Sealing tube reactions in synthesis

Applicable type of reaction

(1) The reaction temperature is slightly lower or higher than the boiling point of the solvent and the reaction raw material, and does not produce a large amount of gas in the reaction.
(2) A solution of gases in the reactants, and the reaction requires heating.

Common reaction pressure and temperature

Vapor pressure above the boiling point of several common solvents:
When methanol is at 140℃, the vapor pressure is 1077.08 kPa and the atmospheric boiling point is 64.5℃. At 150℃, the vapor pressure of ethanol is 982.85 kPa, and the boiling point at atmospheric pressure is 78℃.
At 136℃, the vapor pressure of toluene is 200 kPa, and the atmospheric boiling point is 110℃.
At 103.92℃, the vapor pressure is 199.98 kPa, and the atmospheric boiling point is 80℃.

Benzene and halogenated hydrocarbon compounds on the sealing ring swelling is more serious, it is not recommended to use too high temperature. Due to the different types of sealing tubes we use, it is recommended that the internal pressure should not exceed 6atm. At this time, methanol is about 120℃ and ethanol is about 130℃.
When using gas solution for tube sealing reaction, due to the serious volatilization of gas at high temperature, we should take into account the pressure generated by gas volatilization at high temperature in addition to the pressure generated by solvent exceeding the boiling point at that temperature. If the methanol solution of ammonia is used for ammonolysis, the pressure may exceed 10atm when the temperature is 120℃, due to the serious volatilization of ammonia at high temperature.

The microwave reactor can be heated at the same time to measure the internal pressure of the reaction, it is recommended that the uncertain reaction in the microwave reactor reaction at the target temperature for 10 minutes, to understand how much pressure may reach. The temperature of the oil bath must be controlled during the reaction to prevent overheating. Scratches and impacts will affect the pressure resistance of the sealed pipe. Care should be taken when using and cleaning the sealed pipe.

Problems that may occur during normal use

Sealing ring damage: Sealing ring is the most easily damaged part of the whole reactor. If damaged, it should be replaced in time. An accident happened in the company: during ammonolysis reaction with ammonia ethanol solution at 120℃, the sealing ring of ACE PRESSURE TUBE was damaged and the reaction liquid rushed out.
Tetrafluoroethylene lid to break the glass: the company once happened an accident: the use of domestic sealing tube, the temperature at that time is very low, before heating the lid screw too tight, after heating to 120℃, because the Tetrafluoroethylene expansion faster than the glass, the glass on the mouth of the sealing tube bulge broken, reaction liquid rushed out. It is suggested that domestic sealing tube should not be used in the future, because its quality has not been tested by the authority.
Sealing tube explosion: company accident: domestic sealing tube, the reaction is in progress sealing tube explosion. Three times as much gas can be produced by computational experiments. At 100 ° C, twice the amount of CH3OH, and twice the amount of CO2. There is a precedent for the explosion of the import seal tube in the company, so do not take any chances. The experiment should be carried out under the premise of ensuring safety.

Matters needing attention when sealing pipe is used

1.1 The quality of the inlet sealing tube is good. The new sealing tube can withstand up to 10ATM, but the maximum pressure will decrease after repeated use. The domestic sealing tube has not been strictly tested, as far as possible no longer use, or in the reaction of a gas solution, the temperature does not exceed the solvent boiling point, and to ensure that the pressure is not more than 2atm, can be used;
1.2 When using gas solution for tube sealing reaction, due to the serious volatilization of gas at high temperature, in addition to considering the pressure generated by the solvent exceeding the boiling point at that temperature, the pressure generated by the volatilization of gas in the solution at high temperature is also included in the estimation of pressure. If the methanol solution of ammonia is used for ammonolysis, the pressure may be far more than 10atm when the temperature reaches 120℃ due to the serious volatilization of ammonia at high temperature.
1.3 It is necessary to realize the estimation of the gas that may be generated by the reaction, including the pressure of the gas that may be generated by the main reaction and side reaction, etc., to take into account;
1.4 High pressure reactor is recommended for reactions where the reaction temperature exceeds the solvent boiling point by more than 20℃;

1.5 For uncertain reactions, it is recommended to use a microwave reactor for a small test, the reaction speed is fast and relatively safe;
1.6 The sealing pipe is a pressure instrument, and no collision, scratch or other operation that may lead to internal injury is allowed;
1.7 There are two kinds of sealing rings for the tube. The general brown Viton sealing ring is resistant to oil and acid. If strong alkali is used in the reaction, please use white perfluorine sealing ring;
1.8 When covering the plug, please do not rotate too tight or too loose. It should not be tightened to the extent that it cannot be tightened any more. In this way, it is easy to leak, cause danger and even break the top of the sealing pipe.
1.9 The volume of reagents and solvents in the system should be strictly controlled below 1/3 of the volume of sealing tube, and it is recommended to be less than 1/5;

1.10 When washing and sealing the tube, do not soak in the alkali tank or use ultrasonic washing. Rinse and clean the tube with appropriate solvent according to the reaction situation. It can be washed with a test tube brush instead of a scraper.
1.11 At the end of the sealing reaction, the sealing plug should be opened only after the reaction is lowered to room temperature. It should not be opened under the condition of high temperature;
1.12 When performing sealing reaction, protective baffles must be added to the front and the side where people may be injured. When observing the sealing reaction, do not observe directly, but observe behind the protective glass or baffle.