Solvent and substituent effects on the electrochemical oxidation of para‐ and meta‐substituted anilines

Electrochemical oxidation of 15 para‐ and meta‐substituted anilines in different mole fractions of water in 2‐methylpropan‐2‐ol has been investigated in the presence of 0.1 M sulfuric acid as a supporting electrolyte. The oxidation potential data of anilines correlate well with the Brown–Okamoto's substituent constants affording a negative reaction constant. The effect of para‐ and meta‐substituents on the oxidation potential confirms to Swain's F and R, affording negative reaction constants. The oxidation potential values also correlate satisfactorily with macroscopic solvent parameter such as relative permittivity, ε_r. The results of Kamlet–Taft multiple correlation analysis show that specific solute–solvent interactions play a dominant role in governing the reactivity. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 289–297, 2007     

Linear free‐energy relationships in chromium(VI) oxidation of substituted benzylamines in nonaqueous media

The kinetics of oxidation of 11 para‐ and meta‐substituted benzylamines by imidazolium fluorochromate (IFC) in different organic solvent media has been investigated in the presence of p‐toluenesulfonic acid (TsOH). The reaction was run under pseudo‐first‐order conditions. The rate of the reaction was found to be first order in IFC and found to increase with increase in [TsOH]. Solution IR studies in combination with kinetic measurements were used to get a better insight into the mechanism of the oxidation process. The product analysis was carried out using GC–MS. Various thermodynamic parameters for the oxidation have been reported and discussed along with the validity of the isokinetic relationship. The specific rate of oxidizing species benzylamines reaction (k₂) correlates with Hammett's substituent constants affording positive reaction constants. The rate data failed to correlate with macroscopic solvent parameters, such as ε_r and E^N_T, while showing satisfactory correlation with Kamlet–Taft's solvatochromic parameters (α, β, and π*) which suggests that the specific solute–solvent interactions play a major role in governing the reactivity, and the observed solvent effects have been explained on the basis of solute–solvent complexation. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 362–369, 2007     

Kinetics and mechanism of oxidation of substituted benzaldehydes by quinolinium fluorochromate

The kinetics of oxidation of a number of meta- and para-substituted benzaldehydes by quinolinium fluorochromate, QFC has been studied in aqueous acetic acid medium in the presence of acid. The products of oxidation are the corresponding benzoic acids. The reaction is first order each in substrate, QFC and HClO₄. Electron-withdrawing substituents increase the rate, while electron-releasing substituents decrease it and the rate data obey Hammett's relationship. The reaction constant for the oxidation has a value of 1.16±0.07 at 30°C. The activation enthalpies and entropies are calculated and the possible mechanism for oxidation is discussed.     

Mechanism of the oxidation of some substituted acetophenones byN-Bromosuccinimide in acidic media

The kinetics of the reaction of three substituted acetophenones withN-Bromosuccinimide was studied in perchloric acid media in presence of mercuric acetate. The reactions were found to be zero order with respect toNBS while the order with respect to ketones and [H⁺] was found to be unity. The addition of succinimide mercuric acetate and sodium perchlorate has no effect on the rate of oxidation and the rate increases with the decrease in dielectric constant of the medium. Kinetic investigations have revealed that the order of reactivity ism-nitroacetophenone > p-chloroacetophenone > p-methylacetophenone. TheArrhenius equation has been found to be valid in the temperature range 35–55°. Thermodynamic parameters have been calculated. Mechanistic pathways of the reactions are discussed and a rate equation is derived.Hammett's plot gives a ? value of +0.60 for methyl-aryl-ketones.     

Pyridiniumchlorochromate oxidations: Studies on the kinetics and substituent effect in the oxidation of aniline in nonaqueous systems

Pyridiniumchlorochromate (PCC) oxidizes aniline and substituted anilines except nitro anilines smoothly in chlorobenzene–nitrobenzene mixtures in the presence of dichloroacetic acid. The reaction has unit dependence on each of the aniline, PCC, and dichloroacetic acid concentrations. Electron-releasing substituents accelerate the reaction, whereas electronwithdrawing groups retard the reaction, and the rate data obey Hammett's relationship. The reaction constant ρ is -3.75. Azobenzene and p-benzoquinone have been obtained as products. The observed experimental data have been rationalized in terms of the formation of an intermediate complex involving PCC–amine undergoing a rapid decomposition to products.     

Kinetics and mechanism of the reaction of para‐chlorophenyl aryl chlorophosphates with anilines in acetonitrile

The kinetics and mechanism of the nucleophilic substitution reactions of p‐chlorophenyl aryl chlorophosphates ( 2 ) with anilines are investigated in acetonitrile at 55°C. Relatively large magnitudes of ρ_X and β_X values are indicative of a large degree of bond making in the TS. Smaller magnitudes of ρ_X (0.20 for X = H) and ρ_XY (?0.30) than those for the corresponding reactions with phenyl aryl chlorophosphates ( 1 ) (ρ_X = 0.54 for X = H and ρ_XY = ?1.31) are interpreted to indicate partial electron loss, or shunt, towards the electron acceptor equatorial ligand (p‐ClC₆H₄O‐) in the bipyramidal pentacoordinated transition state. The inverse secondary kinetic isotope effects (k_H/k_D = 0.64–0.87) involving deuterated aniline (ND₂C₆H₄X) nucleophiles, and small ΔH^? and large negative ΔS^? are obtained. These results are consistent with a concerted nucleophilic substitution mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 632–637, 2002     

Column liquid chromatography of some substituted anilines and phenols

Summary A systematic survey of the elution of phenols and anilines from three commercially available column packings has been made in an attempt to gain an understanding of the mechanisms causing retention and the structural factors modifying it. In both cases empirical rules were observed which fitted the experimental behaviour and for phenols these correlations are consistent with the formation of hydrogen bonds between the phenolic hydrogen and electronegative sites in the stationary phase. Retention of anilines is not so well defined in this respect.     

Formation of aromatic radical-cations by oxidation with electronegatively substituted quinones in acid media; kinetics and mechanism

Electronegatively substituted quinones are shown to oxidize electronrich aromatic molecules to the corresponding radical-cations in acid medium via a reversible two step mechanism. The influence of acid strength on the rate of the reaction suggests that a protonated quinone molecule acts as the primary electron acceptor. The rate of formation of the radical cations depends on the one electron oxidation potential of the parent aromatic molecules in a way typical for endothermic outersphere electrontransfer.     

The Photophysics of Pyridine‐Derivatized ortho‐, meta‐, and para‐Dibutylamino Cruciforms

The photophysical properties of a series of para‐substituted donor–acceptor cruciform fluorophores ( p 1 – 4 ) were investigated and compared with their meta and ortho isomers ( m 1 – 4 and o 1 – 4 ). The structural variations were found to have a significant effect on the solvatochromism, fluorescence quantum yields (Φ_fl), fluorescence lifetimes (τ_fl), and response upon addition of trifluoroacetic acid. The observed spectral shifts in absorption and emission caused by protonation of the cruciforms make them promising candidates as chemosensors. Additional computational studies provided more insight into the electronic structure of the systems.     

Dielectric relaxation study of some substituted anilines in various non-polar solvents

The dielectric permittivity (ϵ′) and dielectric loss (ϵ″) have been measured at 9.945 GHz for 2-chloro-6-methylaniline, 3-chloro-2-methylaniline, 2-chloro-4-methyl-aniline, 4-chloro-2-methyl-aniline and 5-chloro-2-methyl-aniline in various solvents, e.g. n-heptane, benzene, cyclohexane, carbon tetrachloride and decalin at 35°C. The static permittivity (ϵ_o) at 300 KHz and high frequency limiting permittivity (ϵ_∞) have also been measured at 35°C. The data are analysed by Higasi's method in terms of the so-called slopes, a_o, a′, a″ and a_∞ The values of relaxation time, distribution parameter (α), and the difference (a_∞−a_D) so obtained, indicated the existence of more than one relaxation mechanism. This has been interpreted in terms of the intramolecular rotations of the amino group occurring simultaneously with the overall molecular orientation. The investigation also includes the determination of free energies of activation ΔF_ϵ, ΔF_η and the dipole moment μ of these substituted anilines in different solvents. Discrepancies have been explained in terms of solute-solvent interactions.     

Studies on kinetics and mechanism of oxidation of D‐sorbitol and D‐mannitol by cerium(IV) in aqueous micellar sulfuric acid media

The kinetics and mechanism of cerium(IV) oxidation of hexitols, i.e. D ‐sorbitol and D ‐mannitol, in aqueous sulfuric acid media have been studied in the presence and absence of surfactants. Under the kinetic conditions, [S]_T ? [Ce(IV)]_T, where [S]_T is the total substrate (D ‐sorbitol or D ‐mannitol) concentration, the overall process shows a first‐order dependence on [Ce(IV)]_T and [S]_T. The process is acid catalyzed and inhibited by [HSO]. From the [HSO] dependence, it has been noted that the both Ce(SO₄)²⁺ and Ce(SO₄)₂ have been found kinetically active. The different rate constants in the presence and absence of surfactants have been estimated with the activation parameters. N‐cetylpyridinium chloride has been found to retard the oxidation process of hexitols, whereas sodium dodecyl sulfate has been found to accelerate the rate process. All these findings including the micellar effects have been interpreted in terms of the proposed reaction mechanism and partitioning behavior of the kinetically active different species of Ce(IV) between the aqueous and pseudomicellar phase. © 2008 Wiley Periodicals, Inc. 40: 445–453, 2008     

Substituent effects on the reactions of aromatic triflones with para‐X‐anilines in methanol: Low intrinsic reactivity and transition state imbalances

A kinetic study is reported for S_NA_r reactions of 2,4,6‐tris(trifluoromethanesulfonyl) anisole 1a with a series of para‐X‐substituted anilines 2a–e in a methanol solution at various temperatures. The substituent effects on free energy (Δ^≠G), enthalpy (Δ^≠H), and entropy (Δ^≠S) of activation are examined. Aniline addition to triflone 1a is characterized by a β_X=0.57, α_Z=0.31, and an imbalance of I = α_Z–β_X=?0.26. The imbalance shows that resonance development lags behind C? N bond formation at the transition state. Interestingly, analysis of the results in terms of Marcus theory reveals that these S_NAr are associated with some extremely low intrinsic reactivity (log k_o=?1.25& © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 255–262, 2011     

meta‐ and para‐Phenylenediamine‐Fused Porphyrin Dimers: Synthesis and Magnetic Interactions of Their Dication Diradicals

meta‐ and para‐Phenylenediamine‐fused nickel(II) porphyrin dimers were synthesized by S_NAr reaction of meso,β,β‐trichloro nickel(II) porphyrin with meta‐ and para‐phenylenediamines and subsequent Pd‐catalyzed intramolecular C?H arylation. Their tetrachlorinated dication diradicals are very stable, allowing SQUID magnetometry and revealing clear open‐shell characters for both meta and para isomers with ferro‐ and anti‐ferromagnetic interactions, respectively. The nitrogen analogue of Thiele's hydrocarbon usually displays predominant closed‐shell nature but its hidden diradical characters increase either in a twisted conformation or upon insertion of an additional phenylene spacer. The observed distinct diradical nature of the para‐congener indicates that diradical properties can be enhanced also by efficient spin delocalization.     

The N-substitution and N-oxidation effects on the carbon-13 chemical shift of some substituted anilines

The N-substitution and the N-oxidation effects on the carbon-13 chemical shift for all ring carbons of some substituted anilines are discussed. Correlation of the N-substitution effect with substituent constants by means of a linear combination of two empirical parameters, σ_I and σ_R has been studied. The best correlation was obtained between the N-methylation effect and the substituent constants.     

Novel amphiphilic homopolymers containing meta‐ and para‐pyridine moieties with living characteristics and their self‐assembly

Amphiphilic monomers containing the isomeric pyridine moieties 3‐(4‐vinylphenyl)pyridine (3VPPy) and 4‐(4‐vinylphenyl)pyridine (4VPPy) were synthesized using the Suzuki coupling reaction. A living anionic polymerization of 3VPPy and 4VPPy was successfully performed under various conditions to overcome the limitations of anionic polymerization and to compare their properties with those of poly(2‐(4‐vinylphenyl)pyridine) as reported previously. Several characteristics of the resulting isomeric P3VPPy and P4VPPy were studied, such as thermal stability, solubility, and the living nature. The block copolymerization of 4VPPy with 2‐vinylpyridine and MMA was carried out without additive to estimate the nucleophilicity of P4VPPy and to confirm its living nature. Additionally, each amphiphilic homopolymer of P3VPPy and P4VPPy containing both a hydrophilic pyridine unit and a hydrophobic styrene unit was tested for self‐assembly behavior in a mixed solvent (THF/water) and monitored with TEM and SEM. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3458–3469     

ortho‐, meta‐, and para‐Dihydroindenofluorene Derivatives as Host Materials for Phosphorescent OLEDs

This work reports the first structure–properties relationship study of ortho [2,1‐c]‐, meta [1,2‐a]‐, and para [1,2‐b]dihydroindenofluorenes, highlighting the influence of bridge rigidification on the electronic properties. This study has made it possible to devise an extended π‐conjugated molecule with both a high triplet state energy level and excellent thermal and morphological stability. As a proof of concept, dihydroindenofluorenes were used as the host in sky‐blue phosphorescent organic light‐emitting diodes (PhOLEDs) w ith high performance.