Tin(II) chloride

Tin(II) chloride

Crystals of SnCl2·2 H2O on a watchglass.
Names
IUPAC names Tin(II) chloride Tin dichloride
Systematic IUPAC name Tin(II) chloride
Other names Stannous chloride Tin salt Tin protochloride
Identifiers
Jmol-3D images	Image
SMILES Cl[Sn]Cl
Properties
Chemical formula	SnCl2
Molar mass	189.60 g/mol (anhydrous) 225.63 g/mol (dihydrate)
Appearance	White crystalline solid
Odor	Odorless
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)
Solubility in water	83.9 g/100 ml (0 °C) Hydrolyses in hot water
Solubility	Soluble in acetone, diethyl ether, ethanol, hydrochloric acid, tetrahydrofuran Insoluble in ethyl acetate, toluene, xylene
Hazards
Safety data sheet	AcrosOrganics (anhydrous) LabChem (dihydrate)
Flash point	Non-flammable
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)
Related compounds
Related compounds	Tin(IV) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Tin(II) chloride, also known as stannous chloride, is a white crystalline solid with the formula SnCl₂. It has many uses, most notably in the tin-plating of steel, as well as many uses in organic chemistry, as catalyst and reducing agent.

Properties

Chemical

Stannous chloride forms a stable dihydrate salt when dry, but aqueous solutions tend to undergo hydrolysis, particularly if hot.

SnCl₂ (aq) + H₂O (l) ⇌ Sn(OH)Cl (s) + HCl (aq)

Because of this inconvenience, tin(II) chloride solutions tend to be made with dilute hydrochloric acid, rather than neutral water.

Solutions of SnCl₂ are also unstable if kept in air:

6 SnCl₂ (aq) + O₂ (g) + 2 H₂O (l) → 2 SnCl₄ (aq) + 4 Sn(OH)Cl (s)

If a base, like sodium hydroxide is added to a solution of SnCl₂, a white precipitate of hydrated tin(II) oxide forms initially, which 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)

Tin(II) chloride is also a reducing agent, capable of reducing silver ions to silver metal:

Sn²⁺ (aq) + 2 Ag⁺ → Sn⁴⁺ (aq) + 2 Ag (s)

This process is used for silvering mirrors, where silver metal is deposited on glass.

In organic chemistry, SnCl₂ is generally used as a reducing agent, like in the Stephen reduction, where a nitrile group is reduced (via an imidoyl chloride salt) to an imine which is easily hydrolyzed to an aldehyde. It can also be used to selectively reduce aromatic nitro groups to anilines.

Physical

Tin(II) chloride is an odorless, white crystalline solid compound. It is soluble in water, and can dissolve in less than its own mass of water without apparent decomposition. It is also soluble in other solvents such as ethanol, acetone and ethers, but it is insoluble in non-polar solvents like xylene.

Availability

Tin(II) chloride is sold by various chemical suppliers, most often in the dihydrate form.

Preparation

Tin(II) chloride dihydrate can be made by dissolving tin in concentrated hydrochloric acid. Lead-free solder can be used. The dihydrate crystals are obtained by cooling the solution in an excess hydrochloric acid.

Anhydrous SnCl₂ can be made by passing dry hydrogen chloride gas over tin metal. The reaction must be performed in a very dry environment.

Projects

• Silver mirrors
• Test for silver and other precious metals when recovering them from scrap electronics
• Reduce aromatic nitro groups to anilines
• Tin(IV) chloride synthesis

Handling

Safety

Tin(II) chloride is toxic if ingested and solutions contain hydrochloric acid which is corrosive.

Storage

Tin(II) chloride dihydrate should be stored in glass or plastic containers, away from any moisture.

Anhydrous tin(II) chloride should be stored in sealed containers, away from air and moisture.

Disposal

Tin(II) chloride should be converted to tin oxide and taken to waste disposal centers or recycled.

References

Relevant Sciencemadness threads

• Tin (II) Chloride
• Stannous Chloride - An Idea
• Tin and Zinc Chloride Synthesis