Base Extraction of Benzoic Acid from Acetanilide

"Base Extraction of Benzoic Acid from Acetanilide"

This lab was performed as a technical experiment in which the details of extraction were to be observed and practiced. Relying on differences in solubility, an extraction was performed on a mixture of benzoic acid and acetanilide in an attempt to isolate the two compounds. Additionally, purification by recrystallization of the isolated products was carried out. The observed values of the pure solids were then compared to the known, pure literature values of each substance in order to determine the effectiveness of the extraction and purification techniques used.

A separatory funnel was cleaned, dried and prepared on a stable ring stand under the fume hood. A mixture of benzoic acid and acetanilide was obtained and weighed to approximately 4 grams and added to the separatory funnel. Wearing neoprene gloves, approximately 30 mL methylene chloride was added next. Using M1V1=M2V2 and the molecular weight for benzoic acid to determine the volume of KOH needed to deprotonate the benzoic acid and cause adequate separation, approximately 24 mL of KOH was added the separatory funnel. The funnel was closed and inverted, and ventilated frequently to release pressure from the system. Next, the funnel was shaken (again taking care to ventilate often) and the mixture was placed back in the ring stand and allowed to separate. Once separated, the bottom layer contained the dimethyl chloride/acetanilide mixture and the top layer acquired the KOH/benzoate salt mixture. The layers were separated into different beakers and labeled. The acetanilide mixture was placed back into the funnel and treated with a second portion of approximately 24 mL KOH. The procedure for separation was repeated and again the bottom layer was separated into the acetanilide flask, while the top layer went into the original benzoate flask. A third separation with 20 mL of water was run and again the mixture was placed in the appropriate flasks, bottom/acetanilide and top/benzoate.

With the separation completed, purification of each compound was then carried out. The purification of acetanilide was accomplished by treatment with anhydrous magnesium sulfate followed by gravity filtration into a round bottom flask. The magnesium sulfate allowed for a removal of any remaining water drawn in from the separation process. The remaining dichloromethane was evaporated in a warm bath using a rotary evaporator. The remaining crystals represented the purified product and were kept in the flask for further air drying. For the benzoate salt in solution, concentrated HCl was added to give the desired product of benzoic acid. Precipitation of the benzoic acid was observed. In order to ensure acidity, a litmus test was administered and showed positive. To obtain the purified crystals, vacuum filtration was used and care was taken to ensure that the filter paper was wet in order to seal the holes well. The crystals were collected and stored in the Buchner funnel for further air drying. Both products were allowed to air dry for one week, thereupon the characterizations of each were analyzed using an analytical balance for weight and a 120Vac digital melting point apparatus for MP. The MP apparatus was tested against a known substance for accuracy determination.

The procedure was carried out as planned, and the following data points, including literature values, were obtained:

Table1.

Compound Molecular Wt.

(g/mol) Weight Crude Melting Point

(range) Weight Pure

Benzoic Acid

(literature) 122.12 __ 121-125 C __

Acetanilide

(literature) 135.15 __

113-115 C __

Benzoic