Preparation of ethyl acetate

Thread Content

Under the catalysis of a small amount of acid (H2SO4 or HCl), carboxylic acids react with alcohols to form esters; this reaction is called esterification. This reaction proceeds through an addition-elimination process. The protonated carbonyl group is attacked by the nucleophilic alcohol in an addition reaction, and dehydration occurs under acidic conditions to form an ester. This reaction is reversible, and to complete it a large excess of the reactant is generally used (an excess of acid or an excess of alcohol, depending on the cost of the reactants). Sometimes, a substance that is azeotropic with water can be added to continuously remove water from the reaction system, thereby shifting the equilibrium (i.e., reducing the concentration of the product). A water separator can also be used in the laboratory to achieve this. Experimental steps: 1. Reaction: A constant-pressure dropper is attached to one of the ports of a 100 mL three-necked flask; the lower end of the dropper is connected via a rubber tube to a J-shaped glass tube that extends into the flask at a distance of about 3 mm from the bottom of the flask. A thermometer is fixed to the other port, while a fractionating column, distillation head, thermometer, and straight condenser are installed at the middle port. The opposite end of the condenser is connected to a guide tube and a conical flask, which is cooled in an ice-water bath. Place 3 mL of ethanol in a small conical flask, slowly add 3 mL of concentrated sulfuric acid while shaking, and transfer this solution to a three-necked flask. Prepare a mixed solution of 20 mL ethanol and 14.3 mL glacial acetic acid and pour it into an eyedropper funnel. Heat the flask using an oil bath, maintaining the temperature of the oil bath at around 140°C; the temperature of the reaction mixture is approximately 120°C. Then, the mixed solution in the dropper funnel was slowly added to the three-necked flask. Adjust the feeding speed so that it is roughly equal to the evaporation rate of the ester. Add material for about 70 minutes. At this time, maintain the reactant temperature at 120-125°C. After the dripping is complete, continue heating for about 10 minutes until no more liquid flows out. 2. Purification: First, neutralize the acid in the distillate using a saturated NaCO3 solution, until no CO2 gas is released ； Subsequently, in an Erlenmeyer flask, the distillate was washed successively with equal volumes of saturated NaCl solution (to wash away the sodium carbonate solution) and saturated CaCl2 solution (to wash away the alcohol; CaCl2 can form complexes with alcohol). Finally, the ethyl acetate in the upper layer was poured into a dry small conical flask, and anhydrous K2CO3 was added to dry it for 30 minutes. Note: 1. Since ethyl acetate can form binary and ternary azeotropes with water and alcohol, water and ethanol are also present in the distillate. 2. The purpose of using a saturated solution here is to reduce the solubility of ethyl acetate in water. 3. Distillation: Transfer the dried crude ethyl acetate to a 50 mL single-necked flask, heat it in a water bath, and carry out distillation at atmospheric pressure, collecting the fraction at 74–84 °C. Weigh and calculate the yield.