hydrogen chloride (HCl) to give alkyl chlorides. For example, the industrial production of chloroethane proceeds by the reaction of ethylene with HCl: H2C=CH2 + HCl → CH3CH2Cl In oxychlorination, hydrogen chloride instead of the more expensive chlorine for the same purpose: CH2=CH2 + 2 HCl + O2 → ClCH2CH2Cl + H2O. Secondary and tertiary alcohols react with hydrogen chloride to give the corresponding chlorides. In the laboratory, the related reaction involving zinc chloride in concentrated hydrochloric acid: {R-OH} + HCl ->[\ce{ZnCl2}][\Delta] \overset{alkyl\ halide}{R-Cl} + H2O Called the Lucas reagent, this mixture was once used in qualitative organic analysis for classifying alcohols. Other chlorinating agents Alkyl chlorides are most easily prepared by treating alcohols with thionyl chloride (SOCl2) or phosphorus pentachloride (PCl5), but also commonly with sulfuryl chloride (SO2Cl2) and phosphorus trichloride (PCl3): ROH + SOCl2 → RCl + SO2 + HCl 3 ROH + PCl3 → 3 RCl + H3PO3 ROH + PCl5 → RCl + POCl3 + HCl In the laboratory, thionyl chloride is especially convenient, because the byproducts are gaseous. Alternatively, the Appel reaction can be used: Reactions Alkyl chlorides are versatile building blocks in organic chemistry. While alkyl bromides and iodides are more reactive, alkyl chlorides tend to be less expensive and more readily available. Alkyl chlorides readily undergo attack by nucleophiles. Heating alkyl halides with sodium hydroxide or water gives alcohols. Reaction with alkoxides or aryloxides give ethers in the Williamson ether synthesis; reaction with thiols give thioethers. Alkyl chlorides readily react with amines to give substituted amines. Alkyl chlorides are substituted by softer halides such as the iodide in the Finkelstein reaction. Reaction with other pseudohalides such as azide, cyanide, and thiocyanate are possible as well. In the presence of a strong base, alkyl chlorides undergo dehydrohalogenation to give alkenes or alkynes. Alkyl chlorides react with magnesium to give Grignard reagents, transforming an electrophilic compound into a nucleophilic compound. The Wurtz reaction reductively couples two alkyl halides to couple with sodium. Applications Vinyl chloride The largest application of organochlorine chemistry is the production of vinyl chloride. The annual production in 1985 was around 13 million tons, almost all of which was converted into polyvinylchloride (PVC). Chloromethanes Most low molecular weight chlorinated hydrocarbons such as chloroform, dichloromethane, dichloroethene, and trichloroethane are useful solvents. These solvents tend to be relatively non-polar; they are therefore immiscible with water and effective in cleaning applications such as degreasing and dry