1. Synthesis of Anhydrous Metal Chlorides

2. Anhydrous metal halides are commonly used starting materials for many organometallic compounds i.e., in reactions with Grignard reagents or the formation of metallocene Many anhydrous metal chlorides, bromides and iodides are commercially available from Sigma-Aldrich or Strem Many of them are very expensive compared to their hydrated counterparts The quality often times not as high as advertised due to prolonged storage

3. Most metal halides are solids due to the fact that they form three-dimensional network structures. However, some of them are liquids: Trichloride: boron, nitrogen, phosphorous and arsenic Tetrachloride: carbon, silicon, germanium, tin, titanium and vanadium Pentachloride: antimony Most metal chlorides are contaminated by hydrates, oxychlorides or oxides as a result of hydrolysis and due to their Lewis acidity Example: PCl 3 (b.p.=74.5 o C) and POCl 3 (b.p.=105.3 o C) can be separated by fractionated distillation

4. Many alkali metal chlorides can be dehydrated by heating in vacuo Cobalt(II) chloride is the indicator in Drierite® Hydrates of metal ions with a high formal charge are acidic Example: Iron(III) chloride hexahydrate cannot be dehydrated by heating Formation of iron(III) hydroxide and hydrogen chloride  Anhydrous iron(II) halides can be obtained by the reaction of iron metal with the corresponding acid in methanol followed by the thermal decomposition of the solvate ([Fe(CH 3 OH) 6 ]X 2 )

5. Many metals can be reacted directly with chlorine at room temperature or elevated temperatures (synthesis reaction) Selenium reacts at room temperature to form Se 2 Cl 2 (reddish-brown liquid) and reacts further to form SeCl 4 (pale yellow solid) when heated Iron and aluminum metal react with chlorine to form FeCl 3 and AlCl 3, respectively A suspension of nickel metal in 1,2-dimethoxyethane reacts with chlorine yields anhydrous NiCl 2 and carcinogenic, chlorinated ethers

6. The reaction of some metals with hydrogen chloride yields anhydrous metal chlorides M + n HCl MCl n + n/2 H 2 MCl 2 : Cd, Fe(II), Mn(II), Sn(II), Zn MCl 3 : Dy, Gd, Pr, Sc, Sm (all III) Note that the metal chloride formed in the reaction is not in the highest oxidation state in many cases A similar approach can be used for bromides

7. Oxides of many metals are available as ores or are intermediates in metal processing i.e., roasting of sulfides Reduction-chlorination Carbon and chlorine: boron, titanium, chromium Carbon tetrachloride: scandium, cerium, samarium Usage of perchloroalkenes like perchloropropylene (PCP), perchlorobutadiene (PCB), and octachlorocyclopentene (OCP)

8. Example 1: Boron trichloride Step 1: Reduction of boron oxide with carbon powder leads to a black powder, B 4 C Step 2: Chlorination of this intermediate affords a mixture of BCl 3 (b.p. 12.5 o C) and CCl 4 (b.p. 76.6 o C) that can be separated using fractionated distillation.

9. Reflux with OCP (b.p. 285 o C) Most reactions employing CCl 4 as reagent are carried out in an autoclave under elevated temperatures. Careful: The bomb builds up a significant pressure due to the formation of carbon monoxide (CO) and phosgene (COCl 2 ), which are both highly toxic. The bomb has to be vented in a well-ventilated hood. Metal oxideProduct (time) Nb 2 O 5 NbCl 5 (5 min) Fe 2 O 3 FeCl 3 (15 min) TiO 2 TiCl 4 (30 h) V2O5V2O5 VOCl 3 (15 min), VCl 3 (6-8 h) WO 3 WOCl 4 (2 h) MoO 2 MoOCl 3 (15 min)

10. In these reactions, the water is chemically consumed in the reaction with thionyl chloride or a ketal Thionyl chloride: sulfur dioxide, hydrogen chloride Examples: NiCl 2, CoCl 2, CrCl 3 Dimethoxyketal: methanol and ketone i.e., acetone Tin(II) chloride (SnCl 2 * 2 H 2 O) can be dehydrated by the reaction with acetic acid anhydride

11. The direct chlorination of a metal at elevated temperatures usually leads to the highest oxidation state possible with chlorine as ligand Many lower oxidation state chlorides are not available by direct chlorination They are be obtained by reduction using different reducing agents like hydrogen, alkenes, carbonyls, metals, etc. or by co-proportion reactions with low oxidation states

12. Tungsten(VI) chloride is obtained by direct chlorination of tungsten metal Tungsten(V) chloride is obtained from the reduction of WCl 6 with hydrogen under mild conditions or by the reaction with aluminum metal at 475 o C or with C 2 Cl 4 Tungsten(IV) chloride is obtained from the reaction of tungsten metal with WCl 5 in a bomb reaction, the reaction of the hexachloride with tin, antimony or bismuth metal, or the syn-proportion reaction of tungsten(VI) chloride with tungsten hexacarbonyl in boiling chlorobenzene

13. Tungsten(II) chloride is obtained by reduction of various higher chlorides with hydrogen at temperatures between 450-500 o C (Note: at higher temperatures it disproportionates into WCl 4 and tungsten metal) Tungsten(III) chloride is obtained from the dichloride, which is reacted with chlorine gas at 100 o C Lower chlorides of tungsten like WCl 4 L 2 (L=THF, DME) or molybdenum MoCl 4 L 2 (L=Et 2 O, DME) can be obtained by reduction of WCl 6 or MoCl 5 using cyclopentene or allyltrimethylsilane The reaction of MoCl 5 with acetonitrile at room temperature affords MoCl 4 (CH 3 CN) 2, which can be reduced with tin metal to form MoCl 3 (CH 3 CN) 3

14. Metal carbonyl compounds can be regarded as metal atoms in an inert matrix Good starting material for many reactions i.e., formation Mo(IV) bromide, Mo(III) iodide or Mo(II) acetate, which exhibits a Mo-Mo quadruple bond The reaction of tungsten hexacarbonyl with phosphorus pentachloride in acetonitrile affords WCl 4 (CH 3 CN) 2 The reaction of molybdenum hexacarbonyl with iodine in tetrahydrofuran affords MoI 3 (OC 4 H 8 ) 3

15. Hydrated and anhydrous metal salts are often very different in color CompoundColor of HydrateColor of anhydride VCl 3 Green-gray (6)Purple-peach CrCl 3 Green (6)Pink MnCl 2 Pink (4)Pale pink FeCl 2 Light blue (4)White/pale brown FeCl 3 Brown (6)Black CoCl 2 Pink-red (6)Blue NiCl 2 Green (6)Yellow-brown CuCl 2 Blue-green (2)Yellow ZnCl 2 White (2)White