Separation of Benzoic Acid and 1,4-DimethoxybenzeneOCH3

COOH Benzoic Acid

OCH3 1,4-Dimethoxybenzene

Procedure:Initial Separation Place 0.2 g of benzoic and 0.3 g of 1,4-dimethoxybenzene in a centrifuge tube. Add 2 mL of 10% NaHCO3 and stir. Then add 2 mL of diethyl ether and stir. Stopper the tube, shake it, then vent it. Continue shaking and venting for about 3 minutes. Allow the tube to stand undisturbed until the layers separate. Carefully draw off the lower layer using a Pasteur pipette with cotton and transfer it to a test tube labeled aqueous layer. Transfer the upper layer to a test tube labeled ether layer. Aqueous Layer Test Tube Add 0.2 mL of diethyl ether to this tube. Shake it, then remove the ether (upper) layer using a Pasteur pipette (with cotton). This ether layer may be discarded. Add concentrated HCl (dropwise) to the tube to acidify the solution of pH less than 2 (check the pH with pH paper). An excess of HCl does no harm. Cautiously heat the tube on a hot plate to dissolve the solid (benzoic acid). Allow the tube to cool slowly to room temperature, then cool it in ice. Filter your crystals with a filter flask and a Hirsh funnel. Wash the crystals using a small amount of ice water. Dry these benzoic acid crystals, weigh them, determine their melting point, and calculate the yield. Return your product in a labeled test tube.

Ether Layer Test Tube Add 0.25 mL of 10% NaHCO3 to this tube. Shake the tube and vent it. Remove the lower, aqueous layer using a Pasteur pipette (with cotton). This aqueous layer may be discarded. Add 0.1 g of anhydrous Na2SO4. Cork the tube and let it dry for 10 minutes. Remove the ether from the drying agent using a Pasteur pipette with cotton. Transfer the ether to a new tube. Wash the drying agent (the Na2SO4) with 0.5 mL of diethyl ether. Combine this ether solution with the ether in the new tube using a Pasteur pipette. Repeat this procedure, then discard the Na2SO4. Gently evaporate the solvent by connecting the tube to a vacuum. If the tube gets cool, place it in a beaker with warm water. 0100090000035400000001001c00000000000400000003010800050000000b02000000000500000 00c025402f302040000002e0118000400000002010100050000000902000000021c000000fb02ceff 0000000000009001000000000440001254696d6573204e657720526f6d616e000000000000000000 0000000000000000040000002d0100000d000000320a2d0000000100040000000000f10252022008 1600030000000000 Cool the tube to room temperature. Add 0.5 mL of methyl alcohol and heat gently on a hot plate to dissolve the crystals. When all the crystals have dissolved, remove from the hot plate and add 2 drops of water. Allow the tube to cool to room temperature, and then place it in an ice bath. Filter your crystals using a filter flask and a Hirsh funnel. Dry these crystals of 1,4-dimethoxybenzene, weigh them, determine their melting point, and calculate the yield. Return this product in a separate, labeled test tube.

Separation of Benzoic Acid and 1,4-DimethoxybenzeneName: Partner: Date: Physical Properties and Results Initial Mass, gbenzoic acid 1,4-dimethoxybenzene diethyl ether

Drawer no.:

MW, g/mol

Moles

Density, g/mL

mp., C

bp., C

Comments

benzoic acid 1,4-dimethoxybenzene

g g

% yield % yield

mp mp

C (lit. mp C (lit. mp

C) C)

Draw a flow chart illustrating the separation of benzoic acid and 1,4dimethoxybenzene. (Use a computer program to draw the structures. Lines can be drawn by hand.)

QUESTIONS: 1. The Ka of benzoic acid is 6.8 10-5 and that of phenol is 1.0 10-10. Calculate pKas for both.

Which one is a stronger acid?

Would you expect phenol to dissolve in 10% NaHCO3? EXPLAIN.

2. Why was diethyl ether rather than acetone chosen as the extraction solvent?

3. How many moles of NaHCO3 are contained in 2 mL of a 10% NaHCO3 solution?

Is this amount of NaHCO3 sufficient to react with all of the benzoic acid?

4. Suppose a reaction mixture, when diluted with water, afforded 200 mL of an aqueous solution of 40 g of the reaction product malononitrile, CH2(CN)2, which is to be isolated by extraction with ether. The solubility of malononitrile in ether at room temperature is 20 g per 100 mL; the solubility in water is 13.3 g per 100 mL. What mass of malononitrile would be recovered by extraction with one 200 mL portion of ether?