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    Home > Chemicals Industry > Chemical Technology > How to use a nitrogen balloon to safely seal the reaction (1)

    How to use a nitrogen balloon to safely seal the reaction (1)

    • Last Update: 2022-01-30
    • Source: Internet
    • Author: User
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    1.
    The role of nitrogen ball

    Nitrogen balloons are widely and frequently used in chemical laboratories
    .
    As long as the reaction does not produce gas or produces very little gas (such as 1 to 2L or less), whether it is a low temperature, room temperature or a closed heating reflux reaction, a nitrogen ball can generally be used to seal the reaction

    .
    Using a nitrogen ball to seal the reaction can play the three functions of avoiding tide (water), absorbing oxygen and buffering explosion-proof, which is very convenient to use, as shown in Figure 23-35

    .

    Figure 23-35 Nitrogen balloon sealing reaction

    However, random use of nitrogen balloons will cause accidents, and there have been many accident lessons, such as the following explosion accident
    .

    A researcher does an amplified alkylation reaction:

    Add 1.
    1L of anhydrous tetrahydrofuran (THF) and 255g of pyrazole (3.
    75mol) into a 3L three-necked flask, cool to 5℃ in an ice bath, add 108g of sodium hydride (NaH, 4.
    5mol) in batches with stirring, and cool to Below 15°C

    .
    After adding sodium hydride, add benzyl bromide (BnBr) dropwise under the protection of a nitrogen balloon, and control the temperature below 15°C in an ice bath

    .
    After the dripping is completed in about 1h, continue to stir, and the temperature has been controlled at about 15°C

    .
    After 1 hour, the person involved found that the reaction temperature was abnormal, the reaction was sudden, and the reaction temperature suddenly rose.
    He asked Zhou Kun's experimenter to take a fire extinguisher in case of accidents, and ran out to get dry ice to prepare to cool the system

    .
    When he rushed into the laboratory carrying a dry ice bucket, he saw the inflated balloon burst suddenly and then exploded

    .
    The fire was quickly extinguished by surrounding personnel with fire extinguishers, but the strong pressure created by the explosion not only damaged the doors of the fume hood, but also exploded the steel frame on the ventilating plate to bulge outwards, severely deformed, and a large area of ​​the ceiling was shaken down.
    The whole floor felt tremor.
    Figures 23-36 show the situation inside the fume hood after the explosion

    .
    The rate did not cause personal injury

    .

    Figure 23-36 Situation in the fume hood after the explosion

    The cause of the accident: According to the theoretical calculation, 100L of hydrogen was produced in this reaction, and there was a significant valve temperature (the temperature required for the melting or dissolution of mineral oil and the temperature required for sodium hydride to remove the active hydrogen from the substrate), and dozens of liters of hydrogen generated instantly would burst.
    Balloons make the space in the fume hood, exhaust duct and ceiling immediately reach the explosive limit, while the electrical appliances in the fume hood such as mechanical agitators are non-explosion-proof, and sparks are generated from time to time

    .

    2.
    How to use the nitrogen ball

    How to use a nitrogen balloon to safely seal the reaction? The chlorine balloon can be tied to the elbow pipe, straight sleeve or tee, as shown in Figure 23-35
    .

    It can also be directly sleeved on the condenser tube or needle tube, as shown in Figure 23-37 and Figure 23-38
    .

    Figure 23-37 The nitrogen ball is placed on the condenser tube

    Figure 23-38 The nitrogen ball is placed on the needle tube

    Among the above methods, it is recommended to tie the nitrogen ball to the tee, because the tee is easy to inflate, easy to operate, and has a larger aperture and is relatively unobstructed
    .
    But be careful when using the tee, it must be in the open direction and cannot be closed

    .
    Especially when the three-way cock is fixed with a rubber band, it is easy to rotate the angle of the three-way cock slowly and automatically due to the torsion of the rubber band itself.
    Once closed, it becomes a rigid closed system, which is extremely dangerous.
    There have been too many explosions

    .

    For reaction flasks below 100mL, you can consider the method of tying a nitrogen balloon to the needle, but before using it, check whether the needle is unblocked
    .
    From a safety point of view, it is generally not recommended to connect the needle tube, especially for large reaction flasks, it is forbidden to tie a helium balloon to the needle tube, because the small needle hole is very easy to cause obstruction or blockage

    .

     

     

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