Chem 335 - CA2

liquid-liquid extraction

solute(s) partitioning between two immiscible liquids in contact.

Usually between an organic solvent and water.

what is immiscible in water?

organic solvents

extraction

Selective partitioning (separation) of components between two immiscible liquids in
contact.

partition coefficient (Kd)

defines the ability of solvent -S2 to remove (extract) solute A from solvent-S1.

Kd equation

(grams of A extracted in S2 / VS2) / (grams of B extracted in S1 / VS1)

if Kd is greater than 1

solute A is more soluble in S2 than S1

a good organic extracting solvent

• Be immiscible in water.
• Dissolve a wide range of organic compounds.
• Offer higher solubility for the compound of interest than the original solvent.
• Be chemically unreactive toward the compound of interest.
• Have a low boiling point so it can be easily evaporated after extraction.

acid-base extraction

a component in a mixture, dissolved in an organic solvent (S1), is chemically converted to a salt to cause it to partition to an aqueous solvent (S2)

How would you convert the salts back to their original acid or base?

by adding a strong acid or base (if starting is a base, add acid)

molecular polarity

measured by the molecular dipole moment

thin layer chromatography

A separation technique where compounds are distributed between the surface of an adsorbent (silica) and a mobile phase (solvent or solvents).
• Separation of components depends on their polarity.

separation based on

adsorption principle

stationary phase

solid adsorbent coated on a solid support [TLC plate]

mobile phase

a liquid solvent or mixture of solvents

moves though the adsorbent

eluent

developing solvent

retention factor (RF)

ratio of the distance travelled by the compound from the index mark to the distance traveled by the solvent from the index mark

Rf = distance solute moved / distance solvent moved

factors that affect RF value

polarity of the compound

polarity of the solvent

polarity of adsorbent

RF values can be used for

identification and characterization of compounds

what travels the furthest?

less polar molecules

saturated hydrocarbons

what travels the least?

more polar compounds

carboxylic acids

RF should be

~20% from the point of origin

what are the popular adsorbents?

alumina (Al2O3) and silica (SiO2)

non-destructive visualization methods

TLC that doesn’t involve a chemical reactions with the components spotted on the plate

ex: UV light

destructive visualization methods

involve a chemical reaction between the aid reagent and components spotted on the plate

ex: ink staining

TLC is used for

qualitative analysis of individual compounds or mixtures

checking purity

monitor progress of reaction

smaller scale - separate components of a mixture

distillation

a process of separating component of a liquid mixture by selective boiling and condensation process

the liquid mixture (distal land) is vaporized in one vessel and the vapors are condensed and collected in another (distillate)