Schiff Base Ester Research Articles

Synthesis, mesomorphic properties and structural studies on 1,3,5-trisubstituted benzene-based star-shaped derivatives containing Schiff base ester as the peripheral arm

Six new symmetrical three-armed star-shaped liquid crystals comprising phloroglucinol (1,3,5-trihydroxybenzene) as a core center and three Schiff base ester as the mesogenic arms have been synthesized. Their molecular structures were supported by spectroscopic techniques (FT-IR, 1H NMR, 13C NMR and two dimensional COSY, HMQC and HMBC). Each of the member differs in the length of the terminal alkyl chain (RCOO where R=C8H17, C10H21, C12H25, C14H29, C16H33, C18H37). All the star-shaped mesogens are found to be monotropic smectogens with the short chain derivative (R=C8H17) exhibits only smectic A phase. While both the smectic A and smectic C phases are common for the derivatives with C10H21C16H33 alkyl chain, the member with C18H37 shows only smectic C phase. Further investigation by X-ray diffraction confirms the smectic phase of the materials whereby two sharp reflections at 28.8Å and 57.3Å recorded via small angle in a ratio of 1:2 indicate unambiguously the presence of layered structure and a diffused scattering via the wide angle (4.5Å) indicates a liquid-like order within the smectic layer. Increasing the length of terminal flexible chain has influenced remarkably the thermal and phase stability of the titled compounds. Besides, the liquid crystalline properties of all intermediary ω-brominated Schiff base ester prior joining to the benzene core were also evaluated.

Synthesis of fatty acid Schiff base esters as potential antimicrobial and chemotherapeutic agents

Schiff base {4-[(pyridine-3-ylmethylimino)-methyl] phenol} was prepared by reacting 4-hydroxybenzaldehyde with 3-aminomethylpyridine in ethanol for 6 h (85 % yield) followed by their esterification via reaction with fatty acids of varying chain lengths. The structure of these Schiff base esters were elucidated using chromatographic and spectroscopic techniques like GC–MS, 1H NMR, 13C NMR, and ESI–MS. Schiff base esters with shorter chain heptanoic (2a) and decanoic acid (2c) showed good activity against all the tested bacterial and fungal strains. The synthesized esters were also studied for cytotoxicity toward different human tumor cell lines like HeLa, HepG2, A549, MDA-MB-231, and MCF 7 and Neuro2a; however, Schiff base esters with shorter chain (2a, 2b) and medium chain fatty acids (2d, 2i) exhibited good anticancer activity and selectively toward MDA-MB-231 and MCF 7, while long chain fatty acid (2g) Schiff base ester exhibited good anticancer activity selectively toward MDA-MB-231 as compared to the parent molecule, Schiff base (1).

Synthesis, Characterization and Mesomorphic Properties of New Rod-like Thiophene Based Liquid Crystals

Two new mesogenic homologous series of Schiff base esters, 2-[4-(4′-n-Alkoxy benzoyloxy) benzylidenamino] 3-cyno thiophine (Series-A) and Schiff base cinnamates, 2-[4-(4′-n-alkoxy cinnamoyloxy) benzylidenamino] 3-cyano thiophene (Series-B), comprising a thiophene moiety were synthesized. Structural elucidation was carried out using elemental analysis and spectroscopic techniques such as FT-IR, 1H-NMR and 13C-NMR, and mass spectrometry. The mesomorphic properties and thermal stabilities of the title compounds were studied by using differential scanning calorimetry and optical polarizing microscopy. All the derivatives are mesomorphic in nature showing the nematic phase, and the higher members of Series-A show a smectic C phase whereas Series-B exhibits only the nematic mesophase. The mesomorphic properties of the present series are compared with other structurally related compounds.

3-Hydroxy-4-[(phenylimino)methyl]phenyl 4-(Hexadecanoyloxy)benzoate

A new Schiff base ester, 3-hydroxy-4-[(phenylimino)methyl]phenyl 4-(hexadecanoyloxy)benzoate was synthesized and its IR, 1H-NMR, 13C-NMR and MS spectroscopic data are presented.

Synthesis, characterisation and liquid crystalline properties of some Schiff base-ester central linkage involving 2, 6- disubstituted naphthalene ring system

Four new mesogenic homologous series, each containing a 6-alkoxy 2-naphthoic acid and Schiff base-ester as central linkage, have been synthesised by esterification of 4-{[(4-hydroxyphenyl) imino] methyl} phenyl 4-propoxy benzoate, 4-{[(4-hydroxyphenyl) imino] methyl} phenyl 4- (pentyloxy) benzoate, 4-{[(4-hydroxyphenyl)imino]methyl}-2-methoxyphenyl 4- nitrobenzoate and 4-{[(4-hydroxyphenyl)imino]methyl}-2-methoxyphenyl 4- chlorobenzoate with different 6-alkoxy 2-naphthoic acid to give Series-A, -B, -C and -D, respectively. These compounds were characterised by elemental analysis, Fourier transform infrared, 1H nuclear magnetic resonance, ultraviolet-visible and mass spectral studies. Their mesomorphic behaviour was studied by polarising optical microscope (POM) with a heating stage. POM data were compared with differential scanning calorimetry thermograms. In Series-A and -B all compounds exhibit mesomorphism. Series-A compounds exhibit a enantiotropic nematic mesophase, while a smectic A mesophase is observed from the butoxy derivative and persists up to the last member of the homologou series. Series-B compounds also exhibit the enantiotropic nematic mesophase, while the smectic A mesophase is observed from the ethoxy derivative and persists up to the last member of the homologou series. The mesomorphic properties of both series are compared with each other and the other structurally related Series-C and –D compounds. In Series-C and -D all compounds exhibit the only nematic mesophase; no smectic mesophase is observed even for higher members of the homologous. The aim of the research was to synthesise and characterise novel liquid crystalline compounds containing 2,6-disubstituted naphthalene and to study their mesomorphic properties.

Synthesis and Thermotropic Properties of Some New Schiff Bases, N‐[4‐(4‐n‐Alkanoyloxybenzoyloxy)‐2‐Hydroxybenzylidene]‐4‐Cyano‐, 4‐Hydroxy‐, 4‐Thio‐ and 4‐Nitroanilines

A series of elongated Schiff base esters containing three aromatic rings with hexadecanoyl chain as one of the terminal group and various R substituents (R = CN, OH, SH, and NO2) at the other end of molecule were prepared, and their structures were confirmed via physical measurement. The thermotropic properties of these compounds were investigated via differential scanning calorimetry and polarizing optical microscopy. The thermal data indicate that all of these compounds exhibit mesomorphic properties. Whilst compounds with R = OH, SH and NO2 show nematic phases, compound containing cyano substituent are smectogenic in nature.

Schiff base liquid crystals with terminal IODO group: synthesis and thermotropic properties

A new homologous series of Schiff base esters comprising a terminal iodo substituent was studied. The iodo substituent contributes to the molecular polarizability, thus, affecting intermolecular interactions, hence, resulting in smectic polymorphism. The mesomorphic properties were studied using differential scanning calorimeter (DSC) and polarizing optical microscope (POM). Whilst the lower members, n-ethanoyloxy, n-propanoyloxy, n-butanoyloxy and n-pentanoyloxy derivatives were non-mesogens, enantiotropic smectogenic A phase was observed in the medium members (n-hexyloxy and n-heptanoyloxy derivatives). Further lengthening of the alkyl chain from C8 to C18 members saw the induction of new phase which was identified as smectic B phase under microscope. The homologous members were compared with structurally related series to establish their chemical structure-mesomorphic behavior relationships. Key words: 4-{[(4-iodophenyl) imino] methyl} phenyl alkanoate, thermotropic properties, smectic A, smectic B, polarizability.

4-({[4-(Methylthio)phenyl]methylene}amino)phenyl Dodecanoate

A new Schiff base ester, 4-({[4-(methylthio)phenyl]methylene}amino)phenyl dodecanoate was synthesized and its IR, 1H NMR, 13C NMR and EI-MS spectroscopic data are presented.

4-{[(4-Iodophenyl)imino]methyl}phenyl Octadecanoate

A new Schiff base ester, 4-{[(4-iodophenyl)imino]methyl}phenyl octadecanoate was synthesized and its IR, 1H NMR, 13C NMR and EI-MS spectroscopic data are presented.

Synthesis, spectral studies of 4-{((3- substitutedphenyl)imino)methyl}-3-hydroxyphenyl octadecanoate and effect of meta substituents on mesomorphic properties

A series of Schiff base esters was synthesized from the reaction between 4-formyl-3-hydroxyphenyl octadecanoate and 3-substituted-anilines. The molecular structures were elucidated using spectroscopic techniques such as FT-IR and NMR. A conformational study associated with the presence of intramolecular hydrogen bonding which entails the formation of the keto-enol tautomerism in the solid and solution states are reported. Phase-transition temperatures and the thermal parameters were obtained from differential scanning calorimetry (DSC). The texture observation was carried out with a polarizing optical microscope (POM) over heating and cooling cycles. The title compounds exhibited direct isotropization process. The substituents at the meta position of the aniline fragment of benzylideneaniline compounds suppressed the formation of mesophase.

4-{[(4-Fluorophenyl)imino]methyl}-3-hydroxyphenyl 4-(Hexadecanoyloxy)benzoate

A new Schiff base ester, 4-{[(4-fluorophenyl)imino]methyl}-3-hydroxyphenyl 4-(hexadecanoyloxy)benzoate was synthesized and its IR, 1H NMR, 13C NMR and EI-MS spectroscopic data are presented.

Orthopalladated complexes as phase-transfer catalysts for asymmetric alkylation of achiral Schiff base esters

The asymmetric C-alkylation of benzophenone Schiff base glycine esters has been achieved using a palladium(II) chiral complex as a phase-transfer catalyst. The aromatic moiety around the metal center and various physicochemical parameters were investigated to study their effect on the asymmetric alkylation reaction under phase-transfer conditions. Moderate enantioselectivity(30–40%) was achieved under room temperature conditions, which is a significant improvement compared to no enantioselectivity with a chiral palladium-salen complex reported earlier. Computer simulation studies indicate that coordination of the metal center with Z-enolate forming a square planar complex provides a favorable steric environment where the α-carbon atom of the enolate is available for enantioselective alkylation.

ChemInform Abstract: Glycosidase Inhibitors: Synthesis of Enantiomerically Pure Aza-Sugars from Schiff Base Amino Esters via Tandem Reduction-Alkenylation and Osmylation.

Nitrogen-in-the-ring “aza-sugars” have been synthesized in enantiomerically pure form from the amino acid l-alanine in excellent overall yield. The O'Donnell's Schiff base of l-alanine methyl ester 9a was converted to aza-sugar l-fuco-1-deoxy-nojirimycin, 18, and to the epimer l-gulo-1-deoxy-nojirimycin, 20, in eight steps. The overall yields were 20 and 29%, respectively. The methodology for the efficient generation of silyl- and benzyl-protected (E)-3-lithio-2-propen-1-ols, and the use of these alkenyllithiums with iBu5Al2H as nucleophiles in the threo-selective tandem reduction−alkenylation of the Schiff base esters is described. Osmium-catalyzed cis-oxygenation of the resulting olefin products was selective for the galacto (fuco) amino polyols in all cases for the acyclic olefins, and was gulo-selective for the cyclic D-4,5-dihydropyridine pivalate, 17c. TEMPO-NaOCl was selective for oxidation of the primary position of the acyclic Schiff bases, and allowed for minimal protection/deprotection of the i...

3-Hydroxy-4-{[(4-methoxyphenyl)imino]methyl}phenyl Octadecanoate

A new Schiff base ester, 3-hydroxy-4-{[(4-methoxyphenyl)imino]methyl}phenyl octadecanoate, was synthesized and its IR, 1H NMR, 13C NMR and MS spectroscopic data are presented.

Mesogenic Schiff base esters with terminal chloro group: Synthesis, thermotropic properties and X-ray diffraction studies

A new homologous series of Schiff base esters comprising a terminal chloro substituent was studied. The chloro substituent contributes to the molecular polarizability, thus, affecting intermolecular interactions, hence, resulting in smectic polymorphism. The mesomorphic properties were studied using differential scanning calorimetry, polarizing optical microscopy and temperature-dependent X-ray diffractometry. Whilst the n-pentanoyloxy and n-heptanoyloxy derivatives exhibited enantiotropic smectogenic A and B phases, monotropic smectogenic A and B phases were observed in the n-butanoyloxy and n-hexanoyloxy derivatives. Enantiotropic smectogenic A and monotropic smectogenic B phases were observed in the n-octanoyloxy to n-hexadecanoyloxy derivatives. The highest member of this series, the n-octadecanoyloxy derivative, exhibited an enantiotropic smectogen A phase. The homologous members were compared with structurally related series to establish their chemical structure-mesomorphic behavior relationships.

Synthesis of new schiff base ester liquid crystals with a benzothiazole core

A series of new calamitic liquid crystals, 6-methoxy-2-(4-alkanoyloxybenzylidenamino)benzothiazoles, comprising a benzothiazole core, terminal methoxy group and a Schiff base linkage were synthesised and characterised. This series comprises 12 members wherein members differ by the length of the alkanoyloxy chain (C n-1H2n-1COO-, where n = 2–8, 10, 12, 14, 16, 18). Their mesomorphic properties were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. The short chain derivatives (n = 2 and 3) were non-mesogenic compounds, while an enantiotropic nematic phase was present throughout the remaining members of the series. The smectic C phase emerged from the decanoyloxy derivative onwards.

New Schiff Bases with Pyridine Core: Spectral, Thermal and Optical Characterizations

Problem statement: Numerous studies have been conducted on the Schiff base's alkyl and alkyloxy possessing aromatic core. However, the thermo tropic properties of Schiff base's ester (or alkanoyloxy) with pyridine core was rare studied. Approach: To study spectral, thermal and optical behaviors of Schiff base ester possessing heterocyclic (pyridine) terminal core. A series of 4-[(pyridin-3-ylmethylene) amino] phenylalkanoates were prepared and all the members are differed by the length of alkanoyloxy chain, Cn-1H2n-1COO, where n = 12, 14, 16 and 18. The thermal and optical characteristics were studied using differential scanning calorimetry and polarizing optical microscopy. Results: DSC studies showed that all of the title compounds exhibited direct isotropization and recrystallization during heating and cooling cycles, respectively. Under polarizing optical microscope, crystal phase texture was observed to change to dark region isotropic without displaying any liquid crystal phase. Conclusion: The presence of terminal pyridine core suppressed the formation of mesosphere in the compounds studied.

3-Hydroxy-4-{[(4-ethylphenyl)imino]methyl}phenyl Octadecanoate

A new Schiff base ester, 3-hydroxy-4-{[(4-ethylphenyl)imino]methyl}phenyl octadecanoate, was synthesized and its IR, 1H NMR, 13C NMR and MS spectroscopic data are presented.

3-Hydroxy-4-{[(4-fluorophenyl)imino]methyl}phenyl Octadecanoate

A new Schiff base ester, 3-hydroxy-4-{[(4-fluorophenyl)imino]methyl}phenyl octadecanoate, was synthesized and its IR, 1H NMR, 13C NMR and MS spectroscopic data are presented.

3-Hydroxy-4-{[(4-bromophenyl)imino]methyl}phenyl Octadecanoate

A new Schiff base ester, 3-hydroxy-4-{[(4-bromophenyl)imino]methyl}phenyl octadecanoate, was synthesized and its IR, 1H NMR, 13C NMR and MS spectroscopic data are presented.