Enzyme-Inspired Lysine-Modified Carbon Quantum Dots Performing Carbonylation Using Urea and a Cascade Reaction for Synthesizing 2-Benzoxazolinone

Abstract

Catalysts as the dynamo of chemical reactions along with solvents play paramount roles in organic transformations in long-lasting modes. Thus, developing effective and biobased catalysts in nontoxic solvents is highly in demand. In this report, carbon quantum dots (CQDs) functionalized with L-lysine (Lys-CQDs) were generated from entirely nature-derived materials; they were demonstrated to be a promising catalyst for C−N bond formation in choline chloride urea (ChCl/U), a natural deep eutectic solvent (NADES). Among a number of synthesized CQDs, Lys-CQD turned out to be a powerful catalyst in the model reaction with aniline to afford phenyl urea. This type of transformation is important because aniline as a nucleophile has low activity, and urea is a very weak electrophile but an abundant natural source of the carbonyl moiety at the same time. The optimized reaction was performed under a highly desirable condition without using tedious and toxic workup processes at a low temperature (37 °C for aliphatic amines and 60 °C for aniline derivatives), as well as by embracing the broad scope of products in good to high yields even with weak nucleophiles such as aniline. A proposed acid-activated mechanism was suggested for the model reaction that was further confirmed by detecting ammonia as the leaving group. To show further multifunctionality of the catalyst, a cascade catalysis approach was developed for synthesizing 2benzoxazolinone, which was furnished in a two-step transformation, starting from 2-aminophenol. Using X-ray crystallography, the structure of the final product in the cascade reaction was also determined. The catalyst was characterized using various analytical techniques including SEM, TEM, AFM, XRD, IR spectroscopy, UV−vis spectroscopy, DLS, and fluorescence spectroscopy. Measuring the acid/base sites by back titration, the catalyst was shown to be highly functionalized by the lysine functional group. The size of the catalyst was determined to be in the range of 1−8 nm, having a well-dispersed surface. In all, Lys-modified CQD, as a metal-free catalyst, was synthesized, characterized, and optimized for carbonylation, as well as a cascade reaction, under mild conditions. The whole process including catalyst synthesis and organic transformations is economically competitive and fulfills all requirements toward viability.

Amine‐Rich Carbon Dots as Novel Nano‐Aminocatalytic Platforms in Organic Synthesis

“…Another example on the use of nitrogen‐doped CDs to catalyze organic reactions was reported recently by Kalhor and co‐workers [38] . This study focuses on the synthesis, characterization and application in catalytic reactions of nitrogen‐doped CDs‐E (Figure 4b).…”

“…Another example on the use of nitrogen‐doped CDs to catalyze organic reactions was reported recently by Kalhor and co‐workers. [38] This study focuses on the synthesis, characterization and application in catalytic reactions of nitrogen‐doped CDs‐E (Figure 4 b). The nanoparticles were prepared from CA and L–Lysine (Lys) that was specifically chosen because of its long carbon chain terminated with a primary amine.…”

Blocking viral infections with lysine-based polymeric nanostructures: a critical review

“…However, such systems appear to have good biocompatibility and ease of synthesis, which are mandatory for the development of biomedical applications 79 or to promote specific chemical reactions. 80 Lysine and arginine-based carbon dots with 5 nm in size have shown antibacterial capability against E. coli and S. aureus , likely due to the formation of induced radical oxygen scavengers species. Furthermore, an interesting effect on tissues growth promotion has also been highlighted.…”

Tailoring the Chemical Structure of Nitrogen‐Doped Carbon Dots for Nano‐Aminocatalysis in Aqueous Media

“…In recent years, the presence of these reactive surface functionalities has allowed the exploitation of CDs in synthetic nano‐organocatalysis for the production of valuable organic compounds under mild operative conditions [13–15,17–19] . In this context, nitrogen‐doped amine‐rich CDs (NCDs) are becoming extremely popular metal‐free, nano‐catalytic platforms due to their interesting properties [2,20,21] . Indeed, NCDs can be easily synthesized through the thermal treatment (i. e., carbonization, pyrolysis, or hydrothermal/microwave treatment) of suitable nitrogen‐containing precursors such as amino acids, amines, and polyamines [3] .…”