Halogen Containing Compounds PDF

60 Halogen Containing Compounds 1159 Chapter E3 25 Halogen Containing Compounds  This reaction is a fast due to in presence of light and trace of an organic peroxide. ID Compounds derived from hydrocarbons by the replacement of one or more hydrogen atoms by the corresponding number of halogen atoms...

60 Halogen Containing Compounds 1159 Chapter E3 25 Halogen Containing Compounds  This reaction is a fast due to in presence of light and trace of an organic peroxide. ID Compounds derived from hydrocarbons by the replacement of one or more hydrogen atoms by the corresponding number of halogen atoms are termed as halogen derivatives. The halogen derivatives of the hydrocarbons are broadly classified into three classes: (2) From alkenes Electrophillic addition) by CH 3  CH  CH  CH 3  HBr CH 3 CH 2  C H  CH 3 U Halogen derivatives of saturated hydrocarbons (Alkanes)- Halo-alkanes. (Hydrohalogenation But  2  ene | Br 2 - Bromobutan e  Addition of HBr to alkene in the presence of organic peroxide take place due to peroxide effect or Kharasch's effect. Halogen derivatives of aromatic hydrocarbons (Arenes)-Halo-arenes.  This addition take place by two mechanism, Peroxide initiates free radical mechanism. General methods of preparation of Alkyl Halides Markownikoff’s mechanism. D YG Halogen derivatives of unsaturated hydrocarbons (Alkenes and alkynes)-Halo-alkene or alkyne. (1) From alkanes (i) By halogenation : hv  C 2 H 6 (Excess) + Cl2  C2 H 5 Cl  Ethyl chloride (Major product) U Ethane HCl Cl 2 CH 3 CH 2 CH 3   CH 3 CH 2 CH 2 Cl  CH 3 CHCH 3 UV light 1  Chloroprop ane (45%) ST Propane This reaction mechanism.  proceed | 2 - Chloroprop ane (55%) free radical Order of reactivity of X 2 for a given alkane is, F2  Cl 2  Br2  I 2.  The reactivity of the alkanes follows the order : 3°alkane > 2°alkane > 1°alkane. (ii) With sulphuryl chloride : hv R  H  SO 2 Cl 2   R  Cl  SO 2  HCl Organic peroxide ( R CO 2 )2 by electrophillic  The order of reactivity of halogen acids is, HI  HBr  HCl. (3) From alcohols (i) By the action of halogen acids Groove’s process Anhy. ZnCl 2  R  OH  H  X  Cl through addition Alcohol 300 C RX Haloalkane  The reactivity order of reaction is : HI  HBr  HCl  HF.  H 2O HX in the above  Reactivity order of alcohols 3  2  1  MeOH.  2° and 3° alcohols undergo S N 1 ; where as 1° and MeOH undergo S N 2 mechanism.  Concentrated HCl + anhy. ZnCl2 is known as lucas reagent. (ii) Using PCl5 and PCl3 : 1160 Halogen Containing Compounds PCl 5  CH 3 CH 2 Cl  POCl 3  Phosphorus Chloroetha ne Phosphorus Oxychloride pentachlor ide room temperature. The alkyl halides upto Phosphorus acid  Bromine and iodine derivatives cannot be obtain from the above reaction, because PBr5 or PI5 are unstable.  This method gives good yield of primary alkyl halides but poor yields of secondary and tertiary alkyl halides. (iii) By the action of thionyl chloride (Darzan's process) : mechanism. Reaction takes place through C18 are colourless liquids while higher members are colourless solids. 3CH 3 CH 2OH  PCl 3  3CH 3 CH 2 Cl  H 3 PO3 Chloroetha ne (i) CH 3 F, CH 3 Cl, CH 3 Br and C 2 H 5 Cl are gases at HCl SN 2 (ii) Alkyl halides are insoluble in water but soluble in organic solvents. (iii) They burn on copper wire with green edged flame (Beilstein test for halogens). (iv) Alkyl bromides and iodides are heavier than water. Alkyl chlorides and fluorides are lighter than water. 60 CH 3 CH 2 OH  (v) Alkyl iodides become violet or brown in colour on exposure as they decompose in light. Light 2 RI  R  R  I 2 CH 3 CH 2 OH  SOCl 2  CH 3 CH 2 Cl  SO 2  HCl CCl 4 R  C  O  Ag  Br  Br  R  Br  CO 2   AgBr  || Decarboxyl ation O  The reactivity of alkyl group is 1  2  3 (vii) Alkyl halides are in general toxic compounds and bring unconsciousness when inhaled in large amounts. (2) Chemical properties : The alkyl halides are highly reactive, the order of reactivity is, U  Only bromide are obtained in good yield. (vi) For a given alkyl group, the boiling points of alkyl halides are in the order RI  RBr  RCl  RF and for a given halogen the boiling points of alkyl halides increase with the increase of the size of the alkyl group. ID (4) From silver salt of carboxylic acids (Hunsdiecker reaction, Decarboxylation by Free radical mechanism) E3 Pyridine  Not suitable for chlorination because yield is poor. D YG  In this reaction iodine forms ester instead of alkyl halide and the reaction is called BirnbournSimonini reaction, 2 R  COOAg  I2  RCOO R  2CO 2  2 AgI. (5) By Finkelstein reaction (Halide exchange Acetone method) : R  X  NaI  R  I  NaX ( X  Cl, Br ) Reflux U  Alkyl fluorides can not be prepared by this method. They can be obtained from corresponding chlorides by the action of Hg 2 F2 or antimony trifluoride. (swart reaction) 2CH 3 Cl  Hg 2 F2 2CH 3 F  Hg 2 Cl 2 Iodide > Bromide > Chloride (Nature of the halogen atom) Tertiary > Secondary > Primary (Type of the halogen atom) Amongst the primary alkyl halide, the order of reactivity is : CH 3 X  C 2 H 5 X  C3 H 7 X , etc. The high reactivity of alkyl halides can be explained in terms of the nature of C  X bond which is highly polarised covalent bond due to large difference in the electronegativities of carbon and halogen atoms. The halogen is far more electronegative than carbon and tends to pull the electrons away from carbon, i.e., halogen acquires a small negative charge and carbon a small positive charge. Methyl fluoride ST (6) Other method KI , H3 PO4 ROH    X 2  ( PhO )3 P ROH    Ry don method Dihalide Zn  Cu   HCl X RMgX 2   ROR  PCl5 Properties of Alkyl Halides (1) Physical properties RX    C X This polarity is responsible for reactions, (i) Nucleophilic substitution reactions (ii) Elimination reactions (i) Nucleophilic substitution (SN) reactions : The  C  site is susceptible to attack by nucleophiles (An electron rich species). Nu   R  X  Nu  R  X  X  Nu  Slow Fast R  X  R   R  Nu ( S N 1 reaction) Nu   R  X  Nu..... R..... X  Nu  R  X  Slow Fast Transition state ( S N 2 reaction) Halogen Containing Compounds 1161 Examples of SN reactions, (a) Hydrolysis : (j) Reaction with halides : RCl  AgOH  ROH  AgX RX Alkylhalide Alky lchloride Alcohol RX  KOH (aq)  ROH  KX  With the help of this reaction an alkene can be converted into alcohol. Alkene is first reacted with HBr to form alkyl bromide and then hydrolysis is done. HBr AgOH  NaBr  RBr Alky l bromide NaI   (ii) Elimination reactions : The positive charge on carbon is propagated to the neighbouring carbon atoms by inductive effect. When approached by a strongest base (B), it tends to lose a proton usually from the -carbon atom. Such reactions are termed elimination reactions. They are also E1 and E2 reactions. CH 2  CH 2  CH 3 CH 2 Br  CH 3 CH 2 OH Ethyl bromide Ethyl alcohol H H (b) Reaction with alkoxides or dry silver oxide : Heat RX  NaOR '  X  NaX RSH | | ID  RX  K  O  N  O  R  O  N  O  KX Alky lnitrite O  AgX O D YG Nitro - alkane (f) Reaction with ammonia : C2 H 5 Br  H  NH 2  C2 H 5 NH 2  HBr C2 H 5 NH 2  BrC2 H 5  C2 H 5 NHC 2 H 5  HBr Diethylamine(sec.) (C2 H 5 )2 NH  BrC2 H 5  (C2 H 5 )3 N  HBr Triethylamine(tert.)   U (C 2 H 5 )3 N  BrC 2 H 5  (C 2 H 5 )4 NBr Tetraethy lammonium bromide(Qu aternary ) (g) Reaction with silver salts of fatty acids : ST BH | | H X H | | | | H X Transiton state H | Fast   R  C  C  H  B  H  X  | H As the above reactions involve leaving of X  , the reactivity of alkyl halides (Same alkyl group, different halogens) should be limited with C  X bond strength. Type of bond C  Br CI C  Cl Bond strength (kcal/mol) 45.5 54 66.5 Ethylamine(p.) R ' COOAg  XR  R ' COOR  AgX Ester (h) Reaction with sodium acetylide : RX  NaC  CH  R  C  CH  NaX Alkyne (i) Reaction with sodium or potassium sulphide : 2 RX  Na 2 S  R  S  R  2 NaX Thioether Thioethers can also be obtained by RX  NaSR '  R  S  R' NaX 3 H U : | | Slow (e) Reaction with potassium nitrite or silver nitrite C 2 H 5 Br  NaSCH  E2 Reaction : R  C  C  H  R  C  C  H Alky lcy anide or Alkane nitrile Sodium acetylide | |  R  C  C  H  B  H Fast B : H H (d) Reaction with alcoholic potassium cyanide and silver cyanide : Alcohol RX  KCN   RCN  KX RX  AgNO 2  R  N | H  Thioalcoho l or Alkanethiol or Alkylmercaptan   E3 (c) Reaction with sodium or potassium hydrogen sulphide :  | H Sym. ether NaSH | | H X 2 RX  Ag 2 O  R  O  R  2 AgX Sodium hydrogen sulphide | Slow E1 reaction : R  C  C  H   R  C  C  H ROR '  NaX Unsym. ether RX  B.. H H 60 Ethylene RI Alky l iodide  C 2 H 5  S  CH 3  NaBr Ethyl methyl thi oether Bond strength increases The breaking of the bond becomes more and more difficult and thus, the reactivity decrease. The order of reactivity (Tertiary > Secondary > Primary) is due to +I effect of the alkyl groups which increases the polarity of C  X bond. R R R R 3o C 2o 2o CH X, X, R CH 2 X R The primary alkyl halides undergo reactions either by S N 2 or E 2 mechanisms which involve the formation of transition state. The bulky groups cause steric hinderance in the formation of transition state. Therefore, higher homologues are less reactive than lower homologues. CH 3 X  C 2 H 5 X  C3 H 7 X , etc. Example of elimination reaction (a) Dehydrohalogenation : C n H 2 n 1 X  KOH  C n H 2 n  KX  H 2 O (Alcoholic) Alkene 1162 Halogen Containing Compounds AlCl 3 C 6 H 6  RCl    C 6 H 5 R  HCl In this reactions, ether is a by-product as potassium ethoxide is always present in small quantity. Benzene C 2 H 5 Br  KOC 2 H 5  C 2 H 5  O  C 2 H 5  KBr AlBr3 C 6 H 6  C 2 H 5 Br   C 6 H 5 C 2 H 5  HBr (b) Action of heat : (f) Substitution (Halogenation) : Alkyl halides undergo further halogenation in presence of sunlight, heat energy or peroxide. 300 C RCH 2 CH 2 X    RCH  CH 2  HX Alkene 300 C C 2 H 5 Br   CH 2  CH 2  HBr Br2 Br2 C2 H 5 Br   C2 H 4 Br2   C2 H 3 Br3..... Ethene hv (iii) Miscellaneous reactions (a) Reduction : Alkyl halides are reduced with nascent hydrogen obtained by Zn / HCl or sodium and alcohol or Zn/Cu couple or LiAlH 4. RX  2 H  R  H  HX (i) Methods of preparation of gemdihalide (a) From alkyne (Hydrohalogenation) : R  C  C  H  HX  R  C  C  H | | X H X  HX Dry ether RX  Mg   R  Mg  X | X (b) From carbonyl compound : RCHO  PCl 5   formed. RCHCl 2  [Terminal dihalide] POCl 3 If ketone is taken internal dihalide (ii) Methods of preparation of vicinal dihalide (a) From alkene [By halogenation] : R  CH  CH 2  Cl 2  R  C H  C H 2 Grignard reagent U Grignard reagents are used for making a very large number of organic compounds. (d) Reaction with other metals : Organometallic compounds are formed.  When heated with zinc powder in ether, alkyl halides form dialkyl zinc compounds. These are called Frankland reagents. Ether 2C2 H 5 Br  2 Zn  (C2 H 5 )2 Zn  ZnBr2 Heat  When heated with lead-sodium alloy, ethyl ST bromide gives tetra ethyl lead which is used an antiknock compound in petrol. 4 C 2 H 5 Br  4 Pb ( Na ) (C 2 H 5 )4 Pb  4 NaBr  3 Pb  Reaction with lithium : Alkyl halides react with | | Cl Cl (b) From vicinal glycol : R  CH  OH | CH 2 OH  2 PCl 5  R  CH  Cl | CH 2 Cl  2 HCl  2 POCl 3 (2) Properties of dihalides (i) Physical properties (a) Dihalide are colourless with pleasant smell liquid. Insoluble in water, soluble in organic solvent. (b) M.P and B.P  -molecular mass. (c) Reactivity of vicinal dihalides > Gem dihalide. (ii) Chemical properties of dihalide (a) Reaction with aqueous KOH : RCHX 2  2 KOH (aq.)   RCH (OH )2  KX lithium in dry ether to form alkyl lithiums. RX  2 Li  R  Li  LiX ; Ether C 2 H 5 Br  2 Li  C 2 H 5  Li  LiBr Ethyl bromide Alkyl lithiums are similar in properties with Grignard reagents. These are reactive reagents also. (e) Friedel-Craft's reaction : |  R  C  CH 3 U D YG (c) Reaction with magnesium : Alkyl halides form Grignard reagent when treated with dry magnesium powder in dry ether. (Powder ) (1) Methods of preparation of dihalides ID Reaction is used for the preparation of pure alkanes (b) Wurtz reaction : An ether solution of an alkyl halide (Preferably bromide or iodide) gives an alkane when heated with metallic sodium. Preparations and properties of Dihalides 60 Iodide > Bromide > Chloride (When same alkyl group is present) and Tertiary > Secondary > Primary (When same halogen is present). hv E3 The decomposition follows the following order, 2RX  2 Na  R  R  2 NaX Alkylbenzene  H 2O    RCHO (b) Reaction with alcoholic KOH : H X | | Alc.KOH RCH 2  CHX 2   R  C  C  H ( KX  H 2 O ) NaNH 2   R  C  CH ( NaX  NH 3 ) Halogen Containing Compounds 1163 Alc. KOH R  CH  CH 2   R  C  C  H  2 KX  2 H 2 O | | X X Hydrolysis    2CHCl 3  (CH 3 COO )2 Ca Chloroform  H 3O    RCH (COOH )2 Hydrolysis (e) Other substitution reaction CH 2  X CH 2  NH 2 NH 3 / 373 K  |    | CH 2  X CH 2  NH 2 Fe / H 2 O CCl 4  2 H   CHCl 3  HCl This chloroform is not pure and used mainly as a solvent. (iii) Pure Chloroform is obtained by distilling chloral hydrate with concentrated sodium hydroxide solution. 60 (c) Reaction with Zn dust  Gem halide (di) form higer symmetrical alkene.  Vicinal dihalide form respective alkene. (d) Reaction with KCN : R  CHX 2  2 KCN   RCH (CN )2 2 KX Calcium acetate (ii) From carbon tetrachloride : Now-a-days, chloroform is obtained on a large scale by the reduction of carbon tetrachloride with iron fillings and water. CCl 3 CH (OH )2  NaOH  CHCl 3  HCOONa  H 2 O Chloral hydrate CH 2  X CH 2 OCOCH 3 2 CH 3 COONa   |  2 NaX.  | CH 2  X CH 2 OCOCH 3 Tri-halides (Chloroform and iodoform) D YG U ID Chloroform or trichloromethane, CHCl3 It is an important trihalogen derivative of methane. It was discovered by Liebig in 1831 and its name chloroform was proposed by Dumas as it gave formic acid on hydrolysis. In the past, it was extensively used as anaesthetic for surgery but now it is rarely used as it causes liver damage. (1) Preparation (i) Chloroform is prepared both in the laboratory and on large scale by distilling ethyl alcohol or acetone with bleaching powder and water. The yield is about 40%. The available chlorine of bleaching powder serves both as oxidising as well as chlorinating agent.  Chloral hydrate is a stable compound inspite of the fact that two OH H O Cl groups are linked to the same carbon Cl  C  C  H O atom. This is due to the fact that Cl H intramolecular hydrogen bonding exists in the molecule between chlorine and hydrogen atom of OH group. (2) Physical properties (i) It is a sweet smelling colourless liquid. (ii) It is heavy liquid. Its density is 1.485. It boils at 61°C. (iii) It is practically insoluble in water but dissolves in organic solvents such as alcohol, ether, etc. (iv) It is non-inflammable but its vapours may burn with green flame. (v) It brings temporary unconsciousness when vapours are inhaled for sufficient time. (3) Chemical properties (i) Oxidation : E3 Ethy lene diam ine CaOCl 2  Bleaching powder H 2 O  Ca(OH )2  Cl 2 (a) From alcohol [Cl 2  H 2 O  2 HCl  O] CH 3 CH 2 OH  O  CH 3 CHO  H 2 O Ethylalcohol Cl Cl C Cl Cl Light and air  [O]   H Cl Chloroform  HCl  U ST Hydrolysis    2CHCl 3  (HCOO )2 Ca Chloroform Calcium formate (b) From acetone CH 3  CO  CH 3  3Cl 2  CCl 3 COCH 3  3 HCl Trichloro acetone COCH 3  H 3 C.CO O Ca O  CO Phosgene agent] Chloral, thus, formed, is hydrolysed by calcium hydroxide. CCl CHO OHC CCl 3 3  H  O  Ca  O  H H Cl Cl Chloral [So Cl 2 acts both as an oxidising and chlorinating CCl 3 Cl OH Unstable Acetaldehyde CH 3 CHO  3Cl 2  CCl 3 CHO  3 HCl Acetaldehyde C CCl 3 Phosgene is extremely poisonous gas. To use chloroform as an anaesthetic agent, it is necessary to prevent the above reaction. The following two precautions are taken when chloroform is stored. (a) It is stored in dark blue or brown coloured bottles, which are filled upto the brim. (b) 1% ethyl alcohol is added. This retards the oxidation and converts the phosgene formed into harmless ethyl carbonate. COCl 2  2C2 H 5 OH  (C2 H 5 O)2 CO  2 HCl Ethyl carbonate (ii) Reduction : Zn / HCl CHCl 3  2 H   CH 2 Cl 2  HCl (alc.) H 1164 Halogen Containing Compounds Zn / H 2 O CHCl 3  6 H   CH 4  3 HCl This reaction is also chloroform. (iii) Chlorination : (4) Uses  HCl (i) It is used as a solvent for fats, waxes, rubber, resins, iodine, etc. Carbon tetrachlo ride (iv) Hydrolysis : H C Cl  Na OH (aq.)    NaCl Cl  Na OH (aq.)     HC  Cl  Na OH (aq.) (ii) It is used for the preparation of chloretone (a drug) and chloropicrin (Insecticide). OH   OH  OH  (iii) It is used in laboratory for the test of primary amines, iodides and bromides. Unstable (Orthoformic acid) H O 2   H  C O NaOH    H  C OH  H 2 O Formic acid (iv) It can be used as anaesthetic but due to harmful effects it is not used these days for this purpose. O ONa Sodium formate (v) Nitration : The hydrogen of the chloroform is replaced by nitro group when it is treated with concentrated nitric acid. The product formed is chloropicrin or trichloronitro methane or nitro chloroform. It is a liquid, poisonous and used as an insecticide and a war gas. Nitric acid (5) Tests of chloroform (i) It gives isocyanide test (Carbylamine test). (ii) It forms silver mirror with Tollen's reagent. (iii) Pure Chloroform does precipitate with silver nitrate.  H 2O CNO 2 Cl 3 (v) It may be used to prevent putrefaction of organic materials, i.e., in the preservation of anatomical species. not Chloropicr in (Tear gas) H  C  Cl 3  6 Ag  Cl 3  C  H  CH  CH  6 AgCl Iodoform resembles chloroform in the methods of preparation and properties. (1) Preparation U Acety lene D YG (vii) Condensation with acetone : Chloroform condenses with acetone on heating in presence of caustic alkalies. The product formed is a colourless crystalline solid called chloretone and is used as hypnotic in medicine. CH 3 HO ( NaOH )   CH 3 Cl3 C C CH 3 CH 3 Chloretone (1,1,1 - Trichloro- 2 - methy l- 2 - propanol) (viii) Reaction with sodium ethoxide : Cl  Na OC 2 H 5  3 NaCl Cl  Na OC 2 H 5   H  C Cl  Na OC 2 H 5 OC 2 H 5 OC 2 H 5 OC 2 H 5 ST 65 C C 6 H 5 OH  CHCl 3  3 NaOH   OH CHO  3 NaCl  2 H 2 O Hy droxy benzaldeh y de(salicylaldehy de) (x) Carbylamine reaction (Isocyanide test) : This reaction is actually the test of primary amines. Chloroform, when heated with primary amine in presence of alcoholic potassium hydroxide forms a derivative called isocyanide which has a very offensive smell.  RNH 2  CHCl 3  3 KOH (alc.)  From ethanol : CH 3 CH 2 OH  I2  CH 3 CHO  2 HI Acetaldehyde CH 3 CHO  3 I 2  CI 3 CHO  3 HI Iodal CI 3 CHO  Tri iodoacetaldehyde KOH  CHI 3  HCOOK Iodoform Pot. formate From Acetone: CH 3 COCH 3  3 I 2  CI 3 COCH 3  3 HI Triiodoaceton e CI 3 COCH 3  KOH  CHI 3  CH 3 COOK Iodoform Pot. acetate Sodium carbonate can be used in place of KOH or NaOH. These reactions are called iodoform reactions. (ix) Reimer-Tiemann reaction : C6 H 4 (i) Laboratory preparation : Ethy l orthoforma te U H C white Iodoform or tri-iodomethane, CHI3 (vi) Heating with silver powder : Cl3 CH  O  C give ID CHCl 3  HONO 2  60 CCl 4 E3 UV light CHCl 3  Cl 2   used for the test of RNC Carby laminoalkane (Alky lisonitrile )  3 KCl  3 H 2 O (ii) Industrial preparation : Iodoform is prepared on large scale by electrolysis of a solution containing ethanol, sodium carbonate and potassium iodide. The iodine set free, combine with ethanol in presence of alkali to form iodoform. The electrolysis carried out in presence of CO 2 and the temperature is maintained at 60-70°C. KI ⇌ K   I  Cathod e K  e K Anod e 2 I  I2  2e  K  H 2 O  KOH  1 H2 2 Halogen Containing Compounds 1165 or 2-ol (CHOH  CH 3 ) and secondary alkyl halide at KOH is neutralised by CO 2 : C 2 (CHCICH 3 ). Also lactic acid ( CH 3  CHOH  COOH ) , C 2 H 5 OH  4 I 2  3 Na 2 CO 3  CHI 3 HCOONa  5 NaI  3CO 2  2 H 2O (2) Physical properties O || Pyruvic acid (CH 3  C  COOH ) and methyl phenyl ketone O || (i) It is a yellow crystalline solid. (C 6 H 5  C  CH 3 ) give this test. (ii) It has a pungent characteristic odour. Tetra-halides (Carbon tetrachloride, CCl4) (iv) It has melting point 119°C. It is steam volatile. (3) Chemical Reactions of iodoform (i) Potassium formate methane : (ii) From carbon disulphide : CH2I2 Fe/I2 / AlCl 3 CS 2  3Cl 2   CCl 4  S 2 Cl 2 Methylene iodide Heating Sulphur monochlori de CH  CH S 2 Cl 2 further reacts with CS 2 to form more of ID Ag powder Acetylene carbon tetrachloride. CS 2  2S 2 Cl 2  CCl 4  6 S C6H5 NC Carbon tetrachloride is separated out by fractional distillation. It is washed with sodium hydroxide and then distilled to get a pure sample. (iii) From propane : U Phenol isocyanide Iodine vapours, 4CHI3+3O2 4CO Heating alone (Less stable than CHCl3) D YG + 6I2 + 2H2O Yellow precipitate of AgI With AgNO3 (This reaction is not given by chloroform) (4) Uses : Iodoform is extensively used as an antiseptic for dressing of wounds; but the antiseptic action is due to the liberation of free iodine and not due to iodoform itself. When it comes in contact with organic matter, iodine is liberated which is responsible U for antiseptic properties. (5) Tests of iodoform (i) With AgNO3 : CHI 3 gives a yellow precipitate ST (ii) Carbylamine reaction : CHI 3 on heating with primary amine and alcoholic KOH solution, gives an offensive smell of isocyanide (Carbylamine). (iii) Iodoform reaction : With I 2 and NaOH or I 2 and Na 2 CO 3 , the iodoform test is mainly given by ethyl O || alcohol From CH 4  4 Cl 2   CCl 4  4 HCl HCOOK Reductio RednP/HI of AgI. (1) Manufacture E3 KOH Carbylamine reaction C6H5NH2+KOH (alc.) of methane. 400 C Hydrolysis CHI3 It is the most important tetrahalogen derivative 60 (iii) It is insoluble in water but soluble in organic solvents such as alcohol, ether, etc. (CH 3 CH 2 OH ), acetaldehyde (CH 3  C  H ), 70 -100 CCl 4  C 2 Cl 6  Carbon tetrachloride Hexachloro ethane (Solid) (Liquid) 8 HCl (2) Physical properties (i) It is a colourless liquid having characteristic smell. (ii) It is non-inflammable and poisonous. It has boiling point 77°C. (iii) It is insoluble in water but soluble in organic solvents. (iv) It is an excellent solvent for oils, fats, waxes and greases. (3) Chemical properties : Carbon tetrachloride is less reactive and inert to most organic reagents. However, the following reactions are observed. (i) Reaction with steam (Oxidation) : 500 C CCl 4  H 2O    COCl 2  Phosgene (Carbonyl chloride) 2 HCl (ii) Reduction : Fe / H 2 O CCl 4  2 H   CHCl 3  HCl (iii) Hydrolysis : - O || 400 C C 3 H 8  9 Cl 2    methyl ketone or 2-one ( C CH 3 ), secondary alcohols 4 KCl CCl 4  4 KOH    [C(OH )4 ] Unstable 2 H 2 O 2 KOH   CO 2    K2CO3  H 2O 1166 Halogen Containing Compounds (iv) Reaction reaction) : with phenol (Reimer-tiemann than in alkyl halides (1.80Å) due to sp 3 hybridization of the carbon atom. OH  4 NaCl  2 H 2 O COOH  4 NaOH C 6 H 5 OH  CCl 4  C 6 H 4 Addition reactions Br2 Salicy lic acid CH2Br – CHBrCl CCl4 1,2-Dibromo-1Chloroethane (4) Uses HBr CH3 – CHBrCl 1-Bromo-1Chloroethane CH2 = CHCl (ii) It is used as a solvent for fats, oils, waxes and greases, resins, iodine etc. Polymerisati on Peroxide (iii) It finds use in medicine as helmenthicide for elimination of hook worms. NaOH (i) From ethylene chloride : | CH 2Cl CHCl  KCl  H 2 O + Alc. KOH || CH 2 Ethy lene chloride Viny lchloride | Allyl iodide or 3-iodopropene-1, ICH2CH = CH2 (1) Synthesis : It is obtained, 500 C   C H 2  CH  CH 2 (i) CH 3 CH  CH 2  Cl 2  CHCl  HCl  600CH 2Cl 650°C (ii) From ethylene : CH 2 Cl (3) Uses : The main use of vinyl chloride is in the manufacture of polyvinyl chloride (PVC) plastic which is employed these days for making synthetic leather goods, rain coats, pipes, floor tiles, gramophone records, packaging materials, etc. || CH 2 500 C D YG CH 2  CH 2  Cl 2   CH 2  CHCl Viny lchloride HgCl 70 C Viny lchloride U (2) Properties : It is a colourless gas at room temperature. Its boiling point is –13°C. The halogen atom in vinyl chloride is not reactive as in other alkyl halides. However, C  C bond of vinyl chloride gives the usual addition reactions. ST The non-reactivity of chlorine atom is due to resonance stabilization. The lone pair on chlorine can participate in delocalization (Resonance) to give two canonical structures...   CH 2  CH  Cl :  C H 2  CH  Cl :.. (i).. (ii) The following two effects are observed due to resonance stabilization. (i) Carbon-chlorine bond in vinyl chloride has some double bond character and is, therefore, stronger than a pure single bond. (ii) Carbon atom is sp 2 hybridized and C  Cl bond length is shorter (1.69Å) and the bond is stronger Cl Ally lchloride Or Heat 3 C H 2  CH  CH 2  PCl 3   3 C H 2  CH  CH 2  H 3 PO 3 | | OH Cl Ally lalcohol (iii) From acetylene : 2 CH  CH  HCl   CH 2  CHCl | Propene U CH 2 Cl No reaction ID (1) Synthesis : Vinyl chloride can be synthesised by a number of methods described below:     n E3 Unsaturated halides (Halo-alkene) Vinyl chloride or chloroethene, CH2=CHCl Cl Cl  | |   CH 2  C H  CH 2  C H Poly viny lchloride (PVC)   60 (i) It is used as a fire extinguisher under the name pyrene. The dense vapours form a protective layer on the burning objects and prevent the oxygen or air to come in contact with the burning objects. Acetone C H 2  CH  CH 2  NaI   C H 2  CH  CH 2  NaCl | | Heat I Cl Ally liodide Ally lchloride This is halogen- exchange reaction and is called Finkelstein reaction. C H 2 OH (ii) C| HOH  3 HI  3 H O | 2 CH 2 OH Glycerol C H2I | C HI C H2I | Heat  | CH 2 I 1,2,3 - Tri-iodopropan e CH  I2 || CH 2 Allyliodide (2) Properties : It is a colourless liquid. It boils at 103.1°C.The halogen atom in allyl iodide is quite reactive. The p-orbital of the halogen atom does not interact with -molecular orbital of the double bond because these are separated by a saturated sp 3 - hybridized carbon atom. Thus, the halogen atom in allyl halides can be easily replaced and the reactions of allyl halides are similar to the reaction of alkyl halides. In terms of valence bond approach, the reactivity of halogen atom is due to ionisation to yield a carbonium ion which can stabilize by resonance as shown below, CH 2  CH  CH 2 I  Halogen Containing Compounds 1167   [CH 2  CH  C H 2  C H 2  CH  CH 2 ]  I  Substitution reactions : Nucleophilic substitution reactions occur, NaOH 2 C6 H 5 COO  Ag    C6 H 5 Br  CO 2  AgBr Br (iv) From Aryl thalium compound : ArH  Tl(OOCCF3 )3    CF CO H CH2 = CH – CH2OH 3 Allyl alcohol KCN (iii) Hunsdiecker reaction : 2 KI ArTl(OOCF3 )2   ArI CH2 = CH – CH2CN  Ary l thallium trifluoroacetate Allyl cyanide (3) Physical properties 60 CH2 = CH – CH2NH2 (i) Physical state : Haloarenes are colourless liquid or crystalline solid. Allyl amine CH3ONa CH2 = CH – CH2OCH3 (ii) Solubility : They are insoluble in water, but dissolve readily in organic solvents. Insolubility is due to inability to form hydrogen bonding in water. Para isomer is less soluble than ortho isomer. Allyl methyl ether AgNO2 CH2 = CH – CH2NO2 3-Nitropropene-1 CH 2  CH  CH 2 I  Br2  CH 2 Br  CHBr  CH 2 I 1,2 Dibromo- 3- iodopropan e CH 2  CH  CH 2 I  HBr  CH 3 CHBrCH 2 I 2 Bromo -1-iodopropan e (iv) B.P. of halo-arenes follow the trend. Iodo arene > Bromo arene > Chloro arene. (4) Chemical properties Inert nature of chlorobenzene : Aryl halides are unreactive as compared to alkyl halides as the halogen atom in these compounds is firmly attached and cannot be replaced by nucleophiles. Such as OH  , NH 2 , CN  etc. U Allyl iodide is widely used in organic synthesis. (iii) Halo-arenes are heavier than water. ID Addition reactions : Electrophilic addition reactions take place in accordance to Markownikoff's rule. E3 NH3 CH2 = CHCH2I Halo-arenes D YG In these compounds the halogen is linked directly to the carbon of the benzene nucleus... : Cl : Cl Cl  (1) Nomenclature : Common name is aryl halide IUPAC name is halo-arene. Example : Cl Br ; Benzylbromide Bromobenzene U Benzylchlorid e Chlorobenzen (2) Methodse of preparation ST (i) By direct halogination of benzene ring + X2 X Lewis acid    + HX  Thus delocalization of electrons by resonance in aryl halides, brings extra stability and double bond character between C  X bond. This makes the bond stronger and shorter than pure single bond. However under vigorous conditions the following nucleophilic substitution reactions are observed, (i) Nucleophilic displacement : NaOH , 350 C C 6 H 5 Cl    C 6 H 5 OH  NaCl 500 atm. (ii) Electrophilic aromatic substitution Lewis acid  FeX 3 , AlX 3 , Tl(OAC )3 ; X 2  Cl2 , Br2 C 6 H 5 NH 2  C 6 H 5 N 2 5C NaNO 2 , HCl  Cl (ii) From diazonium salts  Cl  CuCl CuBr KI HBF4 Cl Cl + HNO3 Cl NO2 H2SO4 + C6H5Cl Cl Cl NO2 Cl C6H5Br Br2 /Fe C6H5I C6H5F Br + Br Cl Cl Cl CH3Cl AlCl3 CH3 + CH3 1168 Halogen Containing Compounds nCF2  CF2 Tetrafluoroethy lene Na C6 H 5 Br  CH 3 Br   C6 H 5 CH 3  2 NaBr Ether (iv) Formation of grignard reagent : Mg  C6 H 5 MgBr C6 H 5 Br  60 Ether (v) Ullmann reaction Cu I + CuI2 CH  CH  2Cl 2  CHCl 2  CHCl 2 (1,1,2,2  Tetrachloroethane) Some more important halogen derivatives (1) Freons : The chloro fluoro derivatives of methane and ethane are called freons. Some of the derivatives are: CHF2 Cl (monochlorodifluoromethane), HCF2 CHCl 2 (1,1- U dichloro-2,2-difluoroethane). These derivatives are non-inflammable, colourless, non-toxic, low boiling liquids. These are stable upto 550°C. The most important and useful derivative is CF2Cl2 which is commonly known as freon and freon-12. In absence of catalyst, the reaction between chlorine and acetylene is highly explosive producing carbon and HCl. The reaction is less violent in presence of a catalyst. It is a heavy, non-inflammable liquid. It boils at 146°C. It is highly toxic in nature. Its smell is similar to chloroform. It is insoluble in water but soluble in organic solvents. On further chlorination, it forms penta and hexachloroethane. On heating with lime (Calcium hydroxide), it is converted to useful product westrosol (CCl 2  CHCl ). ID (dichlorodifluoro-methane), E3 Diphenyl CF2Cl2 Teflon Teflon is chemically inert substance. It is not affected by strong acids and even by boiling aqua-regia. It is stable at high temperatures. It is, thus, used for electrical insulation, preparation of gasket materials and non-sticking frying pans. (3) Acetylene tetrachloride (Westron), CHCl2∙CHCl2 : Acetylene tetrachloride is also known as sym. tetrachloroethane. It is prepared by the action of chlorine on acetylene in presence of a catalyst such as ferric chloride, aluminium chloride, iron, quartz or kieselguhr. (iii) Wurtz – fittig reaction : 2  (CF2  CF2 )n Freon or freon-12 (CF2 Cl 2 ) is prepared by treating D YG carbon tetrachloride with antimony trifluoride in the presence of antimony pentachloride as a catalyst. 2CHCl 2  CHCl 2  Ca(OH )2  Westron 2CHCl  CCl 2  CaCl 2  2 H 2 O Westrosol (Trichloroethene) 5 3 CCl 4  2 SbF 3   3 CCl 2 F2  2 SbCl 3 SbCl Cataly st Or it can be obtained by reacting carbon tetrachloride with hydrofluoric acid in presence of antimony pentafluoride. 5 CCl 4  2 HF  CCl 2 F2  2 HCl SbF ST U Under ordinary conditions freon is a gas. Its boiling point is –29.8°C. It can easily be liquified. It is chemically inert. It is used in air-conditioning and in domestic refrigerators for cooling purposes (As refrigerant). It causes depletion of ozone layer. (2) Teflon : It is plastic like substance produced by the polymerisation of tetrafluoroethylene (CF2  CF2 ). Tetrafluoroethylene is formed when chloroform is treated with antimony trifluoride and hydrofluoric acid. Both westron and westrosol are used as solvents for oils, fats, waxes, resins, varnishes and paints, etc. (4) p-Dichlorobenzene : It is prepared by chlorination of benzene. It is a white, volatile solid having melting point of 325 K, which readily sublimes. It resembles chlorobenzene in their properties. It is used as general insecticides, germicide, soil fumigant deodorant. It is used as a larvicide for cloth moth and peach tee borer. (5) DDT; 2, 2-bis (p-Chlorophenyl) –1,1,1trichloroethane : H H | CCl3–C=O + H SbF3 800 C CHCl 3   CHF2 Cl    CF2  CF2 HF  HCl Cl Conc. H2SO4 H | Cl3C – C Cl + H2O Cl Cl (b.pt. - 76 C) On polymerisation tetrafluoroethylene forms a plastic-like material which is called teflon. Chloral (1mol) Chlorobenzene (2mol) D.D.T. Halogen Containing Compounds 1169 (i) D.D.T. is almost insoluble in water but it is moderately soluble in polar solvents. (ii) D.D.T. is a powerful insecticide. It is widely used as an insecticide for killing mosquitoes and other insects. Side Effects of D.D.T. : D.D.T. is not biodegradable. Its residues accumulate in environment and its long term effects could be highly dangerous. It has been proved to be toxic to living beings. Therefore, its use has been abandoned in many western countries. However, inspite of its dangerous side effects, D.D.T. is still being widely used in India due to non-availability of other cheaper insecticides. (6) BHC (Benzene hexachloride), C6H6Cl6 : Cl Cl Cl Cl BHC (R2 Zn) , Alkyl magnesium halide (R  Mg  X ) (1) Methyl lithium : CH 3 I  Methyliodide  Ether  CH 3 Li  LiI 2 Li  10 C High reactivity of CH 3 Li over grignard (i) CH 3  Li  H  OH  CH 4  LiOH (ii) CH 3  Li  CH 2  CH 2  CH 3 CH 2 CH 2 OLi O H 2O   CH 3 CH 2 CH 2 OH  LiOH U D YG aaaeee conformation of C6 H 6 Cl 6 is most O || (iii) CH 3  Li  CO 2  CH 3  C  O  Li H 2O   CH 3 COOH  LiOH powerful insecticide. (7) Perfluorocarbons (PFCs) : Perfluorocarbons (Cn F2n  2 ) are obtained by controlled fluorination of (iv) CH 3  Li  H  C  O  CH 3 CH 2  O  Li | H vapourized alkanes diluted with nitrogen gas in the presence of a catalyst. C7 H16  16 F2 2  Vapour pha se, N , 573 K CoF 2 (Cataly st) Methyllithium Chemical properties Uses : It is an important agricultural pesticide mainly used for exterminating white ants, leaf hopper, termite, etc. It is also known by the common name gammaxene or lindane or 666.  Example : Methyl lithium (CH 3 Li) , Dialkyl zinc E3 Cl Sunlight Benzene Organic compounds in which a metal atom is directly linked to carbon or organic compounds which contain at least one carbon-metal bond are called organometallic compounds. ID + Organometallic compounds reagent is due to greater polar character of C  Li bond in comparison to C  Mg bond. Cl 3Cl2 liquid ventilation, carbon monoxide poisoning and many medical diagnosis. 60 Properties and uses of D.D.T. C7 F16  16 HF Perfluoroheptane ST U These are colourless, odourless, non-toxic, noncorrosive, non-flammable, non-polar, extremely stable and unreactive gases, liquids and solids. These are stable to ultraviolet radiations and other ionising radiations and therefore, they do not deplete the ozone layer like freons. These are good electrical insulators. These have many important uses such as : (i) These are used as lubricants, surface coatings and dielectrics. (ii) These are used as heat transfer media in high voltage electrical equipment. (iii) These are used for vapour phase soldering, gross leak detection of sealed microchips etc. in electronic industry. (iv) These are also used in health care and medicine such as skin care cosmetics, wound healing, H 2O   CH 3 CH 2 OH  LiOH  Unlike grignard reagents, alkyl lithium can add to an alkenic double bond.  R  Li  CH 2  CH 2  R  CH 2  CH 2  Li (2) Dialkyl zinc : First organometallic compound discovered by Frankland in 1849. Heat Heat 2 RI  2 Zn   2 R  Zn  I   R 2 Zn  ZnI 2 CO 2 CO 2 Dialky l zinc Chemical properties Preparation of quaternary hydrocarbon : (CH 3 )3 CCl  (CH 3 )2 Zn  (CH 3 )4 C  CH 3 ZnCl Neopentane (3) Grignard reagent : Grignard reagent are prepared by the action of alkyl halide on dry burn magnesium in presence of alcohol free dry ether. Dry ether dissolves the grignard reagent through solvation. 1170 Halogen Containing Compounds C2 H5 | :O : C2 H5 R | Mg C2 H5 | :O : | |   C  O  NH 3  Mg | R | X OH X C2 H5 Grignard reagents are never isolated in free sate on account of their explosive nature. Usually alkyl bromides are used.  Iodination of alkanes is a reversible process, 60  For given alkyl radical the ease of formation of a grignard reagent is, Iodide > Bromide > Chloride therefore, formation of iodoalkanes is possible only  For a given halogen, the ease of formation of grignard reagent is, CH 3 X  C2 H 5 X  C3 H7 X.......... in the presence of oxidising agents such as HIO3.  Since tertiary alkyl iodides eliminate HI to form an alkene, tertiary alkyl chlorides are used in place of all.  Grignard reagent cannot be prepared from a compound which consists in addition to halogen, some reactive group such as OH because it will react or  Phosphorous halides are generally used to  SOBr2 is less stable and SOI2 does not exist. Thus, method.  R  Mg X U |   are generally prepared by halide exchange reactions. R – Br and R – I cannot be prepared by Darzan’s what covalent but highly polar. Mg X C– C bonds in higher alkanes. Therefore alkyl fluorides ID The C  Mg bond in grignard reagent is some |  Fluorination of alkanes takes place with rupture of prepare lower alkyl bromides in the laboratory. rapidly with the grignard reagent.  C  E3 tertiary alkyl iodides.  Iodination with methane does not take place at  Hunsdiecker reaction proceeds through free radical mechanism. It is used to reduce the length of carbon chain. (i) Double decomposition with compound containing active hydrogen atom or reactive halogen  Reactivity of halides towards SN1 mechanism is atom  Reactivity of halides towards SN2 mechanism is D YG The alkyl group acts as carbanion. The majority of reaction of grignard reagent fall into two groups: RMgX  HOH  RH  Mg(OH )X 3°>2°>1°. 1°>2°>3°.  Polar solvents favour SN1 mechanism. RMgX  R' OH  RH  Mg(OR ' )X  Non polar solvents favour SN2 mechanism. RMgX  R ' NH 2  RH  Mg(R ' NH )X  High concentration of nucleophile favour SN2 RMgX  R' I  R  R' MgIX mechanism while low concentration of nucleophile favour SN1 mechanism. U RMgX  D2 O  RD  Mg(OD)X ST RMgX  ClCH 2 OR '  RCH 2 OR ' MgClX  SN1 reactions partial racemisation occurs with (ii) Addition reaction with compounds containing CO ; C  N , C  O  RMgX  C  S etc. H OH C  O MgX   Order of nucleophilicity among halide ions decreases in the order I– > Br– > Cl–- > F–. | R C  OH  Mg | R H OH  C  N  RMgX   C  N MgX | O H2 R inverted product predominant in yield whereas in SN2 reactions, inverted product is formed. OH X  During elimination reactions, the H atom is lost from the carbon atom carrying minimum number of H atom.  C2H5SH (Ethyl mercaptan) is added to LPG (household cooking gas) to detect leakage. The Halogen Containing Compounds 1171 compound has a typical smell.  In Sandmeyer reaction, Cl of CuCl is attached to benzene ring.  Nuclear halogenation takes place by electrophilic substitution mechanism whereas side chain halogenation takes place by free radical mechanism.  Aryl halides and vinyl halides (CH2 = CH – X) are 60 less reactive than alkyl halides and are not easily hydrolysed. Thus alkyl halides on reaction with NaOH give coloured precipitate but aryl and vinyl halide does not. anaesthetic it is tested by treating with aqueous solution of AgNO3. A pure sample does not give ppt. with aq. AgNO3. which replace diethyl ether. ID  Halothane, CF3-CHClBr, is a general anaesthetic E3  Before using the sample of chloroform as an  CCl4 resist hydrolysis with boiling water due to non availability of d-orbital in C. U  C2Cl6 is an solid and is known as atificial camphor. ST U process. D YG  Chlorobenzene commercially produced by Raschig