Description
Aluminum hydroxide, insoluble in water, soluble
in dilute mineral acids and alkali hydroxides
(4 % suspension in water), white, amorphous
powder. For other relevant properties and production,
see→Aluminum Oxide, Chap. 1.1.
Available as Al(OH)3·nH2O (algedrate) and
algedrate hexitol complex.
Definition
aluminium hydroxide: A white crystalline compound, Al(OH)3; r.d. 2.42-2.52. The compound occurs naturally as the mineral gibbsite (monoclinic). In the laboratory it can be prepared by precipitation from solutions of aluminium salts. Such solutions contain the hexaquoaluminium( III) ion with six water molecules coordinated, [Al(H2O)6]3+. In neutral solution this ionizes:
[Al(H2O)6]3+→H+ + [Al(H2O)5OH]2+
The presence of a weak base such as S2- or CO32- (by bubbling hydrogen sulphide or carbon dioxide through the solution) causes further ionization with precipitation of aluminium hydroxide
[Al(H2O)6]3+(aq) → Al(H2O)3(OH)3(s) + 3H+(aq)
The substance contains coordinated water molecules and is more correctly termed hydrated aluminium hydroxide. In addition, the precipitate has water molecules trapped in it and has a characteristic gelatinous form. The substance is amphoteric. In strong bases the aluminate ion is produced by loss of a further proton:
Al(H2O)3(OH)3(s) + OH-(aq)→
[Al(H2O)2(OH)4]-(aq) + H2O(l)
On heating, the hydroxide transforms to a mixed oxide hydroxide, AlO.OH (rhombic; r.d. 3.01). This substance occurs naturally as diaspore and boehmite. Above 450℃ it transforms to γ-alumina.
In practice various substances can be produced that are mixed crystalline forms of Al(OH)3, AlO.OH, and aluminium oxide (Al2O3) with water molecules. These are known as hydrated alumina. Heating the hydrated hydroxide causes loss of water, and produces various activated aluminas, which differ in porosity, number of remaining -OH groups, and particle size. These are used as catalysts (particularly for organic dehydration reactions), as catalyst supports, and in chromatography. Gelatinous freshly precipitated aluminium hydroxide was formerly widely used as a mordant for dyeing and calico printing because of its ability to form insoluble coloured lakes with vegetable dyes.
Production Methods
Aluminum hydroxide adjuvant is prepared by the precipitation of a
soluble aluminum salt by an alkali hydroxide, or the precipitation of
an alkali aluminate by acid.
Brand name
Amphojel
(Wyeth-Ayerst); Dialume (Rhone-Poulenc Rorer).
Flammability and Explosibility
Nonflammable
Pharmaceutical Applications
Aluminium hydroxide (Al(OH)3) has several medical applications. It is used as an antacid for treating
heartburn as well as acid indigestion (reflux oesophagitis). It is also known to have healing properties of peptic ulcers. In patients suffering from kidney failure, who show elevated serum phosphate levels (hyperphosphataemia),
Al(OH)3 is used as a phosphate binder.
Al(OH)3 is an amphoteric compound , which means it can react as a base or as an
acid. In its application as an anti-acid, Al(OH)3 reacts with any excess stomach acid (mainly HCl) with the
formation of AlCl3 and water .
Al(OH)3 + 3HCl → AlCl3 + 3H2O
Al(OH)3 is known to cause constipation, so formulations of anti-acids often include a combination with
Mg2+ antacids. Usually, oral antifoaming agents, such as simethicone, are added in order to reduce bloating and discomfort/pain.
Pharmaceutical Applications
Aluminum hydroxide adjuvant is used in parenteral human and
veterinary vaccines.It activates Th2 immune responses, including
IgG and IgE antibody responses. It is also used for the isolation of
certain serum components such as blood clotting factors.
Clinical Use
Phosphate binding agent
Antacid
Safety
Aluminum hydroxide adjuvant is intended for use in parenteral
vaccines and is generally regarded as nontoxic. It may cause mild
irritation, dryness, and dermatitis on skin contact. On eye contact,
aluminum hydroxide adjuvant may also cause redness, conjunctivitis,
and short-term mild irritation. Ingestion of large amounts may
cause gastrointestinal irritation with nausea, vomiting, and
constipation. Inhalation of the dried product may cause respiratory
irritation and cough. Type I hypersensitivity reactions following
parenteral administration have been reported.
Veterinary Drugs and Treatments
Orally administered aluminum hydroxide is used to reduce hyperphosphatemia
in patients with renal failure.
Drug interactions
Potentially hazardous interactions with other drugs
Cytotoxics: concentration of dasatinib and erlotinib
possibly reduced - give at least 4 hours before or 2
hours after erlotinib.
Metabolism
Aluminum hydroxide or oxide is slowly solubilised in
the stomach and reacts with hydrochloric acid to form
aluminium chloride and water. In addition to forming
aluminium chloride, dihydroxyaluminium sodium
carbonate and aluminium carbonate form carbon dioxide,
and aluminium phosphate forms phosphoric acid. About
17-30% of the aluminium chloride formed is absorbed
and is rapidly excreted by the kidneys in patients with
normal renal function.
Aluminium-containing antacids also combine with
dietary phosphate in the intestine forming insoluble,
nonabsorbable aluminium phosphate which is excreted in
the faeces.
storage
Aluminum hydroxide adjuvant is stable for at least 2 years when
stored at 4–308℃ in well-sealed inert containers. It must not be
allowed to freeze as the hydrated colloid structure will be
irreversibly damaged.
Incompatibilities
When exposed to phosphate, carbonate, sulfate, or borate anions,
the point of zero charge for aluminum hydroxide adjuvant
decreases.
Regulatory Status
GRAS listed. Accepted for use in human and veterinary parenteral
vaccines in Europe and the USA. The limits for use in human
vaccines are 0.85 mg aluminum/dose (FDA) and 1.25 mg aluminum/
dose (WHO). There are no established limits for use in
veterinary vaccines. Reported in the EPA TSCA Inventory.
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