Cetylpyridinium bromide-based oil-in-water microemulsions as a medium for hydrolysis of esters of phosphorus acids in the presence of primary amines

High-resolution ¹H NMR technique with Fourier-transform and pulsed-gradient spin-echo was used to study the structure of oil-in-water microemulsions based on cetylpyridinium bromide. The sizes of microdrops and the distribution of components between the disperse and continuous phases were found. It was shown for the hydrolytic decomposition of O,O-bis-(p-nitrophenyl) methyl phosphonate in the presence of amines that the microemulsion medium can affect both the rate and mechanism of hydrolysis. The reaction rate constants depend on the structure of microdrops.     

Molecular-Radical Catalysis of the Chain Reaction of Quinone Imine with Hydroquinone under the Action of Aromatic Amines

Secondary aromatic amines are catalysts of the chain reaction (v = 10³ units) of N-phenyl-1,4-benzoquinone monoimine with 2,5-di-tert-butyl-1,4-hydroquinone. A complex mechanism of amine catalysis reveals that the rate of the chain reaction may increase, decrease, or remain unchanged in the presence of these compounds. In that case the product composition does not change, and amines are not consumed. The effects of temperature and the nature of para substituents (six species) on the activity of aromatic amines as catalysts were studied. A mechanism was proposed for the catalytic reaction; it implies the coupled occurrence of chain and catalytic processes. An expression for the rate of the catalytic reaction was obtained. The rate constants of individual steps with the participation of a catalyst and its radicals were calculated using the method of crossing parabolas. With the use of these data, a theoretical calculation of the dependence of the reaction rate on catalyst concentration was performed; the results were in good agreement with experimental data. The mechanism of the catalytic reaction was discussed; the similarities and distinctions between this mechanism and the mechanisms of other coupled chain reactions were demonstrated.     

Catalysis of enantiomeric ester hydrolysis in polymer domains: Catalytic effects of N-decanoyl-histidine and of dipeptide derivatives containing a histidyl residue

The catalytic activities of N-decanoyl-L -histidine and its methyl ester and of dipeptide derivatives containing an L -histidine residue toward the stereoselective hydrolysis of enantiomeric substrates have been studied at pH 7.30 (in 0.01M Bis-tris buffer) and 25°C in the presence of poly(ethyleneimine) derivatives. The dipeptide catalyst revealed greatest stereoselectivity in a quaternized poly(ethyleneimine) derivative. A comparison of catalytic effects on both the rate constants and stereoselectivities of N-decanoyl-L -histidine and its methyl ester elucidates the cooperative effects of carboxyl groups in the polymer domains. The structure of the substrates influenced both the rate constants and stereoselectivities in polymer domains.     

Effect of amines on the ceric ion-initiated polymerization of vinyl monomers. II. Polymerization of acrylonitrile by ceric ion in presence of various substituted amines

The effect of various substituted amines on the polymerization of acrylonitrile initiated by ceric ammonium sulfate has been studied in aqueous solution at 30°C. It was found that the secondary and tertiary amines considerably increased the rate of polymerization, whereas the primary amines seemed to have no effect at all. From the kinetic studies it was found that the overall polymerization rate R_p is independent of ceric ion concentration and can be expressed by the equation: R_p = k₁ [amine] [monomer] + k₂[monomer]², where k₁ and k₂ are constants (involving different rate constants). The accelerating effect of the amines was attributed to a redox reaction between the ceric ion and the amine involving a single electron transfer, the relative activity of the different amines being thus dependent on the relative electron-donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.     

Kinetics of reactions of ethylp-nitrophenyl ethylphosphonate with anionic nucleophiles in a detergentless microemulsion

The kinetics of reactions of ethylp-nitrophenyl ethylphosphonate with anionic nucleophiles in a detergentless water—oil microemulsion, formed in then-hexane—water—isopropyl alcohol system, was studied. The rate constants of the reactions in the microemulsion are higher than those in aqueous solutions and increase with increasing isopropyl alcohol: water ratio. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2262–2265, December, 1999.     

The Interaction of Ground and Excited States of Lumichrome with Aliphatic and Aromatic Amines in Methanol

The reaction of the ground and excited states of lumichrome (=7,8‐dimethylalloxazine=7,8‐dimethylbenzo[g]pteridine‐2,4(1H,3H)‐dione) with aliphatic and aromatic amines was investigated in MeOH. In the presence of aliphatic amines of high basicity, new bands are observed in the absorption and fluorescence spectra. These bands arise in a proton‐transfer reaction from lumichrome, in the ground and in the singlet excited states, to the amine. On the other hand, amines with lower basicity such as triethanolamine (=2,2′,2″‐nitrilotris[ethanol]) and aromatic amines are not able to deprotonate lumichrome, and hence a quenching of the fluorescent emission takes place without changes in the spectral shape. In this case, bimolecular‐quenching rate constants were determined for the excited singlet and triplet states. Based on laser‐flash‐photolysis experiments, an electron‐transfer mechanism is proposed. Aliphatic amines yield lower rate constants than the aromatic ones for the same driving force. A notable difference arises in the limiting value reached by the singlet and triplet quenching rate constants by aromatic amines. For the singlet quenching, the limit is coincident with a diffusion‐controlled reaction, while those for triplet quenching reach a lower constant value, independent of the driving force. This is explained by an electron‐transfer mechanism, with a lower frequency factor for the triplet‐state process.     

Proteolytic activity in various water-in-oil microemulsions as related to the polarity of the reaction medium

The catalytic behaviors of α-chymotrypsin and of trypsin were studied in anionic AOT-isooctane-water and cationic CTAB-ROH-isooctane-water microemulsion systems. The effects of various parameters, such as the pH and the water content expressed in terms of the molar ratio w_o = [H₂O]/[Surfactant], on the enzyme activity, were examined. The kinetic constants were calculated and it was found that in the case of trypsin the enzyme exhibited a remarkable “superactivityrd, when studied in the CTAB microemulsion systems. The effect of the alcohol cosurfactant used in these cationic systems was investigated in relation to the polarity of the reaction medium. By using the hydrophilic probe 1-methyl-8-oxyquinolinium betaine the micropolarity of the water core was determined and related to the kinetic results.     

Interaction of trimethylchlorosilane with silanol groups silica surface in the presence of amines

Experimental and quantum chemical studies of ClSi(CH₃)₃ interactions with SiOH groups catalyzed by amines were carried out using aerosil samples. The catalytic effects are due to the enthalpy factor of rate constants through transition state stabilization by NR₃.     

Are amines basic or nucleophilic catalysts for oxirane ring opening by proton-donating nucleophiles?

The behavior of amines as catalysts for oxirane acidolysis and phenolysis has been studied using kinetic methods. The apparent catalytic and noncatalytic reaction rate constants have been estimated. It has been demonstrated that the noncatalytic pathway has almost no effect on the apparent reaction rate constant. In order to determine the character of the behavior of amines (bases/nucleophiles) in this reaction, their reactivity has been analyzed within the conceptions of basic and nucleophilic mechanisms of catalysis. Based on the quantitative amine structure—catalytic activity correlation, it has been shown by comparing the values of correlation coefficients (r) of equations describing mechanisms for various reaction systems that, in the reactions of oxiranes with proton donors (carboxylic acids and phenols), the catalytic activity of tertiary amines/pyridines is determined by their nucleophilicity rather than basicity.     

Structural effects on the rates of the ion molecule reactions of organic heterocycles

Rate constants for proton transfer reactions of seven heterocyclic amines, eight heterocyclic ethers and propylene sulfide have been measured by photoionization mass specrometry. Rate constants for dimerization of four sulfides have also been measured. The measured rate constants have also been compared to the theoretical (ADO) rate constants. In all cases the ADO rate constants show only small variations with structure. In fact for the mono-heterocycles all but one of the ADO rate constants are between 2.0 and 1.5 × 10^?9 cc molec^?1 sec^?1. The observed rate constants show considerable dependence on chemical structure. The amines react faster than the oxides which in turn react faster than the sulfides. N-Methyl substitution on pyrrolidine and piperidine lowers their rate constants by about a factor of two while, propylene oxide reacts eighteen percent faster than ethylene oxide. Examination of the variation in the observed rate constants as a function of ring size for each group of heterocycles indicates a distinct structure-reactivity correlation although we have not attempted to rationalize this correlation. There is also a structure-reactivity dependence observed in the six-membered oxygen heterocycles having a second heteroatom O, NH, or S in the 4-position. The rate constants increase with the electronegativity of the second heteroatom.     

Interaction between primary aliphatic amines and carboxylic acid esters in aqueous micellar solutions of cationic surfactants

The effects of cetylpyridinium bromide (CPB) on the acid-base equilibria of primary aliphatic amines and on the kinetics of reactions of the amines withp-nitrophenyl acetate (PNPA) andp-nitrophenyl caprylate (PNPC) were studied by potentiometric titration and UV spectroscopy. The values of apparent pK _a of the amines in the micellar phase, binding constants of their neutral forms, and the surface potentials of micelles were determined. Cetylpyridinium bromide accelerates the aminolysis of PNPA by factors of 3 to 8 by forming mixed micellar aggregates with the amines. The shift of pK _a values of the amines in micellar solutions is not the only factor that enhances their reactivity. The substrate specificity was found: in contrast to the reaction with PNPA, CPB accelerates (by factors of 15 to 65) or retards (by factors of 4 to 6) the aminolysis of PNPA depending on the hydrophobicity of the nucleophilic reagent. The binding constants of substrates, the rate constants in the micellar phase, and the critical concentrations of micellization were determined from the data obtained. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1333–1338, July, 1998.     

Reactive interaction of aromatic amines with dialdehyde cellulose gel

A new chromatographic method was developed for separation of amines based on their interaction with aldehyde groups in stationary phase. Expecting specific interaction with aldehyde groups through imine formation (Schiff base), we introduced dialdehyde groups to a commercial cellulose packing by periodate oxidation and examined eluting behavior of various aromatic amines. Primary amines with acid dissociation constants (pKa) greater than 6 showed no delay at pHs of 4.0–5.5, indicating the lack of interaction because of complete protonation. Primary amines with pKa less than 6 showed remarkable delays according to the amount of aldehyde groups on cellulose. The delay was dependent on the pH of eluent. The amines with pKa of 4–5.3 eluted faster at lower pH, apparently because of the change in proportion of free and protonated species. Amines with pKa less than 3.4 also showed delays but they eluted slower at lower pH. The latter behavior can be ascribed to the change in the ratio of free/protonated species of imines formed. Certain degree of steric effect was also noted, that is, compounds with a primary amino group adjacent to bulky substituents (ortho compounds) showed weaker interaction with aldehyde groups than meta- and para-isomers.     

Correlation of the Catalytic Activity of Pyridines and N-Pyridine Oxides with Their Basicity

N-Pyridine oxides much stronger catalyze formation of organophosphorus thiosemicarbazides than pyridines, even though these two groups of catalysts compare in basicity. Separate correlations were found for pyridines and N-pyridine oxides of the catalytic rate constants with the basicity constants in water and nitromethane, as well as with the abilities of the catalysts to H-bond formation. The high catalytic activity of N-pyridine oxides is associated with the manifestation of the -effect in the reaction studied.     

Structure–Reactivity Relationship in the Frustrated Lewis Pair (FLP)‐Catalyzed Hydrogenation of Imines

The autoinduced, frustrated Lewis pair (FLP)‐catalyzed hydrogenation of 16‐benzene‐ring substituted N‐benzylidene‐tert‐butylamines with B(2,6‐F₂C₆H₃)₃ and molecular hydrogen was investigated by kinetic analysis. The pK_a values for imines and for the corresponding amines were determined by quantum‐mechanical methods and provided a direct proportional relationship. The correlation of the two rate constants k₁ (simple catalytic cycle) and k₂ (autoinduced catalytic cycle) with pK_a difference between imine and amine pairs (ΔpK_a) or Hammett's σ parameter served as useful parameters to establish a structure–reactivity relationship for the FLP‐catalyzed hydrogenation of imines.     

Asymmetric Transfer Hydrogenation of Ketones Catalyzed by Amino Acid Derived Rhodium Complexes: On the Origin of Enantioselectivity and Enantioswitchability

Amino acid based thioamides, hydroxamic acids, and hydrazides have been evaluated as ligands in the rhodium‐catalyzed asymmetric transfer hydrogenation of ketones in 2‐propanol. Catalysts containing thioamide ligands derived from L ‐valine were found to selectively generate the product with an R configuration (95 % ee), whereas the corresponding L ‐valine‐based hydroxamic acids or hydrazides facilitated the formation of the (S)‐alcohols (97 and 91 % ee, respectively). The catalytic reduction was examined by performing a structure–activity correlation investigation with differently functionalized or substituted ligands and the results obtained indicate that the major difference between the thioamide and hydroxamic acid based catalysts is the coordination mode of the ligands. Kinetic experiments were performed and the rate constants for the reduction reactions were determined by using rhodium–arene catalysts derived from amino acid thioamide and hydroxamic acid ligands. The data obtained show that the thioamide‐based catalyst systems demonstrate a pseudo‐first‐order dependence on the substrate, whereas pseudo‐zero‐order dependence was observed for the hydroxamic acid containing catalysts. Furthermore, the kinetic experiments revealed that the rate‐limiting steps of the two catalytic systems differ. From the data obtained in the structure–activity correlation investigation and along with the kinetic investigation it was concluded that the enantioswitchable nature of the catalysts studied originates from different ligand coordination, which affects the rate‐limiting step of the catalytic reduction reaction.     

Silica‐supported Cu(II)–quinoline complex: Efficient and recyclable nanocatalyst for one‐pot synthesis of benzimidazolquinoline derivatives and 2H‐indazoles

The synthesis, characterization and catalytic activity of a Cu(II) complex derived from 2‐oxoquinoline‐3‐carbaldehyde Schiff base supported on amino‐functionalized silica are reported. 3‐(1H‐Benzo[d]imidazol‐2‐yl)quinolines containing piperidine, morpholine and phenylpiperazine skeletons at the C‐2 position were formed in good to excellent yields via the one‐pot reaction of 2‐chloroquinoline‐3‐carbaldehyde, benzene‐1,2‐diamines and secondary amines in the presence of the nanocatalyst under mild conditions. Moreover, the nanocatalyst was found to be recyclable for up to seven runs without significant loss of activity. Also, a series of 2H‐indazoles were synthesized by the catalytic condensation of 2‐bromobenzaldehyde, sodium azide and primary amines.     

Study of association thermodynamics between crystal violet and sodium bis(2-ethylhexyl)sulfosuccinate and kinetics of basic fading of crystal violet in microemulsions

The thermodynamics of the association between 4,4′,4″-tris(dimethyl-amino)triphenylmethyl chloride (crystal violet or CV) and sodium bis(2-ethylhexyl)-sulfosuccinate (aerosol OT or AOT) in water/AOT/n-decane microemulsion and the kinetics of the basic hydrolysis of CV in a water-in-oil microemulsion were investigated by UV–vis spectroscopic measurements. An association model of CV and AOT was used to analyze the experimental data to obtain the association constants at various temperatures. By taking the association into account, the “actual” rate constants and the activation energies of the basic hydrolysis of CV in the media of water/AOT/oil were obtained. The difference in thermodynamics and kinetics between the two media of water/AOT/n-decane and water/AOT/isooctane is discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 294–300, 2008     

Effect of solvent on the free energy of activation of S_N2 reaction between phenacyl bromide and amines

The kinetics of SN2 reaction between phenacyl bromide and various amines in 12 different solvents were studied. Solvent effects on the rate of this reaction and free energy of activation, ΔG# , were interpreted by applying the Abraham-Kam-let-Taft (AKT) equation. UK solvent polarity (π1*), solvent hydrogen-bond basicity (β1) and Hildebrand cohesive density energy (δH2) are those parameters which increase the rate constant and decrease ΔG# , while solvent hydrogen-bond acidity (α1) will have the compensatory effect. A comparison among obtained values of second rate constants, k2, for different amines in a given solvent indicates that the amine reactivities are highly dependent on their structures. The consequent decrease of the rate constant for different amines in any given solvent was found to be: primary > secondary> tertiary. This order results from steric effects of amines.     

Kinetic study of amination of chloromethylated polystyrene with hydroxyalkylic tertiary amines

The kinetics of the amination of chloromethylated polystyrene with two hydroxyalkylic tertiary amines (1-dimethyl-amino-3-propanol and 1-dimethylamino-2-propanol) in dimethylacetamide and dioxane was studied. The amination of benzyl chloride with the two amines in dimethylacetamide was followed. It was found that the amination of chloromethylated polystyrene is a two-step reaction taking place with different rates. The rate constants k₁ and k₂ were calculated for the two stages, and a self-accelerating effect of the reaction was noticed. Also, the influence of the position of the hydroxyl group versus the tertiary nitrogen was investigated. The increase of the dielectric constant of the solvent favorably influences the reaction rate.     

Kinetics and mechanism of oxidation of some para-, meta-, and ortho-substituted ethyl S-phenylmercaptoacetates by chloramine-B(CAB)

The kinetics of oxidation of ethyl S-phenylmercapto acetate and several para-, meta-, and ortho-substituted ethyl S-phenylmercaptoacetates by chloramine-B have been studied in 50% (V/V) aqueous ethanol medium containing phosphate buffer. This oxidation is of first order with respect to substrate and zero order with respect to oxidant. A catalytic effect of mercury is observed and the order with respect to mercury is fractional (0.74). The increase in pH decreases the rate of oxidation and the order with respect to H⁺ is 0.05. In general electron-releasing substituents accelerate the rate while electron-attracting groups retard the rate. A good correlation is found to exist between log k ₁ and Hammett constants. Susceptibility of the reaction to the steric effect of ortho-substituents has been analyzed in the light of application of Taft's steric energy parameters. © John Wiley & Sons, Inc.