Advantages And Disadvantages Of Silylation

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i. Derivatives of alkylation are very stable ii. Some of these reactions can be done in aqueous solutions iii. Alkylation reagents are widely available iv. They are wither strong basic or acidic in nature.
1. They are only limited to acid hydroxyl groups and amines
2. The reagents used are mostly toxic
Alkylating agents and how they act.
a. Boron trichloride in methanol or chloroethanol: an acidic hydrogen group undergoes esterification in the presence of boron trichloride an ester derivative. Acid BCl3
b. Tetra-butyl-ammonium hydroxide (TBH): forms butyl ester with derivative or carboxylic acid that improves the retention time in the gas chromatography column. TBH
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Low volatile and non-volatile compounds can be easily made volatile
II. It is an easy method of derivatization
I. Only aprotic organic solvents can be used.
II. Alcohol or water content is likely to affect the process of Silylation.
III. Carbowax columns are not compatible with silylating agents due to the presence of hydrogen in its stationary phase. Silylation reagents and their mechanisms Trimethylchlorosilane (TMCS),Hexamethyldisilazane (HMDS), Bistrimethylsilyltrifluoroacetamide (BSTFA), trimethylsilylimidazole (TMSI) among others. The listed reagents above react with acids and alcohol to give trimethylsilyl esters that give volatile and easily separable derivatives for Gas chromatography.
3) Acylation in Comparison to Silylation, this process targets the reduction in polarity of highly polar hydroxyl, amino, -thiol groups such as amino acids and carbohydrates by the addition of the addition of acyl group. It also makes it possible for compounds like sugar of high polarity to undergo Gas chromatography. Example of acylation is the reaction of alcohol and acetic anhydride to give acetic acid and acetate ester. CH3OCOCOCH3 + HOR → (in presence of H+ catalyst) CH3OCOR´ +
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Reagents are sensitive to moisture
III. They also have odor and can be hazardous
IV. Acidic by-product is formed by the reagents which can damage the columns during Gas chromatography Acylating reagents used and their mechanism of action;
Reagents used in acylation are mostly halogenated or contain halogen compounds in their structures.
I. Fluorinated anhydrides react with amines, phenols, and alcohols to give highly volatile and stable derivative of the prior analyte to be used. Acid receptor or amines are needed to enhance the reaction.
II. Penta-fluoro-benzoyl Chloride can be used for stoically hindered functional groups. It is can also be used in the derivatization of secondary amines which are highly sensitive and alcohols. An acid by-product e.g. hydrochloric acid is formed during the process but can be neutralized with the use of sodium hydroxide. Chiral derivatization in Gas Chromatography
Special reagents are required for the derivatization of chiral compounds which are superimposable and grouped as enantiomers. The reaction of purely chiral reagents with enantiomeric compounds will proceed to the formation of a racemic mixture that is two derivative enantiomers of one compound and is separated using gas Chromatography to give separate diastereomers for each enantiomer. Chiral derivatization is in high demand due to research on chiral
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