1998 Greener Synthetic Pathways Award
Flexsys America L.P.
Elimination of Chlorine in the Synthesis of 4-Aminodiphenylamine:
A New Process That Utilizes Nucleophilic Aromatic Substitution for Hydrogen
Innovation and Benefits: Flexsys developed a new method to eliminate waste from a critically important reaction used to manufacture a wide range of chemical products. They are using this method to manufacture 4-ADPA, a key, high-volume building block for a rubber preservative. Converting just 30 percent of the world's production capacity of this key building block to the Flexsys process would reduce chemical waste by 74 million pounds per year and wastewater by 1.4 billion pounds per year.
The development of new environmentally favorable routes for the production of chemical intermediates and products is an area of considerable interest to the chemical processing industry. Recently, the use of chlorine in large-scale chemical syntheses has come under intense scrutiny. Solutia, Inc. (formerly Monsanto Chemical Company), one of the world’s largest producers of chlorinated aromatics, has funded research over the years to explore alternative synthetic reactions for manufacturing processes that do not require the use of chlorine. It was clear that replacing chlorine in a process would require the discovery of new atom-efficient chemical reactions. Ultimately, it was Monsanto’s goal to incorporate fundamentally new chemical reactions into innovative processes that would focus on the elimination of waste at the source. In view of these emerging requirements, Monsanto’s Rubber Chemicals Division (now Flexsys), in collaboration with Monsanto Corporate Research, began to explore new routes to a variety of aromatic amines that would not rely on the use of halogenated intermediates or reagents. Of particular interest was the identification of novel synthetic strategies to 4-aminodiphenylamine (4-ADPA), a key intermediate in the Rubber Chemicals family of antidegradants. The total world volume of antidegradants based on 4-ADPA and related materials is approximately 300 million pounds per year, of which Flexsys is the world’s largest producer. (Flexsys is a joint venture of the rubber chemicals operations of Monsanto and Akzo Nobel.)
Flexsys’s current process to 4-ADPA is based on the chlorination of benzene. Since none of the chlorine used in the process ultimately resides in the final product, the pounds of waste generated in the process per pound of product produced from the process are highly unfavorable. A significant portion of the waste is in the form of an aqueous stream that contains high levels of inorganic salts contaminated with organics that are difficult and expensive to treat. Furthermore, the process also requires the storage and handling of large quantities of chlorine gas. Flexsys found a solution to this problem in a class of reactions known as nucleophilic aromatic substitution of hydrogen (NASH). Through a series of experiments designed to probe the mechanism of NASH reactions, Flexsys realized a breakthrough in understanding this chemistry that has led to the development of a new process to 4-ADPA that utilizes the base-promoted, direct coupling of aniline and nitrobenzene.
The environmental benefits of this process are significant and include a dramatic reduction in waste generated. In comparison to the process traditionally used to synthesize 4-ADPA, the Flexsys process generates 74 percent less organic waste, 99 percent less inorganic waste, and 97 percent less wastewater. In global terms, if just 30 percent of the world’s capacity to produce 4-ADPA and related materials were converted to the Flexsys process, 74 million pounds less chemical waste would be generated per year and 1.4 billion pounds less wastewater would be generated per year. The discovery of the new route to 4-ADPA and the elucidation of the mechanism of the reaction between aniline and nitrobenzene have been recognized throughout the scientific community as a breakthrough in the area of nucleophilic aromatic substitution chemistry.
This new process for the production of 4-ADPA has achieved the goal for which all green chemistry endeavors strive: the elimination of waste at the source via the discovery of new chemical reactions that can be implemented into innovative and environmentally safe chemical processes.
Read on about the 1998 Greener Reaction Conditions Award.
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