Fosfite

Fosfite is a polyatomic anion with the chemical formula PO3^3-. It is the conjugate base of phosphorous acid (H3PO3). Fosfite salts are typically soluble in water. The fosfite anion has a central phosphorus atom bonded to three oxygen atoms and one hydrogen atom, with a formal charge of -1. However, in aqueous solution, phosphorous acid exists in equilibrium with its conjugate bases, fosfite and hydrogen fosfite. The oxidation state of phosphorus in fosfite is +3, which is lower than in phosphate (PO4^3-) where it is +5. This lower oxidation state makes fosfite a reducing agent. Fosfite compounds are used in various applications, including as fertilizers, fungicides, and as reducing agents in chemical synthesis. In agriculture, fosfite is applied to plants as a foliar spray or soil drench to improve plant health and disease resistance, particularly against oomycete pathogens like downy mildew and Phytophthora. The mechanism of action is thought to involve direct toxicity to the pathogen and stimulation of the plant's own defense mechanisms.