AN INFRARED STUDY OF THE REACTIONS OF MONOMETHYLAMINE AND TRIMETHYLAMINE WITH SI-O-SIHCL2 MONOLAYERS ON SILICA

High surface area silica was completely dehydroxylated by reaction with HSiCl3, leading to the formation of a monolayer of surface Si-O-SiHCl2 (I) groups. Interactions of I with methylamine (MA) or trimethylamine (TMA) at 22°C were followed by infrared spectroscopy. A series of reactions occurred with MA in which I was converted to a species II*, which was then converted to a species III*. The infrared bands of II* and III*, along with those of other surface species, were consistent with the formation of surface SiHCl(NHCH3):NH3(CH3)Cl groups. The reactions were reversible; degassing up to 100°C in vacuo restored I. The reactions with TMA were more complex. Small amounts of species similar to II* and III* were formed, agTM+. Degassing in vacuo up to 100°C restored I. Another surface of I which had been partially activated by heating above 350°C in vacuo formed appreciable amounts of species similar in band position to II* and III* along with TMA+, but surface Si-NH2 and NHCH3 species were formed upon removal of gas-phase TMA. The surface species in the second case were stable to degassing up to 400°C. The types and extent of reaction of TMA with I suggest that surface [TMAH+SiCl3-] groups were formed by decomposition of a I:TMA complex. Cyclic exposure of I to MA or TMA followed by degassing led to formation of surface Si-O-SiH[NH(CH3)] with MA, but bridging silazane species were formed with TMA, as in the reaction of NH3 with I.