Aromatic Monochlorination Photosensitized by DDQ with Hydrogen Chloride under Visible‐Light Irradiation

Photochlorination of aromatic substrates by hydrogen chloride with 2,3‐dichloro‐5,6‐cyano‐p‐benzoquinone (DDQ) occurs efficiently to produce the corresponding monochlorinated products selectively under visible‐light irradiation. The yields for the chlorination of phenol were 70 % and 18 % for p‐ and o‐chlorophenol, respectively, without formation of further chlorinated products. The photoinduced chlorination is initiated by electron transfer from Cl^? to the triplet excited state of DDQ. The radical intermediates involved in the photochemical reaction have been detected by time‐resolved transient absorption measurements.     

Catalysis by Ir(III), Rh(III) and Pd(II) metal ions in the oxidation of organic compounds with H2O2

Catalytic activities of three transition metals, as iridium (III) chloride, rhodium (III) chloride and palladium (II) chloride, were compared in the oxidation of six aromatic aldehydes (benzaldehyde, p‐chloro benzaldehyde, p‐nitro benzaldehyde, m‐nitro benzaldehyde, p‐methoxy benzaldehyde and cinnamaldehyde), two hydrocarbons (viz. (anthracene and phenanthrene)) and one aromatic and one cyclic alcohol (cyclohexanol and benzyl alcohol) by 50% H₂O₂. The presence of traces (substrate: catalyst ratio equal to 1:62500 to 1:1961) of the chlorides of iridium(III), rhodium(III) and palladium(II) catalyze these oxidations, resulting in good to excellent yields. It was observed that in most of the cases palladium(II) chloride is the most efficient catalyst. Conditions for the highest and most economical yields were obtained. Deviation from the optimum conditions decreases the yields. Oxidation in aromatic aldehydes is selective at the aldehydeic group only and other groups remain unaffected. This new, simple and economical method, which is environmentally safe, also requires less time. Reactive species of catalysts, existing in the reaction mixture are also discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Kinetic study of the reactions of oxoiron(IV) with aromatic substrates in aqueous solutions

The kinetics of the reactions of oxoiron(IV) (FeO²⁺) with phenol, nitrobenzene, m‐, o‐, and p‐nitrophenol in 1 M HClO₄ was investigated by the stopped‐flow technique. The rate constants of these reactions decrease with increasing the one‐electron reduction potentials of the corresponding radical cations of the substrates and with the Hammett parameter of the NO₂ group in the phenol ring. A reaction mechanism is proposed, which accounts for the observed trends and for the nature of the reaction products. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 488–494, 2002     

Synthesis of hetero‐telechelic polymers by self‐polyaddition of monomers containing both oxetanyl and carboxyl groups

The synthesis and self‐polyaddition of new monomers, o‐, m‐, and p‐[(3‐ethyloxetane‐3‐yl)methoxyethyl]benzoic acid (o‐EOMB, m‐EOMB, and p‐EOMB) containing both oxetanyl groups and carboxyl groups were examined. The reactions of o‐EOMB, m‐EOMB, and p‐EOMB in the presence of tetraphenylphosphonium bromide as a catalyst in o‐dichlorobenzene at 150–170 °C resulted in self‐polyaddition to give the corresponding hetero‐telechelic polymers poly(o‐EOMB), poly(m‐EOMB), and poly(p‐EOMB) with M_ns = 14,500–33,400 in satisfactory yields. The M_n of poly(o‐EOMB) decreased at higher reaction temperatures than 150 °C, unlike those of poly(m‐EOMB) and poly(p‐EOMB), possibly due to inter‐ or intraester exchange side reactions. It was also found that the thermal properties and solubilities of these polymers were supposed with the proposed structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7835–7842, 2008     

Theoretical investigation of the first-shell mechanism of nitrile hydratase

The first-shell mechanism of nitrile hydratase (NHase) is investigated theoretically using density functional theory. NHases catalyze the conversion of nitriles to amides and are classified into two groups, the non-heme Fe(III) NHases and the non-corrinoid Co(III) NHases. The active site of the non-heme iron NHase comprises a low-spin iron (S=1/2) with a remarkable set of ligands, including two deprotonated backbone nitrogens and both cysteine-sulfenic and cysteine-sulfinic acids. A widely proposed reaction mechanism of NHase is the first-shell mechanism in which the nitrile substrate binds directly to the low-spin iron in the sixth coordination site. We have used quantum chemical models of the NHase active site to investigate this mechanism. We present potential energy profiles for the reaction and provide characterization of the intermediates and transition-state structures for the NHase-mediated conversion of acetonitrile. The results indicate that the first-shell ligand Cys114-SO- could be a possible base in the nitrile hydration mechanism, abstracting a proton from the nucleophilic water molecule. The generally suggested role of the Fe(III) center as a Lewis acid, activating the substrate toward nucleophilic attack, is shown to be unlikely. Instead, the metal is suggested to provide electrostatic stabilization to the anionic imidate intermediate, thereby lowering the reaction barrier.     

Tetrathienylethene‐based Positional Isomers with Aggregation‐induced Emission Enabling Super Red‐shifted Reversible Mechanochromism and Naked‐eye Sensing of Hydrazine Vapor

AIE‐active positional isomers, TTE‐o‐PhCHO , TTE‐m‐PhCHO and TTE‐p‐PhCHO , tetrathienylethene ( TTE) derivates with peripherally attached ortho‐/meta‐/para‐formyl phenyl groups, were designed and synthesized. The formyl substitution position can effectively modulate their photophysical properties, mechanochromism and fluorescent response to hydrazine. TTE‐o‐PhCHO and TTE‐m‐PhCHO exhibit remarkable AIE characteristics, and TTE‐p‐PhCHO possesses aggregation‐induced emission enhancement performance. They all exhibit high contrast mechanochromism, and TTE‐m‐PhCHO shows larger red‐shift (164 nm) than TTE‐o‐PhCHO (104 nm) and TTE‐p‐PhCHO (125 nm) due to the more twisted molecular conformation and much looser molecular packing. Moreover, TTE‐o‐PhCHO with a higher contrast color change can be used as ink‐free rewritable paper. In addition, TTE‐p‐PhCHO , as a turn‐on fluorescent probe, can selectively detect hydrazine with significant color changes that are visible by the naked eye . Therefore, the position dependence of groups would be an effective method to modulate the molecular arrangement, as well as develop AIE compounds for mechano‐stimuli responsive materials, ink‐free rewritable papers and chemosensors.     

One‐Pot Cascade Biotransformation for Efficient Synthesis of Benzyl Alcohol and Its Analogs

Benzyl alcohol is a naturally occurring aromatic alcohol and has been widely used in the cosmetics and flavor/fragrance industries. The whole‐cell biotransformation for synthesis of benzyl alcohol directly from bio‐based L‐phenylalanine (L‐Phe) was herein explored using an artificial enzyme cascade in Escherichia coli. Benzaldehyde was first produced from L‐Phe via four heterologous enzymatic steps that comprises L‐amino acid deaminase (LAAD), hydroxymandelate synthase (HmaS), (S)‐mandelate dehydrogenase (SMDH) and benzoylformate decarboxylase (BFD). The subsequent reduction of benzaldehyde to benzyl alcohol was achieved by a broad substrate specificity phenylacetaldehyde reductase (PAR) from Solanum lycopersicum. We found the designed enzyme cascade could efficiently convert L‐Phe into benzyl alcohol with conversion above 99%. In addition, we also examined L‐tyrosine (L‐Tyr) and m‐fluoro‐phenylalanine (m‐f‐Phe) as substrates, the cascade biotransformation could also efficiently produce p‐hydroxybenzyl alcohol and m‐fluoro‐benzyl alcohol. In summary, the developed biocatalytic pathway has great potential to produce various high‐valued fine chemicals.     

Rhodium‐catalyzed ortho‐C‐H olefination of aromatic aldehydes employing transient directing strategy

A Rhodium(III)‐catalyzed ortho‐C‐H olefination of aromatic aldehydes in the presence of catalytic amount of TsNH₂ has been developed. The in situ generated imine intermediate from aldehyde and TsNH₂ worked as a transient directing group. Both electron‐rich and electron‐deficient aromatic aldehydes were tolerated, affording the corresponding products in moderate to good yields. Importantly, the present protocol provides a straightforward access to olefinated aromatic aldehydes with aldehydes as the simple starting materials.     

Ceric Ammonium Nitrate Catalyzed Oxidation of Aldehydes and Alcohols

A variety of aromatic, aliphatic and conjugated aldehydes and alcohols were transformed to the corresponding carboxylic acids and ketones with a quantitative conversion in high yields with 70% t‐BuOOH solution in water in the presence of catalytic amounts of ceric ammonium nitrate [Ce(NH₄)₂(NO₃)₆] (CAN) under room temperature conditions. The scope of our catalytic system is applicable for a wide range of aromatic, conjugated and aliphatic substrates. These aldehydes were converted to the corresponding carboxylic acids in good isolated yields in reasonable times. This method possesses a wide range of capabilities since it can be used with other functional groups which may not tolerate oxidative conditions, involves fairly simple method for work‐up, exhibits chemoselectivity and proceeds under ambient conditions. The resulting products are obtained in good yields within reasonable time.     

Synthesis of cyclic polysulfides: Controlled ring‐expansion polymerization of cyclic tetrathioester with thiirane

We synthesized cyclic tetrathioesters containing thioester moieties at the o‐position (o‐CTE) and m‐position (m‐CTE) of an aromatic skeleton. The reaction of phenoxy propylenesulfide (PPS) with o‐CTE and m‐CTE was examined using tetrabutylammonium chloride as a catalyst in 1‐methyl‐2‐pyrrolidinone, yielding the corresponding cyclic polysulfides poly[o‐CTE(PPS)_n] with M_n's = 37,000–54,000 at 34–61% yields and poly[m‐CTE(PPS)_n] with M_n's = 46,600–107,200 at 63–>99% yields. Although the molecular weights of poly[o‐CTE(PPS)_n] could not be controlled, those of poly[m‐CTE(PPS)_n] could be controlled by the feed ratios of PPS and reaction temperature. Furthermore, the glass transition temperature (T_g) and thermal decomposition temperature (T_dⁱ) of poly[m‐CTE(PPS)_n] increased with decreasing molecular weights. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 857–866     

Influence of phenylenediamine additions on the morphology and on the catalytic effect of polyaniline

The influence of para‐, ortho‐, and meta‐phenylenediamine (p‐, o‐, and m‐PDA) additions on the electrochemical synthesis of polyaniline has been investigated by the use of cyclic voltametry. It has been found that small additions (1 and 5 mmol L^?1) of PDA monomers influence significantly the polymerization rate. Whereas p‐PDA increases the polymerization rate, the addition of o‐ or m‐PDA slows it down. Therefore, a different number of potential cycling is necessary to obtain similar thickness of layers. The layers exhibit very different morphology, which changes from “spaghetti‐like” for polyaniline to “sponge‐like” for p‐PDA, to “pebble‐like” for o‐PDA and to “cauliflower‐like” for m‐PDA additions, respectively. The catalytic effect of the synthesized polymer layers has been tested. It has been found that all the layers exhibit catalytic effect in lowering the redox potential of hydroquinone/quinone tested reaction, but the rate of the electrocatalytic reaction varies depending on the PDA monomer added. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1599–1608, 2004     

Preparation and catalytic properties of chitosan bound Schiff base copper complexes

Chitosan, a natural polymer, bound Schiff base copper complexes CT‐She‐Cu, CT‐o‐Bel‐Cu, CT‐m‐Bel‐Cu were prepared and characterize by inductively coupled plasma (ICP), FT‐IR and X‐ray photoelectron spectroscopy (XPS). Their catalytic activity in the oxidation of cyclohexene with molecular oxygen was studied. All the complexes have catalytic activity and the main oxidation products are 2‐cyclohexene‐ol, 2‐cyclohexene‐one and cyclohexene hydroperoxide, which were measured by gas chromatography/mass spectroscopy (GC/MS) and GC/IR. CT‐m‐Bel‐Cu was selected to study the influence of reaction temperature, amount of catalyst and additives such as acid and base on the oxidation of cyclohexene systematically. Copyright © 2004 John Wiley & Sons, Ltd.     

Efficient synthesis and spectral determination of 11‐[(o‐ m‐ and p‐substituted)‐phenyl]‐8‐chloro‐3,3‐dimethyl‐2,3,4,5,10,11‐hexahydro‐1H‐dibenzo[b,e][1,4]diazepin‐1‐ones

A new synthesis to obtain eleven novel derivatives of 11‐[(o‐ m‐ and p‐substituted)‐phenyl]‐8‐chloro‐3,3‐dimethyl‐2,3,4,5,10,11‐hexahydro‐1H‐dibenzo[b,e][1,4]diazepin‐1‐ones with possible pharmacological activity in the central nervous system in two efficient steps has been developed. The final products were obtained by condensation and cyclization between 3‐[4‐chloro‐1,2‐phenylenediamine]‐5,5‐dimethyl‐2‐cyclohexenone with (o‐ m‐ and p‐substituted)benzaldehyde. The structure of all products was corroborated by ir, ¹H‐nmr, ¹³C‐nmr and high resolution in ms.     

芳酰胺-吖啶分子钳对中性分子的识别性能. II. 新型吖啶类分子钳的研究

采用差紫外谱法研究了新型芳酰胺-吖啶分子钳(1～7)对苯胺、苯二胺(邻, 间, 对)等中性分子的识别性能. 测定了结合常数(K_a)和自由能变化(ΔG°), 结果表明, 所有的分子钳受体与所考察的客体分子均形成1∶1型超分子配合物. 识别作用的主要推动力为多重氢键、van der Waals等的协同作用. 主客体间尺寸/形状匹配、几何互补等因素对识别性能均有重要的影响. 利用核磁氢谱与计算机模拟作为辅助手段对主要的实验结果与现象进行了解释.     

Synthesis and characterization of fully aromatic thermotropic liquid‐crystalline copolyesters containing m‐hydroxybenzoic acid units

A series of fully aromatic copolyesters based on p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m‐acetoxybenzoic acid (m‐ABA) were prepared by a modified melt‐polycondensation reaction. The copolyesters were characterized by DSC, thermogravimetric analysis, ¹H NMR, polarized optical microscopy, X‐ray diffraction, and intrinsic viscosity measurements. The copolyesters exhibited nematic liquid‐crystalline phases in a broad temperature range of about 150 °C, when the content of linear (p‐ABA, HQDA, and TPA) units was over 67 mol %. DSC analysis of the anisotropic copolyesters revealed broad endotherms associated with the nematic phases, and the melting or flow temperatures were found to be in the processable region. The flow temperatures and crystal‐to‐nematic and nematic‐to‐isotropic transitions depend on the type of linear monomer units, and these transitions increased as the content of the p‐ABA units increased, as compared to the HQDA/TPA units. When the content of the p‐ABA units increased, as compared to other linear units (HQDA and TPA), the intrinsic viscosity and degree of crystallinity of the copolyesters also increased, implying a higher reactivity for p‐ABA in the p‐ABA/HQDA/TPA/m‐ABA polymer system. The aromatic region in the ¹H NMR spectra of the copolyesters containing equal molar compositions of p‐ABA, HQDA, and TPA units were sensitive to the sequence distribution of aromatic rings. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3263–3277, 2001     

Synthesis and catalytic activity of novel xylyl‐linked benzimidazolium salts

The reaction of 1‐alkylbenzimidazole derivatives with o‐/p‐di(chloromethyl)benzene results in the formation of the new o‐/p‐xylyl‐linked bis(benzimidazolium) salts, 1 and 2, respectively. The salts were characterized by NMR spectroscopy and elemental analysis. The in situ prepared complexes derived from Pd(OAc)₂–1 and 2 exhibit catalytic activity (61–98%), to give the Heck coupling products of aryl bromides and styrene. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and spectral properties of 2‐methylthio‐3H‐7‐[(o‐; m‐ and p‐substituted)phenoxy]‐4‐(p‐substituted‐phenyl)‐[1,5]benzodiazepines

A series of eleven new 2‐methylthio‐3H‐7‐[(o‐; m‐ and p‐substituted) phenoxy]‐4‐(p‐substituted‐phenyl)‐[1,5]benzodiazepines, which have potentially useful pharmacological activities, has been synthesized by condensing the 4‐[(o‐; m‐ and p‐R₁)phenoxy]‐1,2‐phenylendiamines with 3,3‐dimercapto‐1‐(p‐R₂‐phenyl)‐2‐propen‐1‐one. Afterward the lH‐[1,5]benzodiazepine‐2‐thiones obtained were treated with sodium hydride and methyl iodide. The structure of all products was corroborated by ir, ¹H nmr, ¹³C nmr and ms.     

Density functional theory study of p‐chloroaniline adsorption on Pd surfaces and clusters

The adsorption mode of aromatic molecules on transition metal surfaces plays a key role in their catalytic transformation. In this study, by means of density functional theory calculations, we systematically investigate the adsorption of p‐chloroaniline on a series of Pd surfaces, including stepped surfaces, flat surfaces, and clusters. The adsorption energies of p‐chloroaniline on these substrates [Pd(221), Pd(211), Pd(111), Pd(100), Pd₁₃‐icosahedral, Pd₁₃‐cubo‐octahedron, Pd₅₅] are ?1.90, ?2.13, ?1.70, ?2.11, ?2.53, ?2.65, ?2.23 eV, respectively. Benzene ring is adsorpted on catalyst rather than amine group in p‐chloroaniline molecular. A very good linear relationship is further found between the adsorption energies of p‐chloroaniline and the d‐band center of both Pd surfaces and clusters. The lower of d‐band center of Pd models, the stronger adsorption of p‐chloroaniline on catalysts. In addition, the frontier molecular orbital and density of states analysis explain the adsorption energy sequence: cluster Pd₁₃ > stepped Pd(221) surface > flat Pd(111) surface. © 2014 Wiley Periodicals, Inc.     

Nitro‐substituted iron(II) tridentate bis(imino)pyridine complexes as high‐temperature catalysts for the production of α‐olefins

A new series of nitro‐substituted bis(imino)pyridine ligands {2,6‐bis[1‐(2‐methyl‐4‐nitrophenylimino)ethyl]pyridine, 2,6‐bis[1‐(4‐nitrophenylimino)ethyl]pyridine, (1‐{6‐[1‐(4‐nitro‐phenylimino)‐ethyl]‐pyridin‐2‐yl}‐ethylidene)‐(2,4,6‐trimethyl‐phenyl)‐amine, and 2,6‐bis[1‐(2‐methyl‐3‐nitrophenylimino)ethyl]pyridine} and their corresponding Fe(II) complexes [{p‐NO₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐ Me? p‐NO₂}FeCl₂ ( 10 ), L₂FeCl₂ ( 11 ), {m‐NO₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? m‐NO₂}FeCl₂ ( 12 ), and {p‐NO₂? Ph? N?C(Me)? Py? C(Me)?N? Mes}FeCl₂ ( 14 )] were synthesized. According to X‐ray analysis, there were shortenings of the axial Fe? N bond lengths (up to 0.014 Å) in para‐nitro‐substituted complex 10 and (up to 0.015 Å) in meta‐nitro‐substituted complex 12 versus the Fe(II) complex without nitro groups [{o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me}FeCl₂ ( 1 )]. Complexes 10 , 12 , and 14 afforded very active catalysts for the production of α‐olefins and were more temperature‐stable and had longer lifetimes than parent non‐nitro‐substituted Fe(II) complex 1 . The reaction between FeCl₂ and a sterically less hindered ligand [p‐NO₂? Ph? N?C(Me)? Py? C(Me)?N? Ph? p‐NO₂] resulted in the formation of octahedral complex 11 . A para‐dialkylamino‐substituted bis(imino)pyridine ligand [p‐NEt₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? p‐NEt₂] and the corresponding Fe(II) complex [{p‐NEt₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? p‐NEt₂}FeCl₂ ( 16 )] were synthesized to evaluate the effect of enhanced electron donation of the ligand on the catalytic performance. According to X‐ray analysis, there was a shortening (up to 0.043 Å) of the axial Fe? N bond lengths in para‐diethylamino‐substituted complex 16 in comparison with parent Fe(II) complex 1 . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2615–2635, 2006     

Cu(II) bromide catalyzed oxidation of aldehydes and alcohols

A variety of aromatic, aliphatic and conjugated aldehydes and alcohols were transformed to the corresponding carboxylic acids and ketones with a quantitative conversion in high yields with 70% t‐BuOOH solution in water in the presence of catalytic (5 mol%) amounts of CuBr₂ under room temperature conditions. The conversion of 4‐methoxybenzaldehyde to 4‐methoxybenzoic acid is extremely facile in MeCN at ambient temperature in the presence of 5 mol% CuBr₂ and 2 equiv. 70% t‐BuOOH (water) as the oxidant. Oxidation with t‐BuOOH (water) alone in MeCN was found to be negligible. The scope of our catalytic system is applicable for a wide range of aromatic, conjugated and aliphatic substrates. These aldehydes were converted to the corresponding carboxylic acids in good isolated yields in reasonable times. It is pertinent to mention here that mild halogenic oxidants like hypochlorites, chlorites and NBS are not suitable for substrates with electron‐rich aromatic rings, olefinic bonds and secondary hydroxyl groups. Substitutions at different positions on the phenyl ring do not hinder the reaction, although the reaction time is affected. Oxidation of α,β unsaturated derivatives resulted in the formation of the expected acid in good yield. In addition, the transformation of secondary alcohols to ketones is extremely facile. No recemization was observed for menthone. This method possesses a wide range of capabilities since it can be used with other functional groups which may not tolerate oxidative conditions, involves fairly simple method for work‐up, exhibits chemoselectivity and proceeds under ambient conditions. The resulting products are obtained in good yields within reasonable time. Copyright © 2011 John Wiley & Sons, Ltd.