Sodium perchlorate

Sodium perchlorate is an inorganic compound with the chemical formula NaClO4. It consists of sodium cations Na+ and perchlorate anions ClO4−. It is a white crystalline, hygroscopic solid that is highly soluble in water and ethanol. It is usually encountered as sodium perchlorate monohydrate NaClO4*H2O. The compound is noteworthy as the most water-soluble of the common perchlorate salts.

Sodium perchlorate and other perchlorates has been found on the planet Mars, first detected by the NASA probe Phoenix in 2009. This was later confirmed by spectral analysis by the Mars Reconnaissance Orbiter in 2015 of what is thought to be brine seeps which may be the first evidence of flowing liquid water containing hydrated salts on Mars.

Selected properties
Its heat of formation is −382.75 kJ/mol, i.e. it is thermally stable up to high temperatures. At 490 °C it undergoes thermal decomposition, producing sodium chloride and dioxygen. It crystallizes in the rhombic crystal system.

Uses
Perchloric acid is made by treating NaClO4 with HCl. Ammonium perchlorate and potassium perchlorate, of interest in rocketry and pyrotechnics, are prepared by double decomposition from a solution of sodium perchlorate and ammonium chloride or potassium chloride, respectively.

Laboratory applications
Because of its high solubility (2096 g/L at 25 °C) and the inert behaviour of dissolved perchlorate, solutions of NaClO4 are often used as unreactive background electrolyte (supporting electrolyte). Indeed, because the reduction reaction of perchlorate is kinetically limited even if it is a thermodynamically unstable compound, perchlorate is a redox non-sensitive anion. It is also a non-complexing anion with no ligand binding capacity.

Sodium perchlorate is the precursor to ammonium, potassium and lithium perchlorate salts, often taking advantage of their low solubility relative to NaClO4 (209 g/(100 mL) at 25 °C).

It is used for denaturating proteins in biochemistry and in standard DNA extraction and hybridization reactions in molecular biology.

In medicine
Sodium perchlorate can be used to block iodine uptake before administration of iodinated contrast agents in patients with subclinical hyperthyroidism (suppressed TSH).

Production
Sodium perchlorate is produced by anodic oxidation of sodium chlorate (NaClO3) at an inert electrode, such as platinum.


 * Na+ClO3− + H2O → Na+ClO4− + 2 H+ + 2 e− (acidic medium)
 * Na+ClO3− + 2 OH− → Na+ClO4− + H2O + 2 e− (alkaline medium)

Safety
Accute toxicity : The median lethal dose (LD50) is 2 – 4 g/kg (rabbits, oral).

Chronic toxicity : the frequent consumption of drinking water with low concentrations (in the range of μg/L, ppb) of perchlorate is harmful for the thyroid gland as the perchlorate anion competes with the uptake of iodide.