Silicon carboxylates esters

Acylation of a simple thiol with an alkyl carboxylate is not a very suitable method for preparation of S-alkyl thiocarboxylates. Transesterification is, however, possible if either the thiol or the carboxylic ester is activated. The enhanced reactivity of boron, aluminum and silicon thiolates has been utilized for the synthesis of a large variety of thiocarboxylic S-esters, including hydroxy derivatives (from lactones). a,P-Unsaturated thiol esters, e.g. cinnamoyl or 2-butenoyl derivatives, are also accessible. Michael addition, an undesirable side reaction of thiols, is completely avoided if alkyl trimethylsilyl sulfides ortris(arylthio)boranes are applied. ... 

Oxidations - 3,5-Dinitroperbenzoic acid is a stable storable peracid equivalent in activity to trlfluoroperacetic acid. A full paper has appeared which gives the experimental details for the a-hydroxylation of carbonyl compounds by treatment of the anions of enol silanes with Mo05 HMPA (MOOPH). Anions from carboxylic esters (LiN(iPr)2>LDA -78°C) can be efficiently, regiospecifically chlorinated or brominated by treatment with respectively CCl or CBr. Treatment of enol silanes from conjugated ketones with m-chloroperbenzolc acid (MCPBA) followed by removal of silicon affords the a-hydroxyketones. ... 

Without additional reagents Silicon carboxylates from carboxylic acid ferf-butyl esters w.a.r. 

Chem. Descrip. Silicone copolyol-based carboxylate ester, potassium salt Ionic Nature Anionic... 

The chemistry of a-haloketones, a-haloaldehydes and a-haloimines Nitrones, nitronates and nitroxides Crown ethers and analogs Cyclopropane derived reactive intermediates Synthesis of carboxylic acids, esters and their derivatives The silicon-heteroatom bond Syntheses of lactones and lactams The syntheses of sulphones, sulphoxides and cyclic sulphides... 

The analytical control of this step is of special importance the alcaline saponification is performed at a relatively low pH in order to prevent cleavage of the silicon-carbon bond. The closer the electron-with-drawing carboxyl group is located to the Si-C-bond, the larger is the danger of scission. Therefore, for the B-silyl carboxylic acid derivatives the pH during saponification should not surpass 10.5 however, at this pH saponification of the methyl ester requires about 1 day, even at 60°C. For the -silyl derivatives, the pH of the reaction mixture is not critical. We therefore now exclusively utilize the latter. 

The selective dense layer of hydrophilic membranes is made from different polymers with a high affinity for water. These polymers contain ions, oxygen functions like hydroxyl, ester, ether or carboxylic moieties, or nitrogen as imino or imi-do groups. Preferred hydropilic polymers are polyvinylalcohol (PVA) [32], poly-imides, cellulose acetate (CA) or natural polymers like chitosan [33] or alginates. Organophilic membranes usually consist of crosslinked silicones, mostly polydimethyl siloxane (PDMS) or polymethyl octyl siloxane (POMS). 

Alkene esters on the other hand do not require protection as they appear to react primarily via the alkene end, allowing standard chemical transformations to be carried out as summarized in Fig. 5. For example, the terminal esters can be hydrolyzed to form a carboxylic acid terminated surface, or reduced with LiAlfD to form an alcohol modified surface [28]. A concern in carrying out these transformations is that the rather harsh conditions required have the potential to degrade the silicon substrate. Boukherroub and Wayner demonstrated further chemical manipulation of... 

Representative trace constituents HNC,c-C3H2) polyacetylenic compounds Cyanopolyynes, polycarbon sulfides, metal cyanides, silicon compounds Methylated organics Alcohols, ethers, esters, carboxylic acids, amino acids ( )... 

Trialkylsilyl protection of carboxylic acids and amines is rare owing to hydrolytic lability. Nevertheless, synthetically useful silicon protecting groups have been developed for these functional groups in which the requisite stability is achieved by incorporating the silicon atom into a 2-(trimethylsilyl)ethyl substituent. The principle is illustrated [Scheme 1.9] by the reaction of 2-(trimethylsilyl)ethyl esters with tetrabutylammonium fluoride the pentavalent siliconate intermediate fragments with loss of ethylene and fluorotrimethylsilane14-15 to liberate a carboxylic arid as its tetrabutylammonium salt. 

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