Extractions Mixture of benzoic acid, anthracene, and p-nitroaniline O COH NH2 NO2 Mixture of methylene chloride and water Density of CH2Cl2 is 1.33 g/mL H2O CH2Cl2 If we dissolve NaCl in this mixture which phase has the highest salt concentration? Salts concentrate in the water layer If we dissolve benzoic acid in this mixture in which phase would it concentrate? Neutral organic compounds concentrate in the organic phase Salts Salts in water phase Water Neutral organic compounds in the organic phase CH2Cl2 Treatment of benzoic acid with sodium hydroxide converts it into the salt, sodium benzoate. COOH + Na OH Benzoic Acid COO Na Sodium Benzoate COOH + Na OH COO Na NH3 + HCl Base Acid NH4+ ClSalt O2N NH2 + HCl O2N NH3 Cl Use separatory funnel for separations. Shake to be sure phases equilibrate Hold stopper and stopcock benzoic Acid p-nitroaniline anthracene HCl CH2Cl2 Benzoic acid O2N NH3 Cl Anthracene benzoic Acid anthracene NaOH COO CH2Cl2 Na anthracene O2N NH3 Cl NaOH O2N Filter wash dry weigh NH2 COO Na HCl COOH Filter wash dry weigh Dry filter evaporate weigh Addition of acid to the sodium benzoate solution causes benzoic acid to precipitate. The benzoic acid is filtered, washed, and dried. Weigh the benzoic acid and measure its melting point. NaOH O2N NH3 Cl O2N Cool to complete precipitation NH2 Dry the methylene chloride solution of anthracene with a small amount of sodium sulfate. Remove the drying agent by filtration through a fluted filter paper. Evaporate the methylene chloride on a steam bath. Use an inverted funnel connected to the vacuum line to collect the vapor. Weigh your products and measure their melting points. Put your samples in labeled vials and give them to your TA. Partition Coefficients 10 g t-butyl alcohol 100 mL ether 100 mL water 10 grams t-butyl alcohol 2.2 = x g / 200 mL ( 10 - x)g /100 mL x = 8.1 grams Which is better? Extract once with 200 mL or twice with 100 mL? If K = 1.0, a = 10 grams, S2 = 100 mL Extract once with 200 mL yields 6.7 grams Extract once with 100 mL yields 5.0 grams Second extraction with 100 mL yields 2.5 grams Total 2 extractions with 100 mL = 7.5 grams Grams extracted vs. number of extractions for K = 1, 2 and 4