Urea Monohydrochloride

Urea monohydrochloride (CAS 506-89-8) is the hydrochloride salt of urea — formed by combining urea (CO(NH₂)₂) with hydrochloric acid. It dissociates in aqueous solution to release hydrogen chloride (HCl) and urea. The result is a mildly complexed acid source that delivers controlled acidity without the fuming and corrosive aggressiveness of anhydrous HCl. At 5–10% concentration in water it produces solutions with pH < 2. In detailing chemistry, urea hydrochloride is used as the active acid in products marketed as alternatives to "harsh acids" like hydrofluoric acid, phosphoric acid, and ammonium bifluoride. It dissolves calcium and magnesium mineral deposits (water spots, scale) through acid-base neutralization. The urea component may provide some buffering or surface-wetting properties but the primary mechanism is the HCl activity. GHS classification at product mixture levels includes H290 (corrosive to metals), H302 (harmful if swallowed), H315 (skin irritation Cat 2), and H318 (serious eye damage Cat 1). These classifications reflect the corrosive acid chemistry at the concentrations used in commercial detailing formulas.