Involving Bond Cleavage Research Articles

UV-induced photodegradation of emerging para-phenylenediamine quinones in aqueous environment: Kinetics, products identification and toxicity assessments

Substituted para-phenylenediamine quinones (PPD-quinones) are a class of emerging contaminants frequently detected in the aqueous environment. One of them, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone (6PPD-Q), was found to cause acute toxicities to aquatic species at extremely low environmental levels. The ubiquitousness and ecotoxicity of such pollutants underscore the importance of their transformation and elimination. In this work, we demonstrated effective removals of five PPD-quinones in aqueous environments under UV irradiation, with up to 94% of 6PPD-Q eliminated after a 40-min treatment. By applying high-resolution mass spectrometry (HRMS) non-targeted screening in combination with isotope labeling strategies, a total of 22 transformation products (TPs) were identified. Coupling with the time-based dynamic patterns, potential transformation mechanisms were identified as an •OH-induced photocatalysis reaction involving bond cleavage, hydroxylation, and oxidation. Computational toxicity assessment predicted lower aquatic toxicity of the TPs than their parent PPD-quinones. Our results in parallel evidenced an obvious reduction of PPD-quinones accompanied by the presence of their TPs in the effluent after UV disinfection in real municipal wastewater. This work builds a comprehensive understanding of the fate, transformation products, and related toxicological characteristics of emerging PPD-quinone contaminants in the aqueous environment.

Recent progress in C–N coupling for electrochemical CO2 reduction with inorganic nitrogenous species in aqueous solution

The electrocatalytic CO2 reduction in aqueous solution mainly involves bond cleavage and formation between C, H and O, and it is highly desirable to expand the bond formation reaction of C with other atoms to obtain novel and valuable chemicals. The electrochemical synthesis of N-containing organic chemicals in electrocatalytic CO2 reduction via introducing N sources is an effective strategy to expand the product scope, since chemicals containing C–N bonds (e.g. amides and amines) are important reactants/products for medicine, agriculture and industry. This article focuses on the research progress of C–N coupling from CO2 and inorganic nitrogenous species in aqueous solution. Firstly, the reaction pathways related to the reaction intermediates for urea, formamide, acetamide, methylamine and ethylamine are highlighted. Then, the electrocatalytic performance of different catalysts for these several N-containing products are summarized and classified. Finally, the challenges and opportunities are analyzed, aiming to provide general insights into future research directions for electrocatalytic C–N coupling.

A single-molecule blueprint for synthesis.

Chemical reactions that occur at nanostructured electrodes have garnered widespread interest because of their potential applications in fields including nanotechnology, green chemistry and fundamental physical organic chemistry. Much of our present understanding of these reactions comes from probes that interrogate ensembles of molecules undergoing various stages of the transformation concurrently. Exquisite control over single-molecule reactivity lets us construct new molecules and further our understanding of nanoscale chemical phenomena. We can study single molecules using instruments such as the scanning tunnelling microscope, which can additionally be part of a mechanically controlled break junction. These are unique tools that can offer a high level of detail. They probe the electronic conductance of individual molecules and catalyse chemical reactions by establishing environments with reactive metal sites on nanoscale electrodes. This Review describes how chemical reactions involving bond cleavage and formation can be triggered at nanoscale electrodes and studied one molecule at a time.

Bond cleavage, fragment modification and reassembly in enantioselective three-component reactions.

Chemical bond cleavage and reconstruction are common processes in traditional rearrangement reactions. In contrast, the process that involves bond cleavage, fragment modification and then reconstruction of the modified fragment provides an efficient way to build structurally diversified molecules. Here, we report a palladium(II)/chiral phosphoric acid catalysed three-component reaction of aryldiazoacetates, enamines and imines to afford α-amino-δ-oxo pentanoic acid derivatives in good yields with excellent diastereoselectivities and high enantioselectivities. The stereoselective reaction went through a unique process that involves cleavage of a C–N bond, modification of the resulting amino fragment and selective reassembly of the modified fragment. This innovative multi-component process represents a highly efficient way to build structurally diversified polyfunctional molecules in an atom and step economic fashion. A keto-iminium is proposed as a key intermediate and a chiral palladium/phosphate complex is proposed as an active catalyst.

Quantum control of the photoinduced Wolff rearrangement of diazonaphthoquinone in the condensed phase

A shaped UV pump–MIR probe setup is employed for quantum control of the photoinduced Wolff rearrangement reaction of diazonaphthoquinone (DNQ) dissolved in methanol, yielding a ketene photoproduct. Time-resolved vibrational spectroscopy is a well-suited tool to monitor a photoreaction in the liquid phase as the narrow vibrational lines allow the observation of structural changes. Especially in the mid-infrared region, marker modes originating from different photoproducts can be identified unambiguously providing suitable feedback signals for open-loop or closed-loop control schemes. We report an experiment where the initiation of a complicated structural change of a molecule, involving bond cleavage and rearrangement, in the liquid phase can be controlled and mechanistic insight is obtained. Single-parameter scans show that the molecule is sensitive to intrapulse dumping during the excitation. Adaptive optimizations lead to pulse structures which can be understood consistently with this dumping mechanism.

Bond Activation by Low Valent Ruthenium Complexes

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Bond activation by low valent ruthenium complexes

Ru(η4-1,5-cyclo-octadiene)(η6-1,3,5-cyclo-octatriene) (1) is one of the most versatile zero-valent ruthenium complexes bearing two labile cyclopolyenes and acts as a potential precursor for catalytic processes involving bond cleavage reactions in the presence of suitable Lewis bases. However, detailed studies of the bond cleavage step had, until now, been relatively less explored at a molecular level. The present Perspective is an account of our recent studies concerning: (1) the reactions of 1 with Lewis bases, (2) carbon–oxygen, carbon–sulfur, oxygen–hydrogen, nitrogen–hydrogen and carbon–hydrogen bond cleavage reactions by 1 in the presence of tertiary phosphine, (3) selective sp3 carbon–hydrogen bond cleavage by 1 by use of co-ordination of an anchoring chalcogen atom, and (4) preparation of an enolatoruthenium(II) complex derived from 1 as an active intermediate in chemoselective catalytic Knöevenagel and Michael reactions.

Thermal decomposition reactions of acetaldehyde and acetone on Si(100)

We have studied the thermal interactions of acetone and acetaldehyde on Si(100), both sputtered and annealed, using high resolution electron energy loss spectroscopy, (HREELS), x-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD). There is no carbonyl stretch in HREELS and the C and O(1s) XPS peaks reflect two different carbonyl processes, one involving bond cleavage, the other a reduction of the C–O bond order. Hydrogen TPD gives a peak at 840–850 K which is as much as threefold more intense than from H-saturated Si(100). SiO desorbs near 1050 K and XPS shows total loss of oxygen and retention of carbon. Approximately 34% of the acetaldehyde monolayer and 62% of the acetone monolayer decomposes on annealed Si(100) to produce silicon carbide. In contrast, after sputtering with 500 eV Ar ions, these percentages are reduced to 14% and 25%, respectively. We conclude that Si dimers play an important role in the chemistry of carbonyl groups.

Novel reaction of N-methyloctaethylporphyrinatocobalt(II) acetate: intramolecular oxidative alkylation

Reduction of N-methyloctaethylporphyrinatocobalt(II) acetate with NaBH4generates methylcobalt(III)-octaethylporphyrin by a mechanism involving bond cleavage induced by the oxidation of CoI to CoIII.