Tin as reducing agent

Thorium oxybromide, 1 54 Tin, as reducing agent for complex tungsten(VI) chlorides in preparation of complex potassium chlorotungstates(III), 6 149 Tin compounds, halomethyl derivatives, by the diazomethane method, 6 37 (CH8) 2 (CH2C1) SnCl, 6 41 Tin (IV) iodide, 4 119 Titanium, powder by reduction of titanium (IV) oxide with calcium, 6 47... 

D) Preparation of Aniline (M.). (Use of tin as reducing agent.) Place 30 ml (35 g) of nitrobenzene and 65 g of tin in a flask. Provide with a reflux condenser, and add in 10-ml portions, over a period of half an hour, 140 ml of concentrated hydrochloric acid. The reaction should be vigorous it can be controlled by the rate of addition of the acid and by immersing the flask momentarily in a pail of cold water. The rate of addition can be... 

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). 

Cementation. A metal can be removed from solution by displacing it with a mote active metal. This simple, inexpensive method has been commonly used to recover copper from dilute (1—3 kg/m ) solution using shredded iron and de-tinned iron cans as reducing agent. 

Solutions of anhydrous stannous chloride are strongly reducing and thus are widely used as reducing agents. Dilute aqueous solutions tend to hydrolyze and oxidize in air, but addition of dilute hydrochloric acid prevents this hydrolysis concentrated solutions resist both hydrolysis and oxidation. Neutralization of tin(II) chloride solutions with caustic causes the precipitation of stannous oxide or its metastable hydrate. Excess addition of caustic causes the formation of stannites. Numerous complex salts of stannous chloride, known as chlorostannites, have been reported (3). They are generally prepared by the evaporation of a solution containing the complexing salts. 

Tin compounds, as reducing agents 954, 955 Transition metal compounds as oxidizing agents 982—985 as reducing agent 949, 950 Trichloromethanesulphenates, rearrangement of 718, 721 Trienes 748 synthesis of 956... 

The tin hydrides find important applications as reducing agents. Many of their reactions (particularly the reduction of alkyl halides and the hydrostannation of simple alkenes and alkynes) arc known to proceed through RaSn- intermediates, and this aspect of their chemistry is referred to in Section II,G. 

Tellurium, potassium hydroxide, water, phenylacetylene, a trialkylmethylammonium chloride as phase-transfer catalyst, either tin(IJ) chloride or hydrazine hydrate as reducing agent and toluene as the organic solvent upon heating at approximately 100 for six hours produced Z,Z-bis[2-phenylvinyl ditellurium in low yields. Polytelluride radical anions were postulated as intermediates2 3. 

The equilibrium constant of reaction (1), K = [Cu ][Cu ]/[Cu ], is of the order of 10 thus, only vanishingly small concentrations of aquo-copper(I) species can exist at equilibrium. However, in the absence of catalysts for the disproportionation—such as glass surfaces, mercury, red copper(I) oxide (7), or alkali (311)—equilibrium is only slowly attained. Metastable solutions of aquocopper(I) complexes may be generated by reducing copper(II) salts with europium(II) (113), chromium(II), vanadium(II) (113, 274), or tin(II) chloride in acid solution (264). The employment of chromium(II) as reducing agent is best (113), since in most other cases further reduction to copper metal is competitive with the initial reduction (274). 

Organoselenium compounds are very versatile radical precm-sors which are widely used. Due to their stability and ease of preparation, they offer imique advantages over organic halides as radical precm-sors. They can be utilized in tin mediated radical reactions as weU as in group transfer reactions for the formation of carbon-carbon bonds and carbon-heteroatom bonds. Selenols and diselenides have found applications as reducing agents and radical traps, respectively. A survey of these different reaction types wiU be given. Information about new reactions based on electron and photoelectron transfers wiU also be provided. 

The special characteristics of organotin hydrides as reducing agents are rationalized by the fact that the tin-hydrogen bond is both weaker and less polar than the B—H or A1—H bonds. These characteristics are manifested in reactions that proceed by either a free radical chain or polar mechanism, depending on the substrate, catalyst and reaction conditions. 

Comparison of tin and iron as reducing agents. Tin is traditionally used for the preparation of aniline in the laboratory, since it gives good yields. Iron is employed industrially as a reducing agent. The amount of hydrochloric acid used is less than 5 per cent of the... 

Solutions or suspensions of LAH in diethylether or THE in the presence of iron salts, C0CI2, TiCl3, or NiClj [ALl, G02] are used as reducing agents. Similarly, Li or NaBH,j in methanol, THE, or DME may be used in the presence of salts or complexes containing nickel, cobalt, tin, copper, palladium, or lanthanides [ALl, CY2, DGl, G02, PVl, YC2, YL5]. The structures of these reagents are often not... 

Stannous chloride and tin amalgam have been used as reducing agents. 

When tin(II) chloride is used [22], 1.5-3 M HCl is the most suitable medium. With hypophosphite as reducing agent, the acidity of the solution should be kept within the limits 0.1-0.4 M HCl or H2SO4. Since the colour (brown, blue, red) of the sol depends on the acidity and the kind and concentration of the reducing agent, the reaction conditions must be precisely the same for the sample solution and for the standard solutions. 

Water-soluble tin hydrides have been synthesized and studied as reducing agents for halides. The work of Breslow and coworkers is based on methoxyethoxypropyl substituents on the SnH moiety (7) in order to afford a water-soluble substrate [48], Another procedure for the reduction of bromides in the presence of a base-soluble dialkyltin(IV) reagent (8) and NaBH4 has been carried out [49]. The use of BujSnH in water solubilized by a suitable detergent has also been reported for the reduction of halides [50]. 

Another practical tin-free reducing agent for the Barton-McCombie deoxygenation is hypophosphorous acid and its salts. The utility of this reagent as a cheap and ecologically acceptable replacement for triorganostannanes was demonstrated by... 

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