Cotton plant lignins

Abstract

This paper generalizes the results of studies on lignins isolated from the stems, bolls, and seed hulls of cotton plants of a number of varieties as functions of the vegetation periods of the plants. The UV, IR and 1H and 13C NMR spectra It was impossible to characterize the MWL from cotton seed hulls because of its low yield. The molecular masses of the lignins were determined, and they were subjected to nitrobenzene oxidation and to cleavage with sodium in liquid ammonia [4, 5]. The oxidation and cleavage products were found to include substances with gnaiacyl and syringyl structures. The process of isolating MWLs is lengthy and laborious, and the yields of lignins axe low. In view of this, Pepper's method and one involving ultrasound have been used for the isolation of ligrtins [6].However, the results of a study of the lignin obtained with the aid of ultrasound led to the conclusion that during isolation under the action of ultrasound the syringyl structures of the lignin are demethoxylated and the C3 side-chains are destroyed [7, 8]. Isolation of Dioxane Liotmins from the Cotton PlantAs already mentioned, one of the methods of isolating lignin from plants in a little-changed form and with good yield is Pepper's method [3]. It is based on the fact that lignin is extracted by aqueous dioxane (1:9) in the presence of catalytic amounts of hydrochloric acid with heating under a current of nitrogen. It has been confirmed with various plants that the lignin obtained by this method is very similar to the BjOrkman lignin [9][10][11][12][13][14][15].In order to obtain lignin from ripe cotton plant stems in unchanged form we have used a method perfected by V. M. Reznikov the essence of which is that all the operations, beginning with extraction and ending with precipitation of the li~min in water, are carried out under a current of nitrogen. To study the dynamics of the process, we performed the stepwise extraction of lignin for one, two, and three hours [16], so that the lignin being isolated did not undergo elaanges due to its Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 40 64 75.