Separation of a carboxylic acid Essay Example

because it allows JS to convert an insoluble acid into a soluble salt. The salt is its conjugate base, an anion that is soluble in water. The concept is always the same. To make certain that a covalent organic compound is water soluble, convert the organic compound into an ionic salt.

Ionic compounds are soluble in water. Phenols are weak acids.

Strong bases convert phenols into water soluble salts. The reaction of phenol with sodium hydroxide to make phenolate ion is shown below. Summary: To convert water insoluble organic acids (weak acids) into water soluble salts, add a strong base. Reaction of Carboxylate and Phenolate Ions with Strong Acids Acid”base chemistry is all about the transfer of a proton (H+). Above, a strong base proton acceptor) removed a proton. To replace the proton, we need a proton donor Strong acid).

The following equations show how benzoate and phenolate ions are converted into benzoic acid and phenol, respectively, by the strong acid HCl(aq). Reaction of Carboxylic Acids with the Weak Base, Sodium Bicarbonate Carboxylic acids react with sodium bicarbonate much as they do with sodium hydroxide. The difference is that carbon dioxide and water are byproducts of the reaction with bicarbonate. Carbonic acid decomposes as it forms into carbon dioxide and water. The carbon dioxide is visible as bubbles. Thus, sodium bicarbonate is used to determine the presence of a carboxylic acid by the evolution of bubbles.

The reaction of benzoic acid with sodium bicarbonate is shown below. Sodium ion is a spectator and is not shown. Like hydroxide ion, bicarbonate ion converts benzoic acid into benzoate, its conjugate ase. Do phenols react with bicarbonate the

same way as benzoic acid reacts? No, phenols are too weak. They do not react with bicarbonate, and bubbles are not liberated.

How can you distinguish between benzoic acid and phenol with a simple Neither sodium hydroxide nor sodium bicarbonate reacts with organic neutral compounds such as biphenyl and naphthalene. Both compounds contain two benzene rings.

In biphenyl, two phenyl groups are Joined by a sigma bond. In naphthalene, the two rings share a double bond (sigma + p'). Neither compound contains a hydrogen atom that can be easily removed as a proton. Ne are now able to devise a scheme for the separation of a mixture that contains: a Nater insoluble carboxylic acid, a water insoluble neutral compound, and a water insoluble phenol.

We will use a separatory funnel containing two immiscible liquids, ether and water, to make the separations. The two liquids will form two layers. The ether is the top layer, and water is the bottom layer.

Ether is insoluble in water except for trace amounts, and ether is also a good solvent for most water insoluble organic compounds. The solubilities of carboxylic acids, phenols, and neutral organic ompounds in water, ether, sodium hydroxide and sodium bicarbonate are given in the following table.

Solubilities of Benzoic Acid, Phenol, and Naphthalene in Water, Ether, NaOH(aq) and NaHC03(aq) Compound Nater Ether NaOH (aq) NaHC03 (aq) Benzoic Acid Carboxylic acid) Insoluble Soluble phenol family) Naphthalene *rene family) Given a mixture of benzoic acid and naphthalene or biphenyl, we can devise a scheme for the separation of the binary mixture.

A binary mixture contains two components. From the table, carboxylic acids are soluble in NaOH (aq)

and arenes are not. This difference allows us to separate an acid from an arene. We start with the acid”arene mixture and dissolve it in ether (both compounds are soluble in ether).

We place the ether solution in a separatory funnel and add some 5% NaOH :aq). Because the density of ether is about 0. 8 g/mL and it is immiscible with water, it floats. The 5% NaOH (aq) solution is 95% water, so the bottom layer is the water solution of NaOH.

When the funnel is shaken, as the instructor will demonstrate, the sodium hydroxide reacts with the carboxylic acid to make a salt, which is water soluble.

The salt goes into the water layer (bottom), whereas the arene remains in the ether layer (top). We drain the bottom layer into a new container, leaving the top layer in the separatory funnel. In the water layer, we have the acid salt. In the ether layer, we have the arene. To convert the acid salt into an acid, we add the strong acid HCI (aq).

Benzoic acid precipitates from solution.

To retrieve the neutral compound, Ne evaporate the ether under a hood. Now we have two solids in separate containers. That is, we have separated the binary mixture into its two components. "hat reagent would you add to a small sample of each solid in order to tell them apart? SAFETY WARNING: Ether is very flammable (catches fire easily).

Therefore, NEVER use ether around an open flame, such as a Bunsen burner, and NEVER allow ether to Procedure 1 . Get two weigh boats. On one, weigh about 0. 5 g of an organic acid

(benzoic acid). On the other weigh boat, weigh 0.

g of an organic neutral compound (naphthalene). 3enzoic acid contains an acid functional group but is insoluble in water because it contains more than five carbon atoms. Naphthalene is insoluble in water because it is a hydrocarbon and contains no oxygen or nitrogen atoms. 2.

Transfer the solids from both the weigh boats into one separatory funnel. 3. Place the separatory funnel on a ring stand and add 10 mL of ether to the solid mixture in the separatory funnel. Both the organic acid and the organic neutral compound are soluble in ether. 4.

Add 5 mL of water to the separatory funnel.

You have two liquid phases or two layers, an ether layer and an aqueous layer. As you know, ether floats. Therefore, the ether layer is on top of the water layer. 5.

Add 5 mL of 1. 5 M NaOH(aq) to the separatory funnel. Because the NaOH(aq) is mostly water (aq is an abbreviation of aqueous, which means water), the NaOH(aq) solution will add to the bottom aqueous or water layer. . With the stopper in place, remove the separatory funnel from the ring stand.

Hold the separatory funnel in both hands and tilt it so that it can be vented (pressure released through the stopcock) without losing any liquid.

Hold the separatory funnel so that the orange stopcock is pointing up. Shake the separatory funnel vigorously Nith frequent venting (at least five times). Vigorous shaking ensures that the two liquid phases mix. The acid in the organic phase (ether) can then react with the NaOH in the water phase (aqueous). The acid-base

reaction converts the acid into a salt, which is water soluble.

7. Place the separatory funnel on the ring stand, remove the stopper, and wait for the two layers to separate. 3. Drain the bottom aqueous layer into a beaker, being careful not to drain any emulsion (mixture of two phases) into the beaker.

Try to trap the phase boundary in the stopcock, so that the drained portion is all aqueous, and the liquid remaining in the separatory funnel is all ether.

Label the beaker #1. Beaker #1 contains your organic acid in the form of a sodium salt, which is dissolved in the water. 3. Set beaker #1 aside for use in Step 17.

funnel; the NaCl(aq) will form a new bottom layer because it is mostly water. Replace the stopper, shake and vent the separatory funnel three times, as before. The salt extracts the remaining water from the ether layer into the water, because the ionic salt attracts the polar water. 1. Place the separatory funnel on the ring stand and allow the layers to separate. Drain the bottom water layer, including any emulsion, into a beaker.

Set this beaker aside until the lab is complete. [Do not discard any solution until you are sure it does not contain a desired compound. ] 12. Pour the ether remaining in the separatory funnel through the top of the separatory funnel into a clean Erlenmeyer flask. The ether contains your neutral compound, because the neutral compound is unreactive in NaOH and does not dissolve in water.

Therefore, the neutral compound remains in the ether layer throughout the experiment.

13. Using a spatula, add enough of

a drying agent (such as anhydrous sodium sulfate Na2S04) to cover the bottom of the Erlenmeyer flask that contains the cloudy ether solution from Step 12. 14. Swirl the Erlenmeyer flask and note whether or not the ether solution clears up, as the sodium sulfate drying agent absorbs water from the ether. If the ether does not clear up, add more sodium sulfate until the ether does clear up.

A drying agent removes water from an organic solvent.

In some cases, the ether solution will not be cloudy. Nevertheless, you should add the drying agent. [The ether will contain some Nater that should be removed, so the ether will subsequently evaporate rapidly. ] 15. Decant (pour the liquid ether without transferring the solid Na2S04) the ether into a pre-weighed 100 mL beaker and place it in the fume hood.

This will allow the ether to evaporate. The 100 mL beaker should be placed near the front of the hood. rhe window to the hood should be lowered to leave about 3 inches of space, so that ir will be drawn over the beaker facilitating evaporation. 6. Allow the ether to evaporate, leaving your neutral solid compound in the 100 mL beaker. If all the ether evaporates before the end of lab, carefully smell and record the odor of the solid.

Scrape the solid onto a tarred weigh boat and determine the mass of the neutral compound. Calculate a percent recovery. Place in a vial and seal until next week. 17.

Return to beaker #1. Add concentrated hydrochloric acid (HCI) to beaker #1 drop Nise but rapidly, while stirring the solution with a glass stirring rod.

A white precipitate of benzoic acid will form.

Continue adding HCI until you observe no additional white solid being formed.

The organic acid salt is converted back into an organic acid by the hydrochloric acid. The organic acid solidifies because it is 18. Determine the mass of a filter paper for a Buchner funnel. Place the weighed filter paper in a Buchner funnel and collect the benzoic acid with suction filtration. Rinse the beaker with a small amount of water and pour the mixture into the 3?chner funnel. Allow the solid to dry.

Carefully remove the filter paper and determine the combined mass of the filter paper and benzoic acid.

Determine the mass of recovered benzoic acid by difference and determine the percent recovery. 19. Save and allow both solids to dry until next week. We will take an accurate weight and the melting point of both. Cleanup:.

Wash glassware with water and then acetone and store them in the designated locations. Clean and store all equipment and materials. Acetone should be used to rinse glassware that contained ether, naphthalene or benzoic acid. Check [Our area and make sure that it is clean and neat and that you have not left any of [Our items on the bench top. Check the balance areas..