NEET Chemistry Notes, Chapter 25: Halogen Containing Compounds PDF

60 Chapter E3 25 Halogen Containing Compounds CH 3  CH  CH  CH 3  HBr CH 3 CH 2  C H  CH 3 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 hydr...

60 Chapter E3 25 Halogen Containing Compounds CH 3  CH  CH  CH 3  HBr CH 3 CH 2  C H  CH 3 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: | 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.  This addition take place by two mechanism, Peroxide initiates free radical mechanism. Markownikoff’s addition by electrophillic mechanism.  The order of reactivity of halogen acids is, HI  HBr  HCl. (3) From alcohols (i) By the action of halogen acids Groove’s process D YG U Halogen derivatives of saturated hydrocarbons (Alkanes)Halo-alkanes. Halogen derivatives of unsaturated hydrocarbons (Alkenes and alkynes)-Halo-alkene or alkyne. Halogen derivatives of aromatic hydrocarbons (Arenes)-Haloarenes. But  2  ene General methods of preparation of Alkyl Halides (1) From alkanes (i) By halogenation :  C 2 H 6 (Excess) + Cl2  hv Ethane C2 H 5 Cl  Ethyl chloride (Major product) 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%) U Propane | Cl 2 - Chloroprop ane (55%) This reaction proceed through free radical mechanism. ST  Order of reactivity of X2 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  This reaction is a fast due to in presence of light and trace of an organic peroxide. (2) From alkenes (Hydrohalogenation by Electrophillic addition) Anhy. ZnCl 2 R  OH  H  X   300 C Alcohol RX Haloalkane  H 2O  The reactivity order of HX in the above reaction is : HI  HBr  HCl  HF.  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 : CH 3 CH 2 OH  PCl5  CH 3 CH 2 Cl  POCl3  Phosphorus Chloroethane Phosphorus pentachloride Oxychloride 3 CH 3 CH 2 OH  PCl3  3CH 3 CH 2 Cl  Chloroetha ne HCl H 3 PO3 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) : Reaction takes place through SN 2 mechanism. (4) From silver salt of carboxylic acids (Hunsdiecker reaction, Decarboxylation by Free radical mechanism) CCl 4 R  C  O  Ag  Br  Br  R  Br  CO 2   AgBr  Decarboxylation O  The reactivity of alkyl group is 1  2  3  Only bromide are obtained in good yield.  Not suitable for chlorination because yield is poor.  In this reaction iodine forms ester instead of alkyl halide and the reaction is called Birnbourn-Simonini reaction, 2 R  COOAg  I2  RCOOR  2CO 2  2 AgI. (5) By Finkelstein reaction (Halide exchange method) : Acetone  Alkyl fluorides can not be prepared by this method. They can be obtained from corresponding chlorides by the action of Hg 2 F2 Methyl fluoride Fast Nu  R  X  Nu..... R..... X  Nu  R  X  Slow X RMgX 2   ROR  ID D YG PCl5 Fast ( S N 2 reaction) Examples of SN reactions, (a) Hydrolysis :  AgOH  ROH  AgX Properties of Alkyl Halides (1) Physical properties (i) CH 3 F, CH 3 Cl, CH 3 Br and C 2 H 5 Cl are gases at room temperature. The alkyl halides upto C18 are colourless liquids while U higher members are colourless solids. (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. (v) Alkyl iodides become violet or brown in colour on exposure as they decompose in light. Light 2 RI  R  R  I 2 (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. (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, Iodide > Bromide > Chloride (Nature of the halogen atom) Tertiary > Secondary > Primary (Type of the halogen atom) 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. U RX HCl ST Slow  RX Rydon method Zn  Cu   Nu  R  X  R   R  Nu ( S N 1 reaction) Alkylhalide ROH   Dihalide Nu   R  X  Nu  R  X  Transition state or antimony trifluoride. (swart reaction) 2CH 3 Cl  Hg 2 F2 2CH 3 F  Hg 2 Cl 2 X 2  ( PhO )3 P  (i) Nucleophilic substitution (SN) reactions : The C  site is susceptible to attack by nucleophiles (An electron rich species). X  Reflux KI, H 3 PO4 ROH      C X This polarity is responsible for reactions, (i) Nucleophilic substitution reactions (ii) Elimination reactions  R  X  NaI  R  I  NaX (X  Cl, Br) (6) Other method 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. E3 || Amongst the primary alkyl halide, the order of reactivity is : CH 3 X  C 2 H 5 X  C 3 H 7 X , etc. 60 Pyridine CH 3 CH 2 OH  SOCl 2  CH 3 CH 2 Cl  SO 2  HCl HBr AgOH CH 2  CH 2  CH 3 CH 2 Br  CH 3 CH 2 OH Ethylene Ethyl bromide Ethyl alcohol (b) Reaction with alkoxides or dry silver oxide : Heat RX  NaOR'   NaX ROR' Unsym. ether 2 RX  Ag 2 O  R  O  R  2 AgX Sym. ether (c) Reaction with sodium or potassium hydrogen sulphide : RX  NaSH  Sodium hydrogen sulphide RSH  NaX Thioalcohol or Alkanethiol or Alkylmercaptan (d) Reaction with alcoholic potassium cyanide and silver cyanide : Alcohol RX  KCN   RCN  KX Alkylcyanide or Alkane nitrile (e) Reaction with potassium nitrite or silver nitrite :  RX  K  O  N  O  R  O  N  O  KX Alkylnitrite  RX  AgNO 2  RN O  AgX O Nitro- alkane (f) Reaction with ammonia : C2 H 5 Br  H  NH 2  C2 H 5 NH 2  HBr Ethylamine(p.) 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.)   The primary alkyl halides undergo reactions either by S N 2 or (C2 H 5 )3 N  BrC2 H 5  (C2 H 5 )4 NBr E 2 mechanisms which involve the formation of transition state. The Tetraethylammonium bromide(Qu aternary) 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  C 3 H 7 X , etc. (g) Reaction with silver salts of fatty acids : R' COOAg  XR  R' COOR  AgX Ester (h) Reaction with sodium acetylide : Example of elimination reaction (a) Dehydrohalogenation : RX  NaC  CH  R  C  CH  NaX Alkyne C n H 2n 1 X  KOH  C n H 2n  KX  H 2 O (i) Reaction with sodium or potassium sulphide : (Alcoholic) 2 RX  Na 2 S  R  S  R  2 NaX C 2 H 5 Br  KOC 2 H 5  C 2 H 5  O  C 2 H 5  KBr RX  NaSR '  R  S  R' NaX (b) Action of heat : C 2 H 5 Br  NaSCH 3  C 2 H 5  S  CH 3  NaBr 300 C RCH 2 CH 2 X    RCH  CH 2  HX Ethyl methyl thioether Alkene 300 C (j) Reaction with halides :  NaBr  Alkylchloride RBr Alkyl bromide NaI   C 2 H 5 Br   CH 2  CH 2  HBr Ethene RI Alkyl iodide | | |  U | Slow E1 reaction : R  C  C  H   R  C  C  H | X | H X  H H D YG | Fast   R  C  C  H  B  H | H B : H H | | | | BH H | | | | E2 Reaction : R  C  C  H  R  C  C  H Slow H X H X Transiton state H |  R  C  C  H  B  H  X Fast  U | H ST 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 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 X, CH R X, R CH 2 RX  2 H  R  H  HX 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. 2 RX  2 Na  R  R  2 NaX (c) Reaction with magnesium : Alkyl halides form Grignard reagent when treated with dry magnesium powder in dry ether. Dry ether RX  Mg   R  Mg  X (Powder ) Grignard reagent 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 2C 2 H 5 Br  2 Zn  (C 2 H 5 )2 Zn  ZnBr2 Heat  When heated with lead-sodium alloy, ethyl bromide gives tetra ethyl lead which is used an antiknock compound in petrol. 4 C2 H 5 Br  4 Pb(Na) (C2 H 5 )4 Pb  4 NaBr  3 Pb  Reaction with lithium : Alkyl halides react with lithium in dry ether to form alkyl lithiums. Ether RX  2 Li   R  Li  LiX ; 2o 2o The decomposition follows the following order, Iodide > Bromide > Chloride (When same alkyl group is present) and Tertiary > Secondary > Primary (When same halogen is present). (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 LiAlH4. ID (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. B.. H H H H | 60 Thioether Thioethers can also be obtained by RCl Alkene In this reactions, ether is a by-product as potassium ethoxide is always present in small quantity. E3 Sodium acetylide X C 2 H 5 Br  Ethyl bromide 2 Li  C 2 H 5  Li  LiBr Alkyl lithiums are similar in properties with Grignard reagents. These are reactive reagents also. (e) Friedel-Craft's reaction : AlCl3 C 6 H 6  RCl    C 6 H 5 R  HCl  H 3O    RCH (COOH )2 Alkylbenzene Hydrolysis AlBr3 C6 H 6  C 2 H 5 Br   C6 H 5 C 2 H 5  HBr (f) Substitution (Halogenation) : Alkyl halides undergo further halogenation in presence of sunlight, heat energy or peroxide. Br2 Br2 C 2 H 5 Br   C 2 H 4 Br2   C 2 H 3 Br3..... Ethylene diamine hv CH 2  X CH 2 OCOCH 3 2 CH 3 COONa |   |  2 NaX. CH 2  X CH 2 OCOCH 3 60 hv Preparations and properties of Dihalides (1) Methods of preparation of dihalides (i) Methods of preparation of gemdihalide (a) From alkyne (Hydrohalogenation) : Tri-halides (Chloroform and iodoform) R  C  C  H  HX  R  C  C  H | | X H X |  HX  R  C  CH 3 | (b) From carbonyl compound : POCl3  If ketone is taken internal dihalide formed. (ii) Methods of preparation of vicinal dihalide (a) From alkene [By halogenation] : R  CH  CH 2  Cl 2  R  C H  C H 2 | Cl D YG | Cl (b) From vicinal glycol : R  CH  OH | CH 2 OH  2 PCl5  R  CH  Cl | CH 2 Cl  2 HCl  2 POCl3 ST U (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  H 2O    RCHO (b) Reaction with alcoholic KOH : H | X NaNH 2   R  C  CH ( NaX  NH 3 ) Alc. KOH R  CH  CH 2   R  C  C  H  2 KX  2 H 2 O | | X (c) Reaction with Zn dust (a) From alcohol [Cl 2  H 2 O  2 HCl  O] CH 3 CH 2 OH  O  CH 3 CHO  H 2 O Ethylalcohol Acetaldehyde CH 3 CHO  3 Cl 2  CCl 3 CHO  3 HCl Acetaldehyde Chloral [So Cl 2 acts both as an oxidising and chlorinating agent] Chloral, thus, formed, is hydrolysed by calcium hydroxide. CCl CHO OHC CCl 3 3  H  O  Ca  O  H Hydrolysis    2CHCl 3  (HCOO )2 Ca Chloroform Calciumformate (b) From acetone CH 3  CO  CH 3  3Cl 2  CCl 3 COCH 3  3 HCl Trichloroacetone CCl 3 H COCH 3  H 3 C.CO O Ca O  CCl 3 H   2CHCl 3  (CH 3 COO )2 Ca Chloroform Calciumacetate | ( KX  H 2 O ) X H 2 O  Ca(OH )2  Cl 2 Hydrolysis RCH 2  CHX 2  R  C  C  H Alc.KOH CaOCl 2  Bleachingpowder U RCHCl 2  [Terminal dihalide] 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. ID X RCHO  PCl5  (e) Other substitution reaction CH 2  X CH 2  NH 2 NH 3 / 373 K  |   | CH 2  X CH 2  NH 2 E3 Benzene  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 (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. Fe / H 2O 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. CCl 3 CH (OH )2  NaOH  CHCl 3  HCOONa  H 2 O (vi) Heating with silver powder : Chloral hydrate H  C  Cl 3  6 Ag  Cl 3  C  H  CH  CH  6 AgCl Acetylene (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. (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 : Cl Cl Lightand air  [O]   H Cl Chloroform H C Cl  Na OC 2 H 5  3 NaCl Cl  Na OC 2 H 5   H  C Cl  Na OC 2 H 5 Ethyl orthoforma te 65 C C6 H 5 OH  CHCl 3  3 NaOH   CO Phosgene (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.)  D YG U 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 Zn / HCl CHCl 3  2 H   CH 2 Cl 2  HCl (alc.) CHCl 3  6 H  CH 4  3 HCl Zn / H 2 O (iii) Chlorination : HCl U CCl 4  Carbon tetrachloride (iv) Hydrolysis : Cl  Na OH (aq.)    NaCl Cl  Na OH (aq.)     HC  Cl  Na OH (aq.) ST H C H O 2   H  C OH   OH  OH  Unstable (Orthoform ic acid) O NaOH    H  C OH  H 2 O Formic acid 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. CHCl 3  HONO 2  Nitricacid CNO 2 Cl 3  Chloropicrin (Tear gas)  3 NaCl  2 H 2 O Hydroxy benzaldehyde(salicylaldehyde) Cl  HCl  Cl UV light CHCl 3  Cl 2   OH CHO C6 H 4 Unstable (ii) Reduction : OC 2 H 5 OC 2 H 5 OC 2 H 5 (ix) Reimer-Tiemann reaction : Cl OH C CH 3 CH 3 (viii) Reaction with sodium ethoxide : E3 C C Chloretone (1,1,1- Trichloro- 2 - methyl- 2 - propanol) ID Cl Cl CH 3 HO ( NaOH )   CH 3 Cl3 C Cl3 CH  O  C 60  Chloral hydrate is a stable compound inspite of the fact that two OH groups are linked to the same carbon H O atom. This is due to the fact that intramolecular Cl Cl  C  C  H hydrogen bonding exists in the molecule between Cl O H chlorine and hydrogen atom of OH group. H 2O RNC Carbylaminoalkane (Alkylisonitrile)  3 KCl  3 H 2 O This reaction is also used for the test of chloroform. (4) Uses (i) It is used as a solvent for fats, waxes, rubber, resins, iodine, etc. (ii) It is used for the preparation of chloretone (a drug) and chloropicrin (Insecticide). (iii) It is used in laboratory for the test of primary amines, iodides and bromides. (iv) It can be used as anaesthetic but due to harmful effects it is not used these days for this purpose. (v) It may be used to prevent putrefaction of organic materials, i.e., in the preservation of anatomical species. (5) Tests of chloroform (i) It gives isocyanide test (Carbylamine test). (ii) It forms silver mirror with Tollen's reagent. (iii) Pure Chloroform does not give white precipitate with silver nitrate. Iodoform or tri-iodomethane, CHI3 Iodoform resembles chloroform in the methods of preparation and properties. (1) Preparation (i) Laboratory preparation : From ethanol : CH 3 CH 2 OH  I2  CH 3 CHO  2 HI Acetaldehyde CH 3 CHO  3 I2  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 I2  CI 3 COCH 3  3 HI Triiodoaceton e Na 2 CO 3 , the iodoform test is mainly given by ethyl alcohol CI 3 COCH 3  KOH  CHI 3  CH 3 COOK O Pot. acetate || Sodium carbonate can be used in place of KOH or NaOH. These reactions are called iodoform reactions. (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  || one ( C CH 3 ), secondary alcohols or 2-ol (CHOH  CH 3 ) and secondary alkyl halide at C 2 (CHCICH 3 ). Also lactic acid ( O || CH 3  CHOH  COOH ) , Pyruvic acid (CH 3  C  COOH ) and O || Anode methyl phenyl ketone (C 6 H 5  C  CH 3 ) give this test. 2 I  I 2  2e  K  e K O Tetra-halides (Carbon tetrachloride, CCl4) 1 K  H 2 O  KOH  H 2 2 E3 Cathode (CH 3 CH 2 OH ), acetaldehyde (CH 3  C  H ), -methyl ketone or 2- 60 Iodoform (iii) Iodoform reaction : With I 2 and NaOH or I 2 and It is the most important tetrahalogen derivative of methane. (1) Manufacture KOH is neutralised by CO 2 : 400 C CH 4  4 Cl 2    CCl 4  4 HCl (i) From methane : C 2 H 5 OH  4 I 2  3 Na 2 CO 3  CHI 3 (ii) From carbon disulphide :  HCOONa  5 NaI  3CO 2  2 H 2 O ID Fe/I2 / AlCl3 CS 2  3 Cl 2   CCl 4  S 2 Cl 2 D YG (3) Chemical Reactions of iodoform KOH Hydrolysis Reduction Red P/HI Heating Ag powder CHI3 HCOOK Potassium formate Heating alone ST tetrachloride. CS 2  2S 2 Cl 2  CCl 4  6 S 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 : 400 C C 3 H 8  9 Cl 2    70 -100 Methylene iodide Acetylene C6H5 NC Phenol isocyanide Iodine vapours, 4CHI3+3O2 4CO + 6I2 + 2H2O Yellow precipitate of AgI (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 for antiseptic properties. (5) Tests of iodoform (i) With AgNO3 : CHI 3 gives a yellow precipitate of AgI. (ii) Carbylamine reaction : CHI 3 on heating with primary amine and alcoholic KOH solution, gives an offensive smell of isocyanide (Carbylamine). 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 CH  CH (Less stable than CHCl3) With AgNO3 S 2 Cl 2 further reacts with CS 2 to form more of carbon CH2I2 U Carbylamine reaction C6H5NH2+KOH (alc.) Sulphur monochlori de U (2) Physical properties (i) It is a yellow crystalline solid. (ii) It has a pungent characteristic odour. (iii) It is insoluble in water but soluble in organic solvents such as alcohol, ether, etc. (iv) It has melting point 119°C. It is steam volatile. 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 : 4 KCl CCl 4  4 KOH   [C(OH )4 ] Unstable 2 H 2 O 2 KOH   CO 2    K 2 CO 3  H 2 O (iv) Reaction with phenol (Reimer-tiemann reaction) : OH  4 NaCl  2 H 2 O COOH (4) Uses (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. (ii) It is used as a solvent for fats, oils, waxes and greases, resins, iodine etc. (iii) It finds use in medicine as helmenthicide for elimination of hook worms. Vinyl chloride CHCl  HCl  600-650°C Allylalcohol Acetone C H 2  CH  CH 2  NaI   C H 2  CH  CH 2  NaCl | Cl I This is halogen- exchange reaction and is called Finkelstein reaction. | CH 2  CH 2  Cl 2   CH 2  CHCl HgCl Vinyl chloride D YG (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. 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 : |  C HI CH  I2 | CH 2 I 1,2,3- Tri- iodopropan e || CH 2 Allyliodide CH 2  CH  CH 2 I   Substitution reactions : Nucleophilic substitution reactions occur, NaOH Addition reactions CH2 = CH – CH2OH Allyl alcohol KCN (ii) Carbon atom is sp 2 hybridized and C  Cl bond length is shorter (1.69Å) and the bond is stronger than in alkyl halides (1.80Å) due to sp 3 hybridization of the carbon atom.  [CH 2  CH  C H 2  C H 2  CH  CH 2 ]  I  U 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. ST C H2I Heat 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, (ii) CH2 = CH – CH2CN Allyl cyanide CH2 = CHCH2I NH3 CH2 = CH – CH2NH2 Allyl amine CH3ONa CH2Br – CHBrCl CH2 = CH – CH2OCH3 Allyl methyl ether 1,2-Dibromo-1-Chloroethane AgNO2 HBr | (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.. CCl4 C H2I U (iii) From acetylene : 2 CH  CH  HCl   CH 2  CHCl 2 Glycerol Vinyl chloride Br2 Allyliodide Allylchloride CH 2 OH 500 C | Heat C H 2 OH (ii) From ethylene : (i) Cl | (ii) C HOH  3 HI  3 H O.. Allylchloride Cl | OH || CH 2 70 C | Propene ID CH 2Cl 500 C   C H 2  CH  CH 2 (i) CH 3 CH  CH 2  Cl 2  | (1) Synthesis : Vinyl chloride can be synthesised by a number of methods described below: (i) From ethylene chloride : CH 2 Cl CHCl  KCl  H 2 O | || + Alc. KOH CH 2Cl CH 2 | (1) Synthesis : It is obtained, Heat 3 C H 2  CH  CH 2  PCl3   3 C H 2  CH  CH 2  H 3 PO3 Vinyl chloride or chloroethene, CH2=CHCl CH 2 Cl Allyl iodide or 3-iodopropene-1, ICH2CH = CH2 Or Unsaturated halides (Halo-alkene) Ethylene chloride (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. 60 Salicylicacid E3  4 NaOH C 6 H 5 OH  CCl 4   C 6 H 4 CH3 – CHBrCl 1-Bromo-1-Chloroethane CH2 = CHCl CH2 = CH – CH2NO2 3-Nitropropene-1 Addition reactions : Electrophilic addition reactions take place in accordance to Markownikoff's rule. CH 2  CH  CH 2 I  Br2  CH 2 Br  CHBr  CH 2 I 1,2 Dibromo- 3- iodopropan e Polymerisation Peroxide NaOH No reaction CH 2  CH  CH 2 I  HBr  CH 3 CHBrCH 2 I 2 Bromo -1-iodopropan e Allyl iodide is widely used in organic synthesis. Halo-arenes In these compounds the halogen is linked directly to the carbon of the benzene nucleus. (1) Nomenclature : Common name is aryl halide IUPAC name is halo-arene. Example : Cl Br 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 Cl Benzylbromide Bromobenzene Cl Br2 /Fe X + X2 + HX C6H5Cl  NaNO 2 , HCl C 6 H 5 NH 2   C 6 H 5 N 2 C l  CuBr C6H5Br KI C6H5I HBF4 C6H5F D YG (iii) Hunsdiecker reaction : 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 3 2 ArTl(OOCF3 )2   ArI KI  Aryl thallium trifluoroacetate ST U (3) Physical properties (i) Physical state : Haloarenes are colourless liquid or crystalline solid. (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. (iii) Halo-arenes are heavier than water. (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... : Cl : AlCl3 Cl + (iii) Wurtz – fittig reaction : CH3 Na C6 H 5 Br  CH 3 Br   C6 H 5 CH 3  2 NaBr U 5 C CH3 CH3Cl NO2 Br Br Cl ID CuCl + Cl + Cl Lewis acid  FeX 3 , AlX3 , Tl(OAC)3 ; X 2  Cl 2 , Br2 (ii) From diazonium salts Cl E3 (2) Methods of preparation (i) By direct halogination of benzene ring NO2 H2SO4 + HNO3 Benzylchloride Chlorobenzene Cl 60 Cl ; Ether (iv) Formation of grignard reagent : Mg C6 H 5 Br   C6 H 5 MgBr Ether (v) Ullmann reaction 2 Cu I + CuI2 Diphenyl 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), CF2 Cl 2 (dichlorodifluoro-methane), HCF2 CHCl 2 (1,1-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 CF2 Cl 2 which is commonly known as freon and freon-12. Freon or freon-12 (CF2 Cl 2 ) is prepared by treating carbon tetrachloride with antimony trifluoride in the presence of antimony pentachloride as a catalyst. 5 3CCl 4  2SbF3   3CCl 2 F2  2SbCl 3 SbCl Catalyst Or it can be obtained by reacting carbon tetrachloride with hydrofluoric acid in presence of antimony pentafluoride. 5 CCl 2 F2  2 HCl CCl 4  2 HF  SbF Cl Cl  Cl   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 (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. SbF3 800 C CHCl 3   CHF2 Cl    CF2  CF2  HCl HF (b.pt.- 76 C) On polymerisation tetrafluoroethylene forms a plastic-like material which is called teflon.  (CF2  CF2 )n Teflon Cl Cl + 3Cl2 CH  CH  2Cl 2  CHCl 2  CHCl 2 (1,1,2,2  Tetrachloroethane) D YG 2CHCl 2  CHCl 2  Ca(OH )2  2CHCl  CCl 2  CaCl 2  2 H 2 O Westrosol (Trichloroethene) ST U 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) –1,1,1-trichloroethane : H H | CCl3–C=O + Cl Conc. H2SO4 H | Cl3C – C Cl Benzene BHC insecticide. (7) Perfluorocarbons (PFCs) : Perfluorocarbons (Cn F2n  2 ) are obtained by controlled fluorination of vapourized alkanes diluted with nitrogen gas in the presence of a catalyst. Cl + H2O C7 H16  16 F2 2  Vapour pha se, N , 573 K CoF 2 (Catalyst) C7 F16  16 HF Perfluoroh eptane These are colourless, odourless, non-toxic, non-corrosive, nonflammable, 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, liquid ventilation, carbon monoxide poisoning and many medical diagnosis. Organometallic compounds 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. Example : Methyl lithium (CH 3 Li) , Dialkyl zinc (R2 Zn) , Alkyl magnesium halide (R  Mg  X ) H Chloral (1mol) Cl Chlorobenzene (2mol) Properties and uses of D.D.T. Cl Cl 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.  aaaeee conformation of C6 H 6 Cl 6 is most powerful U 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 ). Westron Cl Sunlight ID 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. E3 nCF2  CF2 Tetrafluoroethylene (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 : 60 air-conditioning and in domestic refrigerators for cooling purposes (As refrigerant). It causes depletion of ozone layer. Cl D.D.T. (1) Methyl lithium : CH 3 I  Methyl iodide Ether 2 Li   CH 3 Li  LiI 10 C Methyl lithium  High reactivity of CH 3 Li over grignard reagent is due to greater polar character of C  Li bond in comparison to C  Mg bond. Chemical properties (i) CH 3  Li  H  OH  CH 4  LiOH |  C  |   Mg X  R  Mg X or The alkyl group acts as carbanion. The majority of reaction of grignard reagent fall into two groups: (i) Double decomposition with compound containing active hydrogen atom or reactive halogen atom (ii) CH 3  Li  CH 2  CH 2  CH 3 CH 2 CH 2 OLi RMgX  HOH  RH  Mg(OH )X H 2O   CH 3 CH 2 CH 2 OH  LiOH O || RMgX  D2 O  RD  Mg(OD)X RMgX  R' OH  RH  Mg(OR' )X 60 O RMgX  R' NH 2  RH  Mg(R' NH )X (iii) CH 3  Li  CO 2  CH 3  C  O  Li H 2O   CH 3 COOH  LiOH RMgX  R' I  R  R' MgIX | H E3 RMgX  ClCH 2 OR'  RCH 2 OR' MgClX (iv) CH 3  Li  H  C  O  CH 3 CH 2  O  Li (ii) Addition reaction with compounds containing  CH 3 CH 2 OH  LiOH H 2O  R  Li  CH 2  CH 2  R  CH 2  CH 2  Li C  O  RMgX  C  S etc. H OH C  O MgX  | ID  Unlike grignard reagents, alkyl lithium can add to an alkenic double bond. C  O ; C  N , R C  OH  Mg (2) Dialkyl zinc : First organometallic compound discovered by Frankland in 1849. CO 2 CO 2 Dialkylzinc D YG Chemical properties Preparation of quaternary hydrocarbon : R OH X H OH  C  N  RMgX   C  N MgX | O H2 R U Heat Heat 2 RI  2 Zn   2 R  Zn  I   R 2 Zn  ZnI2 | (CH 3 )3 CCl  (CH 3 )2 Zn  (CH 3 )4 C  CH 3 ZnCl   C  O  NH 3  Mg | R OH X 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. C2 H5 | :O : | | Mg | X C2 H5 | :O : | C2 H 5 U C2 H 5 R ST Grignard reagents are never isolated in free sate on account of their explosive nature.  For given alkyl radical the ease of formation of a grignard reagent is, Iodide > Bromide > Chloride Usually alkyl bromides are used.  For a given halogen, the ease of formation of grignard reagent is, CH 3 X  C2 H 5 X  C3 H 7 X..........  Iodination of alkanes is a reversible process, therefore, formation of iodoalkanes is possible only in the presence of oxidising agents such as HIO3.  Iodination with methane does not take place at all.  Fluorination of alkanes takes place with rupture of C– C bonds in higher alkanes. Therefore alkyl fluorides are generally prepared by halide exchange reactions.  Phosphorous halides are generally used to prepare lower alkyl bromides in the laboratory.  Since tertiary alkyl iodides eliminate HI to form an alkene, tertiary alkyl chlorides are used in place of tertiary alkyl iodides.  SOBr2 is less stable and SOI2 does not exist. Thus, R – Br and  Grignard reagent cannot be prepared from a compound which consists in addition to halogen, some reactive group such as OH because it will react rapidly with the grignard reagent.  Hunsdiecker reaction proceeds through free radical The C  Mg bond in grignard reagent is some what covalent but highly polar. R – I cannot be prepared by Darzan’s method. mechanism. It is used to reduce the length of carbon chain.  Reactivity of halides towards SN1 mechanism is 3°>2°>1°.  Reactivity of halides towards SN2 mechanism is 1°>2°>3°.  Polar solvents favour SN1 mechanism.  Non polar solvents favour SN2 mechanism.  High concentration of nucleophile favour SN2 mechanism while low concentration of nucleophile favour SN1 mechanism.  SN1 reactions partial racemisation occurs with inverted product predominant in yield whereas in SN2 reactions, inverted product is formed. 60  Order of nucleophilicity among halide ions decreases in the order I– > Br– > Cl–- > F–.  During elimination reactions, the H atom is lost from the  C2H5SH (Ethyl mercaptan) is added to LPG (household cooking gas) to detect leakage. The compound has a typical smell.  In Sandmeyer reaction, Cl of CuCl is attached to benzene ring.  Nuclear halogenation takes place by electrophilic substitution ID mechanism whereas side chain halogenation takes place by free radical mechanism. E3 carbon atom carrying minimum number of H atom.  Aryl halides and vinyl halides (CH2 = CH – X) are less U 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.  Before using the sample of chloroform as an anaesthetic it is D YG tested by treating with aqueous solution of AgNO3. A pure sample does not give ppt. with aq. AgNO3.  Halothane, CF3-CHClBr, is a general anaesthetic which replace diethyl ether.  CCl4 resist hydrolysis with boiling water due to non availability of d-orbital in C.  C2Cl6 is an solid and is known as atificial camphor. ST U  Chlorobenzene commercially produced by Raschig process.