Monobutyltin

Monobutyltin is an organotin compound with the chemical formula C₄H₉Sn. It is typically found as a colorless liquid or oil that is soluble in organic solvents such as chloroform, toluene, and benzene. The molecule consists of a single butyl group bonded to a tin atom, which also is coordinated to three thioepoxide ligand groups that confer unique reactivity.

The compound was first synthesized in the 1960s by stoichiometric reactions of tin tetrachloride with butyl magnesium bromide, followed by nucleophilic substitution and oxidative coupling. It is mainly produced on an industrial scale by reacting tributyltin chloride with a reducing agent that selectively extracts one butyl group and yields the monobutyl derivative.

Monobutyltin is employed primarily as an antifungal agent in marine antifouling paints and as a biocidal additive in rubber, plastics, and pharmaceuticals. In these applications it acts by interfering with membrane integrity and enzyme activity in fungi and zooplankton. Its use in antifouling has been reduced by environmental regulations because of concerns about bioaccumulation and toxicity to non‑target organisms.

The compound is hazardous; it is corrosive, can cause skin and eye irritation, and is toxic if ingested or inhaled. Chronic exposure may lead to organ toxicity, especially affecting the kidneys and the nervous system. Environmental assessments indicate that monobutyltin persists in aquatic sediment and can bioaccumulate in fish, prompting strict control measures in many jurisdictions.