| 摘要 |
<p>3-Carene is converted into 4-carene in high yield by isomerisation over a noble metal, base metal or metal oxide hydrogenation catalyst in the presence of H2 at elevated temp. and pressure. Specifically, d-3-carene is used, the catalyst is Cu chromite and H2 pressure is 50 psig., or the catalyst is Ni or Pd, temp. 125-175 degrees and pressure 50-500 psig. Alternatively, a strong base can be used, opt. in the presence of a promoter. The d-4-carene obtd. is converted to d-trans-isolimonene by heating to 180 degrees. The isolimonene can be polymerised to a hard terpene resin, and d-trans-isolimonene can also be selectively hydrogenated to d-trans-2-menthene which can be converted to laevo-menthol. Pt and pref. Ru are suitable catalysts, at a conc. of is not >1 wt.%, at 0-100 degrees and up to 100 psig. The d-trans-2-menthene can also be produced by 1) treatment with a hydrogen halide followed by dehalogenation, or 2) treatment with Al(iBu)3 to give the Al deriv. which is then decomposed by active H cpds., e.g. H2O, with sepn. of Al(OH)3. The d-trans-isolimonene can also be isomerised to d-2,4(8)-p-menthadiene by a strong base, e.g. KOBu-t/Me2SO, which can be converted by known means to l-menthol.</p> |
