Anodic oxidation of the dye materials methylene blue,acid blue 25, reactive blue 2 and reactive blue 15 and the characterisation of novel intermediate compounds in the anodic oxidation of methylene blue

Anodic oxidation of the dye molecules, methylene blue, acid blue 25, reactive blue 2 and reactive blue 15 in chloride solution leads to colour destruction but UV and TOC data show that the oxidation reactions do not lead to complete destruction of the organic molecules. Analysis of the anodic oxidation products of [3,7‐bis (dimethylamino) phenothiazinium] chloride (methylene blue) in a chloride solution provides evidence for formation of seven neutral and two charged intermediates. The main intermediate is identified by its X‐ray diffraction crystal structure and accurate mass spectrometry as the novel leuco dye 4,6‐dichloro‐7‐dimethylamino‐3H‐phenothiazin‐3‐one, C₁₄H₁₀Cl₂N₂OS (I) formed by replacement of one of the dimethylamino groups of methylene blue with oxygen accompanied by regiospecific chlorination of the carbocyclic systems. The mass spectra of other intermediates formed are interpreted in terms of the structure of I. © 2002 Society of Chemical Industry     

Photosensitized Oxidative Dimerization at Tyrosine by a Water-Soluble 4-Amino-1,8-naphthalimide

The oxidation of proteins generates reactive amino acid (AA) residue intermediates, leading to protein modification and cross-linking. Aerobic studies with peptides and photosensitizers allow for the controlled generation of reactive oxygen species (ROS) and reactive AA residue intermediates, providing mechanistic insights as to how natural protein modifications form. Such studies have inspired the development of abiotic methods for protein modification and crosslinking, including applications of biomedical importance. Dityrosine linkages derived from oxidation at tyrosine (Tyr) residues represent one of the more well-understood oxidation-induced modifications. Here we demonstrate an aerobic, visible light-dependent oxidation reaction of Tyr-containing substrates promoted by a water-soluble 4-amino-1,8-naphthalimide-based photosensitizer. The developed procedure converts Tyr-containing substrates into o,o’-Tyr-Tyr linked dimers. The regioselectively formed o,o’-Tyr-Tyr linkage is consistent with dimeric standards prepared using a known enzymatic method. A crossover study with two peptides provides a statistical mixture of three distinct o,o’-Tyr-Tyr linked dimers, supporting a mechanism that involves Tyr residue oxidation followed by intermolecular combination.     

Single‐Turnover Kinetics Reveal a Distinct Mode of Thiamine Diphosphate‐Dependent Catalysis in Vitamin K Biosynthesis

MenD, or (1R,2S,5S,6S)‐2‐succinyl‐5‐enolpyruvyl‐6‐hydroxycyclohex‐3‐ene‐1‐carboxylate (SEPHCHC) synthase, uses a thiamine diphosphate (ThDP)‐dependent tetrahedral Breslow intermediate rather than a canonical enamine for catalysis in the biosynthesis of vitamin K. By real‐time monitoring of the cofactor chemical state with circular dichroism spectroscopy, we found that a new post‐decarboxylation intermediate was formed from a multistep process that was rate limited by binding of the α‐ketoglutarate substrate before it quickly relaxed to the characterized tetrahedral Breslow intermediate. In addition, the chemical steps leading to the reactive post‐decarboxylation intermediates were not affected by the electrophilic substrate, isochorismate, whereas release of the product was found to limit the whole catalytic process. Moreover, these intermediates are likely kinetically stabilized owing to the low biological availability of isochorismate under physiological conditions, in contrast to the tight coupling of enamine formation with binding of the electrophilic acceptor in some other ThDP‐dependent enzymes. Together with the unusual tetrahedral structure of the intermediates, these findings strongly support a new ThDP‐dependent catalytic mode distinct from canonical enamine chemistry.     

Deciphering the structure of itaconate‐based unsaturated polyester resins by high resolution mass spectrometry

Unsaturated polyester (UP) resins are widely used to manufacture composite materials and fulfil a wide panel of specification for industrial or domestic applications at low cost. These resins consist of a highly viscous polyester oligomer and a reactive diluent, which allow their processability and crosslinking. The oligomers are synthesized from diols and saturated or unsaturated diacids. Maleic anhydride is classically used as an unsaturated acid because of its reactivity for esterification and its competitive cost. However, maleic anhydride is petroleum based and classified as skin and respiratory sensitizing by the European Chemicals Agency. Itaconic acid which is recognized as one of the top 12 biobased molecules by the US Department of Energy is a biobased alternative with a reactive unsaturation. In this work, a UP based on propylene glycol, itaconic acid and dimethyl terephthalate was synthesized by polycondensation and characterized by high resolution mass spectroscopy, ¹H, ¹³C 1D and 2D NMR as well as ion mobility spectrometry mass spectrometry. The main structures were linear but cyclic species and a few branched chains due to the intermolecular Ordelt reaction were also detected by NMR and high resolution mass spectroscopy. Molecular modelling has indeed demonstrated that itaconate‐based UPs are more prone to cyclization than fumarate‐based UPs. Moreover, NMR analysis showed a significant consumption of itaconate unsaturation by the Ordelt reaction. Ion mobility spectrometry mass spectrometry allowed an additional structure to be distinguished for the same m/z peaks first attributed to a linear structure only. These results suggest the existence of cyclic species based on an intramolecular Ordelt reaction. © 2020 Society of Chemical Industry     

Nonuniform initiation of photoreactions II. Diffusion of reactive intermediates

The influence of spatially nonuniform initiation is investigated for a class of photoreactions in which diffusion of intermediates is important. The investigation is centered on a differential equation for reaction and diffusion of reactive intermediates. The circumstances are set forth under which the equation is valid for several kinetically similar reaction types. A solution is obtained for Lambert's law attenuation. The characteristics of this solution and the solution obtained by Noyes for linear attenuation are discussed. The practical consequences of these solutions are shown through illustrative calculations based on the photochlorination of tetrachloroethylene.     

Modelling of mass transfer in combination with radical reactions

The diffusion-reaction equations for different model versions have been solved using a finite-differencing technique. In all models a reactant A is transferred from the gas to the liquid phase and reacts in the liquid with B to form P. The calculations comprised a simple stoichiometric model, a system with radical intermediates involved in the propagation steps and a version where also the termination reactions were included. The results show that the diffusion coefficients of radical intermediates can have significant influence on the profiles of concentrations and reaction rates near the G/L interface. Furthermore, it is shown that for very fast reactions differences in diffusion coefficients of the intermediates influence the by-product formation. For systems of two radical intermediates, the so-called mixed termination product is only formed in low quantities whereas the other two termination products dominate. The calculation of enhancement factors required in the design of a G/L reaction system can be performed with simplified models where the reactive intermediates do not occur in the expressions for the reaction rates. The optimum model for a specific design purpose can be found by tuning the functions that correlate the parameters of the complex model to the parameters of the simplified model. In principle it is possible to very easily evaluate a large number of alternatives.     

In situ time-resolved X-ray diffraction of tobermorite formation in autoclaved aerated concrete: Influence of silica source reactivity and Al addition

The hydrothermal formation of tobermorite during the processing of autoclaved aerated concrete was investigated by in situ X-ray diffraction (XRD) analysis. High-energy X-rays from a synchrotron radiation source in combination with a newly developed autoclave cell and a photon-counting pixel array detector were used.To investigate the effects of the silica source, reactive quartz from chert and less-reactive quartz from quartz sand were used as starting materials. The effect of Al addition on tobermorite formation was also studied. In all cases, C-S-H, hydroxylellestadite and katoite were clearly observed as intermediates.Acceleration of tobermorite formation by Al addition was clearly observed. However, Al addition did not affect the dissolution rate of quartz. Two pathways, via C-S-H and katoite, were also observed in the Al-containing system. These results suggest that the structure of initially formed C-S-H is important for the subsequent tobermorite formation reactions.     

Pyrimidine-derived disulfides as potential antimicrobial agents: synthesis and evaluation in vitro

Antibiotic resistance is a worldwide problem. The synthesis and evaluation of new antimicrobial compounds, without cytotoxicity against human cells, are highly desired. In this paper, the preparation of a class of pyrimidine-derived disulfides is described. Sulfenic acids were generated from suitable precursors and used as reactive intermediates that condensed with the thiol function of thiocytosine. An introductory study on the antimicrobial activity of this disulfide family is reported. Three family components, that revealed no cytotoxicity against human erythrocytes, exhibited inhibitory activity against Gram-positive Staphylococcus aureus.     

Adenosyl Radical: Reagent and Catalyst in Enzyme Reactions

Adenosine is undoubtedly an ancient biological molecule that is a component of many enzyme cofactors: ATP, FADH, NAD(P)H, and coenzyme A, to name but a few, and, of course, of RNA. Here we present an overview of the role of adenosine in its most reactive form: as an organic radical formed either by homolytic cleavage of adenosylcobalamin (coenzyme B₁₂, AdoCbl) or by single‐electron reduction of S‐adenosylmethionine (AdoMet) complexed to an iron–sulfur cluster. Although many of the enzymes we discuss are newly discovered, adenosine's role as a radical cofactor most likely arose very early in evolution, before the advent of photosynthesis and the production of molecular oxygen, which rapidly inactivates many radical enzymes. AdoCbl‐dependent enzymes appear to be confined to a rather narrow repertoire of rearrangement reactions involving 1,2‐hydrogen atom migrations; nevertheless, mechanistic insights gained from studying these enzymes have proved extremely valuable in understanding how enzymes generate and control highly reactive free radical intermediates. In contrast, there has been a recent explosion in the number of radical‐AdoMet enzymes discovered that catalyze a remarkably wide range of chemically challenging reactions; here there is much still to learn about their mechanisms. Although all the radical‐AdoMet enzymes so far characterized come from anaerobically growing microbes and are very oxygen sensitive, there is tantalizing evidence that some of these enzymes might be active in aerobic organisms including humans.     

Anodic synthesis of sulfur-bridged polyaniline coatings onto Fe sheets

Sulfur-bridged polyaniline coatings are obtained onto Fe anodes by electrolyzing a basic solution of one aniline and ammonium sulfide. Their sulfur content ranges from 7% to 17%, depending on the substituents on aniline. Variously substituted anilines may be polymerized in this way and coating pollution by azobenzene formed in a side reaction is almost completely avoided. Sulfur probably enters the polymer chains through a free radical mechanism. HS^? intermediates being formed by both homogeneous and anodic oxidation of HS^? anions. Coatings from N-allylaniline, being thermally curable, show satisfactory physical properties.     

Enantioselective Benzylic Hydroxylation with Pseudomonas monteilii TA‐5: A Simple Method for the Syntheses of (R)‐Benzylic Alcohols Containing Reactive Functional Groups

Highly enantioselective benzylic hydroxylations of benzene derivatives ( 1–4 ) containing reactive functional groups were achieved for the first time with Pseudomonas monteilii TA‐5 as biocatalyst, giving the corresponding (R)‐benzylic alcohols 5 – 8 in 93–99% ee as the only products. Preparative biotransformations were demonstrated by the biohydroxylation of 1 and 2 with resting cells of P. monteilii TA‐5 to afford (R)‐ 5 in 94% ee and 66% yield and (R)‐ 6 in 94% ee and 56% yield, respectively. The highly enantioselective biohydroxylations represent a simple access to (R)‐benzylic alcohols containing reactive functional groups that are useful pharmaceutical intermediates and versatile chiral building blocks.     

Electrochemistry of polycyclic aromatic hydrocarbons in molten tetrabutylammonium nitrate

The oxidation and reduction of a series of polycyclic aromatic hydrocarbons have been studied in molten tetrabutylammonium nitrate at 150°C. On the oxidation side nitrated products are formed and on the reduction side butyl-substituted products were obtained. In this solvent, which is slightly unstable at 150°C, limiting cathodic process is the reduction of the NBu₄ ⁺ ion to tributylamine and butenes and the limiting anodic process is the oxidation of NBu₄ ⁺ to carbon dioxide. Attempts to trap the reactive intermediates produced electrochemically with added substances were unsuccessful.     

Ozone and chlorine dioxide: Similar chemistry and measurement issues

The chemical reactions associated with ozone and chlorine dioxide can be complicated and involve numerous intermediates. When ozone is applied, the presence of reactive intermediate species (O₂ ^‐, O₃ ^‐, OH, HO₂, HO₂ ^‐, and H₂O₂) influence the extent of oxidation that takes place and determines the amount and types of by‐products formed. Similarly, when chlorine dioxide is applied the amount of intermediate (Cl₂O₂) formed determines whether chlorine dioxide producing reactions or chlorate ion forming reactions occur. Ozone and chlorine dioxide are excellent agents for inactivating Cryptosporidium and Giardia. Microbiologically, each of the agents are very reactive. In the case of ozone, typically each molecule undergoes a one‐electron change. The mechanism of chlorine dioxide inactivation involves a recycling process whereby chlorine dioxide is reduced to chlorite ion followed by the “regeneration” of chlorine dioxide that continues to react within the cell over and over again. Chlorite ion also has oxidizing power and in some cases, is a biocide. When ozone and chlorine dioxide are used in combination, it is important that the chlorine dioxide application follow the ozone treatment to prevent the formation of unwanted by‐products such as ClO₃ ^‐.     

Simple,Mild, and Practical Esterification,Thioesterification, and Amide Formation Utilizing p‐Toluenesulfonyl Chloride and N‐Methylimidazole

We have developed an efficient method for the esterification or thioesterification of equimolar amounts of carboxylic acids and alcohols or thiols using a novel reagent, p‐toluenesulfonyl chloride (TsCl) together with N‐methylimidazole. The present method is simple, mild, and reactive, uses readily available and economical reagents. The choice of amine is critical for the present method. The amine, N‐methylimidazole, has two roles: (i) as an HCl scavenger for the initial smooth generation of mixed anhydrides between carboxylic acids and TsCl and (ii) successive formation of highly reactive ammonium intermediates from mixed anhydrides. This method could be applied to various types of carboxylic acids, alcohols, and thiols: a) several functionalities were tolerated; b) two N‐Cbz amino acids were smoothly esterified without racemization; and c) the labile 1β‐methylcarbapenem key intermediate and a pyrethroid insecticide, prallethrin, were successfully prepared. The related amide formation between carboxylic acids and primary or secondary amines was also performed. The proposed reaction mechanism involves a novel method for producing the reactive acylammonium intermediates. The production of these intermediates was rationally supported by a careful ¹H NMR monitoring study.     

Initial reaction steps in photocatalytic oxidation of aromatics

Transient reaction at 273 and 300 K was used to study the initial steps in the photocatalytic oxidation (PCO) of benzene, toluene, p-xylene, mesitylene, benzyl alcohol, benzaldehyde, and m-cresol adsorbed on a thin film of TiO₂ catalyst. Adsorbed aromatics were oxidized by O₂ photocatalytically in the absence of gas-phase aromatics, and the compounds remaining on the surface were characterized by temperature-programmed oxidation and desorption (TPO, TPD). Benzene and methyl benzenes oxidize rapidly at 273 or 300 K to form adsorbed intermediates that are more strongly adsorbed and much less reactive than the original aromatic, which is relatively weakly adsorbed on TiO₂. The catalyst is expected to be covered with these intermediates during steady-state reaction. The rates of PCO of benzene and methyl benzenes to CO₂ are slow relative to complete oxidation of alcohols or chlorinated hydrocarbons. The intermediates do not appear to be alcohols or aldehydes formed by oxidation of a methyl group, nor do they correspond to addition of an hydroxyl to the aromatic ring. Benzyl alcohol oxidizes photocatalytically to benzaldehyde and then to CO₂ and H₂O during PCO, but adsorbed m-cresol does not photocatalytically oxidize.     

Polymeric encapsulation of liquids via plasma surface polymerization

This study introduces a new approach of liquid encapsulation using an atmospheric pressure plasma (APP). The technique is similar to interfacial polymerization, though here one phase is liquid (that contains unsaturated C═C bonds) and the other phase is plasma (that contains free radicals). When combined, the atmospheric plasma can induce surface polymerization of an acrylate-based liquid, resulting in a thin polymeric skin on top of the liquid. Measurements with an atomic force microscope and a spectroscopic ellipsometer estimate the thickness of the skin formed on top of di(ethylene glycol) diacrylate to be 40–50 nm. To demonstrate an application of this method, we encapsulated hemispherical capsules of reactive adhesives on a glass substrate. These adhesives are based on thiol-acrylate and thiol-acrylate-epoxy systems that react in the presence of a strong base catalyst. Plasma-induced polymerization can encapsulate, immobilize, and isolate separate droplets of resin and the catalyst in a latent (nonreactive) state. These capsules remain latent until they rupture in response to physical contact. A tensile testing machine reports an adhesive strength of ~ 2 MPa for the formulated resins after curing. The capsules reported here may be useful for storing functional liquids for just-in-time release, such as contact-sensitive adhesives, on-demand lubricants, or self-healing agents. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48880.     

Design and control of transesterification reactive distillation with thermal coupling

In the study, the design and control strategies of a reactive distillation process with partially thermal coupling for the production of methanol and n-butyl acetate by transesterification reaction of methyl acetate and n-butanol are investigated. Since methanol and methyl acetate formed an azeotrope, the products of a reactive distillation column include n-butyl acetate and the mixture of methanol and methyl acetate, which must be separated by an additional column. Partially thermal coupling can be used to eliminate the condenser of the second column. Not only energy reduction but also better operability and controllability can be obtained for the thermally coupled reactive distillation process. Proper selection and pairing of controlled and manipulated variables chosen for three control objectives were determined by using steady-state analysis. A simple control scheme with three temperature control loops is sufficient to maintain product purities and stoichiometric balance between the reactant feeds.     

Zirconocene and Si-tethered diynes: a happy match directed toward organometallic chemistry and organic synthesis

Characterizing reactive organometallic intermediates is critical for understanding the mechanistic aspects of metal-mediated organic reactions. Moreover, the isolation of reactive organometallic intermediates can often result in the ability to design new synthetic methods. In this Account, we outline synthetic methods that we developed for a variety of diverse Zr/Si organo-bimetallic compounds and Si/N heteroatom-organic compounds through the detailed study of zirconacyclobutene-silacyclobutene fused compounds. Two basic components are involved in this chemistry. The first is the Si-tethered diyne, which owes its rich reactive palette to the combination of the Si-C bond and the C≡C triple bond. The second is the low-valent zirconocene species Cp(2)Zr(II), which has proven very useful in organic synthesis. The reaction of these two components affords the zirconacyclobutene-silacyclobutene fused compound, which is the key reactive Zr/Si organo-bimetallic intermediate discussed here. We discuss the three types of reactions that have been developed for the zirconacyclobutene-silacyclobutene fused intermediate. The reaction with nitriles (the C≡N triple bond) is introduced in the first section. In this one-pot reaction, up to four different components can be combined: the Si-tethered diyne can be reacted with three identical nitriles, with differing nitriles, or with a nitrile and other unsaturated organic substrates such as formamides, isocyanides, acid chlorides, aldehydes, carbodiimides, and azides. Several unexpected multiring, fused Zr/Si organo-bimetallic intermediates were isolated and characterized. A wide variety of N-heterocycles, such as 5-azaindole, pyrrole, and pyrroloazepine derivatives, were obtained. We then discuss the reaction with alkynes (the C≡C triple bond). A consecutive skeletal rearrangement, differing from that observed in the reactions with nitriles, takes place in this reaction. Finally, we discuss the reaction with the C═X substrates (where X is O or N), including ketones, aldehydes, and isocyanides. Oxa- and azazirconacycles are formed via a new skeletal rearrangement. Our results show that the zirconocene and the Si-tethered diyne cooperate as a "chemical transformer" after treatment with various substrates, leading to a diverse range of cyclic Zr/Si organo-bimetallic compounds. This mechanism-derived synthesis of organometallic and organic compounds demonstrates that the investigation of metal-mediated reactions and the isolation of reactive organometallic intermediates not only contribute to the understanding of complex reactions but can also lead to the discovery of synthetically useful methods.     

Nitrenes, carbenes, diradicals, and ylides. Interconversions of reactive intermediates

Rearrangements of aromatic and heteroaromatic nitrenes and carbenes can be initiated with either heat or light. The thermal reaction is typically induced by flash vacuum thermolysis, with isolation of the products at low temperatures. Photochemical experiments are conducted either under matrix isolation conditions or in solution at ambient temperature. These rearrangements are usually initiated by ring expansion of the nitrene or carbene to a seven-membered ring ketenimine, carbodiimide, or allene (that is, a cycloheptatetraene or an azacycloheptatetraene when a nitrogen is involved). Over the last few years, we have found that two types of ring opening take place as well. Type I is an ylidic ring opening that yields nitrile ylides or diazo compounds as transient intermediates. Type II ring opening produces either dienylnitrenes (for example, from 2-pyridylnitrenes) or 1,7-(1,5)-diradicals (such as those formed from 2-quinoxalinylnitrenes), depending on which of these species is better stabilized by resonance. In this Account, we describe our achievements in elucidating the nature of the ring-opened species and unraveling the connections between the various reactive intermediates. Both of these ring-opening reactions are found, at least in some cases, to dominate the subsequent chemistry. Examples include the formation of ring-opened ketenimines and carbodiimides, as well as the ring contraction reactions that form five-membered ring nitriles (such as 2- and 3-cyanopyrroles from pyridylnitrenes, N-cyanoimidazoles from 2-pyrazinyl and 4-pyrimidinylnitrenes, N-cyanopyrazoles from 2-pyrimidinylnitrenes and 3-pyridazinylnitrenes, and so forth). The mechanisms of formation of the open-chain and ring-contraction products were unknown at the onset of this study. In the course of our investigation, several reactions with three or more consecutive reactive intermediates have been unraveled, such as nitrene, seven-membered cyclic carbodiimide, and open-chain nitrile ylide. It has been possible in some cases to observe them all and determine their interrelationships by means of a combination of matrix-isolation spectroscopy, photochemistry, flash vacuum thermolysis, and computational chemistry. These studies have led to a deeper understanding of the nature of reactive intermediates and chemical reactivity. Moreover, the results indicate new directions for further exploration: ring-opening reactions of carbenes, nitrenes, and cyclic cumulenes can be expected in many other systems.     

Deuteration of methyl linoleate with nickel,palladium, platinum and copper-chromite catalysts

Samples taken during deuteration of methyl linoleate with the title catalysts were separated into saturate, monoene and diene fractions. Monoenes were further separated intocis andtrans fractions. A comparison of the double bond distribution in monoenes with those from hydrogenation of alkaliconjugated linoleate indicated that up to 59% of the linoleate was reduced through a conjugated intermediate with nickel catalyst. The respective percentages for palladium and platinum catalysts were 51 and 23. Copper catalysts have previously been shown to reduce linoleate solely through conjugated intermediates. Copper-chromite catalyst showed infinite selectivity for the reduction of linoleate, because stearate did not form. The decreasing order of various catalysts for the selective reduction was copper-chromite>>>Ni at 195 C>Pd>Ni at 100 C>Pt. Computer simulation of platinum reduction indicated that ca. 20% of the linoleate was directly reduced to stearate through a shunt. Geometrical isomers of linoleate were formed during reduction with all catalysts except copper-chromite. Nickel catalyst formed bothtrans,trans- andcis,trans-isomers, as well as nonconjugatable dienes. These isomers were favored at the higher temperature and deuterium was incorporated into them. Palladium and platinum did not isomerize linoleate to nonconjugatable dienes. Because conjugated dienes are more reactive than linoleate, they were not found in appreciable amounts during reduction. Conjugated dienes were the only isomers formed with copper-chromite catalyst. Deuterium was found in these conjugated dienes, which were also extensively isomerized. As a result of isomerization and exchange during reduction of linoleate-as well as further exchange between deuterium and monoenes-a wide distribution of isotopic isomers in monoenes was found with nickel, palladium and platinum catalysts. Since isomerization of monoenes with copper-chromite is negligible, the isotopic distribution of monoenes must be due to exchange of intermediate conjugated dienes followed by addition. Presented at the AOCS Meeting, Ottawa, September 1972. ARS, USDA.