Гидроксид магния: свойства, применение и история

Inorganic compound of formula Mg(OH)2
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| verifiedrevid = 476992492
| ImageFile = Hydroxid hořečnatý. PNG
| ImageSize = 250px
| ImageName = Magnesium hydroxide
| ImageFile1 = Mg(OH)2Xray. jpg
| ImageSize1 = 250px
| ImageName1 = Magnesium hydroxide
| IUPACName = Magnesium hydroxide
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| Section5 = Chembox Thermochemistry
| DeltaHf = −924.7 kJ·mol−1
| DeltaGf = −833.7kJ/mol
| Entropy = 64 J·mol−1·K−1
| GHSSignalWord = Warning Magnesium hydroxide is a common component of antacids, such as milk of magnesia.

Most Mg(OH)2 that is produced industrially, as well as the small amount that is mined, is converted to fused magnesia (MgO). Magnesia is valuable because it is both a poor electrical conductor and an excellent thermal conductor.

As an antacid, magnesium hydroxide is dosed at approximately 0.5–1.5g in adults and works by simple neutralization, in which the hydroxide ions from the Mg(OH)2 combine with acidic H+ ions (or hydronium ions) produced in the form of hydrochloric acid by parietal cells in the stomach, to produce water.

As a laxative, magnesium hydroxide is dosed at 5 10g, and works in a number of ways. First, Mg2+ is poorly absorbed from the intestinal tract, so it draws water from the surrounding tissue by osmosis. Not only does this increase in water content soften the feces, it also increases the volume of feces in the intestine (intraluminal volume) which naturally stimulates intestinal motility. Furthermore, Mg2+ ions cause the release of cholecystokinin (CCK), which results in intraluminal accumulation of water and electrolytes, and increased intestinal motility. Some sources claim that the hydroxide ions themselves do not play a significant role in the laxative effects of milk of magnesia, as alkaline solutions (i. e., solutions of hydroxide ions) are not strongly laxative, and non alkaline Mg2+ solutions, like MgSO4, are equally strong laxatives, mole for mole.

On May 4, 1818, American inventor Koen Burrows received a patent (No. X2952) for magnesium hydroxide. In 1829, Sir James Murray used a "condensed solution of fluid magnesia" preparation of his own design to treat the Lord Lieutenant of Ireland, the Marquess of Anglesey, for stomach pain. This was so successful (advertised in Australia and approved by the Royal College of Surgeons in 1838) that he was appointed resident physician to Anglesey and two subsequent Lords Lieutenant, and knighted. His fluid magnesia product was patented two years after his death, in 1873. The term milk of magnesia was first used by Charles Henry Phillips in 1872 for a suspension of magnesium hydroxide formulated at about 8% w/v. It was sold under the brand name Phillips' Milk of Magnesia for medicinal usage. USPTO registrations show that the terms "Milk of Magnesia" and "Phillips' Milk of Magnesia" have both been assigned to Bayer since 1995. In the UK, the non brand (generic) name of "Milk of Magnesia" and "Phillips' Milk of Magnesia" is "Cream of Magnesia" (Magnesium Hydroxide Mixture, BP).

It is added directly to human food, and is affirmed as generally recognized as safe by the FDA. It is known as E number E528. Magnesium hydroxide is marketed for medical use as chewable tablets, as capsules, powder, and as liquid suspensions, sometimes flavored. These products are sold as antacids to neutralize stomach acid and relieve indigestion and heartburn. It also is a laxative to alleviate constipation. As a laxative, the osmotic force of the magnesia acts to draw fluids from the body. High doses can lead to diarrhea, and can deplete the body's supply of potassium, sometimes leading to muscle cramps. Some magnesium hydroxide products sold for antacid use (such as Maalox) are formulated to minimize unwanted laxative effects through the inclusion of aluminum hydroxide, which inhibits the contractions of smooth muscle cells in the gastrointestinal tract, thereby counterbalancing the contractions induced by the osmotic effects of the magnesium hydroxide.

Magnesium hydroxide is also a component of antiperspirant.

Magnesium hydroxide powder is used industrially to neutralize acidic wastewaters. It is also a component of the Biorock method of building artificial reefs. The main advantage of Mg(OH)2 over Ca(OH)2, is to impose a lower pH better compatible with that of seawater and sea life: pH 10.5 for Mg(OH)2 in place of pH 12.5 with Ca(OH)2.