Presentation on theme: "Halogen derivatives of alkanes"— Presentation transcript:
1 Halogen derivatives of alkanes Pharmacy Student1
2 Classification 1. Monohalogen Derivatives : The halogen derivatives containing one halogen atom in a moleculeGeneral formula CnH2n+1Xe.g.methyl ChlorideCH3 Cl2. Dihalogen Derivatives :The halogen derivatives containing two halogen atom in a moleculeGeneral formula CnH2n X2e.g.Methylene ChlorideCH2 Cl2Ethylene ChlorideCH2 Br – CH2 Br
3 3. Trihalogen Derivatives : Classification3. Trihalogen Derivatives :The halogen derivatives containing three halogen atom in a moleculee.g.Trichloro methaneCH Cl34. Tetrahalogen Derivatives :The halogen derivatives containing two halogen atom in a moleculeCarbon TetrafluorideC F4e.g.Carbon TetrachlorideC Cl4
4 1. Alkyl mono halides : General molecular formula Cn H2n+1 X CH3 – ClC2H5 – Cl
5 What Is an Alkyl Halide X (F, Cl, Br, I) replaces H An organic compound containing at least one carbon-halogen bond (C-X)X (F, Cl, Br, I) replaces HIt can contain many C-X bondsProperties and some usesFire-resistant solventsRefrigerantsPharmaceuticals and precursors
6 Alkyl Halides R-X (X = F, Cl, Br, I) Classification of alkyl halides according to the class of the carbon that the halogen is attached to.RCH2-X R2CH-X R3C-X1o o o
7 Alkyl HalidesAlkyl halides are organic molecules containing a halogen atom bonded to an sp3 hybridized carbon atom.Alkyl halides are classified as primary (1°), secondary (2°), or tertiary (3°), depending on the number of carbons bonded to the carbon with the halogen atom.The halogen atom in halides is often denoted by the symbol “X”.
8 2-Naming Alkyl Halides Find longest chain, name it as parent chain (Contains double or triple bond if present)Number from end nearest any substituent (alkyl or halogen)
9 3-Isomerism in alkyl halides 1-Position isomerism:Compounds having the same molecular formula but differ in the position of the halogen atomC4H9Br → CH3CH2CH2CH2Br bromobutaneCH3CHCH2CH bromobutaneBr
10 2- Chain isomerism Depends on the type of the carbon chain; Straight or Branched.CH3CHCH2 Br iso-butylbromideCH3CH3CH2CH2CH2Br bromobutane
11 3- Optical IsomerismPresent in alkyl halides of asymmetrical carbon atomCH CH3H Cl Cl HCH2CH CH2CH3
12 4-Methods Of Preparation 1-From Alcohol: by the action of HX, SOCl2 (thionyl chloride) or PCl5 :C2H5-OH +HCl ZnCl C2H5Cl + H2OCH3(OH)CHCH3 + SOCl2 C5H5N CH3(Cl)CHCH3 +Isopropanol isopropyl chlorideSO2 + HClCH3OH + PCl CH3Cl + POCl3 + HClphosphorous oxychloride
13 exothermic for Cl2 and Br2 2-From Alkene:CH3CH CH2 + HBr CH3CHBrCH3isoppropyl bromide3- Halogenation of AlkanesRH + X2 RX + HXexplosive for F2exothermic for Cl2 and Br2endothermic for I26
14 Chlorination of Methane carried out at high temperature (400 °C)CH Cl2 CH3Cl HClCH3Cl + Cl2 CH2Cl HClCH2Cl Cl2 CHCl HClCHCl Cl2 CCl HCl
15 Physical PropertiesAlkyl halides are weak polar molecules. They exhibit dipole-dipole interactions because of their polar C—X bond, but because the rest of the molecule contains only C—C and C—H bonds, they are incapable of intermolecular hydrogen bonding.
17 REACTIONS OF ALKYL HALIDES Alkyl halides (R-X) undergo two types of reactions :substitution reactions and elimination reactions.In a substitution reaction, the X group in R-X isreplaced by a different group, e.g. R-XR-OH +XӨIn an elimination reaction, the elements of H-X areeliminated from R-X; the product is very often analkene.
18 ALKYL HALIDES – Substitution reactions This is a nucleophilic substitution or nucleophilicdisplacement reaction on which OH displaces Br.The C-Br bond is polar, and the carbon (⊕) issusceptible to attack by an anion or any othernucleophile.ӨOH is the nucleophile (species which “loves nuclei”or has an affinity for positive charges).BrӨ is the leaving group
19 ALKYL HALIDES – Substitution reactions CH3-CH2—Br + ӨOH CH3-CH2—OH + BrӨThe general reaction is:R-X + NuӨ R-Nu + XӨThese are ionic reactions.There are two possible ionic mechanisms for nucleophilicsubstitution, SN1 and SN2.S – substitution; N – nucleophilic;1 – unimolecular (the rate determining, r.d.s., step entails one molecule);2 – bimolecular (the rate determining step entails two species).
20 ALKYL HALIDES The unimolecular (SN1) reaction In the first step, R-X dissociates, forming a carbocation,R⊕, and the leaving group XӨ.This is a slow, rate determining step (r.d.s.) andentails only one species, R-X.(b) R⊕+ NuӨ R-NuIn the second step the carbocation and the nucleophilecombine. This occurs rapidly.The overall reaction is R-X + NuӨ R-Nu + XӨThe rate of the reaction = k[R-X]
21 Other Aspects of SN1 Reactions The most important feature of SN1 reactions isthe carbocation intermediate.A. Alkyl halides which form stable carbocations will undergo SN1 reactions.3o alkyl halides form 3o carbocations (stable) and will undergo SN1 reactions.
22 Alkyl halides which form stable carbocations will undergo SN1 reactions. 2o alkyl halides form 2o carbocations (fairly stable) and it undergo SN1 reactions.1o carbocations are unstable, 1o alkyl halides will not undergo SN1 reactions.Substitution reactions of 1o alkyl halides proceed via the SN2 mechanism.
23 ALKYL HALIDES: The bimolecular (SN2) reaction NuӨ + R-X ⇋ ӨNu---R---XӨThe nucleophile and the alkyl halide combine to form apentacoordinate transition state. This is the slow ratedetermining step (r.d.s); it entails two species, R-X andNuӨ . The dotted lines indicate partially formed orpartially broken covalent bonds.ӨNu---R---XӨ Nu-R + XӨThe pentacoordinate transition state dissociates to formthe product, Nu-R, and the halide ion (the leavinggroup).The rate of the reaction = k[R-X][NuӨ]The rate is dependent of the concentration of two species;higher concentrations increase the frequency of moleculacollisions.
24 ALKYL HALIDES: The bimolecular (SN2) reaction NuӨ + R-X ⇋ ӨNu---R---XӨThe nucleophile and the alkyl halide combine to form apentacoordinate transition state. This is the slow ratedetermining step (r.d.s); it entails two species, R-X andNuӨ . The dotted lines indicate partially formed orpartially broken covalent bonds.ӨNu---R---XӨ Nu-R + XӨThe pentacoordinate transition state dissociates to formthe product, Nu-R, and the halide ion (the leavinggroup).The rate of the reaction = k[R-X][NuӨ]The rate is dependent of the concentration of two species;higher concentrations increase the frequency of molecularcollisions.
25 • Reactivity of Alkyl Halide: Due to highly polar nature of Cδ+ − Cl δ bond ethyl chloride is highly reactive.Therefore alkyl halides are considered as synthetic tools in the hands of organic chemistry.Due to low bond dissociation energy, alkyl halides are more reactive.The order of reactivity of alkyl halides is as follows :R - Cl < R – Br < R – I CH3CH3CH2CH2CH2−Cl <CH3CHCH2CH3 <CH3CClPrimary Cl Secondary CH3tertiary
33 Di-Halogen Derivatives ii) Preparation of Ethylene Dichloridea ) Addition of Chlorine to EthyleneCCl4CH2=CH2+Cl — Cl(g)CH2|CH2||ClClEthyleneEthylene dichloride1,2-Dichloroethane
34 Di-Halogen Derivatives ii) Preparation of Ethylene Dichlorideb ) Action of Ethylene Glycol and PCl5H2 C—CH2H2 C—CH2+ 2 HCl+ 2POCl3————OHOHClClEthylene dichloride+ClCl — PCl — PCl1,2-DichloroethaneEthylene glycol1, 2-Ethanediol
35 Di-Halogen Derivatives iii) Preparation of Ethylidene Dichloridea ) Action of HCl and AcetyleneaddtnH—C C—H+H+ — Cl—H — C C — H=+ H+ — Cl———HClexcessVinyl chlorideAcetyleneEthyneEthenyl chlorideHCl——H — C — C — H——HClEthylidene dichloride1, 1-Dichloroethane
36 Di-Halogen Derivatives iii) Preparation of Ethylidene Dichlorideb ) Action of Acetaldehyde with PCl5HHClClCl||Cl – PCH3|C|+POCl3CH3|C|O+ClCl|ClAcetaldehydeEthanalPhosphorusPentachorideEthylideneDichloridePhosphoruschloride
37 Di-Halogen Derivatives iv) Distinction between Vicinal & Geminal Dihalidesby Hydrolysis reactionH2C|CH2ClH2 C|CH2boil+ 2 KCl+K|OHHydrolysisOHOH1,2-Ethane diol(Glycol)(aq)Ethylene dichloride1,2-DichloroethaneHence aq alkali (NaOH /KOH) is used to distinguish between geminal and vicinal dihalides
38 Di-Halogen Derivatives |H3C|C|Cl+K OHBoil|HydrolysisClK OH– 2KClEthylidene dichloride1,1-DichloroethaneCH3C|HH|– H2OOHH3C|C=OAcetaldehydeOHEthanalunstableIt gives aldehyde or ketone depending on the position of the halogen atom
39 Tri-Halogen Derivatives A ] Chloroform ( CHCl3 )ii) Oxidation of Ethyl alcoholH|OxidationH3C|C|O|H+Cl2H3C|C|O+2HCl||HHEthyl alcoholAcetaldehydeEthanol(Ethanal)
40 Tri-Halogen Derivatives A ] Chloroform ( CHCl3 )iii) Chlorination of AcetaldehydeChlorinationCH3CHO+3Cl2CCl3|CHO+3HClAcetaldehydeTrichloroacetaldehydeEthanol(Choral)iv) Hydrolysis of ChoralH|OHCCl3 –C|OHydrolysis+2 CHCl3+(HCOO)2CaCaHChloroform|Calcium formateOHCCl3 –(Trichloromethane)C|O(Chloral)Calcium Hydroxide
41 Tri-Halogen Derivatives 1. Is Colorless , volatile , and Heavy liquid with sweet smell2. Boiling point – 334 K3. It is Insoluble in water but readily soluble in alcohol & ether4. Is heavier than water5. Produces unconsciousness when inhaled6. Its vapour burns with a green edged flame7. In liquid form , it is non-inflammable
42 Tri-Halogen Derivatives i) OxidationChloroform in presence of sunlight gives highly Poisonous gas phosgene carbonyl chloride hence:It is always stored In dark or amber colored bottlesSunlight2CHCl3+O22COCl2+2HClAirChloroformPhosgeneTrichloromethaneCarbonyl chloride
43 Tri-Halogen Derivatives ii) Action with Concentrated nitric acidClClClC|C|H+HO|NO2||NO2Cl- H2OCon.ClClChloroformNitro chloroform (chloropicrin)CCl3 – NO2is used as insecticide, tear gas.
46 Alcohols R-O-HClassification CH3, 1o, 2o, 3oNomenclature:Common names: “alkyl alcohol”IUPAC: parent = longest continuous carbon chain containing the –OH group.alkane drop -e, add –olprefix locant for –OH (lower number for OH)
47 Alcohols classified as: primary, 1o secondary, 2o tertiary, 3oaccording to their "degree of substitution."Degree of substitution is determined by counting the number of carbon atoms directly attached to the carbon that bears the hydroxyl group.
48 Substitutive Nomenclature of Alcohols Name as "alkanols." Replace -e ending of alkane name by -ol.Number chain in direction that gives lowest number to the carbon that bears the —OH group.CH3CH2OHCH3CCH2CH2CH3OHCH3CH3CHCH2CH2CH2CH3OH
49 Substitutive Nomenclature of Alcohols Name as "alkanols." Replace -e ending of alkane name by -ol.Number chain in direction that gives lowest number to the carbon that bears the —OH group.CH3CH2OHCH3C CH2CH2CH3OHCH3EthanolCH3CHCH2CH2CH2CH3OH2-Methyl-2-pentanol2-Hexanol
53 Reduction of Aldehydes/Ketones Hydride Reductions
54 Reduction of Carboxylic Acids and Esters Lithium Aluminum Hydride Reduction
55 Grignard Addition Reactions Addition to Aldehydes/KetonesAddition to EstersAddition to Epoxides
56 Grignard Additions to Esters Formation of secondary and tertiary alcohols
57 Properties of Alcohol 1-Position isomerism: Compounds having the same molecular formula but differ in the position of the functional group OH groupC4H9OH → CH3CH2CH2CH2OH butanolCH3CHCH2CH butanolOH
58 2- Chain IsomerismDepends on the type of the carbon chain;Straight or Branched.CH3CHCH2 OH iso-butanolCH3CH3CH2CH2CH2OH butanol
59 Optical IsomerismIt present in alcohols which contain asymmetrical carbon atom.Where the molecule has two isomers called enantiomers, which they are optical activeCH3CHCH2 OH iso-butanolCH3CH3CH2CH2CH2OH butanol