Lithium Aluminum Hydride CAS 16853-85-3 LAH
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- Appearance: White powder
- Assay: 99. 0%min
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Lithium Aluminum Hydride: The Complete Guide
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Basic Info of Lithium Aluminum Hydride
Lithium Aluminum Hydride
(T-4)-lithium tetrahydroaluminate; lithium aluminum chloride; lithium aluminium hydride
What is Lithium Aluminum Hydride?
Lithium Alminum Hydride (LAH) is a very powerful reducing agent. Ketones, aldehydes, carboxylic acids and esters can be reduced to alcohols. Even amides can be reduced to amines by them. Some halogenated or sulfonyl-substituted compounds can also react with him to form hydrogen-substituted compounds. For epoxy compounds, react with LAH to obtain the ring-opened product. For this type of reaction, anhydrous THF-diethyl ether, which has good solubility and does not react with LAH, is often used as a solvent. Water and protic solvents react violently with it to generate hydrogen gas, so these cannot be used as reaction solvents.
Lithium aluminum hydride is widely used in medicine, pesticide, fragrance, dye and other industries due to its excellent reducibility, and is used as a reducing agent in other organic synthesis. At the same time, it releases a lot of heat when it burns, and is also used as an additive for missiles and launch vehicle fuels. The technical content of this product is high and the profit margin is large, but the production process involves problems such as high temperature, flammability, and explosion, and the control requirements for process parameters are very strict. Therefore, there are only a few manufacturers in China. mass production.
Lithium Aluminum Hydride Uses
- 1,3-Amino alcohols can be prepared by one-step reduction of β-enaminones with lithium aluminum hydride. By choosing a suitable reaction substrate to reduce the olefinic bond, the post-reduction product (3-dimethylamino-1-aryl-2-propenone), and excess lithium aluminum chloride in tetrahydrofuran solvent is refluxed to achieve N,N- One-step reduction of dimethyl-3-hydroxy-3-arylpropylamine. The process is the first carbonyl. This also provides an example that, under certain conditions, lithium aluminum hydride can reduce carbon-carbon double bonds.
- In the exploration of the antibacterial drug moxifloxacin, 8-benzyl-7,9-dioxo-2,8-diazabicyclo[4.3.0]nonane can be reduced by lithium aluminum hydride to obtain 8-benzyl The optimum yield of -2,8-diazabisheterocyclo[4.3.0]nonane was 93.7%.
- In the process of synthesizing balofloxacin, 3-aminopyridine was selected as the reaction raw material, and 3-carboxamidopyridine was obtained by oxidation with formic acid, and then lithium aluminum hydride was used as a reducing agent to reduce 3-carboxamidopyridine. 3-methylaminopyridine was obtained in a yield of 85%.
- Due to its super reducing ability, lithium aluminum hydride has remarkable efficiency in reducing functional groups such as halides, acids, esters, aldehydes, ketones and cyano groups, and is also a typical representative of metal-organic reducing agents in organic synthesis. , such as fine chemical industry, pharmaceutical synthesis and preparation, pesticide development and production are widely used, and are favored by organic chemists.
- It is used as a polymerization catalyst, reducing agent, jet engine fuel, and also for the synthesis of drugs. Aldehydes, ketones, acids, acid anhydrides, esters, lactones, quinones, acid chlorides, etc. can be reduced to alcohols, nitriles to primary amines, and halogenated hydrocarbons to hydrocarbons. However, carbon-carbon double bonds cannot generally be hydrogenated. purposes : a strong reducing agent. Widely used in medicine, spices, pesticides and other fine organic synthesis.
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Reduction Reactions Involving Lithium Aluminum Hydride
As a reducing agent with strong reducing ability, lithium aluminum hydride can reduce almost all organic functional groups, so it is widely used in organic synthesis reactions.
Using lithium aluminum hydride to reduce halogenated hydrocarbons can produce the corresponding hydrocarbons and also form the corresponding coordination aluminum hydrides. However, when diethyl ether is used as the solvent, the reaction will be relatively slow, so in the reaction with halogenated hydrocarbons, lithium aluminum chloride mostly uses tetrahydrofuran or butyl ether as the solvent, and the reaction is faster at high temperature.
In the reduction of polyfluorohalohydrocarbons, lithium aluminum hydride preferentially reduces one halogen atom, while the ability to reduce the second halogen atom is relatively much weaker. In the reaction of 1-2-dichlorohexafluorocyclobutane with lithium aluminum chloride butyl ether solution, the products obtained the corresponding chlorohexafluorocyclobutane and hexafluorocyclobutane, wherein the product is a chlorohexafluorocyclobutane The butane yield is 70%, and the hexafluorocyclobutane is only 30%.
In almost most organic reduction reactions, lithium aluminum hydride and sodium borohydride are used as a very common metal reducing agent. By comparison, it is found that lithium aluminum hydride has a more prominent reducing ability than sodium borohydride, and can reduce sodium borohydride. Difficult to reduce ester functional groups.
The reduction mechanism in the reduction reaction between lithium aluminum hydride and ester group can be considered as the nucleophilic addition reaction of negative hydrogen ions. First, the carboxylate and lithium aluminum hydride form a lithium carboxylate salt; then, the carboxylate lithium salt is close to the aluminum hydride ion and forms a complex with carbonyl oxygen; then the hydride ion occurs Transfer, transfer to the carbonyl carbon, and finally remove LiAlH3 to obtain the corresponding aldehyde. Immediately after, another molecule of lithium aluminum hydride reacts with the previously generated aldehyde, and finally reacts with alkenoic acid to hydrolyze to obtain the corresponding product alcohol.
Lithium aluminum hydride-reduced ester reactions are widely used in practical and research work. Li Yang et al. used α,β-unsaturated ester as the reaction substrate, and by constantly changing the experimental conditions, it was proved that the final product of the reaction contained a certain amount of 1,3-diol, and changed different solvent conditions, and found that when tetrahydrofuran was used as the solvent, the 1,3-Diol was obtained in the highest yield. And this convenient method for synthesizing 1,3-diol is expected to be applied to the synthesis of natural products with 1,3-diol skeleton structure. Xu Ji reduced the octahydroindolo-2,3-quinolizine compounds containing ester groups with lithium aluminum hydride to obtain unexpected products.
The reaction of lithium aluminum hydride with aldehydes and ketones is a step-by-step reaction process.
The reducing part of LiAlH4 is AlH4-, which can provide hydride ions with strong reducing energy. The hydride ion is transferred to the carbon ion of the aldehyde and ketone carbonyl group, and this process is irreversible. After the completion of the reaction, instead of directly obtaining an alcohol, an alkoxide is obtained.
Therefore, the first step of the reaction is to form the corresponding alkoxide, and the second step is to hydrolyze the salt to form the corresponding alcohol. The preparation of photochemically active alcohols by using lithium aluminum hydride as a reducing ketone is more and more frequently used in the fields of fine chemicals such as medicines and pesticides. Liu Xiang et al. mixed chiral amino alcohol (1S, 2R)-1-dibutylamino-1,2-dihydro-2-indenol (1,R′OH) and lithium aluminum hydride to produce chiral reagents, and This chiral reagent was used in the study of asymmetric reduction of acetophenone.
Nitriles can be converted to amines in high yields under the action of lithium aluminum hydride. Yu Shenyi used the reduction reaction of lithium aluminum hydride and 5-cyano-4-amino-2,6-dialkylthiopyrimidine compounds to prepare pyrimidine products containing bisamino groups.