Question

5 gram of 3-chlorobenzoic acid, 8 grams of 2-heptylamine and 6 grams of anthracene are dissolved in 25 mL of dichloromethane.

This mixture is placed in a separatory funnel and extracted three times with a 3 M HCl solution. Combined aqueous extracts are back extracted with 10 mL of dichloromethane. The combined organic layers are then extracted three times with a 3 M NaOH solution. Combined aqueous extracts are back extracted with 10 mL of dichloromethane. All of the organic layers are combined and allowed to evaporate in the hood till a crystalline mixture forms.

After waiting for crystals to dry for one week, the crystals are recrystallized and 4 grams of crystals are recovered, what is the % recovery of this crystal? what is the identity of the crystal?

Answer 1

1. We have mixture of 3-chlorobenzoicacid, 2-heptylamine and anthracene.

2. Step1.First we are treating this mixture with 3M HCl so only 2-heptylamine will form salt with HCl and will go in aqueous layer while remaining two compounds will be unreacted and will go in DCM layer as shown in step1.

3. Step2. Now organic layer which is having 3-chlorobenzoicacid and anthracene on treatment with 3M NaOH solution only 3-chlorobenzoicacid will form sodium salt and will go to aqueous layer while anthracene will remain in organic layer as shown step2.

4. Step3. So we have organic layer with anthracene which on evaporation we will get crystal of anthracene as shown in step3.

5. So we will get 66.66% of anthracene from last organic layer.