PRINCIPLES OF TOXICOLOGY

390 PROPERTIES AND EFFECTS OF ORGANIC SOLVENTS
Figure 16.15 Carboxylic acid.
16.11 TOXIC PROPERTIES OF REPRESENTATIVE ESTERS
Esters of similar structure are more potent anesthetics than the corresponding alcohols, aldehydes, or
ketones, but are weaker than the ethers or halogenated hydrocarbons. Esters (see Figure 16.16) typically
are degraded in the bloodstream by plasma esterases to the corresponding carboxylic acids and
alcohols. Similarly, the lower molecular weight esters are more potent irritants than the alcohols and
are known to cause eye irritation and lacrimation. Halogen substitution serves to increase the irritant
effects, and unsaturated double bonds in the side chain may increase the toxicity by a large margin.
Unsaturated esters have increased irritancy, and some may act to cause CNS stimulation, rather than
CNS depression. Additional functional groups other than halogens or double bonds between carbons
in the alkyl chain tend to reduce the vapor pressure and the systemic toxicity. Therefore, these esters
are usually of limited interest as irritants to the skin and eyes.
Phthalate esters, used widely as plasticizers, may produce CNS damage at very high concentrations,
may be irritating and have the capacity to act as either convulsants or depressants. Because of the wide
variety of ester structures and the dramatic effect that additional functional groups may have regarding
toxicity, the exact consequences of exposure to each compound should be sought in the literature, and
few generalizations other than the ones indicated here are possible concerning these compounds.
Di(2-ethylhexyl)phthalate (DEHP; BEHP) is classified as a potential carcinogen by some regulatory
agencies. However, the proposed mechanism of action (repetitive tissue injury) renders this
classification of limited practical significance.
Figure 16.16 Ester compounds.
16.12 TOXIC PROPERTIES OF REPRESENTATIVE ETHERS
The ethers (see Figure 16.17) are recognized to have a broad variety of industrial and commercial uses.
They are used in the production of rubber, plastics, cosmetics, paints and coatings, refrigeration, and
foods. They also are widely used in medicine. Ethers as a class are effective anesthetics, and this
property increases with the molecular size. The utility of this property is, however, limited by the irritant
effects of ethers, and the fact that they are easily oxidized or photodegraded to peroxides which may
be quite explosive.
Generally speaking, as chain length increases for the ethers, the oral and inhalation toxic potential
decreases. In contrast, however, dermal penetrability and skin irritation increases with increasing chain
length.
Diethyl ether [or ethyl ether (see Figure 16.18)] is absorbed rapidly through the lungs and,
subsequently, is rapidly excreted through the lungs. It has potent anesthetic properties, and was widely