Magnesium sulfate
Magnesium sulfate is an inorganic salt with the formula MgSO4(H2O)x where 0 ≤ x ≤ 7. It is often encountered as the heptahydrate sulphate mineral epsomite (MgSO4·7H2O), commonly called Epsom salt. The overall global annual usage in the mid-1970s of the monohydrate was 2.3 million tons, of which the majority was used in agriculture.[1]
 hexahydrate | |
 Anhydrous magnesium sulfate | |
 Epsomite (heptahydrate) | |
| Names | |
|---|---|
| IUPAC name
Magnesium sulfate | |
| Other names
Epsom salt (heptahydrate) English salt Bitter salts Bath salts | |
| Identifiers | |
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3D model (JSmol) |
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| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| DrugBank | |
| ECHA InfoCard | 100.028.453 |
| E number | E518 (acidity regulators, ...) |
PubChem CID |
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| RTECS number |
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| UNII | |
CompTox Dashboard (EPA) |
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InChI
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| Properties | |
| MgSO4 | |
| Molar mass | 120.366 g/mol (anhydrous) 138.38 g/mol (monohydrate) 174.41 g/mol (trihydrate) 210.44 g/mol (pentahydrate) 228.46 g/mol (hexahydrate) 246.47 g/mol (heptahydrate) |
| Appearance | white crystalline solid |
| Odor | odorless |
| Density | 2.66 g/cm3 (anhydrous) 2.445 g/cm3 (monohydrate) 1.68 g/cm3 (heptahydrate) 1.512 g/cm3 (11-hydrate) |
| Melting point | anhydrous decomposes at 1,124°C monohydrate decomposes at 200°C heptahydrate decomposes at 150°C undecahydrate decomposes at 2°C |
| anhydrous 26.9 g/100 mL (0 °C) 35.1 g/100 mL (20 °C) 50.2 g/100 mL (100 °C) heptahydrate 113 g/100 mL (20 °C) | |
| Solubility | 1.16 g/100 mL (18°C, ether) slightly soluble in alcohol, glycerol insoluble in acetone |
| −50·10−6 cm3/mol | |
Refractive index (nD) |
1.523 (monohydrate) 1.433 (heptahydrate) |
| Structure | |
| monoclinic (hydrate) | |
| Pharmacology | |
| A06AD04 (WHO) A12CC02 (WHO) B05XA05 (WHO) D11AX05 (WHO) V04CC02 (WHO) | |
| Hazards | |
| Safety data sheet | External MSDS |
| NFPA 704 (fire diamond) | 
0
1
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| Related compounds | |
Other cations |
Beryllium sulfate Calcium sulfate Strontium sulfate Barium sulfate |
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 | |
Epsom salt has been traditionally used as a component of bath salts. Epsom salt can also be used as a beauty product. Athletes use it to soothe sore muscles, while gardeners use it to improve crops. It has a variety of other uses: for example, Epsom salt is also effective in the removal of splinters.[2]
Hydrates and anhydrous material, production
A variety of hydrates are known.[3]
The heptahydrate (epsomite) readily loses one equivalent of water to form the hexahydrate. Epsom salt takes its name from a bitter saline spring in Epsom in Surrey, England, where the salt was produced from the springs that arise where the porous chalk of the North Downs meets non-porous London clay.
The monohydrate, MgSO4·H2O is found as the mineral kieserite. It can be prepared by heating the hexahydrate to approximately 150 °C. Further heating to approximately 200 °C gives anhydrous magnesium sulfate. Upon further heating, the anhydrous salt decomposes into magnesium oxide (MgO) and sulfur trioxide (SO3).
The heptahydrate can be prepared by neutralizing sulfuric acid with magnesium carbonate or oxide, but it is usually obtained directly from natural sources.
Uses
Medical
It is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system.[4]
Magnesium sulfate is a common mineral pharmaceutical preparation of magnesium, commonly known as Epsom salt, used both externally and internally. Its solubility in water is inhibited by lipids in lotions resulting in variable absorption rates when applied to the skin. Temperature and concentration are also factors.[5]
Externally, magnesium sulfate paste is used to treat skin inflammations such as small boils or localised infections. Known in the UK as "drawing paste," it is also used to remove splinters.[6] The standard British Pharmacopoeia composition is dried magnesium sulfate 47.76% w/w, phenol 0.49% w/w. and glycerol (E422).[7]
Epsom salt is used as bath salts and for isolation tanks. Magnesium sulfate is the main preparation of intravenous magnesium.
Internal uses include:
- Replacement therapy for magnesium deficiency[8]
- Magnesium sulfate is an antiarrhythmic agent for torsades de pointes in cardiac arrest under the ECC guidelines and for managing quinidine-induced arrhythmias.[9]
- As a bronchodilator after beta-agonist and anticholinergic agents have been tried, e.g. in severe exacerbations of asthma,[10] magnesium sulfate can be nebulized to reduce the symptoms of acute asthma.[10] It is commonly administered via the intravenous route for the management of severe asthma attacks.
- Magnesium sulfate is effective in decreasing the risk that pre-eclampsia progresses to eclampsia.[11] IV magnesium sulfate is used to prevent and treat seizures of eclampsia. It reduces the systolic blood pressure but does not alter the diastolic blood pressure, so the blood perfusion to the fetus is not compromised. It is also commonly used for eclampsia where compared to diazepam or phenytoin it results in better outcomes.[12][13]
Agriculture
In agriculture, magnesium sulfate is used to increase magnesium or sulfur content in soil. It is most commonly applied to potted plants, or to magnesium-hungry crops, such as potatoes, tomatoes, carrots, peppers, lemons, and roses. The advantage of magnesium sulfate over other magnesium soil amendments (such as dolomitic lime) is its high solubility, which also allows the option of foliar feeding. Solutions of magnesium sulfate are also nearly pH neutral, compared with alkaline salts of magnesium as found in limestone; therefore, the use of magnesium sulfate as a magnesium source for soil does not significantly change the soil pH.[14]
Food preparation
Magnesium sulfate is used as a brewing salt in making beer.[15] It may also be used as a coagulant for making tofu.[16]
Chemistry
Anhydrous magnesium sulfate is commonly used as a desiccant in organic synthesis due to its affinity for water and compatibility with most organic compounds. During work-up, an organic phase is treated with anhydrous magnesium sulfate. The hydrated solid is then removed with filtration, decantation or distillation (if the boiling point is low enough). Other inorganic sulfate salts such as sodium sulfate and calcium sulfate may be used in the same way.
Niche uses
Magnesium sulfate heptahydrate is also used to maintain the magnesium concentration in marine aquaria which contain large amounts of stony corals, as it is slowly depleted in their calcification process. In a magnesium-deficient marine aquarium, calcium and alkalinity concentrations are very difficult to control because not enough magnesium is present to stabilize these ions in the saltwater and prevent their spontaneous precipitation into calcium carbonate.[17]
Magnesium (or sodium) sulfate is also used for testing aggregates for soundness in accordance with ASTM C88 standard, when there are no service records of the material exposed to actual weathering conditions. The test is accomplished by repeated immersion in saturated solutions followed by oven drying to dehydrate the salt precipitated in permeable pore spaces. The internal expansive force, derived from the rehydration of the salt upon re-immersion, simulates the expansion of water on freezing.
Minerals
Magnesium sulfates are common minerals in geological environments. Their occurrence is mostly connected with supergene processes. Some of them are also important constituents of evaporitic potassium-magnesium (K-Mg) salts deposits.
Bright spots observed by the Dawn Spacecraft in Occator Crater on the dwarf planet Ceres are most consistent with reflected light from magnesium sulfate hexahydrate.[18]
Almost all known mineralogical forms of MgSO4 are hydrates. Epsomite is the natural analogue of "Epsom salt". Another heptahydrate, the copper-containing mineral alpersite (Mg,Cu)SO4·7H2O,[19] was recently recognized. Both are, however, not the highest known hydrates of MgSO4, due to the recent terrestrial find of meridianiite, MgSO4·11H2O, which is thought to also occur on Mars. Hexahydrite is the next lower (6) hydrate. Three next lower hydrates—pentahydrite, starkeyite, and especially sanderite are rare. Kieserite is a monohydrate and is common among evaporitic deposits. Anhydrous magnesium sulfate was reported from some burning coal dumps.
Double salts
Double salts containing magnesium sulfate exist; for example, there are several known as sodium magnesium sulfates and potassium magnesium sulfates.
Safety
An abnormally elevated plasma concentration of magnesium is called hypermagnesemia.
References
- Industrial Inorganic Chemistry, Karl Heinz Büchel, Hans-Heinrich Moretto, Dietmar Werner, John Wiley & Sons, 2d edition, 2000, ISBN 978-3-527-61333-5
- "Quick Cures/Quack Cures: Is Epsom Worth Its Salt?". Wall Street Journal. 9 April 2012. Archived from the original on 12 April 2012. Retrieved 15 June 2019.
- Odochian, Lucia (1995). "Study of the nature of the crystallization water in some magnesium hydrates by thermal methods". Journal of Thermal Analysis and Calorimetry. 45 (6): 1437–1448. doi:10.1007/BF02547437.
- "WHO Model List of Essential Medicines" (PDF). World Health Organization. April 2015. Archived (PDF) from the original on 13 May 2015. Retrieved 14 December 2015.
- "Does Epsom Salt Work?". www.PainScience.com. Retrieved 5 May 2018.
- "Removing a splinter with Magnesium Sulphate".
- "Boots Magnesium Sulfate Paste B.P. - Patient Information Leaflet (PIL) - (eMC)".
- "Pharmaceutical Information – Magnesium Sulfate". RxMed. Archived from the original on 3 April 2009. Retrieved 6 July 2009.
- "CPR and First Aid: Antiarrhythmic Drugs During and Immediately After Cardiac Arrest (section)". American Heart Association. Retrieved 29 August 2016.
Previous ACLS guidelines addressed the use of magnesium in cardiac arrest with polymorphic ventricular tachycardia (ie, torsades de pointes) or suspected hypomagnesemia, and this has not been reevaluated in the 2015 Guidelines Update. These previous guidelines recommended defibrillation for termination of polymorphic VT (ie, torsades de pointes), followed by consideration of intravenous magnesium sulfate when secondary to a long QT interval.
- Blitz M, Blitz S, Hughes R, Diner B, Beasley R, Knopp J, Rowe BH (2005). "Aerosolized magnesium sulfate for acute asthma: a systematic review". Chest. 128 (1): 337–344. doi:10.1378/chest.128.1.337. PMID 16002955..
- Duley, L; Gülmezoglu, AM; Henderson-Smart, DJ; Chou, D (10 November 2010). "Magnesium sulphate and other anticonvulsants for women with pre-eclampsia". The Cochrane Database of Systematic Reviews (11): CD000025. doi:10.1002/14651858.CD000025.pub2. PMC 7061250. PMID 21069663.
- Duley, L; Henderson-Smart, DJ; Walker, GJ; Chou, D (8 December 2010). "Magnesium sulphate versus diazepam for eclampsia". The Cochrane Database of Systematic Reviews (12): CD000127. doi:10.1002/14651858.CD000127.pub2. PMC 7045443. PMID 21154341.
- Duley, L; Henderson-Smart, DJ; Chou, D (6 October 2010). "Magnesium sulphate versus phenytoin for eclampsia". The Cochrane Database of Systematic Reviews (10): CD000128. doi:10.1002/14651858.CD000128.pub2. PMID 20927719.
- "Pubchem: magnesium sulfate". Archived from the original on 18 October 2016.
- "Magnesium Sulphate". National Home Brew. Archived from the original on 1 August 2016. Retrieved 4 January 2019.
- US The present invention relates to a novel process for producing packed tofu, particularly a process for producing long-life packed tofu from sterilized soybean milk. 6042851, Matsuura, Masaru; Masaoki Sasaki & Jun Sasakib et al., "Process for producing packed tofu"
- "Do-It-Yourself Magnesium Supplements for the Reef Aquarium". Reefkeeping. 2006. Archived from the original on 22 March 2008. Retrieved 14 March 2008.
- M. C. De Sanctis; E. Ammannito; A. Raponi; S. Marchi; T. B. McCord; H. Y. McSween; F. Capaccioni; M. T. Capria; F. G. Carrozzo; M. Ciarniello; A. Longobardo; F. Tosi; S. Fonte; M. Formisano; A. Frigeri; M. Giardino; G. Magni; E. Palomba; D. Turrini; F. Zambon; J.-P. Combe; W. Feldman; R. Jaumann; L. A. McFadden; C. M. Pieters (2015). "Ammoniated phyllosilicates with a likely outer Solar System origin on (1) Ceres" (PDF). Nature. 528 (7581): 241–244. doi:10.1038/nature16172. PMID 26659184.
- Peterson, Ronald C.; Hammarstrom, Jane M.; Seal, II, Robert R (February 2006). "Alpersite (Mg,Cu)SO4·7H2O, a new mineral of the melanterite group, and cuprian pentahydrite: Their occurrence within mine waste". American Mineralogist. 91 (2–3): 261–269. doi:10.2138/am.2006.1911.