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1,1-Dimethoxy-2,2,5-trimethyl-4-hexene: The Grapefruit Acetal

By: Mchael Zviely, CIC
Posted: June 24, 2011, from the July 2011 issue of P&F magazine.

1,1-Dimethoxy-2,2,5-trimethyl-4-hexene (CAS# 67674-46-8) is a colorless to pale yellow liquid with a fresh, citrus, grapefruit peel-like odor and a vetiveryl acetate aspect. 1,1-Dimethoxy-2,2,5-trimethyl-4-hexene, which is not reported as being found in nature, belongs to a series of natural and synthetic molecules, of which nootkatone is a key material, that can represent the grapefruit note in fragrances. Both molecules show some structure similarity.

1,1-Dimethoxy-2,2,5-trimethyl-4-hexene can be prepared by condensation of 2-methylbut-3-en-ol and isobutanal to form 2,2,5-trimethylhexenal as an intermediate. The intermediate aldehyde is then converted to the dimethyl acetal using trimethyl orthoformate Additional methods of preparation use rather similar chemistry, but some of the reagents are different.

1,1-Dimethoxy-2,2,5-trimethyl-4-hexene, with its fresh bitterness, blends very well with citrus bases. It can also be used as a booster for vetiver accords. This makes 1,1-dimethoxy-2,2,5-trimethyl-4-hexene a key ingredient in modern colognes such as Pleasures for Men (Estee Lauder), Aqua Allegoria Pamplelune (Guerlain), and L’eau de Kenzo Masculine (Kenzo), which contain ca. 3.5% of this ingredient.

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