reductants

Reductants, or reducing agents, are substances that donate electrons to another species in a redox (reduction-oxidation) reaction. In the process, the reductant is oxidized while the species that gains electrons is reduced. The strength of a reductant is described by its tendency to be oxidized, often expressed by standard redox potentials; more negative potentials indicate stronger reducing power in a given environment.

Common reductants include elementary metals such as zinc, iron, and aluminum, which reduce metal ions or oxides; hydrogen gas is a versatile reductant in many gas-phase and solution reactions; carbon monoxide and carbon are used to reduce metal oxides in metallurgical processes and gasification; hydride donors such as sodium borohydride (NaBH4) and lithium aluminium hydride (LiAlH4) are potent reductants in organic synthesis; in biological systems, NADH and ascorbate function as reductants.

In practice, the choice of reductant depends on reaction conditions, including solvent, pH, temperature, and the redox potential of the substrate. Reductants can be reactive and air-sensitive, producing hazardous byproducts, and their use requires appropriate safety measures. Redox chemistry balances the thermodynamics of electron transfer with kinetic factors, determining whether a given reductant can effect the desired reduction under the chosen conditions.