Knowledge point:

Under the action of concentrated sulfuric acid, acids and alcohols can react to form a new substance called ethyl acetate. The reaction of acid to form esters is called esterification.

In the process of preparing ethyl acetate, the hydroxyl group removed from acetic acid combines with the hydrogen atom on the hydroxyl group removed from ethanol to form water, and the carbonyl group is then connected with the oxygen atom to form an ester.

The preparation of ethyl acetate requires heating, so a test tube can be used as a reaction device.

Add the reagent in the order of ethanol, concentrated sulfuric acid, and acetic acid in A, and heat the mixture. The reagent in B is a saturated sodium carbonate solution to absorb ethanol and acetic acid, but it should be noted that the catheter cannot penetrate deep below the liquid level to prevent inversion. Ethyl acetate is insoluble in water. After the reaction is completed, pour the liquid in B into the separation funnel to separate and obtain ethyl acetate.

Precautions

• Mixing of reactants: first ethanol, then concentrated sulfuric acid (adding broken tiles to prevent boiling), finally acetic acid, then heat.
• Concentrated sulfuric acid is used as both a catalyst and a water absorber. The amount of concentrated sulfuric acid used for catalysis is very small. Generally, the mass of sulfuric acid can reach 3% of the mass of ethanol. However, in order to remove the water generated in the reaction, the amount of concentrated sulfuric acid should be slightly higher.
• When preparing ethyl acetate, the reaction temperature should not be too high, and it should be kept at about 60 ° C to 70 ° C. If the temperature is too high, impurities such as ether and sulfur dioxide will be generated. After the liquid is heated to boiling, it should be heated on low heat. A few pieces of broken porcelain can be added to the test tube beforehand to prevent the liquid from boiling.
• The inclined airway is longer, which plays the role of both air conduction and condensation;
• Do not extend the airway into the sodium carbonate solution to prevent the sodium carbonate solution from being sucked into the test tube of the heated reactant due to uneven heating.
• The functions of the saturated sodium carbonate solution are: ① to condense the ester vapor, reducing the solubility of the ester in water (conducive to stratification); ② to dissolve the ethanol mixed in ethyl acetate. ③ It can react with the volatile acetic acid to produce sodium acetate, which is easy to smell the fragrance of ethyl acetate.
• The reason why sodium carbonate cannot be used as a base (NaOH): Although sodium hydroxide can also absorb acetic acid and ethanol, the base will catalyze the complete hydrolysis of ethyl acetate, resulting in experimental failure.
• The esterification reaction is a reversible reaction. In order to increase the yield of esters, an excess of one of the reactants acids and alcohols is generally used. In the laboratory, an excess of ethanol is generally used. The mass fraction of ethanol is higher, and it is better to use absolute ethanol instead of ethanol with a mass fraction of 95%.
• In order to facilitate the formation of ethyl acetate, the following measures can be taken: ① When preparing ethyl acetate, the reaction temperature should not be too high. Do not allow the liquid to boil. ② It is best to use glacial acetic acid and absolute ethanol. At the same time, the method of excessive ethanol is used. ③ The amount of concentrated sulfuric acid should be slightly more than the amount of ethanol.

Exercise:

1. The figure shows the experimental operation flow chart for the separation of ethyl acetate, acetic acid and ethanol mixtures. During the experimental process shown in the figure below, the wrong statement about the operation, instruments and substances in this separation process is

A. The main function of sodium carbonate solution is to remove acetic acid and reduce the solubility of ethyl acetate in water

B. Operation ① is liquid separation, operation ③ is evaporation crystallization and filtration

C. Substance A contains sodium acetate, sodium carbonate, ethanol

D. Operation ② Glass instruments used include alcohol lamps, distillation flasks, condenser tubes, thermometers, and conical bottles

2. To remove impurities from the mixture (impurities in parentheses), the selected reagent and separation method are correct

3. The following experimental devices can achieve the purpose ()

A. ① Device for testing products of 1-bromopropane elimination reaction

B. Production of ethylene from ethanol in the plant laboratory

C. ③ Device for laboratory production of ethyl acetate

D. ④ The device can prove acidic: hydrochloric acid> carbonic acid> phenol

4. As shown in the figure, it is a device diagram for the preparation of a small amount of ethyl acetate in the laboratory. The following statement about the experiment is incorrect ()

A. Add concentrated sulfuric acid to tube a first, then slowly add ethanol and acetic acid while shaking the tube

B. The airway port in test tube b is not immersed below the liquid level to prevent inversion during the experiment

C. The purpose of heating the test tube a during the experiment is to steam out the ethyl acetate in time and speed up the reaction rate

D. The role of the saturated solution in test tube b is to absorb a small amount of acetic acid and ethanol evaporated with ethyl acetate

5. Combine with H ₂ ¹⁸ O, add sulfuric acid as a catalyst, and ethyl acetate is hydrolyzed under heating conditions. After a period of reaction, the substance where ¹⁸ O is located and the position where the bond is broken when ethyl acetate is hydrolyzed are correct

A. Ethyl acetate, acetic acid, ①

B. Ethyl acetate, ethanol, ②

C. Ethanol, water, ②

D. Acetic acid, water, ①

Laboratory supplies

1. Instruments and materials: spherical supported test tubes, small test tubes, right-angled ventilation tubes, alcohol lamps.

2. Pharmaceuticals: 95% ethanol, glacial acetic acid, concentrated sulfuric acid, saturated sodium carbonate solution, phenolphthalein solution, small porcelain (zeolite).

Preparation of ethyl acetate

(1) Place about 1.2 mL of 95% ethanol in a spherical tube, then slowly add about 0.4 mL of concentrated sulfuric acid and 0.8 mL of glacial acetic acid while shaking, and put in a small piece of broken porcelain. Connect the device as shown below.

(2) Heat the side bubble tube evenly with an alcohol lamp over low heat, allowing the resulting vapor to slowly pass through the catheter into a small tube containing about 0.5 mL of saturated sodium carbonate solution and a drop of phenolphthalein solution. When obvious stratification is seen in the small tube and about 0.5 mL of ethyl acetate is collected, stop heating, observe the phenomenon and smell it.

Hydrolysis of ethyl acetate

Remove the small test tube, gently shake it, let it stand, and observe the phenomenon. If there is still stratification, you can carefully heat it with an alcohol lamp, and then observe whether there is stratification and whether the pink fades.

Experience tips

1. Add about 0.5 mL of saturated sodium carbonate and 1 drop of phenolphthalein to a small test tube. Its functions are: (1) to condense ethyl acetate vapor and reduce the solubility of ethyl acetate in water (conducive to stratification). The red color of phenolphthalein and base is better than seeing the generated ethyl acetate floating on the upper layer; (2) Due to the volatilization of acetic acid in the preparation of ethyl acetate, it has an impact on the smell of ethyl acetate. Therefore, after the reaction is completed, the small test tube can be shaken to make Na ₂ CO ₃ react with the volatilized acetic acid to generate odorless sodium acetate, which better feels the fragrance of ethyl acetate. At the same time, ethanol mixed in ethyl acetate can also be dissolved; (3) In the hydrolysis experiment of ethyl acetate, there is no need to add alkali, which makes the experiment more coherent.

2. When preparing ethyl acetate, the reaction temperature should not be too high. It should be kept at about 60 ° C to 70 ° C. If the temperature is too high, impurities such as ether and sulfurous acid or ethylene will be generated. After the liquid is heated to boiling, it should be heated on low heat. A small piece of broken porcelain can be added to the test tube beforehand to prevent the liquid from boiling.

3. Due to the small diameter of the spherical tube, when heating, special care should be taken not to heat too violently to prevent the liquid from flushing out of the tube. If there are signs of liquid rushing up, remove the alcohol lamp slightly and continue heating later.

4. The right-angled snorkel should not be inserted into the liquid level of the small test tube, but should be placed above the saturated Na ₂ CO ₃ solution to prevent uneven heating, resulting in Na ₂ CO ₃ liquid inversion phenomenon.

5. When heating the hydrolysis of ethyl acetate, first shake the ethyl acetate and Na ₂ CO ₃ before heating. Special attention should be paid to controlling the heating distance between the alcohol lamp and the small test tube, because ethyl acetate is an extremely flammable substance, it is necessary to prevent it from burning during the heating process. It is best to put the small test tube into a hot water bath for thermal hydrolysis. The boiling point of ethyl acetate is 77.2 ° C. The temperature of the water bath should not exceed the boiling point of ethyl acetate. Otherwise, the evaporation of ethyl acetate will be mistaken for a hydrolysis reaction.