Manganese is the 25th abundant element on earth. Its name comes from the Latin word ‘magnes’ which means a magnet owing to its magnetic properties. Manganese is one of the few elements that humans need daily. Manganese was first isolated from the reduction of manganese compounds such as manganese dioxide. Manganism which is manganese poisoning could result from exposure to manganese dust or fumes for a long duration.
Abundance of Manganese in Nature: Manganese is considered to be the 25th most abundant element in the earth crust. Manganese cannot be found easily in nature as a free metal. However, it is found as a mineral in the form of oxides, silicates or carbonates. Manganese could be extracted from those ores. It is also found in the ocean floor in the form of nodules that are considered to be large lumps of metallic ores.
Properties and Uses of Manganese: Manganese is a hard, brittle, gray-white metal when found in its pure form. It is commonly known by being used as an alloying agent in steel manufacturing. It enhances the resistance of steel to impact. Long ago, Romans have used manganese in manufacturing their weapons and strong equipment for war due to its hardness. Moreover, romans used manganese as a pigment.
Manganese Compounds: Manganese is a highly reactive metal so it possesses high ability to react with different elements to produce various manganese containing compounds with various uses and functions. This is attributed to manganese’s valence electron that allows diversity of reactions. In biological systems, manganese is a mandatory element in the composition of vitamin B1.
Manganese, as many transition metals, has various oxidation states that could exceed 5 stable oxidation states. Each oxidation state possesses a distinctive color. Therefore, it is commonly used as a chemical reagent or indicator. For instance, it is commonly found in the laboratory as potassium permanganate KMnO4 that is used as a strong oxidizing agent. In addition, MnO2 catalyzes the decomposition of H2O2 as well as production of oxygen gas on a lab scale. Furthermore, manganese is incorporated in some inorganic salts such as manganese chloride whose molecular formula is MnCl2.
Preparation of Manganese Chloride: Manganese chloride could be prepared through the reaction of manganese (IV) oxide with concentrated hydrochloric acid. This reaction has been used also for the preparation of chlorine:
MnO2 + 4 HCl → MnCl2 + 2H2O + Cl2 ↑
Furthermore, on laboratory scale, manganese chloride can be prepared through the reaction of manganese metal or manganese carbonate with hydrochloric acid.
Mn + 2 HCl + 4 H2O → MnCl2.4H2O + H2
MnCO3 + 2 HCl + 3 H2O → MnCl2.4H2O + CO2
Manganese chloride hydrates are water soluble forming acidic solutions of pH 4 containing the metal aqua complex [Mn(H2O)6]2+.
Properties and Uses of Manganese Chloride:
- Manganese chloride is a white powdered salt when it is dehydrated. Its color turns into pink upon its hydration.
- Anhydrous manganese (II) chloride is used to initiate the synthesis of various manganese compounds. For instance, manganocene is prepared through reacting MnCl2 with sodium cyclopentadienide solution in THF.
MnCl2 + 2 NaC5H5 → Mn(C5H5)2 + 2 NaCl
- Manganese chloride reacts with typical organic ligands, so that manganese (II) gets oxidized by air to give Mn (III) complexes such as:
[Mn(EDTA)]−, [Mn(CN)6]3−, and [Mn(acetylacetonate)3].
- For example, triphenylphosphine forms a liable 2:1 adduct as shown below.
MnCl2 + 2 Ph3P → [MnCl2(Ph3P)2]
Manganese chloride is commonly used in dry cell batteries manufacturing. It is also used as precursor for the antiknock compound methylcyclopentadienyl manganese tricarbonyl.
