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  • N&PD Moderators: Skorpio

Ghetto TLC: Solvents?

Alright then, thanks a lot. I also wonder what the biggest changing physical property is when alkylating indolols, but I'm sure I figure that out by the time I actually get working on that.
 
O-alkylation would be the idea, or esterification to be more precise.
Skipping the well known O-acetyls
 
Generally O-alkylation of phenols decreases logP by decreasing ionisability. (decreasing polarity in most cases as well - adding a nonpolar group brings the negative charge on the O slightly more towards the "centre" of the molecule) The pKa of the phenolic OH is lower than that of a "normal" alcohol, & definitely much lower than the alpha hydrogens on an ether/ester.

E.g. tocoperol vs tocopheryl acetate. The acetate is considered significantly less polar than the free phenol.
 
So, just using the basics of partitioning, varying TLC solvent proportions of something like a Pet Et + EtOAc mixture should work until a nice separation is seen? Pet Et can be substituted by naphtha and EtOAc either made by Fisscher (idk if the solvent is practical or needed at all) or substituted I guess. Not sure what would be nice.
Actually ordering non-ghetto solvents is not a problem but I wouldn't like to do that unless I was pretty positive about the solvent being the right choice. Ideally solvent selection is from mix & matching and trial and error if no indications are found in literature (which is probably usually the case).
 
The easiest way to get EtOAc is probably fractionation of nail polish remover or "green" paint stripper. If you can get glacial acetic and ethanol, why can you not just get EtOAc? (Fischer esterification of vinegar and vodka will be a fuck around because of good old Le Chatelier - unless you have a crude steam distillation setup or even better a cleavinger/dean-stark)
I've also seen paint strippers with a good proportion methylene chloride by volume, that should be easy to fractionate off, and is a good general purpose polar aprotic.

And one can always make chloroform (bleach and acetone I guess) if you are so desperate.

Realistically the best off the shelf combo is probably petroleum ether/ligroin/hexanes/heptane (light petroleum, preferably straight chain) plus a drop of acetone, or a drop of isopropanol. The principle will be the same though, vary the proportion of nonpolar to polar (start with a very trifling amount of nonpolar, 0.1% or something, and work up). Most people aren't going to dick around with manufacturing or fractionating anything.

Chromatography is kind of a black art, the best thing is to just experiment until you can effect a seperation, and take good notes...

Of course the other caveat here is that TLC is non quantitative.

If you can't get acetone or IPA you probably shouldn't be running TLC plates.
 
Using naphtha or hexanes/heptanes instead of pe won't be a problem. I guess prepping EtOAc only to use it as tlc solvent isn't really worth the work. Unless you have the resources/time and like or even enjoy doing that, of course :) Perhaps acetone could be an okay substitution. Finding the right mixture is a bit of trial and error anyway, so you could try that before doing an esterification.

It's very nice to see you again Solipsis, hope you're doing well :)
 
Must be that the last time I did TLC it was using EtOAc, other than that there is no real reason so you are absolutely right mentioning the surrogates... just wasn't sure which non-polar one to get but never mind, I can experiment with it and it shouldn't matter thát much.

A little more concerned about the actual reaction, anhydrides are an absolute disaster to get hold of but I'm probably going for the thionyl chloride method. Hope that wasn't too much of a synth discussion. Anyway I'm in a bit of a cooling-down phase now, but already looking forward to embarking on these little projects.

Yeah thanks for the welcome back, doing quite alright - good to see you, too. I wish you all lots of TLC by the way.
 
I think if you can source thionyl chloride but not ethyl acetate you have some supply chain issues to go over. (and by the way acetyl chloride is not particularly nice)

Don't go out of your way to synthesise EtOAc unless you're a masochist, and even then, just buy a steam distillation head and some glassware and do it properly. If you can't get it, use another nonpolar.
 
Yes, definitely try playing around with naphtha/acetone or switch to methylene chloride / methanol / ethanol or another solvent system instead, if that's possible. I can only advise against working with acid chlorides - especially thionyl chloride - outside of an okay equipped lab. Introduction of SO2 and HCl gases (plus the needed gas absorption equipment) into a 'ghetto' TLC project is rather disproportionate.
 
Yes I do know that it's god awful fuming stuff. Still seems better to use it for the reaction in a protected setting and then quench it before walking around with it, or otherwise I'd have to synth my own anhydride without it which isn't all that pretty either - or easy (though I guess much less obnoxious). Hmm haven't decided.
So it has nothing to do with the TLC. And well it's all available but the thionyl chloride just happens to be more of a specialty I was lucky to source while EtOAc has to be backordered at a more official type of place. Like I said, I can get most solvents but I wouldn't go for the backorder unless I knew it was essential to pick and that it would be the correct one to work with.

Thanks for the help, I don't mean for any more offtopic stuff - unless you're ok with that of course.
 
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