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Chemo- and Regioselective Aqueous Phase, Co-Acid Free Nitration of Aromatics Using Traditional and Nontraditional Activation Methods

Publication Date
Authors
Author Name
Kelsey M. Plasse
Author Organization
Department of Chemistry, University of Massachusetts Boston
Author Name
Tara R. Mooney
Author Organization
Department of Chemistry, University of Massachusetts Boston
Author Name
Béla Török
Author Organization
Department of Chemistry, University of Massachusetts Boston

Electrophilic aromatic nitrations are used for the preparation of a variety of synthetic products including dyes, agrochemicals, high energy materials, and pharmaceuticals. Moreover, nitro compounds can be used as intermediates and easily reduced to products such as anilines, that are important feedstock in a broad range of syntheses. Traditional nitration methods use highly acidic and corrosive mixed acid systems which present a number of drawbacks. Aside from being hazardous and waste-producing, these methods also often result in poor yields, mostly due to low regioselectivity, and limited functional group tolerance. As a consequence there is a need for effective and environmentally benign methods for electrophilic aromatic nitrations. In this work the major aim was to develop reaction protocols that are more environmentally benign while also considering safety issues. The reactions were carried out in dilute aqueous nitric acid, and a broad range of experimental variables, such as acid concentration, temperature, time, activation method, were investigated. Mesitylene and m-xylene were used as test substrates for the optimization. While the optimized reactions generally occurred at room temperature without any activation under additional solvent-free conditions, slight adjustments in acid concentration, stoichiometric equivalents, and volume were necessary for certain substrates, in addition to the activation. The substrate scope of the process was also investigated using both activated and deactivated aromatics. The concentration of the acid was lowered when possible to improve upon the safety of the process and avoid over-nitration. With some substrates we compared traditional and nontraditional activation methods such as ultrasounds, microwaves and high pressure, respectively, to achieve satisfactory yields and improve upon the greenness of the reaction while maintaining short reaction times.  

Source
Frontiers in Chemistry
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