A spectrophotometric determination of the formation constants of the inclusion complexes ofα- andβ-cyclodextrins with the azonium and ammonium tautomers of methyl orange and methyl yellow

The color fading caused by the addition of-cyclodextrin or-cyclodextrin to an aqueous solution of a tautomeric mixture of methyl orange or methyl yellow is studied spectrophotometrically at pH 1.1 and 25.0°C. A model involving 1 : 1 stoichiometry has been used to analyze the spectrophotometric data. The addition of a cyclodextrin shifts the tautomeric mixture towards the side of the ammonium tautomer. An expression allowing the calculation of the tautomeric equilibrium constant of the inclusion complexes is derived. The formation constants of the inclusion complexes of the individual tautomers are determined. Both- and-cyclodextrins bind the ammonium tautomer stronger than the azonium tautomer. The inclusion complexes of-cyclodextrin are more stable than the corresponding ones of-cyclodextrin.     

Vapor—liquid equilibria of the binary mixtures methyl chloride — methanol and dimethyl ether — methyl chloride and of the ternary mixture dimethyl ether — methyl chloride — methanol

Vapor Liquid Equilibria in mixtures of dimethyl ether, methyl chloride and methanol were investigated in a static equilibrium apparatus for temperatures 250 K < T <350 K and pressures up to 1 MPa. Temperature, pressure and the composition of the liquid and the vapor phase were determined.The consistency of the binary experimental data was checked and parameters of several g^E-models were fitted. The binary parameters were used to predict the ternary VLE and the calculated results were compared with the experimental data.     

Density functional and chemical model study of the competition between methyl and hydrogen scission of propane and ��-scission of the propyl radical

In this work, we study the competence between the reactions of hydrogen and methyl scission during thermal cracking and combustion of propane, the emergence of the two isomers of the propyl radical, n-propyl and i-propyl, and their subsequent ??-scission reaction to ethene and methyl radical. The purpose of the study was to analyze the accuracy of density functional (DFT) methods as applied on this relatively well-known subset of the reactions implied in the production of propylene oxide from propane and propene. Conventional (B3LYP, B3PW91) and state-of-the-art (PBE0, M06, BMK) DFT methods were employed, and their accuracy checked against experimental data and calculations performed using model chemistries (complete basis set CBS-4M, QB3, and APNO, and G4 methods) and ab initio methods (MP2, CCSD(T) with a large 6-311 ++G(3df,2pd) basis set). The results obtained at the BMK level for the thermodynamics of the reactions are closer to experimental data than those afforded by any other DFT method and very similar actually to CBS or CCSD(T) results, even if a medium size basis set is used. Activation energies determined using two- and three-parameter Arrhenius equations are also very good, but the preexponential factors are incorrect. Tunneling and internal rotation corrections must be applied to obtain semiquantitative results.     

What are the relative steric demands of carboxyl and methyl groups?

The relative steric demands of carboxyl and methyl groups are compared by contrasting the difference quantity H _f ^o (g, ArCOOH) — H _f ^o (g, ArCH₃) for a collection of alkylated benzoic acids and toluenes with the value for Ar=C₆H₅, the archetypical (i.e., unsubstituted) benzoic acid and toluene. We conclude that carboxyl and methyl groups are nearly the same size.     

Cyclization of the methyl ester of α-propionyllevulinic acid

Summary Cyclization of methyl -propionyllevulinate to 2,3-dimethylcyclopenten-2-one and methyl 3,4-dimethylcyclopenten-3-one-2-carboxylate was accomplished.     

A chemoenzymatic approach to the synthesis of enantiomerically pure aza analogues of paraconic acid methyl ester and both enantiomers of methyl β-proline

Enantiopure methyl esters of 1-alkyl-5-oxo-3-pyrrolidinecarboxylic acids were obtained by enzymatic resolution of the corresponding chiral racemic mixtures. A particularly favourable interaction, also supported by molecular mechanics calculations, was observed between the 1-benzyl derivative and α-chymotrypsin, for which the enantiomeric ratio, E, exceeded 200. The absolute configurations of the lactams were determined by means of CD spectroscopy. From the resulting enantiomerically pure (99% e.e.) (S)-(+)-1-benzyl-3-pyrrolidinecarboxylic acid and methyl (R)-(−)-1-benzyl-3-pyrrolidinecarboxylate, the methyl esters of (+) and (−)-β-proline were synthesised in 99% e.e. and 18 and 22% overall yield, respectively.     

Phase behavior and modeling of the poly(methyl methacrylate)–CO2–methyl methacrylate system

Cloud-point data for the system poly(methyl methacrylate) (PMMA)–CO₂–methyl methacrylate (MMA) are measured in the temperature range of 26 to 170°C, to pressures as high as 2500 bar, and with cosolvent concentrations of 10.4, 28.9, and 48.4 wt.%. PMMA does not dissolve in pure CO₂ to 255°C and 2550 bar. The cloud-point curve for the PMMA–CO₂–10.4 wt.% MMA system exhibits a negative slope that reaches 2500 bar at 105°C. With 28.9 wt.% MMA the cloud-point curve remains relatively flat at ∼900 bar for temperatures between 25 and 170°C. With 48.4 wt.% MMA the cloud-point curve exhibits a positive slope that extends to 20°C and ∼100 bar. Pressure-composition isotherms are also reported for the CO₂–MMA system at 40.0, 80.0, 105.5°C. This system exhibits type-I phase behavior with a continuous mixture–critical curve. The Peng–Robinson (PR) and SAFT equations of state model the CO₂–MMA data reasonably well without any binary interaction parameters, although the PR equation provides a better representation of the mixture-critical region. It is not possible to obtain even a qualitative fit of the PMMA–MMA–CO₂ data with the SAFT equation of state. The SAFT model qualitatively shows that the cloud-point pressure decreases with increasing MMA concentration and that the cloud-point curve exhibits a positive slope for very high concentrations of MMA in solution.     

Quantum chemical study on the thermal Diels-Alder reaction of cyclohexadiene and methyl crotonate

AM1 molecular orbital method using the unrestricted Hartree-Fock(UHF) calculations has been applied to investigate the thermal reaction of cyclohexadiene and methyl crotonate. The calculated results indicate that the thermal Diels-Alder reaction proceeds to product through the concerted path and two radical pathways.     

Synthesis and Characterization of the Polyacrylonitrile-block-poly（methyl acrylate） by RAFT Technique

Reversible addition-fragmentation chain transfer polymerization (RAFT) was firstly reported in 1998 by Rizzardo1. This technique provided the possibility to synthesize polymers with controlled molecular weight, narrow molecular weight distribution, and we…     

Semiconductor photoinduced cycloreversion of the dimer of methyl 2-naphthoate

The dimer of methyl 2-naphthoate (1) has been found to undergo efficient cyclorever-sion to its monomer, methyl naphtha)ene-2-carboxylate (2) on illuminated ZnO and TiO2 but not on CdS. An electron transfer and cation radical chain mechanism is proposed. Quantum yields, solvent effect, the role of oxygen, and the quenching of the reaction were investigated, and were consistent with the proposed mechanism.     

Conformational, steric and electronic effects on the site- and chemoselectivity of the metal-catalyzed reaction of N-bis(trimethylsilyl)methyl, N-(2-indolyl)methyl α-diazoamides

The Rh(II)- and Cu(II)-catalyzed reactions of N-bis(trimethylsilyl)methyl, N-(2-indolyl)methyl α-diazoamides are investigated to delineate how conformational, steric and electronic factors influence the site- and chemoselectivity of the metallocarbenoid reaction. The N-bis(trimethylsilyl)methyl (N-BTMSM) group is found to be essential in promoting the metallocarbenoid reaction at the N-(2-indolyl)methyl moiety as well as providing subtle but effective conformational influence about the amide N-C(α) sigma bond in diazoamides carrying an N-C(α) alkoxymethyl side-chain, to afford excellent site- and chemoselectivity. In general, the metal-catalyzed reactions are found to favor metallocarbenoid addition to the indole C(2)-C(3) double bond over C-H insertion to give cyclopropanated products (tetracyclic γ-lactams); however, chemoselectivity is also affected by steric effects, as revealed in the N-[2-(3-methylindolyl)]methyl diazoamides, and to some extent by the nature of the catalyst employed, as seen in the N-C(α)-alkoxymethyl diazoamides. The tetracyclic γ-lactams are found to rearrange to give good to high yields of the tricyclic indole derivatives under the metallocarbenoid reaction conditions or under acidic conditions. The propensity of the tetracyclic γ-lactams to undergo rearrangement is found to be dependent on the nature of the α-substituent on the original diazo carbon and the indole N-substituent.     

Spectral and kinetic characteristics of the α-propionic acid methyl ester radical in cyclohexane and water

The -propionic acid methyl ester radical was produced in dissociative electron capture reaction of 2-chloropropionic acid methyl ester. The absorption maxima of the radical are at 310 and 300 nm in cyclohexane and water with extinction coefficients of 440±50 and 400±50 mol^–1 dm³ cm^–1. The second order decay rate parameter in water is (2.3±0.5)×10⁹ mol^–1 dm³ s^–1. The peroxy radicals have the characteristics: _max=265–270 nm, _max=700–900 mol^–1 dm³ and 2k=(7±2)·10⁸ mol^–1 dm³ s^–1.     

Voltammetric studies on the interaction of amikacin with methyl blue and its analytical application

A new method to determine the concentration of amikacin(AMK)using methyl blue(MB)as electrochemical probe was developed in this paper.In pH 4.5 Britton-Robinson(B-R)buffer solution,the MB reacted with AMK to form ion association complexes,which led to the reductive peak current of MB at-0.275 V(versus SCE)to decrease,and the decreases were linear with the concentration of AMK in the range of 1.0-60.0 mg/L,the regression of equation isΔIp(nA)=-8.48 102.36c(mg/L), correlation coefficientγis 0.997.The conditions for determining the concentration of AMK using linear sweep voltammetry(SLV) were optimized.The method was used to determine the content of amikacin commercially available with satisfactory results.     

Synthesis of a novel centipede-like copolymer of styrene and methyl methacrylate

A well-defined,A2B-type,centipede-like copolymer of styrene and methyl methacrylate(PS-PS-PMMA) was synthesized by the combination of living anionic polymerization and atom transfer radical polym-erization(ATRP) . The synthetic approach involves the coupling reaction of polystyrene(PS) backbone bearing 1,1-diphenylethene(DPE) pendant groups,produced by ATRP and Wittig reaction,with living polystyryllithium(PSLi) ,and subsequent polymerization of the resulting 1,1-diphenylmethyl anions with methy methacrylate. The centipede-like copolymer was characterized by 1H NMR,IR,SEC,SLS,and DSC measurements.     

Catalytic and inhibiting effects of ferrocene on the bulk radical–coordination polymerization of methyl methacrylate from the standpoint of formal kinetics

The kinetic curves and rates of bulk radical–coordination polymerization of methyl methacrylate initiated by the benzoyl peroxide–ferrocene system at 293–373 K, initial benzoyl peroxide concentrations of 10^–4–10^–1 mol/L, and a constant initial ferrocene concentration of 10^–3 mol/L have been calculated using a mathematical model in which the process is considered from the standpoint of formal kinetics. The calculations have demonstrated that, at low methyl methacrylate conversions, ferrocene catalyzes the process at any benzoyl peroxide concentration; at medium and high methyl methacrylate conversions, deficient amounts of ferrocene with respect to benzoyl catalyze the process as well, while excess ferrocene inhibits the process. The observed effect is explained by the specific ferrocene–benzoyl peroxide interaction, which, depending on the ferrocene: benzoyl peroxide ratio, either increases or decreases the concentration of radicals in the reaction mass.     

Photopolymerization of methyl methacrylate in the presence of the tri-n-butyl boron—p-quinone system

The photopolymerization of methyl methacrylate in the presence of tri-n-butyl boron and a number of p-quinones is studied in a wide concentration range. It is shown that the rate of polymerization and the molecular-mass characteristics of the polymers depend on the structure and concentration of p-quinone. PMMA isolated at various conversions initiates the secondary polymerization of methyl methacrylate. The activity of the macroinitator depends on the structure of p-quinone.     

Electronic spectra of o-, m- and p-tolunitrile—substituent effect on internal rotation of the methyl group

The S₁ ← S₀ fluorescence excitation spectra and the S₁→S₀ dispersed fluorescence spectra of o-, m-and p-tolunitrile were measured in supersonic jets. Low-frequency bands due to internal rotation of the methyl group were observed in m- and p-tolunitrile. Observed band positions and relative intensities of the internal rotational bands were reproduced by a calculation using a free rotor basis set. From the analysis, the potential curve of the internal rotation was determined in both S₁ and S₀. It was found that the barrier height increases in going from S₀ to S₁ in m-tolunitrile, while it decreases in p-tolunitrile. In contrast, no low-frequency band was found in o-tolunitrile. It is concluded that the potential curve in o-tolunitrile does not change in going from S₀ to S₁. The change of the barrier height by electronic excitation in tolunitriles differs greatly from that observed in other toluene derivatives. It is suggested that the electronic properties of a substituent are important for the methyl rotation in the excited state.     

SYnthesis and absolute configuration of (−)-pentalenolactone E methyl ester

The naturally occurring enantiomer of pentalenolactone E was synthesized as its levorotatory Me ester1 starting from (+)-2-ethoxycarbonyl-7,7-ethylenedioxybicyclo[3.3.0]octan-3-one3, which was obtained by treating (±)-3 with baker's yeast. The absolute configuration of pentalenolactone E Me ester was established as depicted in1.     

A kinetic and thermodynamic study of the α-cyclodextrin mediated reaction of a range of p-substituted phenyl methyl sulfides with binding and non-binding peroxyacids

This paper presents a thermodynamic study of the rate and equilibria processes involved in the α-cyclodextrin mediated reaction of a range of 4-substituted phenyl methyl sulfides with two peroxyacids of different binding affinities. The results for the inclusion processes show that the formation of 1:1 and 2:1 (host:guest) complexes between α-cyclodextrin and phenyl methyl sulfides are generally enthalpically controlled, particularly so for the 2:1 complexes, as might be expected for a ternary complex. The data from this series of sulfides is presented as enthalpy-entropy compensation plots, yielding slopes of unity for each inclusion process. The formation of a 1:1 complex between cyclodextrin and the strongly associating 3-chloroperbenzoic acid (MCPBA) is also enthapically controlled. The other peroxyacid used, peroxomonosulfate, does not bind to α-cyclodextrin to any measurable degree. As described in our original study of this reaction system (Davies and Deary in J Chem Soc Perkin Trans 2:2423–2430, 1996), catalysis by α-cyclodextrin is effected by activation of the peroxide as a result its inclusion within the cyclodextrin cavity; hence for reactions of phenyl methyl sulfides with MCPBA, catalysis is observed, but is absent for PMS. In this study the reaction rates are analysed using the transition state pseudo-equilibrium approach of Tee (Carbohydr Res 192:181–195, 1989), whereby the transition state pseudoequilibrium constant K _TS reflects the stabilisation imparted to the transition state by the association with one molecule of cyclodextrin. Enthalpy- entropy compensation plots for K _TS give slopes close to unity; this is the first reported example of such plots being applied to transition state pseudoequilibrium constants.