Revisiting the Hitherto Elusive Cyclohexanehexone Molecule: Bulk Synthesis, Mass Spectrometry, and Theoretical Studies

et al. 2022

J. Am. Chem. Soc.

Self Cite

Oxidative C–H/N–H cross-coupling has emerged as an atom-economical method for the construction of C–N bonds. Conventional oxidative C–H/N–H coupling requires at least one of the following: high temperatures, strong oxidizers, transition metal catalysts, organic solvents, light, and electrochemical cells. In this study, by merely spraying the water solutions of the substrates into microdroplets at room temperature, we show a series of oxidative C–H/N–H coupling products that are strikingly produced in a spontaneous and ultrafast manner. The reactions are accelerated by six orders of magnitude compared to the same reactions in the bulk. It has been previously proposed by fluorescence microscopy and theory that the spontaneously generated electric field at the microdroplets peripheries can be in the ∼109 V/m range. Based on mass spectrometric analysis of key radical intermediates, we opine that the ultrahigh electric field catalytically oxidizes the substrates by removing an electron, which further promotes C/N coupling. Taken together, we anticipate that microdroplet chemistry will be an avenue rich in green opportunities of constructing C-heteroatom bonds.

Section: Resultsmentioning

confidence: 99%

High Electric Field on Water Microdroplets Catalyzes Spontaneous and Ultrafast Oxidative C–H/N–H Cross-Coupling

Zhang

et al. 2022

J. Am. Chem. Soc.

Self Cite

“…The lack of monotonicity might be a result of two competing effects, namely, the heating of the system accelerates the reduction but at a higher temperature the decay of Py − becomes dominant. To avoid the possibility that pyridine reduction might be triggered by trace species in the atmosphere, we also performed the experiment with a mass spectrometer whose inlet is inserted into a pure N 2 -protected glove box ( 36 ). No difference in Py − signal intensity was observed ( SI Appendix , Fig.…”

Section: Resultsmentioning

confidence: 99%

“…To capture the C 5 H 5 N − anion with CO 2 , the sheath gas was simply changed from N 2 to CO 2 . To avoid the possibility that the reaction might be triggered by the species in the atmosphere, we also performed the C 5 H 5 N − generation and capture experiments with a mass spectrometer whose inlet was inserted into a glove box filled with pure N 2 ( 36 ). An extended inlet (3 cm) of an LTQ-XL mass spectrometer was inserted into a glove box through an Ultra-Torr fitting welded to the wall of the glove box.…”

Section: Methodsmentioning

confidence: 99%

Sprayed water microdroplets containing dissolved pyridine spontaneously generate pyridyl anions

Zhao

Song

Proc. Natl. Acad. Sci. U.S.A.

et al. 2022

Self Cite

Significance Water microdroplets can accelerate chemical reactions by orders of magnitude compared to the same reactions in bulk water and/or trigger spontaneous reactions that do not occur in bulk solution. Among the properties of water microdroplets, the unique redox ability resulting from the spontaneous dissociation of OH − into a released electron and •OH at the air–water interfaces is especially intriguing. At the air–water interface, OH − exhibits a strong reducing potential, and the resulting •OH is highly oxidative, making water microdroplets a unity of opposites. We report the reduction of pyridine into pyridyl anions (C 5 H 5 N − ) and the oxidation of pyridine into hydroxypyridine, which extends what we know about the redox power of water microdroplets.

“…In addition, increasing the sheath gas pressure will decrease the size of the microdroplets 7,41 and increase the reaction efficiency (Figure S4), further manifesting the importance of the microdroplet surface. Moreover, to avoid the possibility that the reaction might be triggered by the species in the atmosphere, we also performed the same experiment with a mass spectrometer whose inlet is inserted into a glovebox, 44 and no difference was observed (Figure S5). We next discuss the mechanisms of the degradation of EV in water microdroplets (Figure 2).…”

Section: ■ Introductionmentioning

confidence: 99%

Spontaneous Reduction-Induced Degradation of Viologen Compounds in Water Microdroplets and Its Inhibition by Host–Guest Complexation

et al. 2022

J. Am. Chem. Soc.

Self Cite

105

Water serves as an inert environment for the dispersion and application of many kinds of herbicides. Viologen compounds, a type of widely used but highly toxic herbicide, are stable in bulk water, whose half-life can be up to 23 weeks in natural water, imposing a severe health risk to mammals. In this study, we present the striking results of the spontaneous and ultrafast reduction-induced degradation of three viologen compounds in water microdroplets and provide the concentration, time, temperature dependence, mechanism, and scale-up of the reactions. We postulate that the electrons existing at the air−water interface of the microdroplets due to the unique redox potential therein initiate the reduction, from which further degradation occurs. The host−guest complexation between cucurbit[7]uril and viologens only slightly changes the redox potential of viologens in the bulk but completely inhibits the reactions in microdroplets, adding to the uniqueness of the redox potentials at the air−water interfaces of microdroplets. Taken together, microdroplets might have been functioning as naturally occurring ubiquitous tiny electrochemical cells for a plethora of unique redox reactions that were thought to be impossible in the bulk water.