Binding and recognition ability of molecularly imprinted polymer toward p-nitrophenol

p-Nitrophenol is a hazardous phenolic compound and its separation and determination is very necessary to protect public health and environmental quality. In this article, macromolecule polyethyleneimine (PEI) grafted on the surface of silica particles was crosslinked using p-nitrophenol as a template and diepoxyalkyl (669) as a crosslinking agent, and molecularly imprinted polymer on the surfaces of silica gel MIP-PEI/SiO₂ was prepared. The binding and recognition ability of MIP-PEI/SiO₂ for p-nitrophenol were researched using batch and dynamic methods. The experimental results showed that MIP-PEI/SiO₂ had high affinity, specific recognition ability, and excellent selectivity for p-nitrophenol. The saturated binding amount could reach to 155.5 mg g⁻¹. The selectivity coefficients relative to m-nitrophenol and chlorophenol were 45.80 and 117.5, respectively. The empirical Freundlich isotherm was found to describe well the equilibrium binding data. pH of sample solution was found to have a strong influence on the binding amount. MIP-PEI/SiO₂ was regenerated easily using diluted hydrochloric acid solution as eluent and MIP-PEI/SiO₂ possesses better reusability. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Liquid-phase oxidation of p-cresol and Substituted p-Cresols by Air

The liquid-phase oxidation of p-cresol and substituted p-cresols by air under alkaline conditions using cobaltous chloride as a catalyst and methanol as solvent, has been investigated with a view to obtain the corresponding aldehydes with sufficiently high selectivities. In the case of p-cresol, the effects of various process parameters on the reaction rate and selectivity with respect to the aldehyde have been investigated. The results obtained are likely to be useful for the development of processes for the production of industrially relevant products such as 4-hydroxybenzaldehyde, vanillin and syringaldehyde by using p-cresol as the starting material. Various alternative process schemes have been proposed and evaluated.     

Synthesis of p-cymene from limonene, a renewable feedstock

Highly selective limonene conversions to p-cymene in short reaction times were achieved under “solvent free” conditions over mesoporous silica–alumina supports heated by microwave irradiation. An increase in the silica content of these mixed oxides led to increases in the specific surface area, porosity (pore size and volume) and the surface acidity. The conversion and selectivity of limonene to p-cymene under microwave irradiation was also found to rise as the silica content in these mixed oxides was increased. By careful choice of the solid and reaction parameters the activities for the conversion of limonene and selectivity to p-cymene (used as an intermediate in fine chemical syntheses) could be fine tuned. Results are presented under both dry media and reflux conditions.     

Effect of partial poisoning of acid sites on selectivity in the multiple reactions of mono-substituted-t-Butylbenzenes

The decomposition reaction of p–t-butylcumene and t-butylbromobenzene have been carried out over pyridine poisoned silica-alumina and HY zeolite in order to examine the effect of acid strength on selectivity. Since the catalyst deactivation rate for isomerization over the poisoned silica-alumina was greater than that of de-t-butylation in the reaction of p–t-butylcumene, the selectivity of de-t-butylation gradually improved with process time. In the reaction of t-butylbromobenzene over poisoned HY zeolite, the de-bromination rate was suppressed by the poisoning because the nature of active sites was different between silica-alumina and HY zeolite. The poisoned HY zeolite was found to be favorable for the de-t-butylation of halogenated-t-butylbenzenes.     

Liquidphase tert-butylation of cresols catalysed by 12-tungstophosphoricacid and 12-tungstosilicicacid supported onto neutral alumina

A comparative study on tert-butylation of cresols such as o-cresol, m-cresol and p-cresol with tert-butyl alcohol was carried out over 30% 12-tungstophosphoricacid and 12-tungstosilicicacid supported onto neutral alumina in liquid phase under mild conditions. The catalysts show high activity in terms of % conversion and % selectivity for the products, p-tert butyl o-cresol, o-tert butyl m-cresol, o-tert butyl p-cresol, under mild conditions.     

Context-Dependence of the Reactivity of Cysteine and Lysine Residues

The S-alkylation of Cys residues with a maleimide and the N^ϵ-acylation of Lys residues with an N-hydroxysuccinimide (NHS) ester are common methods for bioconjugation. Using Cys and Lys derivatives as proxies, we assessed differences in reactivity depending on the position of Cys or Lys in a protein sequence. We find that Cys position is exploitable to improve site-selectivity in maleimide-based modifications. Reactivity decreases substantially in the order N-terminal>in-chain>C-terminal Cys due to modulation of sulfhydryl pK_a by the α-ammonium and carboxylate groups at the termini. A lower pK_a value yields a larger fraction thiolate, which promotes selectivity while somewhat decreasing thiolate nucleophilicity in accord with =0.41. Lowering pH and salt concentration enhances selectivity still further. In contrast, differences in the reactivity of Lys towards an NHS ester were modest due to an appreciable decrease in amino group nucleophilicity with a lower pK_a of its conjugate acid. Hence, site-selective Lys modification protocols will require electrophiles other than NHS esters.     

Effects of Aromatics on the Stability and Product Distribution of the Methanol to Olefin Process

Methanol to olefin process was investigated over a steam‐treated Ca‐ZSM‐5 catalyst in a flow‐type fixed bed reactor by adding aromatics to the methanol feed. As a comparison, the catalytic performance in the presence of nitrogen and water was also investigated. The experimental results exhibit that in the presence of aromatics, the total light olefin selectivity and the ethylene selectivity increased, while propylene selectivity increased with adding o‐xylene and m‐xylene to the methanol feed, but decreased with adding benzene, toluene, p‐xylene and ethylbenzen to the methanol feed. The catalyst was characterized by temperature‐programmed desorption of ammonia, N₂ adsorption, and scanning electron microscope. The adsorption of water and aromatics on the catalyst was also studied. Based on the results, it is concluded that aromatics may be responsible for the formation of light olefins and be more favorable for ethylene than propylene in methanol conversion.     

Prediction of Selective Extraction of Cresols from Aqueous Solutions by Ionic Liquids Using Theoretical Approach

This work reports the prediction of selective extraction of cresol from aqueous solutions using ionic liquids (ILs) as the solvent. Judicious screening of various ILs was carried out for all the three forms of cresol (i.e., o-cresol, m-cresol, and p-cresol). A quantum chemical based theoretical model “conductor-like screening model for real solvents” (COSMO-RS) was used to predict the selectivity of cresol in aqueous medium at infinite dilution. A screening of 360 possible ILs from 15 cations and 24 anions was carried out to determine the best IL for the removal of cresol from water. Amongst the phosphonium and imidazolium based cations, trihexyl tetradecylphosphonium [THTDP] and 1-octyl-3-methylimidazolium [OMIM] gave the highest selectivity other than the anions bromide and chloride. The selectivities for different cresols followed the pattern: m-cresol > p-cresol > o-cresol. Similarly for pyridinium and quinolium based cations, 1-ethylpyridinium [EPY] and 1-octylquinolium [OQU] gave the highest selectivity. Amongst the two cations studied for pyrrolidinium based cations, 1-hexyl-1-methylpyrrolidinium [HMPL] was the best. Trihexyl tetradecylphosphonium salicyclate [THTDP][SAL] gave the highest selectivity of 662 amongst all the ILs screened.     

Analytical applications of newly synthesized copolymer resin derived from p‐aminophenol,dithiooxamide, and formaldehyde

A copolymer resin (p‐APDF) has been synthesized using the monomers p‐aminophenol, dithiooxamide, formaldehyde in 1 : 1 : 2M proportions in the presence of 2M HCl as catalyst. The structure of p‐APDF copolymer has been elucidated on the basis of elemental analysis and various physicochemical techniques, i.e., UV‐visible, FTIR, and ¹H‐NMR spectroscopy. The number average molecular weight of copolymer resin was determined by nonaqueous conductometric titration in DMF. Viscosity measurement were carried out in DMF indicate normal behavior. The prepared resin proved to be a selective ion exchange resin for some metal ions. The chelating ion exchange properties of this resin was studied for Fe(III) and Cu(II), Ni(II), Co(II), Zn(II), Cd(II), Pb(II) ions. A batch equilibrium method was used to study selectivity of metal ion uptake over a wide pH range and in media of various ionic strength. The resin showed a higher selectivity for Fe(III), Ni(II), Cu(II) ions than for Co(II), Pb(II), Zn(II), and Cd(II) ions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Production of p‐toluenesulfonic acid by sulfonating toluene with gaseous sulfur trioxide

Toluene was sulfonated by gaseous sulfur trioxide to prepare p‐toluenesulfonic acid. The effects of reaction temperature and toluene conversion on the isomer selectivities and the dynamic viscosity of the reaction mixture in a well‐stirred tubular glass reactor of 4 cm diameter and 16 cm height were investigated. Lower selectivity to the m‐isomer was obtained at lower reaction temperature and lower conversion of toluene, whereas the selectivity to the p‐isomer seemed to be less affected by these parameters. With the increase in toluene conversion a sharp increase in viscosity of the reaction mixture was observed, which was attributed to the saturation of the toluenesulfonic acids dissolved in toluene. A pilot‐scale stainless steel jet loop reactor (JLR) of 0.3 m diameter and 4 m height with an external cooler was constructed and used for the continuous sulfonation of toluene. It was found that the JLR was very effective for the fast removal of the large amount of reaction heat, and selectivities to the p‐isomer around 85% and to the m‐isomer below 1.2% were obtained. © 2001 Society of Chemical Industry     

Disproportionation of toluene on ZSM5 washcoated monoliths

ZSM5 washcoated monoliths with zeolite loading ranging from 10 to 60 wt % were prepared, characterized, and examined for disproportionation of toluene. Toluene conversion increased with temperature and W/F_Ao but decreased with washcoat thickness. The selectivity of the most desirable isomer (p‐xylene) increased with a decrease in temperature, W/F_Ao and washcoat thickness. The high selectivity to p‐xylene indicates that the initially formed para isomer is easily removed from the zeolite pores in the thin washcoat to the bulk gas phase preventing further isomerization of the primary product. A reaction scheme has been proposed for this reaction and the kinetic parameters determined for the 10 wt % ZSM5 monolith. A one‐dimensional reactor model was developed to predict the performance of the reactor for disproportionation of toluene. The model equations were coupled with a module to calculate the concentration profile in the washcoat by considering the effect of diffusion and reaction. © 2011 American Institute of Chemical Engineers AIChE J, 00: 000–000, 2011     

Gas transport property of homo- and copolyimides from isomeric thiaphthalic dianhydride and oxydianiline

Gas transport properties of homo- and copolyimides prepared from 3,3′,4,4′- and 2,2′,3,3′-thiaphthalic dianhydride (p-TDPA and m-TDPA, respectively) with 4,4-oxydianiline (ODA) were investigated. The fractional free volume of m-TDPA-ODA is larger than that of p-TDPA-ODA, and the chain segmental mobility of the former is lower than that of the latter. The permeability coefficients of m-TDPA-ODA to H₂, CO₂, and O₂ are more increased by 48, 69 and 75%, at 30°C and 10 atm, respectively, than those of p-TDPA-ODA; but the permselectivities of m-TDPA-ODA for H₂, CO₂, and O₂ toward N₂ are more decreased by 33, 77, and 26%, respectively, than those of p-TDPA-ODA. The permeability coefficients and the diffusion coefficients of the copolyimides can be described by the following equations: log P = Φ_p log P_p + Φ_m log P_m and log D_a = Φ_p log(D_a)p + Φ_m log(D_a)_m, respectively. The variation of the permselectivity is controlled predominantly by diffusivity selectivity. These observations are interpreted in terms of variations in the fractional free volume of polyimides. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1821–1826, 1997     

Reaktivität und Selektivität bei der Oxidation von Styrolderivaten,II. Untersuchungen zur Oxidation von p-substituierten α-Methylstyrolen

Reactivity and Selectivity in the Oxidation of Styrene Derivatives, II. Studies on the Oxidation of p-Substituted α-Methylstyrenes The liquid phase oxidation of p-substituted (Br-, Cl-, t-Bu-, MeO-, CF₃-) α-methylstyrenes and of α,p-dimethoxystyrene with pure oxygen was investigated in chlorobenzene solution and in presence of cumene and of cumene hydroperoxide in the temperature range 65–125°C. The product yields were determined gaschromatographically. The differences of the activation energies of the epoxide formation and the parallel reactions amount to 19–48 kJ/mol. The epoxide selectivity increases with increasing temperature and concentration of olefine. The relative chain propagation constants k_p (CC) were determined by competitive oxidation with cumene. The k_p(CC) values of p-substituted α-methylstyrenes can be correlated by the Hammett equation with both σ and σ⁺ substituent constants.     

Isopropylation of ethylbenzene over MCM-22 molecular sieve

MCM-22 materials (Si/Al ratios 24, 50 and 75) were synthesized and characterized. The catalytic activity was examined in the vapour phase isopropylation of ethylbenzene with isopropyl alcohol. Based on ethylbenzene conversion, the order of activity of the catalysts is found to be MCM-22(50) > MCM-22(24) = MCM-22(75). The selective formation of p-isopropyl ethylbenzene (p-IPEB) suggests that the reaction occurs mainly inside the 10-membered ring channel. The time on stream study over MCM-22(50) showed steady conversion for 6 h with nearly the same selectivity to p-isopropyl ethylbenzene (p-IPEB) and o-isopropyl ethylbenzene (p-IPEB).     

Structure-activity relations of β-adrenergic agents

A review of the structure-activity relations in aryloxypropanolamine β-adrenoceptor drugs is presented. The effect of substitution in various parts of the molecule on β₁/β₂ selectivity and degree of partial agonism is discussed. Cardiac (β₁) selectivity is achieved by hydrophilic compounds with either p-amide substitution in the aryl ring, or a hydrogen bonding group in the amine side chain. Lipophilic compounds with branched chains tend to be β₂ selective. Partial agonist activity may also be controlled by hydrogen bonding groups in the side chain and by aromatic substitution. Here 3,4-dihydroxyl groups give full agonists, mono-and des-hydroxy (OH) groups partial agonists. The size of any o-substituent is critical and a plot of Taft's steric factor versus partial agonism gives a linear relation. By manipulation of the above factors all combinations of selectivity and agonist activity may be achieved.     

Catalytic activity of nickel nanoparticles in hydrogenation of p-nitrophenol to p-aminophenol

Nickel nanoparticles with different sizes and different structures were prepared by reducing nickel oxalate with hydrazine hydrate in the presence of citric acid, sodium dodecyl sulphonate, Tween 80, PEG 6000, and D-sorbitol as organic modifiers. The type of organic modifiers affected the size and the structure of the resultant nickel nanoparticles. The catalytic activities of the nickel nanoparticles increased with decreasing the particle size in the hydrogenation of p-nitrophenol to p-aminophenol. All the as-prepared nickel nanoparticles showed higher catalytic activity and selectivity than conventional Raney Ni catalyst.     

Preparation,characterization, and adsorption performance of p‐hydroxybenzoic acid imprinted polymer and selective catalysis of toluene to para‐chlorotoluene

A p‐hydroxybenzoic acid surface molecularly imprinted polymer (p‐HB– S MIP) with si lica microspheres as a supporting matrix was prepared by the adoption of the surface molecular imprinting technique with acrylamide ( AM) as a functional monomer, ethylene glycol dimethacrylate as a crosslinker, and azoisobutyronitrile as an initiator. The p‐HB–SMIP was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetry. Interactions between the functional monomer and template were observed with UV–visible spectroscopy of the solutions of these components as well. The results indicate that a 1:2 molecular complex was formed between p‐hydroxybenzoic acid (p‐HB) and AM. A kinetic binding study showed that p‐HB–SMIP reached saturation adsorption after about 1 h, and the pseudo‐second‐order model fitted the adsorption kinetics data. Static adsorption experiments revealed that the Freundlich equation fitted the adsorption isotherm data. The thermodynamics parameters (with positive values of enthalpy and entropy and negative values of Gibbs free energy) indicated that the binding system for p‐HB–SMIP was endothermic and entropy was gained and was spontaneous. Selective experiments showed that p‐HB–SMIP had a high affinity and excellent recognition selectivity for the template p‐HB. p‐HB–SMIP was further investigated by the catalysis of toluene to para‐chlorotoluene. The catalytic reaction results showed that the conversion of toluene was 85.5% and the molar ratio of para‐chlorotoluene to o‐chorotoluene was 1.38; this was higher than that of traditional catalysts. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40118.     

Alkylation of toluene with ethene over H-ZSM-5 zeolites

It is shown that the alkylation of toluene with ethylene to give p-ethyltoluene can be conducted selectively on small crystals ( 1μ) of unmodified H-ZSM-5 zeolites to a level higher than that corresponding to a thermodynamic equilibrium composition. A comparison of the ethyltoluene isomers formed with H-Y and H-ZSM-5 zeolites at various conversions and temperatures indicates that p-ethyltoluene is preferentially formed in the channel intersections of the H-ZSM-5 zeolite, even during the initial alkylation step. The final ethyltoluene isomer composition is a result of competition between the rates of alkylation and isomerization and subsequent diffusional transport of individual isomers through the zeolite channels. Zeolite coking causes an apparent increase in the p-ethyltoluene selectivity; however, a more dramatic decrease in toluene conversion results in the formation of a considerably lower amount of p-ethyltoluene. This is caused by a partial blocking of the zeolite channel system.     

Selective Clathration of Aliphatic Alcohols by Dianin's Compound

Abstract

Dianin's Compound (4-p-hydroxyphenyl-2,2,4-trimethylchroman) has been shown to demonstrate a marked selectivity when it forms clathrates from binary alcohol solutions. The relationship between solvent composition in solution and in the crystalline adduct was found to be linear in all but one case. The degree of selectivity was expressed quantitatively as the “preference index.” Results obtained indicated that the molecular shape of a potential guest plays a dominant role in the formation of Dianin's Compound adducts.     

Constant Selectivity in Proton Exchange Reactions Between Aqueous Sulphuric Acid and Acetylenes

Linear Pfluger plots of unit slope are obtained from logarithmic rate constants for acid–catalysed hydration of phenylacetylene and its substituted derivatives p-OCH₃, p-CH₃, m-CH₃, p-Br, m-Cl, m-NO₂, p-NO₂ in aqueous sulphuric acid solution. This direct experimental observation of absence of any dependence on selectivity gives evidence for the applicability of the kinetic acidity function in these systems.