Crystallization

1
Crystallization

• Experiment 3

2
Required Reading Before Class

• Experiments 3A, 3B, 3C
• 4th ed.Techniques
• 8 (Filtration)
• 9 (Melting Pt.)
• 11 (Crystallization)
• 3rd ed.Techniques 4, 5, 6 (Part A)

3
Crystallization

• Objectivetrying to obtain a pure form of
  crystals from an impure source
• Exp. 3A 3BIsolate pure crystals of
  sulfanilamide using 95 ethanol as your solvent.
• Exp. 3CChoose the best solvent for crystallizing
  fluorene from a list of three different solvents.

4
Pre-Lab Exercise

• The key to a good crystallization is figuring out
  the minimum amount of solvent youll need to get
  crystal formation.
• Using the data below, calculate the minimum
  amount of ethanol youll need for obtaining pure
  sulfanilamide crystals, starting with 0.30g of
  impure sulfanilamide for 3A, and 0.10g for 3B.
• 14 mg/mL _at_ 0oC
• 24 mg/mL _at_ 20oC
• 46 mg/mL _at_ 40oC
• 88 mg/mL _at_ 60oC
• 210 mg/mL _at_ 78oC

5
Solubility Graph of Sulfanilamide in Ethanol
6
3A Semimicroscale Crystallization

• This method employs vacuum filtration

7
3B Microscale Crystallization

• This method employs a Craig tube

8
Craig Tube Prepared for Centrifugation
9
3C Choosing an Ideal Solvent For Crystallization
10
Structures Melting Point Ranges
11
Procedural Notes

• 3ASemimicroscale Crystallization
• You will be using a side-arm flask with a Hirsch
  funnel for vacuum filtration. A trap will not be
  necessary.
• You should obtain 150mg of crystals
• 3BMicroscale Crystallization
• Make sure you balance the centrifuge before
  running it. Either balance your tube with
  another group, or create a dummy tube.
• You should obtain 45mg of crystals
• For both techniques, you should maintain a
  temperature of 78oC in your ethanol solvent to
  get an appreciable purity!

12
Procedural Notes

• AnalysisFor all sections, you will need to do
  the following
• Percent Recovery
• Note this is NOT a yield!
• Melting Point Range
• Your crystals must be completely dry before you
  attempt this!
• You will not have to submit samples