User:Aliaksands/Silylation
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[edit]Lead
[edit]Silyl groups improve thermal stability of molecules. This involves the ability to resist changes to chemical and physical properties at increased temperatures.[1] Silyl groups also improve volatility and decrease polarity of the derivatives.[2]
Protection Chemistry
[edit]Alkyl silyl groups are frequently used as alcohol protecting groups.
Deprotection
[edit]Removal of the alkyl silyl/deprotection of the alcohol can be done using either brønsted/lewis acid conditions, or basic conditions. Acidic deprotection occurs fastest for less sterically bulky alkyl silyl groups. A commonly used deprotecting agent in basic conditions are fluoride ions/fluoride salts. Deprotection with a fluoride ion occurs via an SN2 mechanism. The fluoride ion has a strong affinity for silicon due to the strength of the Si-F bond. The primary fluoride ion deprotecting agent is tetra-n-butylammonium fluoride (TBAF), as its aliphatic chains in help incorporate F- into organic solvent.
Modifying Reactivity
[edit]Alkyl substituents with higher steric bulk tend decrease the reactivity of the silyl group. Consequently, bulky substituents increase the silyl group's protective abilities. Since more strenuous conditions are required for protection, groups such as TBDMS and TIPS can be used to selectively protect primary alcohols over secondary alcohols.[3]
[Image: Common silyl groups, increasing left to right in steric bulk]
Enolate Trapping
[edit]Silylation can also be used to trap reactive compounds for isolation and identification uses.[3] A common example of this is reacting a silyl chloride to trap enolates. Since enolate-forming reactions can generate unwanted organic or salt byproducts, silylation is a way to isolate reactive enolates.
Silylation affords an enol silyl ether which can be characterized or stored. The original enolate can be reformed upon reaction with an organolithium, or other strong base.
References
[edit]- ^ "Thermal Stability Science Behind Heat Resistance - Bannari Amman Institute of Technology". 2023-10-09. Retrieved 2024-11-04.
- ^ Pagliano, Enea; Campanella, Beatrice; D'Ulivo, Alessandro; Mester, Zoltán (2018-09-26). "Derivatization chemistries for the determination of inorganic anions and structurally related compounds by gas chromatography - A review". Analytica Chimica Acta. 1025: 12–40. doi:10.1016/j.aca.2018.03.043. ISSN 0003-2670.
- ^ a b Clayden, Jonathan; Greeves, Nick; Warren, Stuart (2012). Organic chemistry (2nd ed.). Oxford: Oxford university press. ISBN 978-0-19-927029-3.