Important aldehydes

The sulfur dioxide can be recovered and recycled. The myrcenol, after purification by distillation, can condense with acrolein to produce Lyral [31906-04-4], an important aldehyde with a strong-lasting odor similar to Lily-of-the-valley (92). 

An example of a biologically important aldehyde is pyridoxal phosphate, which is the active form of vitamin Bg and a coenzyme for many of the reactions of a-amino acids. In these reactions the amino acid binds to the coenzyme by reacting with it to form an imine of the kind shown in the equation. Reactions then take place at the amino acid portion of the imine, modifying the amino acid. In the last step, enzyme-catalyzed hydrolysis cleaves the imine to pyridoxal and the modified amino acid. 

Betterton, E. A., Hoffmann, M. R. (1988) Henry s law constants of some environmentally important aldehydes. Environ. Sci. Technol. 22, 1415-1418. 

Formaldehyde is the most important aldehyde used in Henry reactions in relation to energetic materials synthesis. Nitroform (112) reacts with formaldehyde in the form of trioxane or formalin to yield 2,2,2-trinitroethanol (159). The Henry reaction of nitroform with aldehydes other than formaldehyde gives products which are not isolable. 

The absolute values of the absorption cross sections of HCHO have been somewhat controversial. This appears to be due to a lack of sufficient resolution in some studies as discussed in Chapter 3.B.2, if the spectral resolution is too low relative to the bandwidth, nonlinear Beer-Lambert plots result. The strongly banded structure means that calculations of the photolysis rate constant require actinic flux data that have much finer resolution than the 2- to 5-nm intervals for which these flux data are given in Chapter 3 or, alternatively, that the measured absorption cross sections must be appropriately averaged. One significant advantage of the highly structured absorption of HCHO is that it can be used to measure low concentrations of this important aldehyde in the atmosphere by UV absorption (see Sections A.ld and A.4f in Chapter 11.). 

Table 8.3 shows the solubilities of some potentially important aldehydes in the form of the Henry s law constant (H) and the effective Henry s law constant (// ) (Betterton and Hoffmann, 1988 Olson and Hoffmann, 1989). These aldehydes not only dissolve in aqueous solutions but also hydrate to form gera-diols (Buschmann et al., 1980, 1982) ... 

The next aldehyde is acetaldehyde, a colorless liquid with a pungent taste and a fruity odor. Its molecular formula is CH,CHO. It has a flash point of -40°F, an ignition temperature of 340°F, and is toxic by inhalation. Acetaldehyde is used in die manufacture of many other chemicals. Other important aldehydes are propionaldehyde, butyraldehyde, and acrolein. 

As we would expect in a perfume as distantly related in time as Opium is to both Shalimar and Youth Dew, a number of more modem materials have been introduced. The cis-3-hexenyl salicylate backs up the benzyl salicylate, and Lyral, the hydroxycitronellal. A small amount of Hedione is also included. There have been important developments to the rose aspect of the perfume with the addition of phenylethyl dimethyl carbinol (3%) and Centifolyl. The fresh character of the rose derives from the use of geranyl acetate. Unlike the earlier oriental perfumes there is also an important aldehydic note. 

Carbonyl compounds react with phenols at positions ortho or para to the hydroxy substituents as shown in the generalized Scheme 1. By far the most important aldehyde is formaldehyde, and acetone is the ketone most studied. 

Many aldehydes and ketones are produced industrially as food and fragrance chemicals, medicinals, and agricultural chemicals. They are particularly important to the food industry, in which they are used as artificial and/or natural additives to food. Vanillin, a principal component of natural vanilla, is shown in Figure 14.3. Artificial vanilla flavoring is a dilute solution of synthetic vanillin dissolved in ethanol. Figure 14.3 also shows other examples of important aldehydes and ketones. 

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