Lithium-Aluminium System

Because of the interest in its use in elevated-temperature molten salt electrolyte batteries, one of the first binary alloy systems studied in detail was the lithium-aluminium system. As shown in Fig. 1, the potential-composition behavior shows a long plateau between the lithium-saturated terminal solid solution and the intermediate P phase LiAl , and a shorter one between the composition limits of the P and y phases, as well as composition-dependent values in the single-phase regions [35], This is as expected for a binary system with complete equilibrium. The potential of the first plateau varies linearly with temperature, as shown in Fig. 2. 

In addition to this work on the / phase, both the thermodynamic and kinetic properties of the terminal solid-solution region, which extends to about 9 atom% lithium at 423 °C, were also investigated in detail [36]. 

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The emf of the lithium-aluminium system versus pure lithium in a Lil-KI-LiCl molten eutectic is shown in Fig. 8.2 as a function of temperature and composition. It can be seen that the emf remains constant (at about 300 mV more negative than pure lithium) in the range of stability of the /3-phase (-7-47 atoms per cent of lithium), thus implying a constant lithium activity in the alloy surface. At concentrations greater than 47 atoms per cent, the lithium activity becomes strongly composition-depen-dent. 

Aluminium can be deposited from complex organic solutions if sufficient precautions are taken, and such coatings are now being produced commercially in North America. Two of the systems on record are (1) aluminium trichloride and lithium aluminium hydride dissolved in diethyl ether used at 40°C and 50A/m, and (2) aluminium chloride, n-butylamine and diethyl ether used at 20°C and 970 A/m. Deposits of 0-010 mm can be obtained on mild steel or copper at 20°C and 970 A/m using aluminium-wire anodes and nitrogen or argon atmospheres. 

Wartik, T., and H. I. Schlesinger Reactions of Lithium Aluminium Hydride with Representative Elements of the Main Groups of the Periodic System. J. Amer. chem. Soc. 75, 835 (1953). 

In an approach toward a synthesis of tetraponerine 37, Gevorgyan first synthesized the fully aromatic tricyclic system 49 and then reduced it over two steps, first via hydrogenation under pressure (50 psi) to give 36 followed by a second reduction by lithium aluminium hydride of the amidinium salt (Scheme 1) <2002OL4697, 2004JOC5638>. 

Nonmetallic systems (Chapter 11) are efficient for catalytic reduction and are complementary to the metallic catalytic methods. For example lithium aluminium hydride, sodium borohydride and borane-tetrahydrofuran have been modified with enantiomerically pure ligands161. Among those catalysts, the chirally modified boron complexes have received increased interest. Several ligands, such as amino alcohols[7], phosphino alcohols18 91 and hydroxysulfoximines[10], com-plexed with the borane, have been found to be selective reducing agents. 

Solid lithium aluminium hydride can be solublized in non-polar organic solvents with benzyltriethylammonium chloride. Initially, the catalytic effect of the lithium cation in the reduction of carbonyl compounds was emphasized [l-3], but this has since been refuted. A more recent evaluation of the use of quaternary ammonium aluminium hydrides shows that the purity of the lithium aluminium hydride and the dryness of the solvent are critical, but it has also been noted that trace amounts of water in the solid liquid system are beneficial to the reaction [4]. The quaternary ammonium aluminium hydrides have greater hydrolytic stability than the lithium salt the tetramethylammonium aluminium hydride is hydrolysed slowly in dilute aqueous acid and more lipophilic ammonium salts are more stable [4, 5]. 

Stereoselective reduction of a,(i-unsaturated ketones using lithium aluminium hydride has only been reported in conjunction with the ephedrine bases either in a two-phase system (80-90% yield, ee >70%) or immobilized on a polymer [18, 19]. 

The following examples illustrate typical additions to conjugated systems. Although conjugate addition is more common, Gr pard reagents (see Section 7.6.2) and lithium aluminium hydride (see Section 7.5) are more likely to add directly to the carbonyl. 

It is quite difficult to reduce benzene or pyridine, because these are aromatic stmctures. However, partial reduction of the pyridine ring is possible by using complex metal hydrides on pyridinium salts. Hydride transfer from lithium aluminium hydride gives the 1,2-dihydro derivative, as predictable from the above comments. Sodium borohydride under aqueous conditions achieves a double reduction, giving the 1,2,5,6-tetrahydro derivative, because protonation through the unsaturated system is possible. The final reduction step requires catalytic hydrogenation (see Section 9.4.3). The reduction of pyridinium salts is of considerable biological importance (see Box 11.2). 

A number of cylindrical and flat magnesium-based cells have been developed on a commercial scale, mainly for military applications where high discharge currents and low unit weight are important. However, for most of these applications, magnesium batteries have now been replaced by various lithium/organic systems. There are no commercial aluminium-based Leclanchd cells. Magnesium and aluminium are both exploited as anodes in metal-air cells which are considered below. 

Selective removal of a halogen or tosyl group in a bifunctional molecule has been effected with lithium aluminium hydride in differing solvent systems.10... 

Hyperforin is not reduced by sodium borohydride. Reduction with hydride-transfer reagents such as lithium aluminium hydride (LAH), RED-AL, and DIBAL-H, gave varied products in good yields. Its two dicarbonyl systems are amenable to reduction or deoxygenation upon treatment with alane reducing agents and pave the way to new and interesting modifications of the natural product.301... 

In addition to the preparation of a- and /3-hydrastine described above from the betaine (64), another conversion of a tetrahydroberberine into hydrastine has been reported. Acetylophiocarpine, on treatment with ethyl chloroformate, gives the acetoxy-derivative of (88), which can be hydrolysed to the hydroxymethyl compound and then oxidized to the aldehyde by pyridinium perchlorate. Hydrolysis of the acetoxyl group afforded the hemi-acetal (93 R = H), conversion of which into the mixed acetal (93 R = Et) protected the aldehyde system during reduction of N—C02Et to NMe by lithium aluminium hydride. Hydrolysis of the acetal, followed by oxidation, then gave a-hydrastine, and a similar sequence of reactions starting from O-acetyl-13-epi-ophiocarpine afforded / -hydrastine.119 Methods of synthesis of alkaloids of this group have been reviewed.120... 

Protopine has been isolated from Bocconia frutescens,110 Fumaria judaica,111 F. schleicheri,112 and Papaver bracteatum,146 cryptopine from F. schleicheri,112 and allocryptopine from B. frutescens110 and Zanthoxylum nitidum.141 The protopine ring-system has been prepared from tetrahydrobenzindenoazepines (75) by photo-oxidation to the amides (76) followed by reduction with lithium aluminium hydride and re-oxidation with manganese dioxide.148-150 The tetrahydrobenzindenoazepines have been prepared from A-chloroacetyl-/ -phenylethylamines (73) by cyclization to the lactam (74) followed by reaction with a benzyl bromide and phosphorus oxychloride. -Protopine (77 R R2 — CH2)148 and fagarine II (77 R1 = R2 = Me)149 have been synthesized in this way. 

The trachylobane ring system has been synthesized by homoallylic reduction of the atisene mesylate (83) with lithium aluminium hydride.79 The structure of many of the... 

The n.m.r. characteristics of the isopropylidene acetals of the four possible types of ring A primary, secondary 1,3-glycol systems, exemplified by serratriol (178), lycoclavanol (179), methyl hederagenate (180), and methyl 3-epihederagenate (181), have been tabulated, and provide a useful means of differentiation.132 The reactions of the primary monotosylates of these four types provide further confirmation of stereochemistry.133 With potassium t-butoxide the cis types (178) and (181) afforded oxetans whereas the trans types (179) and (180) were converted into A-seco-aldehydes (182). Appreciable amounts of alkyl oxygen fission products were obtained on lithium aluminium hydride reduction of the monotosylates of (178), (180), and (181), presumably via participation of the 3-hydroxy-group, e.g. (183). 

The compound (70) by epoxide ring-opening with hydrogen fluoride, followed by photocatalysed addition of acetylene to the A16-bond and lithium aluminium hydride reduction, gave (71). Protection of the 1,2-diol system in (71) as the acetonide followed by oxidation, dehydration, and regeneration of the diol grouping produced... 

The conversions shown in Scheme 18 interrelate a number of alkaloids and in conjunction with optical circular dichroism evidence establish the structure of spiropachysine (359), a major alkaloid in the leaves of Pachysandra terminalis Sieb. et Zucc. (Buxaceae), unique in possessing a five-membered spirolactam system.189 Spiropachysine (359) was reduced by lithium aluminium hydride to the deoxo-compound (360), whose dimethiodide on Hofmann degradation yielded two materials, the more strongly basic being a mixture of two olefins (361) which both afforded on hydrogenation the compound (362). The last compound was also prepared from... 

Although 3,8-diamino-l ll/-dibenzo(c,/)-l,2-diazepine-5-oxide [67, R = NH2, and 67, R = N(CH3)2] were first prepared in 190651 52 by reduction of 2,2 -dinitro-4,4 -diaminodiphenylmethane with zinc dust and ammonium chloride and subsequent air oxidation in basic medium, the ring system has not received any attention until recent years. The dibenzo compounds (67, R = C1, Br, and I) were first prepared by the same method.53 The parent diazepine (68, R = H)54 and the dihalodiazepines (68, R = F, Cl, Br, and I)53 have been prepared by lithium aluminium hydride reduction of the appropriate 2,2 -dinitrodiphenylmethane. In the case of the reduction of 2,2 -dinitro-4,4 -diiododiphenylmethane, either 68 (R = H) or 68 (R = I) could be obtained depending upon the amount of reducing agent used. Attempts to prepare the system 68 by oxidation of 2,2 -diamino-diphenylmethanes led to inconclusive results.55... 

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