DETERMINATION OF CHEMICAL STRUCTURE OF METHYL HYDROXYETHYLCELLULOSE BY 13C NMR SPECTROSCOPY

Abstract

This paper discusses the determination of the structural parameters of methyl hydroxyethylcellulose (MHEC) by 13C NMR spectroscopy. Four samples of methyl hydroxyethylcellulose (MHEC, DS ~ 1.7) of different viscosity aqueous solutions were analyzed to determine the distribution of methyl and hydroxyethyl groups in different positions of the anhydroglucose unit of the polymer chain. For this purpose, MHEC samples were subjected to acid-catalyzed hydrolysis in the presence of sulfuric acid. Optimal conditions for complete hydrolysis leading to methyl and hydroxyethyl substituted D-glucose derivatives were determined. The structure of the hydrolysis products was studied by 13С NMR spectroscopy. The assignment of carbon atom signals in the 13С NMR spectra was made based on chemical shifts calculated using BIOPSEL program. Analysis of the integrated intensities of the C-atom groups of the products of hydrolysis allowed us to determine the distribution of substituents in the anhydroglucose unit. The values of the degree of substitution in 2, 3 and 6 positions (DSC-2, DSC-3 и DSC-6) are calculated, the number of methoxyl (DSMe) and hydroxyethoxyl (DSHE) groups is determined, the total degree of substitution (DStotal) is calculated. The distribution of substituents in different positions of the glucopyranose unit indicates the highest reactivity of 2 and 6 positions, as well as hydroxyl in the hydroxyethyl group. In this paper, the degree of substitution in four different MHEC samples with known DS values is determined. Comparative analysis of the results obtained with the data specified by the manufacturer confirms the high accuracy of the considered method. The proposed method for determining the chemical structure of MHEC is informative since the method allows determining the distribution of substituents for different positions of the anhydroglucose unit and the degree of substitution of each substituent.