Nickel Chloride
Nickel (II) chloride (or simply nickel chloride), is the chemical compound NiCl2. The anhydrous salt is yellow, but the best known hydrate, NiCl2 · 6H2O, is green. It is very rarely found in nature as the mineral nickel bischofite.
There is also a dihydrate. In general, nickel (II) chloride is the most important source of nickel for chemical synthesis. Nickel salts are carcinogenic. Salts are also deliquescent in that they absorb moisture from the air to form a solution.
Nickel Chloride, chemical properties
NiCl2 adopts the structure CdCl2.3 In this arrangement, each Ni2 + center is coordinated with six Cl- centers and each chlorine is connected with three Ni (II) centers. In NiCl2 the Ni-Cl bonds are "ionic in character". The yellow NiBr2 and the black NiI2 adopt similar structures, but with a different packing of the halides, adopting the CdI2 scheme.
In contrast, NiCl2 · 6H2O is composed of separate trans molecules - [NiCl2 (H2O) 4] bound more loosely to adjacent water molecules. It is noteworthy that only four of the six water molecules in the formula are attached to nickel, and the remaining two are water of crystallization.3 Cobalt (II) chloride hexahydrate has a similar structure.
Many nickel (II) compounds are paramagnetic, due to the presence of two unpaired electrons at each metal center. However, flat square nickel complexes are diamagnetic.
Nickel (II) chloride solutions are acidic, with a pH close to 4 due to the hydrolysis of the Ni + 2 ion.
Nickel Chloride Applications
NiCl2 and its hydrate are sometimes useful in organic synthesis.6
As a mild Lewis acid, for example, for regioselective isomerization of dieneols:
In combination with CrCl2 for the coupling of an aldehyde and a vinyl iodide to give allylic alcohols.
For selective reductions in the presence of LiAlH4, eg for the conversion of alkenes to alkanes.
As a nickel boride precursor, prepared in situ from NiCl2 and NaBH4. This reagent behaves like Raney nickel, which comprises an efficient system for the hydrogenation of unsaturated carbonyl compounds.
As a precursor of Ni finely divided by reduction with Zn, for the reduction of aldehydes, alkenes and nitro aromatic compounds. This reagent also promotes homo-coupling reactions, that is, 2RX → R – R where R = vinyl, aryl.
As a catalyst for making dialkyl aphosphonates from phosphites and aryl iodides, ArI:
ArI + P (OEt) 3 → ARP (O) (OEt) 2 + EtI
Fuentes. Ecured.cu-Wikipedia
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