Chemistry 234 Organic Chemistry Laboratory Stan Smith [email protected] www.chem.uiuc.edu User Name: netID Password: netID No - in netID Change your password! ChemNet Requires Microsoft Internet Explorer 2 points/lesson Due May 2, 2001 Laboratory Notebook Reference Data Observations Properties: compounds solvents Laboratory Reports Safety Equipment Eye wash faucets Eye wash bottles Overhead showers Fire blanket Fire extinguishers Fire-emergency alarm box First-aid box Exits Room 467 Noyes Lab Mark location of safety equipment on map of room. Contact your TA immediately Grades Laboratory Reports 230 2 50 minute Exams 2x100 = 200 On-line Quizzes 10*10 = 100 ChemNet 16*2 = 36 15% A 30% B 50% C 5% D + E Hour Exam Dates Dates: Exam 1: Thursday, March 1, 2001 Exam 2: Wednesday, April 25, 2001 Time: 7:00 p.m. Breakage Replacement Card Change Section - Makeup Labs Mike Eubanks 469 Noyes Lab Melting Points and Mixed Melting Points Experiment 1: Identify a compound by its melting point and mixed melting points. Acetamide 113 - 115 oC p-Aminobenzoic acid 188 - 189 oC Camphoric Acid 183 - 186 oC trans-Cinnamic Acid 133 - 134 oC Malonic Acid 135 - 137 oC p-Nitrophenol 113 - 115 oC Resorcinol 110 - 113 oC Succinic Acid 187 - 189 oC Urea 133 - 135 oC A sample is put in the bottom of a melting point tube. Put a small amount of the compound in the open end of the melting point tube. Turn over and tape the closed end on the desk top until the compound falls to the bottom. Sample in the melting point tube. Use a Thiele tube filled with mineral oil to heat your sample. Attach the melting point tube to a thermometer. Heat about 5o per minute until within about 10o of the melting point Near the melting point heat at 1 - 2o per minute Mel-Temp in the lab Temperature Starts to melt Finished melting m.p. = Start - Finish Why is salt put on snow covered roads? Ice melts at 0oC What happens to the melting point if salt is added? Ice melts! Impurities such as salt lowers the melting point of water. Putting salt on icy roads causes the ice to melt because it lowers the melting point of water. Impure compounds usually melt lower than pure compounds so the melting point may be used as a measure of the purity of a compound Acetic Acid, CH3COOH, is a colorless liquid that melts at 16.6oC. Let’s look at the melting point of mixtures of water and acetic acid. Plot of melting point vs. mole fraction water for mixtures of water and acetic acid. Eutectic point Cool a acetic acid - water solution with a mole fraction water of 0.9 Heat a acetic acid - water solution with a mole fraction water of 0.9 Heat a acetic acid - water solution with a mole fraction water of 0.2 Pure compounds usually melt over a narrow temperature range, often 1o or less. Impure compounds melt lower than pure compounds and over a wider temperature range. Melting points are a measure of purity m.p. = 115o - 119o m.p. = 118o - 120o m.p. = 121o - 122o Two of these bottles contain benzoic acid and one m-nitrophenylacetic acid. m.p. = 120o - 122o m.p. = 120o - 122o m.p. = 120o - 122o How do you tell what is in each bottle? Mixed Melting Points Grind samples together to be sure they are mixed and then measure the melting point. Results 123 Mixed 1 and 2 m.p. = 120o - 122o Mixed 1 and 3 m.p. = 114o - 117o Mixed 2 and 3 m.p. = 115o - 118o 1. Measure the melting point of your unknown 2. Run mixed melting points to confirm identification Recrystallization Impure benzoic acid Benzoic acid after recrystallization O C-OH Benzoic Acid m.p. = 121 - 122o Purification of Organic Compounds Solids: Recrystallization Liquids: Distillation Solids and Liquids: Gas or liquid chromotography Types of impurities Soluble Insoluble Partly Soluble Solubility of benzoic acid in water Dissolve sample in hot solvent Compound crystallizes upon cooling Impure benzoic acid in hot water Add water and heat until all soluble material dissolves Insoluble material is removed by filtration The hot solution is filtered to remove insoluble impurities Use fluted filter paper to maximize surface area. To avoid crystallization in the funnel: Use GLASS funnel. Put flask on hot plate. Boil off excess solvent Boiling Sticks Hot solution after filtration: Cool Seed Scratch Crystals form in the warm solution Next: Cool, filter, wash, dry, weigh, mp .. Buchner funnel Heavy-walled tubing Filter flask Vacuum Put filter paper in Buchner.. funnel Filter and wash with cold solvent Insoluble Soluble Purified impurities impurities benzoic acid Solubility Example Compound Solubility g/100 mL 25o 100o A 1.0 80 I1 1.5 50 I2 0.0 0.0 Solubility g/100 mL Compound 25o 100o A 1.0 80 I1 1.5 50 I2 0.0 0.0 A = 10 g I1 = 1.0 g I2 = 1.0 g Total = 12.0 g 100 mL water at 1000 A dissolves I1 dissolves I2 insoluble Solubility g/100 mL Compound 25o 100o A 1.0 80 I1 1.5 50 I2 0.0 0.0 A = 10 g I1 = 1.0 g I2 = 1.0 g Total = 12.0 g 100 mL water at 1000 Cool to 25o A dissolves A 9.0 g crystallize I1 dissolves I1 0 g crystallize I2 insoluble Yield = 100 * 9.0/12.0 = 75% Solubility g/100 mL Compound 25o 100o A 1.0 80 I1 1.5 50 I2 0.0 0.0 A = 10 g I1 = 1.0 g I2 = 1.0 g Total = 12.0 g 50 ml of water at 1000 A dissolves I1 dissolves I2 insoluble Solubility g/100 mL Compound 25o 100o A 1.0 80 I1 1.5 50 I2 0.0 0.0 A = 10 g I1 = 1.0 g I2 = 1.0 g Total = 12.0 g o 50 mL water at 1000 Cool to 25 A dissolves A 9.5 g crystallize I1 dissolves I1 0.25 g crystallize I2 insoluble Yield = 100 * 9.75/12.0 = 81% NOT PURE! What volume of solvent is needed to give the maximum yield of pure A? Solubility of I1 = 1.5 g/100 mL 1.5 g 1.0 g = 100 mL x mL X = (100 mL * 1.0 g)/1.5 g = 67 mL What is the yield of pure A from 67 mL solvent? Solubility of A = 1.0 g/100 mL 1.0 g X g = 100 mL 67 mL X = (67 mL x 1.0 g) / 100 mL = 0.67 g Yield = 10.0 g - 0.67 g = 9.33 g % yield = 100 * 9.33 / 12 = 78% Boiling Points - Distillations Ethylene glycol, HOCH2CH2OH, boils at 198oC and melts at -13o C. What happens to the melting point of water if you add antifreeze? Melting point goes down. What happens to the boiling point of water if you add antifreeze? The boiling point goes up. Mixtures Solids Usually melt low Usually boil Liquids between the two components Vapor pressure of water vs. temperature Solution boils when the vapor pressure = applied pressure If you add salt, NaCl, to water what happens to the melting point? Impurities depress the melting point so it goes down. If you add salt, NaCl, to water what happens to the boiling point? The boiling point goes up. Raoult’s Law o Observed Mole Fraction Pressure Pure Substance Two Volatile Liquids O CH3 C CH3 Acetone Benzene b.p = 56o b.p. = 80o Two Volatile Liquids o Pa = P a * Naa o Pb = P b * Nbb Mixture boils when Pa + Pb = Papplied Plot of boiling point vs. mole fraction for a mixture of acetone and benzene. Boiling point of an acetone-benzene mixture with a mole fraction benzene of 0.50 What is the composition of the vapor? Vapor richer in the lower boiling component Fractional Distillation Packed Column HETP = 1.5 cm Vigreux Column HETP = 10 cm Experiment Separate mixture of methanol and water. Plot volume distilled vs. temperature. CH OH 3 H2O methyl alcohol water methanol o b.p. = 64.7o b.p. = 100 CH3OH Methyl alcohol is toxic! Standard Taper Joints 14/20 14 mm 20 mm Grease joints to prevent sticking. Plug the thermowell into the variable transformer Put boiling chips in bottom of flask Boiling Chips Thermometer Adapter Water out Water in IDEAL MIXTURES: Same interactions between like and unlike molecules NONIDEAL MIXTURES: A. Strong attractions between like molecules B. Strong attractions between unlike molecules Ethanol - Benzene Minimum - boiling azeotrope Acetone - Chloroform Maximum-boiling azeotrope Simple Distillation 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 Salts the organic phase Salts in water phase Water Neutral organic CH2Cl2 compounds in the organic phase Treatment of benzoic acid with sodium hydroxide converts it into the salt, sodium benzoate. COOH + Na OH COO Na Benzoic Acid Sodium Benzoate COOH + Na OH COO Na + - NH3 + HCl NH4 Cl Base Acid Salt O2NNH2 + 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 CH2Cl2 anthracene COO Na COO Na O2N NH3 Cl HCl NaOH Dry filter O2N NH2 COOH evaporate Filter Filter weigh wash wash dry dry weigh weigh Addition of acid to the sodium benzoate solution causes benzoic acid to precipitate.