ORGANIC COMPOUND CONTAINING HALOGENS

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1 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , COH 1 ORGAIC COMPOUD COTAIIG HALOGES

2 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , COH 2 COCEPTS C1A Physical Properties : Because of their greater molecular weights, haloalkanes have considerably higher boiling points than alkanes with the same number of carbon atoms. For a given alkyl group, the boiling point increases with increase of atomic weight of halogen. So fluoride has lowest boiling point and iodide has the highest boiling point. With branching boiling point decreases. Inspite of their modest polarity they are insoluble in water probably because of there inability to form hydrogen bonds. They are soluble in typical organic solvents of low polarity like benzene, ether, chloroform etc. Iodo, bromo and polychloro compounds are more dense than water. Alkane and Alkyl halide compounds of low polarity are held together by vander waal s forces or weak dipole-dipole attraction. C1B Method of preparation of Alkyl Halide : 1. From alcohols (Replacement of OH by X) ROH R X PX or HX conc.hbr Examples : CH 2CH 2OH CH 2CH 2Br or abr,h2so4 heat P / I CH 2OH CH 2I Ethyl iodide CH 2 Although certain alcohols tend to undergo rearrangement during replacement of OH by X, this tendency can be minimized by use to phosphorous halide. ROH + PCl 5 RCl + POCl + HCl ROH + SOCl 2 RCl + SO 2 + HCl 2. Halogenation of Hydrocarbons : R H R X HX Examples : X 2 h Br2 0 light,140 C Br 2 h

3 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , Addition of Hydrogen halides to alkenes : COH Peroxide has no effect on HF, HCl and HI 4. Addition of halogen to alkenes and alkynes : ; 5. Halide exchange (Finkelstein reaction) R X + ai R I + ax (X = Cl, Br) acetone An alkyl iodide is prepared often from the corresponding bromide or chloride by treatment with a solution of sodium iodide in acetone; the less soluble bromide or sodium chloride precipitate from the solution and can be removed by filtration. 6. Hunsdiecker or Borodine-Hunsdiecker reaction : Silver salts of the carboxylic acids in carbon tetrachloride solution are decomposed by chlorine or bromine to form the alkyl halide e.g. RCO 2 Ag + Br 2 RBr + CO 2 + AgBr The yield of halide is primary > secondary > Tertiary. 7. Swarts Reaction : Br + AgF F + AgBr Practice Problems : (It is the best way to prepare alkyl florides by halogen exchange) 1. An organic halide with formula C 6 H 1 Br on heating with alc. KOH gives two isomeric alkenes (A) and (B) with formula C 6 H 12. On reductive ozonolysis of mixture (A) and (B), the following compounds are obtained : CO, CHO, CHO and ( ) 2 CHCHO The organic halide is : 2-bromohexane -bromo-2-methylpentane 2, 2-dimethyl-1-bromohexane none of the above 2. Ethene on treatment with bromine in presence of acl solution gives : 1,2-dibromoethane 1, 2-dichloroethane a mixture of 1, 2-dibromo and 2- bromo-1-chloro, ethanes no reaction occurs [Answers : (1) b (2) c]

4 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , C2 Chemical properties of Alkyl Halides : COH 4 ucleophilic Aliphatic Substitution : When Br is treated with sodium hydroxide in solvent that dissolves both reagents, there is obtained methanol and sodium bromide. This is a substitution reaction : the OH group is replaced by Br in the original compound. An alkyl halide is converted into alcohol. : Br + :OH OH + : Br It is clearly heterolytic. This is one example of the class of reactions called nucleophilic substitution reaction. ucleophilic substitution is characteristic of alkyl halide. As halide ion are weak bases. As hydrogen halides show high acidity that is its readiness to release H + ions so halide ions are weak bases and just a halide releases a proton, so it readily releases carbon again to other bases. Basic, electron rich reagents that tend to attack the nucleus of carbon are called nucleophic reagents or simply nucleophiles. When this attack result in substitution it is called nucleophilic substitution reaction. ucleophile can be neutral with electropair like : H, or it can be negatively charged. If :Z is neutral then R : + Z will be positively charged. If :Z is negatively charged then R : Z will be neutral. ucleophilic substitution is possible by two mechanisms S 1 and S 2. Reactions of Alkyl Halides : ( S 2 ) (ucleophilic Substitution) [R-X, X I, Cl, Br, R, 1 0, 2 0 ]. Examples of ucleophilic Substitution are as follows : (i) (iii) R : X + : Z R : Z + :X (ii) R : X + OH ROH + :X R : X + H 2 O ROH (iv) R : X + :O R ROR (Williamson s Synthesis) (v) RX + :C C R R C CR (vi) RX + R M + R R (vii) RX + I Acetone RI + X (viii) RX + KC RC + KX Alkyl iodide Alkyl cyanide (ix) (xi) RX + AgC AgX + R C (x) RX + R COO R COOR + X Alkyl isocyanide Ester RX + :H R H RX RX RX 2 R 2H R R4 Primary amine (xii) R X + (xiii) RX + KSH RSH (xiv) RX + KSR RSR (xv) R X + Ar H + AlCl Ar R (Alkyl benzene) Thio ether (sulfilde) Friedal Craft reaction

5 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , Dehydrohalogenation : Elimination CH alc.koh CHCH CH or KOH / C H OH CH CH CHCH 2 5 (Major) (Minor ) Br Elimination mechanism is possible in two ways i.e., E 1 and E 2 : E 1 E 2 1. Rate law expression is r = k[rx] Rate law expression is r = k[rx] [B ] 2. First order reaction Second order reaction. Intermediate is carbocation Transition state is formed 4. Order of reactivity of RX Order of reaction of RX 0 > 2 0 > > 2 0 > RI > RBr > RCl > RF RI > RBr > RCl > RF overall summary of S 1,E 1,S 2,E 2 reactions COH 5 X (Methyl halide) R X (1 0 ) Biomolecular reactions i.e., S 2 only Gives mainly S 2 reaction With hindered strong base [e.g., ( ) CO ] then gives mainly E 2 Gives mainly S 2 with weak bases (I, C, RCO 2 ) and mainly E 2 with strong bases like RO. Gives mainly S 1 /E 1 or E 2 o S 2 Reaction In water solvent gives S 1 /E 1 Lower temperature S 1 is favoured Following are the examples based on S, 1 2, E 1 and E 2. When a strong base (e.g. RO ) is used E 2 predominates. S (1) Br + O 0 50 C CH OH (2) Br + ( ) CO 0 50 C (CH ) COH

6 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , COH 6 () 0 50 C CH OH 0 50 C (4) ( ) CBr + OH + O C( ) CH OH (5) ( ) CBr 0 25 C CH OH Praparation of Grignard reagent : R X + Mg Reduction : ether R MgX R X + M + H + RH + M + + X D 2 O e.g. ( ) C Cl Mg (H C) C MgCl ( ) CD (e) Wurtz Reaction : 2R X a / dry ether R R + ax. (both molecules of alkyl halides can be used different) (f) Wurtz Fittig Reaction : dry ether + 2 abr (g) Fittig Reaction : dry ether + 2 abr (h) Reduction by metal and acid R X + Zn + H + R H + Zn 2+ + X Example : (i) 4R X + LiAlH 4 4R H + LiX + AlX [X F] R X + :H RH + :X [H: comes from LiAlH 4 ] LiAlH 4 can reduces 1 0 and 2 0 alkylhalide (j) R X + n( C 4 H 9 ) SnH RH + (n C 4 H 9 ) SnX Tributyl tin hydride [It can reduce 1 0, 2 0 and 0 alkyl halide].

7 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , COH 7 (k) Coupling of alkyl halides with organomettalic compounds (Corey-house alkane synthesis) Already discussed in Hydrocarbons. Practice Problems : 1. The non-reactivity of chlorine atom in = CH Cl is due to inductive effect resonance stabilization electromeric effect electronegativity 2. Which of the following is most reactive towards nucleophilic substitution reactions? CH = CHCl = CHCl = CH Cl none of these. 1-Bromopropane and 2-bromopropane on treatment with sodium in presence of ether gives n-hexane 2, -dimethylbutane 2-methylpentane a mixture of all these different alkanes 4. Compound C 4 H 8 Cl 2 (A) on hydrolysis gives a compound C 4 H 8 O (B) which reacts with hydroxylamine and does not give any test with tollen s reagent. What are (A) and (B). 1, 1-dichlorobutane and butanal 2, 2-dichlorobutane and butanal 1, 1-dichlorobutane and butan-2-one 2, 2-dichlorobutane and butan-2-one 5. Secondary butyl chloride on boiling with alcoholic potash gives only 1-butene only 2-butene isobutylene a mixture of 1-butene and 2-butene 6. Aryl halides are less reactive towards nucleophilic substitution reaction as compared to alkyl halides due to the formation of less stable carbonium ion resonance stabilization longer carbon-halogen bond inductive effect 7. C 8 H 18 (A) is chlorination forms only one type of C 8 H 17 Cl(B). Hence A can be : (1)Li 8. (CH ) CHBr A. This is Corey-House method of synthesis of A which is A? 2 (2)CuI ()( ) 2 CHBr ( ) 2 CH CH( ) 2 ( ) 2 CH ( ) 2 CH none is correct ether CO Mg A A is : HO

8 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , COH Major product in the following reaction is : Br + KO O 11.. Which are correct statements : reactivity for S 1 reaction is I < III < II reactivity for S 2 reaction is I < II < III reactivity for S 1 reaction is I > II > III reactivity for S 2 reaction is I > II > III 12. Major product of the following 1 S reaction is : CH C H C H CH OC 2H5 Br CH none is correct 1. Increasing tendency for S 1 and S 2 reaction is : (A) S 1 : 1 < III < II < IV (B) S 2 : IV < II < III < I A and B both are correct only A correct only B correct both incorrect

9 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , COH ethanol 0 In this reaction : 25 C 2-ethoxy-2-methyl butane is the major product in the absence of ethoxide ion mixture of 2-methyl-2-butene and 2-methyl-1-butene is the major product in presence of ethoxide ion both are correct none is correct OH A A is : S both none 16. A halide, C 5 H 11 X, on treating with alc. KOH gives only pentene-2. What is structure of halide? both and are correct 17. An alkyl halide (X) of formula C 6 H 1 Cl on treatment with potassium tertiary butoxide gives two isomeric alkenes (Y) and (Z) of formula C 6 H 12. Both alkenes on hydrogenation give 2, -dimethylbutane. Predict (X). [Answers : (1) b (2) c () d (4) d (5) d (6) b (7) d (8) a (9) a (10) b (11) d (12) c (1) a (14) c (15) b (16) d (17) a]

10 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , COH 10 IITIAL STEP EXERCISE 1. Which one of the following will produce a primary alcohol by reacting with MgI acetone methyl cyanide ethylene oxide ethyl acetate 2. Grignard reagent adds to : C = O C C = S all of these. Only two isomeric monochloro derivatives are possible from : ethane 2, 2-dimethyl pentane neopentane 2-methylpropane 4. When ethyl bromide is treated with dry silver oxide, we get diethyl ether ethanol ethane ethene Cl 2 aoh 5. CCl CHO (A) (B). The product (B) can be used as : Sun light fire extinguisher solvent insecticide all above dil.h SO4 CHCl 6. CH C CH 2 (B) (C) (HgSO 4 ) Compound (C) can be used as : (aoh) an anaesthetic an insecticide a solvent hypnotic 7. Br can be prepared by : COOAg + Br 2 CH 4 + BS both none 8. End product of following sequence of reaction : = O 9. For the reaction, 4 H SO 2 CH = CH predominates = CH predominates Both are formed in equal amounts The product ratio is dependent on the halogen X 10. Which of the following does not react with benzene in presence of anhydrous AlCl C 6 H 5 Cl C 6 H 5 Cl Cl C 6 H 5 Cl 11. The alkyl halide which does not give white precipitate with alcoholic AgO solution is Ethyl chloride Allyl chloride Isopropyl chloride Vinyl chloride 12. Which chloroderivative of benzene among the following would undergo hydrolysis most readily with aqueous aoh to furnish the corresponding hydroxy compound. Br H O / H2O BaO A B C = O OH

11 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , COH The replacement of chlorine from chlorobenzene to give phenol requires a drastic condition, but the chlorine of 2, 4-dichloronitro benzene is readily replaced since nitro groups make the aromatic ring electron rich at ortho/para positions nitro groups withdraw electrons from the meta position of the aromatic ring nitro groups donate electrons at meta position nitro groups withdraw electrons from ortho/para positions of the aromatic ring FIAL STEP EXERCISE 1. With alcoholic potash C H 7 Br (A) gives C H 6 (B). (B) on oxidation gives C 2 H 4 O 2 (C) + carbon dioxide and water. With hydrobromic acid gives (D), an isomer of (A). The compounds (A) and (D) are respectively., A and B are : in both cases in both cases, Br Both have same structure i.e. Br Both have same structure i.e. and 2. and

12 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , COH 12. The product (A), (B) and (C) are respectively CHO HBr Hydrolysis aoh C2H 4 (A) (B) (C) H Br, OH, CHI Br, =, HCOOa CHBr 2, HC CH, HCOOa CBr, HC CH, CHI 4. RCl is treated with Li in ether to form R Li, R Li reacts with water to form isopentane. R Cl also reacts with sodium to form 2, 7-dimethyl octane. The structure of R Cl is I 2 COH 2 COOH HOH 7. Identify Z in the following reaction series, aq.aoh Al2O CH.CH CH Br (X) (Y) Cl 2 / H 2 O (Z) 2 2 heat Mixture of and Cl one 5. With alkali C H 6 Cl 2 (A) gives (B). (B) reacts with dilute H 2 SO 4 containing mercuric sulphate to give C H 6 O (C) which gives idoform test. The possible structure of A is All are possible 6. Identify the product (A) in following reaction series, a / C2H5OH HO2 CH C (X) (Y) [O] Tollen 's (Z) (A) reagent 8. = CHCl reacts with HCl to form Cl Cl CHCl 2 = CHCl. HCl one of these 9. What mass of isobutylene from 7 g of tertiary butyl alcohol by heating with 20% H 2 SO 4 at 6 K, if the yield is 65% 16 g 18.2 g 20 g 22 g 10. What effect should the following reasonance of vinyl chloride have on its dipole moment? C H C l C H 2 CH C l Decreases Increases Remains constant cannot be predicted

13 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , COH 1 ASWERS (IITIAL STEP EXERCISE) ASWERS (FIAL STEP EXERCISE) 1. c 2. d. d 4. a 5. d 6. d 7. a 8. c 9. a 10. a 11. d 12. a 1. d 1. a 2. c. a 4. a 5. d 6. c 7. b 8. b 9. b 10. b

14 Einstein Classes, Unit o. 102, 10, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road ew Delhi , Ph. : , COH 14 TEST YOURSELF 1. The number of isomers of C 4 H 9 I is IUPAC name for is 2-2 dimethyl, 1- chloromethyl cyclopentane 1-chloromethyl, 2-2 dimethyl cyclopentane 1-1 dimethyl, 2-chloromethyl cyclopentane 2-chloromethyl, 1-1-dimethyl cyclopentane. In the following reaction : ROH + abr product what will be the product? aoh RBr both no reaction 4. The product in the given reaction is rac. cis-4-iodoethylcyclohexane + OH product rac. cis-4-ethyl cyclohexanol rac. trans-4-ethylcyclohexanol rac. trans-4-ethyl cyclohexane no reaction 5. What will be the product if CH = CH Cl react with C CH = CH C 8. Which is most reactive for S 2 reactions : I C 2 H 5 I C H 7 I C 4 H 9 I 9. When the reaction between methyl iodide and sodium ethoxide occurs, we get methyl acetate methyl ethyl ketone ethyl acetate methyl ethyl ether 10. Idoform is formed on warming I 2 + aoh with C 2 H 5 OH ( ) 2 CHOH CHO all one BS HBr / ROOR 6. CHCH CH2 X Y Z. What is Z? propane cyclopropane propanoic acid 1- dimagnesium propane 7. ( ) CMgCl on reaction with D 2 O produces : (CH) CD ( ) OD (CD) CD (CD )OD Mg 1. b 2. d. d 4. b 5. c ASWERS 6. b 7. a 8. a 9. d 10. d

Einstein Classes, Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi , Ph. : ,

Einstein Classes, Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road New Delhi , Ph. : , CAH 1 ALLKYL HALIDES C1A Physical Properties : Because of their greater molecular weights, haloalkanes have considerably higher boiling points than alkanes with the same number of carbon atoms. For a given