Chemistry 351 Laboratory - Spring Semester 2010
Expt #5. Electrophilic Aromatic Substitution. Friedel-Crafts
Acylationof Xylene.
Relevant textbook readings - Lab Manual - Pavia Expt 59, Smith chap 18
(especially 18.5-18.11), Mohrig, Technique 11 (especially 11.3 and 11.6)
Overview - Experiment 59 in Pavia will be carried out essentially as
described in the lab manual. (However, the 2008/2009 lab manual gives a "small-scale" procedure that will not be used. We will use the semi-microscale procedure given in the 2009/2010 lab manual. See me for a photocopy of the necessary pages if need be.)
Each group will be assigned one of the three xylene isomers to acylate. Write the prelab assuming it might be any of the three.
The product will be purified by vacuum distillation and characterized using 1H
NMR, IR, and GC-MS.
Procedure Modifications and Notes
- Double the scale of the experiment and use a 25-mL round bottom flask.
- The AlCl3 should be weighed into a dry screw
top vial and the vial immediately tightly capped until use. A balance will be
placed in one of the fume hoods for purposes of weighing out this compound.
- The acetyl chloride is dispensed by volume in a fume
hood into a separate vial, which you will then transport to your hood after
capping it tightly.
- Because you will be working in an efficient
fume hood, no gas trap is necessary. Just connect a reflux condenser to the
round bottom flask to act as an air condenser (no water circulation needed). The additions of the acetyl chloride
and your aromatic compound should be done through the top of the open condenser. Be aware that the reaction gives off
HCl gas, however and that the apparatus should be set well back in the hood and
that you need to keep your head out of the hood during the reaction!
- Vacuum distillation of the product will be performed using the apparatus shown in Figure 11.20 on p 150 of Mohrig.
- The boiling point of the product will not be measured.
- You should obtain 1H NMR and IR spectra of your product. The 1H spectrum will be the most
valuable to you in determining the position at which acylation occurred. Also prepare a sample for GC-MS by diluting one drop of your NMR sample solution in 4 mL acetone.
Assigned Questions
- Question number 8 in Pavia.
- Construct a separation scheme flow chart with branches to show where physical separations occurred. Discuss the separation process referring to this flow chart and identifying the most likely major steps where yield was lost.
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