Which should be used for alkaloid extractions, Tolulene or Xylene?

Question

The organic solvent is used on a baseified aqueous solution with alkaloids. Later the organic solvent is seperated and titerated with sulfuric acid to produce alkaloid salts. From here how should the salts be removed from the organic solvet? Would tolulene be better over Xylene or vice-versa? Thanks!

I am also worried about residue when the solvent evaporates. Should it evaporate at 100% or will there be residue?

Answer 1

I don't think any of these will make any difference, these 2 solvents have virtually the same polarity.

The first step of the method you are using will remove undesirable compounds which are soluble in water as the alkaloids are in basic conditions. Then the addition of acidic will protonate the alkaloids and the addition of organic solvent such as CH2Cl2 will remove other impurities.

See an example from literature and free on-line (http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532006000300013&lng=es&nrm=&tlng=en)

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Solvent extraction

Powdered plant material (10 g) was wetted with 15 mL of NH4OH (25%, m/m) and room temperature solvent extraction was performed with 300 mL of ethyl acetate for 72 h. The extract was filtered and the solvent was evaporated in a rotary evaporator under reduced pressure at 40 °C. The residue, dissolved in H2O and acidified with H2SO4 to pH 3-4, was extracted with petroleum ether and diethyl ether to remove lipophilic, acidic and neutral material. After basifying the aqueous solution to pH 9-10 with NH4OH (25%, m/m), it was extracted with chloroform, the extract washed with distilled water to neutral pH, dried with Na2SO4 and concentrated to dryness under reduced pressure to obtain crude alkaloids.

This part was taken from J. Braz. Chem. Soc. v.17 n.3 São Paulo mayo/un. 2006

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I don't think in my experience these solvents (xylene or toluene) are normally used extraction of alkaloids!