- Regioselective supramolecular catalysis. Exploiting multiple binding motifs in propanediurea molecular clips
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Molecular clips derived from 2,4,6,8-tetraazabicyclo[3.3.1]nonane-3,7-dione promote increased regioselectivity in the SO2Cl2-mediated electrophilic aromatic chlorination of ortho-cresol leading to para/ortho ratios (Rp/o) 25; approximately six times larger than in the absence of the clip. Specific recognition events involving hydrogen-bond, π-π and dative covalent interactions are implicated.
- Bugnet, Emmanuelle A.,Nixon, Tracy D.,Kilner, Colin A.,Greatrex, Robert,Kee, Terence P.
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- Direct and induced phototransformation of mecoprop [2-(4-chloro-2-methylphenoxy)-propionic acid] in aqueous solution
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Mecoprop was irradiated under various conditions of pH, oxygenation and wavelengths in order to study the reactions involved in the phototransformation. Four main photoproducts were identified: 2-(4-hydroxy-2-methylphenoxy)propionic acid (I), o-cresol (II), 2-(5-chloro-2-hydroxy-3-methylphenyl)propionic acid (III) and 4-chloro-o-cresol (IV). When the anionic form of mecoprop was irradiated between 254 nm and 310 nm (UV-C or UV-B), I was the main photoproduct. At 254 nm its formation initially accounted for more than 80 percent of the transformation. It has not previously been reported in the literature. The reaction results from a heterolytic photohydrolysis. Product II accounted for only a low percentage of the transformation. The stoichiometry was different with the molecular form: the main photoproduct, III, resulted from a rearrangement after a homolytic scission. Products I, II and IV were also formed as minor photoproducts. Some other minor photoproducts were also identified. In contrast, IV was the main photoproduct under sunlight irradiation or when solutions were irradiated in near-UV light (UV-A). This wavelength effect is attributed to the involvement of an induced phototransformation; IV is also the main photoproduct when the phototransformation is induced by Fe(III) perchlorate or nitrite ions. In usual environmental conditions the excitation of the molecular form is negligible and the phototransformation is mainly due to induced photoreactions.
- Meunier, Laurence,Boule, Pierre
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Read Online
- 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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Read Online
- Application of two morphologies of Mn2O3for efficient catalyticortho-methylation of 4-chlorophenol
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Vapor phaseortho-methylation of 4-chlorophenol with methanol was studied over Mn2O3catalyst with two kinds of morphologies. Here, Mn2O3was prepared by a precipitation and hydrothermal method, and showed the morphology of nanoparticles and nanowires, respectively. XRD characterization and BET results showed that, with the increase of calcination temperature, Mn2O3had a higher crystallinity and a smaller specific surface area. N2adsorption/desorption and TPD measurements indicated that Mn2O3nanowires possessed larger external surface areas and more abundant acid and base sites. Simultaneously, in the fixed bed reactor, methanol was used as the methylation reagent for theortho-methylation reaction of 4-chlorophenol. XRD, XPS, TG-MS and other characterizations made it clear that methanol reduced 4-chlorophenol and its methide, which were the main side-reactions. And Mn3+was reduced to Mn2+under the reaction conditions. Changing the carrier gas N2to a H2/Ar mixture further verified that the hydrogen generated by the decomposition of methanol was not the reason for dechlorination of 4-chlorophenol compounds. Here we summarized the progress of 4-chlorophenol methylation based on the methylation of phenol. Also, we proposed a mechanism of the 4-chlorophenol dechlorination effect which was similar to the Meerwein-Ponndorf-Verley-type (MPV) reaction. The crystal phase and carbon deposition were investigated in different reaction periods by XRD and TG-DTA. The reaction conditions for the two kinds of morphologies of the Mn2O3catalyst such as calcination temperature, reaction temperature, phenol-methanol ratio and reaction space velocity were optimized.
- Gui, Wenying,Liu, Xiaofei,Wang, Zhenlu,Zhang, Chunlei,Zhang, Hongqiang,Zhang, Li,Zhu, Wanchun
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p. 20836 - 20849
(2021/07/01)
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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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- Directed Structural Transformations of Coordination Polymers Supported Single-Site Cu(II) Catalysts to Control the Site Selectivity of C-H Halogenation
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A main difficulty in C-H bond functionalization is to undertake the catalyst control accurately where the reaction takes place. In this work, to achieve highly effective and regioselective single-site catalysts, a three-dimensional (3D) rhombus-like framework of {[Mn(Hidbt)DMF]·H2O}n (1) [H3idbt = 5,5′-(1H-imidazole-4,5-diyl)-bis(2H-tetrazole)] containing coordinated DMF molecules was constructed. For the dissolution-recrystallization structural transformation process, attractive structural transformations proceeded from 1 to a new crystalline species formulated as {[Mn3(idbt)2(H2O)2]·3H2O}n (2) with a 3D windowlike architecture, and then the Mn ions in 2 could be exchanged with Cu ions through cation exchange in a single-crystal to single-crystal fashion to produce the Cu-exchanged product {[Mn2Cu(idbt)2(H2O)2]·3H2O}n (2a), which had a windowlike framework like that of 2. Furthermore, 2 and 2a were used as heterogeneous catalysts for the regioselective C-H halogenation of phenols with N-halosuccinimides (NCS and NBS) to produce the site selective single monohalogenated products. It was found that the catalytic activity and site selectivity of 2a were much higher than those of 2, because the unique structural features of 2a with the uniformly dispersed CuII active centers served as a single-site catalyst with a site-isolated and well-defined platform to promote the C-H halogenation reaction in regiocontrol and guide an orientation that favored the para selectivity during the reaction process.
- Huang, Chao,Zhu, Kaifang,Zhang, Yingying,Shao, Zhichao,Wang, Dandan,Mi, Liwei,Hou, Hongwei
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supporting information
p. 12933 - 12942
(2019/10/11)
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- Catalytic activation of unstrained C(aryl)–C(aryl) bonds in 2,2′-biphenols
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Transition metal catalysis has emerged as an important means for C–C activation that allows mild and selective transformations. However, the current scope of C–C bonds that can be activated is primarily restricted to either highly strained systems or more polarized C–C bonds. In contrast, the catalytic activation of non-polar and unstrained C–C moieties remains an unmet challenge. Here we report a general approach for the catalytic activation of the unstrained C(aryl)–C(aryl) bonds in 2,2′-biphenols. The key is to utilize the phenol moiety as a handle to install phosphinites as a recyclable directing group. Using hydrogen gas as the reductant, monophenols are obtained with a low catalyst loading and high functional group tolerance. This approach is also applied to the synthesis of 2,3,4-trisubstituted phenols. A further mechanistic study suggests that the C–C activation step is mediated by a rhodium(i) monohydride species. Finally, a preliminary study on breaking the inert biphenolic moieties in lignin models is illustrated.
- Zhu, Jun,Wang, Jianchun,Dong, Guangbin
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- Regioselective synthesis of important chlorophenols in the presence of methylthioalkanes with remote SMe, OMe or OH substituents
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Various methylthio alcohols, methoxy(methylthio)alkanes and bis(methylthio)alkanes have been used as regioselectivity modifiers in the chlorination reactions of various phenols at room temperature. The process involves the use of a slight excess of sulfuryl chloride in the presence of aluminum or ferric chloride as an activator. Methylthio alcohols, methoxy(methylthio)alkanes and bis(methylthio)alkanes having 2 and 3 methylene groups as a spacer were found to be good for the para-selective chlorination of o-cresol and phenol. On the other hand, methylthio alcohols, methoxy(methylthio)alkanes and bis(methylthio)alkanes having 6 and 9 methylene groups were found to be good for the selective para-chlorination of m-xylenol and m-cresol. Calculations using density functional theory on bis(methylthio)alkanes have suggested two different types of stable chlorinated intermediates depending on the number of methylene units as a spacer.
- Smith, Keith,Al-Zuhairi, Ali J.,Elliott, Mark. C.,El-Hiti, Gamal A.
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p. 607 - 621
(2018/07/13)
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- Rate enhancements due to ultrasound in isoquinolinium dichromate and isoquinolinium chlorochromate catalyzed chlorination of aromatic compounds in presence of KHSO4/KCl
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Chlorination of aromatic compounds underwent magnificent rate accelerations in isoquinolinium dichromate and isoquinolinium chlorochromate catalyzed chlorination of aromatic hydrocarbons in the presence of KCl and KHSO4. Reaction times reduced highly significantly from 4-5 h in conventional protocol to 30-40 min under sonication, followed by high yields of monochloro derivatives as products with high regioselectivity.
- Rajanna,Rao, A. Sambashiva,Chakravarthi,Reddy, K. Rajendar
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p. 167 - 170
(2017/12/26)
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- Dimethylglyoxime as an efficient ligand for copper-catalyzed hydroxylation of aryl halides
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The CuI/dimethylglyoxime (CuI/DMG) catalyzed direct hydroxylation of aryl iodides with CsOH takes place at 120°C in a mixed solvent system (DMSO–H 2O ,1:1), afforded the corresponding phenols in good to excellent yield. Aryl bromides are found to be less reactive than aryl iodides under these reaction conditions. Graphical Abstract: SYNOPSIS. (CuI/DMG) catalyzed synthesis of phenol from aryl iodide and aryl bromide in presence of mixed solvents (H 2O : DMSO) is reported in this paper. This protocol is general, economical, easy and convenient for transformation of aryl iodides and bromides to substituted phenols under mild reaction conditions. [Figure not available: see fulltext.].
- Shendage, Suresh S
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- Silica chloride: An efficient promoter for oxidation of arylboronic acids to phenols
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This work reports simple, highly efficient protocol for the oxidation of arylboronic acids. Various arylboronic acids were selectively and completely converted into their corresponding oxidized phenols using H2O2 as an oxidant in presence of catalytic amount of silica chloride. The results show that silica chloride is a suitable and efficient promoter for the oxidation of arylboronic acids. Heterogeneous catalyst, mild reaction conditions, easy availability of the reagent, easy work-up, excellent yield of corresponding phenols, short reaction time and broad substrate scope makes this protocol attractive and a practical alternative to the existing methods.
- Wagh, Ravindra B.,Nagarkar, Jayashree M.
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supporting information
p. 3323 - 3326
(2017/07/27)
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- Method for synthesizing high-content 2-methyl-4-chloric acid and sodium salt
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The invention discloses a method for synthesizing high-content 2-methyl-4-chloric acid and sodium salt. The method comprises the following steps: synthesizing 4-chloro-methylphenol from sulfuryl chloride by using a chlorination process, carrying out condensation with sodium chloroacetate, and drying filter cake, thereby obtaining sodium salt directly, or directly acidifying the filter cake, thereby obtaining 98% 2-methyl-4-chloric acid. Hydrochloric acid generated in the chlorination process can be recycled to an acidification procedure, and generated sulfur dioxide is further reacted with chlorine to prepare sulfuryl chloride which can be recycled for a chlorination procedure, so that a closed circulation green production process can be formed, and the product quality can be relatively greatly improved. According to the method, the cost is relatively low and the pollution is relatively slight, the equipment utilization rate is greatly increased, meanwhile the problem that the content is low if o-cresol is chloridized with chlorine can be solved, and a basis is made for producing 2-methyl-4-chloric acid through chlorination and condensation in sequence.
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Paragraph 0027; 0028; 0029
(2017/02/28)
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- Method for synthesizing chlorophenoxyacetic acid or chlorophenol
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The invention relates to a method for synthesizing chlorophenoxyacetic acid or chlorophenol. The method comprises: (1) heating and melting phenol, methylphenol, phenoxyacetic acid or 2-methylphenoxyacetic acid or adding a solvent to dissolve phenol, methylphenol, phenoxyacetic acid or 2-methylphenoxyacetic acid; and (2) heating the material obtained in the step (1) to achieve a reaction temperature, introducing chlorine gas, adding hydrogen peroxide when the introduced chlorine gas accounts 2-50% of the total introducing amount, and oxidizing hydrogen chloride to generate chlorine gas so as to be recycled. According to the present invention, with the synthesis method, the amount of the by-produced hydrogen chloride is substantially reduced, and the chlorination selectivity of the late-stage reaction is improved.
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Paragraph 0034; 0035
(2018/04/02)
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- Iron(III)-Catalyzed Chlorination of Activated Arenes
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A general and regioselective method for the chlorination of activated arenes has been developed. The transformation uses iron(III) triflimide as a powerful Lewis acid for the activation of N-chlorosuccinimide and the subsequent chlorination of a wide range of anisole, aniline, acetanilide, and phenol derivatives. The reaction was utilized for the late-stage mono- and dichlorination of a range of target compounds such as the natural product nitrofungin, the antibacterial agent chloroxylenol, and the herbicide chloroxynil. The facile nature of this transformation was demonstrated with the development of one-pot, tandem, iron-catalyzed dihalogenation processes allowing highly regioselective formation of different carbon-halogen bonds. The synthetic utility of the resulting dihalogenated aryl compounds as building blocks was established with the synthesis of natural products and pharmaceutically relevant targets.
- Mostafa, Mohamed A. B.,Bowley, Rosalind M.,Racys, Daugirdas T.,Henry, Martyn C.,Sutherland, Andrew
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p. 7529 - 7537
(2017/07/26)
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- Highly Selective Synthesis of Chlorophenols under Microwave Irradiation
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Oxychlorination of various phenols is finished in 60 minutes with high efficiency and perfect selectivity under microwave irradiation. These reactions adopt copper(II) chloride (CuCl2) as the catalyst and hydrochloric acid as chlorine source instead of expensive and toxic ones. Oxychlorination of phenols substituted with electron donating groups (methyl, methoxyl, isopropyl, etc.) at ortho- and meta-positions is accomplished with higher conversion rates, lower reaction time, and excellent selectivity. A proposed reaction mechanism is deduced; one electron transfers from CuCl2 to phenol followed by the formation of tautomeric radical that can be rapidly captured by chlorine atom and converts into para-substituted product.
- Xiong, Yawen,Duan, Hongdong,Meng, Xia,Ding, Zhaoyun,Feng, Weichun
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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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- Synthesis of deuterated benzopyran derivatives as selective COX-2 inhibitors with improved pharmacokinetic properties
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We designed a series of specifically deuterated benzopyran analogues as new COX-2 inhibitors with the aim of improving their pharmacokinetic properties. As expected, the deuterated compounds retained potency and selectivity for COX-2. The new molecules possess improved pharmacokinetic profiles in rats compared to their nondeuterated congeners. Most importantly, the new compounds showed pharmacodynamic efficacy in several murine models of inflammation and pain. The benzopyran derivatives were separated into their enantiomers, and the activity was found to reside with the S-isomers. To streamline the synthesis of the desired S-isomers, an organocatalytic asymmetric domino oxa-Michael/aldol condensation reaction was developed for their preparation.
- Zhang, Yanmei,Tortorella, Micky D.,Wang, Yican,Liu, Jianqi,Tu, Zhengchao,Liu, Xiaorong,Bai, Yang,Wen, Dingsheng,Lu, Xin,Lu, Yongzhi,Talley, John J.
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p. 1162 - 1166
(2014/12/10)
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- Mild and rapid hydroxylation of aryl/heteroaryl boronic acids and boronate esters with N-oxides
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Aryl and heteroaryl boronic acids and boronate esters are rapidly, often within minutes, transformed into the corresponding phenols by N-oxides in an open flask at ambient temperature. This transformation has broad compatibility with a variety of functional groups.
- Zhu, Chen,Wang, Rui,Falck
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supporting information; experimental part
p. 3494 - 3497
(2012/08/28)
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- The phototransformation of 4-chloro-2-methylphenoxyacetic acid under KrCl and XeBr excilamps irradiation in water
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The effect of UV radiation of a KrCl and a XeBr on the photodegradation of 4-chloro-2-methylphenoxyacetic acid (MCPA) was studied. The main photoproducts were identified by gas chromatograph/mass spectrometry (GC/MS). The variation of chlorine-ion and active chlorine in MCPA aqueous solution exposed to excilamp radiation was also defined by analytical methods. Irradiation of MCPA solution with a KrCl excilamp emitting mainly at 222 nm yield 2-methylhydroquinone and lactone of 2-hydroxy-3-methyl-5-chlorophenoxyacetic acid as the main photoproducts. Irradiation of MCPA solution with a XeBr excilamp emitting mainly at 283 nm yield 2-methylhydroquinone as the main photoproduct. Biological processes are not suitable for MCPA removal due to low or total absence of biodegradability of this class of pollutants. Estimation of biodegradability of phototreated MCPA solution was carried out according to ratios of biological oxygen demand (BOD5) to chemical oxygen demand (COD). The biodegradability of MCPA solutions increased after irradiation.
- Tchaikovskaya, Olga N.,Karetnikova, Elena A.,Sokolova, Irina V.,Mayer, Georgy V.,Shvornev, Dmitry A.
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experimental part
p. 8 - 14
(2012/04/10)
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- Cu-Mn spinel oxide catalyzed regioselective halogenation of phenols and N-heteroarenes
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A novel simple, mild chemo- and regioselective method has been developed for the halogenation of phenols using Cu-Mn spinel oxide as a catalyst and N-halosuccinimide as halogenating agent. In the presence of Cu-Mn spinel oxide B, both electron-withdrawing and electron-donating groups bearing phenols gave monohalogenated products in good to excellent yields with highest para-selectivity. The para-substituted phenol gave monohalogenated product with good yield and ortho-selectivity. N-Heteroarenes such as indoles and imidazoles also gave monohalogenated products with high selectivity. Unlike the copper-catalyzed halogenation, the present method works well with electron-withdrawing group bearing phenols and gives comparatively better yields and selectivity. The Cu-Mn spinel catalyst is robust and reused three times under optimized conditions without any loss in catalytic activity. Nonphenolics did not undergo this transformation.
- Singh, Parvinder Pal,Thatikonda, Thanusha,Kumar, K. A. Aravinda,Sawant, Sanghapal D.,Singh, Baldev,Sharma, Amit Kumar,Sharma,Singh, Deepika,Vishwakarma, Ram A.
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scheme or table
p. 5823 - 5828
(2012/09/05)
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- Bifunctional Aryloxylate Esters as potential oxidatively cleavable linkers
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Selectively cleavable linkers are essential parts in environmentally responsive materials. Here, we introduce aryl oxalate esters (AOE) as one of the first examples for oxidatively cleavable linkers. To this end a series of novel AOEs was synthesized and explored regarding the H2O 2-dependent degradation. All AOEs were cleaved selectively at the oxalate group. The degradation rate was clearly dependent on the substituents. Further, it was found that the H2O2 based degradation undergoes an autocatalysis mechanism.
- Czarnecki,Kampert,Barbe,Tiller
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scheme or table
p. 3551 - 3554
(2011/07/29)
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- Simple and efficient method for the halogenation of oxygenated aromatic compounds
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An efficient and mild method for the chlorination and bromination of oxygenated aromatics, with good regioselectivity and excellent yields, using a combination of HX/H2O2/AcOH in petroleum ether is presented. The effect of ultrasound was investigated. Georg Thieme Verlag Stuttgart ? New York.
- Koini, Eftychia N.,Avlonitis, Nicolaos,Calogeropoulou, Theodora
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experimental part
p. 1537 - 1542
(2011/08/03)
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- Arylsilane oxidation - New routes to hydroxylated aromatics
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An efficient route to hydroxylated aromatics has been developed, via the oxidation of aryl organosilanes under functional group-tolerant and relatively mild conditions, using sub-stoichiometric amounts of fluoride promoters.
- Bracegirdle, Sonia,Anderson, Edward A.
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supporting information; experimental part
p. 3454 - 3456
(2010/07/16)
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- Spectral and GC-MS analysis of phototransformation of herbicides in water
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The phototransformation of 2,4-dichlorophenoxyacetic and 2-methyl-4-chlorophenoxyacetic acids in water was studied using the KrCl*(λrad 222 nm) and XeBr*(λrad 283 nm) excilamps as UV radiation source.
- Chaikovskaya,Sokolova,Karetnikova,Mal'Kov,Kuz'Mina
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experimental part
p. 396 - 401
(2009/07/10)
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- High ortho preference in Ni-catalyzed cross-coupling of halophenols with alkyl Grignard reagents
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(Chemical Equation Presented) High preference of substitution at the position ortho to the hydroxy group was observed for Ni-catalyzed cross-coupling reactions of dihalophenols with alkyl Grignard reagents. Reactions of 2,4-dihalophenols, with various com
- Wang, Jia-Rui,Manabe, Kei
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supporting information; experimental part
p. 741 - 744
(2009/08/07)
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- An easy two-step reduction of salicylic acids and alcohols to 2-methylphenols
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Salicylic acids and alcohols can be reduced to 2-methylphenols by a simple two steps procedure. Reaction conditions were optimized carrying out a study on the solvent effect and the amount of the reducing agent. The improved procedure resulted particularly useful in the synthesis of deuterated building blocks of biological interest. Georg Thieme Verlag Stuttgart.
- Mazzini, Francesco,Salvadori, Piero
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p. 2479 - 2481
(2007/10/03)
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- A simple, efficient and regioselective oxychlorination of aromatic compounds using ammonium chloride and oxone
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A simple, efficient, mild and regioselective method for oxychlorination of aromatic compounds is reported. The electrophilic substitution of chlorine generated in situ from NH4Cl as a chlorine source and oxone as an oxidant is reported for the first time.
- Narender,Mohan, K.V.V. Krishna,Srinivasu,Kulkarni,Raghavan
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p. 1335 - 1338
(2007/10/03)
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- On the para-selective chlorination of ortho-cresol
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Merrifield-bound o-cresol undergoes electrophilic aromatic chlorination using SO2Cl2 leading to para/ortho ratios in excess of 50, the highest such ratio reported for this chlorinating agent. Model studies suggest that this significant para/ortho ratio results not just from steric effects but that considerable electronic influence can be detected.
- Bugnet, Emmanuelle A,Brough, Adrian R,Greatrex, Robert,Kee, Terence P
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p. 8059 - 8065
(2007/10/03)
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- OH-radical induced oxidation of phenoxyacetic acid and 2,4-dichlorophenoxyacetic acid. Primary radical steps and products
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The reactions of ·OH radicals with 2,4-dichlorophenoxyacetic acid (2,4-D), k = (6.6 ± 0.5) × 109 M-1 s-1, phenoxyacetic acid (PAA), k = (10 ± 1) × 109 M-1 s-1, and 2,4-dichlorophenol (2,4-DCP), k = (7.1 ± 0.5) × 109 M-1 s-1, have been studied using pulse and gamma radiolysis. The ·OH adducts produced by addition to the ring at positions not occupied by substituted groups were oxidized by K3[Fe(CN)6], with the corresponding hydroxylated species analyzed by HPLC. The distribution of ·OH radical addition to the aromatic ring of 2,4-D is C1, 17%; C2/C4, 20%; C3/C5/C6, 47%; and for ·OH reaction with PAA, it is C1, 5.5%; C2/C6, 45%; C3/C5, 11%; C4, 36%. Whereas the hydroxycyclohexadienyl radicals of 2,4-D have no observable reactivity toward oxygen, those of PAA and 2,4-DCP do react, with k(·OH adduct-PAA) + O2 = (5.1 ± 0.2) × 108 M-1 s-1 and k(·OH adduct-2,4-DCP) + O2 = (1.1 ± 0.1) × 108 M-1 s-1. The phenoxyl radicals formed by chloride elimination from the ipso-chloro-·OH adducts of 2,4-D rapidly oxidize TMPD to TMPD·+, k = (3.6 ± 0.5) × 109 M-1 s-1.
- Zona, Robert,Solar, Sonja,Sehested, Knud,Holcman, Jerzy,Mezyk, Stephen P.
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p. 6743 - 6749
(2007/10/03)
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- Highly efficient, para-selective oxychlorination of aromatic compounds using potassium chloride and Oxone
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A highly efficient, regioselective method for oxychlorination of aromatic compounds is possible through electrophilic substitution of chlorine generated in situ from KCl as a chlorine source and Oxone as an oxidant for the first time.
- Narender,Srinivasu,Kulkarni,Raghavan
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p. 279 - 286
(2007/10/03)
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- N-Chloro-2,3,4,4,5,6-hexachlorocyclohexa-2,5-dienylideneamine as a mild and highly regioselective chlorinating reagent
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N-Chloro-2,3,4,4,5,6-hexachlorocyclohexa-2,5-dienylideneamine was used as a new, mild and highly regioselective chlorinating reagent in the chlorination of phenol and o-cresol in CCl4, DMF and CH3CN. The effects of C2H5OH, C5H5N, DMF and Et3N on the regioselectivity in CCl4 have also been examined.
- Mamaghani,Zolfigol,Shojaei
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p. 735 - 740
(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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- Phototransformation of 4-chloro-2-methylphenoxy acetic acid (MCPA)
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MCPA was irradiated in various conditions: in aqueous solution at different wavelengths, on silica in the absence of water, in the presence of TiO2 in aqueous suspension. In solution a wavelength effect was observed: the formation of 4-hydroxy-2-methylphen-oxyacetic acid is the main pathway at wavelengths shorter than 300 nm, whereas 4-chloro-2-methylphenol is the main product resulting from sunlight irradiation. Direct photolysis on silica and photocatalytic transformation mainly lead to the formation of 4-chloro-2-methylphenol. by Oldenbourg Wissenschaftsverlag, Mu?nchen.
- Zertal,Sehili,Boule
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- Transition metal-catalyzed oxidations. 11 : Para-selective chlorination and bromination of phenols with tert-butyl hydroperoxide and TiX(OiPr)3
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Mononuclear phenols 1-4 are chlorinated or brominated with high para-selectivity and in good yields to the halides 5-11 with the TiXn(OiPr)m/TBHP system (X = Cl or Br). WILEY-VCH Verlag GmbH, 1999.
- Krohn, Karsten,Rieger, Hagen,Steingroever, Klaus,Vinke, Ingeborg
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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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- ORTHO-METHYLATION OF PHENOLS WITH ETHYL(IODOMETHYL)ZINC
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The regioselective ortho-methylation of phenols by in situ generated ethyl(iodomethyl)zinc via an internal alkylation process is described.
- Lehnert, Erich K.,Sawyer, J. Scott,Macdonald, Timothy L.
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p. 5215 - 5218
(2007/10/02)
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- Highly Selective Aromatic Chlorination. Part 3. Kinetics and Mechanism of Chlorination of Electron-rich Aromatic Compounds by N-Chloroamines in Acidic Solution
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The highly selective chlorination of electron-rich aromatic compounds with N-chloroamines in trifluoroacetic acid (TFA) is first order in both the aromatic substrate and the chlorinating agent.Kinetic and competitive kinetic studies show that electron-donating substituents on the substrate and electron-withdrawing substituents on the N-chloroamine have a marked rate-enhancing effect.Two mechanisms that fit the experimentally observed kinetics and that account for the high selectivity for 4-chlorination in terms of an electronic effect are proposed, namely an arenium-ion mechanism and an electron-transfer chain reaction.Evidence from chemical trapping experiments and from other studies suggest that for the majority of the substrates the chlorination proceeds by the arenium ion mechanism.However, for substrates, such as 1,4-dimethoxybenzene, that are very susceptible to one-electron oxidation chlorination may proceed at least in part by the electron-transfer chain reaction.
- Smith, John R. Lindsay,McKeer, Linda C.,Taylor, Jonathan M.
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p. 1529 - 1536
(2007/10/02)
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- HIGH ORTHO-SELECTIVITY IN THE CHLORINATION OF PHENOLS WITH N-CHLORODIALKYLAMINES IN THE PRESENCE OF SILICA.
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Phenols are readily chlorinated by N-chlorodialkylamines in the presence of silica.Furthermore, this approach allows greater selectivity for mono:di and ortho: para chlorination than is possible with many other approaches.
- Smith, Keith,Butters, Michael,Nay, Barry
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p. 1319 - 1322
(2007/10/02)
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- Highly Selective Aromatic Chlorinations. Part 2. The Chlorination of Substituted Phenols, Anisoles, Anilines, and Related Compounds with N-Chloroamines in Acidic Solution
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Phenols, anisoles, anilines, and related compounds are chlorinated in trifluoroacetic acid at room temperature by N-chlorodialkylamines and N-chlorotrialkylammonium salts.With monsubstituted compounds and their 2- and 3-substituted derivatives the reaction occurs efficiently and selectively at the 4-position.The reactivity of these substrates and the selectivity of their chlorinations are determined by electronic rather than steric effects of the substituent.Blocking the reaction with a substituent at the 4-position generally leads to only poor or moderate yields of the 2-chlorinated product.Evidence for radical and cation radical intermediates has been obtained in the reactions of some of the 4-substituted reactants and the mechanism of chlorination is discussed in the light of these findings.The reactions of selected substrates have been scaled up to give laboratory syntheses.
- Smith, John R. Lindsay,McKeer, Linda C.,Taylor, Jonathan M.
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p. 385 - 392
(2007/10/02)
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- Synthetic Methods and Reactions; 127. Regioselective para Halogenation of Phenols, Phenol Ethers and Anilines with Halodimethylsulfonium Halides
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Halodimethylsulfonium halides are efficient regioselective para halogenating agent for activated aromatics, such as phenol, anisole, diphenyl ether and N-alkylanilines.Dihalo and monohalo derivatives of diphenyl ethers were obtained depending upon the reaction conditions.Aniline itself is not suitable in the reaction due to the strong complexation of the lone electron pair of nitrogen with the sulfonium reagent.
- Olah, George A.,Ohannesian, Lena,Arvanaghi, Massoud
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p. 868 - 870
(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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- HIGH SITE-SELECTIVITY IN THE CHLORINATION OF ELECTRON-RICH AROMATIC COMPOUNDS BY N-CHLORAMMONIUM SALTS.
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N-Chlorammonium salts are efficient and very site-selective monochlorinating agents for electron-rich aromatic compounds.
- Smith, John R. Lindsay,McKeer, Linda C.
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p. 3117 - 3120
(2007/10/02)
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- HALOGENATION REGIOSELECTIVE EN SERIE AROMATIQUE-I CHLORATION DES PHENOLS ET LEURS ETHERS A L'AIDE DE REACTIFS METTANT EN JEU DES INTERACTIONS DONNEUR-ACCEPTEUR
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An efficient regiospecific route for the chlorination of phenol involving hexachlorohexadienones is described.The selectivity is attained by using a reagent tailored in such a way that it is able to participate in charge transfer interactions and hydrogen bonding with the substrate.This recognition between substrate (phenol) and 2,3,4,4,5,6-hexachlorocyclohexa 2,5-dien 1-one 1 which we called "reactif p" allows the chlorination of phenol in the para position.The use of 2,3,4,5,6,6-hexachlorocyclohexa 2,4-dien-1 one 2 we have called "reactif o" permits the chlorination in the ortho position.These two reagents are stable and inexpensive materials, synthetized from pentachlorophenol and chlorine.The chlorination of anisole with these two reagents, gives solely the parachloro derivative, under steric control.
- Guy, Alain,Lemaire, Marc,Guette, Jean-Paul
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p. 2339 - 2346
(2007/10/02)
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- Reactions of Alkyl-lithium Compounds with Aryl Halides
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Reation of methyl-lithium with tribromophenols and with other aryl polyhalides leads directly to bi- and tri-aryl products. para-Substituents (Y) of 2,6-dibromo-4-Y-phenols promote arylation of substrates by their own lithiation products as Y becomes more electron-withdrawing.An aryne epoxide is not an intermediate in these reactions. 2,4,6-Tribromo-Z-benzenes react to form coupling products when Z can co-ordinate to an introduced ortho-lithium atom or when Z can be directly lithiated.Dimeric aggregation of the organolithium intermediates occurs so as to favor coupling to halogenated substrates.Both polar (ionic) and free-radical pathways are involved.
- Huddle, Penelope A.,Perold, Guido W.
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p. 2617 - 2625
(2007/10/02)
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- Regiospecific Chlorination of Aromatic Substrates using Donor-Acceptor and Hydrogen Bonding Interactions
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The chlorination of aromatic substances has been achieved with good regioselectivity using 2,3,4,4,5,6-hexachlorocyclohexa-2,5-dien-1-one and 2,3,4,5,6,6-hexachlorocyclohexa-2,4-dien-1-one as chlorinating agents.
- Guy, Alain,Lemaire, Marc,Guette, Jean-Paul
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- Phenol transalkylation process
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Phenols having an unsubstituted ortho position are transalkylated in the ortho position by mixing them with an ortho-alpha-branched alkylphenol (e.g., 2,6-di-sec-butylphenol) and an aluminum phenoxide catalyst and heating the mixture to 100°-350°C., preferably in a closed system and in the presence of olefin corresponding in structure to the ortho-alpha-branched alkyl group.
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