Octaphenylcyclotetrasiloxane (CAS No. 546-56-5) is an important phenyl-based organosilicon compound. According to data from PubChem and NIST, it has the molecular formula C48H40O4Si4 and a molecular weight of approximately 793.17 g/mol; its structure comprises four siloxane units and eight phenyl groups.

Structurally, this compound is a cyclic siloxane with a high proportion of phenyl groups. Consequently, compared to standard methylcyclosiloxanes, its applications lean toward high-temperature environments, specialty organosilicon materials, and phenyl-modified silicone products.

Typically appearing as a white crystalline powder, the product (e.g., IOTA AKT) features a purity of ≥99.0%, a melting point of 203–205°C, a boiling point of approximately 334°C, and a flash point of approximately 200°C; it is insoluble in water but soluble in common organic solvents. Public databases similarly describe it as a white to off-white solid and note its insolubility in water.

The most notable application of CAS 546-56-5 is not in everyday consumer goods, but rather as an intermediate in organosilicon synthesis; it is used to produce high-temperature-resistant phenyl silicone oils and other polymeric compounds.