Organic chemistry laboratories are widely used in university research, chemistry, chemicals, materials, pharmacy, food, biology, environment, agronomy, etc.
I. Research content of organic chemistry laboratory
The organic chemistry laboratory conducts research experiments including general organic matter analysis (quantitative analysis and qualitative analysis, drug testing (content determination and identification, pesticide residue determination) 666 DDT pesticide residues, pyrethroid pesticide residues, organic nitrogen pesticide residues, organophosphorus pesticides Residue, gas analysis (analysis of artificial gas components, composition analysis of natural gas, analysis of liquefied petroleum gas composition), determination of harmful substances (benzopyrene, polycyclic aromatic hydrocarbons, aflatoxin), identification of unknowns in infrared spectrum, identification of unknown mass spectrometry Detect samples (water, food, blood samples), etc.
Second, the organic chemistry laboratory mainly contains equipment
1, rotary evaporator
Rotary evaporator, mainly used for continuous distillation of a large number of volatile solvents under reduced pressure. In particular, the concentration of the extract and the distillation of the receiving liquid in the chromatographic separation can separate and purify the reaction product.
2 , catalytic hydrogenation unit
Catalytic hydrogenation is one of the important contents in organic chemistry experiments. The specific content of this reaction is that gaseous hydrogen is added or reduced with an organic compound in the presence of a catalyst to form a new organic compound. Its advantages are: (1) Some reactions, such as the hydrogenation of carbon-carbon unsaturated bonds, the application of other methods is more complicated and difficult, and the application of catalytic hydrogenation reaction can easily achieve the purpose. (2) It can reduce the aldehydes, nitro groups and nitroso compounds to form the corresponding alcohols and amines, without any reducing agent and special solvent. Hydrogen itself is extremely inexpensive, so the cost is low and the operation is convenient. (3) After the reaction is completed, only the catalyst is filtered off, and the solvent is evaporated to obtain the desired product. The post-treatment is convenient, and the purity and yield of the product are satisfactory.
Catalytic hydrogenation can be divided into atmospheric hydrogenation, low pressure hydrogenation (4-5 atm) and high pressure hydrogenation (>6 atm) depending on the pressure selected for hydrogenation. Figure 2.9 is a diagram of a device for catalytic hydrogenation at atmospheric pressure and low pressure. High-pressure hydrogenation requires very special equipment (due to higher pressure), which is beyond the scope of this book, but open flames, including electric sparks, should not be used at any pressure for hydrogenation.
The catalytic hydrogenation unit mainly comprises a round bottom flask for hydrogenation, a barometer, a quantity (storage) gas pipe and a balance bottle. The volume of the gas storage pipe is generally between 100mL and 2L, and the appropriate gas storage amount can be selected according to the size of the reaction; the liquid contained in the balance bottle is usually water or mercury. During the reflection process, the pressure of the hydrogen can be adjusted by balancing the height of the bottle. After the reaction was completed, the volume of hydrogen participating in the reaction was measured by a balance bottle. The barometer ensures that the hydrogen is measured at the same pressure (typically 1 atm) before and after the reaction.
3 , compressed gas cylinder
In organic chemistry experiments, gases are sometimes used as reactants. For example, hydrogen, oxygen, etc., gas is also used as a shielding gas, such as nitrogen, argon, etc., and some gases are used as fuels, such as gas, liquefied gas, and the like. All of these gases need to be packed in special containers. Compressed gas cylinders are generally used. The gas is stored in a cylinder at a relatively high pressure, which is convenient for transportation and can be used at any time in a general laboratory. Due to the high-pressure compressed gas contained in the cylinder, it is necessary to pay strict attention to safety when using it, otherwise it will be very dangerous.
Compressed gas pressures commonly used in organic chemistry laboratories are typically close to 200 atmospheres. The bottle body of the whole cylinder is very solid, and the most vulnerable is the exhaust valve installed at the outlet of the cylinder. Once the exhaust valve is damaged, the consequences are unimaginable, so for safety, it must be in the exhaust valve. Top with a cover. In addition, these compressed gas cylinders should be kept away from fire and corrosive substances such as acids and bases.
The compressed gas cylinders used in the laboratory are generally about 160 cm in height and have a gross weight of about 70 to 80 kg. For such a large object, if it is not fixed, once it falls down, it will definitely ruin something or hurt people, and there is no danger of high pressure gas itself. Therefore, from the safety point of view, the cylinder should be fixed somewhere, such as fixed at the table or corner.
For the convenience of transfer, a special cart is generally used. How to correctly identify the type of gas contained in the cylinder is also a very important thing. Although all gas cylinders are labeled with a label indicating the type and purity of the gas contained in the bottle, these labels are often damaged or rotted. To be on the safe side, all compressed gas cylinders are painted in different colors according to certain standards.
4 , glass instrument
Organic chemical laboratory glass instruments can be divided into ordinary glass instruments and ground glass instruments.
Standard interface glass instruments are glass instruments with standardized grinding or grinding. Due to the standardization, systemization and frosting of the instrument plug size, any interface of the same type can be connected arbitrarily, and each component can be assembled into various supporting instruments. When it is not possible to assemble directly with parts of different types, use a adapter connection. The use of standard interface glass instruments not only eliminates the troublesome procedure of plugging, but also avoids the risk of contamination of the reactants or products by the plug. The smoothness of the plug is good, so that the adhesion can reach a higher degree of vacuum, especially for distillation. Pressure distillation is advantageous and is safe for experiments with poisons or volatile liquids.
Standard interface glass instruments are manufactured according to internationally accepted technical standards. When a component is damaged, it can be purchased. Each component of the standard interface instrument has a white marking on the top or bottom of the mouthpiece indicating the specification. Commonly used are 10,12,14,16,19,24,29,34,40 and so on. Some standard interface glass instruments have two numbers, such as 10/30, 10 indicates that the large end of the grinding ring has a diameter of 10 mm, and 30 indicates that the height of the grinding port is 30 mm.
5 , heating the instrument
In order to accelerate the organic chemical reaction, as well as to distill, fractionate, etc. the product, heating is often required. However, considering that most organic compounds, including organic solvents, are flammable and explosive, it is prohibited in the laboratory safety regulations to use direct flame heating (except for special needs).
In order to ensure uniform heating, a thermal bath is generally used for indirect heating. As the medium for heat transfer, there are air, water, organic liquid, molten salt, metal, etc., depending on the heating temperature, the rate of temperature rise, etc., the common equipment is as follows:
(1) Water bath and steam bath
When the heating temperature does not exceed 100 ° C, it is more convenient to use a water bath for heating. However, it must be pointed out (emphasis): When using potassium and sodium in metal and waterless operation, it should never be carried out on the water bath, otherwise it will cause fire or make the experiment fail. When using the water bath, do not let the container touch the water bath wall and its bottom. Due to the constant evaporation of the water bath, hot water is added as appropriate so that the water level in the water bath is often kept slightly above the liquid level in the container. The electrothermal porous constant temperature water bath is convenient to use.
(2) oil bath
When the heating temperature is between 100 and 200 ° C, an oil bath is preferably used. The advantage is that the reactants are heated uniformly, and the temperature of the reactants is generally lower than the oil bath temperature by about 20 ° C. Commonly used oil baths are:
1) Glycerin can be heated to 140-150 ° C, when the temperature is too high, it will be carbonized.
2) Vegetable oils such as vegetable oil, peanut oil, etc., can be heated to 220 ° C, often added 1% of hydroquinone and other antioxidants, easy to use. If the temperature decomposes when it is too high, it may burn when it reaches the flash point, so be careful when using it.
3) Paraffin oil can be heated to about 200 ° C, the temperature is slightly higher and does not decompose, but it is easier to burn.
4) Silicone oil Silicone oil is still stable at 250 °C, good transparency and safety. It is a commonly used oil bath in the laboratory.
One, but its price is more expensive.
When using oil bath heating, special care should be taken to prevent fire. When the oil bath is exposed to heat, stop heating immediately. A thermometer should be hung in the oil bath to observe the temperature of the oil bath and whether there is overheating. The temperature should not be too high, otherwise there is a danger of overflow after being heated. When using an oil bath, try to prevent factors that may cause oil bath combustion.
When the reaction vessel is taken out after heating, the reactor is still clamped with an iron clip and left to stand on the oil bath for a while. After the oil adhered to the wall of the vessel is finished, the paper or dry cloth is used to dry the wall.
6 , the mixer
The agitator is also one of the essential instruments for organic chemistry experiments. It can make the reaction mixture more uniform and the temperature of the reaction system is more uniform, which is beneficial to the chemical reaction, especially the heterogeneous reaction.
The agitator is divided into a magnetic stirrer, an electric stirrer and the like.
7 , barometer
The function of the barometer is to indicate the pressure within the system, usually using a mercury barometer. The mercury is filled in the thick glass tube, and the moving ruler is arranged behind the tube. The moving scale adjusts the zero degree to the mercury plane in the glass tube B on the side of the piston. When the pressure reducing pump works, the mercury tube of the A tube drops, and the tube B mercury column Rising, the difference between the two indicates the pressure of the system.
8 , vacuum pump
Vacuum pumps can be divided into three categories depending on the range of use and pumping efficiency:
(1) For general pumps, the pressure can reach 1.333~100kPa (10~760mmHg) as “rough†vacuum.
(2) Oil pump, the pressure can reach 0.133~133.3 Pa (0.001~1mmHg) as the "second highest" vacuum.
(3) Diffusion pump, pressure up to 0.133 Pa, (10-3 mmHg) is "high" vacuum.
The decompression pumps commonly used in organic chemistry laboratories are water pump and oil pump. If the pressure is not required, the pump can be used. If the pump is well constructed and the water pressure is high, the pumping efficiency can reach 1067~3333 Pa ( 8~25mmHg). The minimum pressure that the pump can draw is theoretically equivalent to the water vapor pressure at that water temperature. For example, when the water temperature is 25 ° C, 20 ° C, and 10 ° C, the pressure of water vapor is 3192, 2394, and 1197 Pa (8-25 mmHg), respectively. When pumping with a water pump, install a safety bottle in front of the pump to reduce the water pressure and suck the water; before stopping pumping, first deflate and then turn off the pump.
For lower pressures, use an oil pump. A good oil pump can draw below 133.3Pa (1mmHg). The quality of the oil pump depends on its mechanical structure and the quality of the oil. It must be protected when using the oil pump. If the organic solvent with high volatility is distilled, the organic solvent will increase the vapor pressure by the oil absorption, thereby reducing the pumping efficiency. If it is an acid gas, it will corrode the oil pump. If it is water vapor, the oil will be milked. Drain the vacuum pump with the turbid liquid.
9 , analytical instruments, spectroscopic instruments, etc.
The organic laboratory has large-scale instruments and supporting facilities such as high performance liquid chromatography, gas chromatography, thin layer scanner, elemental analyzer, nuclear magnetic resonance instrument, infrared absorption spectrometer.
10 , auxiliary equipment
Test bench, ventilation cover, medicine cabinet, utensil cabinet, reflux condensing device (small water cup and water copying), suction filter device (pumping faucet, small water cup slot), etc.
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