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Halogen derivatives of alkanes

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1 Halogen derivatives of alkanes
Pharmacy Student 1

2 Classification 1. Monohalogen Derivatives :
The halogen derivatives containing one halogen atom in a molecule General formula CnH2n+1X e.g. methyl Chloride CH3 Cl 2. Dihalogen Derivatives : The halogen derivatives containing two halogen atom in a molecule General formula CnH2n X2 e.g. Methylene Chloride CH2 Cl2 Ethylene Chloride CH2 Br – CH2 Br

3 3. Trihalogen Derivatives :
Classification 3. Trihalogen Derivatives : The halogen derivatives containing three halogen atom in a molecule e.g. Trichloro methane CH Cl3 4. Tetrahalogen Derivatives : The halogen derivatives containing two halogen atom in a molecule Carbon Tetrafluoride C F4 e.g. Carbon Tetrachloride C Cl4

4 1. Alkyl mono halides : General molecular formula Cn H2n+1 X
CH3 – Cl C2H5 – 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 H It can contain many C-X bonds Properties and some uses Fire-resistant solvents Refrigerants Pharmaceuticals 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-X 1o o o

7 Alkyl Halides Alkyl 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 atom C4H9Br → CH3CH2CH2CH2Br bromobutane CH3CHCH2CH bromobutane Br

10 2- Chain isomerism Depends on the type of the carbon chain;
Straight or Branched. CH3CHCH2 Br iso-butylbromide CH3 CH3CH2CH2CH2Br bromobutane

11 3- Optical Isomerism Present in alkyl halides of asymmetrical carbon atom CH CH3 H Cl Cl H CH2CH CH2CH3

12 4-Methods Of Preparation
1-From Alcohol: by the action of HX, SOCl2 (thionyl chloride) or PCl5 : C2H5-OH +HCl ZnCl C2H5Cl + H2O CH3(OH)CHCH3 + SOCl2 C5H5N CH3(Cl)CHCH3 + Isopropanol isopropyl chloride SO2 + HCl CH3OH + PCl CH3Cl + POCl3 + HCl phosphorous oxychloride

13 exothermic for Cl2 and Br2
2-From Alkene: CH3CH CH2 + HBr CH3CHBrCH3 isoppropyl bromide 3- Halogenation of Alkanes RH + X2  RX + HX explosive for F2 exothermic for Cl2 and Br2 endothermic for I2 6

14 Chlorination of Methane
carried out at high temperature (400 °C) CH Cl2  CH3Cl HCl CH3Cl + Cl2  CH2Cl HCl CH2Cl Cl2  CHCl HCl CHCl Cl2  CCl HCl

15 Physical Properties Alkyl 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.

16 Chemical Reaction

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 is replaced by a different group, e.g. R-XR-OH +XӨ In an elimination reaction, the elements of H-X are eliminated from R-X; the product is very often an alkene.

18 ALKYL HALIDES – Substitution reactions
This is a nucleophilic substitution or nucleophilic displacement reaction on which OH displaces Br. The C-Br bond is polar, and the carbon (⊕) is susceptible to attack by an anion or any other nucleophile. 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 + BrӨ The general reaction is: R-X + NuӨ  R-Nu + XӨ These are ionic reactions. There are two possible ionic mechanisms for nucleophilic substitution, 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.) and entails only one species, R-X. (b) R⊕+ NuӨ  R-Nu In the second step the carbocation and the nucleophile combine. This occurs rapidly. The overall reaction is R-X + NuӨ  R-Nu + XӨ The rate of the reaction = k[R-X]

21 Other Aspects of SN1 Reactions
The most important feature of SN1 reactions is the 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---XӨ The nucleophile and the alkyl halide combine to form a pentacoordinate transition state. This is the slow rate determining step (r.d.s); it entails two species, R-X and NuӨ . The dotted lines indicate partially formed or partially broken covalent bonds. ӨNu---R---XӨ  Nu-R + XӨ The pentacoordinate transition state dissociates to form the product, Nu-R, and the halide ion (the leaving group). 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 molecula collisions.

24 ALKYL HALIDES: The bimolecular (SN2) reaction
NuӨ + R-X ⇋ ӨNu---R---XӨ The nucleophile and the alkyl halide combine to form a pentacoordinate transition state. This is the slow rate determining step (r.d.s); it entails two species, R-X and NuӨ . The dotted lines indicate partially formed or partially broken covalent bonds. ӨNu---R---XӨ  Nu-R + XӨ The pentacoordinate transition state dissociates to form the product, Nu-R, and the halide ion (the leaving group). 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 molecular collisions.

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 CH3 CH3CH2CH2CH2−Cl <CH3CHCH2CH3 <CH3CCl Primary Cl Secondary CH3tertiary

26 Chemical Reaction Hydrolysis : With aqueous KOH ethyl chloride gives
CH3CH2CH2-Br KOH  CH3CH2CH2-OH KBr CH3CH2CH2-Br NH3  CH3CH2CH2-NH HBr R-X + aqueous alkali :OH-  ROH :X- alcohol R-X + alcoholic ammonia :NH3  R-NH2 + HX primary amine

27 R-X +alcohlic pot. Cyanide :CN-  R-CN + :X- alkyl cyanide (1) nitrile
R-CN + H2O RCOOH + NH (2) CH3Cl+KCN CH3CN +KCl CH3CN + H2O CH3COOH +NH3 CH3Cl + CH3COOAg  CH3COOCH3 + AgCl R’-X + RCOOAg RCOOR’ + AgX esters

28 R-X + sodium alkoxide :OR´-  R-O-R´ + :X- ether
C2H5Cl + C2H5ONa  C2H5 O C2H5 + NaCl R-X + sodium sulfide :SR´  R-SR´ + :X- thio-ether CH3Cl + Na2S  CH3-S-CH3 + NaCl Formation of Grignard’s reagent R-X + Mg/ether RMgX Grignard’s reagent C2H5 + Mg/ether C2H5MgI

29 Reaction with Grignard’s reagent:
R-X + R’MgX  R- R’ +MgX2 CH3Cl + CH3MgCl  CH3-CH3 + MgCl2 Wurtz reaction : In the presence of dry ether two moles of ethyl chloride reacts with sodium to give butane. R-X Na  R-R + 2 NaX Alkane 2 CH3Cl + 2 Na  CH3-CH3 + 2NaCl Reduction: R-X + H2/Pt  R-H + HX Alkane CH3Cl + H2/Pt  CH4 + HCl

30 Elimination : In the presence of alcoholic KOH
C2H5-Cl + alc KOH  C2H4 + HCl

31 Dihalogen derivatives
CnH2nX2

32 Di-Halogen Derivatives
Geminal Dihalides Vicinal Dihalides Alkyl ene dihalide Alkyl idene dihalide CH2 | CH2 CH2 | CH | CH3 | | | | Cl Cl Cl Cl Terminal Non - Terminal Cl H Ethylene dichloride propylenedichloride | | (1,2 - Dichloroethane) (1,2 - Dichloro propane) CH3 | C | Cl H3C | C | Cl | | Cl CH3 (Ethylidene dichloride) (Isopropylidene dichloride) 1,1 - Dichloroethane 2,2 - Dichloropropane

33 Di-Halogen Derivatives
ii) Preparation of Ethylene Dichloride a ) Addition of Chlorine to Ethylene CCl4 CH2 = CH2 + Cl — Cl(g) CH2 | CH2 | | Cl Cl Ethylene Ethylene dichloride 1,2-Dichloroethane

34 Di-Halogen Derivatives
ii) Preparation of Ethylene Dichloride b ) Action of Ethylene Glycol and PCl5 H2 C CH2 H2 C CH2 + 2 HCl + 2POCl3 OH OH Cl Cl Ethylene dichloride + Cl Cl — P Cl — P Cl 1,2-Dichloroethane Ethylene glycol 1, 2-Ethanediol

35 Di-Halogen Derivatives
iii) Preparation of Ethylidene Dichloride a ) Action of HCl and Acetylene addtn H—C  C—H + H+ — Cl— H — C C — H = + H+ — Cl— H Cl excess Vinyl chloride Acetylene Ethyne Ethenyl chloride H Cl H — C — C — H H Cl Ethylidene dichloride 1, 1-Dichloroethane

36 Di-Halogen Derivatives
iii) Preparation of Ethylidene Dichloride b ) Action of Acetaldehyde with PCl5 H H Cl Cl Cl | | Cl – P CH3 | C | + POCl3 CH3 | C | O + Cl Cl | Cl Acetaldehyde Ethanal Phosphorus Pentachoride Ethylidene Dichloride Phosphorus chloride

37 Di-Halogen Derivatives
iv) Distinction between Vicinal & Geminal Dihalides by Hydrolysis reaction H2C | CH2 Cl H2 C | CH2 boil + 2 KCl + K | OH Hydrolysis OH OH 1,2-Ethane diol (Glycol) (aq) Ethylene dichloride 1,2-Dichloroethane Hence aq alkali (NaOH /KOH) is used to distinguish between geminal and vicinal dihalides

38 Di-Halogen Derivatives
| H3C | C | Cl + K OH Boil | Hydrolysis Cl K OH – 2KCl Ethylidene dichloride 1,1-Dichloroethane C H3C | H H | – H2O OH H3C | C = O Acetaldehyde OH Ethanal unstable It gives aldehyde or ketone depending on the position of the halogen atom

39 Tri-Halogen Derivatives
A ] Chloroform ( CHCl3 ) ii) Oxidation of Ethyl alcohol H | Oxidation H3C | C | O | H + Cl2 H3C | C | O + 2HCl | | H H Ethyl alcohol Acetaldehyde Ethanol (Ethanal)

40 Tri-Halogen Derivatives
A ] Chloroform ( CHCl3 ) iii) Chlorination of Acetaldehyde Chlorination CH3CHO + 3Cl2 CCl3 | CHO + 3HCl Acetaldehyde Trichloroacetaldehyde Ethanol (Choral) iv) Hydrolysis of Choral H | O H CCl3 – C | O Hydrolysis + 2 CHCl3 + (HCOO)2Ca Ca H Chloroform | Calcium formate O H CCl3 – (Trichloromethane) C | O (Chloral) Calcium Hydroxide

41 Tri-Halogen Derivatives
1. Is Colorless , volatile , and Heavy liquid with sweet smell 2. Boiling point – 334 K 3. It is Insoluble in water but readily soluble in alcohol & ether 4. Is heavier than water 5. Produces unconsciousness when inhaled 6. Its vapour burns with a green edged flame 7. In liquid form , it is non-inflammable

42 Tri-Halogen Derivatives
i) Oxidation Chloroform in presence of sunlight gives highly Poisonous gas phosgene carbonyl chloride hence: It is always stored In dark or amber colored bottles Sunlight 2CHCl3 + O2 2COCl2 + 2HCl Air Chloroform Phosgene Trichloromethane Carbonyl chloride

43 Tri-Halogen Derivatives
ii) Action with Concentrated nitric acid Cl Cl Cl C | C | H + HO | NO2 | | NO2 Cl - H2O Con. Cl Cl Chloroform Nitro chloroform (chloropicrin) CCl3 – NO2 is used as insecticide, tear gas.

44 Tri-Halogen Derivatives
iv) Hydrolysis Cl OH Boil H | C | Cl + 3 K OH H | C | OH Unstable Hydrolysis (aq) Cl OH -3 KCl Chloroform Trichloromethane – H2O OH KOH H2O + HCOOK H | C = O Potassium Formate Formic acid Methanoic acid

45 Tri-Halogen Derivatives
v) Hofmann’s Carbylamine Reaction NH2 NC warm + CHCl3 + 3 KOH + 3KCl + 3H2O (alc) (C6H5NH2) (C6H5NC) Aniline Phenyl isocyanide Phenyl amine Phenyl Carbylamine

46 Alcohols R-O-H Classification CH3, 1o, 2o, 3o Nomenclature: Common names: “alkyl alcohol” IUPAC: parent = longest continuous carbon chain containing the –OH group. alkane drop -e, add –ol prefix locant for –OH (lower number for OH)

47 Alcohols classified as:
primary, 1o secondary, 2o tertiary, 3o according 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. CH3CH2OH CH3CCH2CH2CH3 OH CH3 CH3CHCH2CH2CH2CH3 OH

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. CH3CH2OH CH3C CH2CH2CH3 OH CH3 Ethanol CH3CHCH2CH2CH2CH3 OH 2-Methyl-2-pentanol 2-Hexanol

50 Classification CH3CH2CH2CH2CH2OH CH3CHCH2CH2CH3 H OH primary alcohol
secondary alcohol CH3CCH2CH2CH3 OH CH3 CH3CHCH2CH2CH3 OH secondary alcohol tertiary alcohol

51 Methods of Preparation
1-Reduction of Aldehydes/Ketones Hydrogenation

52 CH3CH=CH2 + H.HSO4 CH3-CH-CH3 HOH HSO4 CH3CHCH3 + H2SO4 OH
2- Hydrolysis of Alkali halide R-X + aqueous alkali :OH-  ROH :X- alcohol 3- Indirect hydration of Olefins CH3CH=CH2 + H.HSO4 CH3-CH-CH3 HOH HSO4 CH3CHCH3 + H2SO4 OH

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/Ketones Addition to Esters Addition 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 group C4H9OH → CH3CH2CH2CH2OH butanol CH3CHCH2CH butanol OH

58 2- Chain Isomerism Depends on the type of the carbon chain; Straight or Branched. CH3CHCH2 OH iso-butanol CH3 CH3CH2CH2CH2OH butanol

59 Optical Isomerism It present in alcohols which contain asymmetrical carbon atom. Where the molecule has two isomers called enantiomers, which they are optical active CH3CHCH2 OH iso-butanol CH3 CH3CH2CH2CH2OH butanol

60


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