Hydrolysis of Cellulose Acetate Sulphate in Acetone

Abstract

When cellulose acetate sulphate is dissolved in acetone the hydrolysis of the sulphate ester is rapid compared with that of the acetate ester. In 70% acetone the relative rates are reversed. Hydrolysis of the sulphate ester in acetone is greatly affected by the temperature. At 25°C. or greater the hydrolysis is conlplete after 24 hr. A potentiometric titration method has been developed for the estimation of sulphuric acid in the presence of smaller amounts of acetic acid. INTRODUCTIONT h e nitration of cellulose by a mixture of nitric and sulphuric acids results in a nitrocellulose containing about one per cent of sulphate. T h e sulphate content depends on the composition of the mixed acids and on other factors. In spite of considerable experimentation, there is some doubt about the form of the sulphate which is variously described a s mechanicalljr held ( 2 ) , inorganic (7), fixed sulphuric acid (4), or an acid ester and a neutral ester (5). T h e majority of workers have assumed the existence of some type of chemical bonding without providing direct evidence. Sheppard (8) estimated the sulphate content of unstabilized nitrocellulose by dissolving the ester in acetone and reprecipitating it with water. The acid liberated was titrated directly in the presence of the precipitate. T h e results obtained were said t o correspond t o the acidity extracted with dilute sodium bicarbonate solution. The present work was suggested by an argument advanced by ChCdin and Tribot (2) t o the effect t h a t the removal of sulphuric acid b y solution in acetone and reprecipitation in water supports the idea t h a t the acid is mechanically held. T h e inference appears t o be based on the assumption t h a t sulphate cleavage in acetone is not the likely reaction of a cellulose mixed ester containing sulphate groups. There is however considerable evidence t o show t h a t the rate of solvolysis of the sulphate ester of a cellulose mixed ester depends on several factors of which the liquid medium appears to be the most important. The solvolysis of both the sulphate ester and the acetate ester in acetic acid is well known (6). Cleavage of the acetate ester in water is more rapid than decomposition of the sulphate ester (3). 'Manuscript

Simple, Rapid and Precise Determination of Free Sulfuric Acid in Unstabilized Cellulose Nitrate by the Lead Nitrate-Dithizone Titration Method

“…To con®rm this, experimentation showed that when the samples were dissolved in pure acetone and examined at intervals of 5, 10, 15, 30 min the amount of sulfuric acid was found to increase with the time; and, alternatively, when the samples were dissolved in acetone ± water solutions of lower acetone concentrations, the amount of free sulfuric acid was greatly decreased, and on dissolving in 90 % (vav) acetone ± water solutions no free sulfuric acid was detected in the samples. These results clearly indicate that the use of higher concentrations of acetone (99.0 ± 99.5 % mam) could effect the hydrolysis of the acid sulfate ester and the liberation of free sulfuric acid which was detected by the lead nitrate ± dithizone titration method, and this is in accordance with similar observations noted by Keirstead et al on the hydrolysis of the acid sulfate in high concentrations of acetone (22) .…”

“…To minimize the hydrolysis of the acid sulfate ester, Keirstead et al (22) suggested the use of 70 % (vav) acetone ± water concentration. Such concentration, however, was proved unfavourable for the lead nitrate ± dithizone titration method, since, if the water concentration increases above 25 % (vav), the end point will fade titration.…”

Hydrolysis of Sulphate Acid Ester in Unstabilized Cellulose Nitrates

“…I t has been show11 that the rate of hydrolysis of the sulphate ester of cellulose acetate sulphate depends on various factors of which the liquid medium is coilsidered the most important (1). When cellulose acetate sulphate is dissolved in acetone the hydrolysis of the sulphate ester is rapid compared with that of the acetate ester.…”

“…In 70y0 acetone the relative rates are reversed. A t 25" C. or greater, the hydrolysis of the sulphate ester is complete after 24 hours (1). The solvolysis of both the sulphate ester and the acetate ester in acetic acid is well known (2).…”