Synthesis of Organofunctionalized Silica Gel from Tributylstannylated Silicic Acid and Acyl Chloride

Abstract

KEY WORDSOrganofunctionalized Silica Gel / Acy! Chloride / Tributylstannylated Silicic Acid / Silano!/ Water Glass/ Silica gels modified with organofunctional groups are used widely as industrial materials. The broadened usage such as hybrid materials, immobilization of enzymes, and convenient catalysts requires various synthetic methods of the functionalized gel. 1 • 2 The straightforward reaction of silica gel and organic compounds is generally utilized for the modification as a practical procedure. In addition, the use of oligomeric and/or monomeric silanols obtained from sodium metasilicate or water glass (WG) through neutralization has been investigated as a convenient route to organofunctionalized silica gel. 3 -8 However, such silanols are readily transformed into silica gel by selfcondensation. This sometimes causes difficulties to handle in organofunctionalization. Therefore, recently, the protected monomeric silanols, tetraalkoxysilanes, which are free from the above problems, are often used for incorporation of organic groups into silica gel. 9 We have investigated a new versatile precursor of functionalized silica gel and postulate that tributylstannyl ester of silicic acid (PTBS), the protected polymeric silanol, is a possible candidate. 10 The use of PTBS having Sn-0 bond, which is soluble in common organic solvents such as hexane, benzene, dichloromethane, and chloroform, should make possible efficient reactions with organic compounds. It is well known in organotin chemistry that stannyl ethers having Sn-O bond react with acyl halides easily to afford esters and organotin halide. 11 • 12 In a similar manner, the reaction of acyl chlorides and PTBS having Si-0-Sn bonds is thought to form Si-OC = 0 bonds with the elimination of tributyltin chloride as shown in Scheme 1. Such reaction seems to represent the incorporation of an organofunctional group into silica gel by the use of PTBS. On the other hand, Si-O bond is known to be more stable against halogenation than Sn-0 bond. 13 However, the possibility of the formation of Si-Cl bond, as shown in the reaction of trimethylsilylated silica gel with a well known halogenating agent such as thionyl chloride, is not thoroughly excluded. 6 In this type of reaction, the formation of chlorinated silica gel and tributyltin ester is presumed. Accordingly, with interest in chemoselectivities of the reaction at Si-0-Sn bond, the reaction of PTBS and acyl chlorides is examined as t To whom all correspondence should be addressed. a new approach toward the synthesis of organofunctionalized silica gel in this work. EXPERIMENTAL General ProcedurePTBS was prepared from bis(tributyltin) oxide and water glass according to the reported procedure. The molecular weight (Mn) of PTBS was estimated by GPC (polystyrene standard) to be in the region from 3000 to 15000. 10 The ratio of Si/Sn in PTBS determined by gravimetric analysis was ca. 2.7.The reactions of PTBS with acyl chlorides 1 or diacyl chloride 3 were carried out at room temperature for 6 h in benzene, dimethylformam...

Synthesis of Mesoporous Silicate Gel from Tributylstannyl Ester of Polymeric Silicic Acid and Chlorosilane

“…Gravimetric analysis was conducted as reported. 17 IR spectra were recorded on a JASCO FT/ IR 230. Gel permeation chromatographic (GPC) analysis was carried out on a TOSOH HLC-8020 chromatograph equipped with a refractive index detector.…”

Synthesis of hybrid resins via polysiloxane with methacryloyloxy groups

“…Other reagents were used as supplied from commercial sources. Gravimetric analysis was conducted according to the reported procedure 7. The same MPS derivatives prepared in the previous work were employed for the copolymerizations 1.…”

Synthesis of organofunctionalized polysiloxane from polymeric tributylstannyl ester of silicic acid and chlorosilanes

“…5 In fact, the reaction of acyl chlorides and PTBS having SiOOOSn bonds is reported to form SiOOCAO bonds with the elimination of tributyltin chloride in our previous work. 6 In addition, silica gel having SnOO bonds enables an efficient introduction of organofunctional groups on its surface by the reaction with chlorosilanes at room temperature. 7 From such previous information, the use of PTBS for the reactions with chlorosilanes is expected to proceed under neutral conditions, in which stannyl groups are substituted into the silyl group readily with the elimination of tributyltinchloride as shown in Scheme 1.…”