Aldehydes application aroma production

Citrus fruits contain peel oil, the essence from which oil is obtained during concentration of the juice process. Citrus oils are characterized by a high percentage of terpene hydrocarbons (limonene, C10H16), which contribute little to aroma. The unique characteristics of limonene are its relative insolubility in dilute alcohol and its susceptibility to oxidation, causing off-flavor production. If the monoterpenes are removed, the resulting oil is called terpene-free or terpeneless oil. Aldehydes, esters, and alcohols are the main contributors to the aromas of citrus oil. These compounds are relatively polar and soluble in water therefore, they are satisfactory for applications in food and beverage. 

Induction of Aroma Volatile Production by Application of Aldehydes, Alcohols and Acids... 

Undecanal can be prepared from 1-decene, also employing the Rh(BIPHEP-HOS) catalyst (Table 6.1, entry 4). Similarly, a water-soluble Rh(TPPTS) complex was successfully synthesized (Scheme 6.6, w = 2) [54]. w-Regioselectivities up to 99% were noted in ionic liquids [55]. With its flowery-waxy-citrus odor, it gives the impression of freshness. Therefore the compound is the prototype of perfumery aldehydes and is widely used in different aroma applications. 2-Methyldecanal, which might be formed as isomeric side product, has an aldehydic, citrus-peel-like, waxy-green odor. It is used in perfumery to refresh green and citrus nuances. 

X-Terpineol can be considered as a hydrate of limonene. Indeed, it is available by Markovnikov addition of trifluoroacetic acid to the latter, followed by hydrolysis [141]. The alcohol has a pleasant odor similar to lilac and is a constituent of cajuput, pine, and petitgrain oil. For technical applications, it is produced from a-pinene by acid-catalyzed isomerization/hydration [142]. Hydroformylation of a-terpineol has been conducted with an unmodified Rh catalyst at 69bar (Scheme 6.45) [132]. Under the conditions applied, besides the expected cyclic carbaldehydes also a linear aldehyde with a tertiary alcoholic group were obtained. The reaction product was distilled, and the main fraction collected showed a woody and nutty aroma with minty and floral topnotes. 

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