Comparative study of organic solvent-soluble and water-soluble lipophilic extractives from wheat straw 2: Spectroscopic and thermal analysis

Abstract

As a continuing study of six organic solvent-soluble lipophilic extractives and one water-soluble lipophilic extract from wheat straw, seven extracts were further compared using Fourier transform-infrared (FT-IR) analysis, 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, and thermal analysis. In the FT-IR spectra of two-thirds chloroform/one-third methanol, methyl tertbutyl ether (MTBE), hexane, petroleum ether, and dichloromethane extracts, a strong band at 1746 cm-1 is indicative of the ester carbonyl of triglycerides or steryl esters or waxes, whereas the occurrence of carboxylic carbonyl of free fatty acids or resin acids at 1712-1719 cm-1 is verified in the spectra of two-thirds toluene/one-third ethanol and hot water extracts. Signals at 187.9, 178.4, and 173.3 ppm in the 13C NMR spectrum of MTBE extract correspond to carbonyl groups of resin acids, fatty acids, and fatty acid/steryl esters, respectively. All the extractives were to varying degrees thermally unstable at a temperature of about 200°C, and the melting temperature occurred at about 54°C.