Preparation sodium-potassium alloy

These reactions are usehil for the preparation of homogeneous difunctional initiators from a-methylstyrene in polar solvents such as tetrahydrofuran. Because of the low ceiling temperature of a-methylstyrene (T = 61° C) (26), dimers or tetramers can be formed depending on the alkaU metal system, temperature, and concentration. Thus the reduction of a-methylstyrene by sodium potassium alloy produces the dimeric dianionic initiators in THF (27), while the reduction with sodium metal forms the tetrameric dianions as the main products (28). The stmctures of the dimer and tetramer correspond to initial tail-to-tail addition to form the most stable dianion as shown in equations 6 and 7 (28). 

Sodium—potassium alloy is easily prepared by melting the clean metals ia an iaert atmosphere or under an iaert hydrocarbon, or by the reaction of sodium with molten KCl, KOH, or soHd K CO powder. 

Preparation of Acyloins. When aUphatic esters are allowed to react with metallic sodium, potassium, or sodium—potassium alloy in inert solvents, acyloins (a-hydroxyketones) are formed (45) ... 

Arylsilane radical anions undergo cleavage and coupling reactions, usually under conditions where excess reducing agent is available. Reduction of phenylsilane, diphenylsilane, or triphenylsilane with sodium-potassium alloy under preparative conditions gives high yields of tetraphenylsilane (7). In the reduction of phenylsilanes, the appearance of 1,4-bis(silyl)benzene radical anions is frequently observed (135, 35, 86, 97, 75, 120, 100). Typical results are shown in Table II. 

Higher homologues are coveniently prepared from sodium potassium arsenide and chlorosilanes. The arsenide is a complex mixture formed by mixing a sodium-potassium alloy with powdered arsenic suspended in 1,2-dimethoxyethane (equation l).36... 

The six-membered permethylated analogue dodecamethylcyclohexasilane, however, can be prepared conveniently from Me2SiCl2 with sodium-potassium alloy in THF in the presence of an equilibrating catalyst, which causes depolymerization of the initially formed permethylpolysilane polymer6,7 (equation 2). 

Methylborylene [62785-41-5] B Preparative hazard See Dibromomethylborane Sodium—potassium alloy (next below) See related ALKYLBORANES ch3b... 

Three permethylated cyclosilanes of the formula [(CH3)2Si]B with n=5-7 are prepared by allowing dimethyldichlorosilane to react with sodium-potassium alloy in tetrahydrofuran. From this reaction, an insoluble polymeric mass and a crystalline solid are produced (21, 177). The latter consists, for the most part, of dodecamethylcyclohexasilane but it also contains decamethylcyclopentasilane and tetradecamethylcycloheptasilane in small quantities. The amounts of both five- and seven-membered cyclosilanes are much increased if the reaction is worked up immediately after the addition of the dichlorosilane is completed with little or no refluxing. The three cyclosilanes can be separated by preparative gas chromatography 21). 

Nowadays this important compound can be easily prepared on a scale up to 200 g when an emulsion of white phosphorus in 1,2-dimethoxyethane is treated vrith liquid sodium-potassium alloy and excess chlorotrimethylsilane is added to the suspension of the hitherto scarcely characterized Zintl phases Na3P and K3P, respectively. With decreasing yield the tris(trimethylsilyl) derivatives of arsane [3], stibane [4], and bismuthane [5] have also been obtained in the same way (Eq. 1). Meanwhile, hesitation to handle dangerous sodium-potassium alloy or white phosphorus led to the development of similar methods to prepare the phosphane [6,7]. 

Dimethylphosphido-bridged complexes of the type [ M(CO)4(/ -PMe2)>2] (27) (M = Cr, Mo, and W) undergo reversible two-electron reduction to the corresponding dianions (53, 54)-, NMR spectroscopy showed that [27] , prepared by allowing 27 to react with sodium-potassium alloy, are fluxional (55). The monoanions [27]" were prepared... 

Deoxyiodination has been used for the synthesis of 17 (n = 4). ° For the preparation of bi-cyclo[1.1.0]butane 17 (n = 1) and congeners thereof, special conditions are required. Reaction of l-bromo-3-chlorocyclobutane with sodium in refluxing dioxane gave bicyclo[l. 1. OJbutane in 90% yield a detailed experimental procedure is given.Hexamethylbicyclo[l, 1.0]butane was similarly obtained in 75% yield using sodium-potassium alloy in 1,2-dimethoxyethane. ... 

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