Shirley Possidonio

Application of 1-Allyl-3-(1-butyl)imidazolium Chloride in the Synthesis of Cellulose Esters: Properties of the Ionic Liquid, and Comparison with Other Solvents

The ionic liquid (IL), 1-allyl-3-(1-butyl)imidazolium chloride (AlBuImCl), has been synthesized and its properties determined. Increase in the temperature increased its conductivity and decreased its density, polarity, and viscosity. Microcrystalline cellulose (MCC), dissolves in this IL by heating at 80 degrees C; this did not affect its degree of polymerization, decreased its index of crystallinity (Ic), and changed in morphology after regeneration. Convenient acylation of MCC was achieved by using 50% excess anhydride at 80 degrees C, for 24 or 48 h for acetic and butyric anhydride, respectively. The composition of the mixed esters depended on the initial ratio of the anhydrides, and their order of addition.

Kinetics of the pH-independent hydrolysis of 4-nitrophenyl chloroformate in aqueous micellar solutions: effects of the charge and structure of the surfactant

The pH-independent hydrolysis of 4-nitrophenyl chloroformate in the presence of aqueous micelles of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, alkyltrimethylammonium chlorides, alkyldimethylbenzylammonium chlorides (alkyl group = cetyl and dodecyl) and polyoxyethylene (9) nonylphenyl ether was studied spectrophotometrically. The observed rate constants, kobs, decrease in the following order: cationic micelles > bulk water > non-ionic micelles > anionic micelles. Surfactant–substrate association constants, Ks, were determined from the dependence of kobs on surfactant concentration, and were found to be only slightly dependent on the charge of the surfactant and, for similarly charged micelles, on the length of their hydrophobic tail. A 1H NMR study of the solubilization of a model compound, 4-nitrophenyl chloroacetate, showed that all surfactant segments are affected by the solubilizate and the effect is more pronounced toward the middle of the hydrocarbon chain. The average solubilization site of the acetate ester does not depend on the charge of the micelle or the length of the surfactant hydrophobic tail. Micellar effects on observed rate constants are analyzed in terms of a ‘medium’ effect and an ‘electrostatic’ effect. The lower microscopic polarity at the reaction site retards the reaction, whereas electrostatic interactions of the polar transition state with the charged interface result in a rate decrease by anionic micelles and a rate enhancement by cationic micelles. Copyright

Some aspects of acetylation of untreated and mercerized sisal cellulose

We report here on some aspects of the acetylation in LiCl/N,N-dimethylacetamide, DMAc, of untreated and mercerized sisal cellulose, hereafter designated as sisal and M-sisal, respectively. Fiber mercerization by NaOH solution has resulted in the following changes: 29.9% decrease in the index of crystallinity; 16.2% decrease in the degree of polymerization and 9.3% increase in α-cellulose content. A light scattering study of solutions of sisal, M-sisal, microcrystalline and cotton celluloses in LiCl/DMAc has shown that they are present as aggregates, with (an apparent) average aggregation numbers of 5.2, 3.2, 9.8, and 35.3, respectively. The presence of these aggregates affects the accessibility of cellulose during its functionalization. A study of the evolution of the degree of substitution, DS, of cellulose acetate as a function of reaction time showed an increase up to 5 h, followed by a decrease at 7 h. Possible reasons for this decrease are discussed. As expected, M-sisal gave a higher DS that its untreated counterpart.

EFFECTS OF CHARGE AND STRUCTURE OF SURFACTANTS ON KINETICS OF WATER REACTIONS : THE PH-INDEPENDENT HYDROLYSIS OF BIS (2,4-DINITROPHENYL) CARBONATE

Abstract The pH-independent hydrolysis of bis (2,4-dinitrophenyl) carbonate in the presence of aqueous micelles of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, alkyltrimethylammonium chlorides, alkyldimethylbenzylammonium chlorides (alkyl group = cetyl and dodecyl), and polyoxyethylene (9) nonylphenyl ether has been studied spectrophotometrically. Observed rate constants, kobs, decrease in the following order: alkyldimethylbenzylammonium chlorides > bulk water ≈ alkyltrimethyl- ammonium chlorides > nonionic micelles > anionic micelles. Surfactant-substrate association constants have been determined from the dependence of kobs on [surfactant]. 1H NMR study of the solubilization of a model compound, phenyl-2,4-dinitrophenyl carbonate, showed that all surfactant segments are affected by the solubilizate, and that the ester penetrates deeper in micelles of alkyldimethylbenzylammonium chlorides relative to the corresponding alkyltrimethylammonium chlorides. Micellar effects on kobs are analyzed in terms of “medium” and “electrostatic” effects. The lower microscopic polarity at the reaction site cause rate decrease, whereas electrostatic interactions of the dipolar transition state with the charged interface result in rate decrease by anionic micelles, and rate enhancement by cationic ones.