Anthraquinone in acetonitrile

Figure 3. Photoreduction on p-Si or redox couples with redox potentials lying above the conduction band edge as determined by dark flat-band potential measurements. (a) Photoreduction of 1,3 dimethoxy-4-nitrobenzene in methanol (E0 = —1.0V vs. SCE) (b) photoreduction of anthraquinone in acetonitrile (E0 = —0.95 V vs. SCE) Ec for p-Si in both cases in the dark is —0.85 V vs. SCE (------------------------------) dark (---) light (5).

Styrene derivatives are commonly used addends in the photocycloaddition studies of 1,4-quinones. With Z- and -anethole, 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), and 9,10-anthraquinone in acetonitrile solvent yield spiro-oxetanes in which the trans-isomer (e.g., 4 from naphthoquinone) predominates. The process has been studied in detail by CIDNP techniques from which it is deduced that product formation proceeds from triplet radical ion pairs to the triplet biradical, and that there is no significant contribution from direct conversion of exciplex intermediates into the biradicals. Spiro-oxetane formation between simple alkenes and BQ generally has low regioselectivity but this is markedly improved with alkylidene cyclohexanes (Figure 87.3) such that the major isomer can be used as a new access to useful synthetic building blocks. For the BQ/homobenzvalene 5 system, however, where the difference in stability between the intermediate biradicals can be expected to be considerably less, the selectivity ratio for the spiro-oxetanes 6 and 7 is reduced to 3 1, respectively, and the addition to NQ yields only the cyclobutane derivative 8. Quadricyclane and norbornadiene undergo the same photocycloaddition reaction to BQ, affording the oxolane 9 and the spiro-oxetane 10. Evidence from CIDNP... 

Figure 5. Current-voltage curve for anthraquinone (400 mw/cmz) in acetonitrile...

Anthraquinone photosensitised irradiation of tertiary N-allylamines in the presence of aP-unsaturated esters gives good yields of lactams. Using pyrex-filtered output (X>290 nm) from a 450 W medium pressure Hanovia lamp, for example, A-allylpiperidine and methyl methacrylate reacted in acetonitrile to give a 2 3 diastereomeric mixture (2S, 9S 2R, 95) of the indolizidone 1. 

Fig. 24 Pulsed irradiation of a homogenous solution of anthraquinone 31a, in acetonitrile (c = 8.9x10 mol dm"3), at room temperature. Working potential (a) -800 mV,...

Fig. 12a—e. H CIDNP spectra of diethylvinylamine observed during the reaction of (a) anthraquinone with triethylamine, (b) benzoquinone with triethylamine in acetone-d6, (c) benzoquinone with triethylamine in acetonitrile-d3. Traces (d) and (e) show theoretical spectra calculated for the exclusive involvement of the aminoalkyl radical and of the aminium radical ion, respectively. The change from emission (trace a) to enhanced absorption (trace c) for the doublets near 6.0 ppm indicates an increasing involvement of the aminium radical ion [178]... 

In addition to quinone reduction and hydroquinone oxidation, electrode reactions of many organic compounds are also inner-sphere. In these charge transfer is accompanied by profound transformation of the organic molecules. Some reactions are complicated by reactant and/or product adsorption. Anodic oxidation of chlorpro-mazine [54], ascorbic acid [127], anthraquinone-2,6-disulfonate [128], amines [129], phenol, and isopropanol [130] have been investigated. The latter reaction can be used for purification of wastewater. The cyclic voltammogram for cathodic reduction of fullerene Cm in acetonitrile solution exhibits 5 current peaks corresponding to different redox steps [131]. 

Issaq and McNitt [585] published a computer program for peak recognition on the basis of peak areas. They investigated the reproducibility of the area of some well-separated peaks for three solutes (anthraquinone, methyl anthraquinone and ethyl anthraquinone) in the 10 solvents used for their optimization procedure. The solvents included binary, ternary and quaternary mixtures of water with methanol, acetonitrile and THF. The areas were found to be reproducible within about 2 percent. The wavelength used for the UV detector in this study was not reported. 

Asymmetric functionalization was achieved in the two dendrimers 60 and 61, which contain two branches terminated with electron-donor TTF units and one branch terminated with electron-acceptor anthraquinone (AQ) units [131]. Cyclic voltammetric investigation in acetonitrile showed that each of these electroactive units are noninteracting, giving rise to two waves on oxidation (due to TTF) and to two waves on reduction (due to AQ). The number of electrons exchanged in each of... 

Figure 11. Time-resolved CIDNP spectra in a system described by the mechanism of Chart VI photoreaction of the acceptor anthraquinone 12 (8 x 10-4 M) with the donor /V,/V-dimethylaniline 13 (3.2 x 10 4M) in acetonitrile-d,. Experimental parameters T — 257 K, excitation wavelength 343 nm. Shown is the dependence of the signal I of the dimethylamino protons (marked with in the formula) on the delay time f0 between laser flash and acquisition pulse. [Adapted from ref. [86a] with permission. Copyright 1990 Elsevier Science Publishers B.V.]...

Figure Bl.16.9. Background-free, pseudo-steady-state CIDNP spectra observed in the photoreaction of triethylamine with different sensitizers ((a), anthraquinone (b), xanthone, CIDNP net effect (c), xanthone, CIDNP multiplet effect, amplitudes multiplied by 1.75 relative to the centre trace) in acetonitrile-d3. The structural formulae of the most important products bearing polarizations (1, regenerated starting material 2, N,N-diethylvinylamine 3, combination product of amine and sensitizer) are given at the top R denotes the sensitizer moiety. The polarized resonances of these products are assigned in the spectra. Reprinted from [21).

S. R. Belding, J. G. Limon-Petersen, E. J. P. Dickinson, and R. G. Compton. Voltammetry in the absence of excess supporting electrolyte offers extra kinetic and mechanistic insights Comproportionation of anthraquinone and the anthraquinone dianion in acetonitrile, Angew. Chem. Int. Ed. 49, 9242-9245 (2010). 

In the paper [74] oxidation of ferrocene and anthracene in acetonitrile and dichloromethane was successfully studied using the NPV technique at 5 pm Pt disc microelectrodes. The pulse widths were very short (5 to 20 ps) combined with the waiting times of duration 25 ps. Besides NPV also RPV has been applied. The resulting NP and RP waves for the oxidation of 9,10-anthraquinone are demonstrated in Fig. 28. The model of quasi-reversible charge transfer was fitted and parameters of both processes (k , and E1/2) were estimated. The results show that NP and RP voltammetric experiments retain the advantages over fast CV method even at pulse times as short as 5 ps. They provide effective discrimination against the double-layer charging current as well. 

Consider the following example. Figure 9.27 shows a CV recorded on an n-Si electrode immersed in acetonitrile with two redox couples anthraquinone and its monoanion (AQ/AQ ) and ferrocene/ferrocenium (Fe(Cp)2/Fe(Cp)2 ). In this experiment, care was taken in the experimental set-up so that once the electrode was introduced into the cell, it was not further exposed to the external atmosphere. Thus, effects due to surface oxidation... 

Figure 9.17 Distance-dependence of in some donor-acceptor molecules. Plots of log( et) edge-to-edge distances in a variety of linked donor-acceptor systems, (a) Forward(D) and reverse (x) electron-transfer rate constants for zinc porphyrin-anthraquinone compounds in butyronitrile. (b) Forward ( ) and reverse (x) electron-transfer rate constants for dimethoxynaphthalene-dicyanoethylene compounds in benzene, compared with the forward rate constants for three anthracene-dimethylaniline systems (V) and four analogous pyrene-dimethylaniline molecules (-I-), all in acetonitrile. From J.S. Connolly and J.R. Bolton, in Ref. [21,e, p. 322].

The photophysics and photochemical reactions of 2-(l-hydro3yethyl)-9,10-anthraquinone have been studied by a combination of femtosecond transient absorption, nanosecond transient absorption and nanosecond time-resolved resonance Raman spectroscopy techniques, as well as DFT calculations. In acetonitrile, intersystem crossing to the triplet excited state is the predominating process. In isopropanol, photoreduction to a ketyl radical intermediate is observed. In neutral or moderately acidic aqueous solutions, a photoredox reaction occurs after initial protonation of the carbonyl ojqrgen, while under stronger acidic conditions photohydration takes over. ... 

Figure 3.19 Time-resolved spectra for the system anthraquinone -I- trimethoxybenzene in acetonitrile, excited at 355 nm, under conditions where the quinone absorbs. The spectra were recorded 60, 100 and 300 nsec after irradiation with the laser pulse. Results obtained on an Apphed Photophysics LKS 60 flash photolysis apparatus in the Coimbra Chemistry Centre. (Courtesy of C. Serpa.)...

Solvent Effects. The conversion of dihydroanthracene could be increased by adding water to the pyridine solvent (Table III). An 86% conversion to anthraquinone was obtained when 95% aqueous pyridine was used as the solvent. Furthermore, methanol could be substituted for the water with equivalent results. Other solvents were tried in place of pyridine (Table IV). The data indicate that 95% aqueous pyridine gave the best yields, although aniline gave nearly similar results. When acetonitrile and dimethylformamide were used, the large amounts of unreacted starting material indicate that these solvents may have deactivated the base by undergoing a hydrolysis reaction. 

V in both methanol and acetonitrile. These values, combined with the doping density and the band gap of 1.12 eV for p-Si places the conduction band edge in methanol and acetonitrile at -0.85V (vs SCE). The supraband edqe redox couples chosen for the two electrolytes were 1,3 dimethoxy-4-nitrobenzene (8,=-l -0V vs SCE)for methanol, and 1 nitronaphthalene (E0=-l. 08), 1, 2 dichloro 4-nitrobenzene (E0= -0.95), and anthraquinone (Eo=-0.95) for acetonitrile. These redox couples lie from 0.IV to 0.24V above the conduction band edge of p-Si, and hence, in the conventional model, could not be photoreduced by p-Si. 

This study evaluated the impurity profile of untreated water from a textile plant in Portugal [35]. The organic material was concentrated by extraction from 11 of water into dichloromethane and HPLC-NMR and HPLC-MS experiments were carried out using a reverse-phase separation with an acetonitrile/ D2O gradient elution with H NMR spectroscopic observation at 600 MHz. For the HPLC-NMR studies, the samples were further fractionated into two pools according to their HPLC retention times. The HPLC-NMR studies were carried out in the stop-flow mode and the combination of NMR and MS results yielded the identification or tentative identification of 14 compounds, comprising mainly surfactants, anthraquinone dyes and nonylphenol-related molecules. 

FIGURE 9.5 Polarity-dependent polarization patterns in photosensitized hydrogen abstractions from triethylamine DH (sensitizer A, 9,10-anthraquinone). For the formulas, see Chart 9.3. Shown are the signals of the olehnic a and P protons of the product N, A-di ethyl vinylamine, V-a (6.05ppm) and V-P (3.45ppm), as functions of the relative permittivity e (given at the right). Top, pure acetonitrile-fi 3 bottom, pure chloroform-fi 3 other traces, mixtures of these two solvents. All spectra were normalized with respect of the absolute amplitude of V-a. Further explanation, see text. 

Me R = Br, R = H) by various donors in viscous soJventa are decreased by a factor of <2 in a 0.34 T magnetic field and pressure is reported to accelerate the photoreduction of p-benzoquinone in SOS and CTAB micelles in Aerosol OT reversed micelles, the reaction is retarded.The yield of anthraquinone-2-sulphonate radical anion (AQS) generated by irradiation of AQS in aqueous acetonitrile containing propan-2-oJ has been found to depend on the water concentration and to follow Perrin s equation.Complexation of aryl alkyl ketones with /3-cyclodextrin leads to changes in the ratio of the products of elimination and cyclisation which result from reaction of the... 

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