A Friedel-Crafts Alkylation Of P-Xylene

In this experiment, a Friedel-Crafts alkylation of p-xylene (para-1, 4-dimethylbenzene) is performed by 1-bromopropane (alkyl halide) with an aluminum trichloride catalyst. Figure 2 shows the reaction for this synthesis. Friedel-Crafts reactions can usually be performed by vacuum distillation/ reflux as it prevents polyalkylation or multiple substitutions of alkyl groups. Since small quantities of reagents will be used to perform this synthesis, a microscale reflux apparatus will be used. This synthesis also results in a rearrangement, causing a mixture of two products or isopropyl and n-propyl substituted aromatic rings to be produced. The products will be analyzed by gas chromatography and mass spectrometry to differentiate each product and

In a GC, the compound is injected (time of injection is recorded), vaporized, and moves down a column. As the mixture/compound reaches the column, the different components of the mixture/compound will equilibrate between the liquid and gas phases. The length of time required for a sample to move through the column tells how much time it spends in the liquid and vapor phases. If the compound spends the most time in the vapor phase, the faster it gets to the end of the column (or shorter retention time). The fastest compound is the most volatile, because the amount of time a compound spends in the vapor phase is mostly a function of its vapor pressure. In addition, boiling points also play a role in the separation of compounds in a GC analysis. Compounds with low boiling points generally travel through the gas chromatograph faster than compounds with high boiling points, because low-boiling compounds have higher vapor pressures (indirect relationship) (Padias 187). By performing a GC analysis for the Friedel-Crafts reaction of p-xylene, the products will be separated from the starting materials and the by-products. The GC will also give a ratio of the products that were