Choice Of Reagents

In oxidations, potassium dichromate or permanganate, or lead tetraacetate, is used in the laboratory. However, these stoichiometric reactions involve mole-for-mole amounts of high-molecular-weight oxidants. Therefore, the oxidants must be used in large, absolute quantities. Such reactions are costly and generate large volumes of an effluent, pos-

sibly containing toxic metal salts that must be treated in the scaled-up process (Stinson 1993).

Hydrogen peroxide, peracetic acid, or tert-butyl hydroperoxide should be investigated as alternatives in oxidations catalyzed by trace amounts of transition metals. Such reactions could be easily worked up and result in only water, acetic acid, or tert-butanol as by-products. (Stinson 1993).

DMC can replace phosgene in carbonylation reactions and dimethyl sulfate and methyl chloride in methylation reactions. Oxalyl chloride is another alternative to phosgene.

Phosgene is a valuable agent for converting acids to acid chlorides, amides to nitriles, primary amines to iso-cyanates, and alcohols to chloroformates. The more tractable disphosgene (trichloromethyl chloroformate, Cl CO2 Cl3) can be used as a phosgene substitute in small-scale reactions (Stinson 1993).

An alternative to the highly toxic and potentially explosive fluorinating reagents (such as HF, FClO3, and CF3OF) and the reagent called Selectfluor (or F-TEDA-BF4) is 1-chloromethyl-4-fluoro-1,4-diazonia[2,2,2] bicy-clooctane bis(tetrafluoroborate). Selectfluor provides a tool for developing and producing high-performance fluorine-containing drugs (Illman 1993).

Carbon dioxide has advantages over traditional pH-control chemicals, such as sulfuric acid. The savings come from both the favorable cost of carbon dioxide and the elimination of the costs of handling, storing, and disposing sulfuric acid. Charging a sodium nitrile solution with carbon dioxide under high pressure drops the pH low enough to diazotize p-anisidine. Releasing the pressure afterward raises the pH so that the coupled product precipitates out.

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