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Neha Khawar

What is heating under reflux?

David W Gault  Follow

Many organic reactions are unreasonably slow and can take an extended period of time to achieve any noticeable effect so heating is often used to increase the rate of reaction. However, many organic compounds have low boiling points and will vaporise upon exposure to such high heat, preventing the reaction from proceeding in full.

To address this, heating under reflux is used. This refers to heating a solution with an attached condenser to prevent reagents from escaping.

wikied image

As seen above, any vapor will condense on the cool surface of the attached condenser and flow back into the flask.

The hot water bath pictured is an optional component of heating under reflux and is usually only used for particularly sensitive reactions. Also, using it limits the reaction temperature to 100 degrees Celsius.

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Jon Do  Follow
I agree that countercurrent is desirable. However, in some condensers downward flow may mean that the water does not remain in contact with the whole surface. See, for example, the following video at about 1:00 - the cooling water is initially connected downward, and then corrected to an upward flow. More
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Friar Wire  Follow
youtube.com/watch?v=h54XyEnYZDAMore
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Georg Uray  Follow
Note: water bath on the picture is optional and usually not used except for particularly sensitive reactions.More
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Gerald Cadwell  Follow
Two comments: 1: In organic labs, not using an oil bath for heating is not an option (you get much better temperature control). 2: More
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Joe Miller  Follow
the liquid doesnt always condense back into the flask, another type of condenser can be attached so that the now condensed desirable liquid can flow into a seperate beaker or flask. this can be used later in the experimentMore
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