Solvents preferential oxidation

If, however, the same reaction is attempted in methanolic solution, no olefin oxidative cleavage is detected, and solvent oxidation dominates the observed chemical process. Presumably, the polar solvent preferentially binds to the oxide surface, effectively negating the adsorption of the less polar hydrocarbon. The observed reactivity is then restricted to molecules held at the surface, i.e., to solvent oxidation. 

Figure 6.15. Dielectric constant of styrene-ethylene oxide block copolymers A, B, and C cast from solution in solvents preferential for the polystyrene component (C, ethylbenzene) and in a mutual solvent (A, B,...

Ce(IV) extracts more readily iato organic solvents than do the trivalent Ln(III) ions providing a route to 99% and higher purity cerium compounds. Any Ce(III) content of mixed lanthanide aqueous systems can be oxidi2ed to Ce(IV) and the resultiag solutioa, eg, of nitrates, contacted with an organic extractant such as tributyl phosphate dissolved in kerosene. The Ce(IV) preferentially transfers into the organic phase. In a separate step the cerium can be recovered by reduction to Ce(III) followed by extraction back into the aqueous phase. Cerium is then precipitated and calcined to produce the oxide. 

Lube oil extraction plants often use phenol as solvent. Phenol is used because of its solvent power with a wide range of feed stocks and its ease of recovery. Phenol preferentially dissolves aromatic-type hydrocarbons from the feed stock and improves its oxidation stability and to some extent its color. Phenol extraction can be used over the entire viscosity range of lube distillates and deasphalted oils. The phenol solvent extraction separation is primarily by molecular type or composition. In order to accomplish a separation by solvent extraction, it is necessary that two liquid phases be present. In phenol solvent extraction of lubricating oils these two phases are an oil-rich phase and a phenol-rich phase. Tne oil-rich phase or raffinate solution consists of the "treated" oil from which undesirable naphthenic and aromatic components have been removed plus some dissolved phenol. The phenol-rich phase or extract solution consists mainly of the bulk of the phenol plus the undesirable components removed from the oil feed. The oil materials remaining... 

Electrochemical oxidation of 4-aryl-substituted thiane in aqueous organic solvents containing various halide salts as electrolytes gave selectively the trans-sulfoxide (lOe). Under acidic conditions a preferential formation of the cis-sulfoxide was attained328. The stereoselective potential of this method for the oxidation of cyclic sulfides139,329 is apparent (equation 123). 

A mixture of water/pyridine appears to be the solvent of choice to aid carbenium ion formation [246]. In the Hofer-Moest reaction the formation of alcohols is optimized by adding alkali bicarbonates, sulfates [39] or perchlorates. In methanol solution the presence of a small amount of sodium perchlorate shifts the decarboxylation totally to the carbenium ion pathway [31]. The structure of the carboxylate can also support non-Kolbe electrolysis. By comparing the products of the electrolysis of different carboxylates with the ionization potentials of the corresponding radicals one can draw the conclusion that alkyl radicals with gas phase ionization potentials smaller than 8 e V should be oxidized to carbenium ions [8 c] in the course of Kolbe electrolysis. This gives some indication in which cases preferential carbenium ion formation or radical dimerization is to be expected. Thus a-alkyl, cycloalkyl [, ... 

In solvents that strongly resist anodic oxidation as MeCN, CH2CI2/CF3CO2H, or T SOjH CH-bonds in the alkyl chain can be oxidized. In acetonitrile a preferential acetamidation in the (co-2)- and ((B-l)-position occurs (Eq. 43) [352]. 

Metallic nitrates, supported on clays, have been used for nitrations and oxidations. Recent interesting studies involve nitration of 4-hydroxybenzaldehyde with Fe nitrate and KIO montmori I Ionite, in which nuclear nitration was preferentially realized and practically no oxidation of the aldehyde occurred. Even more interesting, simple addition of Fe nitrate to dealuminated or natural clay gave comparable or even better results. A 100% yield was realized at 60 °C with toluene as the solvent (Bekassy et al., 1998). 

The successes of hydrophilicity scales in correlating much data mean that one should not underestimate the importance of gs(dip). A plot of AHf (heat of formation of metal oxide, a measure of hydrophilicity) versus X(M) - X(Hg) shows two lines. Preferential orientation increases with oxygen affinity. Correlations between A Hf and X(M) - X(Hg) exist also for solvents other than water, with the rate of increase of X(M) - X(Hg) with A/f/being stronger in the sequence acetonitrile < H20 < DMSO, with increasing... 

Bayardon and Sinou have reported the synthesis of chiral bisoxazolines, which also proved to be active ligands in the asymmetric allylic alkylation of l,3-diphenylprop-2-enyl acetate, as well as cyclopropanation, allylic oxidations and Diels-Alder reactions. [62] The ligands do not have a fluorine content greater than 60 wt% and so are not entirely preferentially soluble in fluorous solvents, which may lead to a significant ligand loss in the reaction system and in fact, all recycling attempts were unsuccessful. However, the catalytic results achieved were comparable with those obtained with their non-fluorous analogues. 

The ideal systems for these media are those which do not require any additional solvent, and in which the substrate is more soluble than the product, leading to preferential rejection of the product from the catalyst phase. For fluorous reactions, this would include oxidation reactions where oxygenated products are typically more polar than the substrates. In ionic liquids it is products less polar than the substrates that will normally be less soluble, although the ability to tune the structure of ionic liquids to match a particular application must... 

We reported previously that the addition of H3PO4 (probably present as PO2.5 on the surface after the calcination) to (VO)2P207> which was prepared by an organic solvent method (5), enhanced the selectivity to MA at high conversion levels, while the activity decreased (20). Considering the low selectivity of the side faces, it is possible that the H3PO4 added preferentially deactivated the side faces to suppress the formation of CO and CO2 and/or the secondary oxidation of the product MA there. 

Mercuration of quinoline N-oxide in acetic acid or perchloric acid gives the 8-mercurio-chloride (26) as the main product and small amounts of the 3-, 5-, 6- and 7-isomers. In the absence of solvent mercury(II) sulfate gives all the possible isomers although the total yield is poor. 6-Methylquinoline N-oxide gives the 8-substituted derivative (27). The preferential 8-orientation is accounted for in terms of preliminary coordination of the mercury atom at the oxygen of the N-oxide. When the 8-position is blocked, as in 8-bromoquinoline N-oxide, mercuration is reported to occur at the 4-position (55YZ490, 69CPB906). 

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