34666-24-5

Upstream product

• 143-33-9 sodium cyanide 
• 118-75-2 chloranil 
• 1165952-91-9 cyclohexa-1,3-diene 
• 544-25-2 Cyclohepta-1,3,5-triene 
• 108-67-8 1,3,5-trimethyl-benzene 
• 109-99-9 tetrahydrofuran 
• 87-87-6 2,3,5,6-tetrachlorobenzene-1,4-diol 
• 100-68-5 methyl-phenyl-thioether 
• 831-91-4 Benzyl phenyl sulfide 
• 5023-67-6 4-methoxybenzyl phenyl sulfide 

Downstream Products

• 100-68-5 methyl-phenyl-thioether 
• 118-75-2 chloranil 

Relevant academic research and scientific papers

Singlet Oxygen Generation by Triplet Charge-Transfer Complexes

Quantum yields of singlet oxygen generation by complexes of triplet p-chloranil and various benzene derivatives with partial or complete charge transfer were measured by time-resolved phosphorescence.The probability of 1O2 generation (SΔ/

Photoreduction of p-Benzoquinones: Effects of Alcohols and Amines on the Intermediates and Reactivities in Solution

The photochemistry of 1,4-benzoquinone (BQ) and alkyl-, Cl- and related derivatives, e.g. methyl-, 2,6-dimethyl-, chloro-, 2,5-dichloro-1,4-benzoquinone, duroquinone and chloranil, was studied in nonaqueous solvents by UV-vis spectroscopy using nanosecond laser pulses at 308 nm. The reactivity of the triplet state (3Q*) of the quinones with 2-propanol in the absence of water is largest for BQ and depends mainly on the quinone structure, whereas the rate constant of electron transfer from amines, such as triethylamine (TEA) or 1,4-diazabicyclo[2.2.2]octane, is close to the diffusion-controlled limit for BQ and most derivatives. Photoinduced charge separation after electron transfer from amines to 3Q* and the subsequent charge recombination or neutralization are supported by time-resolved conductivity measurements. The half-life of the decay kinetics of the semiquinone radical (.QH/Q.-) depends significantly on the donor and the medium. The photoconversion into the hydroquinones was measured under various conditions, the quantum yield, λirr = 254 nm, increases with increasing 2-propanol and TEA concentrations. The effects of quenching of 3Q*, the .QH/Q.- radicals and the photoconversion are outlined. The mechanisms of photoreduction of quinones in acetonitrile by 2-propanol are compared with those by TEA in benzene and acetonitrile, and the specific properties of substitution are discussed.

Substituent effects in oxime radical cations. 1. Photosensitized reactions of acetophenone oximes

A variety of ortho-, meta-, and para-substituted (-H, -F, -Cl, -CF 3, -CN (meta and para only), -CH3, -OCH3, and -NO2) acetophenone oximes were synthesized and studied using laser flash photolysis (LFP) and steady-state photolysis experiments in acetonitrile with chloranil as the photosensitizer. In addition, semi-empirical (AM1) calculations were performed on the neutral species, the radical cations, and the corresponding iminoxyl radicals. The data was analyzed in terms of the electrochemical peak potentials of the oximes, the quenching rates of triplet chloranil (LFP), the calculated ionization potentials, and the measured conversions of the oximes in the steady-state photolysis experiments. Photolysis of the oximes in the presence of chloranil results in the formation of the chloranil radical anion, which reacts rapidly with the oxime radical cation to form the semiquinone radical and an iminoxyl radical. Evidence for the formation of the chloranil radical anion and the semiquinone radical was obtained from LFP studies. The measured quenching rates from the LFP studies represent the rates of electron transfer from the oximes to triplet chloranil. This data was correlated to various radical and polar substituent constants. The Hammett studies suggest that steric, polar, and radical effects are important for ortho-substituted acetophenone oximes, polar effects are important for parasubstituted oximes, and radical stabilization is more important than polar effects for the meta-substituted substrates. The calculated ionization potentials of the oximes show an excellent correlation with the measured quenching rates supporting the electron transfer pathway. On the basis of calculated charge densities, we conclude that the measured substituent effects are transition state effects rather than ground state effects. At this point all of the available data suggests that the conversion of the oximes is controlled by two energetically opposing reactions, namely oxidation of the neutral oxime, which is favorable for oximes with electron-donating substituents, and deprotonation of the oxime radical cation, which is favorable for oximes with electron-withdrawing substituents. The overall result is a reaction with little selectivity as far as substituent effects are concerned.

Photoinduced hydrogen- and electron-transfer processes between chloranil and aryl alkyl sulfides in organic solvents. Steady-state and time-resolved studies

The photochemical behavior of three aryl alkyl sulfides, thioanisole (TA), benzyl phenyl sulfide (BPS) and 4-methoxybenzyl phenyl sulfide (MBPS), sensitized by triplet chloranil (CA), was investigated by nanosecond laser flash photolysis and steady-state irradiation in CH2Cl2 and MeCN. The nature of the transients detected upon 355-nm laser excitation was independent of the molecular structure of the aryl alkyl sulfides but strongly affected by the solvent polarity. In particular, in CH2Cl2 the quenching process of triplet CA by aryl alkyl sulfides was accompanied by H- transfer, with formation of the CAH· and TA(-H)·/BPS(-H)·/MBPS(-H)· radicals. In contrast, a charge transfer process between triplet CA and aryl alkyl sulfides, with formation of the radical anion CA·- and radical cations of aryl alkyl sulfides, occurred in MeCN. In this solvent, a transient detected at long delay time was tentatively assigned to the anion CAH- formed by H-transfer between radical ions. In all experiments, transient species were characterized in terms of second-order decay rate constants and quantum yields of formation. Steady-state irradiation of the CA/TA system led to the stable photoadduct C6H5SCH2OC6Cl4OH in both CH2Cl2 and MeCN with quantum yields of 0.033 and 0.27, respectively. In contrast, aldehydes, thioacetals, and disulfides were the main products obtained upon irradiation of the CA/BPS and CA/MBPS systems. The photoaddition products were not observed, probably owing to their low stability. The nature of the photoproducts formed by irradiation of CA/aryl alkyl sulfides was independent of solvent properties, even though the reactivity was higher in MeCN than in CH2Cl2.

Photodynamics of the Paterno-Buechi cycloaddition of stilbene to quinone. Unusual modulation of electron-transfer kinetics by solvent and added salt

Oxetanes are produced in the Paterno-Buechi cycloaddition of stilbene (S) to quinone (Q) via an efficient photoinduced electron transfer. Kinetics analysis of the time-resolved absorption spectra over three distinctive (ps, ns, μs) timescales establishes the coupling (kC) of the initially formed ion-radical pair 3[S+?, Q-?] to the 1,4-biradical ?SQ? as the critical step toward oxetane formation. The (rather slow) rate constant of kC ≤ 107 s-1 in acetonitrile must compete with other faster decay pathways of the ion pair involving ionic separation, ion exchange (with added salt) and back electron transfer. As such, solvent polarity and donicity as well as added salts play an unusually prominent role in modulating the ion-pair microdynamics. Donor-acceptor complexation of the photoexcited quinone with the solvent and cis→trans isomerization of (Z)-stilbene must also be considered in the overall photodynamics of electron transfer.

Direct observation and structural characterization of the encounter complex in bimolecular electron transfers with photoactivated acceptors

The encounter complex between photoexcited quirtones Q* and various aromatic donors (ArH) is observed directly by time-resolved ps spectroscopy immediately before it undergoes electron transfer to the ion-radical pair [Q(°-) ArH(°+)]. The encounter complex (EC) is spectrally characterized by distinctive (near IR) absorption bands, and its temporal evolution is established by quantitative kinetics analysis. The structural characterization of the 1:1 encounter complex [Q*, ArH] identifies the cofacial juxtaposition of the donor and acceptor moieties for optimal overlap of their π-orbitals. Further comparisons of the (excited-state) encounter complex with the corresponding (ground-state) EDA complex of aromatic donors and quinones establish its charge-transfer character, which directly relates to electron transfer within the encounter complex. The mechanistic significance of the encounter complex to bimolecular electron transfer is discussed (Scheme 1).

Direct Detection of the Cation Radical of the Spin Trap α-Phenyl-N-tert-butylnitrone

The radical cation PBN 2 of the spin trap α-phenyl-N-tert-butylnitrone (PBN, 1) was observed directly max(H2O)/nm 410 3 mol-1 cm-1 (5+/-1)*103>> and characterised by pulse radiolysis and laser flash photolysis absorption measurements in solvents of different polarity (water, CH3CN, BuCl) as well as by low-temperature EPR.It was generated by direct two-photon ionisation of PBN, by electron-transfer from PBN to solvent cation radicals or to photoexcited triplet chloranil, and by reaction of PBN with the oxidising anion radical SO4.The γ-irradiation of PBN in alkyl halide glasses at 77 K yielded green-coloured samples containing the stabilised radical cation PBN, whose EPR spectrum indicates the presence of aminoxyl-type radicals.PBN cation radical reacts with a variety of nuclophiles to yield the corresponding stable aminoxyl radicals.Based on spectroscopic, kinetic and chemical evidence it is concluded that PBN cation radical is an aminoxyl substituted phenylcarbenium ion.

AN ELECTRON/PROTON-TRANSFER SEQUENCE FOR QUENCHING CHLORANIL TRIPLETS BY CYCLOPOLYENES

Photolysis of the quinone chloranil (Q) in the presence of 1,3-cyclohexadiene (CHD) and 1,3,5-cycloheptatriene (CHT) has been studied by using steady and flash irradiation techniques.Excitation of the long-wavelength absorption band of Q in trichlorobenzene solutions of CHD (20 mM) led to formation of the redox products tetrachlorohydroquinone (QH2) and benzene with high chemical and quantum efficiency.A flash photolysis investigation of this system (YAG laser, 355 nm) revealed that Q triplets are quenched by CHD at a high rate (k= 3.6 x 1E9 M-1 s-1) and that quenching leads to the semiquinone free radical associated with formal hyd rogen atom transfer from CHD to Q.The second-order decay of free radicals (100 μs time scale) is consistent with radical reconbination reactions leading to stable products.The semiquinone radical was also obtained on quenching the chloranil triplet with CHT in benzene.On conbination of Q with a high concentration of CHD (2.0 M), a ground-state-charge-transfer (CT) complex of quinone and diene absorbed strongly (λmax= 490 nm); on irradiation of the complex (e.g., 436 nm), hydroquinone and benzene were formed again, but with lower quantum yield.The results are discussed in terms of efficient quenching of Q triplets through electron donor-acceptor interaction with CHD or CHT and rapid proton transfer between the components of a highly polar excited complex (essentially a triplet radical-ion pair).A singlet radical-ion pair obtained upon irradiation of the quinone/alkene CT complex behaves differently, leading to photoredox products through the single manifold.

On the Reaction of Chloranil with Cyanide Ions - an ESR Study

The reaction of chloranil 1 with cyanide ions in acetonitrile and methanol solutions has been studied.The ESR spectra revealed the formation of semiquinone anion radicals 7, 8, and 9.The latter has been found as its protonated form in methanol only.In addition, both 1 and 2,3-dicyano-5,6-dichloro-1,4-benzoquinone 4 gave tetracyanoethylene anion radicals 6 upon reaction with cyanide ions in acetonitrile.Using 13C-labelled cyanide 6 was shown to originate from the fragmentation of the cyanide addition product to 4.Using the spin trapping technique it was found that no cyanyl free radicals are formed during the thermal reaction of either 1 or 4 with cyanide ions.