Alternating copolymerization of 2,3-dichloro-5,6-dicyano-p-benzoquinone with styrene and polymerization behavior with vinyloxy compounds

2,3-Dichloro-5,6-dicyano-p-benzoquinone (DDQ) was found to copolymerize alternatingly with styrene (St). DDQ–isobutyl vinyl ether and DDQ–2-chloroethyl vinyl ether systems gave homopolymers of vinyl ethers, while DDQ–phenyl vinyl ether and DDQ–vinyl acetate systems gave oligomers containing both monomer units. In the terpolymerization of DDQ, p-chloranil (pCA), and St, terpolymers obtained were found to have about 50 mole % of St units regardless of monomer feed ratio and DDQ was incorporated much more rapidly into the terpolymer than pCA. The difference in the reactivity of the acceptor monomers could be attributed to that in their electron-accepting character.     

Studies of the interaction of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) with imidazole in acetonitrile

The reaction of DDQ with imidazole in acetonitrile is a two-step process. The formation of an anion radical is followed by slow substitution of Cl atoms to form diaminobenzoquinone. Kinetics of the second step is reported. . - Cl CN- . .     

Utility of 2,3-dichloro-5,6-dicyano-p-benzoquinone in assay of codeine, emetine and pilocarpine

A simple and sensitive spectrophotometric method for the assay of codeine, emetine and pilocarpine is described, based on the interaction of these drugs (as n-electron donors) with 2,3-dichloro-5,6-dicyano-p-benzoquinone (as pi -acceptor) to give a highly coloured radical anion which exhibits maximum absorption at 460 nm. Formation of the radical anion has been established by electron spin resonance measurements. Beer's law is obeyed for the alkaloids investigated. The assay results are in accord with pharmacopoeial assay results. The procedure is sufficiently sensitive to permit unit dose assay of the individual alkaloids in pharmaceutical formulations.     

The use of 2,3-dichloro-5,6-dicyano-p-benzoquinone for the spectrophotometric determination of some cardiovascular drugs

Some basic cardiovascular drugs containing secondary or tertiary amino groups are determined spectrophotometrically. The method is simple and sensitive; it is based on the interaction of the drugs, as n-electron donors, with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) as a pi-acceptor. The highly coloured radical anion exhibits maximum absorption at 460 nm. The drugs determined are pindolol, dipyridamole, hydralazine hydrochloride, quinidine sulphate, prenylamine lactate and tolazoline hydrochloride. Beer's law is obeyed for these drugs. The procedure is sensitive enough to permit unit dose assay of the individual drugs in their pharmaceutical formulations. The assay results are in accord with the pharmacopoeial assay results.     

Charge-transfer interaction of aromatic thiols with 2,3-dichloro-5,6-dicyano-p-benzoquinone: spectral and quantum mechanical studies

Charge-transfer (CT) complexes formed between aromatic thiol donors (thiophenol (TP), benzene-1,4-dithiol (BDT), p-aminothiophenol (ATP), p-hydroxythiophenol (HTP), and p-toluenethiol (TTP)) and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) as an acceptor were studied spectrophotometrically in dichloromethane. Addition of aromatic thiols in dichloromethane to DDQ leads to the formation of colored solutions that exhibit a very broad absorption band in the range 440-800 nm and a band in the region 300-400 nm. On the basis of the energies of LUMO and HOMO from quantum mechanical calculations, the broad band observed in the visible region was assigned to the pi*(a2) <-- pi(b1) transition and a band observed between 300 and 400 nm was assigned to the pi*(a2) <-- pi(a2) transition. The solid CT complexes of aromatic thiols and DDQ were prepared and characterized by FT-IR spectroscopy. The stoichiometry of the CT complexes was determined by Job's continuous variation method. The association constant (KCT), molar extinction coefficient (epsilon), oscillator strength (f), and transition dipole moment (micro) values were calculated from the electronic spectra. The vertical ionization potentials (ID) of the donors were calculated from their corresponding lambdaCT. Quantum mechanical (QM) calculations were performed to determine the ionization potential and the energies of the highest occupied molecular orbital (HOMO) of donors and lowest unoccupied molecular orbital (LUMO) of an acceptor.     

Synthesis of sulfur-sulfur bond formation from thioamides promoted by 2,3-dichloro-5,6-dicyanobenzoquinone

A mild and efficient synthesis of sulfur-sulfur bond formation from thioformanilides with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) is described. Functionality on the aromatic ring plays a key role in the formation of a sulfur-sulfur bond.     

Stereochemistry of Dehydrogenation of 1,4,-Cyclohexadiene with 2,3-Dichloro-5,6-dicyano-p-benzoquinone

cis- and trans-(3,6-D₂)-1,4-cyclohexadienes 1a and 1b have been synthesized from cis-3,4-dichlorocyclobutene (5). Aromatization to benzene with DDQ is cis-stereospecific with an uncertainty of 5%. This result is discussed in relation to concerted or stepwise mechanisms for aromatization of 1,4-dihydroaromatics with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ).     

Unexpected formation of tetrasubstituted 2,3-dihydrofurans from the reactions of beta-keto polyfluoroalkanesulfones with aldehydes

Catalyzed by piperidine, the reactions of beta-keto polyfluoroalkanesulfones with aromatic aldehydes afforded the unexpected tetrasubstituted 2,3-dihydrofurans in good yields, probably proceeding through the normal Knoevenagel condensation products. This reaction provided an efficient and novel method for the stereoselective synthesis of fluorine-containing tetrasubstituted trans-2,3-dihydrofurans.     

Oxidation of styrene by 2,3-dichloro-5,6-dicyano-p-benzoquinone

Styrene is oxidized by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), affording hydroquinone mono(2-phenylethyl) ether. Kinetic studies (50°C in CHCl₃) show that the reaction is faster under N₂ than under air and takes placevia intramolecular H-atom transfer within the 1:1 and 1:2 DDQ-styrene charge-transfer complexes. The semiquinone radical intermediate is reoxidized to DDQ by O₂ when the latter is present, therefore, the apparent rate of DDQ reduction is lower. Stability constants of the CT-complexes and kinetic parameters for the oxidation are reported.     

Interaction of 2,3-dichloro-1,4-naphthoquinone with n-butylamine in halocarbon solvents

The rapid interaction between 2,3-dichloro-1,4-naphthoquinone (DClNQ) and n-butylamine results in the formation of 2N(n-butylamino)-3-chloro-1,4-naphthoquinone as the final product. The reaction is found to proceed through the initial formation of charge-transfer (CT) complex as an intermediate. The final product of the reaction has been isolated and characterized using FTIR, H1 and C13 NMR spectroscopy, mass spectrometry, and elemental analysis. The rate of formation of product has been measured as a function of time in different halocarbon solvents, viz., chloroform, dichloromethane and 1:1 (v/v) mixture of two solvents. The pseudo first order and second order rate constants at various temperatures for the transformation process were evaluated from the absorbance time data. The activation parameters (E(a), DeltaS#, DeltaH#, and DeltaG#) were obtained from temperature dependence of rate constants. The influence of dielectric constant on the properties of reaction was discussed and the probable course of reaction is presented.     

An intriguing reaction of 4-hydroxycoumarins with 2,3-dichloro-5,6-dicyanobenzoquinone

An intriguing reaction of 4-hydroxycoumarins with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) occurred in the presence of catalytic acetic acid in ethanol at reflux with the products being obtained in high yields.     

Regioselective Alcoholysis and Conversion of Thiiranes to Alkoxy-Disulfides with 2,3-Dichloro-5,6-dicyano-p-benzoquinone (DDQ)

Summary: Alcoholysis of thiiranes followed by conversion to their corresponding alkoxy-disulfides with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) is performed in one step. The reactions occur under neutral conditions with high regioselectivity. Alkoxy-disulfides are obtained in 30–90% yields.     

左旋多巴与2,3-二氯-5,6-二氰-1,4-苯醌的荷移反应研究

研究了左旋多巴和2,3-二氯-5,6-二氰-1,4-苯醌(DDBQ)的反应条件,确定在硼砂溶液中,在60℃反应70 min可获得稳定的络合物,其λmax=346 nm,组成比为1∶1,表观摩尔吸收系数ε=1.1×104L.mol-1.cm-1,应用拟定的方法测定药物制剂测定结果与文献方法一致,回收率在97.25%~102.7%之间,相对标准偏差在0.7%以内。     

Reaction of 2,3-dichloro-5,6-dicyanopyrazine with enamines and some tertiary amines

The reaction of 2,3-dichloro-5,6-dicyanopyrazine ( 1 ) with enamines as well as a few tertiary amines as enamine precursors was investigated. Both reactions gave aminovinyl-substituted pyrazine derivatives. During the attempted purification of 3c or 3d by column chromatography on silica gel, 2-chloro-5,6-dicyano-3-(1′-oxocyclopent-2′-yl)pyrazine ( 4 ) was obtained, apparently by hydrolytic cleavage. The products prepared are all of interest as potential pesticides.     

Charge Transfer Complexes of Ketotifen with 2,3-Dichloro-5,6-dicyano-p-benzoquinone and 7,7,8,8-Tetracyanoquodimethane: Spectroscopic Characterization Studies

The reactions of ketotifen fumarate (KT) with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as π acceptors to form charge transfer (CT) complexes were evaluated in this study. Experimental and theoretical approaches, including density function theory (DFT), were used to obtain the comprehensive, reliable, and accurate structure elucidation of the developed CT complexes. The CT complexes (KT-DDQ and KT-TCNQ) were monitored at 485 and 843 nm, respectively, and the calibration curve ranged from 10 to 100 ppm for KT-DDQ and 2.5 to 40 ppm for KT-TCNQ. The spectrophotometric methods were validated for the determination of KT, and the stability of the CT complexes was assessed by studying the corresponding spectroscopic physical parameters. The molar ratio of KT:DDQ and KT:TCNQ was estimated at 1:1 using Job’s method, which was compatible with the results obtained using the Benesi–Hildebrand equation. Using these complexes, the quantitative determination of KT in its dosage form was successful.     

Oxidative transformation of the natural lignan hydroxymatairesinol with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

The oxidative transformation of the two isomers of the natural lignan hydroxymatairesinol from Norway Spruce (Picea abies) by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), has been studied. Significant differences in the outcome of the reactions were observed when the pure isomers of hydroxymatairesinol were reacted with DDQ under the same conditions. The different stereoelectronic effects in the two isomers as well as their conformational structures seem to determine the site of reaction, which results in different reaction products. Several products were identified by GC-MS and NMR spectroscopy. Oxomatairesinol was obtained in a yield of 25%.     

Spectroscopic studies on the interaction of cilostazole with iodine and 2,3-dichloro-5,6-dicyanobenzoquinone

Lanthanide sensitized luminescence and chemiluminescence (CL) are of great importance because of the unique spectral properties, such as long lifetime, large Stokes shifts, and narrow emission bands characteristic to lanthanide ions (Ln³⁺). With the fluoroquinolone (FQ) compounds including enoxacin (ENX), norfloxacin (NFLX), lomefloxacin (LMFX), fleroxacin (FLRX), ofloxacin (OFLX), rufloxacin (RFX), gatifloxacin (GFLX) and sparfloxacin (SPFX), the luminescence and CL properties of Tb³⁺–FQ and Eu³⁺–FQ complexes have been investigated in this contribution. Ce⁴⁺–SO₃²⁻ in acidic conditions was taken as the CL system and sensitized CL intensities of Tb³⁺–FQ and Eu³⁺–FQ complexes were determined by flow-injection analysis. The luminescence and CL spectra of Tb³⁺–FQ complexes show characteristic peaks of Tb³⁺ at 490 nm, 545 nm, 585 nm and 620 nm. Complexes of Tb³⁺–ENX, Tb³⁺–NFLX, Tb³⁺–LMFX and Tb³⁺–FLRX display relatively strong emission intensity compared with Tb³⁺–OFLX, Tb³⁺–RFX, Tb³⁺–GFLX and Tb³⁺–SPFX. Quite weak peaks with unique characters of Eu³⁺ at 590 nm and 617 nm appear in the luminescence and CL spectra of Eu³⁺–ENX, but no notable sensitized luminescence and CL of Eu³⁺ could be observed when Eu³⁺ is added into other FQ. The distinct differences on emission intensity of Tb³⁺–FQ and Eu³⁺–FQ might originate from the different energy gap between the triplet levels of FQ and the excited levels of the Ln³⁺. The different sensitized luminescence and CL signals among Tb³⁺–FQ complexes could be attributed to different optical properties and substituents of these FQ compounds. The detailed mechanism involved in the luminescence and CL properties of Tb³⁺–FQ and Eu³⁺–FQ complexes has been investigated by analyzing the luminescence and CL spectra, quantum yields, and theoretical calculation results.     

Solvent effect on the charge transfer complex of oxatomide with 2,3-dichloro-5,6-dicyanobenzoquinone

The charge transfer complex (CT-complex) between oxatomide drug and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) was studied spectrophotometrically in 10 solvents at different temperatures. The donor oxatomide is found to form stable 1:1 stoichiometric complex with DDQ and the stoichiometry was unaffected by change in polarity of the solvent studied. The DeltaH degrees, DeltaS degrees and DeltaG degrees values are all negative, so the studied complex is reasonably stable and exothermic in nature. The ionization potential of the drug was determined using the CT-absorption bands of the complex in all the solvents. The dissociation energy of the charge transfer excited state for the CT-complex in different solvents was also determined and is found to be constant. The spectroscopic and thermodynamic properties were observed to be sensitive to the nature of the solvent.     

A reexamination of the reactions of 2,3-dichloro-1,4-naphthoquinone with thioamides

2,3-Dichloro-1,4-naphthoquinone reacts with thioamides and thiourea to give mixtures of condensed thiazoles and thianthrenes.