Inorganic phosphite oxidation

Scheme 2.1 Practically irreversible oxidation of inorganic phosphite (hydrogen phospho-nate) to phosphate catalyzed by NADIPj -dependent phosphite dehydrogenase (PTDH).

Method E - catalytic procedure (typical procedure). Benzaldehyde (106 mg, 1.0 mmol), methyl bromoacetate (165 mg, 1.1 mmol), triphenyl phosphite (356 mg, 1.2 mmol), dibutyl telluride (48 mg, 0,2 mmol), KjCOj (179 mg, 1.3 mmol) and THF (4 mL) are mixed and stirred at 50°C for 13 h (monitored by TLC). The reaction mixture is filtered rapidly through a small amount of SiOj with EtOAc as the eluent to remove inorganic salts and dibutyltellurium oxide. Preparative TLC with EtOAc/petroleum ether at 60-90°C (1 9) as the eluent yields 3-phenylpropenoate (160 mg (98%)). 

Protection from Oxidation.—The most common case of oxidation among inorganic compounds occurs with salts in which the metal has two stages of oxidation and tends to pass from the lower to the higher as a result of atmospheric oxidation. The salts of iron, copper, tin, mercury, and chromium are examples. In other cases, the acid radical tends to undergo oxidation, as is true with sulfides, sulfites, phosphites, and nitrites. 

The commercial success of antioxidants depends not only on their intrinsic antioxidant efficiency but also on their chemical, physical and toxicological characteristics. Chemically, antioxidants should be stable to high temperatures throughout the conversion and fabrication processes of the polymer (it is quite normal for a portion of the antioxidant to be chemically consumed, via oxidative transformations, as a consequence of its antioxidant action). Antioxidants should be hydrolytically stable this is particularly important for phosphite antioxidants, which suffer from hydrolytic instability giving rise to inorganic acids, hence increasing the risk of corrosion of metal surfaces and the formation of dark coloured spots in the fabricated polymer. Colour instability of antioxidants is also very important, and is mainly due to the formation of coloured oxidation products of the antioxidant (e.g. quinonoid structures... 

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