Reducing agents sodium amalgam

The exact mechanistic pathway of the classical J-L olefination is unknown. Deuterium-labeling studies showed that the nature of the reducing agent (sodium amalgam or Smb) determines what type of intermediate (vinyl radical or secondary alkyl radical) is involved. Both intermediates are able to equilibrate to the more stable isomer before conversion to the product. The high ( )-selectivity of the Kocienski-modified reaction is the result of kinetically controlled irreversible diastereoselective addition of metalated PT-sulfones to nonconjugated aldehydes to yield anti-P-alkoxysulfones which stereospecifically decompose to the ( )-alkenes. 

Aluminum amalgam is also often used as reducing agent sodium amalgam is not recommended for reduction of aldehydes because of its basicity. 

Whereas mild reducing agents (sodium amalgam, zinc dust in hydrochloric acid) convert nitrosamines into A,A-disubstituted hydrazines, reduction by zinc and sulfuric acid or tin and hydrochloric acid cleaves with regeneration of the secondary amine.159 Nitrosamines are also cleaved smoothly by dilute sulfuric acid containing urea.160... 

It can be seen that the (111) state is highly stable with respect to disproportionation in aqueous solution and is extremely difficult to oxidize or reduce. There is evidence for the existence of the (II) state since tracer amounts of amencium have been reduced by sodium amalgam and precipitated with barium chloride or europium sulfate as earner. The (IV) state is very unstable in solution the potential for americium(III)-ameridum(IV) was determined by thermal measurements involving solid Am02. Amencium can be oxidized to the (V) or (VI) state with strong oxidizing agents, and the potential for the americium(V)-americium(Vl) couple was determined potentiometrically. 

Naphthalenecyclopentadienyliron tetrafiuoroborate, when reduced with sodium amalgam under very mild conditions (at —20°C), gave the product of exchange of arene for another ligand (arene, CO). The reaction does not work in the absence of a reducing agent, hence it may also be supposed to proceed via the reduction of the cation and formation of the intermediate (359). 

This reaction was first reported by Akabori in 1931. It is the synthesis of an aldehyde, an a-amino aldehyde, or a primary amine from a-amino acid under different reaction conditions. In the presence of a reducing agent (usually a reducing sugar), an a-amino acid is oxidized to an aldehyde and ammonia by molecular oxygen (Scheme 1). For comparison, the a-amino acid ester is reduced by sodium amalgam in alcoholic solution in the presence of hydrochloric acid to give an a-amino aldehyde (Scheme 2). However, under pyrolytic condition, the a-amino acid is converted to primary amine in the presence of benzaldehyde (Scheme 3). 

The metal is slowly oxidised by air at its boiling point, to give red mercury(II) oxide it is attacked by the halogens (which cannoi therefore be collected over mercury) and by nitric acid. (The reactivity of mercury towards acids is further considered on pp. 436, 438.) It forms amalgams—liquid or solid—with many other metals these find uses as reducing agents (for example with sodium, zinc) and as dental fillings (for example with silver, tin or copper). 

Dithionites. Although the free-dithionous acid, H2S2O4, has never been isolated, the salts of the acid, in particular zinc [7779-86-4] and sodium dithionite [7775-14-6] have been prepared and are widely used as industrial reducing agents. The dithionite salts can be prepared by the reaction of sodium formate with sodium hydroxide and sulfur dioxide or by the reduction of sulfites, bisulfites, and sulfur dioxide with metallic substances such as zinc, iron, or zinc or sodium amalgams, or by electrolytic reduction (147). 

Hydrocinnamic Acid.—The preparation illustrates the use of sodium amalgam as a reducing agent It should be noted that hydiocinnamic acid may be also obtained from m.donic ester by acting upon the sodium compound nith benzyl chloride, then hydrolysing and removing carbon dioxide,... 

Conversely, sulfites can act as oxidants in the presence of strong reducing agents e.g. sodium amalgam yields dithionite, and formates (in being oxidized to oxalates) yield thiosulfate ... 

Reduction of 16-keto-17(0i)-hydroxyestratrienol-3-methyl to 16,17-dihydroxyestratrienol-3-methyl ether A solution of 800 mg of the alpha ketol methyl ether in 100 cc of ethanol and 10 cc of acetic acid was carefully maintained at 40°C (water bath), and 200 g of freshly prepared sodium amalgam (2%) were added in small pieces with efficient swirling. Before all of the amalgam had been added, a precipitation of sodium acetate occurred, and at this point an additional 100 cc of 50% acetic acid were added. After all the reducing agent had been added, the mixture was transferred to a separatory funnel with ether and water. 

The Julia olefination involves the addition of a sulfonyl-stabilized carbanion to a carbonyl compound, followed by elimination to form an alkene.277 In the initial versions of the reaction, the elimination was done under reductive conditions. More recently, a modified version that avoids this step was developed. The former version is sometimes referred to as the Julia-Lythgoe olefination, whereas the latter is called the Julia-Kocienski olefination. In the reductive variant, the adduct is usually acylated and then treated with a reducing agent, such as sodium amalgam or samarium diiodide.278... 

This is by far the most important reaction of tetrazolium salts and accounts for the bulk of their many applications. A large variety of reagents can reduce tetrazolium salts, e.g., 53 to formazans, e.g., 51. Ascorbic acid, hydrazine, and hydroxylamine have been recommended for the preparation of formazans from tetrazolium salts.245 Stronger reducing agents such as ammonium sulfide, sodium amalgam, sodium dithionite, and catalytic hydrogenation can further reduce the formazans to the amidrazones, e.g.,... 

The resultant radical (86) can, in turn, be reduced back to the carbanion by shaking with sodium amalgam. In suitable cases, e.g. (87), the oxidation of carbanions with one-electron oxidising agents, usually iodine, can be useful synthetically for forming a carbon-carbon bond, through dimerisation (— 88) of the resultant radical (89) ... 

In 1937 Hunter and Hlynka were able to reduce a methanolic solution of 4(5)-nitroimidazole (27 R = H) with sodium amalgam and trap the 4(5)-aminoimidazole (25 R = H) with cyanic acid giving the urea derivative (31) (37BJ488). Other reducing agents gave inferior results. Subsequently, 4(5)-aminoimidazole (25 R = H) was obtained as either its dihydrochloride (30%) or dipicrate salt but the isolation procedures were lengthy and difficult (41 Mil). 

The neutralization values were influenced by reduction with strong reducing agents, lithium aluminum hydride, sodium borohydride, and amalgamated zinc plus hydrochloric acid (35, 46). For the most part, the consumption of NajCOj and of NaOEt decreased in equivalent amounts. This is further confirmation of the assumption that lactones of the fluorescein type or of the lactol type are present. The reaction with sodium ethoxide was shown to be no true neutralization, that is, exchange of H+for Na+, at all, but an addition reaction w ith the formation of the sodium salt of a semi-acetal or ketal ... 

In the non-cyclic alkenone series, regiosdectivity in the hydrodimerization step is not well controlled. Dissolving metal reducing agents such as sodium amalgam,... 

The superiority of catalytic hydrogenation over reduction with sodium or aluminum amalgam as a means of converting hexoses to hexitols is apparent. The yields approach or reach the theoretical and the isomerizing effect of the alkaline reducing agent is avoided. Electrolytic reduction is not suitable as a laboratory method. 

Sodium amalgam can also be employed as a reducing agent. However, in this case a prolonged heating (50 hr at 55-60°) is required because of insolubility of frans-PtCl,[P(eyc/o-C4Hi1)3], in tetrahydrofuran. 

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