Benzoquinone System Research Articles

Recent advances in developing tetrathiafulvalene analogs of electrode materials: discovery of an in-cell polymerization technique

Abstract Lithium-ion batteries are attractive for their use in portable electronics and electric vehicles owing to their high energy and power density. Organic materials as active materials for the positive electrode have attracted attention as an alternative to inorganic materials in sustainable batteries. However, there is a serious drawback that elution into the electrolyte solution. This article describes our attempts in the development of tetrathiafulvalene (TTF) analogs for active materials. We have developed four types of fused TTF systems; multifused TTF systems, TTF analogs extended with cyclohexene moieties, TTF analogs extended with an anthraquinoid spacer, and fused TTF and benzoquinone systems. These molecules were designed based on the idea that increasing the size and planarity of the molecules and intermolecular interactions. They were successfully synthesized and their cell performances were clarified. We also describe that a TTF analog bearing triphenylamines was applied to long-cycle-life electrodes as a recent effort. This molecule was successfully synthesized using palladium-catalyzed C-H arylation and the cycle life of the cells comprising this molecule was markedly improved by in-cell electropolymerization.

Adaptive Landscape Flattening Accelerates Sampling of Alchemical Space in Multisite λ Dynamics.

Multisite λ dynamics (MSλD) is a powerful emerging method in free energy calculation that allows prediction of relative free energies for a large set of compounds from very few simulations. Calculating free energy differences between substituents that constitute large volume or flexibility jumps in chemical space is difficult for free energy methods in general, and for MSλD in particular, due to large free energy barriers in alchemical space. This study demonstrates that a simple biasing potential can flatten these barriers and introduces an algorithm that determines system specific biasing potential coefficients. Two sources of error, deep traps at the end points and solvent disruption by hard-core potentials, are identified. Both scale with the size of the perturbed substituent and are removed by sharp biasing potentials and a new soft-core implementation, respectively. MSλD with landscape flattening is demonstrated on two sets of molecules: derivatives of the heat shock protein 90 inhibitor geldanamycin and derivatives of benzoquinone. In the benzoquinone system, landscape flattening leads to 2 orders of magnitude improvement in transition rates between substituents and robust solvation free energies. Landscape flattening opens up new applications for MSλD by enabling larger chemical perturbations to be sampled with improved precision and accuracy.

Pulse electroanalysis at gold–gold micro-trench electrodes: Chemical signal filtering

Bipotentiostatic control of micro- and nano-trench sensor systems provides new opportunities for enhancing signals (employing feedback currents) and for improved selectivity (by "chemical filtering"). In this study both phenomena are exploited with a gold-gold micro-trench electrode with ca. 70 microm width and ca. 800 microm trench depth. In "generator-collector mode", feedback current enhancement is demonstrated for the hydroquinone/ benzoquinone redox system. Next, a "modulator-sensor mode" experiment is developed in which one electrode potential is stepped into the negative potential region (employing the normal pulse voltammetry method) to induce an oscillating pH change locally in the micro-trench. The resulting shift in the hydroquinone/benzoquinone reversible potential causes a Faradaic sensor signal (employing chronoamperometry). This method provides a "chemical filter" by selecting pH-sensitive redox processes only, and by showing enhanced sensitivity in the region of low buffer capacity. The results for the chemically reversible hydroquinone/benzoquinone system are contrasted to the detection of the chemically irreversible ammonia oxidation.

Step-wise proton-coupled electron transfer extended to aminobenzoquinone modified monolayers

The step-wise proton coupled electron transfer (SW-PCET) model has been expanded to describe instances where three protons are transferred with either one or two electrons. Expressions have been derived describing the pH dependence of the apparent formal potential, apparent standard rate constant, apparent transfer coefficient, and reaction pathway. The expressions can be applied to both Marcus density of states theory as well as Butler-Volmer kinetics depending on the assumptions made about the individual transfer coefficients. An example of 2e3H has been provided for an aminobenzoquinone monolayer system and experimental measurements have been compared to model predictions. Although the large reorganization energy of the benzoquinone system prevents differentiation between Butler-Volmer and Marcus DOS kinetic behaviour, results are consistent with the SW-PCET model. These results indicate how acid/base substituents on tethered organic molecules can participate in PCET even though they themselves are redox inactive.

Electrode Kinetic Studies of the Hydroquinone−Benzoquinone System and the Reaction between Hydroquinone and Ammonia in Propylene Carbonate: Application to the Indirect Electroanalytical Sensing of Ammonia

The oxidation of hydroquinone and reduction of benzoquinone have been studied by cyclic voltammetry at glassy carbon electrodes in propylene carbonate. Diffusion coefficients of the different species obtained from chronoamperometric measurements with use of microdisk electrodes were 2.7 ± 0.3 × 10-6 cm2 s-1 for hydroquinone and 4.2 ± 0.2 × 10-6 cm2 s-1 for benzoquinone. Simulation was used to model the cyclic voltammetric responses of macroelectrodes to give electrode kinetic information for the electrochemical oxidation of hydroquinone and reduction of benzoquinone. Next, the reaction between ammonia and hydroquinone was investigated. It is shown that ammonia reversibly removes one proton from the hydroquinone molecules, resulting in a new wave observed at ca. + 0.15 V (vs Ag wire). Finally by measuring the peak current of the new wave as a function of ammonia concentration its analytical utility for ammonia sensing was examined in the range from 10 and 100 ppm.

Solid-state high-resolution NMR studies on spin fluctuation associated with valence tautomerism of metal–benzoquinone system: Cobalt complex in the stable and meta-stable phases

Abstract Equilibrium between low-spin [CoIII(SQ)(Cat)(N–N)] and high-spin [CoII(SQ)2(N–N)] redox isomers, where SQ is semiquinonate (charge: −1, spin: 1/2), Cat is catecholate (charge: −2, spin: 0) and N–N is chelating nitrogen donor ligand, respectively, is a representative valence tautomeric phenomenon. To elucidate independently the spin state of the cobalt ion and that of benzoquinone-derived ligands in the solid state, we measured 13C MAS NMR spectrum of 3,5-di-t-butyl-1,2-benzoquinone and 2H MAS NMR spectrum of deuterated 2,2′-bipyridine for [Co(3,5-di-t-butyl-1,2-benzoquinone)2(2,2′-bipyridine)] · x(C6H5CH3) and its deuterated analogue in a temperature range of 200–350 K. Irreversible change of an effective magnetic moment μeff of a virgin sample was observed around 370 K due to a partial loss of crystal solvent and a change of crystal structure, whereas the sample annealed at 390 K showed a crystal structure different from the reported one and a reversible change of μeff, which is ascribed to equilibrium between Co(III)-form (S = 1/2) and Co(II)-form (S = 3/2). Based on the shifts and the number of NMR peaks for the annealed sample, we concluded that (1) interconversion between redox isomers occurs faster than NMR time scale (>104 s−1) in the solid state, (2) intraconversion between SQ and Cat in Co(III)-form also occurs much faster than 5 × 104 s−1 even at 198 K and (3) electron spins on SQ ligands in Co(II)-form are quenched probably due to a strong antiferromagnetic coupling between the two SQ ligands. The enthalpy and the entropy of the interconversion were estimated to be 17 kJ/mol and 54 J/(K mol), respectively. For the virgin metastable phase, SQ and Cat were clearly distinguished by 13C MAS NMR spectrum. The solid-state high-resolution NMR spectrum is useful to detect independently the change of spin states of benzoquinone-derived radical and metal ion.

Palladium catalyzed transformations of monoterpenes: stereoselective deuteriation and oxidative dimerization of camphene

Camphene undergoes a highly regio and stereoselective palladium catalyzed deuteriation in deuteriated acetic acid solutions of Pd(OAc) 2. NMR reveals that an outward oriented vinylic hydrogen is selectively exchanged for 2H, resulting in 90% camphene- d 1 (ca. 100% stereoselectivity) and 10% camphene- d 2 at 75% conversion of camphene (6 h, 25 °C). Neither π-allyl nor π-olefin palladium complexes are formed in detectable concentrations during the reaction, whereas palladium hydride (singlet at −6.86 ppm) and palladium deuteride (singlet at −6.78 ppm) intermediates have been detected by 1H and 2H NMR, respectively. At higher temperature, oxidative coupling of camphene readily occurs giving the ( E, E)-diene, i.e., bis(3,3-dimethyl-2-norbornylidene)ethane, which formally originates by abstracting the outward oriented vinylic hydrogens and coupling the resulting fragments of two camphene molecules. The reaction is catalytic at palladium in the Pd(OAc) 2–LiNO 3(cat)–O 2 and Pd(OAc) 2–benzoquinone systems. Similar mechanisms for the deuteriation and oxidative coupling of camphene are proposed, which involve the formation of σ-vinyl palladium hydride intermediates. No deuteriation neither oxidative coupling of limonene, myrcene and β-pinene were observed under the same conditions.

Palladium catalyzed oxidation of monoterpenes: novel oxidation of myrcene with dioxygen

Myrcene can be efficiently and selectively oxidized by dioxygen in glacial acetic acid containing LiCl, in the presence of the PdCl 2–CuCl 2 catalytic combination, yielding two isomers of a new functionalized monoterpene, i.e., 3-(1-acetoxy-1-methylethyl)-1-vinylcyclopentene and 4-(1-acetoxy-1-methylethyl)-1-vinylcyclopentene, as major products. These compounds have a pleasant scent with a flower or fruit tinge and could be used as components of synthetic perfumes. The activities of Pd(OAc) 2–LiNO 3, Pd(OAc) 2–Cu(NO 3) 2 and Pd(OAc) 2–benzoquinone systems in myrcene oxidation have also been examined.

2,6-Dialkoxy-9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene Derivatives: Synthesis, Electrochemistry and X-ray Crystal Structures of Neutral and Dication Species

The synthesis of 2,6-dialkoxy-9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene derivatives 15 and 16 is described. Solution electrochemistry shows that 15 and 16 display three redox waves, representing the sequential formation of the dication, radical trication and tetracation species in an EqEqEq process. The X-ray crystal structures of neutral compounds 15 and 16 and the charge transfer complex (15)2+(TCNQ−•)2· 2MeCN are reported. The neutral molecules adopt a saddle-like conformation; the bis(1,3-dithiole)benzoquinone system is U-shaped through an ‘accumulating bend’ comprising the boat conformation of the central (quinonoid) ring and folding of both 1,3-dithiole rings. In the complex (15)2+(TCNQ−•)2· 2MeCN the anthracene system is planar and aromatic; the dithiolium cations form a dihedral angle of 78° with the anthracene plane. The TCNQ anion radicals form a stack of dimers with interplanar separations of 3.15 Å within a dimer and 3.50 Å between the dimers. The structure contains unusually short intermolecular S···N contacts [2.865(3) Å].

The promoting effect of chelating ligands in the oxidative carbonylation of phenol to diphenyl carbonate catalyzed by Pd–Co–benzoquinone system

The system Pd(OAc) 2/BQ/Co(acac) 3 (BQ=benzoquinone), in combination with tetrabutylammonium bromide (TBAB) as a surfactant agent and a chelating ligand such as 2,9-dimethyl-1,10-phenanthroline (dmphen) or 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (dmdpphen), is an efficient catalyst for the oxidative carbonylation of phenol to diphenyl carbonate (DPC). The best results have been obtained using the system Pd(OAc) 2/BQ/Co(acac) 3/dmphen=1/30/8/5 (molar ratio) in which [Pd]=10 −3 mol l −1 and TBAB/Pd=60/1. This system gives the maximum productivity of 700 mol DPC/mol Pd h at 135°C and under P tot=60 atm (CO/O 2=10/1 molar ratio). The role of each component of the catalytic system is discussed and a catalytic cycle is proposed.

Syntheses and X-ray Crystal Structures of Functionalised 9,10-Bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene Derivatives

The synthesis of new derivatives of 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene has been achieved by two different routes. Deprotonation of 8 using LDA in THF at −78 °C, followed by in situ quenching of the lithiated intermediate 9 with N,N-dimethylformamide, N-methyl isothiocyanate and methyl chloroformate gave aldehyde, thioamide and methyl ester derivatives 10-12, respectively. Sulfur insertion into the lithiated species 9 followed by reaction of the transient thiolate anion with benzoyl chloride gave the thioester derivative 13 which served as a convenient shelf-stable precursor of other mono-functionalised derivatives of 8. Debenzoylation of 13 and trapping of the transient thiolate anion with iodomethane and 6-bromohexan-1-ol yielded 14 and 15, respectively. Reaction of cation salt 17 with the anion of anthrone 18 gave compound 20, the thiolate anion of which reacted with 6-bromohexan-1-ol to afford the alcohol derivative 21. Subsequent reactions gave alcohol derivative 25 of the title system. The unexpected product 29 was obtained from reaction of 28 with triethyl phosphite. The X-ray crystal structures of compounds 12, 14, 28, and 29 are reported. The molecules adopt a saddle-like conformation; the bis(1,3-dithiole)benzoquinone system is U-shaped through an ‘accumulating bend’ comprising the boat conformation of the central (quinonoid) ring, folding of both 1,3-dithiole rings along S···S vectors, and out-of-plane tilting of the exocyclic CC bonds, all in the same (inward) direction.

Reaction of OH radicals with benzoquinone in aqueous solutions. A pulse radiolysis study

Hydroxyl radicals have been generated by pulse radiolysis in N2O-saturated aqueous solutions. Their addition to 1,4-benzoquinone BQ (k3 = 6.6 × 109 dm3 mol–1 s–1 by competition with thiocyanate) in neutral solution leads to a build-up of optical absorption that shows different rates at wavelengths at around 330 and at >400 nm. At 330 nm the rate of build-up is proportional to the benzoquinone concentration, and its rate constant agrees with the value (k3) obtained by competition. At the longer wavelengths, it becomes independent of benzoquinone concentration beyond 4 × 10–4 mol dm–3 (k6 = 6.9 × 105 s–1). Kinetic analysis in the ns time-range show that the primarily-generated benzoquinone–OH-adduct radical 1 undergoes rapid (k4 = 2.5 × 106 s–1) keto–enol tautomerization yielding the 2,4-dihydroxyphenoxyl radical 2. To gain support for this proposed reaction, radical 2 [pKa(2) ≈ 4.9 ± 0.2] has been independently generated by one-electron oxidation of 1,2,4-trihydroxybenzene using ˙OH in acidic or N3˙ in neutral and basic solution. Its absorption characteristics compare favourably with those observed in the benzoquinone system. On the basis of spectrophotometric and conductometric data it is proposed that in neutral solution the radical anion 2a is rapidly oxidized by benzoquinone itself (k15 2 × 109 dm3 mol–1) into the end product 2-hydroxy-1,4-benzoquinone anion 4a [pKa(4) = 4.1 ± 0.1; λmax(4) = 380 nm; λmax(4a) = 482 nm] and the semibenzoquinone radical anion 3a. The latter decays bimolecularly into benzoquinone and hydroquinone (2k16 = 3.1 × 108 dm3 mol–1 s–1). In acidic solution the rate of oxidation of 2 by benzoquinone is considerably slower (k13 ⩽ 2.4 × 107 dm3 mol–1 s–1). The assignment of the final product to 2-hydroxy-1,4-benzoquinone 4 has been confirmed by the absorption characteristics and pKa value of the authentic material obtained by the two-electron electrochemical oxidation of 1,2,4-trihydroxybenzene.

Flow injection amperometric determination of glucose and some other low molecular weight saccharides based on oligosaccharide dehydrogenase mediated by benzoquinone systems

A comparison has been made on the performance of different oligosaccharide dehydrogenase (ODH) modified electrodes as sensors for the detection of a series of mono-, di-, and oligosaccharides. Monomeric benzoquinone (BQ) or poly(ether amine benzoquinone), PEAQ, as electron transfer mediators were used for the preparation of the electrodes. Four sensor configurations operating in the flow injection mode were studied: (i) ODH adsorbed on the surface of solid graphite with BQ in the flow carrier solution; (ii) ODH doped into the bulk of carbon paste electrode with BQ in the flow carrier solution; (iii) ODH and BQ doped into the bulk of carbon paste electrode, and (iv) ODH and PEAQ doped into the bulk of carbon paste electrode. All four systems responded to glucose and equal responses were obtained for the α- and the β-anomeric forms. The best sensitivity for glucose was obtained with the solid ODH-modified electrode, which was equal to 1.8 μA mM −1 cm −2. The lowest noise was inherent for carbon paste electrodes with BQ in the paste. For this electrode configuration the responses for 16 sugars were observed. The highest currents were obtained for glucose (100%), lactose (52%), cellobiose (50%), and maltose (49%). For all four sensor systems selectivity profiles were almost the same.

Subnanosecond burning of persistent spectral holes by donor-acceptor electron transfer in tetraphenylporphine/p-benzoquinone systems

The first observation of subnanosecond spectral hole burning is reported in tetraphenylporphine/p-benzoquinone embedded in poly(methylmethacrylate) at liquid-helium temperature. The hole formation mechanism is photoinduced one-photon donor-acceptor electron transfer, and is consistent with the mechanism predicted by the reaction exothermicity accompanying the reaction. Spectral holes burnt in the present system disappeared almost completely when the temperature was increased to 20 K.

The unusually slow hydrolysis rate of silyl methyl ketals in benzoquinone systems. The question of siloxy stabilization of an adjacent positive charge and stereoelectronic effects on ketal hydrolysis

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe unusually slow hydrolysis rate of silyl methyl ketals in benzoquinone systems. The question of siloxy stabilization of an adjacent positive charge and stereoelectronic effects on ketal hydrolysisAlan J. Stern and John S. SwentonCite this: J. Org. Chem. 1989, 54, 12, 2953–2958Publication Date (Print):June 1, 1989Publication History Published online1 May 2002Published inissue 1 June 1989https://doi.org/10.1021/jo00273a033RIGHTS & PERMISSIONSArticle Views1708Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (844 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts