Benzylidene Aniline Research Articles

Effects of single bond-ion and single bond-diradical form on the stretching vibration of C[dbnd]N bridging bond in 4,4′-disubstituted benzylidene anilines

Fifty-seven samples of model compounds, 4,4′-disubstituted benzylidene anilines, p-X-ArCH=NAr-p-Y were synthesized. Their infrared absorption spectra were recorded, and the stretching vibration frequencies νCN of the CN bridging bond were determined. New stretching vibration mode was proposed by means of the analysis of the factors affecting νCN, that is there are mainly three modes in the stretching vibration of CN bond: (I) polar double bond form CN, (II) single bond-ion form C+–N− and (III) single bond-diradical form C–N. The contributions of the forms (I) and (II) to the change of νCN can be quantified by using Hammett substituent constant (including substituent cross-interaction effects between X and Y groups), whereas the contribution of the form (III) can be quantified by employing the excited-state substituent constant. The most contribution of these three forms is the form (III), the next is the form (II), whose contribution difference was discussed with the viewpoint of energy requirements in vibration with the form (III) and form (II).

Synthesis, crystal growth and characterization of organic NLO material: 4-Bromo-4′-hydroxybenzylidene aniline

One of the novel benzylidene aniline derivatives, 4-bromo-4′-hydroxybenzylidene aniline (BHBA) was synthesized and single crystal of BHBA was grown from solution following slow evaporation method at room temperature. Unit cell parameters of the grown crystal were determined from single crystal X-ray diffraction studies. Functional groups of BHBA were identified from Fourier transform infrared spectral study. UV–vis-NIR analysis of BHBA showed that the crystal is transparent between wavelengths 400 and 1100nm. Thermal stability of the title compound was examined by thermogravimetric and differential scanning calorimetric studies. Fluorescence spectrum of the grown crystal recorded using spectrofluorometer shows emission peak at 450nm. The second harmonic generation efficiency of BHBA estimated by Nd:YAG pulsed laser employing the Kurtz powder technique is ∼1.3 times that of potassium dihydrogen orthophosphate. Microhardness studies reveal that BHBA possesses high Vickers hardness value. The dielectric measurements were carried out at different temperatures and frequencies and the results are discussed.

Organometallic benzylidene anilines: donor-acceptor features in NCN-pincer Pt(ii) complexes with a 4-(E)-[(4-R-phenyl)imino]methyl substituent.

A series of organometallic 4,4'-substituted benzylidene aniline complexes 4-ClPt-3,5-(CH2NMe2)2C6H2CH[double bond, length as m-dash]NC6H4R'-4', abbreviated as PtCl[NCN(CH[double bond, length as m-dash]NC6H4R'-4')-4], with R' = NMe2, Me, H, Cl, CN (, respectively), was synthesized via a Schiff-base condensation reaction involving reaction of PtCl[NCN(CH[double bond, length as m-dash]O)-4] () with the appropriate 4-R'-substituted aniline derivative () in toluene. The resulting arylplatinum(ii) products were obtained in 75-88% yield. Notably, product was also obtained in 68% yield from a reaction in the solid state by grinding solid with aniline . The structures of , , and in the solid state (single crystal X-ray diffraction) showed a non-planar geometry, in particular for compound . The electronic interaction between the donor benzylidene fragment PtCl(NCN-CH) and the para-R' aniline substituent through the azomethine bridge was studied with NMR and UV/Vis spectroscopy. Linear correlations were found between the azomethine (1)H, the (195)Pt NMR and various (13)C NMR chemical shifts, and the substituent parameters σF and σR of R' at the aniline site. In common with organic benzylidene anilines, the azomethine (1)H NMR chemical shift showed anomalous substituent behavior. The (195)Pt NMR chemical shift of the platinum center can be used as a probe for the electronic properties of the delocalized π-system of the benzylidene aniline framework, to which it is connected. The dual substituent parameter treatment of the azomethine (13)C NMR shift gave important insight into the unique behaviour of the Pt-pincer group as a substituent. Inductively, it is a very strong electron-withdrawing group, whereas mesomerically it behaves like a very strong electron donating group.

Synthesis, Growth and Characterization of Organic Nonlinear Optical Single Crystals of 4-Bromo-4’-Methyl Benzylidene Aniline

Organic nonlinear optical material of 4-bromo-4’-methyl benzylidene aniline (BMBA) was synthesized and single crystal of BMBA was grown by solvent evaporation method at room temperature using ethanol as solvent. The crystalline nature of the grown crystals was confirmed using powder X-ray diffraction studies. The crystals were also characterized by single crystal X-ray diffraction method and their lattice parameters were determined. Thermal properties of BMBA were evaluated with thermogravimetric, differential thermal and differential scanning calorimetric analyses. Fourier transform infrared and FT-Raman spectral studies were carried out on the BMBA material to confirm the synthesized compound. 1H and 13C-nuclear magnetic resonance spectral studies were recorded to elucidate the structure of the grown crystals. Fluorescence spectrum recorded shows a peak at 485 nm. UV-Vis-NIR spectral analysis shows transmittance of ~92% in the visible region. The mechanical stability was analyzed by Vickers microhardness tester and the work hardening coefficient of the grown crystal was calculated. Second harmonic generation efficiency of the grown crystal measured by Kurtz powder technique is ~1.8 times that of potassium dihydrogen orthophosphate.

Substituent effects on the UV spectra of extended benzylidene anilines p-X[sbnd]PhCH[dbnd]NPhCH[dbnd]CHPh[sbnd]p-Y

Benzylidene anilines with p-substituted styryl groups substituted on the aniline ring, p-XPhCHNPhCHCHPhp-Y (X=NMe2, OMe, Me, H, Cl, F, CN, or NO2; Y=NMe2, OMe, Me, H, Cl, or CN) have been studied photochemically in ethanol. The substituent effects in the title compounds are more similar to p-XPhCHNPhp-Y than p-XPhCHCHPhp-Y. The introduction of styryl group to XBAY leads to a more planar geometry and a red shift of the maximum absorption wavelength. This can be described as a “styryl conjugation effect”. Furthermore, a quantitative model has been established to correlate the UV maximum absorption wavenumbers of the title compounds and substituent parameters. The results help understand the substituent effects of conjugated compounds consisting of both benzylidene aniline and stilbene moieties.

Long‐range transmission of substituent effects on 13C NMR chemical shifts of imine carbon in benzylidene anilines

The 13C NMR chemical shifts of six kinds of substituted benzylidene anilines, with different backbone conjugation length, have been used as a probe to investigate the long‐range transmission of substituent effects. In this context, it was found that for substituents Y at the aniline unit, the transmission of the inductive and conjugative effects depend on the chemical bond numbers n(Y) between Y and the imine carbon, and the parameters n(Y)−2σF(Y) and n(Y)−2σR(Y) are suitable to scale the corrected inductive and conjugative effects, respectively. However, for substituents X, the chemical bond numbers n(X) between X and the imine carbon influences only the transmission of inductive effects of X, and the n(X)−2σF(X) item is appropriate to evaluate the modified inductive effects of X. Similarly, Δσ(cor)2 was proposed to describe the transmitted effect of the cross‐interaction effect. With the parameters n(X)−2σF(X), σR(X), n(Y)−2σF(Y), n(Y)−2σR(Y), Δσ(cor)2, and δC(parent), the δC(C = N) values of 181 samples can be well correlated. The correlation coefficient is 0.9957, and the standard derivation is only 0.23 ppm. Moreover, the multi‐parameter correlation equation is predicted well the δC(C = N) of other 25 samples of designed conjugated benzylidene anilines. Copyright © 2012 John Wiley & Sons, Ltd.

Design, synthesis, and evaluation of (E)-N-substituted benzylidene–aniline derivatives as tyrosinase inhibitors

We attempted to design and synthesize (E)-N-substituted benzylidene-hydroxy or methoxy-aniline derivatives and to evaluate their inhibitory effect on tyrosinase activity and anti-melanogenesis activity in murine B16F10 melanoma cells. Derivatives with a 4-methoxy- or 4-hydroxy-anilino group exerted more potent inhibition against mushroom tyrosinase than those with a 2-hydroxyanilino group. (E)-4-((4-Hydroxyphenylimino)methyl)benzene-1,2-diol exhibited the most potent and non-competitive inhibition on mushroom tyrosinase showing an IC50 of 17.22 ± 0.38 μM and being more effective than kojic acid (51.11 ± 1.42 μM). This compound decreased melanin production stimulated by the alpha-melanocyte-stimulating hormone and inhibited murine tyrosinase activity in a dose-dependent manner. Therefore, we propose (E)-4-((4-hydroxyphenylimino)methyl)benzene-1,2-diol as a new candidate of potent tyrosinase inhibitors that could be used as therapeutic agent with safe skin-whitening efficiency.

Syntheses and structural diversity of salicylideneaniline derivatives with cobaltadithiolene backbone

► Salicylideneaniline (SA) derivatives of [CpCo(dithiolene)] complexes were prepared. ► Modification of the SA moieties tuned the dihedral angle between two benzene rings. ► Intramolecular OH⋯N hydrogen bonding distance can be modified. Salicylideneaniline (SA) or benzylideneaniline (BA) derivatives with [CpCo(dithiolene)] backbone, which are formulated as [CpCo(S 2 C 2 (H)(R))] (R = 5-chlorosalicylideneaniline ( 2a ), salicylideneaniline ( 2b ), benzylideneaniline ( 2c ) and 3,5-di- t -butylsalicylideneaniline ( 2d )), were prepared from the aniline precursor [CpCo(S 2 C 2 (H)(C 6 H 4 -NH 2 ))] ( 1 ) and the corresponding aldehydes. 1 and 2a–2d were identified with spectral data and electrochemical redox potentials. 1 and 2a–2c were structurally determined by X-ray diffraction studies. 1 and 2a showed dithiolene-H⋯X hydrogen bondings (X = N ( 1 ), O ( 2a )), because the dithiolene proton is usually acidic (ca. 9 ppm by 1 H NMR). In 2a–2c , the dihedral angles between two benzene rings ( θ 1 ) in the SA (or BA) moieties were depending on the substituents on these benzene rings. 2a has small θ 1 angle (7.321°) and the result indicates a short intramolecular OH···N hydrogen bonding distance (1.743 Å). In the crystal of 2b (or 2c ), there are two (or four) crystallographically independent molecules, and their θ 1 angles are different by the flexible SA (or BA) unit. The crystal 2b contains a non-planar molecule ( θ 1 = 37.043°) and a relatively planar molecule ( θ 1 = 22.822°) as well.

An Optical Study on Orientational Order Parameter and Molecular Polarizability in Benzylidene Anilines

Refractive indices measurements are carried out in four alkoxy benzylidene anilines viz., N-(p-n-methoxy and ethoxy benzaldehyde)-p-n-dodecyl and tetra decyl anilines, 1O.12, 1O.14, 2O.12 and 2O.14. First three compounds exhibit monovariant nematic phase while the last compound exhibits nematic and SmA phases with variable thermal ranges. The molecular polarizabilities are calculated from the refractive indices and the density using the well known internal field models by Vuks and Neugebauer. The molecular polarizability anisotropy is estimated from the Lippincott δ-function model as well as molecular vibrational methods. The order parameter is estimated using a) from the Haller’s extrapolation from molecular polarizabilities, b) from the scaling factors obtained from the equations by Vuks and Neugbeaur and c) directly from the birefringence - a method developed by Kuczynski et al without considering any internal field model to the liquid crystal molecule. The results evaluated from these methods are compared from one another and the limitations of the methods used are discussed.

Phase Transition, Birefringence and Orientational Order Parameter Studies in Four Members of Benzylidene Aniline Liquid Crystals

The nature of the phase transitions across isotropic–nematic (IN) and nematic–smectic-A (N-SmA) are carried out using density measurements in N-(p-n-ethoxy benzylidene)-p-n-pentyl aniline, 2O.5, N-(p-n-methoxy benzylidene)-p-n-pentyloxy aniline, 1O.O5, N-(p-n-ethyl benzylidene)-p-n-dodecyl aniline, 2.12 and N-(p-n-butyl benzylidene)-p-n-dodecyl aniline, 4.12. The compounds exhibit IN, IN, IN and INSmA phase sequences respectively with varying thermal ranges suitable for the study of birefringence. The birefringence studies are carried out using Newton’s rings and wedge techniques which provide δn = (ne- no) (the birefringence) ne, and norespectively. The orientational order parameter, S is evaluated (i) directly from δn and Δn (the birefringence in perfect order), independent of the local field that the nematic molecule experiences and (ii) from molecular polarizabilities estimated from ne, noand density values assuming isotropic as well as anisotropic field that the nematic molecule experiences. The estimated order parameter from the different techniques is compared with one another and with the literature data.

Growth and characterization of an organic NLO crystal:4-chloro- 4-methyl benzylidene aniline

Growth and characterization of an organic NLO crystal:4-chloro- 4-methyl benzylidene aniline

Growth and characterization of an organic NLO crystal:4-chloro- 4-methyl benzylidene aniline

In this paper, we report for the first time the synthesis, growth and characterization of a new organic NLO single crystal of 4 choloro-4-methyl benzylidene aniline. The title compound is synthesized and single crystals were grown by the slow evaporation technique at constant temperature. The grown single crystals have been characterized by single crystal XRD; powder XRD, FTIR, NMR, UV-Vis, thermal analysis and microhardness studies. From the XRD study, it is found that the crystals are in the monoclinic system. The FTIR spectrum was recorded to identify the various functional groups present in the group compound. The formation of the product was confirmed from NMR spectral analysis. The optical transparency was determined by UV-visible spectroscopy. The melting point is found to be 108°C from the DSC curve. The second harmonic generation (SHG) efficiency of the crystal was obtained using ND-YAG laser which is found to be 7.5 times that of KDP.

Investigation of the substituent specific cross‐interaction effects on 13C NMR of the CN bridging group in substituted benzylidene anilines

AbstractThe substituent effect on 13C NMR of the CN in benzylidene anilines XPhCHNPhY was investigated, in which the substituents X and Y are in p‐position or in m‐position of the two aromatic rings. The substituent effects including the inductive effects of X and Y, the conjugative effects of X and Y, and the substituent specific cross‐interaction effect were put into one model to quantify the 13C NMR chemical shift δC(CN) of the CN in XPhCHNPhY. A penta‐parameter correlation equation with correlation coefficient 0.9975 and standard error 0.17 ppm was obtained for 80 samples of compounds. The result shows that the substituents X and Y have an opposite effect on the δC(CN). The electron‐withdrawing effects of X decrease the δC(CN); while the electron‐donating effects of X increase the δC(CN). In contrast, the electron‐withdrawing effects of Y increase the δC(CN); while the electron‐donating effects of Y decrease the δC(CN). A new substituent specific cross‐interaction effect parameter Δσ2 was proposed, which indicates that the most substituent specific cross‐interaction effect exists in the pair of max electron‐withdrawing group (EWG) and max electron‐donating group (EDG) or the pair of max EDG and max EWG. Further to verify the obtained correlation equation, 15 samples of model compounds were prepared and their δC(CN) was measured in this work. The predicted δC(CN) values with the obtained equation are in good agreement with the measured ones for these prepared compounds, which confirmed the reliability of the obtained equation. Copyright © 2010 John Wiley & Sons, Ltd.

Mechanistic study on the oxidative coupling of amines to imines on K-10 montmorillonite

A mechanistic study of the K-10 montmorillonite-catalyzed microwave-assisted oxidative self-coupling of benzylamine and cross coupling of benzylamines with anilines and aliphatic amines is described. The coupling of benzylamines readily produced benzylidene benzylamines, while reactions of benzylamine with aliphatic amines and anilines resulted in benzylidene alkylamines and benzylidene anilines. The mechanism of the reaction has been investigated by varying reaction conditions, kinetic studies, thermogravimetric analysis and DRIFT spectroscopy. The data obtained clarified the steps of this multistep reaction sequence and a mechanistic scheme has been proposed.

Synthesis, growth and characterization of 4-bromo-4′chloro benzylidene aniline—A third order non linear optical material

The organic nonlinear optical material of 4-bromo-4′chloro benzylidene aniline (BCBA) was synthesized and single crystal of BCBA was grown from acetone solution by solvent evaporation method at room temperature. Its three dimensional structure was elucidated from single crystal X-ray diffraction analysis at 173 K. Synthesized compound of BCBA was subjected to FTIR and 1H and 13C NMR spectral analyses. The range and percentage of optical transmission of BCBA was determined by UV–vis–NIR spectrum and its fluorescence spectrum was recorded using spectrofluorometer. The mechanical strength of the crystal was estimated using Vickers microhardness test on the (0 0 1) plane. Dielectric constant of the grown crystal was measured for various frequencies along (0 0 1) plane. The third order nonlinear optical properties of BCBA were investigated by Z-scan technique with He–Ne laser radiation of wavelength at 632.8 nm and the corresponding nonlinear refractive index, absorption coefficient and optical susceptibility were calculated.

Reactivity of a low-valent chromium dinitrogen complex

(Nn iPrCr) 2(μ 2-κ 2:κ 2-N 2) ( 1, Nn iPr = bis(2,6-diisopropylphenyl)pentane-2,4-ketiminato), formally a chromium(I) complex, was exposed to a variety of small molecules possessing hetero- or homo-atomic single, double, or triple bonds. Reaction of 1 with adamantyl azide yielded complexes in various higher oxidation states, such as (Nn iPrCr II) 2(μ 2-NAd) ( 2), Nn iPrCr III(κ 2-N 4Ad 2) ( 3), or Nn iPrCr V(NAd) 2 ( 4). Compound 1 was found to reductively couple 3-pentanone to form Nn iPrCr(κ 2-O 2C 2Et 4) ( 5) and reductively couple benzylidene aniline to form both Nn iPrCr III( cis-κ 2-C 28H 22N 2) ( 6a) an Nn iPrCr III( trans-κ 2-C 28H 22N 2) ( 6b). Reaction with a stochiometric amount of benzylidene aniline yielded the imine complex Nn iPrCr(η 2-NPhCHPh) ( 7). Exposure of 1 to a bulky isocyanide formed the octahedral Nn iPrCr I[CN(C 6H 4(Me) 2] 4 ( 9). Complex 1 was also found to break the O–O, N O, and S–S bonds in various small molecules to form Nn iPrCr II(OCMe 3) ( 11), Nn iPrCr V(O)(NPh) ( 8), and [Nn iPrCr II(μ-SPh)] 2 ( 10).

The Influence of Oxygen on Mesomorphic Behavior of Benzylidene Anilines—The Effect of End Chain

A variety of terminal chain modifications were made by placing/removing the electro-negative oxygen atom to either or both sides of the rigid core of the benzylidene aniline compounds, the chosen alkyl chain lengths were n = 5 and m = 16. The mesomorphic properties were determined by polarizing thermal microscopy (TM) and differential scanning calorimetry (DSC). They exhibit two mono-variant and two di-variant phase sequences. The results are discussed in light of the depression in melting temperature, elevation of clearing temperature, and quenching of liquid-crystalline phases as a function of influence of oxygen with the end alkyl chain length.

Crystallization Kinetics Study in Orthogonal Liquid Crystalline Phases Formed by Schiff's Base nO.m Compounds by Calorimetric and Dielectric Techniques – Part 2

A systematic kinetic study of crystallization among two smectogens of higher homologues of the benzylidene aniline nO.m series viz. 4O.16 and 8O.16 has been carried out by thermal microscopy, differential scanning calorimetry (DSC), and dielectric studies. The crystallization kinetics was studied by two techniques, viz., the traditional thermal analysis (i.e., DSC) and dielectric studies, viz., permitivitty and dielectric loss variation with temperature. The DSC thermo grams were run from crystallization temperature to the isotropic melt for different time intervals. The liquid crystalline behavior together with the rate of crystallization of Smectic ordering in newly synthesized nO.m compounds were discussed in relation to the kinetophase (which occurs prior to the crystallization). The molecular mechanism and dimensionality in the crystal growth were computed from the Avrami equation. The characteristic crystallization time (t*) at each crystallization temperature was deduced from the individual plots of log t and ΔH. Further, it was observed that the data obtained from DSC and dielectric studies were in good agreement with one another.

Role of dielectric medium on benzylidene aniline: A computational analysis

A computational analysis of ordering in N-(p-n-ethoxy benzylidene)-p-n-butyl aniline (2O.4) was performed based on quantum mechanics and intermolecular forces. The atomic charge and dipole moment at atomic centre were evaluated using the all valance electron CNDO/2 method. The modified Rayleigh-Schrodinger perturbation theory and multicentre—multipole expansion method were employed to evaluate long-range intermolecular interaction, while a 6-exp potential function was assumed for short-range interactions. The total interaction energy values obtained in these computations were used as input for calculating the probability of each configuration in a noninteracting and nonmesogenic solvent (i.e., benzene) at room temperature (300 K) using the Maxwell-Boltzmann formula. The molecular parameter of 2O.4, including the total energy, binding energy, and total dipole moment were compared with N (p-n-butoxy benzylidene)-p-n-ethyl aniline (4O.2). The present article offer theoretical support to the experimental “observations, as well as a new and interesting way of looking at liquid crystalline molecule in a dielectric medium.

Substituent effects in the 13C NMR chemical shifts of para-(para-substituted benzylidene amino)benzonitrile and para-(ortho-substituted benzylidene amino)benzonitrile

13C NMR chemical shifts were measured in CDCl3 for two series of substituted benzylidene anilines. The substituted benzylidene anilines p-X-C6H4CH=NC6H4-p-CN p-X-C6H4CH=NC6H4-o-CN (X = NO2, F, Cl, Br, H, Me, MeO, NMe2). The substituent dependence of δC(C=N) was used as a tool to study electronic substituent effects on the azomethine unit. The benzylidene substituents X have a reverse effect on δC(C=N): electron-withdrawing substituents cause shielding, while electrondonating ones do the reverse, the resonance effects clearly predominating over the inductive effects. Additionally, the presence of a specific cross-interaction between X and C=N could be verified. The electronic effects of the neighboring aromatic ring substituents systematically modify the sensitivity of the C=N group to the electronic effects of the benzylidene substituents. These results can be rationalized in terms of the substituent-sensitive balance of the electron delocalization (mesomeric effects).