Oxidative removal of hydrogen

The use of oxidizing agents can lead to the union, not only of aromatic nuclei, but also of aliphatic methyl, methylene, or methine groups, with elimination of hydrogen. Such a reaction is an oxidative dimerization. 

It has long been known280,281 that 1,1 -binaphthalene is formed when naphthalene is oxidized by manganese dioxide and sulfuric acid  

Naphthalene is boiled with manganese dioxide and ca. 50% sulfuric acid and then diluted with boiling water. The mixture is filtered and the solids are exhaustively extracted with ethanol. The filtrates are distilled. The distillate above 360° is collected separately and, when crystallized several times from ethanol and light petroleum, gives l,l -binaphthalene, m.p. 160.5°. 

Hey and his co-workers282 used this method successfully with a polycyclic ketone 2-methylbenz[ fe]anthrone is converted by manganese dioxide in 80% sulfuric acid at 0-5° into 2,2 -dimethyl-3,3 -bibenz[ fe]anthrone (78% yield), which affords 16,17-dimethyl-5,10-violanthrenedione only when treated with potassium hydroxide and a little ethanol at 120-130°  

Oxidative dimerization of 2-methyl-1-naphthylamine to 3,3 -dimethyl-l,T-binaphthalene-4,4 -diamine has also been effected by iron(m) oxide and by mercury(n) sulfate.283 

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Lower alkanes such as methane and ethane have been polycondensed ia superacid solutions at 50°C, yielding higher Hquid alkanes (73). The proposed mechanism for the oligocondensation of methane requires the involvement of protonated alkanes (pentacoordinated carbonium ions) and oxidative removal of hydrogen by the superacid system. 

Oxidative removal of hydrogen by cupric chloride was suggested by Schmerling to explain the observations 189... 

Superacids were shown to have the ability to effect the protolytic ionization of a bonds to form carbocations even in the presence of benzene.190 The formed car-bocations then alkylate benzene to form alkylbenzenes. The alkylation reaction of benzene with Ci—C5 alkanes (methane, ethane, propane, butane, isobutane, isopentane) are accompanied by the usual acid-catalyzed side reactions (isomerization, disproportionation). Oxidative removal of hydrogen by SbF5 is the driving force of the reaction ... 

The oxidation of 1,1-disubstituted hydrazines can be achieved by a wide range of oxidants. The oxidative removal of hydrogen formally leads to the production of aminonitrene, or 1,1-diazene, intermediates and many products of such reactions have been interpreted as being derived from aminonitrene intermediates. Indeed, several of these species, derived from sterically hindered hydrazines by oxidation with nickel peroxide or r-butyl hypochlorite, have been detected and characterized in solution at low temperature. Examples include the diazenes (14) and (15). The diazene (16) is stable enough to persist in solution at room temperature for several days. ... 

Oxidative removal of hydrogen has been satisfactory more frequently with phenols and their ethers examples are the conversion of 6-methyl-2-naphthol by iron(ni)284 and of 1-naphthol methyl ether by peroxyformic acid285 into the derived 1,1 -binaphthalene derivatives. 

Superacidic systems are able even to catalyze self-alkylative condensation of alkanes demonstrated here by the condensation of methane (63,78). The reaction requires the oxidative removal of hydrogen involving the pentacoordinate cation (17) (eq. 55). This can be attained by applying the oxidizing superacid Magic Acid (HSOsF-SbFs). The carbocationic pathway leading to C4-C6 alkanes also occurs through the involvement of pentacoordinate cations (18 eq. 56). 

Reduction was then defined as the removal of oxygen or the addition of hydrogen, whilst oxidation was the addition of oxygen or the removal of hydrogen. 

Extensive studies were earried out in reeent years to find ways for the seleetive oxidative eonversion of methane to higher hydroearbons. Because combining two methane molecules to form ethane and hydrogen is itself exothermic by some 16 keal/mol, oxidative removal of H2 is needed to make the reaction feasible. 

The oxidation of vitreous siUca appears to proceed by one of two mechanisms, depending on the material s hydroxyl content (109,111). In hydroxyl-containing material, the rapid oxidation probably occurs by the diffusion and removal of hydrogen, according to the following reaction ... 

Again, as with pyridopyrimidines, the main reaction is oxidation of di- or poly-hydro derivatives to fully aromatic structures, often merely by air or oxygen. In some cases the reagent of choice is mercury(II) oxide, whilst other reagents used include sulfur, bromine, chloranil, chromium trioxide-acetic acid, hydrogen peroxide, and potassium ferricyanide, which also caused oxidative removal of a benzyl group in the transformation (306) (307)... 

Oxidations in the pteridine series comprise (i) replacement of hydrogen by hydroxyl, (ii) glycol formation at the central C=C bond (iii) the removal of hydrogen atoms from dihydro and tetrahydro derivatives. 

In oiological systems, the most frequent mechanism of oxidation is the remov of hydrogen, and conversely, the addition of hydrogen is the common method of reduc tion. Nicotinamide-adenine dinucleotide (NAD) and nicotinamide-adenine dinucleotide phosphate (NADP) are two coenzymes that assist in oxidation and reduction. These cofactors can shuttle between biochemical reac tions so that one drives another, or their oxidation can be coupled to the formation of ATP. However, stepwise release or consumption of energy requires driving forces and losses at each step such that overall efficiency suffers. 

Oxidation loss of electrons by a species during a chemical or electrochemical reaction addition of oxygen or removal of hydrogen from a substance. 

After the precatalyst is completely converted to the active catalyst Xq, three steps are required to form the desired reduction product. The first step is the coordination of dehydroamino acid (A) to the rhodium atom forming adducts (Xi) and (Xi ) through C=C as well as the protecting group carbonyl. The next step is the oxidative addition of hydrogen to form the intermediate (X2). The insertion of solvent (B) is the third step, removing the product (P) from X2 and regenerating Xq. Hence, the establishment of the kinetic model involves these three irreversible steps. 

Birch has made good use of oxidative decarboxylation in hydrofuroic acids (Section VI,B,2) but otherwise the direct removal of hydrogen from a hydrofuran is usually regarded as impracticable, and while the dismutation catalyzed by palladium on alumina at 180 C is interesting, it depends too much upon the substitution pattern to be sufficiently general18 ... 

Another useful compound is the 1 2 telomer of malonate and butadiene, 137. The first example is the synthesis of pellitorine (138), a naturally occurring pesticide (126). The terminal double bond was hydrogenated selectively with RuCl2(PPh3)3 as a catalyst. Partial hydrolysis afforded the monoester, which was treated with PhSeSePh to displace one of the carboxyl group with phenylselenyl group. Oxidative removal of the phenylselenyl group afforded 2,4-decadienoate (139), which is converted to pellitorine (138) ... 

Reversible inhibition caused by materials that can function as ligand. Many compounds will bind to a metal this might be the solvent or impurities in the substrate or the solvent. It can also be a functional group in the substrate or the product, such as a nitrile. Too many ligands bound to the metal complex may lead to inhibition of one of the steps in the catalytic cycle. Likely candidates are formation of the substrate-catalyst complex or the oxidative addition of hydrogen. Removal of the contaminant will usually restore the catalytic activity. 

For an organism to eliminate a lipophilic, chemically inert xenobiotic, it is usually hrst necessary to oxidize it to a more polar form. In addition, many biosynthetic pathways that produce steroid hormones, prostaglandins, leukotrienes, etc. involve oxidative steps. Organisms have evolved many enzymes to carry out these oxidations. Oxidation can occur by addition of oxygen (without addition of hydrogen which would represent hydration), removal of hydrogen atoms (without removal of oxygen which would represent dehydration), or simply removal of electrons. 

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