Bismuth chloride (or butter of bismuth) is an
inorganic compound
An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bondsthat is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''.
Inorgan ...
with the chemical formula BiCl
3. It is a covalent compound and is the common source of the Bi
3+ ion. In the gas phase and in the crystal, the species adopts a pyramidal structure, in accord with
VSEPR theory
Valence shell electron pair repulsion (VSEPR) theory ( , ) is a conceptual model, model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. It is also named the Gill ...
.
Preparation
Bismuth chloride can be synthesized directly by passing
chlorine
Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
over
bismuth
Bismuth is a chemical element; it has symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs nat ...
.
:2 Bi + 3 Cl
2 → 2 BiCl
3
or by dissolving bismuth metal in
aqua regia
Aqua regia (; from Latin, "regal water" or "royal water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar concentration, molar ratio of 1:3. Aqua regia is a fuming liquid. Freshly prepared aqua regia is colorless, but i ...
, evaporating the mixture to give BiCl
3·2H
2O, which can be distilled to form the anhydrous trichloride.
Alternatively, it may be prepared by adding
hydrochloric acid
Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
to
bismuth oxide and evaporating the solution.
:Bi
2O
3 + 6 HCl → 2 BiCl
3 + 3 H
2O
Also, the compound can be prepared by dissolving bismuth in concentrated
nitric acid
Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
and then adding solid
sodium chloride
Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...
into this solution.
:Bi + 6 HNO
3 → Bi(NO
3)
3 + 3 H
2O + 3 NO
2
:Bi(NO
3)
3 + 3 NaCl → BiCl
3 + 3 NaNO
3
Structure
In the gas phase BiCl
3 is pyramidal with a Cl–Bi–Cl angle of 97.5° and a bond length of 242 pm. In the solid state, each Bi atom has three near neighbors at 250 pm, two at 324 pm and three at a mean of 336 pm,
[Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition, pp. 879–884, Oxford Science Publications, ] the image above highlights the three closest neighbours. This structure is similar to that of
AsCl3, AsBr
3,
SbCl3 and SbBr
3.
Chemistry
Bismuth chloride is
hydrolyzed
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysi ...
readily to
bismuth oxychloride, BiOCl:
:(aq) + (aq) + (l) ⇌ BiOCl (s) + 2 (aq)
This reaction can be reversed by adding an acid, such as
hydrochloric acid
Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
.
Reaction of solid BiCl
3 with water vapour below 50 °C has been shown to produce the intermediate monohydrate, BiCl
3·H
2O.
Bismuth chloride is an oxidizing agent, being readily reduced to metallic bismuth by reducing agents.
Chloro complexes
In contrast to the usual expectation by consistency with periodic trends, BiCl
3 is a
Lewis acid
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any ...
, forming a variety of chloro complexes such as
iCl6sup>3− that strongly violates the
octet rule
The octet rule is a chemical rule of thumb that reflects the theory that main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. The ru ...
. Furthermore, the octahedral structure of this
coordination complex
A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...
does not follow the predictions of VSEPR theory, since the
lone pair
In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC ''Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lone ...
on bismuth is unexpectedly stereochemically inactive. The dianionic complex
iCl5sup>2− does however adopt the expected square pyramidal structure.
Organic catalysis
Bismuth chloride is used as a
catalyst
Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
in
organic synthesis
Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...
. In particular, it catalyzes the
Michael reaction and the
Mukaiyama aldol reaction. The addition of other metal
iodides increases its catalytic activity.
References
{{DEFAULTSORT:Bismuth Chloride
Bismuth compounds
Chlorides
Metal halides