Heat LiAlH

The previous product was added to LiAlH (6 eq.) in THF. The solution was heated at reflux for 1 h. The excess hydride was destroyed by dropwise addition of water and the resulting mixture filtered through Celite. The filtrate was diluted with EtOAc, washed with brine and dried (Na2S04). The product was an oil (3.4 g, 98%). 

In Fig. 1.27 and Table 1.5 a typical DSC peak position shift related to various heating rates for thermal decomposition of LiAlH is presented. 

Figure 3.9a shows a typical DSC trace at the heating rate of 10°C/min obtained in our laboratory from as-received LiAlH (purity 97%). It is clearly seen that (Rla) is proceeded by an exothermic peak centered at 152.5°C. In the literature, this first... 

Fig. 3.9 (a) DSC trace of as-received, undoped LiAlH (97% purity) and (b) the same hydride after milling in the magneto mill Uni-BaU-Mill 5 under HES57 mode (two magnets at 5 and 7 o clock positions) for 20 h in argon. DSC heating rate 10°C/min at argon flow 50 ml/min... 

Another factor which suppresses melting of LiAlH is catalysts. Andreasen [67] used 1 min ball milling to disperse 2 mol%TiCl3 l/3AlCl3 in LiAlH. DSC experiments with the heating rates 3-5°C showed only two endothermic reactions, the... 

The synthesized nanostructured composites (nanocomposites) (MgH -i- LiAlH ) were subjected to desorption experiments after ball milling for 20 h. Figure 3.34 shows desorption curves obtained under continuous heating up to 300°C (quasi-TPD)... 

Furthermore, Fig. 3.35 shows the desorption cnrves of the ball-milled (MgH h-50 wt%LiAlH ) composite dnring continuous heating np to 250,260,275 and 300°C under 0.1 MPa hydrogen atmosphere. Under these conditions the composite desorbs 4.3 and 4.9 wt%H2 at 250 and 260°C, respectively. The pnrity-corrected amonnt of hydrogen which conld be desorbed from the 50 wt%LiAlH constitnent in a composite at these temperatnres which are higher than the temperatnres of the solid state reaction (Rib) of (3.12) and (R2) of (3.13) in Fig. 3.30b, is 3.8 wt%. Experimentally observed values are larger by about 0.5-1.0 wt% than the theoretical one. This excess could only be desorbed from MgH. That means that MgH is able to desorb at temperatnres 250 and 260°C, which are lower than its eqnilibrinm temperature of desorption nnder 0.1 MPa equal to 275°C. Apparently, MgH is thermodynamically destabilized by the second composite constituent LiAlH. Additional evidence that MgH is, indeed, destabilized is provided by the shape of the desorption cnrves at 250 and 260°C in Fig. 3.35 in which one can see a clearly discernible third... 

Fig. 3.35 Hydrogen desorption curves of baU milled (MgH + 50 wt%LiAlH ) during continuous heating up to 250, 260, 275 and 300°C under 0.1 MPa hydrogen atmosphere (corrected for increasing pressure due to hydrogen temperature change)...

The final step is to convert the carboxylic acid into a primary alcohol by heating it with lithium aluminium hydride (LiAlH ) dissolved in ether (ethoxyethane). This is a reduction reaction and delivers the target molecule, propan-l-ol. 

The benzyl group has been widely used for the protection of hydroxyl functions in carbohydrate and nucleotide chemistry (C.M. McCloskey, 1957 C.B. Reese, 1965 B.E. Griffin, 1966). A common benzylation procedure involves heating with neat benzyl chloride and strong bases. A milder procedure is the reaction in DMF solution at room temperature with the aid of silver oxide (E. Reinefeld, 1971). Benzyl ethers are not affected by hydroxides and are stable towards oxidants (e.g. periodate, lead tetraacetate), LiAlH, and weak acids. They are, however, readily cleaved in neutral solution at room temperature by palladium-catalyzed hydrogenolysis (S. Tejima, 1963) or by sodium in liquid ammonia or alcohols (E.J. Reist, 1964). 

Reduction of [V(bipy)3]l2 with the metals Mg or Zn yields the complex [V(bipy)3], which will undergo ftulher reduction by lithium aluminum hydride to Li[V(bipy)3] 4THF, which formally contains V". Similarly, reduction of [V(phen)3] with dUithium naphthalenide or dihthium benzophenone in THF yields [V(phen)3]l2. Further reduction with dilithium benzophenone gives the V complex Li[V(phen)3] 3.5THF. The terpyridyl complex [V(terpy)2] can be obtained as black crystals by reduction of DMF solutions of [V(terpy)2]l2 with Mg or LiAlH. Such low oxidation state complexes are highly air sensitive and decompose if heated to 100 - 200 °C in a vacuum. In these systems, the ligands may have an anion radical character. ... 

When heated with a deficit of LiAlH, solid powdered P40,g produces small quantities of PHj ... 

Ge3Hg and (GeHp form also. Germanium dioxide, when heated with a deficit of powdered LiAlH, at 148-170°C, produces GeH,, Ge H and Ge3Hg in 4, 3 and 1% yield, respectively. ... 

The LiAlH used as promoter is obtained by reaction between LiH and AlClj in diox-ane or ether. This process affords LiAlH., in low yields ( 30%), and the reaction mixture requires heating to 50°C in dioxane or periodic cooling with liq Nj when ether is the solvent. 

Lithium aluminum hydride, LiAlH, is another reducing agent often used for reduction of ketones and aldehydes. A grayish powder soluble in ether and tetrahydrofuran, LiAlH4 is much more reactive than NaBH4 but also more dangerous. It reacts violently with water and decomposes explosively when heated above 120°C. 

To a solution of the tosylate (2 g, 6.2 mmol) in anhyd EtjO (50 mL) was added LiAlH (0.3 g, 7.8 mmol). The mixture was heated at reflux for 6 h. The cooled mixture was treated with 10% HjSO until neutral and extracted with EtjO (50 mL). The organic phase was dried (Na2S04) and the solvent was removed under vacuum on a rotary evaporator. The residue was recrystallized (Et O/pentane) yield 0.98 g (96%) mp 64 °C. 

NaAlH2(0CH2CH20CH3)2, benzene or toluene, reflux, 20 h, 65-75% yield." Note that LiAlH, does not cleave sulfonamides of primary amines those from secondary amines must be heated to 120°C. In the following case, dissolving metal reduction failed. ... 

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