Carboxymethylcellulose synthesis in organic media containing ethanol and/or acetone

Influence of Organic Diluents on Cellulose Carboxymethylation

“…We reported previously [7] that the degree of substitution of CMC obtained in ethanol-acetone mixtures depends on the composition of the reaction medium. Thus, at molar ratios NaOH/AGU of 2.11 and MCA/cellulose of 1.11, maximum values for DS and carboxymethylation efficiency were obtained in a reaction medium containing 30% ethanol.…”

“…Also, the X-ray diffractograms of cellulose regenerated from alkalicellulose obtained in this solvent mixture revealed partial conversion of crystalline cellulose I to cellulose II and partial decrystallization during alkalization. [7] The structural changes produced in cellulose after alkalization in ethanol-acetone mixtures of different proportions at a molar ratio NaOH/AGU of 3.4, as compared with pure solvents, are illustrated in Figure 1. Diffraction curve b reveals almost no modification of the crystalline Table 1.…”

“…However, at a molar ratio of NaOH/ AGU of 2.11, a higher amount of cellulose I remains in the cellulose regenerated after alkalization in pure isopropyl alcohol, as compared with acetone, while in mixtures of ethanol and isopropyl alcohol, a maximum of efficiency is obtained at the ratio 50/50, in comparison with 30/70 in ethanol-acetone. [7,10] The difference between the effects of these solvents is diminished at higher molar ratio NaOH/AGU. The X-ray diffractograms for celluloses regenerated from alkalicelluloses obtained at molar ratio NaOH/AGU of 3.4 in isopropyl alcohol-containing systems are presented in Figure 2.…”

“…[5] The rate constants of the pseudo-first-order reaction have been a good measure of the reactivity of the two types of cellulose. In previous articles [6,7] we discussed the kinetics of cellulose carboxymethylation in three organic media, namely ethanol, acetone, and ethanol-acetone mixtures, in connection with cellulose crystallinity and the concentration of sodium hydroxide in the alkalization step. For a molar ratio NaOH/anhydroglucose unit (AGU) of 3.4, the reaction rate in an ethanol-acetone mixture of 50/50 (w/w) was found to be higher than that in other mixtures or in ethanol or acetone, and dependent neither on the crystallinity nor the particle size of the starting cellulose.…”

“…[6] On the other hand, at a molar ratio of NaOH/AGU of 2.11, the maximum reaction rate values were obtained for another composition of ethanol-acetone mixture, 30/70 (w/w), and these rate constants were dependent on the crystallinity of the starting cellulose. [7] In the present paper, a comparative study of the structural transformations of cellulose during alkalization in different organic media (ethanol, acetone, isopropyl alcohol and ethanol-acetone and ethanol-isopropyl alcohol mixtures of various composition) is performed, and the influence on the kinetics of carboxymethylation is discussed on the basis of X-ray analysis data. In particular, the kinetic behaviour of the reaction systems containing isopropyl alcohol as well as the distribution of carboxymethyl groups in position C 6 , evaluated from 1 H NMR spectra are tentatively explained by specific decrystallization and changes of polymorphism caused in the alkalization step by different organic systems used as reaction media.…”