DraconicAcid
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Stupid question - drying organics in an oven.
When I were a wee lad in college, we would put out organic products in the oven to dry before taking a melting point.
Now when I am supervising a lab, and the students are drying their stuff before taking melting points. And half the stuff sublimes, despite the oven
being well below the mp. I'm really tired of having to clean crystals of salicylic acid and cinnamic acid off of the oven door. What temperature
should I be drying this stuff at? Will a much lower temp still dry the compounds? I'd do a bunch of trial runs, but I really hate cleaning the oven.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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unionised
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Another very important point to remember is that vapour from flammable solvents may form an explosive mixture with air inside the oven.
That kind-of stops you needing to clean it but it does turn the glass door that's typical of lab ovens into shrapnel.
Most drying ovens are really only designed to remove water.
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PHILOU Zrealone
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Normal reduced pressure silica gel beads or other dehydratants (white CuSO4, CaO, CaCl2, conc H2SO4, Ba(ClO4)2, ...) Inside a dessicator should work
like a charm.
[Edited on 24-3-2016 by PHILOU Zrealone]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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DraconicAcid
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Quote: Originally posted by unionised  | Another very important point to remember is that vapour from flammable solvents may form an explosive mixture with air inside the oven.
That kind-of stops you needing to clean it but it does turn the glass door that's typical of lab ovens into shrapnel.
Most drying ovens are really only designed to remove water.
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They're recrystallized from water or alcohol-water mixtures, so it is the water we're trying to get rid of.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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aga
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Erm, what do you imagine those students are there for ?
Teach them how to do cleaning and set a Practical whenever the oven needs cleaning.
Fun it up and compose a Chemical Test so the oven can be checked after cleaning.
If the winning team get a 'Well Done' or a sticker, they'll compete with each other to clean up better.
Just to really fire them up, the Last winning team gets to do the tests - it will teach them cleaning, also how to test for 'cleanliness'.
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WGTR
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One thing that I've noted, is that it helps to make sure that air can circulate freely in the oven. Also, make sure that the temperature probe isn't
being closely shadowed by the sample. Someone I knew set up a sample on some paper towels in the oven to gently dry, almost completely blocking off
the shelf in the process. The heating elements ran up darn near 100%, catching the paper towels on fire.
Drying temperature aside, it may help to shield the sample from the heating elements with some aluminum foil. That would cut down on direct heating
from radiation, which may cause the sample to get hotter than intended. That's just a random idea, though; I'm not sure if it would give an
improvement in your situation.
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DJF90
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I assume you're talking about a regular glassware-drying oven, typically around 110 *C? If thats the case, I'm not surprised you're having trouble.
Use the right tool for the job - either a (vacuum) dessicator and appropriate dessicant as PZ has suggested, or use a vac oven set at 40*C. Most of
the time its possible to obtain dry material off of the filter so long as it's had long enough at the pump. Perhaps you could use sublimation to
prepare an "analytical sample" for melting point determination (quite an old school approach).
Bear in mind that when doing real research no-one dries their organic products in the oven. Doing so usually causes more trouble than its worth
(potential for decomposition with novel/poorly investigated compounds)
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Magpie
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If I'm not in a hurry - which is usually the case - I often air dry at room temperature, especially if I suspect that heating would cause problems. I
realize this may not be possible in a school lab due to time limitations.
I think the use of the desiccator is a good idea if hygroscopy is suspected.
[Edited on 25-3-2016 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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brubei
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| Quote: Originally posted by aga | Erm, what do you imagine those students are there for ?
Teach them how to do cleaning and set a Practical whenever the oven needs cleaning. |
Good point, it is
important to teach all the side about chemistry.
Cleaning is the most important thing, I'm working in a university laboratory and many students (and graduating student) seems to not care about
cleaning all their mess.
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mayko
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also make sure that the compounds you're drying are heat-stable
al-khemie is not a terrorist organization
"Chemicals, chemicals... I need chemicals!" - George Hayduke
"Wubbalubba dub-dub!" - Rick Sanchez
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Sorbead
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Silica gel beads would be more effective, safe and much better way to dry the organic products.
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