Presidential Green Chemistry Challenge: 1996 Greener Synthetic Pathways Award
Monsanto Company
Innovation and Benefits: DSIDA is a key building block for the herbicide RoundUp®. Monsanto's novel synthesis of DSIDA eliminates most of the manufacturing hazards associated with the previous synthesis; it uses no ammonia, cyanide, or formaldehyde. This synthesis is safer to operate, has a higher overall yield, and has fewer process steps.
Summary of Technology: Disodium iminodiacetate (DSIDA) is a key intermediate in the production of Monsanto's Roundup® herbicide, an environmentally friendly, nonselective herbicide. Traditionally, Monsanto and others have manufactured DSIDA using the Strecker process requiring ammonia, formaldehyde, hydrochloric acid, and hydrogen cyanide. Hydrogen cyanide is acutely toxic and requires special handling to minimize risk to workers, the community, and the environment. Furthermore, the chemistry involves the exothermic generation of potentially unstable intermediates, and special care must be taken to preclude the possibility of a runaway reaction. The overall process also generates up to 1 pound of waste for every 7 pounds of product, and this waste must be treated prior to safe disposal.
Monsanto has developed and implemented an alternative DSIDA process that relies on the copper-catalyzed dehydrogenation of diethanolamine. The raw materials have low volatility and are less toxic. Process operation is inherently safer, because the dehydrogenation reaction is endothermic and, therefore, does not present the danger of a runaway reaction. Moreover, this zero-waste route to DSIDA produces a product stream that, after filtration of the catalyst, is of such high quality that no purification or waste cut is necessary for subsequent use in the manufacture of Roundup®. The new technology represents a major breakthrough in the production of DSIDA because it avoids the use of cyanide and formaldehyde, is safer to operate, produces higher overall yield, and has fewer process steps.
The metal-catalyzed conversion of amino-alcohols to amino acid salts has been known since 1945. Commercial application, however, was not known until Monsanto developed a series of proprietary catalysts that made the chemistry commercially feasible. Monsanto's patented improvements on metallic copper catalysts afford an active, easily recoverable, highly selective, and physically durable catalyst that has proven itself in large-scale use.
This catalysis technology also can be used in the production of other amino acids, such as glycine. Moreover, it is a general method for conversion of primary alcohols to carboxylic acid salts; it is potentially applicable to the preparation of many other agricultural, commodity, specialty, and pharmaceutical chemicals.
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