Лития диизопропиламид

Химические свойства

Lithium diisopropylamide (LDA) is a white pyrophoric powder. Freshly prepared, it is soluble in hydrocarbons (in hexane about 10 %), but it tends to precipitate irreversibly from solution as a polymer on heating or prolonged storage. In ethers the solubility is much higher, but with the exception of tetrahydropyran, LDA is decomposed at a rate depending on the ether, concentration, and temperature.
Lithium diisopropylamide can be conveniently prepared from butyllithium and diisopropylamine or purchased as a 2 mol/L (25 %) solution in THF and a mixture of various hydrocarbons. Although LDA is unstable in pure THF (at room temperature a 25% solution loses about 1% of its activity per day), the commercially available compositions containing only a limited amount of THF are satisfactory stable for technical applications.

Использование

Lithium diisopropylamide is a sterically hindered nonnucleophilic strong base used for selective deprotonations, especially for the production of kinetic enolates (i.e., the thermodynamically less favored isomer) and (hetero-)aromatic carbanions. In the production of the serum lipid regulating agent Gemfibrozil one key intermediate is formed by quenching an ester enolate with 1-bromo-3-chloropropane.

Общее описание

This material is in a solution of THF/Hexanes (ca. 1:7 ratio, respectively)

Методы очистки

It is purified by refluxing over Na wire or NaH for 30minutes and then distilled into a receiver under N2. Because of the low boiling point of the amine, a dispersion of NaH in mineral oil can be used directly in this purification without prior removal of the oil. It is HIGHLY FLAMMABLE, and is decomposed by air and moisture. [Wittig & Hesse Org Synth 50 69 1970, Beilstein 4 H 154, 4 I 369, 4 II 630, 4 III 274, 4 IV 510.]