Question

Phenol is soluble in NaOH (aq) and not NaHCO3 (aq) while benzoic acid is soluble in both solutions. Explain how a mixture of phenol, benzoic acid, p-nitroaniline and anthracene can be separated by extraction. PLEASE Dont forget to talk about anthracene!

Answer 1

a mixture comprised each of benzoic acid, p-nitroaniline, phenol and anthracene will be separated into the individual components by acid-base extractions. All components except phenol are soluble in dichloromethane (CH2Cl2) but only slightly soluble in cold water.

FIrst, dissolve all components in Dichloromethane and phenol seperates out leaaving benzoic acid and p-nitroaniline and anthracene

Your para-nitroaniline is not water soluble. Therefore when exposed to water, it will crash out. You can then collect it by centrifuge and deal with the phenol and benzoic acid which should still be in your solution. Adding bicarbonate will cause the phenol to precipitate, and that may be separated as well.

Summary

Add Dichloromethane

----> Collect phenol

Add water
?Collect solid p-nitroanaline
Add NaHCO3
?Collect solid phenol
Remaining solution contains only benzoic acid
Done.

If complete separation of components is required using Acid base extractions:

Procedure Obtain 1.5 g of a 1:1:1 mixture of benzoic acid, p-nitroaniline, and anthracene and dissolve it in 40 mL of dichloromethane in an Erlenmeyer flask. Pour this solution into a separatory funnel which has a teflon stopcock. (Use the addition funnel from your organic kit if necessary.) If small amounts of solid material do not dissolve, the solution should be gravity-filtered through a small cotton plug into the separatory funnel. Extract the organic solution with 25 mL of 2M sodium hydroxide solution. Separate the layers and extract the organic layer with a second 25 mL of 2M sodium hydroxide. Combine the basic extracts in an Erlenmeyer flask and label the flask "basic extract". Now similarly extract the organic layer twice with 25 mL portions of 6M hydrochloric acid. Combine the acidic extracts in a second Erlenmeyer flask and label the flask "acidic extract". Transfer the organic layer into a third Erlenmeyer flask and label the flask "neutral fraction". Add approximately 2-3 g of anhydrous sodium sulfate to this neutral fraction, swirl and let stand for at least 15 minutes with occasional swirling to hasten the drying. Cool the flasks containing the "acidic extract" and the "basic extract" in an ice-water bath. Neutralize the "acidic extract" by carefully adding 6M sodium hydroxide until the solution is distinctly basic to pH paper. Similarly, neutralize the "basic extract" by carefully adding concentrated (12M) hydrochloric acid until the solution is distinctly acidic to pH paper. Precipitates should form in each flask upon neutralization. The neutralizations will liberate considerable amounts of heat, so let the flasks stand in the ice-water bath until their contents are at, or below, room temperature. Collect each precipitate by vacuum filtration using a Buchner funnel and wash the filter cakes with a small amount of cold distilled water. Allow the collected solids to air-dry until the next laboratory period. Decant the "neutral fraction" from the sodium sulfate into a tared round-bottomed flask (the flask should be of sufficient size such that it will be no more than half-filled by the solution). Rinse the Erlenmeyer flask and the sodium sulfate with a small amount of dichloromethane, decanting it into the round-bottomed flask. Remove the solvent on a rotary evaporator. Reweigh the flask with its contents, determine the weight of the neutral material, and calculate a percent recovery. Transfer this neutral material to a labelled vial and store it until the next laboratory period. NEXT LAB After the base (p-nitroaniline) is dry, transfer it to labelled and tared vial. Reweigh the vial to determine the weight of the solid and calculate it’s percent recovery. After benzoic acid is dry, transfer it to a tared flask. Reweigh the flask to determine the weight of the solid and calculate it’s percent recovery. Recrystallize benzoic acid from a minimum amount of hot water. (Use the solubility data to calculate the approximate amount below, based on the grams you recovered.) Add an extra 2-5 mLs of hot water if there is still solid present after adding the minimum amount of solvent. If this does not dissolve the solid, you will need to perform a hot filtration (perform over a steam bath, use a small plug of cotton). Before cooling, heat on a hot plate to remove the extra solvent added prior to the hot filtration (if performed). Dry and weigh the crystals. Determine melting points for benzoic acid and p-nitroaniline and compare them to literature values. Separately, dissolve a small amount of each of the three compounds in chloroform and spot a silica gel TLC plate with these solutions. Develop the TLC plate using chloroform. Visualize the spots under both short and long wavelength UV light and record your observations.