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Silylating  Agents

|Our product list |   The Functions on Organic Compounds   |   Selectivity   |   Examples of Applications|

      A silylating agent is an organosilicon compound that replaces an activated hydrogen in an organic molecule with an organosilicon group. In the field of pharmaceuticals, silylating agents are mainly used to protect the activated hydrogens of specific functional groups in raw materials or intermediates as they are processed. In the field of electronics, silylating agents are widely used as surface modifiers for a variety of substrates such as silicon wafers or glasses.

  1. trichlorosilane [10025-78-2]

  2. trimethoxysilane [2487-90-3]

  3. triethoxysilane [998-30-1]

  4. methyldichlorosilane [75-54-7]

  5. methyldimethoxysilane [16881-77-9]

  6. methyldiethoxysilane [2031-62-1]


  • The Functions on Organic Compounds

    The activated hydrogen such as hydroxyl group, amino group, carboxyl group, or amide group in the organic compounds can be substituted by silicon with the use of silylating agents. The purposes of substitution are as follows:

    (1) To protect reactive group during chemical reaction
    (2) To improve reaction selectivity
    (3) To improve solubility in solvents
    (4) To improve stability during distillation
    (5) To improve applications for gas chromatograph and mass- spectrometry

    At present, most uses are for the protection of the reactive group. Recently, many references have indicated preferential selectivity through use of a silylating agents. It is possible this application will gain more wide spread use in the near future. Silylating agents can protect against the reactive groups of alkaline reagents, oxidizing agents, reducing agents, Grignard reagents, and Wittig reagents used in the following processes.


Compounds are selected for reaction in accordance with reactivity, by-products, and prices.

KA 31 The best general-purpose silylating agent, lowest price
HMDS NH3 is the only by-product and no deposition of salts
BTSU By-product (urea) is insoluble, easy to remove
BSTFA Activity is high and neutral, by-product is volatile and can be removed by distillation
TMST The most powerful silylating agent, and can be used as a Lewis acid.

 

Silylating Agent with Large Steric Bulk

TESC As a protective group, TESC is approximately 100 times more stable than KA 31
TBMS As a protective group, TBMS is approximately 10,000 times more stable than KA. Recommended for use under very severe reaction conditions

*TBMS is solid at room temperatures, 50% toluene solution and 50% acetic acid ethyl solutions are usually available for industrial use.

The stability of silylated functional groups is affected by the bulkiness of the organic substituents. The stability of the silylated functional group can be estimated from Taft's 3D parameters (the greater the negative values the higher mass) in the following table.

 

Taft's 3D Parameters

Substitution Group ESSi
Me 0
Et - 0.261
n-Pr - 0.315
n-Bu - 0.348
i-Bu - 0.400
Me3CCH2 - 0.589
i-Pr - 0.677
s-Bu - 0.704
c-C6H11 - 0.757
Et2CH - 0.816
t-Bu - 1.670

 

2Bi-Functional Silylating Agent

CIPS CIPS is best suited for use in protecting the hydroxyl group of polysaccharides and nucleosides, and is effective in the synthesis of 3' and 5' hydroxyl groups of nucleoside. CIPS is reactive bi-functionaly and selectively and is now used for developing nucleic acid anticancer agents and anti-HIV drugs.

We have received many reports on the silylated agent, described are the applications of CIPS.

The above content was quoted from www.silicone.jp/e/

 

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