Cindyara Nayanda / T. Bioproses 2014Silva Amanat Taqwa / T. Bioproses 2014Chlorobenzene1OutlineIntroductionWhat is Chlorobenzene?Chlorobenzeneis anaromaticorganic compoundwith the chemical formula C6H5Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals.4Other Names...Physical and Chemical PropertiesUsageChlorobenzene is volatile (vapor pressure, 11.7 mm Hg) and slightly soluble in water (466.3 mg/L). The chemical may also adsorb moderately onto organic sediments. If released to moist soil, most of the chlorobenzene should volatilize to the atmosphereIf released to sandy soil, the chemical is mobile and is expected to leach into groundwater. It will biodegrade very slowly or not at all. Because of that, chlorobenzene will be good for making pesticides.Why is Chlorobenzene good for making DDT Pesticide? (Physical Properties)Miscible with nearly all organic solvents is an important properties for pesticides and insecticides.Chlorobenzene is miscible with nearly all organic solvents, even after being reacted with chloral(CCl3CHO) to form DDT....ContdProduction
Main ContentBenzene reacts with chlorine in the presence of a catalyst, replacing one of the hydrogen atoms on the ring by a chlorine atom.The reaction happens at room temperature. The catalyst is either aluminium chloride or iron.Reaction Mechanism of Producing ChlorobenzeneStrictly speaking iron isn't a catalyst, because it gets permanently changed during the reaction. It reacts with some of the chlorine to form iron(III) chloride, FeCl3.
This compound acts as the catalyst and behaves exactly like aluminium chloride, AlCl3, in this reaction.The reaction between benzene and chlorine in the presence of either aluminium chloride or iron gives chlorobenzene.
or, written more compactly:
Reaction Mechanism with aluminium chloride
Step1The non-polar and uncharged chlorine molecule is not a strong enough an electrophile to disrupt thepielectron system of the benzene ring. The aluminium chloride reacts with a chlorine molecule to form a positive chlorine ionCl+which is amuch strongerelectron pair acceptingelectrophileand a tetrachloroaluminate(III) ion (either this or an AlCl3-Cl2complex - details not needed for A level).
Step2An electron pair from the delocalisedpielectrons of the benzene ring forms a C-Cl bond with the electron pair accepting positive chlorine ion forming a highly unstable carbocation. It is very unstable because the stable electron arrangement of the benzene ring is partially broken to give a 'saturated' C (top right of ring).
The tetrachloroaluminate(III) ion, formed in step (1), abstracts a proton from the highly unstable intermediate carbocation to give the chloro-aromatic product, hydrogen chloride gas and reform the aluminium chloride catalyst.
ClosingThe Demand of Chlorobenzene in the WorldSafety and HazardChlorobenzene can be irritating to the eyes and respiratory tract of humans. In animals, the chemical is moderately irritating to the eyes and skin. Chlorobenzene has low to moderate systemic toxicity in animals, causing death at moderate to high oral doses and at high inhalation concentrations. Thank YouNIOSH Pocket Guide to Chemical Hazards. National Institute for Occupational Safety and Health(NIOSH)O'Neil, M.J. (ed.). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. Whitehouse Station, NJ: Merck and Co., Inc., 2006., p. 351Lewis, R.J. Sr.; Hawley's Condensed Chemical Dictionary 15th Edition. John Wiley & Sons, Inc. New York, NY 2007., p. 277Lide, D.R. CRC Handbook of Chemistry and Physics 88TH Edition 2007-2008. CRC Press, Taylor & Francis, Boca Raton, FL 2007, p. 3-92ITII. Toxic and Hazarous Industrial Chemicals Safety Manual. Tokyo, Japan: The International Technical Information Institute, 1982., p. 120U.S. Coast Guard, Department of Transportation. CHRIS - Hazardous Chemical Data. Volume II. Washington, D.C.: U.S. Government Printing Office, 1984-5.References