Physical and chemical properties of cycloalkanes

Cycloalkanes are insoluble in water; cyclopropane and cyclobutane are gases, cyclopentane and cyclohexane liquids and the higher members solids; boiling point and density rise with molar mass. Chemically the small-ring cyclopropane and cyclobutane are strained and unstable: with a catalyst they add H₂, Br₂ or HBr and become open-chain alkane derivatives, e.g. C₃H₆ + H₂ → C₃H₈ (Ni, gentle heating). Cyclopentane does this with more difficulty (about 300 °C), while cyclohexane mostly undergoes substitution like alkanes: C₆H₁₂ + Cl₂ → C₆H₁₁Cl + HCl. N. D. Zelinsky dehydrogenated cyclohexane over a platinum catalyst to benzene: C₆H₁₂ → C₆H₆ + 3H₂. When cycloalkanes burn, equal amounts of CO₂ and H₂O (in moles) form: CₙH₂ₙ + 1.5nO₂ → nCO₂ + nH₂O. Hexachlorocyclohexane C₆H₆Cl₆ (hexachlorane; one of its isomers is lindane) was once used as an agricultural insecticide; it persists in the environment and accumulates in organisms, so since 2009 it has been listed under the Stockholm Convention on Persistent Organic Pollutants and its agricultural use is banned.