Experiment 1: Bromination of Acetanilide1 Precautions: Ethanol is flammable Sodium hypochlorite is an oxidizing agent and releases toxic fumes (handle in fume hood) Acetic acid is corrosive, harmful if inhaled, flammable and can cause burns (handle in fume hood) Gloves are recommended to avoid chemical contact with skin Reaction Scheme: Conversion of acetanilide to p-bromoacetanilide
Procedure: To a 125 mL Erlenmeyer flask containing a mixture of 95% ethanol (6 mL) and acetic acid (5 mL), dissolve acetanilide (7.4 mmol) and sodium bromide (1.8 g). Place the reaction flask in an ice bath (at least 5oC) for 5 minutes (keep this reaction in the hood). Add sodium hypochlorite (8.3 mmol) by addition of household bleach; leave the reaction flask in the ice bath 5 min. After removing the flask from the ice bath and placing a watch glass over the opening, allow the reaction mixture to come to room temperature over 15 minutes. Place the reaction flask into the ice bath and quench the unreacted bromine by addition of both 5 mL of sodium thiosulfate solution (1 g/5 mL) and 5 mL sodium hydroxide solution(1 g/5 mL ); collect the product by suction filtration. Recrystalllize the brominated product from a minimum amount of solvent. You will need to select a solvent from water, 50% ethanol or 95% ethanol. To identify the best solvent, use what you have learned in Organic I Chemistry Lab, hint: think about what properties makes a good recrystallization solvent. Test your recrystallization solvent in test tubes using the tip of a spatula of your compound. Remember to use a water bath to heat organic solvents. NEVER heat organic solvents directly on a hot plate-always use a hot water bath! Dry the product and obtain melting point range (one fast and one slow) and an IR spectrum. Be sure to record observations in your laboratory notebook.
From “A Multistep Synthesis Incorporating a Green Bromination of an Aromatic Ring” J. Chem. Educ. 2012, 89, 1063
Prelab: In your lab notebook, write: 1. Date, Title of lab, Purpose and Mechanism of Reaction 2. Copy the following tables into your laboratory
notebook and fill in MM 3. Write a brief description (bullet points) of the procedure Substance Acetanilide Sodium Bromide Sodium Hypochlorite 95% Ethanol Acetic Acid MM (g/mol) mmol g mL –
Product Data MM (g/mol) mmol g before recrystallization recrystallization solvent mL recrystallization solvent g after recrystallization % Recovery Theoretical Yield, g Percent yield Melting point range fast Melting point range slow Literature Mp Value Reference for Lit. Mp Value
Waste Disposal: Place the filtrate from the reaction in the basic halogenated waste. Place the filtrate from recrystallization in the halogenated waste (as it may contain some p-bromoacetanilide). For your lab report: Continue in your lab notebook from the prelab. Complete the tables and show all calculations (clearly label where each calculation is in the notebook by providing each calculation with a title). Finally write a conclusion that includes a discussion of results and attach the IR (assign peaks) and the 1H NMR (be sure to assign all peaks on the NMR). Hand in the original of the carbonless copy pages as your lab report.
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