Chemistry 351 Laboratory - Spring Semester 2009

Expt #6. Electrophilic Aromatic Substitution. Friedel-Crafts Acylation.

Relevant textbook readings - Lab Manual #17 (expt 59), Smith chap 18 (especially 18.5-18.11)

Overview - Experiment 59 in Pavia will be carried out essentially as described in the lab manual. Each group will be assigned its own particular monosubstituted benzene to acylate. Assignments are here. The product will be purified and then identified using ¹H  NMR and IR spectrometry. Each group will submit an initial report identifying the product formed and giving the percent yield. Then all class results will be pooled and provided for purposes of a final lab report which addresses the effect of substituents on the acylation reaction. 

Special note for 2009 - The publisher messed up our order on this lab and included in your lab manuals the "small-scale" rather than the "semi-microscale" procedure that we will be using. For this reason I will be handing out copies of the procedure to use in lieu of the information given on pages 136-138 of the lab manual.

Procedure Modifications

    1. 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.

    2. 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.

    3. 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!

    4. The boiling point of the product will not be measured.

    5. 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.

Initial Report

    This report should give results tables that serve to identify the product of the reaction and state the yield and % yield obtained. All spectral data should be summarized in table form and the actual spectra should be attached with all peaks labeled. If the NMR shows the product to be a mixture then the table should give data for each compound in the mixture and use peak integrations to estimate the ratio between the products formed. 

    No conclusions section or assigned questions need to be included with the initial report.

Final Report

      The final report for this experiment will consider the class results as a whole. The instructor will pool the results and provide them in Excel format via the Web. 

Assigned Questions

Use the table of class results as a basis for your answer.

(1) How important is the steric bulk of an alkyl substituent to determining the o:p ratio in Friedel-Crafts acylation? Explain thoroughly and suggest how the mechanism we wrote in class for these reactions might be modified to better explain these results.