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What are the advantages and disadvantages of the various types of condensers commonly found in

the laboratory? Obviously more intricate pieces of glassware are more costly but assuming they are

all available why would one use a Dimroth condenser vs. a Friedrichs when refluxing something?

I've heard that Graham condensers are to be avoided when refluxing due to the possibility of

clogging, and yet it is still very common - when is it appropriate to use one?

Illustration made with ChemDraw. Feel free to reference other designs but please attach a

schematic for clarity.

Edit: This question was motivated by an organic preparation which involved the bromination of an

alkene in boiling water. Bromine has a boiling point of 58.8 °C and on top of that the reaction was

exothermic. It was difficult to avoid the loss of Br2 gas with your typical Allihn condenser, but the

increased cooling capacity provided by a Friedrichs returned Br2 back to the flask as it was

produced.

Also, while the Friedrichs forces vapors up a spiral path, the path itself is wide, and in my

condenser at least, there was a bit of leeway for liquid to drop down the sides, helping to prevent

blockages. I didn't try a Graham condenser but I imagine a much slower rate of addition would be

supported by this condenser.

experimental-chemistry   glassware

share improve this question edited Jun 13 '12 at 14:18 asked Jun 6 '12 at 19:15

Radu

31318

Also, I should mention that I've looked at the wiki page on condensers:en.wikipedia.org/wiki/Condenser_(laboratory)but I found it lacking in practical detail and there is little comparison between the different types. – Radu19:44

2  Rule of cool. More loops = more science. – Richard Terrett Jun 7 '12 at 11:00

1 Answeractive oldest votes

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@Mart 's comment impelled me to return to this question and correct my answer. I've

deleted incorrect material and expanded the discussion to, hopefully, provide correct

information. There is a good discussion (better than the reference previously cited) of the

issue here.

Reflux is the process of boiling reactants while continually cooling the vapor returning it

back to the flask as a liquid. It is used to heat a mixture for extended periods and at certain

temperatures...A condenser is attached to the boiling flask, and cooling water is circulated

to condense escaping vapors.

If you are refluxing a mixture, as you might in organic synthesis to increase the speed of the

reaction by doing it at a higher temperature (i.e., the boiling point of the solvent), then any

of the condensers that worked well enough to avoid the loss of solvent and avoid "flooding"

would work equally well. When you're refluxing, you want the "reflux ring", the place

where the vapor is visibly condensing into a liquid, to be no more than 1/3 of the way up

the reflux column.

You have two different basic types of condensers shown, Graham-type condensers (the first

3) and coil condensers (the last two). In the coil condensers (the left condenser in the

picture below), the water flows through the coil and the vapor moves up in the larger,

outside area of the condenser, condenses onto the cooled coils, then drips back into the pot.

In a Graham-type condenser (the right condenser in the picture below), the water flows

around a tube (whether straight or coiled) that contains the vapor/condensed liquid.(picture

source) The Graham-type condensers clog (or flood) more easily since they have a more

restricted path for the liquid to return to the pot.

Graham-type condensers: The Liebig condenser is simple, but has low cooling capacity

and can be fairly easily clogged as the condensed liquid flows back into the flask and blocks

the vapor that is trying to escape. The Allihn improves on this design by having a wider

bore at the bottom and condensing the liquid on the "bubbles" where it can run down the

sides and avoid blocking the vapor. (I've used this to good effect in refluxing many

reactions.) The Graham condenser is the same basic design as the other two, but the

condensation tube is coiled which provides more surface area for cooling...but also tends to

send the condensed liquid right into the path of the vapor trying to move up. It is

particularly prone to flooding.

Coil condensers, such as the Dimroth and Freidrichs, have high capacity for cooling with

fewer problems from flooding since the vapor condenses on the coils and drips back from

the little prominence at the bottom of the coils into the center of the pot. The vapor has an

easy time getting past the drops falling into the pot. If you can afford it, this seems like a

good choice for most applications. The Freidrichs condensers, which incorporate a cold-

finger with the spiral, are higher capacity, quite bulky and heavy. I have seen them used

with rotovaps where you are taking a lot of solvent off quickly, but not with an ordinary

reflux apparatus. This would be over-kill for a simple reflux reaction situation.

Sorry for the incorrect information (for those of you who looked at this before) and hope

this is helpful.

share improve this answer edited Jun 10 '12 at 22:39 answered

Janice DelMar

2,217818

I'm not sure the "number of (theoretical) plates" concept applies to the condensor. In the condensor condensation energy is carried away by the coolant, a re-vaporation should hardly take place. The plates concept explains the rectification column. Important parameters for condensors are exchange area (for heat transfer), Volume (for retention time) and sucspetibility to clogging. However, I'm not a lab rat, my experience with that kind of equipment is very limited! – mart Jun 8 '12 at 8:33

Good points...I messed this one up and have gone back and (hopefully) corrected my answer. Thanks for the heads-up. Next time I'll listen to that little voice that says "somethings not right in this". –