The measurement of a compound’s melting point is a fundamental technique in chemistry, offering a precise physical constant that helps characterize a substance. For the organic compound acetanilide, knowing this specific thermal property is useful for both identification and quality control. This measurement reflects the energy required to break the crystalline structure and provides a snapshot of the compound’s purity and identity.
The Identity of Acetanilide
Acetanilide is an organic compound with the chemical formula C8H9NO, often referred to as N-phenylacetamide. It presents as a white, odorless solid, typically forming plate-like crystals when purified. It is structurally derived from aniline, a simple aromatic amine, through a chemical reaction called acetylation.
The compound was first discovered in 1886. Its synthesis involves reacting aniline with acetic anhydride. Acetanilide’s stability and its slightly water-soluble nature contributed to its early commercial and pharmaceutical use.
The Measured Melting Point
The accepted melting point for a pure sample of acetanilide is a specific temperature. The value most often cited in chemical literature is approximately 114.3 °C. This temperature marks the precise point at which the solid-to-liquid phase transition occurs.
Because slight variations can occur, the melting point is frequently reported as a narrow range. The common literature range for pure acetanilide is 113–115 °C, which corresponds to 235–239 °F. A narrow range of only one to two degrees Celsius is a strong indicator of a high-purity substance.
Significance of Melting Point Determination
The determination of a melting point serves as a rapid and inexpensive tool in the organic chemistry laboratory. The primary purpose of this measurement is to assess the purity of a crystalline solid. A pure substance melts at a precise temperature over a very narrow range, typically less than 1 °C.
The presence of impurities disrupts the crystalline lattice structure of the solid. This results in melting point depression, causing two effects: the sample begins to melt at a lower temperature, and it melts over a much broader temperature range. For instance, an impure sample of acetanilide might melt from 105–112 °C, signaling the need for further purification. The melting point can also be used as an identification method by comparing the experimental value to known literature values.
Practical Applications of Acetanilide
Acetanilide has a history in pharmaceuticals, as it was one of the first synthetic drugs discovered to possess both analgesic (pain-relieving) and antipyretic (fever-reducing) properties. Introduced in 1886 under the trade name Antifebrin, its direct use was later discontinued due to toxic side effects, specifically methemoglobinemia.
Scientists discovered that acetanilide is metabolized in the body into paracetamol, the active compound in modern acetaminophen. This finding led to the development of safer alternatives. Today, the compound’s role is primarily industrial, serving as a versatile chemical intermediate in various manufacturing processes:
- The synthesis of dyes.
- Rubber accelerators.
- A precursor for pharmaceutical products, including certain sulfa drugs and penicillin.
- A stabilizer for hydrogen peroxide.
- The production of synthetic camphor.