Chlorobutanol, or trichloro-2-methyl-2-propanol, is a chemical preservative, sedative hypnotic and weak local anaesthetic similar in nature to chloral hydrate. It has antibacterial and antifungal properties. Chlorobutanol is typically used at a concentration of 0.5% where it lends long term stability to multi-ingredient formulations. However, it retains antimicrobial activity at 0.05% in water. In pure state it's a white, volatile solid with a menthol-like odor.