Acid-catalysed dehydration of dehydroretinol.

1. Treatment of dehydroretinol with hydrogen chloride in light petroleum or toluene-p-sulphonic acid in benzene produces a substance with u.v.-absorption maxima at 284, 296, 310, 350, 368, 388, 408 and 433nm. and antimony trichloride colour maximum at 620nm. This compound is tentatively named compound 433 after its absorption maximum at 433nm. 2. Treatment of dehydroretinol with ethanolic hydrogen chloride produces, besides 3-ethoxyanhydroretinol, some compound 433 also. 3. Compound 433 is present in several freshwater-fish liver oils. 4. The i.r. spectrum of compound 433 shows only a band attributable to a conjugated ethylenic system. 5. The course of changes that lead to the formation of compound 433 is discussed.