Reducing agents lithium tetrahydridoaluminate

Carboxylic acids can be reduced to their corresponding primary alcohol by using the reducing agent lithium tetrahydridoaluminate, LiAlH, in dry ether at room temperature. Dry ether is used because LiAlH reacts violently with water. 

LiAlH4, lithium tetrahydridoaluminate ("lithium aluminium hydride . so-called) is an excellent reducing agent in ether solution for both organic and inorganic compounds it may be used to prepare covalent hydrides SiH ether, for example... 

The tetrahydridoborate ion, as "sodium borohydride" NaBH is soluble in water and is similarly an excellent reducing agent in this solvent. (Lithium tetrahydridoaluminate cannot be used in water, with which it reacts violently to give hydrogen.)... 

Grignard reagents and lithium tetrahydridoaluminate achieved SN2 displacement of fluoride anion (Eq. 100). Displacement of a second fluoride ion occurred with excess reducing agent, and upon the action of butyllithium. These reactions have not found extensive use in target synthesis. 

The reaction of methyllithium with dimethylzinc in 1 1 and 2 1 molar ratios in diethyl ether solution produces lithium tri- and tetramethyl-zincates.1 Two equivalents of lithium trimethylzincate( 1 -) react with three equivalents of lithium tetrahydridoaluminate(l -), and one equivalent of lithium tetramethylzincate(2 —) reacts with two equivalents of lithium tetra-hydridoaluminate(l —) to give lithium trihydridozincate( 1 -) and lithium tetrahydridozincate(2 —), respectively, in quantitative yields. Both reactions proceed in diethyl ether at room temperature and are complete within 5 min. The compounds are air-sensitive and therefore must be prepared in an airfree atmosphere (nitrogen or argon). They may be used as reducing agents in organic syntheses. 

The crude Na[Zn2(CH3)2H3] solution in THF may be used as a reducing agent.4 Like lithium tetrahydridoaluminate(l —), the zinc reagent reduces aliphatic ketones and esters to the corresponding alcohols and aliphatic nitriles to amines. However, of the two, the zinc compound is a somewhat milder reducing agent as shown by the reduction of benzonitrile to the corresponding imine under conditions in which lithium tetrahydrido-aluminate(l —) yields the amine. 

While lithium tetrahydridoaluminate(l -) is used extensively as a reducing agent,1 relatively little is known about the utility of amine and/or amino complexes (compounds of the general formulas H3A1(NR3) and H3 A1-... 

Tin or tin(n) chloride,171 zinc in an acid medium,172 sodium dithionite,173 and sulfur dioxide174 are also effective for reducing A-oxides. Azoxy compounds are converted into azo or hydrazo compounds by relatively mild reducing agents azoxybenzene is reduced to hydrazobenzene by zinc in alkaline solution10 and to azobenzene (99% yield) by lithium tetrahydridoaluminate.35... 

Lithium tetrahydridoaluminate aluminum chloride Alcohols from oxido compounds Direction of ring opening s. 11,59 aAz j-Markovnikov ring opening with diborane-BFg cf. H. C. Brown and N. M. Yoon, Chem. Commun. 1968, 1549 effect of reducing agent s. . Laurent and P. Villa, Bl. 1969, 249... 

In 1956 Herbert C. Brown (b. 1912) discovered that in ethereal solution diborane (B2H5) dissociates into borane (BH3), which can add to an alkene. The organoborane formed can be converted to an alcohol by treatment with hydrogen peroxide, and the overall result of this hydroboration reaction is the anti-Markovnikoff addition to the double bond. Brown was also responsible for the introduction into organic chemistry of the reducing agents sodium borohydride (sodium tetrahydridoborate(lll)) and lithium aluminium hydride (lithium tetrahydridoaluminate(lll)). 

There are two common hydride reducing agents sodium borohydride (7 NaBH4) and lithium aluminum hydride (8 LiAlH4). Borohydride is an ate complex (see Chapter 6, Section 6.5.4, for definition of an ate complex) of BHg (7 is a tetrahydridoborate) and aluminum hydride is an ate complex of AlHg (8 is a tetrahydridoaluminate their respective lUPAC names are sodium tetrahydridoborate and lithium tetrahydridoaluminate. The borate anion is the Lewis acid-Lewis base complex of BHg (borane) and a hydride, whereas the alumi-nate anion is the Lewis acid-Lewis base complex of AlHg (aluminum hydride) and a hydride. Examination of the periodic table reveals that hydrogen is more... 

The organic solvent has to be dry because lithium tetrahydridoaluminate is a more powerful reducing agent than sodium tetrahydridoborate and reacts vigorously in water. 

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