The preparation of organic ethyl acetate plays a very important role in the college entrance examination. In recent years, it has appeared frequently in the college entrance examination questions in various provinces. The following is an analysis of the test centers of ethyl acetate and the real questions about this test center over the years.
Formula for the preparation of ethyl acetate:
Add 3mL of ethanol to a test tube, then slowly add 2mL of concentrated sulfuric acid and 2mL of acetic acid while shaking the test tube. Connect the device as shown in the figure, slowly heat it with an alcohol lamp, and pass the generated vapor through the catheter to the liquid surface of the saturated sodium carbonate solution to observe the phenomenon.
(1) Mixing of reactants: first add ethanol, then concentrated sulfuric acid (add broken porcelain to prevent boiling), finally add acetic acid, and then heat.
(2) 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 to complete the catalysis. However, in order to remove the water generated in the reaction, the amount of concentrated sulfuric acid should be slightly higher.
(3) 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 broken porcelain pieces can be added to the test tube beforehand to prevent the liquid from boiling.
(4) The inclined airway is longer, which plays the role of air conduction and condensation at the same time;
(5) Do not extend the airway into the sodium carbonate solution to prevent the sodium carbonate solution from being sucked into the test tube heating the reaction due to uneven heating.
(6) The function of saturated sodium carbonate solution is to: ① Condensate ester vapor to reduce the solubility of the ester in water (conducive to stratification); ② Dissolve ethanol mixed in ethyl acetate. ③ It can react with volatile acetic acid to generate sodium acetate, which is convenient for smelling the aroma of ethyl acetate.
(7) Reasons why alkali (NaOH) cannot be used with sodium carbonate: Although sodium hydroxide can also absorb acetic acid and ethanol, alkali catalyzes the complete hydrolysis of ethyl acetate, resulting in experimental failure.
(8) The esterification reaction is a reversible reaction. In order to increase the yield of esters, an excess of one of the reactant 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 replace ethanol with absolute ethanol with 95% mass fraction.
(9) 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 make the liquid 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.
The experimental scheme designed below can achieve the experimental purpose ()
A. Preparation of Al (OH)
Suspension: Add an excess of 6mol · L
NaOH solution to 1mol · L B. Purification of ethyl acetate containing a small amount of acetic acid: Add an excess of saturated sodium carbonate solution to ethyl acetate containing a small amount of acetic acid, leave the solution to stand after shaking, and remove water from the organic phase C. Test whether the solution contains Fe ³: Take a small amount of the solution to be tested, add a small amount of new chlorine water to it, and then add KSCN solution dropwise to observe the experimental phenomenon D. Explore the effect of catalysts on the decomposition rate of H 2O ²: under the same conditions, add 2ml5% H 2O ³ and 1mlH2O to one test tube, and add 2mL of 5% HO2 and 1mL of FeCl to another test tube to observe and compare experimental phenomena Answer : BD Analysis : A, Al (OH) is an amphoteric hydroxide, which can react with excess sodium hydroxide to produce sodium metaaluminate, so aluminum hydroxide suspension cannot be prepared, wrong; B, The acidity of acetic acid is stronger than that of sodium carbonate, and saturated sodium carbonate removes acetic acid. It can also reduce the solubility of ethyl acetate to precipitate, and then separate the liquid, so it is correct; C, chlorine water has strong oxidation, and may oxidize Fe ² to Fe ³
Isoamyl acetate is one of the components that make up bee pheromones and has a rubber fragrance. The reaction, device schematic diagram and related information for the preparation of isoamyl acetate in the laboratory are as follows:
| Substance | Relative molecular mass | Density/(g · cm ³) | Boiling point/℃ | Solubility in water |
|---|---|---|---|---|
| isoamyl alcohol | 88 | 0.8123 | 131 | Slightly soluble |
| acetic acid | 60 | 1.0492 | 118 | solution |
| isoamyl acetate | 130 | 0.8670 | 142 | Insoluble |
Experimental steps:
Add 4.4 g of isoamyl alcohol, 6.0 g of acetic acid, a few drops of concentrated sulfuric acid, and 2 to 3 pieces of broken porcelain to A, start heating A slowly, reflux for 50 minutes, the reaction liquid is cooled to room temperature, pour into the separation funnel, wash with a small amount of water, saturated sodium bicarbonate solution, and water respectively, the separated product is added to a small amount of anhydrous magnesium sulfate solid, let stand for a while, filter to remove the magnesium sulfate solid, distillate and purify, collect 140~ 143 ° C fractions, and obtain isoamyl acetate 3.9 g. Answer the following questions:
(1) The name of device B is:
(2) In the washing operation, the main purpose of the first wash is:; the main purpose of the second wash is:.
(3) During washing and liquid separation operations, it should be fully shaken and then left to stand. After delamination (fill in the label),
A. Pour isoamyl acetate directly from the top of the separation funnel
B. Directly release isoamyl acetate from the lower mouth of the separation funnel
C. First release the water layer from the lower port of the separation funnel, and then release the isoamyl acetate from the lower port
D. First release the water layer from the lower mouth of the separation funnel, and then release the isoamyl acetate from the upper mouth
(4) The purpose of adding excess acetic acid in this experiment is:
(5) The purpose of adding a small amount of anhydrous magnesium sulfate to the experiment is:
(6) In the distillation operation, the correct instrument selection and installation are: (fill in the number)
(7) The yield of this experiment is:
A, 30% B, 40% C, 50% D, 60%
(8) During the distillation operation, if the distillate is collected from 130 ° C, the yield is biased (high or low) because
Answer :
(1) Spherical condenser
(2) Wash off most of the concentrated sulfuric acid and acetic acid; wash off sodium bicarbonate.
(3) d.
(4) Increase the conversion rate of isoamyl alcohol
(5) Dry
(6) b
(7) c
(8) High, a small amount of unreacted isoamyl alcohol will be collected.
Parsing :
(1) Instrument B is a spherical condenser
(2) The first wash mainly washes off concentrated sulfuric acid and excess acetic acid. The second wash mainly washes off the saturated NaHCO added in the previous step. Mainly consider the solubility of the substance and the presence of impurities.
(3) Isoamyl acetate is lighter than water. When separating the liquid, the lower layer must be discharged from the lower port, and the upper liquid must be poured from the upper port. So choose d.
(4) Due to the lowest boiling point of acetic acid, there will be more volatile loss of acetic acid. Adding excess acetic acid can ensure that more isoamyl alcohol is converted into products
(5) Anhydrous MgSO has fast water absorption and does not react with isoamyl acetate, which can absorb water and facilitate the next distillation.
(6) The thermometers of a and d are in the wrong position, and the condenser pipe should be a straight condenser pipe. If a spherical condenser pipe is used, the condensed liquid cannot all flow down, so b should be used.
(7) If an excess of acetic acid can be seen from the reaction equation, it is calculated as isoamyl alcohol. Theoretically, 6.6g of isoamyl acetate can be formed. The yield is: 3.9g/6.5g × 100% = 60%.
(8) will make the yield higher, and isoamyl alcohol dissolved in isoamyl acetate will enter the product.
