Sodium periodate
Sodium periodate is an inorganic salt, composed of a sodium cation and the periodate anion. It may also be regarded as the sodium salt of periodic acid. Like many periodates, it can exist in two different forms: sodium "meta"periodate (formula‍ NaIO) and sodium "ortho"periodate (normally NaHIO, but sometimes the fully reacted salt NaIO). Both salts are useful oxidising agents. Preparation. Classically, periodate was most commonly produced in the form of sodium hydrogen periodate (NaHIO). This is commercially available, but can also be produced by the oxidation of iodates with chlorine and sodium hydroxide. Or, similarly, from iodides by  oxidation with bromine and sodium hydroxide: Modern industrial scale production involves the electrochemical oxidation of iodates, on a PbO anode, with the following standard electrode potential: Sodium metaperiodate can be prepared by the dehydration of sodium hydrogen periodate with nitric acid. Structure. Sodium metaperiodate (NaIO) forms tetragonal crystals (space group "I"4/) consisting of slightly distorted ions with average I–O bond distances of 1.775 Å; the Na ions are surrounded by 8 oxygen atoms at distances of 2.54 and 2.60 Å. Sodium hydrogen periodate (NaHIO) forms orthorhombic crystals (space group Pnnm). Iodine and sodium atoms are both surrounded by an  octahedral arrangement of 6 oxygen atoms; however the NaO octahedron is strongly distorted. IO and NaO groups are linked via common vertices and edges. Powder diffraction indicates that NaIO crystallises in the monoclinic system (space group C2/m). Uses. Sodium periodate can be used in solution to open saccharide rings between vicinal diols leaving two aldehyde groups. This process is often used in labeling saccharides with fluorescent molecules or other tags such as biotin. Because the process requires vicinal diols, periodate oxidation is often used to selectively label the 3′-ends of RNA (ribose has vicinal diols) instead of DNA as  deoxyribose does not have vicinal diols. NaIO is used in organic chemistry to cleave diols to produce two aldehydes. In 2013 the US Army announced that it would replace environmentally harmful chemicals barium nitrate and potassium perchlorate with sodium metaperiodate for use in their tracer ammunition.