What Is Oxazole?
Oxazole is an organic compound with the chemical formula C3H3NO, belonging to the class of heterocyclic aromatic compounds. Its CAS registration number is 288-42-6. Oxazole is a colorless to light yellow liquid at room temperature, with a molecular weight of 69.06, a melting point of -87 to -84°C, and a boiling point of 69-70°C. It has a density of 1.05 g/mL and exhibits a low pKa of 0.8 for its conjugated acids.
This compound is highly flammable, both as a liquid and vapor, with a flash point as low as 66°F (19°C).
Uses of Oxazole
Oxazole is utilized in various applications due to its property as a raw material for heat-resistant, high-strength polymers. Its applications include construction curing sheets in industrial sheet materials requiring heat and pressure resistance, and in the electronics field, for insulating films in semiconductor chips and adhesive polymer films in heat sinks for electronic devices.
Properties of Oxazole
While oxazole is an aromatic compound, it is considered less aromatic than thiazole. It is an isomer of imidazole, with the nitrogen replaced by oxygen, and exhibits weak basicity. The pKa of oxazole’s conjugate acid is 0.8, compared to imidazole’s pKa of about 7. Oxazole can undergo de-protonation at the C2 position, potentially leading to ring-opened isonitrile formations. In addition, oxazole participates in Diels-Alder reactions, leading to the formation of pyridine bodies and the loss of an oxygen atom.
4-Acyloxazoles are known to undergo thermal rearrangement reactions, such as conforcing, where acyl residues rearrange to the C5 position. Oxazole also undergoes various oxidation reactions; for instance, adding three equivalents of cerium ammonium nitrate (CAN) to 4,5-diphenyloxazole yields formamide and benzoic acid, consuming three equivalents of water per oxazole equivalent.
Types of Oxazole
Oxazole is primarily sold as a reagent for research and development in small quantities, such as 1 g or 10 g, and is relatively expensive. Large quantities require individual quotations from manufacturers. Depending on the specific type, oxazole reagents may be stored at room temperature or under refrigeration. Many analogs of oxazole, including non-halogenated heterocyclic building blocks like 2,4,5-trimethyloxazole, benzoxazole, and their derivatives, are also available.
Other Information on Oxazole
Synthesis of Oxazole
There are various methods reported for synthesizing oxazole. Classical methods include Robinson-Gabriel synthesis from 2-acylaminoketones, Fischer’s oxazole synthesis from cyanohydrin and aldehydes, and the Brederek reaction involving α-haloketone and formaldehyde. Other methods include cycloisomerization of propargylic amides and reactions of benzoyl chlorides with isonitrile to produce oxazole derivatives.