(1) Preliminary understanding and mastery of research ideas and experimental research methods for chemical product development.
(2) Learn to organize whole-process experiments and obtain high-purity products.
(3) Learn to analyze the experimental process and experimental results, and propose experimental improvement plans.
The reaction of acid and alcohol to produce esters is a typical reversible reaction:
In order to improve product yield, the following measures are generally adopted:
There are usually three methods for preparing esters directly from acids and alcohols.
The first is the azeotropic distillation water separation method. The resulting esters and water are evaporated in the form of boiling water, and after condensation, the water is separated through a water separator, and the oil layer is returned to the reactor.
The second is the extraction esterification method, adding a solvent to make the reactant and the generated ester dissolve in the solvent and separate from the water layer.
The third method is direct reflux, a reactant excess, direct reflux.
Preparation of n-butyl acetate is better with azeotropic distillation water method. In order to remove the water generated in the reactants, the ester, acid and water are used to form binary or ternary azeotropics, and the azeotropic distillation water method is adopted. The resulting ester and water escape in the form of azeotropics, and after condensation, the water layer is separated through a water separator, and the oil layer is returned to the reactor.
Instrument Distillation device Glass grinding mouth instrument, spherical condenser, water separator, round bottom flask (250ml), thermometer (200 ° C), conical bottle (50ml), beaker (400ml), oil bath, liquid separation funnel, measuring cylinder (10ml, 50ml), electric heating sleeve, iron frame table, iron clip and cross head, iron ring, rubber water pipe, balance
Reagents Butanol (23ml, 0.25mol), glacial acetic acid (16.5ml, 0.28mol slightly excess), KHSO4 1g (catalyst), NaCl, anhydrous magnesium sulfate, ice, zeolite, glycerin, pH paper
device
In 1,250 mL round bottom flask, add 23 mL (0.25 mol) n-butanol, 16.5 mL glacial acetic acid (0.28 mol) and 1 g KHSO4 (catalytic reaction), mix well.
2. Connect the reflux condenser and the water separator. Add a small amount of water to the water separator in advance to be slightly lower than the branch pipe mouth (about 1 to 2 cm). The purpose is to make the alcohol in the upper ester reflux back into the flask to continue participating in the reaction, mark it with a pen and heat it to reflux without controlling the temperature. Control the reflux speed of 1 to 2 d/s.
3. After a period of reaction, separate the water and keep the water level in the water separator at its original height. Note the amount of water produced.
4. After about 40 minutes, no more water is generated (that is, the liquid level does not rise), indicating that the reaction is complete.
5. Stop heating and record the amount of water separated.
6. Pour the ester layer separated from the water separator into the separation funnel together with the reaction liquid, wash with 10 mL of water, and remove the lower water layer (remove acetic acid and a small amount of n-butanol); the organic phase continues to be washed with 10 mL 10% Na 2 CO 3 until neutral (remove sulfuric acid); the upper organic phase is washed with 10 mL of water to remove a small amount of inorganic salt dissolved in the ester, and finally the organic layer is placed in a small conical bottle and dried with anhydrous magnesium sulfate.
Distillation: The dried n-butyl acetate is filtered into a 50 mL flask and distilled at atmospheric pressure to collect the fraction at 124-126 ° C.8. Calculate the yield.
1. The reflux water separation reaction device can separate the water generated by the reaction in time, shortening the entire experiment time. In this experimental system, there are n-butanol-water azeotrope with a boiling point of 93 ° C; n-butyl acetate-water copolymer with a boiling point of 90.7 ° C. At different stages of the reaction, different azeotropics can be used to take the water out of the system. After condensation, the water is separated, and the alcohol and ester return to the reaction system. In order to make the alcohol return to the reaction system in time to participate in the reaction, before the reaction starts, metered water should be added to the water separator to make the water surface slightly lower than the lower edge of the reflux branch of the water separator. When there is reflux condensate, only a very shallow layer of oil layer exists on the water surface. During the operation, the generated water is continuously released to keep the thickness of the oil layer unchanged. Or in the water separator, water is added to the branch in advance to release the theoretical amount of water generated by the reaction (with a small measuring cylinder). During the washing operation, n-bromobutane is sometimes in the upper layer and sometimes in the lower layer. According to the relative density data, determine whether the product is in the upper layer or in the lower layer.
The composition and boiling point of n-butyl acetate, water and n-butanol to form binary or ternary azeotropic fluids
| Boiling point (℃) | Composition (%) | ||
|---|---|---|---|
| Butanol | Water | n-butyl acetate | |
| 117.6 | 67.2 | 32.8 | |
| 93 | 55.5 | 45.5 | |
| 90.7 | 27 | 73 | |
| 90.5 | 18.7 | 28.6 | 52.7 |
2. Washing operation (use of separation funnel):
(1) Check the tightness of the separation funnel cock before washing.
(2) When washing, it should be fully shaken lightly. Do not use too much force or oscillate for too long, otherwise an emulsion will be formed, which will be difficult to stratify and cause difficulty in separation. Once an emulsion is formed, a small amount of electrolyte or water such as salt can be added to stratify it.
(3) After oscillation, pay attention to opening the cock in time to release the gas to balance the internal and external pressures. When deflating, make the tail pipe of the separation funnel face up, and avoid the tail pipe facing people.
(4) After the oscillation is over, let stand and layer; when separating the liquid layer, the lower layer is released through the cock, and the upper layer is poured out from the upper port.
3. Distillation, the equipment used is dry, so that n-butyl acetate is fully dried, thereby improving product quality.
1. Glacial acetic acid condenses into an icy solid at low temperature (melting point 16.6 ° C). When taking it, it can be heated in a warm water bath to melt it and measured. Be careful not to touch the skin to prevent burns.
2. Before adding the reactants, the instrument must be dry. (Why?)
3. Concentrated sulfuric acid acts as a catalyst, only a small amount is required. Solid superacid can also be used as a catalyst.
4. When the esterification reaction is carried out to a certain extent, the ternary azeotrope of n-butyl acetate, n-butanol and water can be continuously evaporated (constant boiling point 90.7 ° C). The composition of the reflux is: the upper three are 86%, 11%, 3%, and the lower layer is 19%, 2%, and 97%. Therefore, do not divide too much water when dividing the water, but allow the upper liquid to overflow back to the round bottom flask to continue the reaction.
5. Anhydrous calcium chloride cannot be used as a desiccant in this experiment because it can form complexes with the product and affect the yield.
6. According to the total amount of water released (note that the amount of water added to the water separator in advance is deducted), the purity of the esterification reaction can be roughly estimated.
7. The purity of the product can also be determined by infrared spectroscopy.
