Maleic Anhydride → Maleic acid, monosodium salt

Participants

Reaction Steps

102 g (1.224 mol as pure sodium hydroxide) of 48% aqueous sodium hydroxide solution was added to an aqueous solution containing 117.6 g (1.2 mol) of maleic anhydride to obtain 50 wt. % aqueous solution of monosodium maleate. The whole quantity of the aqueous solution was transferred into a 500 ml autoclave. Nitrogen was introduced therein under stirring and the temperature of the reaction system was elevated to 90° C. 10.13 g (8.104 g as pure t-butyl peroxide) of 80% t-butyl peroxide (molecular weight: 90) was introduced into the reaction system as a polymerization initiator through a sample-inlet tube. Thereafter, the introduction of nitrogen was stopped. The autoclave was closed and the temperature was elevated to 130° C. The stirring was continued at that temperature for 2 h and the reaction system was cooled to 90° C. At this time, the aqueous solution had a pH of 5.2 and a concentration of 3%. Hydrochloric acid was added to the mixture through another sample-inlet pipe to control the pH of the 3% aqueous solution to 4.1, since a pH in the range of 3.5 to 5.0 is preferred for accelerating the reaction. Additional 10.13 g of 80% t-butyl hydroperoxide was introduced in the reaction system through the sample-inlet tube. The autoclave was closed and the temperature was elevated to 130° C. The stirring was effected at this temperature for 1.5 h. Then, the reaction system was cooled to 90° C. 5.4 g of 80% t-butyl hydroperoxide was added to the mixture. The pH of the 3% aqueous solution was controlled to 4.12 with hydrochloric acid. The temperature was elevated to 130° C. and the mixture was stirred at this temperature for 1.5 h to complete the reaction. The quantity of the polymerization initiator was about 0.23 mol per mol of maleic anhydride. A filter aid (trade name: Radiolite #900) was added to the reaction mixture to effect filtration through a glass filter and obtain 3% aqueous solution of monosodium polymaleate having a solid content of 43% and a pH of 4.4. The polymerization rate was determined from the results of determination of maleic acid residue according to the bromine/bromide method.

Provenance & Evidence