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Tin(II) chloride

2007 Schools Wikipedia Selection. Related subjects: Chemical compounds

                               Tin(II) chloride
                               Tin(II) chloride
                                    General
           Systematic name                                      Tin(II) chloride
               Other names                         Stannous chloride
                                                                        Tin salt
                                                                  Tin dichloride
                                                               Tin protochloride
         Molecular formula                                               SnCl[2]
                Molar mass                              189.60 g/mol (anhydrous)
                                                              225.63 (dihydrate)
                Appearance                               White crystalline solid
                CAS number                               [7772-99-8] (anhydrous)
                                                        [10025-69-1] (dihydrate)
                                  Properties
         Density and phase                          3.95 g/cm^3, anhydrous solid
                                                  2.71 g/cm^3, dihydrate (15 °C)
       Solubility in water                                 83.9 g/100 ml (0 °C)
                                                         Hydrolyses in hot water
In ethanol, diethyl ether,
     acetic acid, acetone,
             ethyl acetate                                               soluble
             Melting point                                        246 °C (519 K)
             Boiling point                                        623 °C (896 K)
                                   Structure
           Molecular shape                                      Bent (gas phase)
     Coordination geometry                        Trigonal pyramidal (anhydrous)
                                                 Dihydrate also three-coordinate
         Crystal structure                                       Layer structure
                                                      (chains of SnCl[3] groups)
                                    Hazards
                      MSDS                                         External MSDS
              Main hazards                                             Corrosive
                  NFPA 704 Image:nfpa h2.png Image:nfpa f0.png Image:nfpa r0.png
             R/S statement                                           R: 22-34-37
                                                               S: 26-36/37/39-45
              RTECS number                                 XP8700000 (anhydrous)
                                                           XP8850000 (dihydrate)
                            Supplementary data page
    Structure & properties                                         n, ε[r], etc.
        Thermodynamic data                                       Phase behaviour
                                                              Solid, liquid, gas
             Spectral data                                       UV, IR, NMR, MS
                               Related compounds
              Other anions                                      Tin(II) fluoride
                                                                 Tin(II) bromide
             Other cations                        Tin(IV) chloride
                                                            Germanium dichloride
                                                               Lead(II) chloride
               Except where noted otherwise, data are given for
                          materials in their standard state (at 25°C, 100 kPa)
                                              Infobox disclaimer and references

   Tin(II) chloride (stannous chloride) is a white crystalline solid with
   the formula SnCl[2]. It forms a stable dihydrate, but aqueous solutions
   tend to undergo hydrolysis, particularly if hot. SnCl[2] 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 (SnCl[4]).

Structure

   SnCl[2] has a lone pair, such that the molecule in the gas phase is
   bent. In the solid state, crystalline SnCl[2] 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.

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:

   Therefore if clear solutions of tin(II) chloride are to be used,
   hydrochloric acid must be added in order to maintain the equilibrium
   towards the left-hand side (using Le Chatelier's principle). Solutions
   of SnCl[2] are also unstable towards oxidation by the air:

          6 SnCl[2]( aq) + O[2](g) + 2 Water (molecule)( l) → 2
          SnCl[4](aq) + 4 Sn(OH)Cl(Solid|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 silver and gold salts to the metal, and iron(III) salts
   to iron(II), for example:

          SnCl[2](aq) + 2 FeCl[3](aq) → SnCl[4](aq) + 2 FeCl[2](aq)

   Solutions of tin(II) chloride can also serve simply as a source of
   Sn^2+ ions, which can form other tin(II) compounds via precipitation
   reactions, for example brown (or black) tin(II) sulfide:

          SnCl[2](aq) + Na[2]S(aq) → SnS(s) + 2 NaCl(aq)

   If alkali is added to a solution of SnCl[2], a white precipitate of
   hydrated tin(II) oxide forms initially; this then dissolves in excess
   base to form a stannite salt such as sodium stannite:

          SnCl[2](aq) + 2 NaOH(aq) → SnO·H[2]O(s) + 2 NaCl(aq)

          SnO·H[2]O(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 lithium salt of
   4-methyl-2,6-di-tert-butylphenol reacts with SnCl[2] in THF to give the
   yellow linear two-coordinate compound Sn(OAr)[2] (Ar = aryl).^

   Tin(II) chloride also behaves as a Lewis acid, forming complexes with
   ligands such as chloride ion, for example:

          SnCl[2](aq) + CsCl(aq) → CsSnCl[3](aq)

   Most of these complexes are pyramidal, and since complexes such as
   SnCl[3] 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 :

          SnCl[2] + Fe(η^5-C[5]H[5])(CO)[2]HgCl →
          Fe(η^5-C[5]H[5])(CO)[2]SnCl[3] + Hg

   SnCl[2] can be used to make a variety of such compounds containing
   metal-metal bonds, for example:

          SnCl[2] + Co[2](CO)[8] → (CO)[4]Co-(SnCl[2])-Co(CO)[4]

Preparation

   Anhydrous SnCl[2] is prepared by the action of dry hydrogen chloride
   gas on tin metal. The dihydrate is made by a similar reaction, using
   hydrochloric acid:

          Sn( s) + 2 HCl( aq) → SnCl[2](aq) + H[2](g)

   The water is then carefully evaporated from the acidic solution to
   produce crystals of SnCl[2]·2H[2]O. This dihydrate can be dehydrated to
   anhydrous using acetic anhydride.

Uses

   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).

   Tin(II) chloride also finds wide use as a reducing agent. This is seen
   in its use for silvering mirrors, where silver metal is deposited on
   the glass:

          Sn^2+(aq) + 2 Ag^+ → Sn^4+(aq) + 2 Ag(s)

   A related reduction was traditionally used as an analytical test for
   Hg^2+(aq). For example, if SnCl[2] is added dropwise into a solution of
   mercury(II) chloride, a white precipitate of mercury(I) chloride 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 gold compounds. SnCl[2] turns bright purple in the presence
   of gold.

   This very reaction between stannous chloride and gold was used in
   episode #215: Clueless of House, M.D. to affirm gold poisoning.

   In organic chemistry, SnCl[2] is mainly used in the Stephen reduction,
   whereby a nitrile is reduced (via an imidoyl chloride salt) to an imine
   which is easily hydrolysed to an aldehyde.^ The reaction usually works
   best with aromatic nitriles Aryl-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

   The Stephen reduction is less used today, because it has been mostly
   superseded by diisobutylaluminium hydride reduction.

   Additionally, SnCl[2] is used to selectively reduce aromatic nitro
   groups to anilines.^
   Aromatic nitro group reduction using SnCl2

   SnCl[2] also reduces quinones to hydroquinones.

   Stannous chloride is also added as a food additive with E number E512
   to some canned and bottled foods, where it serves as a colour-retention
   agent and antioxidant.

   How to make Tin(II)-iodide:

   1.) Sn + 2HCl + CuSO4 --> SnCl2 + CuSO3 + H2 (This step takes about 2H)

   2.) Zn + I2 + H2O --> ZnI2 (Icebath)

   3.) SnCl2 + ZnI2 --> SnI2 + ZnCl2

   Tin(II)-iodide is an neon-Orange powder and Toxic!
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