C HEM 51LB:E XPERIMENT 1P ART 2
PURIFICATION AND C HARACTERIZATION OF SUBSTITUTION PRODUCT
TECHNIQUES: recrystallization, melting point, thin layer chromatography
This is the second part of a two-part experiment. Previously, you have reacted one of three possible
nucleophiles with benzyl bromide in the presence of sodium hydroxide to produce a solid product.
In this lab period you will purify the product using recrystallization and identify it and, therefore,
your unknown nucleophile via melting point and thin layer chromatography (TLC). Additionally,
you will analyze the saved aliquot of your filtrate for the presence of reactants, product, or products
of side reactions.
Technique 14:rdelting Points and Melting Ranges in Techniques in Organic
Chemistry 3 Ed. pgs 175-183.
Technique 15: Recrystallization in Techniques in Organic Chemistry 3 Ed. pgs
Tecrdique 17: Thin-Layer Chromatography in Techniques in Organic Chemistry
3 Ed. pgs 221-233.
Follow the instructions in the “51LB Report & Presentation Guidelines” document
located on the course website to prepare your pre-lab.
Complete the online Sapling pre-lab questions.
Ethanol, hexanes, and ethyl acetate are volatile, toxic and flammable. Use in the fume hood.
Immediately set aside ~20mg of your crude product for later.
Heat approximately 20 mL of ethanol and 20 mL of water in separate flasks or beakers but on the
same hot plate. Adjust the temperature of the hot plate so that the ethanol is hot but not boiling.
Recrystallize your crude product from ethanol/water by placing your product into an appropriately
sized Erlenmeyer flask and slowly adding portions of the hot ethanol just until the solid is
completely dissolved. You will need to stir or swirl the flask containing your product solution and
keep it warm during this process. Be careful not to add too much solvent! Add water dropwise and
while swirling your recrystallization flask just until all a slight cloudiness persists. Add hot ethanol
again dropwise until the cloudiness disappears. Allow the solution to cool to room temperature and
then place the flask into an ice bath to complete recrystallization. Cool a small beaker of water in
ice while you wait for crystallization to occur. (Note that this is the general procedure for
recrystallizing from mixed solvent when the exact solvent ratios needed are not known.)
CHEM 51LB Page 1
Rev 12/04/2013 Vacuum filter the solid and rinse with ice-cold water. Allow the solid to dry in the filter funnel
while pulling air through the sample for at least 15 minutes. Record the mass of the dried product.
Obtain a melting range for the recrystallized product and your crude product you set aside earlier (if
you did not do so in the previous lab period or if the previous crude melting