why add vinegar 3 times instead of all at once?

[spinCycle]

SWIM has had good luck with the D-Limonene tek, but he is wondering something. After mixing with vinegar and separating it off the tek says to repeat the addition and separation of the vinegar 2 more times.

What is the advantage of adding the vinegar 3 different times rather than just using 3 times as much vinegar all at once? This seems to be pretty common with other teks too, so I am assuming there is some actual chemical advantage to using 3 mix/separations? Or can I be lazy and just add it all at once?

 

[d*l*b]

A thread linked to in the FAQ covers this rather well—

Several Small Extractions are Better than One Big One

 

[spinCycle]

Thanks.

 

[benzyme]

that FAQ is misleading, simply for the fact that it goes by a gravimetric basis
rather than protonation. realize that DMT has an amine that is fully protonated at around pH 5.2. assuming all cells are lysed, there's really no need to acidify multiple times, if the solution is at that pH, unless you like having a very salty solution.
multiple pulls is more relevant to the organic solvent used, not the aqueous phase.

also, that 1 g mhrb to 1 g NaOH implies a stoichiometric ratio. now we all know that mhrb isn't 100% DMT. my suggestion is prepare your 0.4 M NaOH before adding it. it is highly advisable to have a pH meter

 

[endlessness]

Yeah but even if there's no cells in the story and you're talking about salting a non-polar solvent where in theory all the alkaloids are 'exposed', I know from experience there's ALWAYS alkaloids left behind in the non-polar and that multiple saltings with acidified water are necessary.

 

[benzyme]

if you somehow know the concentration of the dmt in the organic phase, then you could
salt with an equimolar equivalent of acid.

but since ppl don't know what the conc. is, this is why multiple saltings are done.

it's no longer an issue of solubility, but stoichiometry... anions and cations.

 

[Yerba]

I think there's more to it. The tek is written for people 'shaking milk jugs', not those with a proper magnetic stirring apparatus. Otherwise even without being precise with the stoichiometry, people could just add an excess of acid and accomplish the same result in one operation, right?

 

[benzyme]

same result? no.
excess salts

again, this isn't a problem, per se, particularly if the next step is to basify.
and it has little to do with the container used, or stirring apparatus. it's solely a function of amine protonation. extra acid and/or base generally leads to less pure product,
but that's why people re-x