Diastereo- and enantioselective synthesis by nontraditional activation methods: Ultrasonic, microwave, electro-, photo- and mechanochemically activated reactions

Mishra, Manisha; Török, Béla

doi:10.1016/b978-0-12-819009-8.00012-8

Cited by 1 publication

(1 citation statement)

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“…The rationale regarding the use of ultrasound was that in the nitration due to the presence of the aqueous HNO 3 and the non-polar hydrocarbon, one is dealing with a two-phase system and the reaction rates are likely limited by the mass transfer over the phase boundary. In addition to its efficacy as an activation method (Török et al, 2001;Török et al, 2002), sonication is also well-know for its mixing efficiency and its strong contribution to green synthesis (Mishra and Török, 2021;Mishra and Török, 2023). The data in Table 3, however, indicates that although sonication works well under most conditions, producing nearly quantitative yields, it does not seem to enhance the results as compared to the conventional stirring of the reaction mixture (Table 3, entries 3 vs. 5).…”

Section: Resultsmentioning

confidence: 99%

Chemo-and regioselective aqueous phase, co-acid free nitration of aromatics using traditional and nontraditional activation methods

Plasse,

Mooney,

Mastyugin

et al. 2024

Front. Chem.

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Electrophilic aromatic nitrations are used for the preparation of a variety of synthetic products including dyes, agrochemicals, high energy materials, fine chemicals and pharmaceuticals. 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, and 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 ultrasonic irradiation, microwave and high pressure, respectively, to achieve satisfactory yields and improve upon the greenness of the reaction while maintaining short reaction times.

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Section: Resultsmentioning

confidence: 99%