Phenolphthalein
[CAS# 77-09-8]

Identification

• Classification: API >> Digestive system medication >> Laxative antidiarrheal
• Name: Phenolphthalein
• Synonyms: 2-[Bis(4-hydroxyphenyl)methyl]benzoic acid; 3,3-Bis(4-hydroxyphenyl)-1(3H)-isobenzofuranone; 3,3-Bis(4-hydroxyphenyl)phthalide
• Molecular Formula: C₂₀H₁₄O₄
• Molecular Weight: 318.33
• CAS Registry Number: 77-09-8
• EC Number: 201-004-7
• SMILES: C1=CC=C2C(=C1)C(=O)OC2(C3=CC=C(C=C3)O)C4=CC=C(C=C4)O

Properties

• Density: 1.299
• Melting point: 258-263 °C
• Water solubility: <0.1 g/100 mL

Safety Data

• Hazard Symbols: GHS08 Danger
• Risk Statements: H350-H341-H361f
• Safety Statements: P203-P280-P318-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Carcinogenicity	Carc.	1B	H350
Germ cell mutagenicity	Muta.	2	H341
Reproductive toxicity	Repr.	2	H361
Skin irritation	Skin Irrit.	2	H315
Reproductive toxicity	Repr.	2	H361f
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411
Reproductive toxicity	Repr.	2	H361fd
Reproductive toxicity	Repr.	2	H361f

Discovery and Applications

Phenolphthalein, with the chemical formula C20H14O4, is a widely recognized and versatile compound in chemistry, known for its use as a pH indicator and in various other applications. It was first synthesized in 1871 by the German chemist Rudolf Vergin. The compound is derived from the reaction of phenol with phthalic anhydride under acidic conditions, leading to the formation of a colorless crystalline solid that becomes pink to red in basic solutions.

Phenolphthalein is best known for its role as an acid-base indicator in titrations. It changes color in the pH range of approximately 8.2 to 10.0. In acidic solutions, phenolphthalein remains colorless, but as the pH increases and the solution becomes more basic, the compound turns pink. This color change is attributed to the ionization of phenolphthalein in the basic environment, where it forms a colored anionic species. This property makes it a valuable tool in analytical chemistry for determining the endpoint of titrations involving weak acids and strong bases.

In addition to its use in titrations, phenolphthalein has applications in various fields, including medicine and industry. Historically, it was used as a laxative due to its ability to stimulate bowel movements. However, its use in this capacity has diminished due to concerns over safety and potential side effects. In modern times, phenolphthalein is primarily used in laboratory settings and in the manufacturing of certain dyes and chemicals.

Phenolphthalein's role extends to educational demonstrations and chemical experiments. It is commonly used in classroom settings to illustrate the concept of pH indicators and to visually demonstrate the changes that occur during acid-base reactions. Its vivid color change makes it an effective teaching tool for visualizing the principles of acid-base chemistry.

In industrial applications, phenolphthalein is used as a reagent in the synthesis of other chemicals and as a component in certain types of pH-sensitive materials. Its stability and color-changing properties make it useful in various chemical formulations and quality control processes.

Overall, phenolphthalein remains a significant compound in both academic and practical chemistry. Its ability to indicate pH changes makes it an invaluable tool in titrations and educational demonstrations, while its applications in industry and historical use as a laxative highlight its versatility.

References

1984. Kinetic study of beta-cyclodextrin-dye system by high-pressure temperature-jump method. The Journal of Biochemistry, 96(1).
DOI: 10.1093/oxfordjournals.jbchem.a134830

2011. Laxative-Induced Buttock Dermatitis. The Journal of Emergency Medicine, 40(2).
DOI: 10.1016/j.jemermed.2008.06.013

1964. The diagnostic value of the twenty-four hour pH gastric analysis—A preliminary report. Irish Journal of Medical Science (1926-1967), 39(10).
DOI: 10.1007/bf02944846