Recrystallization - Purify Samples of Organic Compounds That Are Solids at Room Temperature

Objective:

The objective of this experiment is to purify samples of organic compounds that are solids at room temperature. The purpose of the experiment involves using a solid to determine solubility of the substance and subsequently obtain a pure substance by recrystallization.

Background:

Phthalic acid, which was discovered in 1836 by Laurent, is a product of the oxidation of many benzenoid compounds. Phthalic acid is used mainly in the form of the anhydride to produce other chemicals such as dyes, perfumes, saccharin, phthalates and many others. Phthalic acid, also known as 1,2 benzenedicarboxylic acid, O-phthalic acid, Benzene-1, 2-dicarboxylic acid, and o-dicarboxybenzene. Has a molecular formula of C8H6O4. Phthalic acid is a white crystal substance or fine white powder. It is an aromatic dicaroxylic acid. It is an isomer of isophthalic and terephthalic acid. Phthalic acid is one the three isomers of benzenedicarboxylic acid. The bacteria pseudomonas degrades phthalic acid.

Table of Physical Constants:

Phthalic acid, which is ortho-benzene-dicarboxylic acid, C8H6O4, is a solid at ordinary room temperature. According to the Handbook of Chemistry & Physics, its melting point is about 207°C, but if you heat it more, it will decompose instead of boiling.

It acts similar to ordinary table sugar, which decomposes when heated - gives off steam and leaves a gunky black residue behind.

Hazards:

Phthalic acid, if inhaled, may cause irritation to the respiratory tract. Symptoms may include coughing, sore throat, labored breathing and chest pain. If ingested, do not induce vomiting and seek immediate medical attention. May cause skin irritation with redness and pain. If in contact with eyes, it may cause irritation, redness and pain. Immediately flush eyes with plenty of water for at least 15 minutes lifting up and lower eyelids.

Procedure:

First, use the solubility data given to calculate the volume of boiling water required to dissolve 1.0 g of phthalic acid. Then add 1.0 g of phthalic acid to a 25-mL erlenmeyer flask. Fill a 10-mL graduated cylinder with distilled water. Using a pipette, add 5.0 mL of water from the graduated cylinder. Add a boiling stick to the flask, in this case a wood stick. It facilitates even boiling and prevents bumping. Gently heat the solution to boiling on a hot plate. As soon as boiling begins, continue to add water drop-wise until the entire solid dissolves. If 10 mL of water has been added and the solid still has not completely dissolved, refill the graduated cylinder and continue to add water, but at a faster rate. Record the total volume of water required to dissolve the crystals. Remove the boiling stick. Place the flask on an insulator and allow it to cool undistributed to about 25 C (room temperature) during with time the recrystallization process can be observed. Slow cooling favors large crystals. Then cool the flask in an ice bath for 10 minutes. Set up a vacuum filtration apparatus using the small Hirsh funnel and a 25 mL filter flask. Collect the crystals by vacuum filtration. Use a spatula to assist in transferring the crystals to the funnel, then wash the phthalic acid in the funnel with small amounts of ice cold water. Place a filter, paper on a watch glass. Transfer