Question

1. If one wanted to reduce the solubility of benzoic acid in water to get it better partitioned into diethyl ether, would it be better to add potassium carbonate or sodium chloride? WHY?

Please explain in terms of anions!

2. Even if a cospotted TLC analysis of an unknown with an authentic standard is performed, one still does not know with complete certainity that the unknown and the standard are identical. Why is this true? What alternatives would one consider to prove the structural identity of the unknown without any ambiguity ?

Answer 1

a) If we wish to reduce solbulity of benzoic acid in water then we should not add K2CO3 to it as it will form salt of benzoic acid which is readily soluble in water.

So we will add NaCl to benzoic acid. NaCl is soluble in water and will push benzoic acid more towards non aqeous phase.

b) This could be due to high structural similarity hence same solublity in the moving phase.

In order to anaylze the structural identity of unkown

Make three spots

(i) unknown (ii) Standard (iii) co spot

Even now if the three are on same Rf value then unknown and standard are same.