Phosphorous acid is an intermediate in the preparation of other phosphorus compounds. Typical examples of weak acids include acetic acid and phosphorous acid. These salts are prepared by treating phosphorous acid with the metal carbonate. Organic derivatives of phosphorous acid, compounds with the formula RPOH, are called phosphonic acids. This colourless viscous liquid is the ester of phosphorous acid and phenol. Some evidence suggests that phosphorous acid may inhibit proteoid root formation. These materials are moisture sensitive, hydrolysing to give phosphorous acid. The IUPAC recommended name for phosphorous acid is phosphonic acid. These anions are the conjugate bases of phosphorous acid (HPO). Unlike phosphorous acid, arsenous acid is genuinely tribasic, with the formula As(OH). It is closely related to the corresponding anhydride of phosphorous acid, PO. Diorganophosphites are derivatives of phosphorus(V) and can be viewed as the di-esters of phosphorous acid. In contrast, the nominally related phosphorous acid HPO adopts the structure HPO(OH). Some phosphites can be considered esters of the dominant tautomer of phosphorous acid (HP(O)(OH)). They are structurally closely related to (and often prepared from) phosphorous acid.