Reaction #56549

Reaction equation

retinal

hydrochloric acid

→

beta-carotene

Yield 20.0%

Solvents

tetrahydrofuran

Conditions

Workup

1. 1
   TemperatureAfter refluxing for two hours
2. 2
   Extractionextracted several times with ether
3. 3
   Washwashed with saturated aqueous sodium chloride solution, dried sulfate
4. 4
   Concentrationconcentrated by solvent removal at the rotary evaporator
5. 5
   OtherThe residue was purified by chromatography over silica gel
6. 6
   WashElution with hexane

Procedure

A slurry of titanium trichloride (770 mg, 5.0 mmol) in 20 ml dry tetrahydrofuran was prepared under an inert atmosphere (nitrogen or argon), and magnesium turnings (120 mg, 5.0 mmol) were added. The resulting mixture was refluxed overnight to form the Ti(II) reagent, and a solution of retinal (710 mg, 2.5 mmol) in 5 ml dry tetrahydrofuran was added. After refluxing for two hours, the solution was poured into 50 ml 2 N aqueous hydrochloric acid and extracted several times with ether. The ether extracts were combined, washed with saturated aqueous sodium chloride solution, dried sulfate, and concentrated by solvent removal at the rotary evaporator. The residue was purified by chromatography over silica gel. Elution with hexane gave 130 mg (20% yield) beta-carotene identified by thin-layer chromatographic comparison with an authentic sample, and by its characteristic ultraviolet spectrum.

Source