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Can you reflux without any problems/dangers with a tilted condenser (e.g. because you don't have enough space in your fumehood)? I would say there isn't a problem, because both the surface area of the refluxed liquid and the length of the condenser (and thus the length of the trajectory of the water flowing through the condenser) remain unchanged. Is this thought correct?

This is my current setup

My setup

Also you should use countercurrent exchange right?

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3 Answers 3

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As long as everything is clamped and balanced - so that there isn't excessive weight on the joint connecting the flask to the condenser - the system should be OK. After all, many rotary evaporators have the flask plus condenser tilted at an angle.

enter image description here

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  • $\begingroup$ Yes, I just realized that. Would it work for a Allihn condenser too? Thanks Ron. $\endgroup$
    – Jori
    Commented Jun 22, 2014 at 20:59
  • $\begingroup$ I recommend to estimate the thickness of the glass in the condenser here. $\endgroup$
    – permeakra
    Commented Jun 22, 2014 at 21:04
  • $\begingroup$ @Jori I would think so, as long as it is not "packed" with anything. And since you're not rotating your flask like a rotary evaporator does, you can clamp it and the condenser to alleviate stress on the connecting joint. $\endgroup$
    – ron
    Commented Jun 22, 2014 at 21:18
  • $\begingroup$ @ron "packed"? Also note that I clamped the condenser and the flask, but I guess you mean a broader clamp (like the one used to hold the condenser to the stand). $\endgroup$
    – Jori
    Commented Jun 22, 2014 at 21:43
  • $\begingroup$ @Jori 1) Sometimes columns are "packed" with glass helices or other high surface area materials to increase the fractionation efficiency of the column. You wouldn't want to do that with a tilted column as it might cause flooding of the column (to much liquid in the column unable to drain back to the flask quick enough). 2) Looks OK, now I see it, couldn't see the second clamp before. $\endgroup$
    – ron
    Commented Jun 22, 2014 at 22:51
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I can think about three problems in the case

1) Glass is fragile, so if any significant load falls onto flask's or condenser's necks, it is a risk. Thus, the condenser should be light and have separate support, and the flask should have a second support for bottom or have a very small load (say, if it would be more than 100 g, I would hesitate.)

2) even round-bottom flasks does not necessarily have a perfectly spherical bottom, so fast stirring is absolutely out of question, and even gentle stirring for medium loads is not good.

3) If highly tilted, Allihn condenser may trap significant amount of liquid in its spheres. Dimroth and Inland Revenue condenser may trap some (little) amount of solvent on their coils too. Dimroth condenser MAY be used for refluxing even if should not ideally, and for solvents with high BP (say, toluene) should be OK. In fact, in case if violent reaction may occur it is PREFERABLE to use condenser with low internals resistance to straight float so the stream of boiling reaction mixture runned through the condenser in did not lift and smash it or teared the flask apart.

Actually, if no gas exhaust is expected, solvent, reactants and products do not have low bp and high toxicity I would prefer to reflux outside of the fume hood rather then tilted. It is OK. Even if some gas exhaust is expected, I would shrug of nonviolent non-toxic gas exhaust.

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  • $\begingroup$ 1) You mean that the flask would break from the condenser at the joint? I could hardly imagine that, if you keep reactants weight under 1kg, especially if the flask also rests on the bottom of a water bath. Adding an extra support for the condenser could be an option, although again, does it really gain that much weight from the condensing liquid? 2) ??? 3) Can't this be compensated with a little bit of extra reactants in situ? Gas exhaust is toxic (cyclohexylamine and perhaps nitrogen dioxide) $\endgroup$
    – Jori
    Commented Jun 22, 2014 at 20:32
  • $\begingroup$ 1) Well, the tilted flask/condenser is a lever. It has MUCH larger load near joint than it looks imaginable and given glass fragility... I wouldn't take risks. 2) Anchor for a magnetic stirrer, especially for heavy loads and fast stir rates should rotate at the axis of symmetry. Otherwise it may break the flask. 3) It probably can, but I would prefer Liebig condenser in this setup. And post experiment details if possible. $\endgroup$
    – permeakra
    Commented Jun 22, 2014 at 21:01
  • $\begingroup$ Yes I will. If everything works out fine and I'm not killed in an explosion or anything, you'll be the first to hear! Also note that I clamped the condenser and the flask, but I guess you mean a broader clamp (like the one used to hold the condenser to the stand). "Anchor for a magnetic stirrer, especially for heavy loads and fast stir rates should rotate at the axis of symmetry. Otherwise it may break the flask" you mean because of the extra side ward pressure on the joint due to centripetal force? (should also be balanced out by an extra clamp I guess) $\endgroup$
    – Jori
    Commented Jun 22, 2014 at 21:39
  • $\begingroup$ I mean, the condenser must have support in the middle. Otherwise, load near the joint may become too much. In fact, it is common to fic large condenser at the middle even in vertical setups. ||| Nope, if uncentered, it may either cause vibration at best case or break from its position and start jumping in the flask. At higher RPMs the risk is much higher, at lower RPMs are almost negligible. ] $\endgroup$
    – permeakra
    Commented Jun 22, 2014 at 22:22
  • $\begingroup$ Add that the fluid runs back into the vessel at the wall, where it starts to boil before reaching the reaction mixture,. $\endgroup$
    – Karl
    Commented Nov 29, 2015 at 22:18
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Support notwithstanding, those water hoses indicate the device is a Graham condenser, in which case it should always be vertical. Perhaps a Dimroth condenser would be better employed here.

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