Presentation on theme: "Pharmacy Student. ClassificationClassification 1. Monohalogen Derivatives : The halogen derivatives containing one halogen atom in a molecule General."— Presentation transcript:
ClassificationClassification 1. Monohalogen Derivatives : The halogen derivatives containing one halogen atom in a molecule General formula C n H 2n+1 X e.g. methyl Chloride CH 3 Cl CH 3 Cl 2. Dihalogen Derivatives : The halogen derivatives containing two halogen atom in a molecule General formula CnH2n X2 e.g. Methylene Chloride CH 2 Cl 2 CH 2 Cl 2 Ethylene Chloride CH 2 Br – CH 2 Br CH 2 Br – CH 2 Br
ClassificationClassification 3. Trihalogen Derivatives : The halogen derivatives containing three halogen atom in a molecule e.g. Trichloro methane CH Cl 3 4. Tetrahalogen Derivatives : The halogen derivatives containing two halogen atom in a molecule e.g. Carbon Tetrachloride C Cl 4 Carbon Tetrafluoride C F4C F4C F4C F4
1. Alkyl mono halides : General molecular formula Cn H 2n+1 X CH3 – Cl C2H5 – Cl
5 What Is an Alkyl Halide 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
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. RCH 2 -XR 2 CH-XR 3 C-X 1 o 2 o 3 o
7 Alkyl halides are organic molecules containing a halogen atom bonded to an sp 3 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”. Alkyl Halides
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)
3-Isomerism in alkyl halides 1-Position isomerism: Compounds having the same molecular formula but differ in the position of the halogen atom C 4 H 9 Br → CH 3 CH 2 CH 2 CH 2 Br 1-bromobutane CH 3 CHCH 2 CH 3 2-bromobutane Br
2- Chain isomerism Depends on the type of the carbon chain; Straight or Branched. CH 3 CHCH 2 Br iso-butylbromide CH 3 CH 3 CH 2 CH 2 CH 2 Br 1-bromobutane
3- Optical Isomerism Present in alkyl halides of asymmetrical carbon atom CH3 CH3 H Cl Cl H CH2CH3 CH2CH3
4-Methods Of Preparation 1-From Alcohol: by the action of HX, SOCl2 (thionyl chloride) or PCl5 : C2H5-OH +HCl ZnCl2 C2H5Cl + H2O CH3(OH)CHCH3 + SOCl2 C5H5N CH3(Cl)CHCH3 + Isopropanol isopropyl chloride SO2 + HCl CH3OH + PCl5 CH3Cl + POCl3 + HCl phosphorous oxychloride
2-From Alkene: CH3CH CH2 + HBr CH3CHBrCH3 isoppropyl bromide isoppropyl bromide Halogenation of Alkanes RH + X 2 RX + HX RH + X 2 RX + HX explosive for F 2 exothermic for Cl 2 and Br 2 endothermic for I 2
15 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. Physical Properties
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 +X Ө 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 nucleophilic substitution 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 nucleophile. Ө OH is the nucleophile (species which “loves nuclei” or has an affinity for positive charges). Br Ө is the leaving group
19 ALKYL HALIDES – Substitution reactions CH 3 -CH 2 —Br + Ө OH CH 3 -CH 2 —OH + Br Ө The general reaction is: R-X + Nu Ө R-Nu + X Ө These are ionic reactions. There are two possible ionic mechanisms for nucleophilic substitution, S N 1 and S N 2. 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 (S N 1) reaction (a) In the first step, R-X dissociates, forming a carbocation, R ⊕, and the leaving group X Ө. This is a slow, rate determining step (r.d.s.) and entails only one species, R-X. (b) R ⊕ + Nu Ө R-Nu In the second step the carbocation and the nucleophile combine. This occurs rapidly. The overall reaction is R-X + Nu Ө R-Nu + X Ө The rate of the reaction = k[R-X]
Other Aspects of S N 1 Reactions The most important feature of S N 1 reactions is the carbocation intermediate. A.Alkyl halides which form stable carbocations will undergo S N 1 reactions. 3 o alkyl halides form 3 o carbocations (stable) and will undergo S N 1 reactions.
Alkyl halides which form stable carbocations will undergo S N 1 reactions. 2 o alkyl halides form 2 o carbocations (fairly stable) and it undergo S N 1 reactions. 1 o carbocations are unstable, 1 o alkyl halides will not undergo S N 1 reactions. Substitution reactions of 1 o alkyl halides proceed via the S N 2 mechanism.
ALKYL HALIDES: The bimolecular (S N 2) reaction (a)Nu Ө + R-X ⇋ Ө Nu---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 Nu Ө. The dotted lines indicate partially formed or partially broken covalent bonds. (b) Ө Nu---R---X Ө Nu-R + X Ө 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][Nu Ө ] The rate is dependent of the concentration of two species; higher concentrations increase the frequency of molecula collisions.
24 ALKYL HALIDES: The bimolecular (S N 2) reaction (a) Nu Ө + R-X ⇋ Ө Nu---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 Nu Ө. The dotted lines indicate partially formed or partially broken covalent bonds. (b) Ө Nu---R---X Ө Nu-R + X Ө 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][Nu Ө ] The rate is dependent of the concentration of two species; higher concentrations increase the frequency of molecular collisions.
Reactivity of Alkyl Halide: Due to highly polar nature of C δ+ − 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
Di-Halogen Derivatives ii) Preparation of Ethylene Dichloride a ) Addition of Chlorine to Ethylene CH 2 = + Cl — Cl (g) CH 2 CCl 4 | CH 2 Cl Ethylene dichloride 1,2-Dichloroethane Ethylene | Cl |
Di-Halogen Derivatives ii) Preparation of Ethylene Dichloride b ) Action of Ethylene Glycol and PCl5 + Cl — P Cl Cl — P H 2 C—CH 2 —— OH + 2 HCl+ 2POCl 3 H 2 C—CH 2 —— Cl Ethylene glycol 1, 2-Ethanediol Ethylene dichloride 1,2-Dichloroethane
Di-Halogen Derivatives iii) Preparation of Ethylidene Dichloride a ) Action of HCl and Acetylene H—C C—H + H + — Cl — addt n Acetylene Vinyl chloride Ethyne Ethenyl chloride Ethylidene dichloride 1, 1-Dichloroethane H — C C — H — H — Cl = + H + — Cl — H — C — C — H —— HCl H —— excess
Di-Halogen Derivatives iii) Preparation of Ethylidene Dichloride b ) Action of Acetaldehyde with PCl5 + Cl – P Cl H + POCl 3 Acetaldehyde Ethanal Phosphorus Pentachoride Ethylidene Dichloride Phosphorus chloride | C | H | | O | C | | | Cl CH 3
Di-Halogen Derivatives iv) Distinction between Vicinal & Geminal Dihalides by Hydrolysis reaction by Hydrolysis reaction H2CH2C | CH 2 || Cl + KK || OH + 2 KCl H 2 C | CH 2 || OH boil Hydrolysis Ethylene dichloride 1,2-Dichloroethane (aq) 1,2-Ethane diol (Glycol) Hence aq alkali (NaOH /KOH) is used to distinguish between geminal and vicinal dihalides
Di-Halogen Derivatives Boil Hydrolysis H3CH3C | | C H | Cl | +K OH CH3CH3C | H | | | OH – H 2 O H3CH3C | H | C = O Ethylidene dichloride 1,1-Dichloroethane unstable Acetaldehyde Ethanal – 2KCl It gives aldehyde or ketone depending on the position of the halogen atom
Tri-Halogen Derivatives A ] Chloroform ( CHCl 3 ) ii) Oxidation of Ethyl alcohol H Oxidation Ethyl alcohol Ethanol Acetaldehyde (Ethanal) | H3CH3C | C | H | O | H+Cl 2 H3CH3C | C | H | | O +2HCl
Tri-Halogen Derivatives A ] Chloroform ( CHCl 3 ) iii) Chlorination of Acetaldehyde CH 3 CHO + 3Cl 2 Chlorination CCl 3 | CHO+ 3HCl Acetaldehyde Ethanol Trichloroacetaldehyde (Choral) iv) Hydrolysis of Choral Ca O O H H + CCl 3 – H | C | | O H | C | | O Hydrolysis 2 CHCl 3 +(HCOO) 2 Ca Calcium Hydroxide (Chloral) Chloroform (Trichloromethane) Calcium formate
Tri-Halogen Derivative s 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
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 2CHCl 3 + O2O2O2O2 Sunlight 2COCl 2 +2HCl Chloroform Phosgene Trichloromethane Carbonyl chloride Air
Tri-Halogen Derivatives ii) Action with Concentrated nitric acid Cl | C | NO 2 Cl | C | NO 2 Cl - H 2 O Chloroform Nitro chloroform (chloropicrin) CCl 3 – NO 2 is used as insecticide, tear gas. H+ HO | Con.
Tri-Halogen Derivatives iv) Hydrolysis Cl H | C | + 3 K OH Boil Hydrolysis H | C OH | (aq) Chloroform Trichloromethane Unstable – H 2 O H2OH2O+ HCOOK KOH H C | OH = O Potassium Formate Formic acid Methanoic acid -3 KCl
AlcoholsR-O-H Classification CH 3, 1 o, 2 o, 3 o 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)
Alcohols classified as: primary, 1 o secondary, 2 o tertiary, 3 o 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.
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. Substitutive Nomenclature of Alcohols CH 3 CH 2 OH CH 3 CHCH 2 CH 2 CH 2 CH 3 OH CH 3 CCH 2 CH 2 CH 3 OH CH 3
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. Substitutive Nomenclature of Alcohols CH 3 CH 2 OH CH 3 CHCH 2 CH 2 CH 2 CH 3 OH CH 3 C CH 2 CH 2 CH 3 OH CH 3 Ethanol 2-Hexanol 2-Methyl-2-pentanol
1-Reduction of Aldehydes/Ketones Hydrogenation Hydrogenation Methods of Preparation
R-X + aqueous alkali :OH - ROH + :X - alcohol 2- Hydrolysis of Alkali hal ide 3- Indirect hydration of Olefins CH3CH=CH2 + H.HSO4 CH3-CH-CH3 HOH HSO4 CH3CHCH3 + H2SO4 OH
Reduction of Aldehydes/Ketones Hydride Reductions
Reduction of Carboxylic Acids and Esters Lithium Aluminum Hydride Reduction
Grignard Addition Reactions Addition to Aldehydes/Ketones Addition to Aldehydes/Ketones Addition to Esters Addition to Esters Addition to Epoxides Addition to Epoxides
Grignard Additions to Esters Formation of secondary and tertiary alcohols
Properties of Alcohol 1-Position isomerism: Compounds having the same molecular formula but differ in the position of the functional group OH group C 4 H 9 OH → CH 3 CH 2 CH 2 CH 2 OH 1-butanol CH 3 CHCH 2 CH 3 2-butanol OH
2- Chain Isomerism Depends on the type of the carbon chain; Straight or Branched. CH 3 CHCH 2 OH iso-butanol CH 3 CH 3 CH 2 CH 2 CH 2 OH 1-butanol
Optical Isomerism It present in alcohols which contain asymmetrical carbon atom. Where the molecule has two isomers called enantiomers, which they are optical active CH 3 CHCH 2 OH iso-butanol CH 3 CH 3 CH 2 CH 2 CH 2 OH 1-butanol