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Carbinolamines and Geminal Diols in Aqueous Environmental Organic Chemistry^
The beginning environmental chemist or environmental scientist with a bachelor's degree most likely has taken one or two courses of organic chemistry. In general, the reactions and mechanisms studied will have been staged in organic solvents: ethers, alcohols, ketones, hydrocarbons, halogenated hydrocarbons, etc. While these solvents are sometimes encountered as discrete phases in environmental sites (e.g., dense nonaqueous phase liquids or DNAPLs), most environmental chemistry takes place in water or in its presence-very much unlike the conditions of a Grignard reaction, for example. The traditional organic chemistry sequence is not intended to prepare students for careers in environmental chemistry and may mislead them. What is generally true in an organic solvent may not apply at all in an aqueous solution. Both courses and texts tend to emphasize synthetic utility, and exercises are geared to promote synthesis reasoning. This approach has served organic chemists well, and no curriculum can cover every nuance. Thus, it falls to teachers of environmental chemistry to treat aqueous organic chemistry.
Carbinolamines and Geminal Dials
Carbinolamines or hemiaminals form as intermediates in the reactions of aldehydes and ketones with ammonia and amines. For primary amines, this often leads to the formation of an imine (eq 1), the most stable of which are the Schiff bases (which usually have at least one aryl R or Z group).
Naturally Occurring Species and Disinfection Byproducts
Several short-chain oxo-containing compounds are formed as ozonation byproducts (OBPs) from the disinfection of drinking water supplies (39, 40). Methanal is ubiquitous and results from natural processes, in addition to anthropogenic ones. Although the very low concentrations of the nonhalogenated compounds that occur in potable water supplies have not been implicated in any adverse health effects, they can serve as nutrients for microbes in the distribution system. Some chlorinated aldehydes and ketones are found as chlorination byproducts (CBPs), for instance, 2,2,2-trichloroethane-1,1diol (39). There are two important consequences of the hydrophilicity associated with gem diol formation: lower volatility and reduced partitioning into organic solvents. Because these compounds are quantitated by extraction into organic solvents, such as t-butyl methyl ether (41, 42), this behavior raises the lower limit of detection relative to what would be expected for the aldehydes.
Nonetheless, these compounds...