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Magnesium perchlorate is a powerful oxidizing agent, with the formula Mg(ClO4)2. It is also a superior drying agent for gas analysis.

Magnesium perchlorate
Magnesium perchlorate
3D model (JSmol)
ECHA InfoCard 100.030.086
RTECS number
  • SC8925000
Molar mass 223.206 g/mol
Appearance white powder,
Odor odorless
Density 2.21 g/cm3 (anhydrous)
1.98 g/cm3 (hexahydrate)
Melting point 251 °C (484 °F; 524 K) (anhydrous)
95-100 °C (hexahydrate)
Boiling point decomposition
99.3 g/100 mL
Solubility in ethanol 23.96 g/100 mL
Main hazards Oxidizer
Safety data sheet External MSDS
GHS pictograms GHS03: OxidizingGHS07: Harmful
GHS signal word Danger
H272, H315, H319, H335
P220, P261, P305+351+338
NFPA 704
Related compounds
Other cations
Calcium perchlorate
Barium perchlorate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Magnesium perchlorate decomposes at 250 °C.[2] The heat of formation is -568.90 kJ mol−1.[3]

The enthalpy of solution is quite high, so reactions are done in large amounts of water to dilute it.

It is sold under the trade name anhydrone. Manufacture of this product on a semi-industrial scale was first performed by G. Frederick Smith in his garage in Urbana Illinois, but later at a permanent facility in Columbus, OH called G. Frederick Smith Chemical Co. He sold the magnesium perchlorate to A. H. Thomas Co., now Thomas Scientific, under the trade name Dehydrite.

It is used as desiccant to dry gas or air samples,[4][5] but is no longer advised, for use as a general desiccant, due to hazards inherent in perchlorates.[6] It is dried by heating at 220 °C under vacuum.

Magnesium perchlorate is produced by the reaction of magnesium hydroxide and perchloric acid.

Magnesium and other perchlorates have been found on Mars, appearing especially abundant and/or hydrated in locations where active flows are observed.[7] Being a drying agent, magnesium perchlorate retains water from the atmosphere and may release it when conditions are favorable and temperature is above 250K. Because briny solutions that contain magnesium perchlorate have a lower melting point than that of pure water, their abundance on Mars could serve as evidence that liquid water may exist on its surface, where temperature and pressure conditions would ordinarily cause water to freeze.


  1. ^ "Magnesium Perchlorate, Anhydrous". American Elements. Retrieved August 28, 2019.
  2. ^ CRC Handbook
  3. ^ Lange's
  4. ^ H. H. Willard, G. F. Smith (1922). "The Preparation and Properties of Magnesium Perchlorate and its Use as a Drying Agent". Journal of the American Chemical Society. 44 (10): 2255–2259. doi:10.1021/ja01431a022.
  5. ^ L. Wu, H. He (1994). "Preparation of perlite-based magnesium perchlorate desiccant with colour indicator". The Chemical Educator. 41 (5): 633–637. doi:10.1016/0039-9140(94)80041-3.
  6. ^ W. L. F. Armarego and C. Chai (2003). Purification of laboratory chemicals. Oxford: Butterworth-Heinemann. ISBN 0-7506-7571-3.
  7. ^ Chojnacki, Matt; Massé, Marion; Hanley, Jennifer; James J. Wray; McEwen, Alfred S.; Murchie, Scott L.; Wilhelm, Mary Beth; Ojha, Lujendra (2015). "Spectral evidence for hydrated salts in recurring slope lineae on Mars". Nature Geoscience. 8 (11): 829–832. doi:10.1038/ngeo2546. ISSN 1752-0908.