Decantation, continuous equipment

Solvent Process. In the solvent process, or solvent cook, water formed from the reaction is removed from the reactor as an a2eotropic mixture with an added solvent, typically xylene. Usually between 3 to 10 wt % of the solvent, based on the total charge, is added at the beginning of the esterification step. The mixed vapor passes through a condenser. The condensed water and solvent have low solubiUty in each other and phase separation is allowed to occur in an automatic decanter. The water is removed, usually to a measuring vessel. The amount of water collected can be monitored as one of the indicators of the extent of the reaction. The solvent is continuously returned to the reactor to be recycled. Typical equipment for this process is shown in Figure 2. The reactor temperature is modulated by the amount and type of refluxing solvent. Typical conditions are ... 

Note 5) is equipped with a powerful mechanical stirrer and a thermometer and is immersed to a depth of 20 cm. in an ice bath. A mixture of 11. of thiophene-free benzene and 2 1. of 6 A hydrochloric acid is placed in the copper vessel. The above reaction mixture is added to the vigorously stirred contents of the copper can at such a rate that the temperature does not rise above 25° (about two hours is required). When the addition is. complete, the reaction flask is rinsed with a little ice water, and the rinsings are added to the hydrolysis mixture. Stirring is continued for ten minutes longer. The benzene layer is decanted, and the aqueous layer is diluted with 1 1. of ice water. The aqueous layer is extracted with 500 cc. of benzene and is discarded. The combined benzene solutions are washed with 250 cc. of ice-cold hydrochloric acid and are dried for two hours in a stoppered flask over 250 g. of anhydrous calcium chloride. 

To a 1-1., three-necked, round-bottomed flask is added 7.2 g. (0.15 mole) of a 50% dispersion of sodium hydride in mineral oil (Note 1). The sodium hydride is washed several times by decantation with dry ether and is then covered with 300 ml. of dry benzene (Note 2). The flask is equipped with dropping funnel, stirrer, and reflux condenser. Diethyl ethylmalonate (28.2 g., 0.15 mole) (Note 1) is added dropwise over a 5-minute period, and the reaction mixture is stirred for 2 hours until a clear solution forms. The solution is cooled in an ice bath, and 24.2 g. (0.1 mole) of benzoyl peroxide (Note 3) in 300 ml. of dry benzene is added dropwise over a 1-hour period with continuous stirring After another 30 minutes, a peroxide test (Note 4) is made to ensure that all the peroxide has reacted. 

The crude ester obtained in this way was then treated with a solution of 7.5 g of flaked sodium hydroxide in 67.5 ml of water. The mixture was introduced into a 250 ml spherical flask, equipped with a condenser, and then the reaction medium was slowly brought to 60°-70°C. This temperature was maintained for 3 hours, whereafter the mixture was cooled to about 50°C and the ethanol which had formed and the residue of n-propanol were eliminated under a pressure of 70 mm Hg. The solution thus obtained was cooled to 20°C and acidified, while stirring, by addition of 26.25 g of 36% hydrochloric acid. During this operation, the temperature of the reaction medium was kept below 40°C by cooling. Stirring was continued for 30 minutes, whereafter the mixture was left standing for 30 minutes. The oily layer of di-n-propyl cyanacetic acid was decanted and the aqueous phase extracted with 35 ml of toluene. The extract in toluene was then added to the decanted di-n-propyl cyanacetic acid, whereafter the solution in toluene was washed, in a separation funnel, with a solution of 1.5 g of sodium chloride in 14 ml of water. The toluenic phase was decanted and the toluene distilled under atmospheric pressure. 

A reaction vessel equipped with a Dean-Stark decanter was charged with 10 parts of the condensation polymer of 2,2-bis(hydroxymethyl)propionic acid having a Mn of 2920 daltons, a Mw of4280 daltons, and a PDI of 1.47. This mixture was then treated with tin(di(chloro-dimethylsiloxy)-tin chlorodimethylsilane) (0.25 parts), ethyl acrylate (100 parts), and hydroquinone (0.05 parts). The mixture was then heated to between 92°C and 95°C so that the amount of distillate to the decanter was 15 to 20 parts per hour. Fresh ethyl acrylate was added to the reaction vessel as needed while the reaction continued for 20 hours. 

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