Abstract
Focusing on green chemistry protocols, a series of carbohydrate derivatives (5a–l) have been synthesized by Fischer glycosylation of α-D-glucose, D-xylose, and α-maltose with several nonpolar phenolic ester aglycones (3a–d) derived from menthol by employing solid-supported Si-H+ as the catalyst. In order to study the extent of mesomorphism in target molecules, the thermotropic behaviour has been studied by using the thermoanalytic DSC/TGA technique and polarized optical microscope. Phase transitions in the DSC thermograms of 5a–l with two endothermic melting point peaks and various exothermic crystalline transitions exhibits the existence of mesophases. However, optical photomicrographs revealed that the new glycopyranosides formed smectic A phases. Moreover, all the compounds (3a–d and 5a–l) were confirmed by FTIR and 1H NMR.
Highlights
Mesogens, the emerging scientific domain is thermodynamically stable, dimensionally ordered, flowing state of matter that exist between isotropic liquid and crystalline solid. ey have been experiential for over hundred years but were first recognized systematically by Friedrich Reinitzer [1,2,3]
Glycosides are of special interest due to their role as thermotropic and lyotropic mesogens, surfactants, lubricants, solvents, drug delivery systems and membrane crystallizers in pharmaceutics, food, biotechnology and material chemistry [4]. e existence of mesogens primarily depends upon the nature of glycone used as a hydrophilic part, hydrophobic aglycone part attached to the polar carbohydrate, ether or the ester linkage and the effect of any rigid spacer or unsaturation imparting the mesophase behaviour to the overall molecule [5]
FTIR spectra were scanned in a Shimadzu IR Tracer-100 FT-IR spectrometer. 1HNMR spectra of all the compounds were recorded in ppm at 400 MHz in DMSO-d6 on the Bruker NMR spectrometer. e thermal behaviour and the phase transitions were analyzed by differential scanning calorimetry (DSC)/thermal gravimetric analysis (TGA), SDT-Q600TA Instrument, USA, from 25°C to 600°C at 10°C /min heating rate (Exo Up)
Summary
The emerging scientific domain is thermodynamically stable, dimensionally ordered, flowing state of matter that exist between isotropic liquid and crystalline solid. ey have been experiential for over hundred years but were first recognized systematically by Friedrich Reinitzer [1,2,3]. E variety of catalyst ranges from the organic catalyst such as N-iodosuccinimide, boron trifluoride etherate, 4-dimethylaminopyridine, pentamethyldiethylenetriamine, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide to the metal catalyst including tin tetrachloride and indium [11,12,13,14,15,16,17,18,19,20]. Their toxicity, prohibitive prices and increased waste disposal costs add up to serious drawbacks for the large-scale applications. Direct condensation of mono-, di-, and trihydroxy phenolic acids with menthol was accomplished
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