Preferential oxidation

Chemistry. Fire refining of bhster copper is achieved by oxidation, fluxing, and reduction. The copper is partially oxidized by blowing air into the fire-refining furnace, where the copper oxide and the impurities that oxidize preferentially react. 

To return to a more historical development the mercuric acetate oxidation of substituted piperidines (77) should be discussed next. This study established that the normal order of hydrogen removal from the aW-carbon is tertiary —C—H > secondary —C—H > primary —C—H, an observation mentioned earlier in this section. The effect of substitution variations in the piperidine series can be summarized as follow s l-mcthyl-2,6-dialkyl and 1-methyl-2,2,6-trialkyl piperidines, as model systems, are oxidized to the corresponding enamines the 1,2-dialkyl and l-methyl-2,5-dialkyl piperidines are oxidized preferentially at the tertiary a-carbon the 1-methyl-2,3-dialkyl piperidines gave not only the enamines formed by oxidation at the tertiary a-carbon but also hydroxylated enamines as found for 1-methyl-decahydroquinoline (48) (62) l-methyl-2,2,6,6-tctraalkyl piperidines and piperidine are resistant to oxidation by aqueous mercuric acetate and... 

The calculation shows that zinc is oxidized preferentially over iron. Later in this chapter we describe the use of zinc as a sacrificial anode to prevent corrosion of iron. 

Various strategies are employed to prevent corrosion. The use of paint as a protective coating is described in our chapter introduction. A metal surface can also be protected by coating it with a thin film of a second metal. When the second metal is easier to oxidize than the first, the process is galvanization. Objects made of iron, including automobile bodies and steel girders, are dipped in molten zinc to provide sacrificial coatings. If a scratch penetrates the zinc film, the iron is still protected because zinc oxidizes preferentially ... 

Steel making, broadly speaking, is an oxidation process in which impurities such as carbon, silicon, manganese, phosphorus and sulfur present in the pig iron are removed to specified levels. It can be anticipated from the Ellingham diagram that at about 1600 °C, the elements C, Si, and Mn would oxidize preferentially before iron undergoes excessive oxidation. The oxidation reactions may be represented by... 

Alkyl-substituted benzenes are oxidized both on the benzene ring and on the side chain. Additionally, some dimerization occurs.36 Alkylbenzenes containing linear alkyl groups are oxidized preferentially at the side chain33 nearest the benzene ring for example, ethylbenzene oxidizes first to 1-phenyl ethanol and then to acetophenone.36... 

The oxidation of sulfides to sulfoxides (1 eq. of oxidant) and sulfones (2 eq. of oxidant) is possible in the absence of a catalyst by employing the perhydrate prepared from hexafluoroacetone or 2-hydroperoxy-l,l,l-trifluoropropan-2-ol as reported by Ganeshpure and Adam (Scheme 99 f°. The reaction is highly chemoselective and sulfoxidation occurs in the presence of double bonds and amine functions, which were not oxidized. With one equivalent of the a-hydroxyhydroperoxide, diphenyl sulfide was selectively transformed to the sulfoxide in quantitative yield and with two equivalents of oxidant the corresponding sulfone was quantitatively obtained. 2-Hydroperoxy-l,l,l-fluoropropan-2-ol as an electrophilic oxidant oxidizes thianthrene-5-oxide almost exclusively to the corresponding cw-disulfoxide, although low conversions were observed (15%) (Scheme 99). Deprotonation of this oxidant with sodium carbonate in methanol leads to a peroxo anion, which is a nucleophilic oxidant and oxidizes thianthrene-5-oxide preferentially to the sulfone. 

The oxidation of preformed ir-allylpalladium complexes with MCPBA proceeds by attack at the metal to give oxidation at the less substituted allyl terminus (equation 305).272 Mo02(acac)2-But02H oxidations also involve attack at palladium, but, in contrast to MCPBA, give oxidation preferentially at the more substituted allyl end (equations 306-308).275... 

As noted in the section on Preparation , the formation of this material is objectionable, since it coats the equipment piping. By a suitable variation in conditions, this reaction can be minimized, with the alcohol and aldehyde being oxidized preferentially to the acid. Crude TNT contains small amounts of all four of these compds... 

The first synthesis50 of akagerine (67) makes use of the tetracyclic lactam (68a), previously synthesized. Formation of the ( )-dilactam (69) was observed from both (68a) and its (Z)-isomer. Preferential opening of the Nb,21 lactam function in (69) was followed by reduction stages to the diol (70), which was then oxidized preferentially at the allylic alcohol function to give akagerine (Scheme 10). 

Two further papers report lithium-ammonia reductive cleavage of some A3-THC-related compounds374 and selenium dioxide oxidation of A -THC and A6-THC.375 In the latter, it is shown that A -THC yields oxidation products predominantly from attack at C-6, whereas A6-THC is oxidized preferentially at the exocyclic allylic C-7 methyl group, to yield, for example, (269). 

Pepper JM, Casselman BW, Karapally JC (1967) Lignin oxidation Preferential use of cupric oxide Can J Chem 45 3009-3012... 

This vanadium method enables the cross-coupling only in combinations of silyl enol ethers having a large difference in reactivity toward radicals and in their reducing ability. To accomplish the crosscoupling reaction of two carbonyl compounds, we tried the reaction of silyl enol ethers and a-stannyl esters based on the following consideration. a-Stannyl esters (keto form) are known to be in equilibrium with the enol form such as stannyl enol ethers, but the equilibrium is mostly shifted toward the keto form. When a mixture of an a-stannyl ester such as 45 and a silyl enol ether is oxidized, it is very likely that the stannyl enol ether will be oxidized preferentially to the silyl enol ether. The cation radical of 45 apparently cleaves immediately giving an a-keto radical, which reacts with the silyl enol ether selectively because of the low concentration of the stannyl enol... 

Thienylpyridazines were prepared from 2- or 3-thienyllithium and py-ridazine. In diethyl ether, the thienyl ring is attached at position 3 to give first the corresponding 2,3-dihydro derivatives accompanied by a small amount of 1,4-dihydro isomers, whereas in tetrahydrofuran and at low temperature, position 4 of the pyridazine ring is attacked. Aromatization can be achieved with various oxidants, preferentially with chloranil [81JCR(S)104 82CJC2668],... 

---