In search of green notes. The green phenomena in aroma chemicals begins in the C6 group in a number of examples. The green effect extends thru C7 and C8 to end at the C9 level with the nonadienols. The green effect slowly fades into a floral tone and then disappears into the oily-fatty area in the higher aliphatic molecules above C9. The nonadienols are truly representative of the term, “specialty aroma chemical,” because their singular and collective volume is small by any standard. The 3,6-Nonadienol used above in Figure 1 as the structural illustration for this group represents the latest product introduced, and the dedication aroma-chemical manufacturers have invested in their markets. It is forecast that the R&D expenditure needed to develop this latest Figure 1. 3,6 Nonadien-1-ol specialty will most likely never be recouped, based upon the projected sales volume and its present price level.
Organoleptically, the nonadienols are an interesting group of medium-volatility range alcohols because they possess unique green-vegetable-cucumber-melon properties. These organoleptic attributes cannot be readily found in any other materials, save their related aldehydes. Table 1 presents their organoleptic profiles along with those of the corresponding aldehydes.
There are a number of nonadienols found in nature; 2,4- nonadien-1-ol, 2,6- nonadien-1-ol and 3,6- nonadien-1-ol. Their structures are complicated by their existence in cis and trans forms for each double bond, leading to a number of possibilities. Their exact identification has sometimes been tenuous, thus the reports of finding one isomer are sometimes in error and the entity found is in reality another isomer or a mixture of isomers.