Phenolpthalein

Phenolphthalein is a chemical compound that is widely used as an acid-base indicator. Its formula is C20H14O4. Phenolphthalein is often used in titration experiments in chemistry to determine the concentration of an unknown acid or base. It is colorless in acidic solutions and turns pink in basic solutions, with the color change occurring over the pH range of 8.2 to 10.0. This characteristic makes phenolphthalein particularly useful in experiments involving pH determination.

Properties

Phenolphthalein is a laxative when used in medical applications, although its use has declined due to concerns over its safety. It is poorly soluble in water, but it is readily soluble in alcohols and various organic solvents. This solubility property is exploited in its use as an indicator, where it is usually dissolved in alcohol before being added to a titration mixture.

Synthesis

The synthesis of phenolphthalein involves the condensation of phthalic anhydride with two equivalents of phenol under acidic conditions. This reaction produces phenolphthalein and water as byproducts. The process is an example of a Friedel-Crafts acylation, a type of electrophilic aromatic substitution.

Applications

Chemical

In the laboratory, phenolphthalein is primarily used as a pH indicator. Its transition from colorless to pink under basic conditions allows it to indicate the endpoint of titrations involving strong acids and bases. It is also used in the determination of the equivalence point in acid-base reactions.

Medical

Historically, phenolphthalein was used as an over-the-counter oral laxative. However, its use has significantly decreased due to studies suggesting a potential link to cancer with long-term use. As a result, it is less commonly used in medical settings today.

Safety

Phenolphthalein has been the subject of health and safety concerns, particularly regarding its use as a laxative. Studies have suggested that long-term use of phenolphthalein-containing laxatives may increase the risk of certain types of cancer. Consequently, regulatory agencies in some countries have restricted or banned the sale of laxatives containing phenolphthalein.

See Also

• Acid-base titration
• pH indicator
• Friedel-Crafts reaction