Chromyl chloride 4613176 213267585 2008-05-18T16:18:03Z Benjah-bmm27 126395 fixing typo {{Chembox new | ImageFileL1 = Chromyl-chloride-2D.png | ImageFileR1 = Chromyl-chloride-3D-balls.png | IUPACName = Chromium(VI) dichloride dioxide | OtherNames = Chromyl chloride; chromium oxychloride; chromic acid chloride; Etard Reagent | Section1 = {{Chembox Identifiers | CASNo = 14977-61-8 | PubChem = | SMILES = | RTECS = GB5775000 }} | Section2 = {{Chembox Properties | Formula = CrO<sub>2</sub>Cl<sub>2</sub> | MolarMass = 154.9008 g/mol | Appearance = deep red fuming liquid | Density = 1.911 g/mL, liquid | MeltingPt = -96.5 °C | BoilingPt = 117 °C | Solubility = Decomposes }} | Section3 = {{Chembox Hazards | MainHazards = | FlashPt = | Autoignition = | RPhrases = {{R49}} {{R46}} {{R8}} {{R35}} {{R43}} {{R50/53}} | SPhrases = {{S53}} {{S45}} {{S60}} {{S61}} }} | Section8 = {{Chembox Related | OtherCpds = [[sulfuryl chloride|SO<sub>2</sub>Cl<sub>2</sub>]]; [[Vanadium oxytrichloride|VOCl<sub>3</sub>]]; MoO<sub>2</sub>Cl<sub>2</sub>; [[Tungsten dichloride dioxide|WO<sub>2</sub>Cl<sub>2</sub>]]}} }} '''Chromyl chloride''' is a chemical compound with the formula CrO<sub>2</sub>Cl<sub>2</sub>. This compound is an opaque dark blood-red liquid at room temperature and pressure. It is tetrahedral, somewhat like [[sulfuryl chloride|SO<sub>2</sub>Cl<sub>2</sub>]]. CrO<sub>2</sub>Cl<sub>2</sub> is similar to the most commonly encountered chromium(VI) derivative [[chromate]], [CrO<sub>4</sub>]<sup>2−</sup>; both are tetrahedral Cr(VI) compounds. They differ in physical properties, one is a liquid and the other forms salts. And they differ in oxidizing power as well. CrO<sub>2</sub>Cl<sub>2</sub> is a neutral molecular species. This means that in the liquid and solid forms, the individual CrO<sub>2</sub>Cl<sub>2</sub> entities interact purely via [[Van der Waals force|van der Waals bonding]]. Such weak bonding leads to low melting and boiling points, which is related to the fact that it is a distillable liquid. The diminished oxidizing power of [CrO<sub>4</sub>]<sup>2−</sup> vs. CrO<sub>2</sub>Cl<sub>2</sub> can be ascribed to its anionic nature, which diminishes its electron affinity. Also, chloride is a poorer pi-donor ligand than is oxide. ==Preparation== CrO<sub>2</sub>Cl<sub>2</sub> is prepared by the action of HCl on [[chromic acid|CrO<sub>3</sub>]]. [[potassium chromate|K<sub>2</sub>CrO<sub>4</sub>]] is treated with concentrated HCl followed by the addition of [[sulfuric acid|H<sub>2</sub>SO<sub>4</sub>]] as a dehydrating agent. The heavy CrO<sub>2</sub>Cl<sub>2</sub> separates as an immiscible, dense liquid. It then can be separated using a separatory funnel or by simple distillation, which is normally performed.<ref>Sisler, H. H. "Chromyl Chloride" Inorganic Synthesis McGraw-Hill: New York, 1946; Vol. 2, pp 205–207.</ref> CrO<sub>2</sub>Cl<sub>2</sub> can also be prepared using other chlorinating agents such as [[phosphorus pentachloride|PCl<sub>5</sub>]] and [[titanium tetrachloride|TiCl<sub>4</sub>]], or by addition of concentrated sulphuric acid to an intimate mixture of [[sodium chloride]] and [[potassium dichromate]], followed by gentle distillation.<ref>{{cite book |last= Moody |first= B.J. |title= Comparative Inorganic Chemistry |origyear= 1965 |edition= 1 |publisher= Edward Arnold |location= London |language= English |pages= 381 |chapter= 22 }}</ref> ::[[Potassium dichromate|K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub>]] + 4[[Sodium chloride|NaCl]] + 6[[Sulfuric acid|H<sub>2</sub>SO<sub>4</sub>]] → 2CrO<sub>2</sub>Cl<sub>2</sub> + 2[[Potassium bisulfate|KHSO<sub>4</sub>]] + 4[[Sodium bisulfate|NaHSO<sub>4]] +3[[Water|H<sub>2</sub>O]] ==Chemical properties== CrO<sub>2</sub>Cl<sub>2</sub> is highly electrophilic and an aggressive [[oxidizing agent]], e.g. causing spontaneous combustion when dripped onto [[Allotropes of sulfur|amorphous sulfur]]. Its electrophilicity is demonstrated by its rapid [[hydrolysis]] to give chromic and [[hydrochloric acid]]s: ::CrO<sub>2</sub>Cl<sub>2</sub> + 2H<sub>2</sub>O → H<sub>2</sub>CrO<sub>4</sub> + 2HCl Its high reactivity toward water is further indicated by the fact that CrO<sub>2</sub>Cl<sub>2</sub> fumes in moist air. ===Chromyl chloride test for chloride=== The chromyl chloride test entails heating a sample suspected of containing chloride is with potassium dichromate and concentrated sulfuric acid. If chloride is present, chromyl chloride is formed and red fumes of CrO<sub>2</sub>Cl<sub>2</sub> are evident. If there is no chloride present, no red fumes are produced. No analogous compounds are formed with [[fluorides]], [[bromide]]s, [[iodides]] and [[cyanides]], so this test is therefore specific for chlorides. The test is related to the synthesis shown above, exposure of CrO<sub>4</sub><sup>2−</sup> to HCl. ===Reagent for oxidation of alkenes=== Depending on solvent, CrO<sub>2</sub>Cl<sub>2</sub> oxidizes terminal [[alkene]]s to [[aldehyde]]s. Internal alkenes give alpha-chloroketones or related derivatives.<ref>{{OrgSynth | author = F. Freeman, R. H. DuBois, T. G. McLaughlin | title = Aldehydes by Oxidation of Terminal Olefins with Chromyl Chloride: 2,4,4-Trimethylpentanal | collvol = 6 | collvolpages = 1028 | prep = cv6p1028}}</ref> It will also attack [[benzyl]]ic [[methyl group]]s to give aldehydes via the [[Étard reaction]]. ===Compatible solvents=== CrO<sub>2</sub>Cl<sub>2</sub> is such an aggressive reagent that solvents must be chosen judiciously. In light of its high reactivity toward water, CrO<sub>2</sub>Cl<sub>2</sub> can be expected to decompose upon exposure to alcohols, similar to the behavior of other highly electrophilic chlorides such as VOCl<sub>3</sub>, TiCl<sub>4</sub>, and SO<sub>2</sub>Cl<sub>2</sub>. Typical for other electrophilic chlorides, chlorocarbons are excellent solvents, especially [[dichloromethane]] As a further practical complication, CrO<sub>2</sub>Cl<sub>2</sub> attacks most greases. ==Safety considerations== CrO<sub>2</sub>Cl<sub>2</sub> reacts with water to release [[hydrochloric acid|hydrochloric acid (HCl)]] and [[hexavalent chromium|hexavalent chromium (Cr<sup>VI</sup>)]] '''Acute''': HCl can be acutely lethal. Exposure to chromyl chloride vapour irritates the [[respiratory system]] and severely irritates the eyes, and the liquid burns the skin and eyes. Ingestion would cause severe internal damage.<ref name="Gray1966">{{cite book |editor= Prof CH Gray |title= Laboratory Handbook of Toxic Agents |origyear= 1966 |edition= 2 |publisher= [[Royal Institute of Chemistry]] |location= London |language= English |pages= 79 |chapter= IV }}</ref> '''Chronic''': Cr<sup>VI</sup> can produce [[chromosome abnormality|chromosomal aberrations]] and is a human [[carcinogen]] via inhalation.<ref>{{cite book | author = IARC | authorlink = International Agency for Research on Cancer | title = Volume 49: Chromium, Nickel, and Welding | origyear = 1990 | url = http://monographs.iarc.fr/ENG/Monographs/vol49/volume49.pdf | format = PDF | accessdate = 2008-03-26 | pages = 21-23 | date = 1999-11-05 | id = ISBN 92-832-1249-5}}</ref> Frequent exposure of the skin to chromyl chloride may result in [[Ulcer|ulceration]].<ref name="Gray1966" /> Thus, CrO<sub>2</sub>Cl<sub>2</sub> should be carefully handled in a well ventilated area. CrO<sub>2</sub>Cl<sub>2</sub> is so aggressive that its storage can be problematic as it attacks rubber and most plastics as well as greases. ==References== <references/> * F. Freeman "Chromyl Chloride" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289. [[Category:Chlorides]] [[Category:Chromium compounds]] [[Category:Oxidizing agents]] [[ar:كلوريد كروميل]] [[pt:Cloreto de cromilo]]