ABSTRACT
References ...................................................................................................................................... 113
Many plants contain a variety of free acids which are colorless compounds soluble in water, ethanol, and ether, but insoluble in the nonpolar solvents benzene or petroleum ether. These acids are weakly acidic and can accumulate in the cellular vacuoles of certain plants. Some of the acids are components of the citric acid cycle, while others are intermediates in the pathway leading from carbohydrates to either aromatic compounds or isoprenoid derivatives. 1 Figure 9.1 presents the chemistry of certain of these organic acids. Table 9.1 summarizes their possible functions. Oxalic acid appears to be of marked significance in fungal-induced wood decay, i.e., the acid could serve as a proton donor for oxidative (Fenton's reaction) cleavages of wood cellulose.2·3
Acetic Citric Chelidonic Daucic
coo-0,'(." I CH CH10H H I HCOOH HC cootoo-
Fonnic Fumaric Glycolic Glyoxylic
Isocitric a-Ketoglutaric Lactic Malic
HO HO o o-COOH ~~ ~c/ I Q-ca,H COOH I HO OH HO CH2 I HO HO c o-' 'oMalonic Oxalic Quinic Shikimic
.f'c, o oSuccinic Tartaric
Figure 9.1 Structure of some biologically important organic acids. Certam of these are optically acttve and can occur as salts.
