Hydrochloride

Hydrochloride is a chemical salt derived from a basic compound and hydrogen chloride. In chemistry and pharmacology, the term most commonly refers to the hydrochloride salt of an amine, formed when the base is protonated by hydrochloric acid to yield an ammonium cation with chloride as the counterion.

Formation and properties: The typical salt is represented as RNH3+ Cl−, where RNH2 is the parent amine. It is usually prepared by reacting the base with hydrogen chloride gas or with aqueous hydrochloric acid. These salts are generally white to colorless crystalline solids that dissolve readily in water and are often more water-soluble than the corresponding free base. They may be hygroscopic and, depending on the compound, can have different stability profiles.

Uses and examples: Hydrochloride salts are extensively used in pharmaceuticals because enhanced water solubility improves formulation options, dosing accuracy, and bioavailability. They are found in many drugs as prescribed medications, including morphine hydrochloride, lidocaine hydrochloride, sertraline hydrochloride, fluoxetine hydrochloride, and tramadol hydrochloride. In some cases, dihydrochloride salts (two HCl units per molecule) are used to achieve even higher solubility.

Notes: The hydrochloride form is a salt, distinct from plain hydrochloric acid or hydrogen chloride gas. The salt form can affect pharmacokinetics, stability, and patent status, and may require specific storage conditions. When discussing a drug, the hydrochloride form is often specified in the product name (for example, morphine hydrochloride) to indicate the salt form used.