Tin(II) chloride, also known as stannous chloride, is a white crystalline solid with the formula SnCl2. It forms a stable dihydrate, but aqueous solutions tend to undergo hydrolysis, particularly if hot. SnCl2 is widely used as a reducing agent (in acid solution), and in electrolytic baths for tin-plating. Tin(II) chloride should not be confused with the other chloride of tin; tin(IV) chloride or stannic chloride (SnCl4).
3D model (JSmol)
|E number||E512 (acidity regulators, ...)|
|Molar mass||189.60 g/mol (anhydrous)|
225.63 g/mol (dihydrate)
|Appearance||White crystalline solid|
|Density||3.95 g/cm3 (anhydrous)|
2.71 g/cm3 (dihydrate)
|Melting point|| 247 °C (477 °F; 520 K) (anhydrous) |
37.7 °C (dihydrate)
|Boiling point||623 °C (1,153 °F; 896 K) (decomposes)|
|83.9 g/100 ml (0 °C)|
Hydrolyses in hot water
|Solubility||soluble in ethanol, acetone, ether, Tetrahydrofuran |
insoluble in xylene
(chains of SnCl3 groups)
|Trigonal pyramidal (anhydrous)|
Dihydrate also three-coordinate
|Bent (gas phase)|
|Main hazards||Irritant, dangerous for aquatic organisms|
|Safety data sheet||See: data page|
ICSC 0955 (anhydrous)
ICSC 0738 (dihydrate)
|NFPA 704 (fire diamond)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|700 mg/kg (rat, oral)|
10,000 mg/kg (rabbit, oral)
250 mg/kg (mouse, oral)
|Supplementary data page|
|Refractive index (n),|
Dielectric constant (εr), etc.
|UV, IR, NMR, MS|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
SnCl2 has a lone pair of electrons, such that the molecule in the gas phase is bent. In the solid state, crystalline SnCl2 forms chains linked via chloride 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.
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 acid (typically of the same or greater molarity as the stannous chloride) to maintain the equilibrium towards the left-hand side (using Le Chatelier's principle). Solutions of SnCl2 are also unstable towards oxidation by the air:
- 6 SnCl2 (aq) + O2 (g) + 2 H2O (l) → 2 SnCl4 (aq) + 4 Sn(OH)Cl (s)
- 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 Sn2+ ions, which can form other tin(II) compounds via precipitation reactions. For example, reaction with sodium sulfide produces the brown/black tin(II) sulfide:
- SnCl2 (aq) + Na2S (aq) → SnS (s) + 2 NaCl (aq)
- SnCl2(aq) + 2 NaOH (aq) → SnO·H2O (s) + 2 NaCl (aq)
- SnO·H2O (s) + NaOH (aq) → NaSn(OH)3 (aq)
Anhydrous SnCl2 can be used to make a variety of interesting tin(II) compounds in non-aqueous solvents. For example, the lithium salt of 4-methyl-2,6-di-tert-butylphenol reacts with SnCl2 in THF to give the yellow linear two-coordinate compound Sn(OAr)2 (Ar = aryl).
- SnCl2 (aq) + CsCl (aq) → CsSnCl3 (aq)
Most of these complexes are pyramidal, and since complexes such as SnCl3 have a full octet, there is little tendency to add more than one ligand. The lone pair 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 ferrocene-related product of the following reaction :
- SnCl2 + Fe(η5-C5H5)(CO)2HgCl → Fe(η5-C5H5)(CO)2SnCl3 + Hg
SnCl2 can be used to make a variety of such compounds containing metal-metal bonds. For example, the reaction with dicobalt octacarbonyl:
- SnCl2 + Co2(CO)8 → (CO)4Co-(SnCl2)-Co(CO)4
- Sn (s) + 2 HCl (aq) → SnCl2 (aq) + H
A solution of tin(II) chloride containing a little hydrochloric acid is used for the tin-plating of steel, in order to make tin cans. An electric potential is applied, and tin metal is formed at the cathode via electrolysis.
It is used as a catalyst in the production of the plastic polylactic acid (PLA).
It also finds a use as a catalyst between acetone and hydrogen peroxide to form the tetrameric form of acetone peroxide.
- Sn2+ (aq) + 2 Ag+ → Sn4+ (aq) + 2 Ag (s)
A related reduction was traditionally used as an analytical test for Hg2+(aq). For example, if SnCl2 is added dropwise into a solution of mercury(II) chloride, a white precipitate of mercury(I) chloride is first formed; as more SnCl2 is added this turns black as metallic mercury is formed. Stannous chloride can be used to test for the presence of gold compounds. SnCl2 turns bright purple in the presence of gold (see Purple of Cassius).
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.
The Stephen reduction is less used today, because it has been mostly superseded by diisobutylaluminium hydride reduction.
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