Original question.
What are the most commonly used preparations of Iron, and in what form does the metal exist in them ?
The main distinction is between metallic iron, iron(II) preparations, iron(III) preparations, and mixed iron oxides. The old prefixes “proto-” and “per-” ordinarily distinguish the lower and higher oxidation states here. “Peroxide of iron” means the historical iron(III) oxide preparation, not a modern peroxide containing an oxygen–oxygen bond.
The principal medicinal preparations can be grouped by the chemical form supplied:
- Iron(II) sulfate: Ferri sulphas, its granulated form, and its dried form supply iron(II). The ordinary and granulated salts are represented as ; the 1867 dried preparation is represented as . Drying principally changes the water of crystallization, rather than converting iron(II) into iron(III).
- Iron(II) carbonate: Ferri carbonas saccharata, the carbonate pill, and the compound iron mixture contain freshly formed iron(II) carbonate, . Exposure to air introduces higher iron oxides; sucrose helps preserve the lower oxidation state. Thus the saccharated material is a protected preparation rather than a pure, permanently stable salt.
- Iron(II) iodide: Ferri iodidum, its syrup, and its pill supply mainly . The historical solid includes water of crystallization and some iron oxide; the syrup again employs sucrose to retard deterioration.
- Iron(II) phosphate: Ferri phosphas and the corresponding syrup supply the lower iron phosphate, conventionally . The official precipitated material is partly oxidized, so describing the actual powder as chemically pure iron(II) phosphate would be too strong.
- Iron(III) chloride: the solution and tincture of “perchloride of iron” contain the higher chloride, , in an acidic liquid. This historical “perchloride” is unrelated to a perchlorate.
- Iron(III) nitrate: solution of “pernitrate of iron” contains the higher nitrate, , again in an acidic liquid. The solution of “persulphate” used to manufacture several other preparations supplies iron(III) sulfate, ; it is useful to distinguish this manufacturing reagent from the widely administered iron(II) sulfate.
- Iron(III) with organic acids: citrate of iron and ammonium, and tartarated iron, contain the higher iron in citrate or tartrate combinations. Citrate of iron and quinine is prepared from a higher iron compound, but should not be assumed to contain exclusively iron(III): the 1867 monograph reports blue reactions with both potassium ferrocyanide and potassium ferricyanide, consistent with an iron(II) component as well. The tartarated preparation also contains potassium; citrate of iron and quinine is made with Ammonia. They should be described as soluble pharmaceutical combinations, without pretending that every historical batch had a single simple molecular formula. The acetate tincture similarly contains the higher iron combined with acetic acid.
- Iron oxides: Ferri peroxidum hydratum (dried hydrated “peroxide”) and Ferri peroxidum humidum (the moist material) contain iron(III) as iron(III) oxide or hydrated iron(III) oxide. The magnetic oxide is a mixed iron(II)–iron(III) oxide preparation; expresses the ideal mixed oxide, rather than a claim that the historical hydrated powder was pure crystalline magnetite.
- Metallic iron: Ferrum redactum, used also in lozenges, contains finely divided iron in oxidation state zero together with magnetic oxide. The official preparation is therefore not all elemental iron. Iron wine made by contacting wire with wine obtains a dissolved tartrate-containing iron preparation from reaction with the wine's acids; the wire placed in the vessel should not be confused with the chemical form in the liquid ultimately dispensed.
These identifications follow the historical monographs, rather than the names of present commercial supplements.[ref]
British Pharmacopoeia by the General Medical Council (1867). “Ferri carbonas saccharata” through “Ferrum tartaratum”, pp. 130–141; the iron solutions, pp. 186–189; “Vinum ferri”, p. 367
A green iron(II) sulfate solution gives the characteristic blue reaction with potassium ferricyanide, whereas the higher iron solutions give blue with potassium ferrocyanide. Those diagnostic reactions explain why the official tests distinguish the two oxidation states; the historical colour test alone does not establish every detail of a complex preparation's composition. Articles by others on the same topic
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