Lithium amalgam

Benzyne can also be generated from o-dihaloaromatics. Reaction of lithium amalgam or magnesium results in formation of a transient organometallic compound that decomposes with elimination of lithium halide. l-Bromo-2-fluorobenzene is the usual starting material in this procedure. 

Highly fluonnated alkanes are also reduced by alkali metals Lithium amalgam converts polytetrafluoroethyleneto acarbon polymer composed of monolayer nbbons of six membered rings with hthium atoms bound to the edges [i]... 

The reaction of an alicyclic enamine with benzyne intermediate yields simple arylation products and/or 1,2-cycloaddition products, depending upon the reaction conditions 102). This is illustrated by the reaction of l-(N-pyrrolidino)cyclohexene with benzyne (86) (obtained from fluoro-benzene and butyl lithium or o-bromofluorobenzene and lithium amalgam), which produces benzocyclobutene 87 102). 

Treatment of dihalogeno aromatics with lithium amalgam, magnesium, zinc, etc.,... 

Pyridyne (26) has been shown to exist by trapping it with furan. It must be considered to be an intermediate in the reaction of 3-bromo-2-chloropyridine (49) with lithium amalgam because in the presence of furan a small amount (2%) of quinoline (50) is formed. ... 

Quinolynes are generated and behave analogously to pyridynes. The reaction of 3-bromo-4-chloro- and 3-bromo-2-chloro-quinoline with lithium amalgam in the presence of furan gives phenanthridine (83, 9% yield) and acridine (85, 0.1% yield), respectively, via 3,4-... 

Lithium aluminum tn t butoxyhj dride in reduction of 3 acetoxy 5-pregnene 20 one, 46, 58 Lithium amalgam, reaction with 3,4-dichloro 1,2,3,4 tetramethylcy clobutene, 46, 36... 

For example, the reaction enthalpy for the reduction of PC proceeding at lithium amalgam to form propylene gas and lithium carbonate is estimated to be -I41kcal (molPC)-1 [149]. PC is reduced at noble-metal electrodes at potentials below 1.5 V vs. Li, and yields lithium alkyl carbonates when lithium salts are the supporting electrolytes. Reduction occurs at 0.7-0.8 V vs. Li with Bu4NC104as supporting electrolyte [150],... 

P9.3 The potentials (emfs) of lithium amalgam electrodes in the cell... 

Interaction to form lithium amalgam is violently exothermic and may be explosive if large pieces of lithium are used [1]. An improved technique, using p-cymene as inerting diluent, is described in the later reference [2],... 

Lithium amalgam, reaction with 3,4-dichloro-1,2,3,4-tetramethylcy-clobutene, 46, 36... 

The classical method for lithium isotope separation employed chemical exchange between lithium amalgam and an aqueous solution of lithium hydroxide. 

A silver-cyclobutadiene complex is obtained when the mercury-containing, bromine-free oil, obtained by treatment of 1,2,3,4-tetrabromo-cyclobutane with lithium amalgam, is treated with silver nitrate (5). The complex forms colorless crystals which, on treatment with steam, evolve... 

Dehalogenation has also been employed in the preparation of cyclobutenes. For example, stereoisomerically pure l,2-dichloro-3,4-dibromocyclobutane (18) reacts with 0.5% lithium amalgam in diethyl ether to give the nnf/ -tricyclooctadiene 32, which is isolated as its corresponding disilver(I) complex 31.11 However, similar treatment only converts tetrachlorocy-clobutane (16) to yyn-tricyclooctadiene 34 in very low yield.11... 

A solution of m-l,2-dichloro-cw-3,nwv-4-dibromocyclobutane (18 1.4 g, 5 mmol) in anhyd Et2O(30 mL) was shaken with lithium amalgam (0.5% lithium. 35 g) in a glass stoppered flask until the exothermal reaction ceased and then mechanically stirred for 12 h. The mixture was steam-distilled and the ethereal layer was shaken with aq AgN03 to give the disilver(I) complex 31 of the product yield 0.55 g (50%) mp 150 C, The disilver(I) complex was treated with brine to give the product 32. 

Pentafluorophenyllithium can be readily prepared by direct reaction of penta-fluorophenyl halides with lithium amalgam [193,194] or lithium-hydrogen and lithium-halogen exchange reactions of pentafluorophenyl halides with alkyl-lithiums [195-205] (Scheme 70). 

Pyridynes are also formed from ort/m-dihalides and alkali metals. Thus, reaction of 3-bromo-4-chloropyridine (889) with lithium amalgam and furan gives product (891) by trapping of the 3,4-pyridyne (890). Although 2,3-pyridyne is not formed from 3-halopyridines, because of the weaker acidity of the 2- as compared to the 4-hydrogen atom (see Section 3.2.1.8.2), it can be trapped by furan in small yield from the reaction of 3-bromo-2-chloropyridine with lithium amalgam. 

The use of lithium amalgam electrodes allows better control of electrode potential than the potassium amalgam electrode. Separations of Sm from Gd, Eu from Sm, Sm from Eu and of Yb from heavy rare earths have been successfully carried out by Onstott [135—137]. 

Metallic actinium cannot be obtained by electrolytic means because it is too electropositive, II has been prepared on a milligram-scale through the reduction of actinium fluoride in a vacuum with lithium vapor at about 350 °C The metal is silvery white, faintly emits a blne-rinted light which is visible in darkness because of its radioactivity, The metal takes the form of a face-centered cubic lattice and has a melting point of 1050 50°C. By extrapolation, it is estimated that the metal boils at about 3300 0. An amalgam of metallic actinium may be prepared by electrolysis on a mercury cathode, or by the action of a lithium amalgam on an actinium citrate solution (pTT — 1.7 lo 6.8). 

Several transition-metal complexes of cyclobutadiene have been prepared, and this is all the more remarkable because of the instability of the parent hydrocarbon. Reactions that logically should lead to cyclobutadiene give dimeric products instead. Thus, 3,4-dichlorocyclobutene has been de-chlorinated with lithium amalgam in ether, and the hydrocarbon product is a dimer of cyclobutadiene, 5. However, 3,4-dichlorocyclobutene reacts with diiron nonacarbonyl, Fe2(CO)9, to give a stable iron tricarbonyl complex of cyclobutadiene, 6, whose structure has been established by x-ray analysis. The 7r-electron system of cyclobutadiene is considerably stabilized by complex formation with iron, which again attains the electronic configuration of krypton. 

Reduction under nitrogen of totracarbonyl nickel with alkali metals or sodium and lithium amalgams (71) in THF, or with alkali hydroxides in methanol, gives a mixture of the dianions [Ni5(CO) 42]2- and pMi6(CO) i2]2 (28, 95). The final composition of the reaction mixture greatly depends on the experimental conditions owing to the easily reversed equilibrium ... 

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