Author Topic: choice of base for basification?  (Read 902 times)

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elfspice

  • Guest
choice of base for basification?
« on: March 22, 2004, 10:23:00 AM »
I'm not quite sure how or why this happened, but for some reason the convention for base to use for acid/base extraction is to use NaOH... why? For ghetto chemists, there needs to be a simple way to get the pH right so that the extraction goes properly and you don't extract other things because you raised the pH too high (ie 13+)

sodium carbonate and calcium hydroxide both produce a pH of around 12, which is sufficient yet within two pH points of the pKa of most simple monoamine alkaloids, such as methamphetamine, dmt, psilocin, mdma etc etc.

sodium carbonate is simple enough to use but can be a problem if there is something that prompts the carbonates to form back into carbon dioxide (eg, from a reaction mixture perhaps?) but on the other hand if one took hydrated lime and used it for a base, you would have to first dissolve it in water and settle out any calcium carbonate that probably will be present in domestic 'hydrated lime' as well as the excess from overshooting the right quantity... it only dissolves to the extent of 0.18 g/100 mL but at that rate of dissolution the pH is raised to 12ish... that works out to 1.8g per L to change the pH to 12... 1/4 of a teaspoon.

anyway, could somebee more wise than me explain why one wouldn't want to use sodium carbonate or calcium hydroxide as a base for acid/base extraction? thanks :D

oh... just remembered - clear ammonia, of course only raises the pH to 12ish as well... What are the criteria for selecting an extraction solvent?

I was thinking that maybe a different base that forms an insoluble salt with some undesirable material in the extract might be helpful in reducing the garbage that comes across into the nonpolar solvent (eg, tannic acid(s), which precipitate in calcium (?) i can't recall if that's correct, i know that lead ions precipitate it too though)

fanofshulgin

  • Guest
This is real easy to answer.
« Reply #1 on: March 22, 2004, 04:09:00 PM »
This is real easy to answer.

Typically NaOH or KOH solutions are used, as they are very soluble in water and are strongly alkaline.  Small volumes can be added to basify and not cause huge volumes to which has to be extracted.  The same goes for the use of HCl to acidify.

However, depending on molecular stability....these are not always used.  For instance molecules containing acid sensitive protecting groups, or functional groups would probably be better acidified using aqueous acetic acid...or even aqueous KHSO4.  Base sensitive molecules would be better basified using bases such as potassium hydrogen carbonate etc.

These weaker bases, are much less soluble in water, and using a saturated solution of sodium bicarbonate for instance would result in very large volumes (and thus problems in handling) compared to a stronger and more soluble base.

Another benefit of using HCl / NaOH when working with acid/base extractions is that the end product is simple table salt, which is safe, inert and can be flushed safely down the sink.

Fan of Shulgin


Newton

  • Guest
the garbage that comes across into the ...
« Reply #2 on: March 22, 2004, 08:44:00 PM »
the garbage that comes across into the nonpolar solvent (eg, tannic acid(s)

I was just wondering in what kind of extractions would you expect tannic acid as a contaminant? Extraction of plant matter or post reaction solutions?

SWIN suspects tannic acid to be the brown gunk that comes over with steam distillation of ephedra, it is also said to be contained many other plant species.

BongTech101

  • Guest
TSP
« Reply #3 on: March 23, 2004, 04:34:00 AM »
Both on here and on a few other forums there has been some discussion of using TSP - tri-sodium phosphate in lieu of NaOH (lye)......
It is weaker and as has been pointed out requires more volume, but it can be used and there is less risk of over-basifying.