Excess-oxidant oxidation, description

The only satisfactory method of preparing /3-naphthoquinone is by the oxidation of 1,2-aminonaphthol in acid solution, and the chief problem involved is that of the preparation of this intermediate in suitable yield and purity. This problem and the literature pertaining to it are discussed elsewhere. Most reports of the preparation of the aminonaphthol include some description of its oxidation, but the only particularly helpful comment on the reaction is that ferric chloride is a better oxidizing agent than chromic acid because at a low temperature it docs not attack the quinone, even when present in excess. ... 

The traditional unpredictably violent nature of the Skraup reaction (preparation of quinoline and derivatives by treating anilines with glycerol, sulfuric acid and an oxidant, usually nitrobenzene) is attributed to lack of stirring and adequate temperature control in many published descriptions [1], A reaction on 450 1 scale, in which sulfuric acid was added to a stirred mixture of aniline, glycerol, nitrobenzene, ferrous sulfate and water, went out of control soon after the addition. A 150 mm rupture disk blew out first, followed by the manhole cover of the vessel. The violent reaction was attributed to doubling the scale of the reaction, an unusually high ambient temperature (reaction contents at 32°C) and the accidental addition of excess acid. Experiment showed that a critical temperature of 120°C was attained immediately on addition of excess acid under these conditions [2],... 

As follows from the results obtained, numerous parameters influence the quality of precipitates, vs raw materials used (such as, manganese sulphate, nitrate, chloride) pH of initial and final solutions the excess of the oxidant the type of a neutralizing agent (lithium, sodium, potassium hydroxide) the washing method, and pH of leachates. More detailed description of the synthetic routine will be published elsewhere. 

Nickel oxide is a classical nonstoichiometric oxide that has been studied intensively over the last 30-40 years. Despite this, there is still uncertainty about the electronic nature of the defects present. It is well accepted that the material is an oxygen-excess phase, and the structural defects present are vacancies on cation sites. Although it is certain that the electronic conductivity is by way of holes, there is still hesitancy about the best description of the location of these charge carriers. 

Dimesityldioxirane, a crystalline derivative, has been isolated by Sander and colleagues and subjected to X-ray analysis. The microwave and X-ray data both suggest that dioxiranes have an atypically long 0—0 bond in excess of 1.5 A. Those factors that determine the stability of dioxiranes are not yet completely understood but what is known today will be addressed in this review. A series of achiral, and more recently chiral oxygen atom transfer reagents, have been adapted to very selective applications in the preparation of complex epoxides and related products of oxidation. A detailed history and survey of the rather remarkable evolution of dioxirane chemistry and their numerous synthetic applications is presented in Chapter 14 of this volume by Adam and Cong-Gui Zhao. Our objective in this part of the review is to first provide a detailed theoretical description of the electronic nature of dioxiranes and then to describe the nuances of the mechanism of oxygen atom transfer to a variety of nucleophilic substrates. 

In summary, catalytic C-H transformations in small unfunctionalized alkanes is a technically very important family of reactions and processes leading to small olefins or to aromatic compounds. The prototypical catalysts are chromia on alumina or vanadium oxides on basic oxide supports and platinum on alumina. Reaction conditions are harsh with a typical minimum temperature of 673 K at atmospheric pressure and often the presence of excess steam. A consistent view of the reaction pathway in the literature is the assumption that the first C-H abstraction should be the most difficult reaction step. It is noted that other than intuitive plausibility there is little direct evidence in heterogeneous reactions that this assumption is correct. From the fact that many of these reactions are highly selective toward aromatic compounds or olefins it must be concluded that later events in the sequence of elementary steps are possibly more likely candidates for the rate-determining step that controls the overall selectivity. A detailed description of the individual reactions of C2-C4 alkanes can be found in a comprehensive review [59]. 

The thermodynamic approach considers micropores as elements of the structure of the system possessing excess (free) energy, hence, micropore formation processes are described in general terms of nonequilibrium thermodynamics, if no kinetic limitations appear. The applicability of the thermodynamic approach to description of micropore formation is very large, because this one is, in most cases, the result of fast chemical reactions and related heat/mass transfer processes. The thermodynamic description does not contradict to the fractal one because of reasons which are analyzed below in Sec. II. C but the nonequilibrium thermodynamic models are, in most cases, more strict and complete than the fractal ones, and the application of the fractal approach furnishes no additional information. If no polymerization takes place (that is right for most of processes of preparation of active carbons at high temperatures by pyrolysis or oxidation of primary organic materials), traditional methods of nonequilibrium thermodynamics (especially nonequilibrium statistical thermodynamics) are applicable. 

On p-hydroxyalkyl phenyl selenides, die oxidation-elimination is best achieved with an excess of 30% aqueous hydrogen peroxide according to die original description of Sharpless (Scheme 174, c and d). Although l-(l -hycyclohexyl phenyl selenide p uces under these conditions a hydroperoxide (Scheme 174, a), the sired elimination reaction has been successfully achieved with sodium periodate in ethanol (Scheme 174, b). 

A specific description of a preferred practice of the invention with vanillin as the aromatic compound is as follows. Vanillin is dissolved in water with one molar equivalent of sodium hydroxide while the solution is warmed to 50°-100° C. One molar equivalent of iodine and two molar equivalents of sodium iodide are added to water to prepare one molar equivalent of NalS.Nal. This sodium triiodide solution is added to the sodium vanillate solution along with a catalytic amount of sulfuric acid--preferably from 5 to 10 mole %. The mixture is stirred about one hour at a temperature of 50°-100° C., then sodium hydroxide is added to make the solution alkaline (from 1 to 5N). The copper catalyst is then added and the mixture heated at reflux until the iodovanillin is consumed, about 12 hours. The excess hydroxide is then neutralized and the 5-hydroxyvanillin extracted with a water-immiscihle organic solvent. The aqueous phase bearing the sodium iodide is then subjected to oxidizing conditions and the resultant iodine precipitates from solution. The solid element is filtered out, and a sodium triiodide solution prepared by reducing a portion of the iodine to sodium iodide and dissolving the iodine in the iodide to make the sodium triiodide solution. 

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