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A one-step approach for esterification of zein with methanol



Zein (corn protein) was reacted with methanol in the presence of para-toluenesulphonic acid under mild conditions to give a material formed by esterification of predominantly the amide groups of the protein. The formation of methyl zeinate was confirmed by proton NMR. The new signal appeared at 3.67 ppm in zein methylation product, which is absent for pure zein can be assigned to the protons of the CH3 group of an ester. The strong C[DOUBLE BOND]O stretching vibration due to the presence of ester group in the region of 1739 cm−1 in case of methylated zein was also noticed from FTIR studies. The increase in the C : N atom ratio in the zein methylation product obtained from elemental analysis results further indicates the conversion of a significant proportion of the [BOND]CONH2 groups in zein to [BOND]COOCH3 groups in the esterified product. The methylated product had glass transition temperature about 20°C lower than that of the unmodified zein. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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