Reduction by Other Methods

When the conditions are controlled properly, Zn can mediate the reduction of the C-C double bond of a, P-unsaturated carbonyl compounds in the presence of a nickel catalyst in aqueous ammonium chloride (Eq. 10.7). The use of ultrasonication enhances the rate of the reaction. Sodium hydrogen telluride, (NaTeH), prepared in situ from the reaction of 

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A number of salts of the monofluoro- and hexafluorophosphoric acids are known and some are commercially important. The salts of difluorophosphoric acid are typically less stable toward hydrolysis and are less well characterized. Sodium monofluorophosphate [7631-97-2] the most widely used dentifrice additive for the reduction of tooth decay, is best known (see Dentifrices). Several hexafluorophosphates can be prepared by neutralization of the appropriate base using hexafluorophosphoric acid. The monofluorophosphates are usually prepared by other methods (57) because neutralization of the acid usually results in extensive hydrolysis. 

Starting compounds include hexa- and pentarylethanes the latter require higher temperatures (ca 100°C) than the former to break the carbon—carbon bond. In the presence of oxygen, stable radicals that are generated by other methods, eg, reduction of arylmethyl ethers and haUdes, also have been converted to diaralkyl peroxides (66). 

Although this reduction is more expensive than the Bnchamp reduction, it is used to manufacture aromatic amines which are too sensitive to be made by other methods. Such processes are used extensively where selectivity is required such as in the preparation of nitro amines from dinitro compounds, the reduction of nitrophenol and nitroanthraquinones, and the preparation of aminoazo compounds from the corresponding nitro derivatives. Amines are also formed under the conditions of the Zinin reduction from aromatic nitroso and azo compounds. 

Carbon Reduction. The production of ferrovanadium by reduction of vanadium concentrates with carbon has been supplanted by other methods. An important development has been the use of vanadium carbide as a replacement for ferrovanadium as the vanadium additive in steelmaking. A... 

Pyrazolopyridines isomeric to those described previously have been obtained by other methods. Thus, the derivative (558) was formed by Raney nickel reduction of the 4-nitrosopyrazole (557) (7UHC1035), and the pyrazolo[3,4-c]pyridine derivative (560) was prepared from the azide (559) (79CC627). 

The present procedure was developed from those of Wallach and Freylon, based upon the general method discovered by Leuckart. a-Phenylethylamine also can be prepared satisfactorily by the reduction of acetophenone oxime with sodium and absolute alcohol or sodium amalgam, but the reagents are more expensive and the processes less convenient. The amine has been obtained by reducing acetophenone oxime electro-lytically, by reducing acetophenone phenylhydrazone with sodium amalgam and acetic acid, from a-phenylethyl bromide and hexamethylenetetramine, and by the action of methyl-magnesium iodide upon hydrobenzamide, as well as by other methods of no preparative value. 

Reduction of benzofuroxans is usually the most convenient route to benzofurazans and o-quinone dioximes (see Section VI, C). Reduction of 4-nitrobenzofuroxan would seem to be a method of synthesis of 1,2,3-triaminobenzene, while the haloalkoxy-substitution reaction (Section VTT,B) and the rearrangements of Section VIII provide compounds accessible only with difficulty by other methods. Apart from these reactions, the benzofuroxans appear to be of limited synthetic utility. 

ZnTe The electrodeposition of ZnTe was published quite recently [58]. The authors prepared a liquid that contained ZnGl2 and [EMIM]G1 in a molar ratio of 40 60. Propylene carbonate was used as a co-solvent, to provide melting points near room temperature, and 8-quinolinol was added to shift the reduction potential for Te to more negative values. Under certain potentiostatic conditions, stoichiometric deposition could be obtained. After thermal annealing, the band gap was determined by absorption spectroscopy to be 2.3 eV, in excellent agreement with ZnTe made by other methods. This study convincingly demonstrated that wide band gap semiconductors can be made from ionic liquids. 

The reductive alkylation of DAP with acetone led to high conversions and selectivity to the dialkylated product over Al, Bl, and BS2 catalysts. The ASl catalyst, which typically has lower activity than the Al or Pt-based catalysts showed greater formation of heterocycles. These results indicate that a more active catalyst, a shorter reaction time, a higher operating temperature, or sterically hindered amines/ketones will help minimize the formation of the heterocycles. Similar high selectivities were obtained with DAP-MIBK reaction over BSl and BS2 catalysts with no heterocycles being formed. However, over Al, the undesired heterocyclic compound was over 15%. This indicates that the reaction between diamines and ketones has a significant potential to form heterocyclic compounds unless the interaction between these is kept to a minimum by the use of a continuous flow reactor as proposed by Speranza et al. (16) or by other methods. 

Reduction by diimide can be advantageous when compounds contain functional groups that would be reduced by other methods or when they are unstable to hydrogenation catalysts. There are several methods for generation of diimide and they are illustrated in Scheme 5.4. The method in Entry 1 is probably the one used most frequently in synthetic work and involves the generation and spontaneous decarboxylation of azodicarboxylic acid. Entry 2, which illustrates another convenient method, thermal decomposition of p-toluenesulfonylhydrazide, is interesting in that it... 

An extension of the reduction-chlorination technique described so far, wherein reduction and chlorination occur simultaneously, is a process in which the oxide is first reduced and then chlorinated. This technique is particularly useful for chlorinating minerals which contain silica. The chlorination of silica (Si02) by chlorine, in the presence of carbon, occurs above about 1200 °C. However, the silica present in the silicate minerals readily undergoes chlorination at 800 °C. This reaction is undesirable because large amounts of chlorine are wasted to remove silica as silicon tetrachloride. Silica is, therefore, removed by other methods, as described below, before chlorination. Zircon, a typical silicate mineral, is heated with carbon in an electric furnace to form crude zirconium carbide or carbonitride. During this treatment, the silicon in the mineral escapes as the volatile oxide, silicon monoxide. This vapor, on contact with air, oxidizes to silica, which collects as a fine powder in the furnace off-gas handling system ... 

Although it has been known since 19051 that very pure chromium metal reacts with acids, under oxygen-free conditions, to produce large quantities of chromium (II), this approach to the preparation of chromium(II) compounds has not been developed. Rather, syntheses generally involved (1) reduction of chro-mium(III), either by electrolytic means or by chemical agents (for example Zn/Hg), or (2) metathetical procedures. Both methods are inefficient and often lead to impure products. Recently2-8 extensive use of reactions between electrolytic chromium and various acids has led to the synthesis of a wide variety of chromium (II) complexes which would be considerably more difficult to prepare by other methods.9-11... 

In the virial methods, therefore, the activity coefficients account implicitly for the reduction in the free ion s activity due to the formation of whatever ion pairs and complex species are not included in the formulation. As such, they describe not only the factors traditionally accounted for by activity coefficient models, such as the effects of electrostatic interaction and ion hydration, but also the distribution of species in solution. There is no provision in the method for separating the traditional part of the coefficients from the portion attributable to speciation. For this reason, the coefficients differ (even in the absence of error) in meaning and value from activity coefficients given by other methods. It might be more accurate and less confusing to refer to the virial methods as activity models rather than as activity coefficient models. 

The reduction of an isolated carbon-carbon double bond by other methods is exceptional. Occasionally an isolated double bond has been reduced elec-Irolylicolly 344 and by dissolving melols. Sodium under special conditions -using tert-butyl alcohol and hexamethylphosphoramide as solvents - reduces alkenes and cycloalkenes in 40-100% yields [345. 3-Methylenecholestane, for example, afforded 3-methylcholestane in 74% yield on heating for 2 hours at 55-57° with lithium in ethylenediamine [346]. 

Methods of synthesis of 3-chloro- and 3,4-dichloro-thiophenes have usually involved tedious procedures in which tri- and tetra-chloro derivatives are dechlorinated by reductive or other methods. Gthanolic potassium hydroxide converted 2,3,4,5-tetrachlorothiophene into a 50 50 mixture of 2,4- and 3,4-dichlorothiophenes direct heating of the same tetrachloro substrate gave a mixture of 2,3- and 2,4-dichloro isomers (48JA1158). 3,4,5-Trichlorothiophene was readily prepared by the reaction of 1,1,2,3-tetrachloro-l,3-butadiene with sulfur (82JOU348). 

In a first reactor, where benzoylformate decarboxylase (BFD) is retained, benz-aldehyde and acetaldehyde are coupled to yield (S)-hydroxy-l-phenylpropanone. This hydroxy ketone is then reduced to the corresponding diol in a second reactor by an alcohol dehydrogenase (ADH). Regeneration of the necessary cofactor is achieved by formate dehydrogenase (FDH) or by other methods. To avoid additional consumption of redox equivalents by unselective reduction of residual starting material from the first reactor, the volatile aldehydes are removed via an inline stripping module between the two membrane reactors. In this setup the diol was produced with high optical purity (ee, de > 90%) at an overall space-time yield of 32 g L d . ... 

Diphenyl-methanol, Diphenylmethylol, Benz-hydrol or Diphenylcarhinol, (CgHs CHOH, mw 184,23 ndls, mp 68—69°, bp 298.5° si sol in w v sol in ale, eth, chlf CC14 insol in iigroin can be prepd by reduction of benzophenone (C8H5)2CO with Mg or Zn dust and by other methods (Refs 1 2)... 

Materials obtained from the LDH show a reduction in SSA with the temperature as reported in the literature. This reduction can be attributed to the crystallisation of the material [15,17]. However, post-treatment with mineral acid was an increase in the SSA for all temperatures. It is possible to attribute this increase to two combined effects, which can both increase the porosity of the materials, as well as yield more active adsorption sites (i) the elimination of ZnO and (ii) the elimination Zn(II) cations occupying octahedral sites in the spinel oxide structure. Even though the SSA had varied sensibly, the average pore size (APS) remained fairly constant with temperature. Acid treatment increases the APS value for all temperature tested, although the effect was very small (Figure 5b). Comparison of the materials obtained by the different synthesis methods showed that spinel oxides obtained from the LDH presented greater SSA values than those obtained by other methods, principally after the posttreatment with mineral acid. On other hand, the treatment with acid had little influence on the textural properties of the spinel oxides obtained by the other methods. 

Carbon-carbon multiple bonds are most commonly reduced to saturated hydro carbons by hydrogenation or by other methods, such as the use of hydrides. While a large number of alkenes have been reduced under microwave irradiation, surprisingly little work has been published on microwave-assisted reduction of alkynes. 

This preparation illustrates the alkylation of malononitrile under acid-catalyzed conditions, and the use of diborane for the reduction of a dinitrile to a diamine. The procedure for the preparation of tert-butylmalononitrile has been outlined briefly by Boldt and co-workers.2 The generation of diborane in situ and the general method for nitrile reduction is that described by Brown and co-workers.3 Attempts to reduce the dinitrile to the diamine by other methods including catalytic hydrogenation (5% rhodium on alumina, 5 atm.), lithium aluminum hydride, and lithium aluminum hydride-aluminum chloride were singularly unsuccessful. 

Amino biphenyl, leaflets(from ale), mp 53-55°, bp 302° diff sol in cold w sol in ale, eth, chlf hot w. Was first prepd by Hofmann (Ref 2) from the high boiling residue obtained in the manuf of aniline and named "Xenyla-min . It can also be prepd by the reduction of 4-nitrobiphenyl or by other methods(Ref 1) When a salt of 4-aminobiphenyl, such as the hydrochloride, is treated with NaN02+acid, diazotization takes place. If diazotization of aminobiphenyl is followed by treatment with perchloric acid the resulting compd is an explosive, biphenyldiazonium perchlorate. 

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