Tin(II) chloride 2020855 217257993 2008-06-05T07:24:13Z CommonsDelinker 2304267 Replacing [[Image:SnCl2_Stephen_reduction.png]] with [[Image:SnCl2_Stephens_reduction.png]] (by [[commons:User:Siebrand|Siebrand]] because: Was in category "Duplicate", exact duplicate). {{Chembox new | Name = Tin(II) chloride | ImageFile = Tin(II) chloride.jpg <!-- | ImageSize = 200px --> | ImageName = Tin(II) chloride | IUPACName = Tin(II) chloride | OtherNames = Stannous chloride</br>Tin salt<br />Tin dichloride</br>Tin protochloride | Section1 = {{Chembox Identifiers | CASOther =<nowiki>[7772-99-8]</nowiki> (anhydrous)<br /><nowiki>[10025-69-1]</nowiki> (dihydrate) | RTECS = XP8700000 (anhydrous)<br />XP8850000 (dihydrate) }} | Section2 = {{Chembox Properties | Formula = SnCl<sub>2</sub> | MolarMass = 189.60 g/mol (anhydrous)<br />225.63 (dihydrate) | Appearance = White crystalline solid | Density = 3.95 g/cm³, anhydrous solid<br />2.71 g/cm³, dihydrate (15 °C) | Solubility = 83.9 g/100 ml (0 °C)<br />[[Hydrolysis|Hydrolyses]] in hot water | MeltingPt = 246 °C (519 K) | BoilingPt = 623 °C (896 K) }} | Section3 = {{Chembox Structure | MolShape = Bent (gas phase) | Coordination = [[Trigonal pyramidal]] (anhydrous)<br />Dihydrate also three-coordinate | CrystalStruct = Layer structure<br />(chains of SnCl<sub>3</sub> groups) }} | Section7 = {{Chembox Hazards | MainHazards = Corrosive | RPhrases = 22-34-37 | SPhrases = 26-36/37/39-45 }} | Section8 = {{Chembox Related | OtherAnions = [[Tin(II) fluoride]]<br />[[Tin(II) bromide]] | OtherCations = [[Tin(IV) chloride]]<br />[[Germanium dichloride]]<br />[[Lead(II) chloride]] }} }} '''Tin(II) chloride''' (stannous chloride) is a white [[crystal]]line solid with the formula {{Tin}}{{Chlorine}}<sub>2</sub>. It forms a stable dihydrate, but [[aqueous]] solutions tend to undergo [[hydrolysis]], particularly if hot. SnCl<sub>2</sub> is widely used as a [[Redox|reducing agent]] (in acid solution), and in [[Electrolysis|electrolytic]] baths for [[Electroplating|tin-plating]]. Tin(II) chloride should not be confused with the other chloride of tin; [[tin(IV) chloride]] or stannic chloride (SnCl<sub>4</sub>). ==Chemical structure== SnCl<sub>2</sub> has a [[lone pair]] of [[electron]]s, such that the molecule in the gas phase is bent. In the solid state, crystalline SnCl<sub>2</sub> 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. [[Image:SnCl2 structure.jpg|400px]] ==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: :SnCl<sub>2</sub>(aq) + H<sub>2</sub>O(l) ↔ Sn(OH)Cl(s) + HCl(aq) <!-- wrote out equation for consistency --> <!-- [[Image:SnCl2 hydrolysis.png|300px]] --> Therefore if clear solutions of tin(II) chloride are to be used, [[hydrochloric acid]] must be added in order to maintain the [[chemical equilibrium|equilibrium]] towards the left-hand side (using [[Le Chatelier's principle]]). Solutions of SnCl<sub>2</sub> are also unstable towards [[Redox|oxidation]] by the air: :6 SnCl<sub>2</sub>([[Aqueous|aq]]) + [[Oxygen|O<sub>2</sub>]]([[Gas|g]]) + 2 [[Water (molecule)|H<sub>2</sub>O]]([[Liquid|l]]) → 2 [[Tin(IV) chloride|SnCl<sub>4</sub>]](aq) + 4 Sn(OH)Cl([[Solid|s]]) This can be prevented by storing the solution over lumps of tin metal.<ref>{{cite book | author = H. Nechamkin | title = The Chemistry of the Elements | publisher = McGraw-Hill | location = New York | year = 1968}}</ref> 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<sub>2</sub>(aq) + 2 [[Iron(III) chloride|FeCl<sub>3</sub>]](aq) → [[Tin(IV) chloride|SnCl<sub>4</sub>]](aq) + 2 [[Iron(II) chloride|FeCl<sub>2</sub>]](aq) Solutions of tin(II) chloride can also serve simply as a source of Sn<sup>2+</sup> ions, which can form other tin(II) compounds via [[precipitation (chemistry)|precipitation]] reactions, for example brown (or black) tin(II) sulfide: :SnCl<sub>2</sub>(aq) + [[sodium sulfide|Na<sub>2</sub>S]](aq) → SnS(s) + 2 [[Sodium chloride|NaCl]](aq) If [[alkali]] is added to a solution of SnCl<sub>2</sub>, 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<sub>2</sub>(aq) + 2 [[sodium hydroxide|NaOH]](aq) → SnO·H<sub>2</sub>O(s) + 2 [[Sodium chloride|NaCl]](aq) :SnO·H<sub>2</sub>O(s) + NaOH(aq) → NaSn(OH)<sub>3</sub>(aq) Anhydrous SnCl<sub>2</sub> can be used to make a variety of interesting tin(II) compounds in non-aqueous solvents. For example, the [[lithium]] [[salt]] of [[BHT|4-methyl-2,6-di-tert-butylphenol]] reacts with SnCl<sub>2</sub> in [[Tetrahydrofuran|THF]] to give the yellow linear two-coordinate compound Sn(OAr)<sub>2</sub> (Ar = [[aryl]]).<ref>{{cite journal | author = B. Cetinkaya, I. Gumrukcu, M. F. Lappert, J. L. Atwood, R. D. Rogers and M. J. Zaworotko | title = Bivalent germanium, tin, and lead 2,6-di-tert-butylphenoxides and the crystal and molecular structures of M(OC6H2Me-4-But2-2,6)2 (M = Ge or Sn) | year = 1980 | journal = [[J. Am. Chem. Soc.]] | volume = 102 | issue = 6 | pages = 2088–2089 | doi = 10.1021/ja00526a054}}</ref> Tin(II) chloride also behaves as a [[Lewis acid]], forming [[complex (chemistry)|complexes]] with [[ligand]]s such as [[chloride]] ion, for example: :SnCl<sub>2</sub>(aq) + [[Caesium chloride|CsCl]](aq) → CsSnCl<sub>3</sub>(aq) Most of these complexes are [[pyramidal]], and since complexes such as SnCl<sub>3</sub> have a full [[Octet rule|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<sub>2</sub> + Fe(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)(CO)<sub>2</sub>HgCl → Fe(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)(CO)<sub>2</sub>SnCl<sub>3</sub> + {{Mercury}} SnCl<sub>2</sub> can be used to make a variety of such compounds containing metal-metal bonds, for example: :SnCl<sub>2</sub> + [[Dicobalt octacarbonyl|Co<sub>2</sub>(CO)<sub>8</sub>]] → (CO)<sub>4</sub>Co-(SnCl<sub>2</sub>)-Co(CO)<sub>4</sub> ==Preparation== Anhydrous SnCl<sub>2</sub> is prepared by the action of dry [[hydrogen chloride]] gas on [[tin]] metal. The dihydrate is made by a similar reaction, using [[hydrochloric acid]]: :[[Tin|Sn]]([[Solid|s]]) + 2 [[Hydrochloric acid|HCl]]([[Aqueous|aq]]) → SnCl<sub>2</sub>(aq) + [[Hydrogen|H<sub>2</sub>]]([[Gas|g]]) The water is then carefully evaporated from the acidic solution to produce crystals of SnCl<sub>2</sub>·2H<sub>2</sub>O. This dihydrate can be [[dehydration reaction|dehydrated]] to anhydrous using [[acetic anhydride]]. ==Uses== A solution of tin(II) chloride containing a little [[hydrochloric acid]] is used for the [[Electroplating|tin-plating]] of steel, in order to make [[tin can]]s. An electric potential is applied, and [[tin]] metal is formed at the [[Electrode|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 [[Redox|reducing agent]]. This is seen in its use for silvering mirrors, where [[silver]] metal is deposited on the glass: :Sn<sup>2+</sup>(aq) + 2 Ag<sup>+</sup> → Sn<sup>4+</sup>(aq) + 2 {{Silver}}(s) A related reduction was traditionally used as an analytical test for {{Mercury}}<sup>2+</sup>(aq). For example, if SnCl<sub>2</sub> is added [[Wiktionary|dropwise]] into a solution of [[mercury(II) chloride]], a white precipitate of [[mercury(I) chloride]] is first formed; as more SnCl<sub>2</sub> is added this turns black as metallic mercury is formed. Stannous chloride can be used to test for the presence of [[gold]] [[chemical compound|compounds]]. SnCl<sub>2</sub> turns bright [[violet (color)|purple]] in the presence of gold. This very reaction between stannous chloride and gold was used in episode #215:[[Clueless (House episode)|Clueless]] of ''[[House (TV series)|House]]'' to affirm gold poisoning.{{Fact|date=May 2007}} In [[organic chemistry]], SnCl<sub>2</sub> 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]].<ref>{{OrgSynth | title = &beta;-Naphthaldehyde | author = Williams, J. W. | collvol = 3 | collvolpages = 626 | year = 1955 | prep = cv3p0626}}</ref> The reaction usually works best with [[aromaticity|aromatic]] nitriles [[Aryl]]-CN. A related reaction (called the Sonn-Müller method) starts with an amide, which is treated with [[Phosphorus pentachloride|PCl<sub>5</sub>]] to form the imidoyl chloride salt. [[Image:SnCl2_Stephens_reduction.png|center|500px|The Stephen reduction]] The Stephen reduction is less used today, because it has been mostly superseded by [[diisobutylaluminium hydride]] reduction. Additionally, SnCl<sub>2</sub> is used to selectively reduce [[aromatic]] [[nitro]] groups to [[aniline]]s.<ref>{{cite journal | author = F. D. Bellamy and K. Ou | title = Selective reduction of aromatic nitro compounds with stannous chloride in non acidic and non aqueous medium | year = 1984 | journal = [[Tetrahedron Letters]] | volume = 25 | issue = 8 | pages = 839–842 | doi = 10.1016/S0040-4039(01)80041-1}}</ref> [[Image:SnCl2 Nitro Reduction Scheme.png|center|350px|Aromatic nitro group reduction using SnCl<sub>2</sub>]] SnCl<sub>2</sub> also reduces [[quinone]]s to [[hydroquinone]]s. Stannous chloride is also added as a [[food additive]] with [[E number]] '''E512''' to some canned and bottled foods, where it serves as a color-retention agent and [[antioxidant]]. ==In popular culture== This compound was featured in the ''[[House (TV series)|House, M.D.]]'' episode “[[Clueless (House episode)|Clueless]],” wherein it was used to detect the presence of [[Sodium aurothiomalate|gold sodium thiomalate]] used by the patient’s wife to poison him.{{Fact|date=May 2007}} ==References== * N. N. Greenwood, A. Earnshaw, ''Chemistry of the Elements'', 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997. * ''Handbook of Chemistry and Physics'', 71st edition, CRC Press, Ann Arbor, Michigan, 1990. * ''The Merck Index'', 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960. * A. F. Wells, '''Structural Inorganic Chemistry'', 5th ed., Oxford University Press, Oxford, UK, 1984. * J. March, ''Advanced Organic Chemistry'', 4th ed., p. 723, Wiley, New York, 1992. {{reflist}} [[Category:Metal halides]] [[Category:Chlorides]] [[Category:Tin compounds]] [[Category:Coordination compounds]] [[Category:Deliquescent substances]] [[cs:Chlorid cínatý]] [[de:Zinn(II)-chlorid]] [[fr:Chlorure d'étain II]] [[it:Cloruro stannoso]] [[hu:Ón(II)-klorid]] [[ja:塩化スズ(II)]] [[pl:Chlorek cyny(II)]] [[pt:Cloreto de estanho (II)]] [[ru:Хлорид олова(II)]] [[sr:Калај(II) хлорид]] [[sv:Tenn(II)klorid]] [[zh:氯化亞錫]]