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Study on protection of dehydroxylation silicon Ether Catalyzed by solid acid

Author: LiYingZhi
Tutor: LaiGuoQiao
School: Hangzhou Normal University
Course: Organic Chemistry
Keywords: Silyl ether Deprotection SSA SBA-15-SO3H
CLC: O643.32
Type: Master's thesis
Year: 2007
Downloads: 28
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Abstract


The hydroxyl groups exist in many significance compounds in the physiology and the synthesis, such as carbohydrate and steroid. When using or synthesizing these compounds we have to consider protection and deprotection of hydroxyl groups. The organosilicon reagent being used as hydroxyl protecting agent has been developed quickly in the recent years, because both of the protection and deprotection reactions can be carried out under mild conditions. Furthermore, organosilicon protective groups have different steric hindrance substituting groups attached on the silicon, so they can selectively protect different chemical environment hydroxyl groups.The silyl ethers can be deprotected selectivity and highly effective by the different catalyst. A lot of silyl ethers were deprotected by using various liquid acids, but few supported solid acid have been used as catalysts for deprotection of silyl ethers. However, solid acids are regarded as green catalysts in synthesis for they have no volatility and no corrosiveness. We chose two solid acids, silica sulfuric acid (SSA) and sulfonic acid-functionalized mesoporous SBA-15(SBA-15-SO3H), to research the catalytic deprotection of silyl ethers, respectively. Sulfonic acid groups of SSA were immobilized on the surface of silica gel through Si-O chemical bond, and sulfonic acid groups of SBA-15-SO3H were functionalized on SBA-15mesoporous silica. The thesis is about deprotection of silyl ethers catalyzed by SBA-15-SO3H and SSA, respectively.The primary, secondary alcohol TBS ethers could be completely deprotected by0.5mol%SSA in dozens of minutes in methanol at room temperature, however, deprotection of phenol TBS ethers were more difficult. Alcohol TBS ethers could be selectively deprotected in present of phenol TBS ethers by using SSA. TMS and MDPS silyl ethers all could be deprotected by using0.1mol%SSA in methanol at the room temperature in short time. And SSA does not affect the stability of phenmethyl ether under same conditions.We have established another mild, simple and highly method for deprotection of alcoholic TBS, TMS and MDPS ethers using a catalytic amount of SBA-15-SO3H in methanol at room temperature. The method could selectively cleave alkyl TBS ethers from systems containing both alkyl and aryl TBS ethers using SBA-15-SO3H. And SBA-15-SO3H did not affect the stability of phenmethyl ether under same conditions too.In summary, both sulfonic acid-functionalized mesoporous SBA-15(SBA-15-SO3H) and silica sulfuric acid (SSA) were found to be efficient and environmentally benign solid acid catalysts for the deprotection of tert-butyldimethylsilyl (TBS) ethers under mild conditions. Particularly, TBS-protected alcohols could be selectively removed by using SBA-15-SO3H in the presence of TBS-protected phenols, and SBA-15-SO3H could be easily recovered and reused. Nevertheless, SSA was been validated to be more significant catalytic activity than SBA-15-SO3H.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalytic reaction
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