Reaction #56555

Reaction equation

Calcium hydride

retinal

hydrochloric acid

→

beta-carotene

Yield 75.0%

Solvents

tetrahydrofuran

tetrahydrofuran

Conditions

Workup

1. 1
   OtherA solution was prepared
2. 2
   Temperaturethe reaction was refluxed for three hours
3. 3
   Extractionwas extracted several times with ether
4. 4
   Washwashed with saturated aqueous sodium chloride solution
5. 5
   Dryingdried over magnesium sulfate
6. 6
   Concentrationconcentrated by solvent removal at the rotary evaporator
7. 7
   OtherThe residue was further purified by chromatography on silica gel
8. 8
   WashElution with hexane

Procedure

A solution was prepared by dissolving titanium tetrachloride (1.10 ml, 10.0 mmol) in 25 ml tetrahydrofuran under an inert atmosphere. Calcium hydride (420 mg, 10.0 mmol) was added, and the resulting solution was stirred for two hours at room temperature. A solution of retinal, (1.42 gm, 5.0 mmol) in 5 ml dry tetrahydrofuran was then added, and the reaction was refluxed for three hours. After this, the solution was poured into 50 ml 2 N aqueous hydrochloric acid, and was extracted several times with ether. The ether extracts were combined, washed with saturated aqueous sodium chloride solution, dried over magnesium sulfate, and concentrated by solvent removal at the rotary evaporator. The residue was further purified by chromatography on silica gel. Elution with hexane gave 1.0 gm (75%) beta-carotene, identified by thin-layer chromatographic comparison with an authentic sample, and by its melting point, mp 180°-182°.

Source