Environmental Engineering Reference
In-Depth Information
Table 2.2
Major cyclic compounds found in plant waxes.
Cyclic compounds
Structure
Sterols
H
H
H
HO
OH
Flavonoids
HO
O
OH
OH
OH
O
Terpenoids
H
H
HO
H
H
On the other hand, in the case of primary alcohols, aldehydes and fatty acids,
the predominant compounds are those which possess an even number of carbon
atoms [11]. In a number of plant waxes, the chain length of ketones is related to
the hydrocarbon chain length. Two examples are nonacosan-15-one and hentriac-
ontan-16-one, which are normally present in plant waxes where the predominant
hydrocarbons are nonacosane and hentriacontane, respectively [18-21]. In addi-
tion, in some plant tissues, mixtures of ketones occur where mixtures of alkanes
are present [22]. However, in the case of β-diketones, the chain length of the
compounds is not related to the hydrocarbon chain length of the same tissue.
Tritriacontan-16,18-one appears to be the most common β-diketone [23, 24].
Occasionally, the type of secondary alcohol present is closely related to the type
of ketone found in the plant wax [25, 26].
Wax esters generally comprise
n
-alkanoic acids and
n
-alkan-1-ols and often
possess an even number of carbon atoms. In plant waxes, the presence of double
bonds and branches in wax esters is rare, unlike microbial and animal waxes. The
fatty acid and fatty alcohol portions of the ester usually correspond to the free
fatty acid and free fatty alcohol in the plant wax [27].
