Mercury (I) chloride is a dense white powder and insoluble in water and may be light sensitive. It is incompatible with strong bases, carbonates, sulphides, cyanides, alkalis, sulphites, sulphates, hydrogen peroxide, ammonia, iodine, and hydrogen bromide.
Mercury(I) chloride is used in calomel electrodes; in ceramic painting; as a fungicide; in pyrotechnics for producing dark green light; in agriculture for controlling root maggots; and as an antiseptic and antisyphilitic agent in medicine.
Mercury(I) chloride is prepared by passing a limited amount of chlorine gas over mercury in a heated silica retort. Excess chlorine should be avoided as it can oxidize mercury(I) chloride to mercury(II) chloride.
2Hg + Cl2 → Hg2Cl2
The product generally contains some mercury(II) chloride which is removed by treating the product mixture with water and filtering out the insoluble mercury(I) salt from the soluble mercury(II) salt.
The compound also can be made by heating mercury(II) chloride with mercury. The product Hg2Cl2 sublimes and is collected:
HgCl2 + Hg → Hg2Cl2
Mercury(I) chloride is obtained as a white precipitate by adding a cold acidic solution of sodium chloride or other soluble chloride to a solution of mercurous salt, such as mercury(I) nitrate:
[Hg2]2+ (aq) + 2Cl¯ (aq) → Hg2Cl2 (s)
The precipitation method, however, does not form high-purity product as it contains small amounts of reactant and product ions that stick to the Hg2Cl2 precipitate and are difficult to remove by washing with water.
Mercury(I) chloride oxidizes to mercury(II) chloride when heated with chlorine:
Hg2Cl2 + Cl2 → 2HgCl2
Mercury(I) chloride is a reducing agent and, therefore, its reaction with oxidizing substances can oxidize it to Hg(II) compounds.
When heated at elevated temperatures, it partially dissociates to mercury metal and mercury(II) chloride:
Hg2Cl2 → Hg + HgCl2
This disproportionation (or breakdown of a compound into two products containing the same element but in different oxidation states) also occurs to some degree when mercury(I) chloride is heated and sublimed in an open container. Reaction with ammonia in solution forms an unstable black adduct which slowly converts to mercury(II) amidochloride, NH2HgCl, releasing mercury:
Hg2Cl2 + 2NH3 → ClHg—HgNH2 + NH4Cl
ClHg—HgNH2 → NH2HgCl + Hg
Mercury(I) chloride is highly toxic by ingestion and other routes of exposure. The symptoms include nausea, vomiting, abdominal pain, diarrhea and kidney damage.
Mercury(I) chloride, a colorless solid also known as the mineral calomel, is the compound with the formula Hg2Cl2, with
the connectivity Cl-Hg-Hg-Cl. It reacts with chlorine to form mercuric chloride, which resists further oxidation. Hg2Cl2 is
a linear molecule. Mercurous chloride forms through the reaction of elemental mercury and mercuric chloride.
Hg + HgCl2→Hg2Cl2
White, rhombic crystals or crystalline
powder; odorless. Stable in air but darkens on exposure to light.decomposed by alkalies. Insoluble in water, ether, alcohol,
and cold dilute acids.
Mercurous chloride forms tetrahedral white
crystals, and, unlike the mercuric salt,
is only very slightly soluble in water (about 2mg/L water
at 20°C).
Calomel is used as a laboratory reagent, as a fungicide, and as
a depolarizer in dry batteries.
This compound is used by the pharmaceutical
industry and is used also as a fungicide, as a poison, in fireworks, and to control maggots.
Dark green Bengal lights; calomel paper, mixed with gold in painting on porcelain; for calomel electrodes; as fungicide; in agriculture to control root maggots on cabbage and onions.
Mercurous chloride
is produced by exposing mercury metal to limited
amounts of chlorine gas, insufficient to form mercuric chloride
as the major product; it can also be prepared by precipitation
from mercurous nitrate solution.
ChEBI: Dimercury dichloride is a mercury coordination entity.
Odorless white solid. Sinks in water.
MERCUROUS CHLORIDE is incompatible with acetylene, ammonia, chlorine dioxide, azides, calcium (amalgam formation), sodium carbide, lithium, rubidium, copper .
Acute poisoning can result from inhaling dust concentrations of 1.2-8.5 mg/m 3 in air; symptoms include pain and tightness in chest, coughing, and difficulty in breathing. Compound is an irritant, cathartic, or purgat ive; rarely, ``calomel sickness,'' a benign reaction with fever and rash, appears after about 1 week; seldom causes systemic poisoning but may be fatal if retained to 30-40 mg/kg. Contact with eyes causes mild irritation.
An acute oral
dose in humans of 1 g HgCl2 may cause corrosive damage
to the GI tract; there is, however, little quantitative information
on dose–effect relationships during low-level
exposure to inorganic mercury. A dose of 2 g may be
expected to increase mortality greatly among victims of
the poison. Death from acute oral exposure is usually
caused by cardiovascular collapse and renal failure.
Ingestion of inorganic compounds may cause gastrointestinal
corrosion and irritation, such as vomiting, bloody diarrhea,
and stomach pains.
Calomel can generate reactive oxygen species and deplete
glutathione levels. Both genotoxic and nongenotoxic mechanisms
may contribute to renal carcinogenic effect of mercury.
Calomel decomposes gradually in the presence of sunlight.
It slowly decomposes to mercury and mercuric chloride under
aqueous conditions.
