What pH is required to obtain 99% of amine? Show all of your work. Toluidine is

Question

What pH is required to obtain 99% of amine? Show all of your work.

Toluidine is a weak organic base. We will use this property to protonate it with 3M HCl and form a hydrochloride salt to move it from the organic to the aqueous phase then recover it by neutralizing the aqueous layer. The amine is soluble in the organic phase, the salt is soluble in the aqueous phase. At acidic pH, it will exist in the hydrochloride salt form, but once the pH is neutral the equilibrium will be shifted to favor the amine. Benzoic acid has a pKa of 4.2. At high pH the base will deprotonate benzoic acid forming a sodium benzoate salt. The sodium benzoate salt is soluble in the water.

Explanation / Answer

According to the question,

We know that,

Given,

pKa of toluidine = 4.2

So,

Use the Hendersen-Hasselbalck equation,

pH = pKa + log(base/acid)

when,

(base/acid) = 99/1 = 99

So,

pH = 4.2 + log(99)

= 6.19

So,

We would require pH=6.19 to isolated 99% amine

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