SM2
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Simplification of multi-step purifications
Often, what the scientist produced, and publishes, is just his(her) way of running an experiment. Educated guesses are made, and a little
experimentation is done to perhaps, optimism the procedure. But there are always other ways.
For the hobbyist chemist without access to all the chemicals used typically by chemists for isolating/purifying a product, a simplification is needed.
Perhaps more time consuming, maybe at peril of lower yields, but maybe also more elegant, and not dependent on multi step chemical purification. To
further complicate things, I am referring to nothing in particular, just a general philosophy which represents one factor to make the hobbyists' job a
little easier. Often times, the purification and isolation steps are several times longer than the actual synthesis. So, maybe we start a sticky
where we report on both general, and specific short cuts to the purification isolation process. Alternate routes, and compare them to the published
routes. Both specific, and especially, general purifications/isolations.
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smaerd
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Mood: hmm...
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Been looking into this as well. Most of my interests are in organic synthesis. As a hobbyist I don't have the cash or were-with-all to use a liter of
an 'exotic'(to a hobbyist) solvent to pull a gram of impure compound. Sure it can usually be redistilled and reused, but it's not efficient. So I've
been reading more about separation science and trying to think outside of the box. Limiting waste and maximizing product are critical for the home
scientist as well as most any industrial process.
It all starts with the reaction, the reactants, and the catalysts. A well designed reaction can simplify work-up exponentially. Often though these
kinds of reactions need expensive and exotic reagents.
Column chromatography is great but to purify a gram of compound, a rather wide diameter column is required. Let alone if one wanted 10 grams, that's
means running twenty or so columns. A simple flash-set up can overcome a lot of pain-staking leg-work there. Separations can very clearly limit the
amateur experimenter. Granted micro-scale is more up our alley anyways. Though with limited analytical techniques available to a hobbyist, having a
little more of a compound is always appreciated.
Some under-taught techniques and concepts for the undergraduate chem major, but useful thing's I've looked into are:
Solvent partition theory(liquid liquid extraction theory) - just because a paper used preparative column chromatography to separate 10 grams of
alkenes and diol's doesn't mean we have to. Using a very non-polar solvent system with a polar solvent to aid an aq. phase will aid in removing the
majority of alkenes lessening the column work.
Solid phase extraction(with improvised solid-phases) - This is tricky because most solid-phase extractions are done with commercially made columns. In
some cases activated carbon, silica, montmorillonite(bentonite), can really help things along.
Solid-phase reactions - Allows for easier work-up in a lot of cases.
Green-chemistry - sure a lot of the journals are ionic solvent based 'bally-hoo' but there are a few diamonds in the rough. Some key concepts being
atom-efficiency, less waste, regenerable catalysts, and 'cleaner' waste. Usually this translates to cheaper and easier.
It seems like work-up is something learned only in the field and through a lot of head-aches and misery. In my organic class's the majority of the
labs were about learning the techniques, not so much sewing them altogether. If anyone has any good references for work-up techniques I'd be very
interested.
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SM2
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Great post! Keep them coming! One of my very early columns used decapped, cleaned out fluorescent tubes (T12). To these I added a toilet paper
slurry which I made with virgin TP, water, and an Blender. You really have to homogenize the mixture. Of course, it is very polar. But this is a
great way of doing separations, and the only consumable is TP! The consistency of the TP water matrix, for most separations, should be almost
gelatinous like, without the rebound.
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Nicodem
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Thread Moved
12-10-2012 at 23:59 |
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