Mechanistic study of the oxidation of -ascorbic acid by chloranil at the nitrobenzene water interface

The redox reaction between -ascorbic acid in water and chloranil in nitrobenzene has been studied by means of polarography with an ascending water electrode as well as cyclic voltammetry with a stationary interface. Through accurate measurement of the limiting currents, it has been suggested that the redox reaction should be a two-electron reaction rather than a one-electron reaction described previously. A spectrophotometric technique has also been used to observe that the redox reaction proceeds spontaneously under certain conditions even without electrochemical control. Based on these findings, it has been concluded that the present heterogeneous charge transfer reaction is the ion transfer of chloranil semiquinone radical, which is driven by the homogeneous electron transfer between ascorbic acid and chloranil in the aqueous phase.     

Nachweis von chloranil in der tüpfelanalyse

Mixing chloranil with tetrabase in ether solution gives no reaction. The redox reaction, with formation of a blue diphenylmethane dye, occurs only after evaporation of the ether. On this. effect can be based a selective identification of chloranil. It can be carried out as a spot test showing an identification limit of 0.25 γ of chloranil. The authors describe a preliminary test for aromatic compounds, which consists in heating the test material with potassium chlorate and conc. hydrochloric acid and identifying the hereby formed chloranil by means of tetrabase. The investigation of 71 compounds has shown that not all aromatic compounds can be converted to chloranil. but that there exist characteristic exceptions.     

缺电子芳烃侧链基的光氧化

研究了9,10-二氰蒽(DCA)和四氯对苯二醌(TCBQ)敏化的甲苯、对氯甲苯、对氰基甲苯和对硝基甲苯的电子转移光氧化反应。DCA和TCBQ均可敏化甲苯和对氯甲苯的光氧化。产物为相应的取代苯甲酸和取代苯甲醛。DCA和TCBQ均不能有效敏化对氰基甲苯和对硝基甲苯的光氧化, 但在反应体系中加入与反应物等摩尔的联苯为共敏化剂后, 两者即可顺利氧化为相应的取代苯甲酸和取代苯甲醛。通过荧光淬灭和共敏化剂联苯、无水盐高氯酸镁、O2捕获剂对苯二醌以及电子给体对二甲氧基苯等外加试剂对光氧化的影响讨论了反应历程。     

Indole derivatives

Tris (1-benzyl-5-indolinyl)phosphine oxide, the structure of which was confirmed by alternative synthesis, is formed as a side product along with the previously described dimethyl-1-benzylindoline-5-phosphonate in the reaction of 1-benzyl-5-lithioindoline with dimethyl chlorophosphate. Dimethyl l-benzylindole-5-phosphonate was obtained by the dehydrogenation of dimethyl 1-benzylindoline-5-phosphonate with chloranil. The catalytic dehydrogenation of this same indollne is accompanied by debenzylation, which leads to dimethyl indole-5-phosphonate, and by splitting of the p-C bond.See [1] for communication LXXV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 498–501, April, 1972.     

Hydride shift reactions with the participation of two-ring sulfides

2,3-Dihydrobenzothiophenes are dehydrogenated to the corresponding benzothiophenes on reaction with the hydride-ion acceptors triphenylmethyl tetrafluoroborate and chloranil. Thiochroman reacts with chloranil to give 2-methyl-2,3-dihydrobenzothiophene and 2-methylbenzothiophene and reacts with triphenylmethyl tetrafluoroborate to give a thiochromenylium salt.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 328–330, March, 1976.     

The interaction between polymerization initiators and inhibitors in solutions—VIII. The mechanism of the reaction of azobisisobutyronitrile with p-benzoquinone and chloranil in polar and nonpolar solvents

The reactions of azobisisobutyronitrile (AIBN) with p-benzoquinone (BQ) and chloranil in toluene, chlorobenzene and acetonitrile, have been investigated by isolation and identification of the reaction products. In toluene and chlorobenzene, isobutyroylamino hydroquinone together with tetramethyl dioxazinobenzene are formed in the case of (BQ); the corresponding mono- and dioxazinobenzene derivatives are formed in the case of chloranil. In acetonitrile, however, only polyquinonoid resinous derivatives of the quinones are obtained. The crystalline derivatives as well as the resinous products have no nitrile groups in their structures and the nitrogen atom is directly attached to the parent quinone nucleus. This fact indicates that the radicals from AIBN react with quinones exclusively in the ketenimine form. A mechanism based on the possibility of electron-transfer from the radical to the quinone molecule to form charged species has been suggested. The degree of separation of these species is determined by the polarity of the solvent. Combination of the charged entities produces nuclear-substituted intermediates which may be eventually isolated as hydroquinones or subjected to further radical reactions with the ketenimine substituent to form the oxazinobenzene derivatives. The formation of ether derivatives of hydroquinone and tetrachlorohydroquinone in the reaction of BQ and chloranil with AIBN is accordingly excluded.     

N-haloamidines—III: S-Triazine derivatives from N-halobenzamidines and enamines

The reaction of N-haloamidines with enamines affords 1,4-dihydro-s-triazine derivatives as the main reaction product. The dihydro derivatives are aromatisable through oxidation with chloranil. The mass spectra of the isolated products are discussed in detail.     

Degradation of polyisoprene induced by chloranil

The aim of this work was to study the degradation of polyisoprene and polybutadiene in the presence of chloranil (tetrachloro-1,4-benzoquinone). The influences of polymer concentration, chloranil concentration and temperature were evaluated using a 2³ factorial design. The efflux times of toluene solutions containing different polymer and chloranil contents at 25, 45 and 65 °C were measured, using a Ubbelohde viscometer. When high concentrations of polymer and chloranil were used, at 65 ° C, the efflux time decreased to approximately 10% of its initial value after 7 min, and, after 250 min, the efflux time reduced to approximately 50% of its initial value. The efflux time of polybutadiene solutions containing chloranil did not decrease with the reaction time. ¹H NMR of polyisoprene and polybutadiene, dissolved in CDCl₃ containing chloranil, were used to evaluate the changes in polymer unsaturation. ¹H NMR measurements showed an exponential decrease in the area for peaks due to the hydrogen bound to the unsaturated carbon in polyisoprene solutions. These results suggest the occurrence of degradation of polyisoprene. Using the same conditions, it was observed that polybutadiene degradation did not occur. Thus, it was concluded that the methyl group in polyisoprene is very important in the degradation in the presence of chloranil.     

A study on the mechanism of reaction between BNAH and chloranil:Evidence for electron transfer

The reaction between chloranil and N-benzyldihydronicotinamide(BNAH)in boratebuffer/DMF was investigated.The reaction mixture gave a strong esr signal,which is consistentwith that of chloranil anion radical,and tetrachlorohydrophenol(QH_2)and N-benzylnicotinamide(BNA~+)were obtained as the sole products.When the reaction was run in benzene solution,a greencoloured charge-transfer complex between the reactants could be isolated,which decomposed in polarsolvents to give BNA-+ and QH_2.Based on kinetic studies by esr spectroscopy by the stopped-flowtechnique,a two-step electron-transfer mechanism for the reactionis proposed in contrast to thehydride-transfer mechanism reported in the literature.     

醋酸钯和四氯对苯醌催化氧化低浓度煤矿瓦斯制甲醇

利用自制的实验系统进行了醋酸溶液中低浓度瓦斯催化氧化制甲醇研究。实验结果表明,以Pd(OAc)₂为催化剂,反应体系中添加对苯醌或四氯对苯醌可改善甲烷活化环境,四氯对苯醌对瓦斯催化氧化过程的作用效果好于对苯醌。四氯对苯醌用量、反应压力和反应温度对瓦斯催化氧化具有重要影响。甲醇生成量随四氯对苯醌用量、反应压力和反应温度升高而增加。CH₃OH是通过反应过程中产生的H₂O₂与CH₄相互作用形成的。CH₃COOCH₃一部分是由Pd²⁺直接氧化CH₄得到的;另一部分是由CH₃OH与反应溶剂CH₃COOH通过酯化反应形成的。     

Potentiometric determination of p-chloranil and the kinetic study of its alkaline hydrolysis, using a chloranilate selective electrode

Two Ion-Selective Electrodes (ISEs), one commercial chloride ISE and one home-made chloranilate (Chl(2-)) ISE, were applied to study the alkaline hydrolysis of p-chloranil. This reaction proceeds through a very fast first step producing monochloranilate (Chl(-)) and chloride ions followed by a slow, rate determining step, producing chloranilate (Chl(2-)) and chloride ion. Kinetic equations specific for this reaction scheme, were derived to calculate reaction rate constants from E-t curves. The potentiometric selectivity coefficient K(pot) = 2.23 x 10(4) was determined for the response of the chloranilate electrode to Chl(-) anion and used for the kinetic calculations. The reaction rate constant for the slow step of the hydrolysis was found to be 0.227 M(-1) . sec(-1) at 25 degrees and the activation energy 1.56 x 10(4) Cal/mol. The total potential change following the completion of the first fast step is proportional to the log C of chloranil. Concentrations of chloranil 5-500 ppm can be determined with a precision of about 2%. This potentiometric method was evaluated for the determination of chloranil in fungicide preparations (Spergon) and the results obtained were compared with those of the official iodometric method. Good agreement was found.     

The synthesis of triphenylene-based discotic mesogens New and improved routes

The synthesis of discotic liquid crystal materials based on the triphenylene core normally involves the preparation of hexahydroxytriphenylene. This has traditionally been accomplished by a chloranil promoted trimerization of 1,2-dimethoxy-benzene followed by demethylation of the hexamethoxytriphenylene produced. Hexahydroxytriphenylene is subsequently alkylated to give the required derivative. The overall yield of this three step procedure is low and it is difficult to perform on a large scale. It is herein shown that a modified procedure using iron III chloride instead of chloranil yields hexa-alkoxytriphenylenes in a single step. The reaction is high yielding and can be performed on a large scale. This also provides a better route than those currently available for making the unsymmetrically substituted tri-phenylenes required in the synthesis of polymeric discotic liquid crystals. Some related elaborations of the triphenylene nucleus are also discussed.     

Kinetic study of the fast step of the alkaline hydrolysis of p-chloranil using stopped flow technique

The alkaline hydrolysis of p-chloranil or 2,3,5,6-tetrachloro-1,4-benzoquinone (C₆Cl₄O₂, Q) was studied, using stopped flow spectrophotometry and Electron Spin Resonance techniques (E.S.R.). In the present study it was shown for the first time, that a free radical is produced chemically and that it can account for the propagation of the reaction. It was found that in alkaline conditions chloranil in a “Michael” fashion undergoes 1,2 addition being hydrolyzed and in turn produces a chloranil free radical (Q^•) The hydrolysis then proceeds via a number of intermediates yielded by this radical and a number of different products is formed. The formation of these products, both quantitatively and qualitatively has a strong dependence on the concentration of the OH⁻ species and chloranil. The various possible routes of the hydrolysis are studied either spectrophotometrically or by E.S.R. Two different intermediates are observed absorbing at 426 nm and at 540 nm, respectively. Each species was formed and destroyed within 10 s to 30 min depending on the exact conditions. The reaction rate constants for the formation and the decay of the intermediates was estimated using the Guggenheim method. At both wavelengths the rate constants seem to have a complex relation to the concentration of the anion. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 385–391, 1997     

Photochemical acetalization of carbonyl compounds in protic media using an in situ generated photocatalyst

Carbonyl compounds are conveniently converted into their corresponding dimethyl acetals in good yields and short reaction times by means of a photochemical reaction in methanol with a catalytic amount of chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone, CA) as the sensitizer. Using aldehydes gives better results than using ketones, which also tend to form enol ethers as side products. These results are similar to those of simple acid-catalyzed acetalization reactions, suggesting the involvement of a photochemically generated acid. On the basis of steady state and laser flash photolysis data the reaction is proposed to involve the in situ generation of a photocatalyst (2,3,5,6-tetrachloro-1,4-hydroquinone, TCHQ) via reaction of CA with the solvent. The acetalization process is initiated by ionization of TCHQ, followed by loss of a proton to the solvent or the carbonyl, which starts a catalytic reaction. The photocatalyst is regenerated via a disproportionation reaction.     

Spectroscopic study of chloranil charge-transfer complexes of amino acids and related compounds

The absorption maxima, molar absorptivities, infrared spectra, compositions, formation constants, and pH dependence of amino acid—chloranil complexes have been determined with purified chloranil The n-π charge-transfer interaction depends on the presence of an unprotonated amino group; pH 9 is optimal for complex formation, but once formed, the complex is stable in a highly acidic medium and may be quantitatively extracted by hexanol. The molar absorptivities of the chloranil complexes of glycine, iminodiacetic acid, NTA, EDTA, DTPA and TTHA were measured. There is a linear relationship between the logarithm of the molar absorptivities of their chloranil complexes and the number of carboxylic groups in the molecule. There is an inverse linear relationship between the molar absorptivities of chloranil—metal—EDTA complexes and the logarithm of the stability constants of the EDTA chelates. This leads to a new method of determining the stability constants of complexes involving a nitrogen-donating group.     

The use of chloranil for spectrophotometric determination of some tranquillizers and antidepressants

Chlorpromazine hydrochloride, promethazine hydrochloride, promazine hydrochloride, perphenazine, thioridazine hydrochloride, chlorprothexine, opipramol hydrochloride, amitriptyline hydrochloride, imipramine hydrochloride and hydroxyzine hydrochloride are estimated in their pure state and in pharmaceutical formulations by means of the reaction of the free bases with chloranil in dioxan-ethanol medium to give a coloured product with maximal absorbance at 550 nm. The method is precise, accurate and specific and recommended for routine analysis for the drugs mentioned.     

Uber die reaktionen der 1,4,7-triketone mit hydrazin

According to reaction conditions, 1,4,7-triketones yield the dihydropyridazine hydrazones (1-8) or the dihydropyrrolo[1,2-b]-pyridazones (9-19). The latter are dehydrogenated by chloranil to the pyrrolo[1,2-b]pyridazines (20-23).     

The mechanisms of retardation and inhibition in radical polymerizations by quinones

The sensitized polymerizations of styrene, vinyl acetate (VA), acrylonitrile (AN), methyl methacrylate (MMA) and ethyl acrylate (EA) in the presence of benzoquinone (BQ), 2,5-dichlorobenzoquinone(Dich.BQ), chloranil and duroquinone (DQ) have been studied by isolation and investigation of the polymers formed during the induction periods. Quinonoid polymeric derivatives of BQ and Dich.BQ, were obtained for all monomers. In the case of chloranil, quinonoid products were formed only with MMA and EA. Most of the DQ was recovered intact in all systems; only in the case of styrene could quinonoid polymers be detected. The results indicate that substitution of the polymer chains into the quinone nucleus is the predominant mechanism for retardation and inhibition. The feasibility of substitution is determined by the electron-donating power of the polymeric radical, the redox potential of the quinone and the presence of hydrogen atoms in its nucleus. The tendency of the acrylate radicals for disproportionation accounts for the formation of quinonoid products with chloranil. The suggested mechanisms account for the variety of observations on inhibition reactions.     

Fast and easy detection of aromatic amines on solid support

The use of p-nitrophenyl ester 1 has been shown to offer a reliable method for the detection of free aromatic amines. As little as 3.4 μmol g⁻¹ of free aniline amino groups can be detected. The method has shown to be more sensitive for the detection of sterically hindered aromatic amines than the existing alternative based on reaction with chloranil.     

Charge-transfer complexes as polymerization inhibitors. I. Amine–chloranil complexes as inhibitors for the radical polymerization of methyl methacrylate

Charge-transfer complexes of N,N-dimethylaniline (DMA) and triethylamine (TEA) with chloranil have been investigated as inhibitors for the sensitized polymerization of methyl methacrylate (MMA) in bulk and in solution. Complete inhibition is achieved by the complexes of both amines followed by retardation only in case of DMA. The higher inhibiting efficiency of the TEA complexes is attributed to their greater stability. The polymers formed in the presence of chloranil alone or its complexes with both amines are quinonoid and contain no combined nitrogen. The results support the idea that inhibition reaction involve electron transfer from the growing chains to the quinone, with formation of molecular complexes of polymeric cations and semiquinone anions. The latter are the actual inhibiting species, so that the efficiency of inhibiting depends on their concentration, which is determined by the stability of the molecular complexes formed. The inhibition reactions should accordingly be considered as oxidation–reduction processes in which the growing chains are the electron donors. The suggested mechanism affords an explanation for the great differences in the inhibiting power of a particular quinone for the polymerization of different monomers.