demax - 2-8-2007 at 18:55
Hey all,
i need some advice with regards to a dean stark trap. demax is wanting to hook up a dean stark trap to a two litre flask . He has had a look at some
of these traps online and it seems they can be rigged up differently.
1-the trap is connected to the smaller side neck of a two neck flask with a thermometer being placed in a thermoter socket which is then connected to
the main neck of the flask.
2-the trap is connected to the main neck of the flask and the thermometer enters the flask via the second smaller neck (a reverse of the above setup)
Is one set up preferable over the other?
Do these traps come in different sizes or is it a case that they only come in one size and that they are transferable to all flask sizes?
Are there any other things one should consider in purchasing one of these things such as condensor length (is that important?) etc
best wishes,
demax
bio2 - 2-8-2007 at 19:06
It doesn't matter as long as it fits with the other apparatus. A good reflux type condensor like an Allihn is best to use.
Make sure you get the type (Barret) with the valve for draining the water when
doing larger water removals.
There is not much selection, the ones with an extra overflow tube helps efficiency and
allows faster take off.
chemrox - 3-8-2007 at 13:21
The extra overflow tubes are nice especially for working with volatile oils. I like the kind that has a stopcock for draining purposes. I ended up
with more of these than I need so if you want to buy one ...let me know
PS-I added this postscript- I take "Dean-Stark" as a generic term for the apparatus that removes water as it's generated during reflux and catches the
water in a tube with an overflow back to the reaction flask. The various configurations have their own names after the men that designed them.
[Edited on 3-8-2007 by chemrox]
evil_lurker - 3-8-2007 at 15:19
The actual name is called a "moisture test reciever", the dean stark and barret are styles of both.
And I'd like to add that you don't need a thermometer in the flask as they are designed to be operated at gentle reflux... that in itself will self
regulate the temperature based on the solvent.
chemrox - 3-8-2007 at 19:21
I think the ones I have are barret traps. I've got'em with and without stopcocks. e_l, can you explain the difference? I'd like to know .. don't
know whether I've seen a dean-stark....
demax - 6-8-2007 at 03:19
ok thanks guys.
Couple of Q's tho;
1-is the condensor length relevant to this set up. Is there a minimum /maximum length?
2-does the top of the condensor have to be closed/sealed from the surrounding air?
thanks,
demax
bio2 - 6-8-2007 at 13:27
Condensor length is determined by boiling point of the reflux
and temperature of the cooling water.
A six bulb Allihn is suitable for most purposes and ice cold
water used for low boiling solvents like DCM, ether or acetone.
Do no seal the condensor and use a drying tube if needed
for hygroscopic substances.
demax - 12-8-2007 at 21:12
Dont think i can get the allihn condensor that is mentioned.
Would a liebig condensor work effectively and if so is there a recommended length? I think i can only get a 200mm one.
'Condensor length is determined by boiling point of the reflux
and temperature of the cooling water' could some one please elaborate on this reply by bio2.
thanks,
demax
[Edited on by demax]
[Edited on by demax]
bio2 - 13-8-2007 at 11:41
An Allihn or a Graham is no more difficult to purchase than
a Liebig. A Freidrichs is a good choice as well/
A 200mm Leibig is too short unless maybe using ice water try a 300 or 400mm. The surface area of the inner tube of the Liebig is not very much
compared to the other types.
The reflux should not travel more than about 1/3 of the way up the condensor and this is one way to determine if you have adequate length.
Condensor length is determined by the difference in temperature between the cooling water and vapor temp.
At least 50 degrees delta T is preferable.
A 300mm Liebig is suitable for most uses except for the solvents boiling below about 60 degrees as already mentioned. The reflux rate will be lower
however compared to the more efficient designs.
A Friedrichs makes a good dual purpose condensor as it has no holdup like an Allihn has (when used diagonally).
A Friedrichs is always used vertically as is an Allihn.