Overview of Reflux A reflux setup Figure 1. Step-by-Step Procedures Figure 1. Pour the solution to be refluxed into a round bottomed flask, and clamp it to the ring stand or latticework with an extension clamp Figure 1.
The flask should be no more than half full. Add a stir bar or few boiling stones for bump prevention. Boiling stones should not be used when refluxing concentrated solutions of sulfuric or phosphoric acid, as they will colorize the solution. For example, when a stir bar is used for bump prevention with concentrated sulfuric acid, the solution remains colorless Figure 1.
When the same reaction is conducted using a boiling stone, the solution darkens during heating Figure 1. Place rubber hoses on a condenser wet the ends first to allow them to slide on , then attach the condenser vertically to the round bottomed flask. If using a tall condenser, clamp the condenser to the ring stand or latticework Figure 1.
Be sure the condenser fits snugly into the flask. Safety note: if the pieces are not properly connected and flammable vapors escape, they may be ignited by the heat source. Do not connect the round bottomed flask and condenser with a plastic clip, as shown in Figure 1. Plastic clips can sometimes fail especially when they are heated , and this setup does not allow for the flask to be reliably removed from the heat source at the end of the reflux.
Connect the hose on the lower arm of the condenser to the water faucet and allow the hose on the upper arm to drain to the sink Figure 1. To avoid this, simply add a stirring bar to your flask.
You could alternatively add boiling chips anti-bumping granules to your solution before heating to help it boil more gently. Mistake: starting the timer too soon. The final mistake many make is beginning to time the reaction too soon. The solution should not only be boiling, but actively refluxing in the condenser when your timer starts, otherwise you may produce inaccurate data.
By avoiding these common mistakes, you can ensure you run a safe reactions that result in a good yield. Many Radleys products have been designed specifically to help prevent such mistakes. The Findenser , for example, is an air-cooled condenser — which completely eliminates the risk of water leaks. How to optimise the performance of your Findenser. For the unported Hickman head, the Pasteur pipet is used to draw the liquid out from the top.
If a condenser or internal thermometer is used, the distilling apparatus must be partially disassembled in order to do this. In some stills the inner diameter of the head is so small that it is difficult to reach in at an angle with the pipet and make contact with the liquid.
To solve this issue, the tip of the pipet should be bent slightly in a flame. Once removed, the liquid is transferred to a small vial and capped with a Teflon-sealed cap.
If there is more than one volatile compound in the vial, it will be necessary to start with low heat to distill the lower boiling compound first. This way, compounds with a difference of boiling point of at least 50 oC can be separated relatively cleanly. The conical vial should not be more than half filled in order to leave enough room for the liquid to boil.
Otherwise the solution will spill out or over when it starts to boil. A good seal between the joints minimizes the loss of target compound during the distillation. It also prevents dripping of a compound onto the hotplate, and a possible fire accident. An appropriate temperature setting has to be used. Often times, a water or oil bath is used for better temperature control. If a heating mantle is used as heat source, it has to be plugged into a variable power control.
Skip to main content. It is important to connect the cooling water circuit correctly. For some reason, most images found on the internet, including the one in the other answer, suggest a suboptimal cooling. The most optimal cooling efficiency is given in a countercurrent setup.
To quote Wikipedia :. The maximum amount of heat or mass transfer that can be obtained is higher with countercurrent than co-current parallel exchange because countercurrent maintains a slowly declining difference or gradient usually temperature or concentration difference.
In cocurrent exchange the initial gradient is higher but falls off quickly, leading to wasted potential. Thus, in the image above, the water supply should be connected to the top connector while the bottom one should be used as water outlet. This allows the strongest cooling efficiency to be at the top of the condensor, which is important, because if vapour manages to get that high up it needs a quick and efficient cooling.
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Learn more. What is "heating under reflux"?
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