Silylation
Encyclopedia
Silylation is the introduction of a (usually) substituted silyl group (R3Si–) to a molecule.
Nearly all functional groups which present a problem in gas chromatogaphic separation (hydroxyl, carboxylic acid, amine, thiol, phosphate) can be derivatized by silylation reagents. It involves the replacement of an acidic hydrogen on the compound with an alkylsilyl group, for example, trimethylsilyl
(-SiMe3). The derivatives are generally less polar, more volatile and more thermally stable. The introduction of a silyl group(s) can also serve to enhance mass spectrometric properties of derivatives, by producing either more favorable diagnostic fragmentation patterns of use in structure investigations, or characteristic ions of use in trace analyses employing selected ion monitoring and related techniques.
Similarly, silylation is used to introduce silyl groups as protecting group
s. A general technique is to deprotonate the substrate with a suitable strong base (e.g. butyl lithium
), and allow it to react with a silyl chloride (e.g. trimethylsilyl chloride
). An auxiliary base is usually used to remove the hydrogen chloride formed:
Desilylation is the reverse of silylation: the silyl group is exchanged for a proton. Various fluorides (e.g. sodium
, potassium
, tetra-n-butylammonium fluoride
s) are popular for this purpose.
Nearly all functional groups which present a problem in gas chromatogaphic separation (hydroxyl, carboxylic acid, amine, thiol, phosphate) can be derivatized by silylation reagents. It involves the replacement of an acidic hydrogen on the compound with an alkylsilyl group, for example, trimethylsilyl
Trimethylsilyl
A trimethylsilyl group is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom [−Si3], which is in turn bonded to the rest of a molecule...
(-SiMe3). The derivatives are generally less polar, more volatile and more thermally stable. The introduction of a silyl group(s) can also serve to enhance mass spectrometric properties of derivatives, by producing either more favorable diagnostic fragmentation patterns of use in structure investigations, or characteristic ions of use in trace analyses employing selected ion monitoring and related techniques.
Similarly, silylation is used to introduce silyl groups as protecting group
Protecting group
A protecting group or protective group is introduced into a molecule by chemical modification of a functional group in order to obtain chemoselectivity in a subsequent chemical reaction...
s. A general technique is to deprotonate the substrate with a suitable strong base (e.g. butyl lithium
Butyl lithium
Butyllithium may refer to one of three isomeric organolithium reagents used in chemical synthesis:*n-Butyllithium, abbreviated BuLi or nBuLi*sec-Butyllithium, abbreviated sec-BuLi or sBuLi...
), and allow it to react with a silyl chloride (e.g. trimethylsilyl chloride
Trimethylsilyl chloride
Trimethylsilyl chloride, also known as chlorotrimethylsilane is a silyl halide, with a variety of different uses in chemistry. It has the formula 3SiCl, and under standard conditions it is a colourless liquid, which is stable in the absence of water...
). An auxiliary base is usually used to remove the hydrogen chloride formed:
- RH → R− + H+
- R− + R'3SiCl → R-SiR'3 + Cl−
Desilylation is the reverse of silylation: the silyl group is exchanged for a proton. Various fluorides (e.g. sodium
Sodium fluoride
Sodium fluoride is an inorganic chemical compound with the formula NaF. A colorless solid, it is a source of the fluoride ion in diverse applications. Sodium fluoride is less expensive and less hygroscopic than the related salt potassium fluoride....
, potassium
Potassium fluoride
Potassium fluoride is the chemical compound with the formula KF. After hydrogen fluoride, KF is the primary source of the fluoride ion for applications in manufacturing and in chemistry. It is an alkali metal halide and occurs naturally as the rare mineral carobbiite...
, tetra-n-butylammonium fluoride
Tetra-n-butylammonium fluoride
Tetra-n-butylammonium fluoride or TBAF is a quaternary ammonium salt with the chemical formula 4N+F-. It is commercially available as the trihydrate and as a solution in tetrahydrofuran....
s) are popular for this purpose.