Acetanilide Recrystallization

Acetanilide Recrystallization

ABSTRACT

This experiment involved using various techniques to recrystallize Acetanilide. In addition to recrystallizing acetanilide, the experiment involved trying to recover the crystals with the least impurities. The major laboratory technique used in this lab was hot vacuum filtration, which involved pouring the heated test tube of acetanilide and water through a Buchner funnel that's on top of an Erlenmeyer flask. Following the recrystallization, the recovery of pure crystals from solution, measurements were taken which included melting point and percent recovery. The percent recovered of the filtrated solution should weigh less than the initial acetanilide meaning that impurities were taken out while vacuum filtration was occurring. The melting of the recovered material should be lower than the recovered crystals probably still contains impurities which caused the melting point to decrease.

INTRODUCTION

One of the most commonly used ways to obtain purified crystals from solutions is to use a technique called solution crystallization. For this technique, information about the solute is needed. One of the information is its solubility within the solvent. If the solute were not soluble within the designated solvent within any temperature range then clearly this would not be the best solvent to use when trying to dissolve the solute at high temperatures. Since solutes usually dissolve in solutes at higher temperatures, then the opposite is true. After heating and allowing the mixture of the acetanilide and water cool down (with the help of an ice-water bath), crystals should be seen forming on the funnel paper within the Buchner funnel. When the temperature is lower, the formation of crystals is slower thus making them purer compared to crystals that form faster. The theory is that the crystals seen on the filter should contain pure material, because the impurities should've flowed down the funnel and be present in the solution that was poured through the funnel. However some of the impure substances are small enough to be incorporated into the structure of the crystals in the funnel causing the pure material to consist of impure materials. For this, another round of vacuum filtration will be needed in order to ensure the most pure material is formed on top.

Recrystallization is a useful technique but there are many problems that may arise during the experiment meaning this technique can be very time consuming. First of all, when the solute separates from the solvent it may not always be present in solid form. Instead of being solid, an oil layer can form in place. When this happens there are various ways to resolve this. First of all, there is the addition of heated solvent using a pipet. Usually about 3-5 drops are added at a time to ensure that boiling still occurs. Sometimes when too much solvent is added a phenomenon called super saturation can occur which can be solved in one of two ways. Either the mixture can be boiled longer so that some of the solvent can be evaporated or a tool such as a microspatula could be used to stir up the mixture, allowing recrystallization to resume.

In everyday life, application of recrystallization can be seen. Some of these include the salt crystals in the saltshakers, sugar, and sucrose. In addition the microchips that are found in computers are made of silicon that has been processed through recrystallization. Recrystallization is also of growing importance in the pharmaceutical department. When recrystallizing certain types of drugs, the crystals themselves can display different properties depending on the method to gain those crystals. Some properties include melting point, solubility, and density.

TABLE OF REAGENTS

Compound/ Reagent Molecular Weight

(g/mol) Moles Theoretical Theoretical Weight Actual Weight / Percent Yield Structure

Acetanilide 135.16 .00074 .1 grams .107 grams (7.2 % Recovered)

Water (H2O) 18.01528 .0555 .001 Liters -

METHODS/PROCEDURES

The procedure stated that a maximum of five drops should be added to the beaker, however more than five drops were added. The crystals went into the filtration without the initial cleansing with water.

RESULTS

After the initial few minutes of boiling the test tube, there was an oil layer that was seen. It was yellowish and seemingly caused the efficiently of the solubility to decrease. After the oil layer disappeared and the hot plate was turned off, the mixture seemed to be clear but almost instantly the test tube became encased in fog or what seemed like instant crystallization. However, there were actually no crystals present. After pouring through the filter paper that was present in the Buchner funnel, crystals were seen encased in a white sticky substance that probably resulted from not enough heating.

...