Proton Transfer Complex Formation Research Articles

CATALYTIC INFLUENCE OF NITROGEN-CONTAINING BASE ON COMPLEXATION OF OCTA(m-TRIFLUOROMETHYLPHENYL)PORPHYRAZINE AND HEXA(m-TRIFLUOROMETHYLPHENYL)BENZOPORPHYRASINE

The review presents data on the complexation of octa(m-trifluoromethylphenyl)porphy-razine and hexa(m-trifluoromethylphenyl)benzoporphyrazine with zinc acetate in a system nitrogen-containing base - benzene. It was shown that the investigated porphyrazines, having pronounced acidic properties at the incyclic NH bonds, interact with n-butylamine, tret-butylamine, morpholine and piperidine in benzene with the formation of proton-transfer complexes. In these complexes, the intocyclic protons of the NH-groups associated with the oxygen atom of the dimethyl sulfoxide molecule and the intocyclic nitrogen atoms are located above and below the plane of the macrocycle. In an inert, low-polar benzene, the degree of proton transfer from acid to base is limited by the stage of the H-complex (H-associate) formation or ionic complex (ion-ion) associate. It was found that proton transfer complexes of octa(m-trifluoromethylphenyl)porphyrazine and hexa(m-trifluoromethylphenyl)benzoporphyrazine exhibit low kinetic stability. The role of this acid - base interaction in the complexation reaction of octa(m-trifluoromethylphenyl)-porphyrazine and hexa(m-trifluoromethylphenyl)benzoporphyrazine with zinc acetate is shown. High kinetic stability of zinc complexes with the investigated porphyrazines in contrast to complexes with proton transfer was revealed. Based on the analysis of kinetic data, it was found that the introduction of Zn2+ into the coordination center of octa(m-trifluoromethylphenyl)porphyrazine and hexa(m-trifluoromethylphenyl)benzoporphyrazine is preceded by the stage of interaction of porphyrazine with a nitrogen-containing base. This leads to the formation of an intermediate reactive acid-base complex that differs in composition from complexes with proton transfer of porphyrazines. It was shown that piperidine and n-butylamine exert the maximum catalytic effect on the formation of zinc complexes with the investigated porphyrazines. A decrease in the pKa of the nitrogen-containing base, as well as an increase in the spatial shielding of the nitrogen atom in the amine by alkyl substituents, counteracts the formation of an intermediate acid-base complex and, as a result, reduces the complexation rate of octa(m-trifluoromethylphenyl)porphyrazine and hexa(m-trifluoromethylphenyl)benzoporphyrazine with zinc acetate in benzene.

A few insensitive energetic nitrogen rich compounds composed of substituted azoles and 3,5-dinitrobenzoic acid: Synthesis, characterization, physicochemical, detonation properties and pyrolytic products

Hydrogen bonded proton transfer crystals 1–4 were synthesized, using substituted azoles and 3,5-dinitrobenzoic acid, in a ratio 1:1 and ethanol as solvent at room temperature. The structure elucidation for the synthesized energetic crystals was carried out using spectral techniques such as, IR, 1H, and 13C NMR spectroscopy. The formation of proton transfer complexes occurred due to the transfer of lone pair of electrons from the donor azoles such as 3-nitropyrazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, and 5-aminotetrazole to the acceptor 3,5-dinitrobenzoic acid through N+-H…O− type of hydrogen bond and was ascertained by X-ray crystallographic and proton NMR studies. Mathematical calculations propounded by various scientists are used to determine the explosive properties. The thermal stability was carried out using DSC-TGA studies. Sensitivity parameters were also calculated for the synthesized compounds. The results indicated that the proton transfer complexes are more stable, insensitive to impact, have high energetic parameters and thus classified into the category of High-energy-density materials (HEDMs). The high nitrogen content compounds gives out nitrogen gas (N2) as major detonation product, which will burn cleanly, producing less carbon monoxide and paving the way for new generation of environmentally compatible energetic materials.

Spectroscopic investigation on proton transfer reaction in the complex of 2-aminopyridine with 2, 6-dichloro-4-nitrophenol in different solvents

Proton transfer (PT) reaction between 2-aminopyridine (2AP) with 2,6-dichloro-4-nitrophenol (DCNP) has been investigated spectrophotometrically in methanol (MeOH), acetonitrile (AN) and acetonitrile with 1,2-dichloroethane binary mixtures (1:1, ANDEI) and (3:1, ANDEII). A long wavelength band in the range 395–424 nm due to the proton transfer complex formation has been recorded. The formation constants of the PT-reaction (K PT) have been estimated using Benesi–Hildebrand equation. It has been found that K PT recorded larger value in AN than MeOH and binary mixtures. This result was interpreted in terms of solvatochromic parameters like, solvent polarizability (π ⁎), hydrogen bond donor (α), and hydrogen bond acceptor (β). The molecular composition of the PT-complex has been identified by Job's and photometric titration methods where 1:1 complex is formed. Based on the rapidity and simplicity of the PT-reaction as well as the stability and simple composition of the formed complex, a rapid, accurate and sensitive spectrophotometric method for determination of 2AP was proposed. In addition, the solid PT-complex (2AP-DCNP) has been isolated and characterized using elemental analyses and FTIR measurements.

Spectrophotometric studies of proton transfer complexes between 2-amino-4-methoxy-6-methyl-pyrimidine and 2-amino-4,6-dimethyl-pyrimidine with 2,6-dichloro-4-nitrophenol in acetonitrile

2-Amino-4-methoxy-6-methyl-pyrimidine (AMMP) and 2-amino-4,6-dimethyl-pyrimidine (ADMP) react with 2,6-dichloro-4-nitrophenol (DCNP) to form yellow proton transfer (PT) complexes in acetonitrile at absorption maxima around 420 nm. These PT reactions have been applied to the simultaneous spectrophotometric determination of (AMMP) and (ADMP) in acetonitrile. Factors controlling the PT process were studied and optimized. Job 's method of continuous variations was applied to identify the composition of the formed complexes. The PT complex formation constants ( K PT) and the molar extinction coefficients ( ε) were estimated using Benesi–Hildebrand equation. Moreover, the solid PT complexes were isolated and characterized using elemental analysis and infrared measurements.

Intermolecular hydrogen bonds and proton transfer equilibrium in some nitro cresols-aliphatic amines-acetonitrile or methanol systems

Intermolecular hydrogen bonds between two nitro cresols, 2-nitro-4-methylphenol (NMP) and 3-methyl-4-nitrophenol (MNP) with three aliphatic amines morpholine (MO), Benzylamine (BA) and triethylamine (TEA) have been investigated in acetonitrile and methanol applying UV-Vis spectroscopy. It has been found that the proton transfer complex formation is retarded in acetonitrile leading to a sharp decrease in the proton transfer equilibrium constants (K PT). On the other hand, the proton transfer complex formation is strongly favored in methanol leading to a sharp increase in K PT. The presence of a single ortho substituent and strong intramolecular hydrogen bond does not inhibit the proton transfer process. It has been recorded from this work that the intramolecular hydrogen bond is not broken in acetonitrile but broken in methanol. It has been found alsa that TEA is sterically hindered in forming hydrogen bonds when compared to primary and secondary amines. Moreover, the present contribution proved that acetonitrile binds the phenol OH as hydrogen bonding proton acceptor while methanol binds as a proton donor with the phenol OH.

Infrared spectra of proton transfer complexes of the cycleanine alkaloid in solid state

Proton transfer complexes obtained between the cycleanine alkaloid and hydrogen chloride, hydrogen bromide and nitric acids have been investigated by infrared spectroscopic technique between 4000 and 400 cm −1 in KBr. The vibrational perturbations brought about by proton transfer complex formation, discussed in terms of preferred site of interaction, show that the proton of the inorganic acids is transferred to cycleanine through one of its N sites.

Factors affecting the adsorption of stabilisers on to carbon black (flow micro-calorimetry studies) Part III Surface activity study using acid/base model probes

The first and second part of this series of papers investigated the interaction between carbon black and stabilisers (phenolic antioxidants and HALS, respectively) and showed that the mechanism was dependent on both the chemical nature of the carbon black surface and the molecular structure of stabilisers. In this third part, the interactions between model compounds, of varying acidity, and the same four carbon blacks, are investigated using flow micro-calorimetry (FMC) and Fourier transform Infrared spectroscopy (FTIR). As with the first and second parts, differences in adsorption behaviour between the four types of carbon black were evident and were principally related to the chemical nature of the surfaces and the adsorbates. In this study further insight in to the nature of the interactions between the carbon black surface functional groups and the acidic and basic probes has been acquired. The main forms of interaction are hydrogen bonding and Lewis and Bronsted acid/base interactions, formation of proton transfer complexes was also considered possible in cases of strong adsorption. The adsorption behaviour of acid and basic aromatic probes, together with octadecanol and stearic acid, was also found to be dependant on the carbon black surface topography. Flat graphene layers containing minimal heteroatoms favoured adsorption of the latter species as flat adsorption and/or structural ordering was permissable.

Proton transfer equilibria, temperature and substituent effects on hydrogen bonded complexes between chloranilic acid and anilines

The proton transfer equilibrium constants (KPT) for 1 : 1 complex formation between Chloranilic Acid (CA) and a series ofp- andm‒substituted anilines have been measured in 1,4-dioxane spectrophotometrically. The results supported the concept of amine-solvent hydrogen bond formation (short range solvation effect). Beside, this effect, theKPTvalues were apparently affected by the electron donation power of the aniline ring substituent, which was transmitted to the interaction center via resonance and inductive effects. Linear relationships betweenKPTand σ-Hammett substituent constants, or pKvalues formandpanilines,were obtained verifying the above conclusions. The solute-solvent hydrogen bond formation might increase the reactivity of the aniline nitrogen than would the inductive effect of the alkyl group, in case of CA-N-alkyl aniline complexes. The thermodynamic parameters for the proton transfer complex formation were estimated and it was indicated that the solvent–aniline hydrogen bond formation was preferred in the case ofp-substituted aniline complexes more than in the case of the correspondingm‒isomer. It has been found that the proton transfer process was enthalpy and entropy controlled.

Short range solvation by fluorinated alcohols of proton transfer complex formation between pentachlorophenol and triethylamine: determination of solvation constants and stoichiometries

Abstract Primary and secondary solvation binding constants and stoichiometries are reported for the protic solvation by pentadecafluorooctanol (PFO) and trifluoroethanol (TFE) of the non-bonding electrons on triethylamine (TEA) and on the oxygen of the proton-transfer complex formed by pentachlorophenol (PCP) and TEA. The solvation-sensitive apparent proton-transfer formation constant KPT is measured in varying low concentrations of the protic solvent S in benzene bulk solvent, and the solvation binding constants and stoichiometries are determined. A two-stage solvation model is supported, as observed in earlier studies of similar systems. The primary solvation stage involves a single solvent alcohol molecule, whereas the secondary stage involves several solvent molecules.

Solvation Effect on Proton Transfer Complex Formation between 2,4-Dinitro-1-naphthol and Amines

The equilibrium constants for the proton transfer complex formation K eq of 2,4-dinitro-1-naphthol (DNN) with some amines in benzene-dimethylformamide, ethyl acetate, dioxane, and acetonitrile mixed solvents were measured. The sharp increase in K eq for the reaction of DNN with primary and secondary amines suggests the formation of a hydrogen bond between the amine hydrogen(s) and the electron-donating solvents. A linear correlation between K eq , for the DNN-DEA reaction, and Taft's β parameter is found except for dioxane. The increase in the equilibrium constants between DNN and TEA is explained on the grounds of a long-range solvation effect. It is shown that K eq in these systems is qualitatively related to the dielectric constant (e) and Taft's n parameters of the solvents used. It is found that the short-range solvation effect increases K eq more sharply than the long-range one.

Spectrophotometric Determination of Proton Transfer Equilibria and Thermodynamic Parameters of 1:1 Hydrogen Bonded Complexes in Chloranilic Acid-Amine Systems in 1,4-Dioxan

Abstract The equilibrium constants for 1:1 proton transfer complex formation between chloranilic acid (CA) and quinoline, α-picoline, benzyl amine (BA), triethyl amine (TEA) and diethyl amine (DEA) have been measured in 1,4-dioxan by using UV spectroscopy. A linear correlation between the logarithm of the proton-transfer equilibrium constant and the pK of the amine has been found, except for primary and secondary amines. The results support the concept of amine-solvent hydrogen bond formation, which increases the reactivity of tha amine as a base. Such hydrogen bonds increase amine basicity more than would the inductive effect of an added alkyl group. The thermodynamic parameters were found in agreement with these results. Moreover, the thermodynamic data showed that the strength of the hydrogen bonds involved are among the strongest hydrogen bonds known.

Short range solvation effects with primary and secondary amines

Equilibrium constants for proton transfer complex formation between 2,4-dinitrophenol and aliphatic amines have been measured at 25°C for benzene solvents containing small amounts of dimethylformamide, acetonitrile, ethyl acetate, or dioxane. The results support the concept of amine-solvent hydrogen bond formation, which increases the reactivity of the amines as bases. Such hydrogen bonds increase amine basicity more than would the inductive effects of an added alkyl group.

Specific patterns of short range solvation — aliphatic amines in benzene–dimethylsulfoxide mixed solvents

The trends in the values of equilibrium constants for the formation of proton transfer complexes between 2,4-dinitrophenol and various aliphatic amines are used to infer the nature of the short range solvation of the amines in benzene–DMSO solvent mixtures. Hydrogen bonds between the DMSO oxygen and the amine proton increase the basicity of the primary and secondary amines. Equilibrium constants for this bond formation are estimated for secondary amines.

Models of intermolecular interactions involving proton transfer in biopolymers

The results of spectrophotometric and conductimetric studies of the ionization of several phenol derivatives in the presence of amines in dioxane and aqueous dioxane solutions, were used to delineate the ranges of solvent polarity over which 1:1 proton transfer complexes are formed. Increasing polarity favors the formation of proton transfer complexes up to a point determined by the nature of the acid-base pair. Proton transfer complexes display a measurable stability over an appreciable range of solvent polarity varying from low ( D < 11) to medium (11 < D < 45). Their formation involves a free energy change ranging from −2.0 to −7.1 kcal · mole −1 and a decrease in enthalpy ranging from 6.1 to 16.8 kcal · mole −1. The effects of proton transfer complex formation between side chain groups of biopolymers are subdivided into structural, chemical and kinetic, and the relevance of the results obtained from model studies to biopolymers is discussed. It is suggested that formation of proton transfer complexes can affect the direction of conformational change in macromolecules and play an important role in the formation of oligomeric structures. The numerical inferiority of proton transfer complexes in biopolymers, relative to hydrophobic and hydrogen bonding interactions should be partially offset by the greater contribution of the former to the total free energy and enthalpy of formation of specific biopolymer conformations.