Unknown Ketone Lab Overview

Objectives

• Identify two unknown ketones using different techniques.
• Determine the boiling point, derivative melting point, and use TLC for one ketone.
• Use proton NMR for identifying the second ketone.

Techniques for Characterization

Boiling Point Measurement

• Concept: Boiling point is where vapor pressure equals atmospheric pressure.
• Challenges:
  • Atmospheric pressure varies with elevation affecting the boiling point.
  • Thermometer placement: ensure it's just above the boiling liquid for accuracy.
  • Avoid boiling the ketone too quickly to prevent lag in thermometer reading.

Derivative Reaction

• Reagent: 2,4-dinitrophenylhydrazine forms a hydrazone derivative with the ketone.
• Observations:
  • Solid color varies (reddish, orange, yellow) based on R groups.
  • Measure melting point of this solid to compare against ketone's boiling point.
• Procedure:
  • Dissolve 2,4-dinitrophenylhydrazine in methanol and HCl.
  • Add ketone, allow reaction at room temperature.
  • Use vacuum filtration to retrieve and measure the melting point of the solid.

Thin Layer Chromatography (TLC)

• Purpose: To confirm ketone identity by comparing retention factors (Rf).
• **Process: Use 9:1 methylene chloride:hexane as mobile phase.
• Steps:
  • Prepare unknown and standard ketone derivatives.
  • Spot TLC plate with solutions and develop.
  • Compare developed spots for Rf values.**

Example Experiment

• Measurement: Simulated boiling point measurement shows 122°C.
• Derivative Reaction:
  • Used 100 mg dinitrophenylhydrazine with methanol and HCl.
  • Unknown ketone added, derivative color observed.
  • Melting point range determined around 142.8°C to 144.6°C.
• Result: Consistent with cyclopentanone.
• TLC Confirmation: Spots match, indicating correct ketone identification.

Second Unknown Ketone Identification

• Method: Proton NMR provided for analysis.
• Task:
  • Identify ketone from NMR spectrum.
  • Draw molecular structure, label hydrogens, and peaks.

Conclusion

• The combination of boiling point, derivative melting point, and TLC allows for accurate ketone identification.
• Proton NMR for the second ketone adds a comprehensive tool for structural analysis.