Reinecke's salt is a chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula NH₄[Cr(NCS)₄(NH₃)₂].H₂O

Water of crystallization

In crystallography, water of crystallization or water of hydration or crystallization water is water that occurs in crystals. Water of crystallization is necessary for the maintenance of crystalline properties, but capable of being removed by sufficient heat...

. The dark-red crystal

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

line compound is soluble in boiling water, acetone

Acetone

Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...

, and ethanol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

.

Structure

The chromium atom is surrounded by six nitrogen atoms in an octahedral geometry

Octahedral molecular geometry

In chemistry, octahedral molecular geometry describes the shape of compounds where in six atoms or groups of atoms or ligands are symmetrically arranged around a central atom, defining the vertices of an octahedron...

; the NH₃ ligands are mutually trans. The salt crystallizes with one molecule of water. It was first reported in 1863.
According to Organic Syntheses, NH₄[Cr(NCS)₄(NH₃)₂] is prepared by treatment of molten NH₄SCN (ca. 145–150 °C) with (NH₄)₂Cr₂O₇

Ammonium dichromate

Ammonium dichromate is the inorganic compound with the formula 2Cr2O7. In this compound, as in all chromates and dichromates, chromium is in a +6 oxidation state, commonly known as hexavalent chromium...

.

Use

This salt was once widely used to precipitate primary and secondary amine

Amine

Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

s as their ammonium

Ammonium

The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...

 salts. Included in the amines that effectively form crystalline precipitates are those derived from the amino acids, including proline

Proline

Proline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that the human body can synthesize it. It is unique among the 20 protein-forming amino acids in that the α-amino group is secondary...

 and hydroxyproline

Hydroxyproline

-4-Hydroxyproline, or L-hydroxyproline , is a common non-proteinogenic amino acid, abbreviated as HYP, e.g., in Protein Data Bank.-Structure and discovery:...

. It also reacts with Hg²⁺ compounds, giving a red color or a red precipitate.