Synthesis of Acetophenone by Friedel-Crafts Reaction

Friedel-Crafts reaction refers to the reaction of aromatic compounds with electrophilic reagents such as halogenated hydrocarbons and acyl halides catalyzed by acids (Lewis acids or protonic acids) to introduce alkyl or acyl groups on the aromatic ring, which can be divided into Friedel-Crafts alkylation and Friedel-Crafts acylation. Friedel-Crafts reaction is a kind of aromatic electrophilic substitution reaction, which is one of the most important methods for aromatic compounds to form C-C bond from C-H bond. C.Friedel and J.M.Crafts first reported this reaction in 1877.

Reaction Formula

The reaction formula for the synthesis of acetophenone by Friedel-Crafts acylation is as follows.

Reagents

Anhydrous thiophene 40mL (0.45mol); anhydrous aluminum trichloride 20.0g (0.15mol); acetic anhydride 6.0mL (0.06mol); concentrated hydrochloric acid; benzene 20mL (for extraction); 5% sodium hydroxide aqueous solution; anhydrous magnesium sulfate; anhydrous calcium chloride.

Operation Steps

In the 250mL three-port flask with a reflux condensing tube and constant pressure drop funnel, 40mL anhydrous thiophene benzene and 20g anhydrous aluminum trichloride are added (act quickly), and a calcium chloride drying tube and a hydrogen chloride gas absorption device (absorbed by diluted sodium hydroxide solution) are added to the upper mouth of the condensing tube. First, add a few drops of acetic anhydride to the three-mouth bottle, wait for the reaction to begin, and then continue to shake the three-mouth bottle while adding acetic anhydride to control the dripping speed so as not to make the reaction too intense. After the reaction is moderated, reflux is heated in a water bath until anhydrous calcium chloride gas is produced (about 30 min). Cool to room temperature, and pour into a beaker containing 50mL concentrated hydrochloric acid and 50g crushed ice under constant stirring (in a ventilation cupboard or outdoor). If there is any insoluble matter, add a small amount of hydrochloric acid to dissolve it. The organic layer was separated by a liquid separation funnel and extracted twice with 20mL of benzene. The organic layer is combined, washed with 5% sodium hydroxide solution and water, respectively, and dried with anhydrous magnesium sulfate.

The dried organic layer is filtered into a distillation bottle and benzene is evaporated in a water bath. After all the benzene is evaporated, use an electric heating sleeve to steam off the residual benzene. When the temperature rises to about 140℃, the heating is stopped, and after cooling slightly, it is changed into an air condensation tube, and the fractions of 198℃ ~ 202℃ are collected to obtain an anhydrous liquid of about 4g.

Vacuum distillation can also be used. The boiling point of acetophenone at different pressures is shown in the table below.