Lithium aluminum hydride decomposition

Methylindole has also been prepared by lithium aluminum hydride reduction of 1-methylindoxyl. Compounds giving rise to NH absorption in the infrared (indole, skatole) can be completely removed by refluxing the crude 1-methylindole over sodium for 2 days and then distilling the unreacted 1-methylindole from the sodio derivatives and tarry decomposition products. 

The isotopic purity of the products from a lithium aluminum deuteride reduction is usually equivalent to that of the reagent. The presence of moisture has little effect on the isotope composition of the products, causing only the decomposition of some of the reagent. For the best results, however, it is advisable to distill the solvent— usually ether, tetrahydrofuran or dioxane depending on the desired reaction temperature—from lithium aluminum hydride directly into the reaction flask. In this manner the reduction of 3-keto-5a-steroids (60), for example, gives the corresponding 3a-di alcohols (61) in 98% isotopic purity. ... 

An ethynylation reagent obtained by decomposition of lithium aluminum hydride in ethers saturated with acetylene gives a satisfactory yield of (64), Best results are obtained with the lithium acetylide-ethylene diamine complex in dioxane-ethylenediamine-dimethylacetamide. Ethynylation of (63) with lithium acetylide in pure ethylenediamine gives (64) in 95% yield. 

Reduction of l-methyl-2-alkyl-.d -pyrroline and l-methyl-2-alkyl-.d -piperideine perchlorates with complex hydrides prepared in situ by partial decomposition of lithium aluminum hydride with the optically active alcohols (—)-menthol and (—)-borneol affords partially optically active l-methyl-2-alkyl pyrrolidines (153, n = 1) and 1-methy 1-2-alkyl piperideines (153, n = 2), respectively (241,242). 

Cyclohexyloxyethanol has also been prepared by reduction of cyclohexyloxyacetic acid with lithium aluminum hydride 8 and by decomposition of cyclohexanone methanesulfonylhydrazone with sodium in ethylene glycol.9... 

From the equation showing the mechanism it is evident that 1 mol of lithium aluminum hydride can reduce as many as four molecules of a carbonyl compound, aldehyde or ketone. The stoichiometric equivalent of lithium aluminum hydride is therefore one fourth of its molecule, i.e. 9.5 g/mol, as much as 2 g or 22.4 liters of hydrogen. Decomposition of 1 mol of lithium aluminum hydride with water generates four molecules of hydrogen, four hydrogens from the hydride and four from water. 

Reaction of the products of reduction with lithium aluminum hydride with water is very exothermic. This is especially true of reductions in which an excess of lithium aluminum hydride has been used. In such cases it is advisable to decompose the unreacted hydride by addition of ethyl acetate (provided its reduction product - ethanol - does not interfere with the isolation of the products). Then normal decomposition with water is carried out followed by acids [5i] or bases [121]. 

If the reduction has been carried out in ether, the ether layer is separated after the acidification with dilute hydrochloric or sulfuric acid. Sometimes, especially when not very pure lithium aluminum hydride has been used, a gray voluminous emulsion is formed between the organic and aqueous layers. Suction filtration of this emulsion over a fairly large Buchner funnel is often helpful. In other instances, especially in the reductions of amides and nitriles when amines are the products, decomposition with alkalis is in order. With certain amounts of sodium hydroxide of proper concentration a granular by-product - sodium aluminate - may be separated without problems [121],... 

Isolation of amines is best accomplished by adding a calculated amount of water (2 milliliters of water for n grams of lithium aluminum hydride followed by n milliliters of 15% sodium hydroxide and Sn milliliters of water). Other methods of decomposition can result in obstinate emulsions [1104],... 

The hydrazide of 2,2-diphenyl-3-hydroxypropanoic acid was reduced with lithium aluminum hydride in 7V-ethylmorpholine at 100° to 3-amino-2,2-di-phenylpropanol in 72.5% yield [1145], Much more useful is reduction of N-arenesulfonylhydrazides of acids to aldehydes McFadyen-Stevens reduction) [284, 285] based on an alkali-catalyzed thermal decomposition according to Scheme 174. 

Of many analytical methods described in the literature, the most simple and sufficiently accurate one is decomposition of lithium aluminum hydride suspended in dioxane by a dropwise addition of water and by measurement of the evolved hydrogen gas. 

Reduction of 1-ethoxycarbonyl-l/f-azepine with lithium aluminum hydride in ether at -15 °C yields the thermally unstable 1-(hydroxymethyl) derivative in boiling ether further reduction occurs to N-methyl- lH-azepine, which subsequently dimerizes to the [6+6]ir adduct (see Section 5.16.3.2.3) (B-69MI51600). Surprisingly, the action of phenyllithium on 1 -ethoxycarbonyl-l//-azepine produced the carbinol (2 R CPlhOH, R2 = H), thermal decomposition of which led to the first characterization of 3//-azepine (73CB1033). 

The oxidation of azo compounds with hydrogen peroxide in an acetic acid medium or with peracetic acid has been carried out by many investigators. For example, in a study of the 4,4 -dialkoxyazoxybenzenes, which are of interest in the field of liquid crystals, the corresponding alkoxynitrobenzenes were reduced with lithium aluminum hydride to the corresponding azo stage and, after decomposition of the reducing agent and removal of the solvent, the product residue was taken up in acetic acid and oxidized at 65°C for 36 hr with... 

Surprising results have been encountered in the hydrogenolysis of enamines to alkenes in the course of their reduction with an 1 1 mixture of lithium aluminum hydride and aluminum chloride in ether.301 From 1-pyrrolidinocyclopentene, 83% of cyclopentene was thus obtained. Formation of a-pyrrolidinocyclopentylaluminum chloride on addition of monochloroaluminum hydride to the enamine must be postulated, followed by decomposition of the intermediate complex to the cyeloalkene. The single known instance of reduction of a free enamine is represented by the reaction with dichloroaluminum hydride.302 Addition of the reagent leads to a complex which, on decomposition with water, affords the saturated base (Scheme 12). 

The alkaloid behaved similarly to voaeangine, since on the one hand its dihydro derivative was readily decarbomethoxylated to 4-epi-ibogamine (XLIII), mp 162°-164°, [a]D + 86° (hydrochloride in MeOH), and on the other its lithium aluminum hydride reduction product, catharanthinol, afforded an acetonide (XXXVII), mp 188°-191°. To account for the difficulty with which catharanthine eliminated the carbomethoxy group, it has been suggested that an intermediate in this reaction (XLIV) is highly strained (40). Since XLIV can be readily constructed from Dreiding Atomic Models, this explanation may not be correct. In actual fact, it is probable that the acid-catalyzed decomposition of catharanthine takes a different course. It has more recently... 

Z-Eburnamonine (XXXVI) has been produced by other reactions of vincamine. Oxidation of vincaminic acid (XL R = H) by means of ammoniacal silver nitrate was one way, and periodic acid fission of vincaminol was another (16). A different group of workers, who had probably attempted to prepare vincaminol by lithium aluminum hydride reduction of vincamine, obtained instead Z-ebumamonine in excellent yield (18). This has been rationalized as illustrated (partial formulas) by analogy with the base-induced decomposition of formic esters to carbon monoxide and alkoxide ion ... 

Asymmetric reduction of ketones. Lithium aluminum hydride, after partial decomposition with 1 equiv. of 1 and an amine additive such as N-benzylmethylamine, can effect asymmetric reduction of prochiral ketones at temperatures of —20°. The highest... 

The preparation of free 3-carbaldehydes (which must be A-substituted in order to avoid hemiaminal formation) is best carried out by oxidation of the triazolylmethanols obtainable by reduction of the corresponding esters with lithium aluminum hydride. Potassium fer-ricyanide in ammonia or lead tetraacetate are suitable oxidants but thermal decomposition of benzenesulfonylhydrazides (330) appears best (62JCS575). 

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