Chloroauric acid
Chloroalic acid is also known as "gold chloride", "gold chloride tetrahydrate". Chemical formula is HAuCl4 • 4H2O. Molecular weight is 411.85. It is a yellow needle crystal. It is toxic and corrosive. It is easily soluble in water, and soluble in ethanol and ether, and slightly soluble in chloroform. Anhydrous chloroauric acid can be crystallized from the ethanol solution. It will decompose under heat condition, and decompose into gold trichloride at 120 ° C. Exposure of it leads to black spots. In alkaline solution, it reacts with KI to precipitate brown gold. In the acidic solution, it generates "cinnamon purple in the case of tin dichloride. Its aqueous solution was purple after dealing with methyl orange, and it turns green after 1 to 3 drops of hydrochloric acid, and then it becomes lavender after gold salt solution. We get gold hydroxide precipitation after adding cold potassium hydroxide solution. It was reduced to gold powder with sulfur dioxide.
Preparation
Dissolve the pure gold in aqua regia (or hydrochloric acid saturated by chlorine gas). After distillation and crystallization, we get the product.
Application
Chlorine acid is mainly used for alkaloid determination, electroplating gold, photography, gold powder, porcelain coloring, red glass manufacturing, special ink and treatment of tuberculosis. It can also be used as analytical reagent, such as microanalysis of rubidium (Rb) and cesium (Cs). It is used for semiconductor, electronic connector and local gold-plated of integrated circuit lead frame, also for printing circuit boards.
Chemical Properties
golden to yellowish brown crystals or powder
Uses
Hydrogen tetrachloroaurate(III) acts as a precursor used in the purification of gold by electrolysis. It is also used for the recovery, concentration, purification and analytical determination of gold. It acts as a key starting material for the preparation of gold compounds. It plays an important role as a catalyst in the preparation of 2-arylbenzoxazoles.
Uses
The HCl plus the HNO2
(hydrochloric and nitric acids) are combined to produce agua regia acid, which is the only
acid that can dissolve gold.
Purification Methods
It is obtained as a dark red crystalline mass by dissolving Au in aqua regia and evaporating. When sublimed at 180o, the crystals are ruby red. The anhydrous salt is hygroscopic, soluble in H2O but sparingly soluble in EtOH and Et2O. Aurochloric acid is formed when AuCl3 is dissolved in HCl. [Diemer J Am Chem Soc 35 553 1913, Glemser & Sauer Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol II p1 056 1965.]
Properties and Applications
Chloroauric acid is an orange-yellow crystal that is very easy to deliquesce and soluble in water. It decomposes into gold when heated. The aqueous solution of chloroauric acid contains square planar [AuC14]- ions, from which many salts containing planar square ions [AuX4]- (X=F, Cl, Br, I, CN, SCN, NO3) can be prepared. It can be used for local gold plating of semiconductor and integrated circuit lead frames, gold plating of printed circuit boards, electronic connectors and other electrical contact components. It can also be used to make red glass. It is used as an analytical reagent, specifically for microanalysis of clocks and absolutes and measurement of alkaloid composition. It is also used for photographic materials. Chloroauric acid salts, especially sodium chloroaurate NaAuCl4 (prepared by the reaction of AuCls and NaCl), can replace toxic mercury (II) salts as catalysts for alkyne reactions. At the same time, chloroauric acid has important applications in the preparation of nano-level gold. Generally, the fluorescent nano-gold prepared by direct reduction of chloroauric acid with a reducing agent has important applications in analytical chemistry.
