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pm | Common reaction devices for organic experiments _ (16th Nov 22 at 2:28am UTC)
Common reaction devices for organic experiments _ Reflux |   | Original Title: Common Reaction Devices for Organic Experiments 1. Water-free and oxygen-free operation device Chemical experiments often need to be carried out in the absence of water and must be kept at a pressure comparable to that of the atmosphere. Therefore, acid or basic drying tubes are used to prevent moisture in the air from entering the experimental system. For example, the preparation of Grignard reagent and its related reactions, Friedel-Crafts reaction, as well as the use of strong alkaline, strong water absorption reagents, such as sodium alkoxide, alkyl sodium, phosphorus pentoxide and other experiments need to avoid the entry of water vapor. Moreover, some experiments require the absence of oxygen in addition to the absence of water. At this time, inert gases such as N2 and argon are often used. Air, oxygen, water, carbon dioxide, etc. Are expelled by this gas stream. For example, the preparation of butyl lithium and its related experiments,wiped film evaporator, the treatment of anhydrous and oxygen-free solvents, etc. The following figures show several representative experimental devices, which can be used for various experiments without water or oxygen. Device 1: It can isolate the contact between the reaction system and the atmosphere, and prevent the device from cracking due to the pressure difference between the reaction system and the atmosphere caused by sealing. Unit 2: Can handle multiple solvents. Is convenient and safe, can be heated and refluxed, and can take out the processed solvent at any time. The device 3 can be used for carrying out various water-free and oxygen-free reaction experiments. A continuous flow of inert gas is not required. The nitrogen stored in the balloon gives the reaction system a slight positive pressure,jacketed glass reactor, which prevents air from entering. Expand the full text Packing 4: It can be used for waterproof distillation, so as not to open the device due to airtightness. A small amount of volatile matter can also be collected in the balloon without leakage. (Reference: DOI: CNKI: SUN: DXHX.0.1987-03-014) II. Reflux Condensing Device At room temperature, the reaction rate is very small or difficult to carry out, and in order to carry out the reaction as soon as possible, it is often necessary to keep the reactant boiling for a long time. In this case, it is necessary to use a reflux condensing device to continuously condense the vapor in the condensing tube and return it to the reactor, so as to prevent the escape and loss of substances in the reactant. Three. Reflux dropping device Some reactions are more violent in the reflux state, and the heat release is large. If the reactants are put in at one time, the reaction will be difficult to control; Or in some reactions, in order to control the selectivity of the reaction, the reactants also need to be added in batches. In this case, rotovap distillation ,nutsche filter dryer, a reflux dropping device with a dropping funnel is used to slowly drop one of the reactants. In addition, cold water or ice water can be used outside the reaction bottle or heated by a heat source as required. In many synthetic experiments (such as heterogeneous reaction), stirring devices are often used in order to make the reaction go smoothly, control the reaction temperature better, shorten the reaction time and improve the yield. IV. Backflow water distribution device In some reversible equilibrium reactions, one of the reactants can be continuously removed from the reaction mixture in order to make the forward reaction complete. If one of the products is water and the water produced can form an azeotropic mixture with one of the reactants, a reflux water separator can be used. The function of the water separator is to separate the water produced by the reaction from the reaction system, that is, to reduce the concentration of the product so that the equilibrium reaction moves to the right, thereby increasing the yield of the reaction. The reactant or solvent and water are required to be immiscible, and the density should be smaller than that of water, so that the water in the water separator can be layered with the reactant or solvent, the upper reactant or solvent can continue to flow back to the reaction system to continue the reaction, and the lower water can be separated from the reaction system. A water-carrying agent is a substance that reacts with water to produce an azeotrope that makes it easier for water to be distilled out. A water separator should not be used in the preparation of ethyl acetate because reactants, products, and water are mutually soluble and cannot be separated. As long as it is evaporated with ethyl acetate, it can be removed with a desiccant. V. Fractionation unit For the reversible reaction with water generation, if the boiling point difference between the generated water and one of the reactants is small (less than 30 ℃), and the two are mutually soluble, such as water and acetic acid, if you want to separate the water generated by the reaction, the reactant such as acetic acid is also separated at the same time, then you can not use the reflux water separation device to improve the reaction yield, but use the separation device.
VI. Distillation unit For a reversible reaction with water generation, if the boiling point difference between the generated water and the reactants and other products is very small, and the generated water and the reactants and other products form an azeotropic mixture, and the boiling point of the reactants is lower than that of water, such as ethanol, bromoethane and so on, if you want to separate the water generated by the reaction, the reactants such as ethanol and bromoethane are easier to be separated. In this case, a distillation apparatus while adde dropwise can be used. In order to prevent more reactants from being evaporated and lost, the reaction should be distilled while dropping. If the reaction is difficult to occur, the device of reflux while dropping can also be used. VII. Vacuum Distillation Unit Distillation under reduced pressure is suitable for substances that decompose, oxidize, or polymerize under heat before they reach the boiling point when distilled under atmospheric pressure. VIII. Steam Distillation Unit Steam distillation units are mainly used in the following situations: 1. Separation of some organic compounds which are easily decomposed near the high boiling point ； 2. Separation of desired components from non-volatile or undesirable resinous material ； 3. Removing volatile by-products or unreacted starting materials from the reactant ； 4. Separation and purification of compounds with certain operational difficulties by other separation and purification methods 。 The substance to be purified must meet the following conditions: 1. Insoluble or poorly soluble in water ； 2. No chemical reaction with water under co-boiling ； 3. At At about 100 ℃,wiped film distillation, there is a certain vapor pressure, generally not lower than 667 Pa (5mmHg). If it is lower than this value and steam distillation is necessary, superheated steam distillation should be used. Return to Sohu to see more Responsible Editor:. toptiontech.com | |
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