Tin chloride (stannous chloride) is a white
crystalA 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 solid with the formula
2. It forms a stable dihydrate, but aqueous solutions tend to undergo
hydrolysisHydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
, particularly if hot. SnCl
2 is widely used as a
reducing agentRedox reactions describe all chemical reactions in which atoms have their oxidation state changed....
(in acid solution), and in
electrolyticIn chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
baths for
tin-platingElectroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal...
. Tin(II) chloride should not be confused with the other chloride of tin;
tin(IV) chlorideTin chloride, also known as tin tetrachloride or stannic chloride is a chemical compound with the formula SnCl4.At room temperature it is a colourless liquid, which fumes on contact with air, giving a stinging odor...
or stannic chloride (SnCl
4).
Chemical structure
SnCl
2 has a
lone pairIn chemistry, a lone pair is a valence electron pair without bonding or sharing with other atoms. They are found in the outermost electron shell of an atom, so lone pairs are a subset of a molecule's valence electrons...
of
electronThe electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s, such that the molecule in the gas phase is bent. In the solid state, crystalline SnCl
2 forms chains linked via
chlorideThe chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
bridges as shown. The dihydrate is also three-coordinate, with one water coordinated on to the tin, and a second water coordinated to the first. The main part of the molecule stacks into double layers in the crystal lattice, with the "second" water sandwiched between the layers.
Chemical properties
Tin(II) chloride can dissolve in less than its own mass of water without apparent decomposition, but as the solution is diluted hydrolysis occurs to form an insoluble basic salt:
- SnCl2 (aq) + H2O (l) Sn(OH)Cl (s) + HCl (aq)
Therefore if clear solutions of tin(II) chloride are to be used, it must be dissolved in
hydrochloric acidHydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
(typically of the same or greater molarity as the stannous chloride) to maintain the
equilibriumIn a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...
towards the left-hand side (using
Le Chatelier's principleIn chemistry, Le Chatelier's principle, also called the Chatelier's principle, can be used to predict the effect of a change in conditions on a chemical equilibrium. The principle is named after Henry Louis Le Chatelier and sometimes Karl Ferdinand Braun who discovered it independently...
). Solutions of SnCl
2 are also unstable towards
oxidationRedox reactions describe all chemical reactions in which atoms have their oxidation state changed....
by the air:
- 6 SnCl2 (aq) + O2 (g) + 2 H2O (l) → 2 SnCl4 (aq) + 4 Sn(OH)Cl (s)
This can be prevented by storing the solution over lumps of tin metal.
There are many such cases where tin(II) chloride acts as a reducing agent, reducing
silverSilver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
and
goldGold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
salts to the metal, and iron(III) salts to iron(II), for example:
- SnCl2 (aq) + 2 FeCl3 (aq) → SnCl4 (aq) + 2 FeCl2 (aq)
It also reduces copper(II) to copper(I).
Solutions of tin(II) chloride can also serve simply as a source of Sn
2+ ions, which can form other tin(II) compounds via
precipitationPrecipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...
reactions. For example, reaction with
sodium sulfideSodium sulfide is the name used to refer to the chemical compound Na2S, but more commonly it refers to the hydrate Na2S·9H2O. Both are colorless water-soluble salts that give strongly alkaline solutions...
produces the brown/black
tin(II) sulfideTin sulfide is a chemical compound of tin and sulfur. The chemical formula is SnS. Its natural occurrence concerns herzenbergite, a rare mineral.-Synthesis:...
:
- SnCl2 (aq) + Na2S (aq) → SnS (s) + 2 NaCl (aq)
If
alkaliIn chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
is added to a solution of SnCl
2, a white precipitate of hydrated
tin(II) oxideTin oxide is a compound of tin and oxygen where tin has the oxidation state of +2. There are two forms, a stable blue-black form and a metastable red form.-Preparation and reactions:...
forms initially; this then dissolves in excess base to form a stannite salt such as sodium stannite:
- SnCl2(aq) + 2 NaOH (aq) → SnO·H2O (s) + 2 NaCl (aq)
- SnO·H2O (s) + NaOH (aq) → NaSn(OH)3 (aq)
Anhydrous SnCl
2 can be used to make a variety of interesting tin(II) compounds in non-aqueous solvents. For example, the
lithiumLithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
saltIn chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
of
4-methyl-2,6-di-tert-butylphenolButylated hydroxytoluene , also known as butylhydroxytoluene, is a lipophilic organic compound that is primarily used as an antioxidant food additive as well as an antioxidant additive in cosmetics, pharmaceuticals, jet fuels, rubber, petroleum products, electrical transformer oil, and embalming...
reacts with SnCl
2 in
THFTetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor...
to give the yellow linear two-coordinate compound Sn(OAr)
2 (Ar =
arylIn the context of organic molecules, aryl refers to any functional group or substituent derived from an aromatic ring, be it phenyl, naphthyl, thienyl, indolyl, etc....
).
Tin(II) chloride also behaves as a
Lewis acid]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
, forming
complexesIn chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...
with
ligandIn coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
s such as
chlorideThe chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
ion, for example:
- SnCl2 (aq) + CsCl (aq) → CsSnCl3 (aq)
Most of these complexes are pyramidal, and since complexes such as SnCl
3 have a full
octetThe octet rule is a chemical rule of thumb that states that atoms of low The octet rule is a chemical rule of thumb that states that atoms of low The octet rule is a chemical rule of thumb that states that atoms of low (The octet rule is a chemical rule of thumb that states that atoms of low (...
, there is little tendency to add more than one ligand. The
lone pairIn chemistry, a lone pair is a valence electron pair without bonding or sharing with other atoms. They are found in the outermost electron shell of an atom, so lone pairs are a subset of a molecule's valence electrons...
of electrons in such complexes is available for bonding, however, and therefore the complex itself can act as a Lewis base or ligand. This seen in the
ferroceneFerrocene is an organometallic compound with the formula Fe2. It is the prototypical metallocene, a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central metal atom. Such organometallic compounds are also known as sandwich compounds...
-related product of the following reaction :
- SnCl2 + Fe(η5-C5H5)(CO)2HgCl → Fe(η5-C5H5)(CO)2SnCl3 + Hg
SnCl
2 can be used to make a variety of such compounds containing metal-metal bonds. For example, the reaction with
dicobalt octacarbonylDicobalt octacarbonyl is the inorganic compound Co28. This metal carbonyl is a reagent and catalyst in organometallic chemistry and organic synthesis. It is used as a catalyst for hydroformylation, the conversion of alkenes to aldehydes....
:
- SnCl2 + Co2(CO)8 → (CO)4Co-(SnCl2)-Co(CO)4
Preparation
Anhydrous SnCl
2 is prepared by the action of dry
hydrogen chlorideThe compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
gas on
tinTin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
metal. The dihydrate is made by a similar reaction, using
hydrochloric acidHydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
:
- Sn (s) + 2 HCl (aq) → SnCl2 (aq) + (g)
The water is then carefully evaporated from the acidic solution to produce crystals of SnCl
2·2H
2O. This dihydrate can be
dehydratedIn chemistry and the biological sciences, a dehydration reaction is usually defined as a chemical reaction that involves the loss of water from the reacting molecule. Dehydration reactions are a subset of elimination reactions...
to anhydrous using
acetic anhydrideAcetic anhydride, or ethanoic anhydride, is the chemical compound with the formula 2O. Commonly abbreviated Ac2O, it is the simplest isolatable acid anhydride and is a widely used reagent in organic synthesis...
.
Uses
A solution of tin(II) chloride containing a little
hydrochloric acidHydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
is used for the
tin-platingElectroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal...
of steel, in order to make
tin canA tin can, tin , steel can, or a can, is a sealed container for the distribution or storage of goods, composed of thin metal. Many cans require opening by cutting the "end" open; others have removable covers. Cans hold diverse contents: foods, beverages, oil, chemicals, etc."Tin" cans are made...
s. An electric potential is applied, and
tinTin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
metal is formed at the
cathodeAn electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
via
electrolysisIn chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
.
Tin(II) chloride is used as a
mordantA mordant is a substance used to set dyes on fabrics or tissue sections by forming a coordination complex with the dye which then attaches to the fabric or tissue. It may be used for dyeing fabrics, or for intensifying stains in cell or tissue preparations. The term mordant comes from the Latin...
in textile
dyeingDyeing is the process of adding color to textile products like fibers, yarns, and fabrics. Dyeing is normally done in a special solution containing dyes and particular chemical material. After dyeing, dye molecules have uncut Chemical bond with fiber molecules. The temperature and time controlling...
because it gives brighter colours with some dyes e.g.
cochinealThe cochineal is a scale insect in the suborder Sternorrhyncha, from which the crimson-colour dye carmine is derived. A primarily sessile parasite native to tropical and subtropical South America and Mexico, this insect lives on cacti from the genus Opuntia, feeding on plant moisture and...
. This mordant has also been used alone to increase the weight of silk.
It is used as a catalyst in the production of the plastic
polylactic acidPoly or polylactide is a thermoplastic aliphatic polyester derived from renewable resources, such as corn starch , tapioca products or sugarcanes...
(PLA).
Tin(II) chloride also finds wide use as a
reducing agentRedox reactions describe all chemical reactions in which atoms have their oxidation state changed....
. This is seen in its use for silvering mirrors, where
silverSilver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
metal is deposited on the glass:
- Sn2+ (aq) + 2 Ag+ → Sn4+ (aq) + 2 Ag (s)
A related reduction was traditionally used as an analytical test for
2+(aq). For example, if SnCl
2 is added
dropwiseWiktionary is a multilingual, web-based project to create a free content dictionary, available in 158 languages...
into a solution of
mercury(II) chlorideMercury chloride or mercuric chloride , is the chemical compound with the formula HgCl2. This white crystalline solid is a laboratory reagent and a molecular compound. It is no longer used for medicinal purposes Mercury(II) chloride or mercuric chloride (formerly corrosive sublimate), is the...
, a white precipitate of
mercury(I) chlorideMercury chloride is the chemical compound with the formula Hg2Cl2. Also known as calomel or mercurous chloride, this dense white or yellowish-white, odorless solid is the principal example of a mercury compound...
is first formed; as more SnCl
2 is added this turns black as metallic mercury is formed. Stannous chloride can be used to test for the presence of
goldGold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
compoundsA 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...
. SnCl
2 turns bright
purpleAs the name of a color, violet is synonymous with a bluish purple, when the word "purple" is used in the common English language sense of any color between blue and red, not including either blue or red...
in the presence of gold (see
Purple of CassiusPurple of Cassius is a purple pigment formed by the reaction of gold salts with tin chloride. It has been used to impart glass with a red coloration , as well as to determine the presence of gold as a chemical test....
).
When mercury is analyzed using atomic absorption spectroscopy, a cold vapor method must be used, and tin (II) chloride is typically used as the reductant.
In
organic chemistryOrganic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...
, SnCl
2 is mainly used in the Stephen reduction, whereby a
nitrileA nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, one example being super glue .Inorganic compounds containing the -C≡N group are not called...
is reduced (via an imidoyl chloride salt) to an
imineAn imine is a functional group or chemical compound containing a carbon–nitrogen double bond, with the nitrogen attached to a hydrogen atom or an organic group. If this group is not a hydrogen atom, then the compound is known as a Schiff base...
which is easily hydrolysed to an
aldehydeAn aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
.
The reaction usually works best with
aromaticIn organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...
nitriles
ArylIn the context of organic molecules, aryl refers to any functional group or substituent derived from an aromatic ring, be it phenyl, naphthyl, thienyl, indolyl, etc....
-CN. A related reaction (called the Sonn-Müller method) starts with an amide, which is treated with PCl
5 to form the imidoyl chloride salt.
The Stephen reduction is less used today, because it has been mostly superseded by
diisobutylaluminium hydrideDiisobutylaluminium hydride, DIBAL, DIBAL-H or DIBAH, is a reducing agent with the formula 2, where i-Bu represents isobutyl...
reduction.
Additionally, SnCl
2 is used to selectively reduce aromatic
nitroNitro compounds are organic compounds that contain one or more nitro functional groups . They are often highly explosive, especially when the compound contains more than one nitro group and is impure. The nitro group is one of the most common explosophores used globally...
groups to
anilineAniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Being a precursor to many industrial chemicals, its main use is in the manufacture of precursors to polyurethane...
s.
SnCl
2 also reduces
quinoneA quinone is a class of organic compounds that are formally "derived from aromatic compounds [such as benzene or naphthalene] by conversion of an even number of –CH= groups into –C– groups with any necessary rearrangement of double bonds," resulting in "a fully conjugated cyclic dione structure."...
s to
hydroquinoneHydroquinone, also benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, having the chemical formula C6H42. Its chemical structure, shown in the table at right, has two hydroxyl groups bonded to a benzene ring in a para position. It is a white granular solid...
s.
Stannous chloride is also added as a
food additiveFood additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...
with
E numberE numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...
E512 to some canned and bottled foods, where it serves as a color-retention agent and
antioxidantAn antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
.
Finally, aqueous Stannous Chloride is used by many precious metals refining hobbyists as an indicator of
GoldGold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
and Platinum group metals in solutions.