Methods of reduction

A great variety of reduction methods have been used for the preparation of amines. Among these are  

Metal and acid. Iron and acid (B champ method) is the major example in this category, but other metals (tin, zinc) have also been employed. Generally, hydrochloric acid is preferred, but sulfuric, acetic, and formic acids have also been used. 

Catalytic. This method involves the use of hydrogen (or hydrogen-containing gases) and a catalyst such as nickel, copper, platinum, palladium, or molybdenum sulfide. 

Sulfide. This is used mainly for the partial reduction of pol3mitro aromatic compounds to nitroamines and for the reduction of nitroanthra-quinones to aminoanthraquinones. 

Metal and alkali. This method is used mainly for the production of azoxy, azo, and hydrazo compounds. The latter are important in the manufacture of the benzidine series. 

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Aliphatic hydrocarbons can be prepared by the reduction of the readily accessible ketones with amalgamated zinc and concentrated hydrochloric acid (Clemmensen method of reduction). This procedure is particularly valuable for the prep>aration of hydrocarbons wdth an odd number of carbon atoms where the Wurtz reaction cannot be applied with the higher hydrocarbons some secondary alcohol is produced, which must be removed by repeated distillation from sodium. 

As mentioned previously, aldehydes can be prepared by Stephen s method of reduction of nitriles by stannous chloride (37, 91). Polaro-graphic reduction of thiazolecarboxylic acids and their derivatives gives lower yields of aldehydes (58). Ozonolysis of styrylthiazoles, for example, 2-styryl-4-methylthiazole, followed by catalytic reduction gives aldehyde with 47% yield of crude product (30). 

In the alternative method of reduction, which is particularly valuable for the determination of small amounts of tellurium, the procedure is as follows. Treat the solution containing, say, up to about 0.01 g Te in 90 mL with 10 mL of 1 3-sulphuric acid, then add 10 g sodium hypophosphite (phosphinate), and heat on a steam bath for 3 hours. Collect and weigh the precipitated tellurium as above. 

But then is the characteristic polynomial of A, and its coefficients are the elements of / and can be found by solving Eq. (2-11). This is essentially the method of Krylov, who chose, in particular, a vector et (usually ej) for vx. Several methods of reduction of the matrix A can be derived from applying particular methods of inverting or factoring V at the same time that the successive columns of V are being developed. Note first that if... 

The treatment in this chapter has been theoretical. For a brief, dear, and very practical description of computational details for a number of standard problems, [10] is unsurpassed, and [12] can be recommended for programming techniques for automatic computers. For information on ordinary differential equations, the reader should consult [2], and for partial differential equations, [1]. For general methods of reduction to algebraic form as well as methods of solution, see [5], [7], and [8]. 

This is evidently the most popular method of reduction depending on the reaction ... 

This procedure is illustrative of the general method of reduction of aromatic compounds by alkali metals in liquid ammonia known as the Birch reduction. The theoretical and preparative aspects of the Birch reduction have been discussed in excellent reviews,4-4... 

The Leuckart-Wallach reaction is the oldest method of reductive amination of carbonyl compounds. It makes use of formamide, formic acid or ammonium formate at high temperature. The final product is a formamide derivative, which can be converted to an amine by reduction or hydrolysis. The method has been applied to the preparation of 1,2-diamines with a norbornane framework, which are interesting rigid analogues of 1,2-diaminocyclohexanes. As a matter of fact, starting from N-acetyl-2-oxo-l-norbornylamine 222, the diamide 223 was obtained with excellent diastereoselectivity and then converted to the M-methyl-N -ethyl derivative 224 by reduction with borane [ 104] (Scheme 34). On the other hand, when the reac-... 

Reactions of Mg Generated by Lithium/Naphthalene. Although we have not exhaustively duplicated the previous reactions with the newer method of reduction, examination of Table I shows comparable reactivity for the reagents tested. Instead, we hav branched out to look at other facets of the chemistry accessible with Mg. ... 

Most of the methods for preparation of /3-naphthaldehyde have been given previously.2 A recent procedure describes the preparation of /3-naphthaldehyde from 2-bromomethylnaphthalene and hexamethylenetetramine in boiling acetic acid.3 The method of reduction of nitriles by stannous chloride was discovered by Stephen.4... 

Cross-coupling reactions of nitrones with aldehydes and ketones make it possible to synthesize vicinal amino alcohols, which are common in natural products. These transformations have been performed by a new method of reduction... 

From the seminal studies of Sabatier [43] and Adams [44] to the more recent studies of Knowles [45] and Noyori [46], catalytic hydrogenation has been regarded as a method of reduction. The results herein demonstrate the feasibility of transforming catalytic hydrogenation into a powerful and atom-economical method for reductive C-C bond formation. Given the profound socioeconomic impact of al-kene hydroformylation, the development of catalysts for the hydrogen-mediated... 

A different method of reduction involves the reaction with strong base, such as OH- and OR-. In this case, the primary reaction is nucleophilic attack on a carbon atom of a terminal carbonyl group as shown by the formation of a carboalkoxy group on reaction with alkoxide ... 

The least powerful method of reduction, boiling nitrobenzene with sodium methoxide in solution in methyl alcohol, provides azoxybenzene in excellent yield (Zinin) the methoxide is converted into formate. (Write the equation.)... 

This PSH technique was later utilized as an effective method of reductive modification for the unsaturated polymers such as polydiene rubbers and polypentenamer by Mango (2) and Samui et al ( ) ... 

The stereoselectivity of different catalysts in catalytic hydrogenations is discussed in the chapter on catalysts (pp. 4, 50). In addition to catalytic hydrogenation, a few other methods of reduction can be used for saturation of carbon-carbon double bonds. However, their practical applications are no match for catalytic hydrogenation. 

Triple bonds in side chains of aromatics can be reduced to double bonds or completely saturated. The outcome of such reductions depends on the structure of the acetylene and on the method of reduction. If the triple bond is not conjugated with the benzene ring it can be handled in the same way as in aliphatic acetylenes. In addition, electrochemical reduction in a solution of lithium chloride in methylamine has been used for partial reduction to alkenes trans isomers, where applicable) in 40-51% yields (with 2,5-dihydroaromatic alkenes as by-products) [379]. Aromatic acetylenes with triple bonds conjugated with benzene rings can be hydrogenated over Raney nickel to cis olefins [356], or to alkyl aromatics over rhenium sulfide catalyst [54]. Electroreduction in methylamine containing lithium chloride gives 80% yields of alkyl aromatics [379]. 

Screttas and Micha-Screttas synthesized various dilithiated alkyls by the method of reductive sulphur-carbon bond cleavage with metallic lithium. The example of compound 147 shows that thioethers 146 are cleaved selectively in the presence of ether functionalities (Scheme 53). ... 

The procedure avoids the troubles of filtration incidental to the method of reduction with ferrous sulfate and ammonia, and the yield is better. Inasmuch as the only by-product is the very soluble ammonium acetate, a large yield can be secured by close evaporation. 

So the principal idea of the method of ansatzes, as well as of the direct method of reduction of partial differential equations is a special choice of the class of functions to which the solution to be found should belong. Within the framework of the preceding methods, a solution of system (46) is sought in the form... 

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