a fumed and a precipitated silica. The H-D exchange reaction was simi-
larly studied with D2O, ND3, and deuterated methanol, isopropyl alcohol, and tert-butyl alcohol. The surface
areas of the two silicas are similar, but the silanol density on the precipitated silica is about twice that on the
fumed silica. Approximately equal fractions of the total number of OH groups per square nanometer
undergo H-D exchange with a given probe, and this fraction decreases as the size of the molecule increases.