Organic Halogen Compounds By Dr. Nahed Nasser

THE CHEMISTRY OF Organic halide compounds CONTENTS Structure and classes of halocompounds Nomenclature Physical properties Preparation of halocompounds Reactions of halocompounds Uses of haloalkanes

STRUCTURE OF HALOGENOCOMPOUNDS Halocompounds: contain the functional group C-X where X is a halogen (F,Cl,Br or I) The halogen atom may be attached to an aliphatic skeleton - alkyl group; Halogenoalkanes or to a benzene (aromatic) ring Classes of haloalkanes: Halogenoalkanes are classified according to the type of carbon atom bearing the halogen into: Primary alkyl halide CH3-X and R-CH2-X Secondary alkyl halide (R)2-CH-X Tertiary alkyl halide (R)3-C-X PRIMARY 1° SECONDARY 2° TERTIARY 3°

Nomeclature OF HALOGENOALKANES IUPAC names derived from original alkane with a prefix indicating halogens and their positions. While common names derived from the corresponding alkyl group followed by the name of halogen atom CH3-Cl CH3-CH2-Br (CH3)2-CH-F Common Methyl Chloride Ethyl bromide Isopropyl fluoride IUPAC Chloromethane Bromoethane 2-Fluoropropane Class 1° 1° 2° Common Cyclohexyl Iodide t-Butyl bromide Methylcyclopentyl chloride IUPAC Iodocyclohexane 2-Bromo-2- 1-Chloro-1-methyl methylpropane cyclopentane Class 2° 3 ° 3 °

Physical Properties Solubility : All organic halides are insoluble in water and soluble in common organic solvents. Boiling point : The boiling points increases with increasing in molecular weights. Therefore, the boiling points increases in the order F<Cl<Br<I. M.W bp / °C 1- Chloropropane 78.5 47 1- Bromopropane 124 71 Boiling point also increases for “straight” chain isomers. i.e. Greater branching = lower boiling points bp / °C 1-bromobutane CH3CH2CH2CH2Br 101 2-bromobutane CH3CH2CHBrCH3 91 2-bromo -2-methylpropane (CH3)3CBr 73

Preparation of Halogen Compounds 1- Direct halogenation of hydrocarbons a) Halogenation of alkanes b) Halogenation of alkenes

d) Halogenation of alkyl benzene and aromatic compounds c) Halogenation of alkynes

2- Halogenation of alcohols

Reactions of Organic Halides 1- Nucleophilic Subtitution Reactions Nu- = OH, OR, OCOR, NH2, RNH, SH, SR, RC=C, CN, acytilide anion, I-

2- Elimination Reactions: Alkyl halides can lose HX molecule to give an alkene. e.g.1 e.g.2 If the haloalkane is unsymmetrical (e.g. 2-bromobutane or 2-bromopentane) a mixture of isomeric alkene products is obtained. C3H7Br + NaOH(alc) ——> C3H6 + H2O + NaBr

3- Reactions of Grignared reagent a) Formation of Grignard reagent b) Reactions of Grignard reagent

4- Reduction of alkyl halides a- Reduction by Znic metal and acids or by metal hydrides b- Reduction by sodium metal (coupling reaction) c- Reduction using lithium dialkyl cuprate

USES OF HALOALKANES Synthetic The reactivity of the C-X bond means that halogenoalkanes play an important part in synthetic organic chemistry. The halogen can be replaced by a variety of groups via nucleophilic substitution. Polymers Many useful polymers are formed from halogeno hydrocarbons Monomer Polymer Repeating unit chloroethene poly(chloroethene) PVC - (CH2 - CHCl)n – USED FOR PACKAGING tetrafluoroethene poly(tetrafluoroethene) PTFE - (CF2 - CF2)n - USED FOR NON-STICK SURFACES Chlorofluorocarbons - CFC’s dichlorofluoromethane CHFCl2 refrigerant trichlorofluoromethane CF3Cl aerosol propellant, blowing agent bromochlorodifluoromethane CBrClF2 fire extinguishers CCl2FCClF2 dry cleaning solvent, degreasing agent All are/were chosen because of their LOW REACTIVITY, VOLATILITY, NON-TOXICITY