Xn:Harmful;
106-41-2Relevant articles and documents
Synthesis of Phenols: Organophotoredox/Nickel Dual Catalytic Hydroxylation of Aryl Halides with Water
Yang, Liu,Huang, Zhiyan,Li, Gang,Zhang, Wei,Cao, Rui,Wang, Chao,Xiao, Jianliang,Xue, Dong
, p. 1968 - 1972 (2018)
A highly effective hydroxylation reaction of aryl halides with water under synergistic organophotoredox and nickel catalysis is reported. The OH group of the resulting phenols originates from water, following deprotonation facilitated by an intramolecular base group on the ligand. Significantly, aryl bromides as well as less reactive aryl chlorides served as effective substrates to afford phenols with a wide range of functional groups. Without the need for a strong inorganic base or an expensive noble-metal catalyst, this process can be applied to the efficient preparation of diverse phenols and enables the hydroxylation of multifunctional pharmaceutically relevant aryl halides.
Untersuchungen zur H-Brueckenassoziation von Azaaromaten mit OH-Bruecken-II. H-Brueckenassoziationgleichgewichte von 1,2,7,8-Dibenzacridin mit verschiedenen OH-Donatoren: Ein Vergleich ir-Spektroskopischer und uv-vis-Spektroskopischer Messungen
Juffernbruch, J.,Perkampus, H.-H.
, p. 1093 - 1096 (1983)
The equilibrium of association of 1,2,7,8-dibenzacridine with 7 different OH-donors was investigated in CCl4 as solvent.The results show, that the values measured by infrared spectroscopy as well as by uv-vis-spectroscopy are identical within the respective accuracy limits.
Flavin-Dependent Halogenases from Xanthomonas campestris pv. campestris B100 Prefer Bromination over Chlorination
Ismail, Mohamed,Frese, Marcel,Patschkowski, Thomas,Ortseifen, Vera,Niehaus, Karsten,Sewald, Norbert
, p. 2475 - 2486 (2019)
Flavin-dependent halogenases selectively introduce halogen substituents into (hetero-)aromatic substrates and require only molecular oxygen and halide salts for this regioselective oxidative CH-functionalization. Genomic analysis of Xanthomonas campestris pv. campestris B100 identified three novel putative members of this enzyme class. They were shown to introduce halogen substituents into, e. g., substituted indoles, while preferring bromide over chloride. (Figure presented.).
Ultrasonically assisted halogenation of aromatic compounds using isoquinolinium bound hypervalent chromium and tetrabutylammonium halides in PEG-600 solutions under acid free and solvent-free conditions
Sambashiva Rao,Ramesh, Kola,Rajanna,Chakrvarthi
, p. 1892 - 1896 (2018)
Isoquinolinium bound Cr(VI) reagents like isoquinolinium dichromate (IQDC) and isoquinolinium chlorochromate (IQCC) have been successfully accomplished as efficient reagents for oxidative halogenation of aromatic compounds using tetrabutylammonium halide (TBAX) as halogenating agents in aqueous polyethylene glycol (PEG-600) under acid free conditions. Tetrabutylammonium bromide (TBAB) has been used for bromination and tetrabutylammonium iodide (TBAI) for iodination. The halogenation reactions that occurred smoothly in 2 to 7 h under conventional conditions are accelerated magnificently under sonication with few minutes (25 to 70 min) of reaction time and fairly good yields. The reactions occurred at moderate temperature under mild and environmentally safe conditions with simple work up.
Organic hypervalent iodine(III) catalyzed ipso-hydroxylation of aryl- and alkylboronic acids/esters
Chatterjee, Nachiketa,Goswami, Avijit
, p. 1524 - 1527 (2015)
An organo-hypervalent iodine(III) catalyzed highly efficient methodology for ipso-hydroxylation of diversely functionalized aryl- and alkylboronic acids/esters has been developed using NaIO4 as a co-oxidant. This protocol is also applicable to N-heterocyclic boronic acids and esters. Further mechanistic studies revealed that the organoboronic acid (an electron demanding moiety) is acting as a nucleophile in the presence of hypervalent iodine for hydroxylation reactions. In summary, this is the first Letter of a generalized route for organic hypervalent iodine(III) catalyzed hydroxylation of organoboronic compounds.
Solar-driven conversion of arylboronic acids to phenols using metal-free heterogeneous photocatalysts
Xu, Tiefeng,Lu, Wangyang,Wu, Xiao-Feng,Chen, Wenxing
, p. 63 - 67 (2019)
Solar-driven conversion of arylboronic acids to phenols was achieved by employing graphitic carbon nitride (g-C3N4) as heterogeneous photocatalyst, where [rad]O2? was the main active species. By loading g-C3N4 onto the easy weaving low melting point sheath-core composite polyester fibers (LMPET), g-C3N4-based artificial photosynthetic catalytic fabric (g-C3N4/LMPET) with a large light receiving area was prepared. It displayed the efficient conversion of arylboronic acid and excellent recycling performance. This system offers more possibilities to construct an artificial photosynthetic system with excellent solar-to-chemicals conversion efficiency.
Transition metal-catalyzed oxidations. 11 : Para-selective chlorination and bromination of phenols with tert-butyl hydroperoxide and TiX(OiPr)3
Krohn, Karsten,Rieger, Hagen,Steingroever, Klaus,Vinke, Ingeborg
, p. 59 - 61 (1999)
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.
A comparative study of the hydrolysis pathways of substituted aryl phosphoramidate versus aryl thiophosphoramidate derivatives of stavudine
Venkatachalam,Yu,Samuel,Qazi,Pendergrass,Uckun
, p. 665 - 683 (2004)
A comparative study of aryl phosphoramidate and aryl thiophosphoramidate derivatives of 2′,3′-didehydro-2′,3′-dideoxythymidine (d4T) was performed. The study focused on the nature of the substituents and the influence of a thiophosphoramidate in the structure of these derivatives. The rate of alkaline hydrolysis of these two types of d4T derivatives indicated that replacement of oxygen with sulfur decreases the rate of hydrolysis by twofold. Additionally, the activation energy (Ea) for the sulfur analogs is comparatively higher than that of the oxygen analogs. Notably, an intermediate was formed in the hydrolysis reaction of the sulfur analogs of d4T that was absent in the case of the oxygen analog, and the tentative structure of the intermediate was proposed based on LC/mass spectroscopy data. Using both HPLC and 31P-NMR techniques, we identified the hydrolysis product of the phosphoramidate derivatives and were able to show in in vitro studies that porcine liver esterase can hydrolyze the methyl ester portion of the phosphoramidate derivatives. Aryl phosphoramidate derivatives of d4T were 1000-fold more active than the corresponding aryl thiophosphoramidate derivatives, indicating that the energy of activation of hydrolysis of these phosphoramidate derivatives plays a significant role in their biological potency.
Rongalite-promoted metal-free aerobic ipso-hydroxylation of arylboronic acids under sunlight: DFT mechanistic studies
Golla, Sivaparwathi,Poshala, Soumya,Pawar, Ravinder,Kokatla, Hari Prasad
, (2020)
A novel rongalite-promoted metal-free aerobic ipso-hydroxylation of arylboronic acids has been developed. This method employs low-cost rongalite as a radical initiator and O2 as a green oxidizing agent for ipso-hydroxylation. This protocol is compatible with a wide variety of functional groups with good to excellent yields at room temperature. Furthermore, mechanistic insight into the role of superoxide radical anions in C-B cleavage has also been provided based on DFT studies.
Highly efficient, recyclable and alternative method of synthesizing phenols from phenylboronic acids using non-endangered metal: Samarium oxide
Yusoff, Hanis Mohd,Bala Chandran, Prasana Devi,Sayuti, Fatin Amira Binti,Kan, Su-Yin,Mohd Radzi, Siti Aisha,Yong, Fu-Siong Julius,Lee, Oon Jew,Chia, Poh Wai
, (2021)
Oxidation of phenylboronic acid to phenol is one of the important industrial processes and it is generally employed in the plastic, explosive and drug manufacturing industries. Over the past decades, numerous efficient methods have been described for the generation of phenols from phenylboronic acids in the presence of oxidant. However, these methods suffered from various limitations, including the use of expensive, toxic reagents and sophisticated protocol to synthesise the phenols. Additionally, some of these reported literatures employed endangered metals, in which mankind is facing the risk of limited supply of these elements in 20 years’ time from now. As such, a viable alternative and green method for achieving organic synthesis is highly sought after by the chemists of today. Herein, we report for the first time a facile, efficient and alternative method in the preparation of phenols from phenylboronic acids using non-endangered metal as catalyst. In all cases, all phenols were afforded in satisfactory yields (81–96%) by employing column-free method. In the recyclability study, the Sm2O3 catalyst was found to possess good catalytic performance, even after being reused for five consecutive times (96–91%). In addition, SEM result revealed that the morphology of the recycled Sm2O3 catalyst was well preserved after five successive uses, which indicate no observable changes occurred in the recovered catalysts. As a final note, the current method is anticipated to be useful for industries manufacturing chemical intermediates as it provides an alternative method of catalysis by using a non-endangered metal in organic transformations.
The Catalyst-Controlled Regiodivergent Chlorination of Phenols
Maddox, Sean M.,Dinh, Andrew N.,Armenta, Felipe,Um, Joann,Gustafson, Jeffrey L.
, p. 5476 - 5479 (2016)
Different catalysts are demonstrated to overcome or augment a substrate's innate regioselectivity. Nagasawa's bis-thiourea catalyst was found to overcome the innate para-selectivity of electrophilic phenol chlorination, yielding ortho-chlorinated phenols that are not readily obtainable via canonical electrophilic chlorinations. Conversely, a phosphine sulfide derived from 2,2′-Bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) was found to enhance the innate para-preference of phenol chlorination.
Accelerated Discovery in Photocatalysis using a Mechanism-Based Screening Method
Hopkinson, Matthew N.,Gómez-Suárez, Adrián,Teders, Michael,Sahoo, Basudev,Glorius, Frank
, p. 4361 - 4366 (2016)
Herein, we report a conceptually novel mechanism-based screening approach to accelerate discovery in photocatalysis. In contrast to most screening methods, which consider reactions as discrete entities, this approach instead focuses on a single constituent mechanistic step of a catalytic reaction. Using luminescence spectroscopy to investigate the key quenching step in photocatalytic reactions, an initial screen of 100 compounds led to the discovery of two promising substrate classes. Moreover, a second, more focused screen provided mechanistic insights useful in developing proof-of-concept reactions. Overall, this fast and straightforward approach both facilitated the discovery and aided the development of new light-promoted reactions and suggests that mechanism-based screening strategies could become useful tools in the hunt for new reactivity. Enlightened! A mechanism-based screening approach can accelerate discovery in photocatalysis. It focuses on a single mechanistic step of a reaction class: the quenching step central to photocatalytic transformations. Luminescence spectroscopy was used to screen 100 compounds, identifying two promising substrate classes. A second, more-focused screen provided mechanistic insights for developing proof-of-concept reactions.
A facile and catalytic method for selective deprotection of tert-butyldimethylsilyl ethers with copper(II) bromide
Bhatt, Suchitra,Nayak, Sandip K.
, p. 8395 - 8399 (2006)
Copper(II) bromide is found to be a simple and efficient catalyst for selective deprotection of tert-butyldimethylsilyl ethers of alcohols/phenols at ambient temperature. Various labile functional groups such as ketal, alkene, ketone, OTBDPS, OTHP and allyl and benzyl ethers are found to be compatible under the reaction conditions.
Lewin,Cohen
, p. 3844,3849 (1967)
Halogenation Using N-Halogenocompounds. I. Effect of Amines on ortho-Bromination of Phenols with NBS
Fujisaki, Shizuo,Eguchi, Hisao,Omura, Atsushi,Okamoto, Atsushi,Nishida, Akiko
, p. 1576 - 1579 (1993)
Primary and secondary amines, especially diisopropylamine and dibutylamine, catalyzed ortho-dibromination of phenol and ortho-monobromination of 2-substituted phenols with NBS in dichloromethane to give selectively 2,6-dibromophenol and 2-bromo-6-sybstituted phenols, respectively.The effective intermediates are inferred to be N-bromoamines.The scope and limitations of the bromination are also presented.
Base-promoted, mild and highly efficient conversion of arylboronic acids into phenols with tert-butyl hydroperoxide
Guo, Shengmei,Lu, Lin,Cai, Hu
, p. 1712 - 1714 (2013)
A mild and efficient protocol for the synthesis of phenols from arylboronic acids has been developed by using tert-butyl hydroperoxide with base as promoter. The corresponding phenols were obtained in good to excellent yields within several minutes. Georg Thieme Verlag Stuttgart New York.
Transformation of diphenyl ethers by Trametes versicolor and characterization of ring cleavage products
Hundt, Kai,Jonas, Ulrike,Hammer, Elke,Schauer, Frieder
, p. 279 - 286 (1999)
The white-rot fungi Trametes versicolor SBUG 1050, DSM 11269 and DSM 11309 are able to oxidize diphenyl ether and its halogenated derivatives 4- bromo- and 4-chlorodiphenyl ether. The products formed from diphenyl ether were 2- and 4-hydroxydiphenyl ether. Both 4-bromo- and 4-chlorodiphenyl ether were transformed to the corresponding products hydroxylated at the non- halogenated ring. Additionally, ring-cleavage products were detected by high performance liquid chromatography and characterized by gas chromatography/mass spectrometry and proton nuclear magnetic resonance spectroscopy. Unhalogenated diphenyl ether was degraded to 2-hydroxy-4- phenoxymuconic acid and 6-carboxy-4-phenoxy-2-pyrone. Brominated derivatives of both these compounds were formed from 4-bromodiphenyl ether, and 4- chlorodiphenyl ether was transformed in the same way to the analogous chlorinated ring cleavage products. Additionally, 4-bromo- and 4-chlorophenol were detected as intermediates from 4-bromo- and 4-chlorodiphenyl ether, respectively. In the presence of the cytochrome-P450 inhibitor 1- aminobenzotriazole, no metabolites were formed by cells of Trametes versicolor from the diphenyl ethers investigated. Cell-free supernatants of whole cultures with high laccase and manganese peroxidase activities were not able to transform the unhydroxylated diphenyl ethers used. The white-rot fungi Trametes versicolor SBUG 1050, DSM 11269 and DSM 11309 are able to oxidize diphenyl ether and its halogenated derivatives 4-bromo- and 4-chlorodiphenyl ether. The products formed from diphenyl ether were 2- and 4-hydroxydiphenyl ether. Both 4-bromo- and 4-chlorodiphenyl ether were transformed to the corresponding products hydroxylated at the non-halogenated ring. Additionally, ring-cleavage products were detected by high performance liquid chromatography and characterized by gas chromatography/mass spectrometry and proton nuclear magnetic resonance spectroscopy. Unhalogenated diphenyl ether was degraded to 2-hydroxy-4-phenoxymuconic acid and 6-carboxy-4-phenoxy-2-pyrone. Brominated derivatives of both these compounds were formed from 4-bromodiphenyl ether, and 4-chlorodiphenyl ether was transformed in the same way to the analogous chlorinated ring cleavage products. Additionally, 4-bromo- and 4-chlorophenol were detected as intermediates from 4-bromo- and 4-chlorodiphenyl ether, respectively. In the presence of the cytochrome-P450 inhibitor 1-aminobenzotriazole, no metabolites were formed by cells of Trametes versicolor from the diphenyl ethers investigated. Cell-free supernatants of whole cultures with high laccase and manganese peroxidase activities were not able to transform the unhydroxylated diphenyl ethers used.
Light-Induced Efficient Hydroxylation of Benzene to Phenol by Quinolinium and Polyoxovanadate-Based Supramolecular Catalysts
Gu, Yaqi,Huang, Yichao,Li, Qi,Wei, Yongge,Yu, Han,Zang, Dejin
, p. 13310 - 13316 (2021)
Direct Hydroxylation of benzene to phenol with high yield and selectivity has been the goal of phenol industrial production. Photocatalysis can serve as a competitive method to realize the hydroxylation of benzene to phenol owing to its cost-effective and environmental friendliness, however it is still a forbidding challenge to obtain good yield, high selectivity and high atom availability meanwhile. Here we show a series of supramolecular catalysts based on alkoxohexavanadate anions and quinolinium ions for the photocatalytic hydroxylation of benzene to phenol under UV irradiation. We demonstrate that polyoxoalkoxovanadates can serve as efficient catalysts which can not only stabilize quinolinium radicals but also reuse H2O2 produced by quinolinium ions under light irradiation to obtain excellent synergistic effect, including competitive good yield (50.1 %), high selectivity (>99 %) and high atom availability.
A practical highly selective oxybromination of phenols with dioxygen
Menini, Luciano,Parreira, Luciana A.,Gusevskaya, Elena V.
, p. 6401 - 6404 (2007)
A simple, low cost and highly selective method for the synthesis of mono-bromophenols from phenol and electron-rich phenolic compounds has been developed. Bromide ions are used as halogenating agents, dioxygen as a final oxidant, and Cu(OAc)2 as a catalyst.
Development of a palladium-catalyzed α-arylation of cyclopropyl nitriles
McCabe Dunn, Jamie M.,Kuethe, Jeffrey T.,Orr, Robert K.,Tudge, Matthew,Campeau, Louis-Charles
, p. 6314 - 6317 (2014)
1,1-Disubstituted aryl cyclopropyl nitriles are useful moieties in biologically active compounds and provide access to a range of cyclopropyl derivatives. Herein, we describe the development of a palladium-catalyzed α-arylation of cyclopropyl, cyclobutyl, and cyclopentyl nitriles that affords these functional groups in one step from a variety of aryl bromides in good to excellent yields. Furthermore, we demonstrate the transformation of aryl cyclopropyl nitriles into aryl trifluoromethyl cyclopropanes.
Molecular cloning, structure, and reactivity of the second bromoperoxidase from Ascophyllum nodosum
Wischang, Diana,Radlow, Madlen,Schulz, Heiko,Vilter, Hans,Viehweger, Lutz,Altmeyer, Matthias O.,Kegler, Carsten,Herrmann, Jennifer,Mueller, Rolf,Gaillard, Fanny,Delage, Ludovic,Leblanc, Catherine,Hartung, Jens
, p. 25 - 34 (2012)
The sequence of bromoperoxidase II from the brown alga Ascophyllum nodosum was determined from a full length cloned cDNA, obtained from a tandem mass spectrometry RT-PCR-approach. The clone encodes a protein composed of 641 amino-acids, which provides a mature 67.4 kDa-bromoperoxidase II-protein (620 amino-acids). Based on 43% sequence homology with the previously characterized bromoperoxidase I from A. nodosum, a tertiary structure was modeled for the bromoperoxidase II. The structural model was refined on the basis of results from gel filtration and vanadate-binding studies, showing that the bromoperoxidase II is a hexameric metalloprotein, which binds 0.5 equivalents of vanadate as cofactor per 67.4 kDa-subunit, for catalyzing oxidation of bromide by hydrogen peroxide in a bi-bi-ping-pong mechanism (kcat = 153 s-1, 22 °C, pH 5.9). Bromide thereby is converted into a bromoelectrophile of reactivity similar to molecular bromine, based on competition kinetic data on phenol bromination and correlation analysis. Reactivity provided by the bromoperoxidase II mimics biosynthesis of methyl 4-bromopyrrole-2-carboxylate, a natural product isolated from the marine sponge Axinella tenuidigitata.
Luminescent ruffled iridium(iii) porphyrin complexes containing N-heterocyclic carbene ligands: structures, spectroscopies and potent antitumor activities under dark and light irradiation conditions
Lam, Tsz-Lung,Tong, Ka-Chung,Yang, Chen,Kwong, Wai-Lun,Guan, Xiangguo,Li, Ming-De,Kar-Yan Lo, Vanessa,Lai-Fung Chan, Sharon,Lee Phillips, David,Lok, Chun-Nam,Che, Chi-Ming
, p. 293 - 309 (2019)
A panel of iridium(iii) porphyrin complexes containing axial N-heterocyclic carbene (NHC) ligand(s) were synthesized and characterized. X-ray crystal structures of the bis-NHC complexes [IrIII(ttp)(IMe)2]+ (2a), [IrIII(oep)(BIMe)2]+ (2d), [IrIII(oep)(IiPr)2]+ (2e) and [IrIII(F20tpp)(IMe)2]+ (2f) display ruffled porphyrin rings with mesocarbon displacements of 0.483-0.594 ? and long Ir-CNHC bonds of 2.100-2.152 ?. Variable-temperature 1H NMR analysis of 2a reveals that the macrocycle porphyrin ring inversion takes place in solution with an activation barrier of 40 ± 1 kJ mol?1. The UV-vis absorption spectra of IrIII(por)-NHC complexes display split Soret bands. TD-DFT calculations and resonance Raman experiments show that the higher-energy Soret band is derived from the 1MLCT dπ(Ir) → π*(por) transition. The near-infrared phosphorescence of IrIII(por)-NHC complexes from the porphyrin-based 3(π, π*) state features broad emission bands at 701-754 nm with low emission quantum yields and short lifetimes (Φem III(por)(IMe)2]+ complexes (por = ttp and oep) are efficient photosensitizers for 1O2 generation (Φso = 0.64 and 0.88) and are catalytically active in the light-induced aerobic oxidation of secondary amines and arylboronic acid. The bis-NHC complexes exhibit potent dark cytotoxicity towards a panel of cancer cells with IC50 values at submicromolar levels. The cytotoxicity of these complexes could be further enhanced upon light irradiation with IC50 values as low as nanomolar levels in association with the light-induced generation of reactive oxygen species (ROS). Bioimaging of [IrIII(oep)(IMe)2]+ (2c) treated cells indicates that this Ir complex mainly targets the endoplasmic reticulum. [IrIII(oep)(IMe)2]+ catalyzes the photoinduced generation of singlet oxygen and triggers protein oxidation, cell cycle arrest, apoptosis and the inhibition of angiogenesis. It also causes pronounced photoinduced inhibition of tumor growth in a mouse model of human cancer.
Formation and reactivity of 4-oxocyclohexa-2,5-dienylidene in the photolysis of 4-chlorophenol in aqueous solution at ambient temperature
Grabner, Gottfried,Richard, Claire,K?hler, Gottfried
, p. 11470 - 11480 (1994)
Nanosecond laser flash photolysis of an aqueous solution of 4-chlorophenol (λexc = 266 nm) produces, at pulse end, a transient with absorption maxima at 384, 370, and ca. 250 nm; upon addition of an H-donor such as 2-propanol, this spectrum is converted into that of the phenoxyl radical (λmax = 400 and 385 nm), and in presence of O2, it is converted into a transient with a broad absorption band peaking at 460 nm. This reaction behavior can be understood by assuming formation of the carbene, 4-oxocyclohexa-2,5-dienylidene, by elimination of HCl from excited 4-chlorophenol; the pulse end transient spectrum is assigned to this species, while the 460 nm band is assigned to benzoquinone O-oxide formed by addition of O2 to the carbene. Both phenoxyl radical and benzoquinone O-oxide are produced upon photolysis of 4-chlorophenol in neat alkanols as well. On the other hand, photolysis in n-hexane yields the triplet-triplet absorption, which is absent in polar solvents, and no indication of carbene formation. It can be concluded that the primary step of 4-chlorophenol photolysis in aqueous or alcoholic solution is heterolytic C-Cl bond scission; a quantum yield of 0.75 is determined for it in neutral or acid aqueous medium upon excitation at 266 nm. Photolysis of chlorophenolate produces the same transients, but with a markedly lower yield, and, in addition, eaq- and 4-chlorophenoxyl radicals. The proposed reaction mechanism provides a straightforward explanation of the results of photoproduct analysis, published by previous authors as well as contributed in the present work. In particular, formation of p-benzoquinone in the presence of O2 can be accounted for by intermediate formation of benzoquinone O-oxide. Production of 4-oxocyclohexa-2,5-dienylidene with high yield allows, for the first time, extensive investigation of the kinetics and mechanism of the reactions of a carbene in an aqueous environment. In the present work, we have studied (a) the addition reaction with O2 on the one hand and with halides on the other; (b) H abstraction reactions with alkanols; (c) reaction with 4-chlorophenol itself; and (d) reaction with H2O. The rate constants for reaction with O2 (3.5 × 109 M-1 s-1) and with I- (4.6 × 109 M-1 s-1) are close to the diffusion-controlled limit, whereas reactions with Br- (6.8 × 107 M-1 s-1) and Cl- (5 M-1 s-1) are slower. Rate constants for reaction with alkanols follow the pattern known for their reactions with radicals, with values ranging from 5 × 105 M-1 s-1 for tert-butyl alcohol to 1.9 × 107 M-1 s-1 for 2-butanol. All these observations are consistent with the triplet character of the carbene. A rate constant of 1.5 × 103 M-1 s-1 has been determined for reaction with H2O. This reaction is not accompanied by formation of OH radicals; it is concluded that it proceeds by insertion into the O-H bond rather than by O-H cleavage. The exceptional stability of the carbene in aqueous solution is thus mainly attributed to the high barrier for O-H rupture in the water molecule. Additionally, a specific carbene-H2O interaction is revealed by semiempirical calculations, which could contribute to energetic and orientational hindrance of the reaction. Further theoretical results support the interpretation of both spectroscopic and kinetic properties of the carbene.
2,4-Diamino-1,3-thiazole Hydrotribromide; A New Brominating Agent
Forlani, Luciano
, p. 487 - 489 (1980)
-
C70 Fullerene-Catalyzed Metal-Free Photocatalytic ipso-Hydroxylation of Aryl Boronic Acids: Synthesis of Phenols
Kumar, Inder,Sharma, Ritika,Kumar, Rakesh,Kumar, Rakesh,Sharma, Upendra
, p. 2013 - 2019 (2018)
A metal-free C70 fullerene-catalyzed method has been developed for the ipso-hydroxylation of aryl and heteroaryl boronic acids to corresponding phenols under photocatalytic conditions. The reaction proceeds under oxygen atmosphere and the mechanistic study revealed that C70 plays a critical role in the generation of reactive oxygen species in the presence of blue light. Reactions in the presence of 18O-labelled water and oxygen confirmed the generation of reactive oxygen species from oxygen molecule. Amine used as a reductant could be recovered in the form of imine. The current method is also applicable to the synthesis of aryl ethers in one-pot two-step process. (Figure presented.).
Imidazolium-urea low transition temperature mixtures for the UHP-promoted oxidation of boron compounds
Martos, Mario,Pastor, Isidro M.
, (2022/01/03)
Different carboxy-functionalized imidazolium salts have been considered as components of low transition temperature mixtures (LTTMs) in combination with urea. Among them, a novel LTTM based on 1-(methoxycarbonyl)methyl-3-methylimidazolium chloride and urea has been prepared and characterized by differential scanning calorimetry throughout its entire composition range. This LTTM has been employed for the oxidation of boron reagents using urea-hydrogen peroxide adduct (UHP) as the oxidizer, thus avoiding the use of aqueous H2O2, which is dangerous to handle. This metal-free protocol affords the corresponding alcohols in good to quantitative yields in up to 5 mmol scale without the need of further purification. The broad composition range of the LTTM allows for the reaction to be carried out up to three consecutive times with a single imidazolium salt loading offering remarkable sustainability with an E-factor of 7.9, which can be reduced to 3.2 by the threefold reuse of the system.
Aryl phenol compound as well as synthesis method and application thereof
-
Paragraph 0075-0079, (2021/05/12)
The invention discloses a synthesis method of an aryl phenol compound shown as a formula (3). All systems are carried out in an air or nitrogen atmosphere, and visible light is utilized to excite a photosensitizer for catalyzation. In a reaction solvent, ArNR1R2 as shown in a formula (1) and water as shown in a formula (2) are used as reaction raw materials and react under the auxiliary action of acid to obtain the aryl phenol compound as shown in a formula (3). The ArNR1R2 in the formula (1) can be primary amine and tertiary amine, can also be steroid and amino acid derivatives, and can also be drugs or derivatives of propofol, paracetamol, ibuprofen, oxaprozin, indomethacin and the like. The synthesis method has the advantages of cheap and easily available raw materials, simple reaction operation, mild reaction conditions, high reaction yield and good compatibility of substrate functional groups. The fluid reaction not only can realize amplification of basic chemicals, but also can realize amplification of fine chemicals, such as synthesis of drugs propofol and paracetamol. The invention has wide application prospect and use value.
