Problems in laboratory preparation of ethyl acetate

Faint ......Don't mislead people upstairs, don't talk nonsense if you don't know.

Both ethanol and acetic acid are volatile, and ethanol is often overdosed in experiments to maximize the conversion of acetic acid, so ethanol is added first to reduce the volatilization of acetic acid.

And concentrated H2SO4 must be added last. This step is somewhat similar to the dilution of concentrated H2SO4, doesn't it have to be "acid into water" when diluting? It's the same thing here. If you concentrate H2SO4 first, it will most likely spill out.

In addition, the mechanism of this reaction is a nucleophilic addition-elimination reaction. First, H+ in the acid is added to carbonyl oxygen, and then the charge is transferred to form carbocation; Then a lone pair of electrons of the O atom on the alcohol attacks the carbocation, and H+ detachs to form an addition intermediate; This intermediate is unstable and then dehydrates to form esters.

The order is ethanol, concentrated sulfuric acid, acetic acid.

The reasons are: after putting ethanol, put concentrated sulfuric acid, ethanol is less volatile than acetic acid, and you can continue to add acetic acid after putting sulfuric acid and cooling, I think there is 95% ethanol used in the experiment, and the stability of ethanol in sulfuric acid is better than that of acetic acid in sulfuric acid (involving the -oh activity of acetic acid ethanol, of course, it is the activity of acetic acid, after adding concentrated sulfuric acid, it may dehydrate and condense between -cooh), to prevent acetic acid and sulfuric acid from being dehydrated first, therefore, choose ethanol to add first, and then talk about concentrated sulfuric acid. Moreover, chemical experiments are more cost-effective, and acetic acid is more expensive than ethanol.

I don't know if your teacher said it was okay.

Our teacher said to add ethanol first, then concentrated sulfuric acid, and finally acetic acid.

The essence of the reaction is that ethanol is esterified with sulfuric acid first, and then acetic acid replaces the sulfonic acid group, so the reaction is accelerated.

Seems to be yes, you can ask the teacher.

In the same way, sulfuric acid is the catalyst here, and it can be added whenever you want.

It doesn't matter what you add first, the most important thing is to control the dosage ratio of the reactants.

Laboratory extraction of ethyl acetate is as follows:

A colorless, oily liquid appears above the layer of saturated sodium carbonate solution, and a fragrance can be smelled.

1. Device diagram for preparing ethyl acetate:

2. Experimental operation:

1. Chemical formula for the preparation of ethyl acetate:

CH3COOH + CH3CH2OH = (concentrated sulfuric acid, heated) CH3COOC2H5 + H2O (reversible reaction).

2. Specific experimental procedures:

1) Correctly set up experimental equipment according to the experimental requirements.

2) Fill the large test tube with broken porcelain pieces (to prevent boiling).

3) Add an appropriate amount (about two milliliters) of absolute ethanol to the large test tube.

4) Add 2ml of concentrated sulfuric acid (**) and 2ml of acetic acid while **.

5) Add saturated sodium carbonate solution to another test tube.

6) Connect the experimental device (the catheter cannot be inserted into the sodium carbonate solution, and the catheter mouth and the liquid level should be kept at a certain distance to prevent suction).

7) Light the alcohol lamp and heat the test tube until it boils.

8) After a certain amount of product is collected in the test tube, stop heating, withdraw the test tube B and shake vigorously, and then stand to be stratified, separate the ethyl acetate layer, wash and dry. Ethyl acetate is ready. At the end of the experiment, the device was washed.

3. The conduit that passes steam in the device cannot be inserted into the saturated sodium carbonate solution

Prevent the Na2CO3 solution from being sucked back into the tube where the reactant is heated due to uneven heating.

Preparation of ethyl acetate: ethanol is added first, then concentrated sulfuric acid is added (crushed porcelain pieces are added to prevent overboiling), and finally acetic acid is added, and then heated (the experiment can be controlled).

1: Esterification is a reversible reaction. In order to increase the yield of esters, it is necessary to try to make the reaction as favorable as possible for ester formation.

Generally, it is an excess of reactants acids and alcohols. In industrial production, what kind of excess is better, generally depends on whether the raw materials are easy to obtain, whether they are cheap and whether they are easy. In the laboratory, ethanol overdose is generally used.

The mass fraction of ethanol should be high, and it would be better if absolute ethanol could be used instead of ethanol with a mass fraction of 95%. The amount of concentrated sulfuric acid used in catalysis is very small, generally only the mass of sulfuric acid reaches 3% of the mass of ethanol to complete the catalytic effect, but in order to remove the water generated in the reaction, the amount of concentrated sulfuric acid should be slightly more.

2: The reaction temperature should not be too high when preparing ethyl acetate, and it should be kept at 60

When the temperature is too high, impurities such as ether and sulfurous acid or ethylene will be produced. Once the liquid is heated to boiling, it should be heated over low heat instead. A few pieces of broken porcelain can be added to the tube beforehand to prevent the liquid from boiling.

3. Do not extend the trachea into the Na2CO3 solution to prevent the Na2CO3 solution from being sucked into the test tube of the heating reactant due to uneven heating.

Concentrated sulfuric acid is used as a catalyst, a water absorbent, and a dehydrating agent.

The effects of the Na2CO3 solution are:

1) The function of saturated sodium carbonate solution is to condense the ester vapor, reduce the solubility of the ester in water (conducive to stratification), remove the acetic acid mixed in ethyl acetate, and dissolve the ethanol mixed in ethyl acetate.

2) Na2CO3 can react with volatile acetic acid to produce odorless sodium acetate, which is convenient for smelling the aroma of ethyl acetate.

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 and kept at 60

The liquid cannot be boiled.

2) It is best to use glacial acetic acid and absolute ethanol. At the same time, the method of ethanol overdose is used.

3) The amount of concentrated sulfuric acid that plays a catalytic role is very small, but in order to remove the water generated in the reaction, the amount of concentrated sulfuric acid is slightly more than the amount of ethanol.

4) Use an inorganic salt Na2CO3 solution to absorb the volatilized acetic acid.

The reason why the base (NaOH) cannot be used with Na2CO3.

Although acetic acid and ethanol can also be absorbed, the alkali catalyzes the complete hydrolysis of ethyl acetate, resulting in the failure of the experiment.

Excess acetic acid can avoid the formation of isoboiling substances by ethyl acetate and ethanol.

Acetic acid and ethyl acetate are not azeotropic, and excess acetic acid does not affect the distillation of the product.

The cost of ethanol and acetic acid is negligible in laboratory preparation, and there is not much difference.

Hope it helps, satisfied, dear! If you have any questions, feel free to ask!

Protocol Procedure:

Inject 2ml of ethanol into a large test tube, then slowly add concentrated sulfuric acid and 2ml of acetic acid, and connect the device for preparing ethyl acetate.

Heat the mixture in the tube over low heat. Pass the resulting vapor through the catheter to 3 ml of saturated sodium carbonate solution about 2 mm above 3 mm and inject.

Observe the change of the test tube containing the sodium carbonate solution, wait for the transparent oily liquid to float on the liquid surface, remove the test tube containing the sodium carbonate solution, and stop.

Stop heating. Shake the test tube containing the sodium carbonate solution, let it stand, wait for the solution to stratify, observe the upper layer of liquid, and smell it.

After heating the mixture for a period of time, gas can be seen to be released, and there is an oily substance in the test tube containing the sodium carbonate solution.

Experimental attention problems;

The reagents used are ethanol, acetic acid, and concentrated sulfuric acid.

The order of adding reagents is ethanol--- concentrated sulfuric acid --- acetic acid.

Collect the resulting ethyl acetate in a tube containing sodium carbonate saturated solution.

The catheter should not be inserted into the sodium carbonate solution (to prevent the phenomenon of back-suction).

The reaction should not be heated too quickly.

A few notes: a role of concentrated sulfuric acid: catalyst absorbent.

b.Effect of saturated sodium carbonate solution: neutralizes the acetic acid that has evaporated the past; dissolution of ethanol that has evaporated past; Reduce the solubility of ethyl acetate.

Measures taken to increase yield: (The reaction is reversible).

Absorb water with concentrated sulfuric acid to balance the positive movement of heating to evaporate the ester.

Measures to increase production:

Concentrated sulfuric acid is used as a catalyst and absorbent. Heating (both to speed up the reaction rate and to evaporate the ester).Collect B with saturated sodium carbonate solution.

Ethyl ester (loss reduction).