CHEM 334 Experiment 19.2

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CHEM 334Experiment 19.2

• Synthesis of trans-Cinnamic Acid
• via the Haloform Reaction

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trans-Cinnamic Acid

• Isolated from a wood-rotting fungus
• Used to prepare esters for perfume industry
• Ethyl ester used in glass prisms lenses

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Background

• Haloform reaction
• Synthetic route to carboxylic acids
• Formation of CHX3
• Used in qual schemes expt. 28.3
• Clorox is a reagent?!

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Generic Haloform Reaction

• Where does halogen come from?
• Where does base come from?
• What structure must be present in the starting
  material?

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Generic Haloform Reaction

• What haloform is formed?
• How is the haloform removed in the workup?
• Why is the desired product soluble in aqueous
  base but not aqueous acid?

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Prelab Preparation

• Read Background Expt. 19.2
• read Microscale Solvent-Pair Recrystallization,
  p. 40
• Prepare Notebook
• Title, reference, reaction, mechanism,
  theoretical yield (in grams), flow chart, and
  table of reagents
• Prelab quiz

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In Lab

• Follow procedure in lab book
• stir vigorously enough to mix all reagents
• heat gently
• While doing the lab think about
• why extract reaction mixture with diethyl ether?
• what layer contains product?
• why is drying organic layer not part of
  procedure?
• what reaction occurs when HCl is added?
• Record all data observations

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Solvent Pair Recrystallization

• Heat ethanol water
• Dissolve crude product in minimum amount of hot
  ethanol
• Add hot water dropwise to
• cloud point
• Add 1 or 2 drops of ethanol clear solution
• Allow crystals to reform as in single solvent
  technique

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Characterization Calculations

• melting point
• theoretical yield
• percent yield

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Report

• Standard format
• Discuss Conclusions
• Discuss results with respect to yield and purity
  (m.p.). How was product identified? What
  by-product was formed how was it removed during
  the workup? What factors affected yield what
  would you do differently next time?

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Flow Chart