Under the catalysis of a small amount of acid (H2SO4 or HCl), carboxylic acid reacts with alcohol to form ester, which is called esterification. The reaction goes through an addition-elimination process. Proton-activated carbonyl group is attacked and added by nucleophilic alcohol, and dehydrated into ester under the action of acid. The reaction is reversible, and in order to complete the reaction, a large amount of excessive reagents (depending on the price of reactants, excessive acid or excessive alcohol) are generally used. Sometimes, substances with constant boiling with water can be added to continuously bring water out of the reaction system, so as to achieve balanced movement (i.e., reduce product concentration). Water separators can also be used in laboratories.

The possible process of esterification reaction is:

In this experiment, we reacted glacial acetic acid with ethanol to obtain ethyl acetate. The reaction formula is as follows:

Second, the experimental instruments and drugs needed

Instruments: constant pressure funnel, three-neck round bottom flask, thermometer, spike fractionator, distillation head, direct condensing tube, connecting tube and conical flask.

Drugs: glacial acetic acid, 95% ethanol, concentrated sulfuric acid, saturated sodium carbonate solution, saturated salt solution, saturated calcium chloride solution, anhydrous potassium carbonate.

Third, the experimental steps

1, reaction

In a 100 mL three-necked flask, a constant-pressure dropping funnel is installed on one side, and the lower end of the dropping funnel is connected with a J-shaped glass tube through a rubber tube, and the rubber tube extends into the three-necked flask about 3 mm from the bottom of the bottle. A thermometer is fixed on the other side, and a fractionator, a distillation head, a thermometer and a direct condensing tube are installed in the middle. The end of the condensing tube is connected with a connecting tube and a conical bottle, and the conical bottle is cooled by an ice water bath.

Put 3 ml of ethanol in a small conical flask, slowly add 3 ml of concentrated sulfuric acid while shaking, and pour this solution into a three-necked flask. Prepare a mixed solution of 20 mL ethanol and 14.3 mL glacial acetic acid, and pour it into the dropping funnel. Heat the flask with oil bath, keeping the temperature of oil bath at about 65438 040℃ and the temperature of reaction system at about 65438 020℃. Then slowly drop the mixed solution in the dropping funnel into a three-necked flask. Adjust the feed rate to make it almost equal to the steaming rate of ester. Feed for about 70 minutes. At this time, the temperature of reactants was kept at 120- 125℃. After dripping, continue to heat for about 10 min until no more liquid flows out.

Step 2 purify

Firstly, neutralizing the acid in the distillate with saturated NaCO3 solution until no CO2 gas overflows; Then, the distillate was washed with saturated NaCl solution (washing sodium carbonate solution) and saturated CaCl _ 2 solution (washing ethanol, CaCl _ 2 can form a complex with ethanol) in turn in a separatory funnel. Finally, the upper layer of ethyl acetate was poured into a small drying conical flask, and anhydrous K2CO3 was added for drying for 30 minutes.

note:

1. Because ethyl acetate can form binary and ternary boiling substances with water and ethanol, there are still water and ethanol in the distillate.

2. The purpose of using saturated solution here is to reduce the solubility of ethyl acetate in water.

3. Distillation

The dried crude ethyl acetate was transferred to a 50 ml single-mouth flask, heated in water bath, distilled at atmospheric pressure, and the fractions at 74-84℃ were collected. Weigh and calculate the output.

Four, the key and matters needing attention in the experiment

1, control the reaction temperature at 120- 125℃, too high temperature will increase the content of by-product ether;

2. Control the dropping speed of concentrated sulfuric acid. If it is too fast, it will release a lot of heat locally, causing boiling;

3. Pay attention to deflation when washing. After washing the organic layer with saturated NaCl, the aqueous phase was separated as cleanly as possible.

4. When the dried crude product is distilled, a fraction of 74-84.d egree. C. is collected.

Verb (abbreviation of verb) Physical constants of main reagents and products (literature values)

Molecular weight characteristic refractive index specific gravity melting point℃ boiling point℃ solubility: g/ 100 mL

Water alcohol ether

Glacial acetic acid 60.05 is colorless.

Liquid1.36981.04916.616.5438+08.1

Ethanol 46.07 is colorless

Liquid1.36140.780-11778.3 ∣∣ 33

Ethyl acetate 88. 10 is colorless.

Liquid1.3722 0.905-84 77.158.6 ∣∣ 3

Six, thinking about the problem

1, experimental report

1. What are the characteristics of esterification? How to create conditions in this experiment to make esterification proceed as far as possible in the direction of products?

2. What are the possible side effects of this experiment?

3. Is it okay to use too much acetic acid? Why?

A: No, in this experiment, we use excessive ethanol to increase the concentration of reactants and shift the equilibrium to the right. In addition, ethanol can also be distilled off with the generated water and ethyl acetate to form binary or ternary boiling substances, thus promoting the esterification reaction.