Dehydrodimerization oxidation

R. DiCosimo, J.D. Burrington, and R.K. Grasselli, Oxidative dehydrodimerization of propylene over a Bi203-La203 oxide ion-conductive catalyst, J. Catal. 102, 234-239 (1986). 

Anodic oxidation of 1,2,3-trimethoxybenzene in acetone containing dilute sulphuric acid gives 2,6-dimethoxybenzoquinone but in contrast 1,2,4-trimethoxy-benzene affords the dehydrodimer 11 in good yield [82]. Dehydrodimerization becomes an important process in the oxidation of methoxybenzenes in dichlo-... 

Anodic oxidation of malonate esters in alkaline solution gives the dehydrodimerization product by carbon-carbon coupling. The reaction mechanism has been... 

Anodic oxidation of the alkali metal salts of a-oximinoesters results in dehydrodimerization [32],... 

The so-called toluene-to-styrene process [Eq. (12.33)], first reported in a patent by Monsanto,148 applies bismuth or lead oxides in dehydrodimerization of toluene to stilbene, which, in turn, is cleaved with ethylene to styrene 149... 

Electrochemical oxidation of hydrazidoyl halides (330) also affords 1,4-dihydro-1,2,4,5-tetrazines (104). A nitrilimine intermediate is not suggested for this reaction. The main process is the dehydrodimerization of the initially formed hydrazonyl radical, while a concurrent side-reaction leads to the l,4-dihydro-l,2,4,5-tetrazines (104), which are transformed into the corresponding cation radicals (336) on further oxidation (77IZV393, b-75MI22102). 

One-electron oxidation of aromatic compounds (ArH) leads primarily to corresponding radical cation which exist either in monomeric (ArH +) or dimeric form [(ArH)2 ] the latter usually formulated as r-dimer [70]. However, radical cations are reactive species and can undergo further reaction yielding more persistent radical cations e.g. oxidation of rert-butylbenzene or of toluene or o-xylene yielded radical cation of 4,4 -di-rerf-butyl biphenyl, 4,4 -bitoluene or 3,3, 4,4 -tetramethyl biphenyls, products of further a-coupling, proton loss and further one-electron oxidation [71]. This is a well-known pathway of biaryl dehydrodimerization, explored in anodic and metal-ion oxidation of ArH [72, 73]. Other compounds with high reactivity in (T-coupling are alkoxy and amino substituted ArH [73]. Thus a risk with characterization of radical cations is that hardy survivors and not primary radical... 

Figure 19. ZnS-photocatalyzed dehydrodimerization of 2,5-DHF dependence of apparent product quantum yield on substrate oxidation potential.

Electron transfer oxidation of 4-methoxyphenol using wjeio-tetraphenylporphyrin as the electron acceptor brings about dehydrodimerization of the phenol to yield 5. The presence of the radical cation of the phenol has been detected by CIDNP techniques. The same product is obtained by irradiation of the tetraphenylporphyrin/benzoquinone/p-methoxyphenol system . Pyrimidinopteridine Af-oxide has been used as a sensitizer to effect the hydroxylation of phenols, also involving the radical cation of the phenol. Thus phenol can be converted to catechol and hydroquinone while cresol yields 4-methyl-catechol . Hydroquinone can itself be oxidized by the cobalt azide complex in aqueous... 

With C-C bond fission V2O5 1.2. oxidative dehydrodimerization and dehydrocycliza- MoO,-Al,0,... 

A typical example for the oxidative dehydrodimerization of alkenes by heterogeneous catalysis is the conversion of isobutene to 2,5-dimethyl-1,5-hexadiene (DMH) catalyzed by metal oxides. The overall reaction scheme is ... 

Marchenko L.S., Zhuk S.Ya., Kir yakov N.V., Nersesyan M.D., Grigoryan E.H., Oxidative Dehydrodimerization of Methane Over Complex Oxide Catalysts Prepared by Self-Propagating High-Temperature Synthesis, Catal. Today, 13 (1992) 593. 

Pathways (la) and (Id) are the most frequent routes employed for the electrochemical generation of radicals. The radicals can be used in homocoupling, heterocoupling and addition reactions. In some cases these reactions have to compete with further oxidation or reduction of the radicals (see Sections 2.6.3.5 and 2.6.4.3). Electrogenerated radical ions (lb), (le), (If), cations (Ic) and anions (Ig) have been very efficiently used in electroorganic synthesis, e.g. for cathodic hydrodimerization, anodic dehydrodimerization, anodic substitution, cathodic cleavage or ring closure reactions [2, 5, 6]. These conversions are not treated in this review. 

Dehydrodimerization of toluene to stilbene. Toluene can be oxidized to stUbene when heated at elevated temperatures in a conventional flow system over a catalyst composed of bismuth trioxide and stannic oxide. Benzene and... 

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