Paraquat is usually formulated as the dichloride salt
The molecular formula of the cation is C12H14N2 with a molecular weight of 186.3. The dichloride salt has the formula C12H14Cl2N2 and a molecular weight of 257.2. Paraquat dichloride forms colourless, hygroscopic crystals which decompose at 300°C. It is practically non-volatile with a vapour pressure of 0.1 mPa. It is very soluble in water (700 g/l at 20°C) and practically insoluble in most other organic solvents. It is stable in neutral and acidic media, but readily hydrolysed in alkaline media. Paraquat is photochemically decomposed by ultraviolet radiation in aqueous solution.