Some comments to the earlier reports on the preparations, spectral characteristics, and stabilities of 5, 6- and 5, 8-monoepoxyretinyl acetates were described.
1. The 5, 6-monoepoxide was obtained from the acetate and perphthalic acid, followed by a preparative thin layer chromatography on activated alumina using 10-15% acetone in hexane as a developer and 20% ether in hexane as an eluant.
2. The 5, 6-monoepoxide indicated a distinct fine structure in its UV spectrum at 326, 312, and 298mμ in hexane and its extent was similar to that of β-carotene 5, 6-monoepoxide and less than β-carotene 5, 6, 5′, 6′-diepoxide.
3. The IR spectrum of the 5, 6-monoepoxide showed a medium peak at 9.58μ. From the accumulated data on β-carotene epoxides, this peak was assigned to the 5, 6-epoxy group in the molecules of epoxypolyene hydrocarbons.
4. The 5, 8-monoepoxide showed a degraded structure in its UV spectrum and λ_max was located at 280.5mμ in hexane accompanied by two shoulders at 291.5-292 and 268-270mμ.
5. The 5, 6-monoepoxide was easily transformed to its 5, 8-monoepoxide with CHCI₃-HCI or ethanolic 0.05N HCI. The former epoxide was also decomposed rapidly on irradiation with UV light in the presence of l₂. On the contrary, the 5, 8-epoxide was far stable under the same circumstances.