Lithium amalgam, reduction

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],... 

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). 

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 ... 

Hex-5-enyl-l-mercuric bromide (III) is reduced to 1-hexene (IV) by sodium amalgam, whereas sodium borohydride, lithium aluminum hydride, and tri-77-butyltin hydride gave a mixture of IV and methylcyclopentane. This is taken as evidence that sodium amalgam reduction of alkylmercury salts does not proceed via a free radical pathway [72]. 

The reduction of the p-acyloxy sulfone is most often carried out with sodium amalgam, as the examples below indicate. The reductive elimination can be buffered with disodium hydrogenphosphate for sensitive substrates. In certain applications it has proven advantageous to utilize lithium or sodium in ammonia. For example, Keck s synthesis of pseudomonic acid C made use of the lithium/ammonia reductive elimination to simultaneously form an alkene and deprotect a benzyl ether.In studies directed toward the same target, Williams made use of a reductive elimination procedure developed by Lythgoe, involving the formation of the xanthate ester followed by reduction with tri-n-butyltin hydride. ... 

Thebaine will add acrolein in boiling benzene to give an aldehyde [5], which is most probably [xi] rather than [xn], as is shown by consideration of the forms [xm] and [xiv], in which it is seen that the terminal carbon of acrolein is electron-deficient and that the electron density of tho dienoid system in thebaine is greatest at C-14. Sodium amalgam reduction of the aldehyde affords an amorphous substance that gives bonzyl and acetyl derivatives [5], Presumably this is the alcohol [xv], which is also obtained by reduction of [xi] with lithium aluminium hydride [3]. 

Various other reagents can be used for this reductive debromination. 1,2-Dipropylcyclopropane was prepared from 4,6-dibromononane using chromium(II) perchlorate in dimethylformami-de/water (yield 93%), lithium amalgam in tetrahydrofuran (75%), lithium biphenylide in te-trahydrofuran (78%), potassium-sodium alloy in tetrahydrofuran (68%), zinc dust and zinc(II) chloride in propan-2-ol/water (95%) and alkyllithiums in tetrahydrofuran (BuLi 16%, i-BuLi 18%, t-BuLi 47%). Ring closure of 1,3-dibromobutane to methylcyclopropane was achieved by treatment with zero-valent copper, which was obtained from reaction of lithium naphthalen-ide and copper(I) iodide/tributylphosphane in tetrahydrofuran (yield 91%) ... 

As another example, the lithium isotope Li (used as LiOH for pH control in some nuclear power plants because of its small neutron cross-section) is produced in 99.99% purity by countercurrent chemical exchange of lithium between an aqueous solution of LiOH and lithium amalgam. A separation factor of 1.06 to 1.07 is reported. Reflux of lithium is obtained at one end by electrolytic reduction of LiOH to Li(Hg) at a mercury cathode and at the other end by spontaneous oxidation of Li(Hg) on graphite by water producing hydrogen gas and LiOH. 

A comparison of the electrochemical and chemical reduction— the latter using potassium or lithium amalgams—of a series of a,j3-unsaturated esters has shown that in all cases the electrochemical syntheses were superior (see Table The products of several of these reactions also showed that... 

Samarium, europium and ytterbium can readily be removed from lanthanon mixtures by reductive extraction from a buffered acidic solution into a dilute (0.5% or less) sodium amalgam, Marsh (1957), or by electrolyzing an alkaline citrate solution with a lithium amalgam cathode, Onstott (1955, 1956). Europium can be obtained especially pure from such amalgams by treatment with cold concentrated HCl, which causes precipitation of sparingly soluble EuC. 2H2O, Hulet et al. (1972), by the common-ion effect. Both Sm(II) and Yb(II) are rapidly oxidized by hydronium ion to the very soluble trihalides, but oxidation of Eu(II) in the absence of oxygen proceeds slowly. 

The reduction of iminium salts can be achieved by a variety of methods. Some of the methods have been studied primarily on quaternary salts of aromatic bases, but the results can be extrapolated to simple iminium salts in most cases. The reagents available for reduction of iminium salts are sodium amalgam (52), sodium hydrosulfite (5i), potassium borohydride (54,55), sodium borohydride (56,57), lithium aluminum hydride (5 ), formic acid (59-63), H, and platinum oxide (47). The scope and mechanism of reduction of nitrogen heterocycles with complex metal hydrides has been recently reviewed (5,64), and will be presented here only briefly. 

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