Question

How does acid-base extraction separate different types of compounds with different pka?Draw a flow chart illustratring this type of separation.Write chemical equatiions for each transformation (converting compounds from organic soluble to aqueous soluble and vice-versa) that could be used.

Answer 1

Q1.

acid / base will try to force ionization of compounds via pH manipulation

for instsnce

(molecular) HA <-> H+ + A- (ions) ; has a certain pK, for low pH, the species is found as molecular, HA, for higher pH values, expect A- ionic state. this way we can exploit pH/pKa via extraction

the same is true for bases:

(molecuar) B + H2O <-> BH+ + OH- (ionioc); pKb

Q2-.

typical example is:

phenol, benzoic acid and naphthalene

first, we add mild base, so

benzoic acid = goes into benzoate ion, this is solubl eonly in aqueous solution, separate

add HCl in order to recover benzoic acid from benzoate ion in this solution --> benzoic acid is seprated

then phenol --> add strong base, NAOH, so there is reaction, phenol ion is present, soluble only in aqueous phase

separate --> add mild acid, so we recover phenol alcohol, in aqueous phase

finally, the organic layer --> naphthalene only, since no reactino occurs (nonpolaR)

HC7H5O2 + CO3-2 = C7H5O2- + HCO3- (aqueous) --> separate

Phenol

C6H5OH + OH- = H2O + C6H5O- (aqueous) --> separate

naphthalene

C10H8 + No reaction with cO3-2 or OH- --> organic layer