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Lithium aluminium hydride also reduces alkyl halides to alkanes. [36] [37] Alkyl iodides react the fastest, followed by alkyl bromides and then alkyl chlorides. Primary halides are the most reactive followed by secondary halides. Tertiary halides react only in certain cases. [38] Lithium aluminium hydride does not reduce simple alkenes or arenes.
Stereospecific trans hydroalumination is possible through the use of lithium aluminium hydride. The mechanism of this transformation involves the addition of hydride to the carbon less able to stabilize the developing negative charge (viz., in the β position to an electron-withdrawing group). [10]
Sodium borohydride and lithium aluminium hydride are commonly used for the reduction of organic compounds. [3] [4] These two reagents are on the extremes of reactivity—whereas lithium aluminium hydride reacts with nearly all reducible functional groups, sodium borohydride reacts with a much more limited range of functional groups. Diminished ...
McMurry and Fleming coupled retinal to give carotene using a mixture of titanium trichloride and lithium aluminium hydride. Other symmetrical alkenes were prepared similarly, e.g. from dihydrocivetone, adamantanone and benzophenone (the latter yielding tetraphenylethylene).
In organic chemistry, aluminium hydride is mainly used for the reduction of functional groups. [32] In many ways, the reactivity of aluminium hydride is similar to that of lithium aluminium hydride. Aluminium hydride will reduce aldehydes, ketones, carboxylic acids, anhydrides, acid chlorides, esters, and lactones to their corresponding alcohols.
For instance, conversion of the ketone to an alcohol by lithium aluminium hydride can be considered a reduction but the hydride is also a good nucleophile in nucleophilic substitution. Many redox reactions in organic chemistry have coupling reaction reaction mechanism involving free radical intermediates.
Lithium aluminium hydride (LAH) modified with chiral alkoxide ligands has been shown to proceed in good yield and high enantioselectivity. Chelating ligands such as BINOL [6] are used to avoid disproportionation and background reduction by LAH. Chiral diamines and amino alcohols have also been used to modify LAH for enantioselective reductions. (4)
The industrially most important aluminium hydride is lithium aluminium hydride (LiAlH 4), which is used in as a reducing agent in organic chemistry. It can be produced from lithium hydride and aluminium trichloride: [25] 4 LiH + AlCl 3 → LiAlH 4 + 3 LiCl. The simplest hydride, aluminium hydride or alane, is not as important.