- para-Selective chlorination of cresols and m-xylenol using sulfuryl chloride in the presence of poly(alkylene sulfide)s
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Chlorination of o-cresol, m-cresol, and m-xylenol using sulfuryl chloride in the presence of a range of poly(alkylene sulfide)s and a Lewis acid (aluminum or ferric chloride) has been studied. The sulfur containing catalysts used led to the production of para-chlorophenols in high yields and higher para/ortho ratios than for reactions in the absence of such poly(alkylene sulfide)s. The effectiveness of the polymers was found to be dependent on the length of the spacer groups between the sulfur atoms. For example, polymers with shorter spacers provided high yields of 4-chloro-o-cresol (ca. 97%), while polymers with at least one longer spacer provided high yields of both 4-chloro-m-cresol (up to 94.6%) and 4-chloro-m-xylenol (up to 97.6%).
- Smith, Keith,Hegazy, Amany S.,El-Hiti, Gamal A.
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p. 345 - 356
(2020/03/23)
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- Regioselective chlorination of phenols in the presence of tetrahydrothiopyran derivatives
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Four six-membered cyclic sulfides, namely tetrahydrothiopyran, 3-methyltetrahydrothiopyran, 4-methyltetrahydrothiopyran and 4,4-dimethyltetrahyrdrothiopyran have been used as moderators in chlorination reactions of various phenols with sulfuryl chloride in the presence of aluminum or ferric chloride. On chlorination of phenol, ortho-cresol and meta-cresol the para/ortho chlorination ratios and yields of the para-chloro isomers are higher than when no cyclic sulfide is used for all of the cyclic sulfides, but chlorination of meta-xylenol is less consistent, with some cyclic sulfides producing higher p/o ratios and others producing lower ratios than reactions having no sulfide present.
- Smith, Keith,Williams, Des,El-Hiti, Gamal A.
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p. 529 - 538
(2019/06/13)
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- The highly efficient air oxidation of aryl and alkyl boronic acids by a microwave-assisted protocol under transition metal-free conditions
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Molecular oxygen is the most important green-oxidant due to its excellent properties. However, the effective utilization of molecular oxygen remains a major challenge in modern chemistry. Herein, we report the development a rapid, green and efficient microwave-assisted protocol for the air oxidation of boronic acids to phenols and alcohols under transition metal-free conditions. In the presence of KOH and DMSO, high yields of the expected phenols and alcohol were obtained with microwave-assistance, and a variety of functional groups were tolerated in this procedure. Notably, this transition metal-free method represents a breakthrough in both organic synthesis and green chemistry for the oxidative hydroxylation of boronic acids to phenols and alcohols.
- Yin, Weiyan,Pan, Xizhi,Leng, Wenxi,Chen, Jian,He, Haifeng
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supporting information
p. 4614 - 4618
(2019/09/09)
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- IPSO-hydroxylation of boronic acid via ozonolysis: A metal-, ligand-, and base-free method
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Here, we have developed a simple, efficient, and metal-, ligand-, and base-free method for the synthesis of functionalized aryl and alicyclic alcohols via ozonolysis of corresponding boronic acids in aqueous ethanol. The procedure is compatible with a variety of functional groups and can be utilized as an alternative method for the synthesis of hydroxy arenes and alicyclic alcohols.
- Bommegowda, Yadaganahalli K.,Mallesha, Ningegowda,Vinayaka, Ajjampura C.,Sadashiva, Maralinganadoddi P.
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supporting information
p. 268 - 270
(2016/05/02)
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- Comparison of cyclic and polymeric disulfides as catalysts for the regioselective chlorination of phenols
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Two cyclic and two polymeric disulfides have been synthesized and established to be useful catalysts for the chlorination of m-xylenol, o-cresol, m-cresol and phenol using freshly distilled sulfuryl chloride in the presence of aluminum or ferric chloride as a co-catalyst at room temperature. The yields of p-isomers and para/ortho ratios were higher compared to cases where no catalyst was used with most catalysts for most phenols even when a very low concentration of disulfide was used.
- Smith, Keith,Al-Zuhairi, Ali J.,El-Hiti, Gamal A.,Alshammari, Mohammed B.
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- Oxidation of p-chlorotoluene and cyclohexene catalysed by polymer-anchored oxovanadium(iv) and copper(ii) complexes of amino acid derived tridentate ligands
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3-Formylsalicylic acid (Hfsal), covalently bound to chloromethylated polystyrene (PS) and cross-linked with 5% divinylbenzene reacts with d,l-alanine and l-isoleucine to give the Schiff-base tridentate ligands PS-H 2fsal-d,l-Ala and PS-H2fsal-l-Ile, respectively. These anchored ligands upon reaction with VOSO4 and Cu(CH 3COO)2?H2O form the complexes PS-[VO(fsal-d,l-Ala)(H2O)], PS-[Cu(fsal-d,l-Ala)(H2O)], PS-[VO(fsal-l-Ile)(H2O)] and PS-[Cu(fsal-l-Ile)(H2O)]. The structures of these immobilized complexes have been established on the basis of scanning electron micrographs, spectroscopic (infrared, electronic and EPR), thermogravimetric and elemental analysis studies. The oxidation of p-chlorotoluene and cyclohexene has been investigated using these complexes as the catalysts in the presence of H2O2 as the oxidant. Reaction conditions have been optimised by considering the concentration of the oxidant, the amount of catalyst used and the temperature of the reaction mixture. Under the optimised conditions, p-chlorotoluene gave a maximum of 14% conversion using PS-[VO(fsal-d,l-Ala)(H2O)] as the catalyst, with the main products having a selectivity order of: p-chlorobenzaldehyde >> p-chlorobenzylalcohol > p-chlorobenzoic acid > 2-methyl-5-chlorophenol > 3-methyl-6-chlorophenol. The oxidation of cyclohexene with PS-[VO(fsal-d,l-Ala)(H2O)] proceeds with 79% conversion, which is followed by PS-[VO(fsal-l-Ile)(H2O)] with 77% conversion, and the oxidation of cyclohexene by Cu-based catalysts occurs with considerably lower conversions (29-32%). The selectivity of the products follows the order: 2-cyclohexene-1-ol > cyclohexene oxide > cyclohexane-1,2-diol > 2-cyclohexene-1-one. Recycling studies indicate that these catalysts can be reused at least three times without any significant loss in their catalytic potential. However, EPR studies indicate that while the polymer supported V(iv)O-complexes do not change after being used, the EPR spectra of the Cu-complexes show significant changes. The corresponding non-polymer bound complexes [VO(fsal-d,l-Ala)(H2O)], [Cu(fsal-d,l-Ala)(H 2O)], [VO(fsal-l-Ile)(H2O)] and [Cu(fsal-l-Ile)(H 2O)] have also been prepared in order to compare their spectral properties and catalytic activities. The non-polymer bound complexes exhibit lower conversion, along with lower turn-over frequency as compared to their polymer-bound analogues. Several EPR, 51V NMR and UV-vis studies have been undertaken to detect the intermediate species, and outlines for the mechanisms of the catalytic reactions are proposed.
- Maurya, Mannar R.,Kumar, Maneesh,Kumar, Amit,Pessoa, Joao Costa
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experimental part
p. 4220 - 4232
(2009/02/03)
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- Investigations of the reactions of monochloramine and dichloramine with selected phenols: Examination of humic acid models and water contaminants
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The phenols are an important area of investigation because they are substituents in the humic acids and are common contaminants in water. The reactivities and orientations of two common phenols (phenol and m-cresol), and some of their chlorinated intermediates with aqueous monochloroamine and dichloroamine were presented. m-Cresol was more reactive than phenol with both chlorinating agents. NH2Cl and NHCl2 showed extensive reactivity toward the phenols, even the partially chlorinated less reactive intermediates would be expected to fully chlorinate the activated positions in phenolic substituents in the humic acids.
- Heasley, Victor L.,Fisher, Audra M.,Herman, Erica E.,Jacobsen, Faith E.,Miller, Evan W.,Ramirez, Ashley M.,Royer, Nicole R.,Whisenand, Josh M.,Zoetewey, David L.,Shellhamer, Dale F.
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p. 5022 - 5029
(2008/04/18)
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- On the Mechanism of the Oxidation of Toluenes in Artificial P450 Model Systems: Formation of Benzyl Alcohols, Benzaldehydes and Phenols
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Systems with pentafluoroiodosylbenzene (PFIB) and hemin (FeTPPCl8Cl) in dichloromethane were adopted to study the activities of the model system using toluenes as substrates for P450 enzymes. The oxidation products were mainly corresponding benzyl alcohols and benzaldehydes. Previously reported suspension systems were extended to homogeneous mixed solution systems of CH2Cl2/CH3OH/H2O to study the oxidation of benzyl alcohols to the corresponding benzaldehydes: the Hammett relation with ρ = -0.86 against ?+. As benzaldehydes were scarcely observed in natural P450 systems, the formation of benzaldehyde seemed characteristic only of the "open" model systems. In suspension systems, the product ratios between corresponding benzaldehydes and benzyl alcohols (ald/alc) were about 0.1-0.4, specific to the substituents and conditions applied. Curiously, the ratios (ald/alc) increased with the electronegativity of the substituents on the phenyl rings of the toluene derivatives. Time course experiments in suspension systems indicated that benzyl alcohols and benzaldehydes were formed not stepwise, but simultaneously from toluene. Separate experiments indicated that the reaction of benzyl alcohol to benzaldehyde was four-fold faster than that of toluene to benzyl alcohol. The rate was not enough to elucidate the amount of benzaldehyde. We suggest that the benzyl radical is formed by hydrogen abstraction and is attacked by the second oxidant, PFIB. Rebounding of the hydroxyl radical and the reaction with the oxidant were competitive depending on the conditions. Additionally, small amounts of phenols were formed from toluenes with electron-donating substituents. This was a minor reaction on which the aromatic hydroxylation occurred via epoxidation under the present conditions.
- Nakano, Taku,Kawabata, Sally,Sugihara, Tamami,Agatsuma, Noriko,Kakuda, Hiroko,Mori, Yoshihiro
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p. 2353 - 2360
(2007/10/03)
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- Kinetics of chlorination of phenol and monosubstituted phenols by t-butyl hypochlorite in aqueous alkaline medium
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The kinetics of chlorination of the parent and sixteen monosubstituted phenols (2-chloro, 2-methyl, 2-carboxy, 2-nitro, 3-chloro, 3-methyl, 3-carboxy, 4-fluoro, 4-chloro, 4-bromo, 4-methyl, 4-ethyl, 4-methoxy, 4-carboxy, 4-acetyl and 4-nitro) by t-BuOCl have been studied in aqueous alkaline medium. The rates of reactions show first order kinetics each in |t-BuOCl| and |XC 6H4OH| and inverse first order in |OH-|. Variation in either ionic strength or addition of reaction product has no significant effect on the rates of reactions, while lowering of the dielectric constant of the medium increases the rate. The rates are measured at different temperatures and the activation parameters for all the phenols computed. A mechanism involving the electrophilic attack of phenoxide ions by HOCl in the rate determining step is suggested. The rates decrease in the order: 3-CH 3 > 2-CH3 > 4-OCH3 > 4-CH3 > 4-C2H5 > H > 3-Cl > 3-COO- > 4-F > 2-COO- > 4-Br > 2-Cl > 4-Cl > 4-COO- > 4-COCH3 > 2-NO2 > 4-NO2. Hammett equation of the type, log k = -3.44 - 2.35 ρ is found to be valid for substituent effects. The enthalpy and entropy of activation are correlated.
- Moodithaya,Gowda, B. Thimme
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p. 420 - 425
(2007/10/03)
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- Kinetics and mechanism of chlorination of phenol and substituted phenols by sodium hypochlorite in aqueous alkaline medium
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The kinetics of chlorination of the parent and thirteen substituted phenols (2-methyl, 2-chloro, 2-carboxy, 3-methyl, 3-chloro, 3-carboxy, 4-methyl, 4-ethyl, 4-chloro, 4-bromo, 4-carboxy, 4-acetyl and 4-nitro phenols) by NaOCl have been studied in aqueous alkaline medium under varying conditions. The rates show first order kinetics each in [NaOCl] and [(X)C6H4(OH)] and inverse first order in [OH-]. Variation in ionic strength of the medium and addition of Cl have no significant effect on the rates of reactions. The rates of the reactions are measured at different temperatures and the activation parameters for all the phenols computed. A mechanism involving the electrophilic attack of the phenoxide ions by NaOCl in the rate determining step has been considered. The values of the pre-equilibrium and the rate determining steps have been calculated for all the phenols. The rates decrease in the order: 3-CH3 >2-CH3 >4-C2H5 = 4-CH3 >phenol >3-COO = 3-Cl > 2-COO >4-COO >2-Cl ? 4-Cl ? 4-Br > 4-COCH3 >4-NO2. Hammett plot of the type, log kobs = -2.88 -3.2980σ is found to be valid. The correlation between the enthalpies and the free energies of activations is reasonably linear with an isokinetic temperature of 300 K. Further, the energies of activation of all the phenols are optimised corresponding to the log A of the parent phenol through the equation, Ea = 2.303 RT (log A - log kobs). Similarly log A values of all the phenols are optimised corresponding to the Ea of PhOH through the equation, log A = log kobs + Ea/2.303RT. Ea increases with the introduction of electron-withdrawing groups into the benzene ring, while the introduction of the electron-releasing groups lowers Ea for the reaction. Similarly log A decreases with the substitution of electron-withdrawing groups, while log A increases on substitution with the electron-releasing groups.
- Gowda,Mary
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p. 1196 - 1202
(2007/10/03)
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- Oxidation of benzyl radicals by Fe(CN)63-
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Hydroxyl radicals and their anions [O?- radicals, pK a(?OH) = 11.9] have been generated radiolytically in N2O-saturated aqueous solution and reacted with 4-chlorotoluene. While the ?OH radical mainly produces hydroxycyclohexadienyl- type radicals, the O?- radical practically only abstracts H atoms from the methyl group yielding 4-chlorobenzyl radicals (k = 1.9 x 10 9 dm3 mol-1 s-1; determined by pulse radiolysis). The radicals formed by ?OH radical attack at pH 7 (mainly hydroxycyclohexadienyl-type radicals) are oxidized by Fe(CN) 63- (k = 1.8 x 107 dm3 mol -1 s-1) giving rise to the following products (G values in units of 10-7 mol J-1 are given in parentheses): 4-chloro-2-hydroxytoluene (2.9), 4-chloro-3-hydroxytoluene (2.4), 4-chlorobenzyl alcohol (0.05), 4-chlorobenzaldehyde (0.1) and 4-chloro-2-hydroxybenzaldehyde (0.15). The 4-chlorobenzyl radical is the main species formed at pH 13.7 and is oxidized by Fe(CN)63- with a similar rate constant (k = 4.2 x 107 dm3 mol-1 s-1), the major products being 4-chlorobenzaldehyde (3.7), 4-chloro-2-hydroxybenzaldehyde (0.65) and 4-chlorobenzyl alcohol (0.5). From ?OH radical attack (ca. 10% at this pH), 4-chloro-2-hydroxytoluene (0.4) and 4-chloro-3-hydroxytoluene (0.3) are also formed. It is suggested that the oxidation of the 4-chlorobenzyl radical by Fe(CN)63- yields in the first step a carbocation which cyclizes by deprotonation. The resulting cyclohexadienyl-type radical undergoes β-fragmentation yielding the 4-chlorobenzyloxyl radical. A 1,2-H shift and subsequent oxidation leads to 4-chlorobenzaldehyde. The unsubstituted benzyl radical is also oxidized by Fe(CN)63- yielding benzaldehyde in high yields.
- Merga, Getahun,Schuchmann, Heinz-Peter,Rao, B. S. Madhava,Von Sonntag, Clemens
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p. 551 - 556
(2007/10/03)
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- Single Step Selective Oxidation of para-Chlorotoluene to para-Chlorobenzaldehyde over Vanadium Silicate Molecular Sieves
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Selective formation of para-chlorobenzaldehyde (> 65percent) in a single step from para-chlorotoluene is reported for the first time using H2O2 as an oxidant and vanadium silicate molecular sieves as the catalyst.
- Selvam, T.,Singh, A. P.
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p. 883 - 884
(2007/10/02)
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- Reactions of OH and SO4.- with Some Halobenzenes and Halotoluenes: A Radiation Chemical Study
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The optical absorption and kinetic characteristics of the transients formed in the reactions of OH and SO4.- with bromobenzene, ortho and meta-isomers of chloro- and bromobenzenes, and monobromotoluenes have been studied by pulse radiolysis technique.The rates for OH reaction are generally higher (k = (1.7-4.4)X109 M-1s-1) than those found for the SO4.- reaction (k = (0.4-2.3)x109 M-1s-1). ρ+ values of -0.4 for OH and -1.2 for SO4.- reactions were obtained from the Hammett analysis.The formation of substituted hydroxycyclohexadienyl radicals (λmax = 315-330 nm) is the major reaction channel, and the phenoxyl type radical (λ >/=400 nm) formation is an additional minor process in the SO4.- reaction.Abstraction of H by SO4.- from the -CH3 group is only significant with the para-isomers of bromo- and chlorotoluenes.This result is in accord with the observed yields (70 percent of SO4.-) of the products resulting from the oxidation of the 4-chlorobenzyl radical in the presence of K3Fe(CN)6 under steady-state conditions.The total yields of the phenolic products accounting for >90 percent of OH and SO4.- suggest that the attack at the ipso positions is considerably small.The rate constants for OH reactions relative to benzene at positions 3 and 6 of 2-chlorotoluene and positions 2 and 3 of 4-chlorotoluene are between 1.18 and 1.39, indicating that the directing effects of -CH3 and -Cl groups are comparable.This is also reflected in the additive effects of activation of the ortho and para-positions and deactivation of meta-positions by these substituents in 3-chlorotoluene.
- Merga, Getahun,Rao, B. S. M.,Mohan, H.,Mittal, J. P.
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p. 9158 - 9164
(2007/10/02)
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- PhSeCl AS A CHLORINATING AGENT FOR ACTIVATED BENZENE DERIVATIVES
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Regiospecific chlorination of some aromatic compounds using benzeneselenyl chloride are reported.
- Ayorinde, Folahan O.
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p. 2077 - 2078
(2007/10/02)
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