Preparation of .alpha.- and .beta.-cyclocitral, and the N-methylaldimines of these compounds
AssigneeBASF SE
InventorsLothar Janitschke, Werner Hoffmann
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Abstract
An improved process for the preparation of cyclocitrals of the general formula I ##STR1## via the novel N-methylaldimines of the general formula II ##STR2## and the novel N-methylaldimines of the formula II. The cyclocitrals of the formula I are obtained in yields of 80-90%, based on citral employed. The compounds I and II are important intermediates for the preparation of fragrances and carotinoids, such as vitamin A, and products related thereto.
Claims6
A process for the preparation of a cyclocitral of the general formula I ##STR8## where R is hydrogen or methyl and where the bonds shown in broken lines indicate the presence of a double bond in the 1- or 2-position of the cyclohexene ring, in which an open-chain aldehyde of the general formula III ##STR9## is reacted with methylamine at a suitable temperature to give its N-methylaldimine, the latter is cyclized at a suitable temperature with a multi-molar excess of concentrated sulfuric acid within the range of 1:2 to 1:10, to give the cyclocitral N-methylaldimine of the general formula II ##STR10## and the last-mentioned compound, with or without intermediate isolation from its reaction mixture, is hydrolyzed to the cyclocitral I in a conventional manner.
Cyclocitral N-methylaldimines of the general formula II ##STR11## where R is hydrogen or methyl and where the bonds shown in broken lines indicate the presence of a double bond in the 1- or 2-position of the cyclohexene ring.
Dependencies are inferred from the claim text.