Silylation: Difference between revisions
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{{Short description|Process of addition of silyl group(s) to compounds}} |
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{{expand|date=March 2009}} |
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{{Confuse|silanization|sialylation}} |
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'''Silylation''' is the introduction of a (usually) substituted silyl group (R<sub>3</sub>Si–) to a molecule. |
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'''Silylation''' is the introduction of one or more (usually) substituted silyl groups (R<sub>3</sub>Si) to a molecule. Silylations are core methods for production of [[organosilicon chemistry]]. [[Silanization]] involves similar methods but usually refers to attachment of silyl groups to solids.<ref>{{cite book |doi=10.1002/0471238961.1909122516011605.a01.pub3 |chapter=Silylating Agents |title=Kirk-Othmer Encyclopedia of Chemical Technology |year=2017 |last1=Pape |first1=Peter G. |pages=1–15 |isbn=9780471238966 }}</ref> |
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==Of organic compounds== |
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Nearly all functional groups which present a problem in [[Gas chromatography|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]] (-SiMe<sub>3</sub>). 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 pattern]]s of use in structure investigations, or characteristic ions of use in trace analyses employing selected ion monitoring and related techniques.<ref>http://www.sigmaaldrich.com/analytical-chromatography/analytical-reagents/derivatization-reagents/silylation.html</ref> |
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:[[File:Bis(trimethylsilyl)acetamide.svg|220px|thumb|[[Bis(trimethylsilyl)acetamide]], a popular reagent for silylation]] |
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Alcohols, carboxylic acids, amines, thiols, and phosphates can be silylated. The process involves the replacement of a proton or an anion with a trialkylsilyl group, typically [[trimethylsilyl]] (-SiMe<sub>3</sub>), as illustrated by the synthesis of a trimethyl[[silyl ether]]s from alcohols and [[trimethylsilyl chloride]] (Me = CH<sub>3</sub>): |
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:{{chem2|ROH + Me3SiCl → ROSiMe3 + HCl}} |
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Generally a base is employed to absorb the HCl coproduct. |
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[[Bis(trimethylsilyl)acetamide]] ("BSA", Me<sub>3</sub>SiNC(OSiMe<sub>3</sub>)Me is an efficient silylation agent. The reaction of BSA with alcohols gives the corresponding trimethyl[[silyl ether]], together with acetamide as a byproduct (Me = CH<sub>3</sub>):<ref>{{cite journal |doi=10.15227/orgsyn.063.0079 |title=2-Methyl-2-(Trimethylsiloxy)pentan-3-one |journal=Organic Syntheses |year=1985 |volume=63 |page=79|first1=Steven D.|last1=Young|first2=Charles T.|last2=Buse|first3=Clayton H.|last3=Heathcock }}</ref> |
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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: |
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:{{chem2|2 ROH + MeC(OSiMe3)NSiMe3 → MeC(O)NH2 + 2 ROSiMe3}} |
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==Use of silylation== |
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: RH → R<sup>−</sup> + H<sup>+</sup> |
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Silylation has two main uses: manipulation of functional groups and preparation of samples for analysis. |
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===Manipulation of functional groups=== |
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Desilylation is the reverse of silylation: the silyl group is exchanged for a proton. Various fluorides (e.g. [[sodium fluoride|sodium]], [[potassium fluoride|potassium]], [[tetra-n-butylammonium fluoride]]s) are popular for this purpose. |
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Often silylation is employed to protect OH and NH groups. The derivatives, silyl ethers and silyl amides, are resilient toward many reagents that would attack their precursors. The other main role of silylation is to trap [[silyl enol ether]]s, which represent a reactive tautomer of many carbonyl compounds. |
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===Silylation for analysis=== |
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The introduction of a silyl group(s) gives derivatives of enhanced volatility, making the derivatives suitable for analysis by [[gas chromatography]] and electron-impact [[mass spectrometry]] (EI-MS). For EI-MS, the silyl derivatives give more favorable diagnostic [[fragmentation pattern]]s of use in structure investigations, or characteristic ions of use in trace analyses employing selected ion monitoring and related techniques.<ref>{{cite web|url=http://www.sigmaaldrich.com/analytical-chromatography/analytical-reagents/derivatization-reagents/silylation.html |title=Silylation of Non-Steroidal Anti-Inflammatory Drugs|author1=Luis-Alberto Martin|author2=Ingrid Hayenga|website=sigmaaldrich.com|access-date=24 September 2023}}</ref><ref>{{cite book |title=Handbook of Derivatives for Chromatography |edition=2nd|last=Blau |first=Karl |author2=J. M. Halket |year=1993 |publisher=[[John Wiley & Sons]] |isbn= 0-471-92699-X |url=http://eu.wiley.com/WileyCDA/WileyTitle/productCd-047192699X.html }}</ref> |
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===Desilylation=== |
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Desilylation is the reverse of silylation: the silyl group is exchanged for a proton. Various fluoride salts (e.g. [[sodium fluoride|sodium]], [[potassium fluoride|potassium]], [[tetra-n-butylammonium fluoride]]s) are popular for this purpose.<ref>Mercedes Amat, Sabine Hadida, Swargam Sathyanarayana, and Joan Bosch "Regioselective Synthesis of 3-Substituted Indoles: 3-Ethylindole" Organic Syntheses 1997, volume 74, page 248. {{doi|10.15227/orgsyn.074.0248}}</ref><ref>Nina Gommermann and Paul Knochel "N,N-Dibenzyl-n-[1-cyclohexyl-3-(trimethylsilyl)-2-propynyl]-amine from Cyclohexanecarbaldehyde, Trimethylsilylacetylene and Dibenzylamine" Organic Syntheses 2007, vol. 84, page 1. {{doi|10.15227/orgsyn.084.0001}}</ref> |
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==Of metals== |
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[[File:FpTMS.png|170px|right|thumb|CpFe(CO)<sub>2</sub>Si(CH<sub>3</sub>)<sub>3</sub>, a trimethylsilyl complex.]] |
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{{main|Transition metal silyl complexes}} |
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[[Coordination complex]]es with silyl ligands are well known. An early example is CpFe(CO)<sub>2</sub>Si(CH<sub>3</sub>)<sub>3</sub>, prepared by silylation of CpFe(CO)<sub>2</sub>Na with [[trimethylsilyl chloride]]. Typical routes include [[oxidative addition]] of Si-H bonds to low-valent metals. Metal silyl complexes are intermediates in [[hydrosilation]], a process used to make [[organosilicon compound]]s on both laboratory and commercial scales.<ref>Moris S. Eisen "Transition-metal silyl complexes" in The Chemistry of Organic Silicon Compounds. Volume 2 Edited by Zvi Rappoport and Yitzhak Apeloig, 1998, John Wiley & Sons</ref><ref>{{cite journal|doi=10.1021/CR9701086 |title=Reactions of Hydrosilanes with Transition-Metal Complexes: Formation of Stable Transition-Metal Silyl Compounds |year=1999 |last1=Corey |first1=Joyce Y. |last2=Braddock-Wilking |first2=Janet |journal=Chemical Reviews |volume=99 |issue=1 |pages=175–292 |pmid=11848982 }}</ref> |
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==See also== |
==See also== |
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* [[Silyl ether]] |
* [[Silyl ether]] |
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* [[Hydrosilylation]] |
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== References == |
== References == |
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{{reflist}} |
{{reflist}} |
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== External links == |
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*[http://littlemsandsailing.wordpress.com/2011/05/01/identification-of-silylation-artifacts-in-derivatization-reactions/ Identification of Silylation Artifacts in Derivatization Reactions for Gas Chromatography] |
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* [https://www.organic-chemistry.org/synthesis/O1H/cleavagesilylethers.shtm Desilylation methods] |
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[[de:Silylierung]] |
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[[Category:Organosilicon compounds]] |
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[[nl:Silylatie]] |
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Latest revision as of 04:58, 10 January 2024
Silylation is the introduction of one or more (usually) substituted silyl groups (R3Si) to a molecule. Silylations are core methods for production of organosilicon chemistry. Silanization involves similar methods but usually refers to attachment of silyl groups to solids.[1]
Of organic compounds
[edit]
Bis(trimethylsilyl)acetamide, a popular reagent for silylation
acetamide.svg)
Alcohols, carboxylic acids, amines, thiols, and phosphates can be silylated. The process involves the replacement of a proton or an anion with a trialkylsilyl group, typically trimethylsilyl (-SiMe3), as illustrated by the synthesis of a trimethylsilyl ethers from alcohols and trimethylsilyl chloride (Me = CH3):
- ROH + Me3SiCl → ROSiMe3 + HCl
Generally a base is employed to absorb the HCl coproduct.
Bis(trimethylsilyl)acetamide ("BSA", Me3SiNC(OSiMe3)Me is an efficient silylation agent. The reaction of BSA with alcohols gives the corresponding trimethylsilyl ether, together with acetamide as a byproduct (Me = CH3):[2]
- 2 ROH + MeC(OSiMe3)NSiMe3 → MeC(O)NH2 + 2 ROSiMe3
Use of silylation
[edit]Silylation has two main uses: manipulation of functional groups and preparation of samples for analysis.
Manipulation of functional groups
[edit]Often silylation is employed to protect OH and NH groups. The derivatives, silyl ethers and silyl amides, are resilient toward many reagents that would attack their precursors. The other main role of silylation is to trap silyl enol ethers, which represent a reactive tautomer of many carbonyl compounds.
Silylation for analysis
[edit]The introduction of a silyl group(s) gives derivatives of enhanced volatility, making the derivatives suitable for analysis by gas chromatography and electron-impact mass spectrometry (EI-MS). For EI-MS, the silyl derivatives give 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.[3][4]
Desilylation
[edit]Desilylation is the reverse of silylation: the silyl group is exchanged for a proton. Various fluoride salts (e.g. sodium, potassium, tetra-n-butylammonium fluorides) are popular for this purpose.[5][6]
- ROSiMe3 + F− + H2O → ROH + FSiMe3 + OH−
Of metals
[edit]
Coordination complexes with silyl ligands are well known. An early example is CpFe(CO)2Si(CH3)3, prepared by silylation of CpFe(CO)2Na with trimethylsilyl chloride. Typical routes include oxidative addition of Si-H bonds to low-valent metals. Metal silyl complexes are intermediates in hydrosilation, a process used to make organosilicon compounds on both laboratory and commercial scales.[7][8]
See also
[edit]References
[edit]- ^ Pape, Peter G. (2017). "Silylating Agents". Kirk-Othmer Encyclopedia of Chemical Technology. pp. 1–15. doi:10.1002/0471238961.1909122516011605.a01.pub3. ISBN 9780471238966.
- ^ Young, Steven D.; Buse, Charles T.; Heathcock, Clayton H. (1985). "2-Methyl-2-(Trimethylsiloxy)pentan-3-one". Organic Syntheses. 63: 79. doi:10.15227/orgsyn.063.0079.
- ^ Luis-Alberto Martin; Ingrid Hayenga. "Silylation of Non-Steroidal Anti-Inflammatory Drugs". sigmaaldrich.com. Retrieved 24 September 2023.
- ^ Blau, Karl; J. M. Halket (1993). Handbook of Derivatives for Chromatography (2nd ed.). John Wiley & Sons. ISBN 0-471-92699-X.
- ^ Mercedes Amat, Sabine Hadida, Swargam Sathyanarayana, and Joan Bosch "Regioselective Synthesis of 3-Substituted Indoles: 3-Ethylindole" Organic Syntheses 1997, volume 74, page 248. doi:10.15227/orgsyn.074.0248
- ^ Nina Gommermann and Paul Knochel "N,N-Dibenzyl-n-[1-cyclohexyl-3-(trimethylsilyl)-2-propynyl]-amine from Cyclohexanecarbaldehyde, Trimethylsilylacetylene and Dibenzylamine" Organic Syntheses 2007, vol. 84, page 1. doi:10.15227/orgsyn.084.0001
- ^ Moris S. Eisen "Transition-metal silyl complexes" in The Chemistry of Organic Silicon Compounds. Volume 2 Edited by Zvi Rappoport and Yitzhak Apeloig, 1998, John Wiley & Sons
- ^ Corey, Joyce Y.; Braddock-Wilking, Janet (1999). "Reactions of Hydrosilanes with Transition-Metal Complexes: Formation of Stable Transition-Metal Silyl Compounds". Chemical Reviews. 99 (1): 175–292. doi:10.1021/CR9701086. PMID 11848982.