Pyridines oxidative process

Acetaldehyde, first used extensively during World War I as a starting material for making acetone [67-64-1] from acetic acid [64-19-7] is currendy an important intermediate in the production of acetic acid, acetic anhydride [108-24-7] ethyl acetate [141-78-6] peracetic acid [79-21 -0] pentaerythritol [115-77-5] chloral [302-17-0], glyoxal [107-22-2], aLkylamines, and pyridines. Commercial processes for acetaldehyde production include the oxidation or dehydrogenation of ethanol, the addition of water to acetylene, the partial oxidation of hydrocarbons, and the direct oxidation of ethylene [74-85-1]. In 1989, it was estimated that 28 companies having more than 98% of the wodd s 2.5 megaton per year plant capacity used the Wacker-Hoechst processes for the direct oxidation of ethylene. 

The raw material has to be washed to remove impurities. Diluted sodium hydroxide allows the removal of phenols and benzonitrile, and diluted sulphuric acid reacts with pyridine bases. The resulting material is distilled to concentrate the unsaturated compounds (raw feedstock for coumarone-indene resin production), and separate and recover interesting non-polymerizable compounds (naphthalene, benzene, toluene, xylenes). Once the unsaturated compounds are distilled, they are treated with small amounts of sulphuric acid to improve their colour activated carbons or clays can be also used. The resulting material is subjected to polymerization. It is important to avoid long storage time of the feedstock because oxidation processes can easily occur, affecting the polymerization reaction and the colour of the coumarone-indene resins. 

Purex process, 6,940 Barium, pentakis(diacetamide)-stereochemistry, 1, 99 Barium alkoxides synthesis, 2,336 Barium complexes cryptands, 3,53 phthalocyanines, 2, 863 porphyrins, 2,820 pyridine oxide, 3,9 urea, 3,9... 

The aluminum is incorporated in a tetrahedral way into the mesoporous structure, given place to Bronsted acidic sites which are corroborated by FTIR using pyridine as probe molecule. The presence of aluminum reduces the quantity of amorphous carbon produced in the synthesis of carbon nanotubes which does not happen for mesoporous silica impregnated only with iron. It was observed a decrease in thermal stability of MWCNTs due to the presence of more metal particles which help to their earlier oxidation process. 

Yudin and Sharpless reported on the utilization of much cheaper, readily available inorganic Re catalysts [Re207, ReOsfOH), ReOs (0.5-1 mol%)] in combination with bis(trimethylsilyl) peroxide as oxidant and 0.5-1 mol% of pyridine (equation 52) . In this oxidation process high epoxide yields (78-96%) were obtained using CH2CI2 or THF as solvent. Traces of water or other protic species have been found to be essential for rapid turnover and accelerate the reaction. 

Related compound (D) has been reported to result from an oxidation process, and has the systematic name 5-[l-(2-chlorophenyl)-2-methoxy-2-oxoethyl]-6,7-dihydrothieno[3,2-c]pyridine-5-ium [8]. 

The oxidation of occurs with pyridine oxide, dimethylsul-foxi< and N 0,. The expected final product Jji has been detected (6 P = +18 ) isolated and characterized. The detailed oxidation process is not simple and intermediates are detected before the accomplishment of the oxidation. Compound 14 also collapses into several tetracoordinated phosphorus entities. 

Marcoux and Adams have carried out a study of the anodic oxidation of a range of azines in acetonitrile at a platinum electrode.347 With the exception of pyridine which could not be oxidized under these conditions, all the other azines were oxidized in a complicated process in which one electron per molecule was transferred to the electrode. The reaction was investigated in some detail for acridine, and the main product was found to be an acridyl-acridinium perchlorate (perchlorate being supplied by the supporting electrolyte). This result, which is directly comparable with that for pyridine oxidation by peroxydisulfate is persuasive evidence for the mediation of the... 

Dinuclear gold(I) and gold(II) complexes of pyridine-2-thiolate, 27, 28a and 28b, were studied by cyclic voltammetry at a Pt working electrode in CH2CI234. The dinuclear gold complex, 27, has an irreversible, extended oxidation process at +0.53 V vs SCE. No reduction wave was observed out to —1.8 V. The cyclic voltammograms for the dinuclear gold(II) complexes show irreversible reduction waves at —0.44 V (28a) and —0.43 V (28b). After reduction, the return oxidation scan shows an irreversible oxidation process at +0.55 V, indicative of the presence of 27. 

In the determination of benzene, interfering effects of dinitrotoluene and dinitroxylenes originating from toluene and xylenes are removed by oxidation of methyl groups with a chromic acid solution. Dinitrobenzene is stable during this oxidation process. After adding pyridine and alkalization of the diluted nitration mixture, the two layers are separated from each other. Sodium salts of nitrocarbonic acids formed by the oxidation remain in the aqueous layer, whereas m-dinitrobenzene passes into the pyridine layer. The pyridine layer is separated, methyl ethyl ketone is added and the red-violet colour is evaluated by photometry [18]. 

IP s oxidation processes directly affecting the imidazole and pyridine rings were seldom observed. But oxidation of 1,3-dimethyl-IbP iodide and other salts of a similar structure by potassium ferrocyanide in alkaline medium at temperatures below 10 °C afforded 1,3-disubstituted IbP-2-one (68KG954) (Section IV.C.l). 

Tandem oxidation processes have also been applied to five-and six-membered heterocycle synthesis. New examples of six-membered rings include pyrimides and p)mdines. In one approach, an cK-arylpropargyl alcohol is oxidized to the corresponding ynone, which then reacts with ethyl a-aminocrotonate or an amidine to afford pyridines or p)Timidines, respectively (eqs 105 and 106). In both cases, the reactions were limited in scope, but the former was subsequently inproved by implementation of 8-keto esters and ammonium acetate in place of the a-amino cro-tonate s)mthon (eq 107). ... 

---