Tetramethyl pyromellitate

The search for different or specific electron transfer sensitizers continues. Tetramethyl pyromellitate has been shown to be a useful sensitizer for the photochemical reactions of a,P-unsaturated ketones with tetraalkylstannanes. ... 

The facile photosensitized oxidation of tetraalkylstannanes (R4 n) and related group-14 compounds has been widely exploited by Mella and co-workers to form carbon-centered radicals. Photoinduced electron transfer from tetraalkylstannanes to a sensitizer, such as aromatic nitriles and esters (including tetramethyl pyromellitate, TMPM), affords a radical cation [R4 n] that can fragment to form an alkyl radical (R) together with the R3Sn+ cation. The alkyl radicals can then react with electron-poor alkenes, alkynes, aromatics, or the radical anion formed from the photosensitizer to form new carbon-carbon bonds. Careful choice of the photosensitizer can ensure that the radical anion selectively reduces the radical adduct (derived from addition to a double bond) rather than the first-formed alkyl radical (Scheme 5). 

Pyromellitic acid tetramethyl ester, mp 142-143 °C, prepared by diazomethane methylation of pyromellitic acid, is used as the internal standard and is stored as a dichloromethane solution (—1 mg/ml) in a freezer. (Any loss of solvent from the solution is conveniently verified by weighing.) From this solution, the exact volume corresponding to from 200 to 1000 pg of the internal standard is withdrawn and added to the ester mixture to be analyzed. The amount of internal standard chosen is dependent on the amount and type of sample. For samples where a high yield of esters is expected, the upper level of internal standard is used. 

The first commercial polyimide was produced by the polycondensation of pyromellitic anhydride with 4,4 -diaminodiphenyl ether. The first stage is carried out in very polar solvents such as dimethyl formamide, dimethyl acetamide, tetramethyl urea, or dimethyl sulfoxide, when what is known as polyamic acid is formed ... 

A high-temperature-stable polyimide occurs from the reaction of pyromellitic anhydride with aromatic diamines such as p,p-diaminodi-phenyl ether. Pyromellitic acid is produced either by direct oxidation of 1,2,4,5-tetramethyl benzene (Durol) or from xylylene. The xylylene mixture is chloromethylated. Crystalline l,3-dimethyl-4,6-di(chloromethyl)-benzene (I) is separated from the two liquid isomers (II) and (III) and oxidized to pyromellitic acid with HNO3 ... 

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