Diisobutylaluminium hydride

Description

Diisobutylaluminium hydride (DIBALH, DIBAL, DIBAL-H or DIBAH) is a reducing agent with the formula (i-Bu2AlH)2, where i-Bu represents isobutyl (-CH2CH(CH3)2). It can be used for various homogeneous reductions such as alkynes to alkenes, esters or nitriles to aldehydes. It is available commercially as the neat reagent and as a solution in several different solvents (hexane, dichloromethane, tetrahydrofuran, etc.). The neat reagent is a liquid and is supplied in metal cylinders. It is pyrophoric and highly reactive and therefore must be handled with great care. The molar solutions in organic solvents are more stable and easier to handle provided that the normal precautions are taken for working with air-sensitive compounds. They must all be handled in an atmosphere free from oxygen and water. Commonly used solvents for diisobutylaluminium hydride are dichloromethane, diglyme, dioxane and tetrahydrofuran. Even when the substrate is not completely soluble in these solvents successful reductions can be accomplished.

Description

Diisobutylaluminum hydride (DIBAL-H) is an organoaluminum reagent typically used for the reduction esters or nitriles to aldehydes. DIBAL-H is usually obtained and used as a 1.0 M solution in a wide variety of solvents (ex. DCM, THF, hexanes, heptane, toluene, and cyclohexane). Some of the advantages of using DIBAL-H over other organoaluminum reagents include its greater selectivity, its ease of handing as a liquid, and its miscibility with a wide range of solvents (including hydrocarbons and aromatic solvents).

Chemical properties

Diisobutylaluminium hydride, also known as Dibal. colorless liquid. Viscosity 18.0mPa-s(25℃). Reacts violently with water to form hydrogen and isobutane. Tetrahydrofuran is not suitable as Dibal solvent, because the two react to produce coordination compounds. Diisobutylaluminium hydride is a useful reducing agent in organic synthesis. It can reduce ketones, carboxylic acids and esters to the corresponding alcohols. Dibal can also reduce lactones to o-hydroxy lactones.

The Uses of Diisobutylaluminium hydride

Diisobutylaluminum hydride is commonly used as a reducing agent in organic synthesis.
Diisobutylaluminum hydride can be used in the following protocols:
As a promotor of Tishchenko reaction of aldehydes.
Conversion of benzylidene acetals of 1,2-and 1,3-glycols to the corresponding monobenzyl ethers of the glycols.
To generate a novel chiral reducing agent based on (S)-proline for the asymmetric reduction of prochiral ketones.

The Uses of Diisobutylaluminium hydride

To a solution of the SM (45.5 g, 131 mmol) in THF (350 mL) at -78 C was added DIBAL-H (1.5M in toluene, 50 g, 350 mmol) dropwise over 75 min maintaining the internal temp between -65 C and -60 C. After completion of the addition, the reaction mixture was warmed to -10 C for 90 min. A 4M aq KOH solution (350 mL, 10.7 eq) was carefully added dropwise, maintaining the temp at -10 C. The mixture was allowed to slowly warm to RT with vigorous stirring, and then was stirred at RT for 20 h. MTBE (200 mL) and heptane (400 mL) were added. The org phase was separated and washed with 1M aq KHSO4, brine, and dried over a mixture of MgSO4 and 30 g silica gel. The solids were removed by filtration and the filtrate was concentrated in vacuo. Upon concentration a precipitate began to form. The resulting wet residue was triturated with 10% MTBE/heptane (500 mL) at 60 C for 1 h. The resulting suspension was slowly cooled to RT under stirring. The resulting solids were filtered and dried in a vac oven at 40 C to provide the product. [31.2 g, 78%]

The Uses of Diisobutylaluminium hydride

Diisobutylaluminum hydride is used as reducing agent in pharmaceuticals. It is also used as raw material in organic synthesis, agrochemicals and dyestuffs.

The Uses of Diisobutylaluminium hydride

Diisobutylaluminum hydride (DIBAL-H) is a common reducing agent to reduce aldehydes, ketones, esters, acids and acid chlorides to the corresponding alcohols. Some of the applications are:
Synthesis of α-acetoxy ethers by reduction and subsequent acetylation of esters.
Synthesis of coniferyl, sinapyl, and p-coumaryl alcohol by selective reduction of corresponding cinnamate esters.
Reduction of secondary phosphine oxides (SPOs) to the corresponding phosphines.
DIBAL-H can also be used in the hydroalumination of alkene and alkynes.

Flammability and Explosibility

Spontaneously flammable in air (pyrophoric)

Safety Profile

Mddly toxic by inhalation. Dangerous fire hazard; iptes spontaneously in air. To fight fire, do not use water, foam, or halogenated extinguisking agents. See also HYDRIDES and ALUMINUM COMPOUNDS.