Schiff Base Ester Research Articles

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

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

Synthesis and mesomorphic properties of Schiff base esters possessing terminal chloro substituent

A homologous series of Schiff base esters, 4-chlorobenzylidene-4′- n-alkanoyloxyanilines, containing even number of carbons at the end groups of the molecules (C n−1 H 2 n−1 COO–, n = 4, 6, 8, 10, 12, 14, 16) were synthesized. The mesomorphic properties were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). It was found that the end groups of the molecules had an effect on the mesomorphic properties. n-Butanoyloxy was found non-mesogenic, whilst n-hexanoyloxy exhibited monotropic smectic phase. The higher members in this homologous series were enantiotropic smectogens.

Mesogenic Schiff base esters with benzothiazole core: synthesis and phase transition studies

A series of new rod-shaped mesomorphic compounds, 6-ethoxy-2-(4-alkanoyloxybenzylidenamino)benzothiazoles, consisting of a 2,6-disubstituted benzothiazole core and a Schiff base central linkage, were synthesized and their structures were ascertained via elemental analysis and spectroscopic techniques. Their mesomorphic properties were studied using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD) analysis. All compounds showed enantiotropic mesomorphism. Whilst the lower members of the series, hexanoyloxy and octanoyloxy derivatives exhibited nematic phase, the higher members (decanoyloxy, dodecanoyloxy, tetradecanoyloxy, hexadecanoyloxy and octadecanoyloxy derivatives) exhibited nematic and smectic C phases.

New Mesogenic Schiff Base Esters with Polar Chloro Substituent: Synthesis, Thermotropic Properties and X-Ray Diffraction Studies

Problem statement: Many studies have been conducted on the Schiff base’s alkyl and alkyloxy possessing terminal halogen substituent. However, the thermotropic properties of Schiff base’s ester (or alkanoyloxy) with chloro terminal group remained unstudied. Approach: Synthesis a series of new Schiff base ester possessing polar chloro group and investigate its mesomorphic properties. The title compounds were prepared via condensation and esterification reactions. The molecular structures were confirmed using spectroscopic techniques. All the members are differed by the length of alkanoyloxy chain, Cn-1H2n-1COO, where n = 2-8, 10, 12, 14, 16 and 18. The mesomorphic properties were studied using differential scanning calorimetry, polarizing optical microscopy and temperature-dependent X-ray diffractometry. Results: Whilst short members (n = 2-5) were not mesogenic compounds, n-hexanoyloxy and n-heptanoyloxy derivatives exhibited monotropic SmA and SmB phases. Enantiotropic smectogenic A and monotropic smectogenic B were observed in n-octanoyloxy to n-hexadecanoyloxy derivatives. Highest member of the series, n-octadecanoyloxy derivatives exhibited monotropic SmA phase. Conclusion: The ester linkage and polar terminal group in the present series are essential for the formation of liquid crystal phase in Schiff bases.

3-Hydroxy-4-[(phenylimino)methyl]phenyl Myristate

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

3-Hydroxy-4-{[(3-nitrophenyl)imino]methyl}phenyl Tetradecanoate

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

4-{[(3-Chlorophenyl)imino]methyl}-3-hydroxyphenyl Myristate

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

4-{[(3-Cyanophenyl)imino]methyl}-3-hydroxyphenyl Tetradecanoate

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

Synthesis of a New Liquid Crystal, 3-Hydroxy-4-{[(6-methoxy-1,3-benzothiazol-2-yl)imino]methyl}phenyl Palmitate

A new Schiff base ester comprising of heterocyclic moiety, 3-hydroxy-4-{[(6-methoxy-1,3-benzothiazol-2-yl)imino]methyl}phenyl palmitate was synthesized and its IR, 1H NMR, 13C NMR, elemental analysis and MS spectroscopic data are presented.

New mesogenic Schiff base esters comprising benzothiazole moiety: Synthesis and mesomorphic properties

A homologous series of Schiff base esters, 6-methoxy-2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles, comprising a benzothiazole moiety as the core was synthesized. All the members of this series exhibited an enantiotropic nematic phase. The azomethine linkage along with the lateral hydroxyl and terminal methoxyl groups were found to exert an effect on the mesomorphic properties.

Synthesis of 4-[(4-dimethylaminobenzylidene)amino]phenyl tetradecanoate

A new Schiff base ester, 4-[(4-dimethylaminobenzylidene)amino]phenyl tetradecanoate, was synthesized and its IR, 1H NMR, 13C NMR and MS spectroscopic data are reported.

Synthesis and mesomorphic properties of new Schiff base esters with different alkyl chains

A new series of Schiff base esters, 4-(dimethylamino)benzylidene-4′-alkanoyloxyanilines containing even number of carbons at the end group of the molecules (C n−1 H 2 n−1 COO, n = 6, 8, 10, 12, 14, 16, 18) were synthesized. The present compounds were monotropic liquid crystals. It was also found that the end groups of the molecules had effect on the mesomorphic properties.

Synthesis and Mesomorphic Properties of Fluorinated Schiff's Base Esters Containing Alkyl and Alkoxy End Groups

Two series of fluorinated Schiff's base esters have been synthesized and characterized. Their chemical structures were identified by FTIR, 1H NMR, and elemental analysis (EA). Their mesomorphic properties were studied by polarizing optical, microscopy (POM) and differential scanning calorimeter (DSC). It was found that most of the compounds with alkyl end group exhibited enantiotropic smectic A and nematic phase; while that with alkoxyl behaved differently, some exhibited enantiotropic smectic A and nematic phase; others exhibited monotropic smectic A and enantiotropic nematic phase or unique enantiotropic nematic phase. And for both series, their melting point and clearing point temperature decreased and thermal ranges of mesophase increased with the length of their end groups (n). Furthermore, it was also found that the increase of n was propitious to the stability of smectic phase but went against for that of nematic.

Efficient Synthesis of α-Substituted Amino Acid Ester: Alkylation and Hydrogenation Removal of Schiff's Base Protecting Group

A general and efficient synthetic route to α-amino acids by alkylation of the sodium salt of Schiff base ester 1 has been described previously. The α-substituted ethyl glycinates 4a–g are prepared in excellent yield by a two-step sequence involving regioselective alkylation of the anionic glycine synthon 2 with various alkyl halides, followed by purification of the alkylated Schiff base on florisil and cleavage by catalytic hydrogenolysis. Reducible groups on the side chain may be reduced or preserved depending upon the deprotecting method utilized. Scheme 1

Synthesis and mesomorphic properties of fluorinated Schiff's base liquid crystals containing vinyl end groups

Abstract Three kinds of fluorinated Schiff's base esters, 4-allyloxy-2-X-6-X-benzoic acid 4-[(2, 3, 4-trifluorophenylimino)-methyl]phenyl ester, where X=H or F, were synthesized and characterized. Their chemical structures were identified by Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance ( 1H NMR). Their mesomorphic properties were studied by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). It was found that all the three compounds exhibited enantiotropic nematic phases only. And their clearing point temperature and thermal range of mesophase decreased with the number of fluorine atoms on the rigid core of the compounds; while their melting point temperature showed no distinct regularity.

Nematic and Smectic a Phases in Ortho-Hydroxy-Para-Hexadecanoyloxbenzylidene-Para-Substituted Anilines

Four Schiff base esters containing the different substituents of R=CN, OH, SH, and NO2 were synthesized, and the physical characterization was carried out along with spectroscopic techniques (FT-IR and NMR). Thermal properties were analyzed by using differential scanning calometry (DSC), and their liquid crystal textures were observed under polarized optical microscope. All compounds thus obtained exhibit mesomorphic properties of which the alignment of molecules are inclined to either nematic, N (R=SH), or smectic, SmA (for R=CN, OH, and NO2). The unidentifiable subphases in crystal region were recorded in all compounds except that with R=OH. The presence of a lateral hydroxyl group has been claimed to contribute to the enhanced molecular ordering, leading to a higher clearing temperature.

Synthesis and Characterization of Some New Mesogenic Schief Base Esters N-[4-(4-n-Hexadecanoyloxybenzoyloxy)-Benzylidene]-4-Substituted Anilines

Series of elongated Schiff base esters containing three aromatic rings with palmitoyl moiety as one of the terminal carbon chain and various substituents R(R=H, F, Cl, Br, OCH3, CH3, and C2H5) at the other end of molecule have been isolated, and their structures were proposed via physical measurement. The mesomorphic properties of these compounds were investigated via differential scanning calometry and polarizing optical microscopy. The thermal data indicate that all of these compounds exhibit mesomorphic properties. Although compounds with R=H, OCH3, CH3, and C2H5 show nematic phases, the remaining compounds containing halogen F, Cl, and Br are smectogenic in nature. The structural changes that result in the variation of transition temperature and the electronic polarizability of the respective molecules are discussed.

Synthesis, physical and mesomorphic properties of Schiff's base esters containing ortho‐, meta‐ and para‐substituents in benzylidene‐4′‐alkanoyloxyanilines

Three series of Schiff's base esters, 2‐hydroxy‐4‐methoxybenzylidene‐4′‐alkanoyloxyaniline, 2‐hydroxy‐3‐methoxybenzylidene‐4′‐alkanoyloxyaniline and 3‐methoxy‐4‐alkanoyloxybenzylidene‐4′‐alkanoyloxyaniline, which possess mono‐ and di‐substituted moieties at both ends of the molecules have been synthesized and their mesomorphic properties investigated along with physical characterization (elemental analysis, mass spectrometry, Fourier transform IR and high resolution NMR). The effect of lateral methoxy and polar hydroxy groups on the mesomorphism of the title compounds was studied, based on the thermal properties and textural analysis. The results indicate that compounds with the larger number of carbons in the alkyl chain prefer smectic phase formation and possess higher transition temperatures and molecular polarizability along the long axis. Further analysis shows that the greater shielding effect (through the formation of intramolecular interaction) leads to lower molecular broadening and results in higher clearing points. Increase in melting point due to the lengthening of the alkyl chain is associated with the increase in van der Waals attraction between the molecules. These compounds exhibit nematic, smectic (SmA and SmC) phases depending on the type and position of the substituents.

Mesogenic Schiff's base ester with chloroethyl tail

Two new mesogenic homologous series of Schiff's base ester with chloroethyl tail having the following general formulahave been synthesized. The molecular structures of the synthesized compounds were characterized by the standard spectroscopic methods and elemental analysis. The mesomorphic behaviour of these new Schiff's base esters was mainly investigated with the help of optical polarizing microscope. For some representative compounds differential scanning calorimetric study was carried out to support the optical observation of transition temperatures and associated enthalpies. In series I, lower members are non-mesogenic, whereas higher members exhibit smectic mesophase. In series II, methoxy to n-hexyloxy derivatives exhibit nematic mesophase, while the smectic A phase commences from n-propyloxy derivative and persists up to the last member synthesized. The mesomorphic properties of these two series of compounds are compared with each other and with structurally related systems.

The Enantioselective Synthesis of α‐Amino Acids by Phase‐Transfer Catalysis with Achiral Schiff Base Esters

AbstractFor Abstract see ChemInform Abstract in Full Text.