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Hydrocarbon 1081 Chapter 24...

Hydrocarbon 1081 Chapter 24 Hydrocarbon Aliphatic Hydrocarbon unpleasant smell of petroleum is due to sulphur compounds. Nitrogenous compounds are pyridines, Organic compounds composed of only carbon and quinolines and pyrroles. Oxygen compounds present in hydrogen are called hydrocarbons. Hydrocarbons are petroleum are. Alcohols, Phenols and resins. two types Compounds like chlorophyll, haemin are also present in (1) Aliphatic Hydrocarbon (Alkanes, Alkenes and it. Alkynes). (v) Natural gas : It is a mixture of Methane (2) Aromatic Hydrocarbon (Arenes) (80%), Ethane (13%), Propane (3%), Butane (1%), (1) Sources of aliphatic hydrocarbon Vapours of low boiling pentanes and hexanes (0.5%) Mineral oil or crude oil, petroleum [Petra rock; and Nitrogen (1.3%). L.P.G. Contain butanes and oleum oil] is the dark colour oily liquid with pentanes and used as cooking gas. It is highly offensive odour found at various depths in many inflammable. This contain, methane, nitrogen and regions below the surface of the earth. It is generally ethane. found under the rocks of earth’s crust and often floats over salted water. (vi) C.N.G. : When natural gas compressed at (2) Composition very high pressure is called compressed natural gas (CNG). Natural gas has octane rating of 130 it consists, (i) Alkanes : found 30 to 70% contain upto 40 mainly of methane and may contain, small amount of carbon atom. Alkanes are mostly straight chain but ethane and propane. some are branched chain isomers. (ii) Cycloalkanes : Found 16 to 64% cycloalkanes (3) Theories of origin of petroleum : Theories present in petroleum are; cyclohexane, methyl must explain the following characteristics associated cyclopentane etc. cycloalkanes rich oil is called with petroleum, asphaltic oil. Its association with brine (sodium chloride (iii) Aromatic hydrocarbon : found 8 to 15% solution). The presence of nitrogen and sulphur compound present in petroleum are; Benzene, Toluene, compounds in it. The presence of chlorophyll and Xylene, Naphthalene etc. haemin in it. Its optically active nature. Three (iv) Sulphur, nitrogen and oxygen compound : important theories are as follows. Sulphur compound present to the extent of 6% include mercaptans [R-SH] and sulphides [R-S-R]. The (i) Mendeleeff’s carbide theory or inorganic theory  1082 Hydrocarbon (ii) Engler’s theory or organic theory (5) Petroleum refining : Separation of useful fractions by fractional distillation is called petroleum (iii) Modern theory refining. (4) Mining of petroleum : Petroleum deposits occurs at varying depth at different places ranging from 500 to 15000 feet. This is brought to the surface by artificial drilling. Table : 24.1 Fraction Boiling range ( oC) Approximate Uses composition Uncondensed gases Upto room C1 – C4 Fuel gases: refrigerants; production of temperature carbon black, hydrogen; synthesis of organic chemicals. Crude naphtha on 30 – 150o C5 – C10 refractionation yields, (i) Petroleum ether 30 – 70o C5 – C6 Solvent (ii) Petrol or gasoline 70 – 120o C6 – C8 Motor fuel; drycleaning; petrol gas. (iii) Benzene derivatives 120 – 150o C8 – C10 Solvent; drycleaning Kerosene oil 150 – 250o C11 – C16 Fuel; illuminant; oil gas Heavy oil 250 – 400o C15 – C18 As fuel for diesel engines; converted to gasoline by cracking. Refractionation gives, (i) Gas oil, (ii) Fuel oil, (iii) Diesel oil Residual oil on Above 400o C17 – C40 fractionation by vacuum distillation gives, (i) Lubricating oil C17 – C20 Lubrication (ii) Paraffin wax C20 – C30 Candles; boot polish; wax paper; etc (iii) Vaseline C20 – C30 Toilets; ointments; lubrication. (iv) Pitch C30 – C40 Paints, road surfacing Petroleum coke As fuel. (on redistilling tar) (6) Purification 2 RSH  Na 2 PbO 2  S RSSR  PbS  2 NaOH Mercaptan Disulphide s (i) Treatment with concentrated sulphuric acid : The gasoline or kerosene oil fraction is shaken with (iii) Treatment with adsorbents : Various fractions are passed over adsorbents like alumina, sulphuric acid to remove aromatic compounds like silica or clay etc, when the undesirable compounds get thiophene and other sulphur compound with impart offensive odour to gasoline and kerosene and also make adsorbed. them corrosive. (7) Artificial method for manufacture of Petrol or gasoline (ii) Doctor sweetening process : (i) Cracking, (ii) Synthesis  Hydrocarbon 1083 (i) Cracking : It is a process in which high boiling The tendency to knock falls off in the following fractions consisting of higher hydrocarbons are heated order : Straight chain alkanes > branched chain alkanes strongly to decompose them into lower hydrocarbons > olefins > cyclo alkanes > aromatic hydrocarbons. with low boiling points. Cracking is carried out in two (2) Octane number : It is used for measuring the different ways. knocking character of fuel used in petrol engine. The (a) Liquid phase cracking : In this process, the octane number of a given sample may be defined as the heavy oil or residual oil is cracked at a high percentage by volume of iso-octane present in a temperature (475 – 530oC) under high pressure (7 to 70 mixture of iso-octane and n-heptane which has the atmospheric pressure). The high pressure keeps the same knocking performance as the fuel itself. reaction product in liquid state. The conversion is CH 3  CH 2  CH 2  CH 2  CH 2  CH 2  CH 3 approximately 70% and the resulting petrol has the n-heptane; octane no. = 0 octane number in the range 65 to 70. CH 3 CH 3 | | The cracking can be done in presence of some CH 3  C  CH 2  C  CH 3 ; Octane no. = 100 | catalysts like silica, zinc oxide, titanium oxide, ferric CH 3 oxide and alumina. The yields of petrol are generally 2, 2, 4-Trimethyl pentane or Iso-octane. high when catalyst is used. For example : a given sample has the knocking (b) Vapour phase cracking : In this process, performance equivalent to a mixture containing 60% kerosene oil or gas oil is cracked in vapour phase. The iso-octane and 40% heptane. The octane number of the temperature is kept 600 – 800oC and the pressure is gasoline is, therefore, 60. about 3.5 to 10.5 atmospheres. The cracking is Presence of following types of compounds facilitated by use of a suitable catalyst. The yields are increases the octane number of gasoline. about 70%. (i) In case of straight chain hydrocarbons octane number decreases with increase in the length of the (ii) Synthesis : Two methods are applicable for chain. synthesis. (ii) Branching of chain increases the value of (a) Bergius process : This method was invented octane number (iii) Introduction of double bond or triple bond by Bergius in Germany during first world war. increases the value of octane number. Coal  H 2 2o Mix. Of hydrocarbons or crude Fe O3 (iv) Cyclic alkanes have relatively higher value of 450 500 C octane number. 250 atm (v) The octane number of aromatic hydrocarbons oil are exceptionally high (b) Fischer- tropsch process : The overall yield of (vi) By adding gasoline additives (eg TEL) this method is slightly higher than Bergius process. (3) Antiknock compounds : To reduce the o knocking property or to improve the octane number of H 2 O  C   CO  H 2 1200 C a fuel certain chemicals are added to it. These are Water gas called antiknock compounds. One such compound, xCO  yH 2  Mix. Of hydrocarbon  H 2 O. which is extensively used, is tetraethyl lead (TEL). TEL is used in the form of following mixture, The best catalyst for this process is a mixture of TEL = 63%, Ethylene bromide = 26%, Ethylene cobalt (100 parts), thoria, (5 parts), magnesia (8 parts) chloride = 9% and a dye = 2%. and kieselguhr (200 parts). However, there is a disadvantage that the lead is Characteristics of hydrocarbons deposited in the engine. To remove the free lead, the (1) Knocking : The metallic sound during ethylene halides are added which combine with lead to working of an internal combustion engine is termed as form volatile lead halides. knocking. Pb  Br  CH 2  CH 2  Br PbBr 2  CH 2  CH 2 Ethy lene bromide Volatile Ethy lene “The greater the compression greater will be efficiency of engine.” The fuel which has minimum However, use of TEL in petrol is facing a serious knocking property is always preferred. problem of Lead pollution, to avoid this a new compound cyclopenta dienyl manganese carbonyl  1084 Hydrocarbon (called as AK-33-X) is used in developed countries as The flash point in India is fixed at 44 o C , in antiknocking compound. France it is fixed at 35oC, and in England at 22.8oC. The flash point of an oil is usually determined by means of (4) Other methods of improving octane number “Abel’s apparatus”. of hydrocarbon. Chemists have prepared some hydrocarbons with (i) Isomerisation [Reforming] : By passing an octane number even less than zero (e.g., n-nonane has alkane over AlCl 3 at 200 o C. octane number – 45) as well as hydrocarbon with octane number greater than 100 (e.g., 2, 2, 3 trimethyl- CH 3 butane. has octane number of 124). | (7) Petrochemicals : All such chemicals which are CH 3 CH 2 CH 2 CH 2 CH 3   AlCl 3 o CH 3 CHC H 2 CH 3 derived from petroleum or natural gas called Pentane 200 C Isopentane (Octane number  62) (Octane number  90 ) petrochemicals. Some chemicals which are obtained from petroleum are summarised in table : (ii) Alkylation : Table : 24.2 CH 3 CH 3 CH 3 CH 3 | | | | Hydrocarbons Compounds derived H SO 4 CH 3 CH  CH 2  C CH 3 2 CH 3 CCH 2 CHCH 3 Methane Methyl chloride, chloroform, methanol, | Isobutylene | formaldehyde, formic acid, freon, CH 3 CH 3 hydrogen for synthesis of ammonia. Isobutane Iso- octane (Octane number  100) Ethane Ethyl chloride, ethyl bromide, acetic acid, acetaldehyde, ethylene, ethyl (iii) Aromatisation : acetate, nitroethane, acetic anhydride. CH 3 Ethylene Ethanol, ethylene oxide, glycol, vinyl chloride, glyoxal, polyethene, styrene, CH 3 (CH 2 )5 CH 3  o   Pt / Al2 O3  4H2 Heptane 500 C butadiene, acetic acid. Propane Propanol, propionic acid, isopropyl ether, Toluene acetone, nitromethane, nitroethane, The octane no. of petrol can thus be improved. nitropropane.  By increasing the proportion of branched chain Propylene Glycerol, allyl alcohol, isopropyl alcohol, acrolein, nitroglycerine, dodecylbenzene, or cyclic alkanes. cumene, bakelite.  By addition of aromatic hydrocarbons Benzene, Hexane Benzene, DDT, gammexane. Toluene and Xylene (BTX). Heptane Toluene  By addition of methanol or ethanol. Cycloalkanes Benzene, toluene, xylenes, adipic acid. Benzene Ethyl benzene, styrene, phenol, BHC  By additon of tetraethyl lead (C2 H 5 )4 Pb (insecticide), adipic acid, nylon, cyclohexane, ABS detergents. (5) Cetane number : It is used for grading the diesel oils. Toluene Benzoic acid, TNT benzaldehyde, saccharin, chloramine-T, benzyl chloride, CH 3  (CH 2 )14  CH 3 Cetane cetane no. = benzal chloride. 100 CH3 Alkanes [Paraffines] “Alkanes are saturated hydrocarbon containing Cetane no. = 0 only carbon-carbon single bond in their molecules.” -Methyl naphthalene Alkanes are less reactive so called paraffins; because under normal conditions alkanes do not react The cetane number of a diesel oil is the with acids, bases, oxidising agents and reducing agent. percentage of cetane (hexadecane) by volume in a General formula : Cn H 2n2 mixture of cetane and  -methyl naphthalene which Examples are CH 4 , C2 H6 , C3 H8 , has the same ignition property as the fuel oil under consideration. (1) General Methods of preparation (6) Flash point : The lowest temperature at (i) By catalytic hydrogenation of alkenes and which an oil gives sufficient vapours to form an alkynes (Sabatie and sanderen’s reaction) explosive mixture with air is referred to as flash point of the oil.  Hydrocarbon 1085 C n H 2 n  H 2  C n H 2 n  2 ; Cn H 2n2  2 H 2  Cn H 2n2 At anode [Oxidation] : Ni Ni Alkene heat Alkane Alkyne heat Alkane   2 R  C  O   2e   2 R  C  O  2 R  2CO 2  Methane is not prepared by this method || || O O (ii) Birch reduction :  2 R  R  R (alkane) R  CH  CH 2  R  CH 2  CH 3 3 1. Na / NH 2. CH 3 OH At cathode [Reduction] : (iii) From alkyl halide 2 Na   2e   2 Na   2 NaOH  H 2 (  ) 2 H 2O (a) By reduction : RX  H 2   RH  HX Zn / HCl (b) With hydrogen in presence of pt/pd :  Both ionic and free radical mechanism are RX  H 2  RH  HX Pd orPt. involved in this reaction. (c) With HI in presence of Red phosphorus : (c) Reduction of carboxylic acid : RBr  2 HI  RH  HBr  I2 CH 3 COOH  6 HI    CH 3 CH 3  2 H 2 O  3 I2 Re duction Purpose of Red P is to remove I2 in the form of PI3 Acetic acid p Ethane (iv) By Zn-Cu couple : (x) By reduction of alcohols, aldehyde, ketones 2CH 3 CH 2 OH  Zn   (CH 3 CH 2 O)2 Zn 2 H Cu or acid derivatives Zn-Cu couple Zinc ethoxide RX  2 H  RH  HX CH 3 OH  2 HI   CH 4  H 2 O  I2 Red P Methanol 150 o C Methane (v) Wurtz reaction : (Methy l alcohol) R X  2 Na  X R    R  R  2 NaX Dry ether CH 3 CHO  4 HI   C2 H 6  H 2 O  2 I2 Red P Alky l halide Alky l halide Alkane Acetaldehyde 150 o C Ethane  R  Br or RI preferred in this reaction. The net (Ethanal) result in this reaction is the formation of even no. of CH 3 COCH 3  4 HI   CH 3 CH 2CH 3  H 2O  2 I2 Red P carbon atoms in molecules. Acetone 150 o C Propane (Propanone ) (vi) Frankland’s reaction : O 2 RX  Zn  R  R  ZnX 2 || CH 3  C  Cl  6 HI   CH 3  CH 3  H 2 O  HCl  3 I2 Red P (vii) Corey-house synthesis Acety lchloride 200 o C Ethane (Ethanoy l chloride) 1. Li CH 3  CH 2  Cl CH 3  CH 2  Cl (CH 3  CH 2 )2 LiCu   2. CuI O CH 3  CH 2  CH 2  CH 3 || CH 3  C  NH 2  6 HI   CH 3  CH 3  H 2 O  NH 3  3 I2 Red P  Reaction is suitable for odd number of Alkanes. Acetamide 200 o C Ethane (Ethanamid e) (viii) From Grignard reagent  Aldehyde and ketones when reduced with (a) By action of acidic ‘H’ : amalgamated zinc and conc. HCl also yield alkanes. RMgX  HOH  RH  Mg(OH )X Alkylmagnesium Water Alkane Clemmenson reduction : halide Zn  Hg CH 3 CHO  4 H    CH 3  CH 3  H 2 O (b) By reaction with alkyl halide : Acetaldehyde HCl Ethane (Ethanal) R  X  RMgX  R  R  MgX 2 Zn  Hg CH 3 COCH 3  4 H    CH 3 CH 2 CH 3  H 2 O Acetone HCl Propane (ix) From carboxylic acids (Propanone ) (a) Laboratory method [Decarboxylation reaction  Aldehydes and ketones ( C  O) can be reduced or Duma reaction] to hydrocarbon in presence of excess of hydrazine and R COONa  NaOH  R  H  Na 2 CO 3 heat sodium alkoxide on heating. CaO Alkane Wolff-kishner reduction :  NaOH and CaO is in the ratio of 3 : 1. R R R C  O 2   C  NNH 2 2    (Sodalime) 2 H NNH 5 C H ONa CH 2 H 2O 180 o C ,  N 2 (b) Kolbe’s synthesis : R R R O || (xi) Hydroboration of alkenes Electrolysis   R  C  O Na R  C  O   Na  (a) On treatment with acetic acid Ionization || O R  CH  CH 2    (R  CH 2  CH 2 )3 B  B2 H 6  CH 3 COOH Alkene Trialky l borane  1086 Hydrocarbon R  CH 2  CH 3  Iodination of methane is done in presence of Alkane oxidising agent such as HNO 3 / HIO3 / HgO which (b) Coupling of alkyl boranes by means of silver neutralises HI. nitrate o  Chlorination of methane : 6[R  CH  CH 2 ]   [2 R  CH 2  CH 2 ]3 B  2 B2 H 6   AgNO 3 25 C NaOH CH 4  2Cl  Cl   CH 2  Cl 2  u. v. light 2 u. v. light , Cl 3[RCH 2 CH 2  CH 2 CH 2 R]  2 HCl  HCl  HCl (2) Physical Properties CHCl 3   CCl 4 Cl 2 (i) Physical state : Alkanes are colourless, (ii) Reaction based on free radical mechanism odourless and tasteless. (a) Nitration : Alkanes State R  H  HONO 2   R  NO 2  H 2 O High C1  C4 Gaseous state Alkane temp. Nitroalkan e C5  C17 Liquid state [Except neo pentane Nitrating mixture : (i) (Con. HNO 3  Con. H 2 SO 4 ) at which is gas] 250 o C C18 and above Solid like waxes (ii) (HNO 3 vapour at 400 o  500 o C ). (ii) Density : Alkanes are lighter than water. (b) Sulphonation : Free radical mechanism (iii) Solubility : Insoluble in water, soluble in 1 R  H  HOSO 3 H   SO 3  R  SO 3 H  H 2 O organic solvents, solubility  Prolonged heating M olecular mass  Lower alkanes particularly methane, ethane, (iv) Boiling points and Melting points : Melting do not give this reaction. points and boiling points.  Molecular mass 1 (iii) Oxidation  No. of branches (a) Complete Oxidation or combustion : Alkane C3 H8 C4 H10 C5 H12 C6 H14 C7 H16 C8 H18  3n  1  : Cn H 2n  2   O 2  nCO 2  (n  1)H 2 O  Q  2  M.P.(K 85.9 138 143.3 179 182.5 216.2  This is exothermic reaction. ):  Melting points of even > Odd no. of carbon (b) Incomplete combustion or oxidation atoms, this is because, the alkanes with even number of 2CH 4  3 O 2   2CO  4 H 2 O Burn carbon atoms have more symmetrical structure and result in closer packing in the crystal structure as CH 4  O 2  C 2 H 2 O compared to alkanes with odd number of carbon atoms. (c) Catalytic Oxidation : C C C C C C Cu  tube CH 4  [O]  o CH 3 OH 100 atm / 200 C C C C C C C This is the industrial method for the manufacture C Odd no. of Even no. of carbons of methyl alcohol. Carbons  Higher alkanes are oxidised to fatty acids in (3) Chemical properties presence of manganese stearate. (i) Substitution reactions of Alkanes CH 3 (CH 2 )n CH 3   O2 o CH 3 (CH 2 )n COOH 100 160 C (a) Halogenation : R  H  X  X  R  X  HX The reactivity of halogen is : F2  Cl 2  Br2  I2 (d) Chemical oxidation :  Fluorine can react in dark Cl 2 , Br2 require light (CH 3 )3 CH   (CH 3 )3.C.OH KMnO 4 Isobutane Tertiary buty l alcohol energy. I2 doesnot show any reaction at room (iv) Thermal decomposition or cracking or temperature, but on heating it shows iodination. pyrolysis or fragmentation  Hydrocarbon 1087 CH 3  CH 2  CH 3  SO 2  Cl 2    u.v light o CH 4   C  2H 2 1000 C Methane CH 3  CH 2  CH 2 SO 2 Cl  HCl 500 o C C 2 H 6   CH 2  CH 2  H 2 This reaction is known as reed’s reaction. Ethane Cr2 O 3  Al 2 O 3 Ethy lene  This is used in the commercial formation of C 3 H 8  C 2 H 4  CH 4 or C 3 H 6  H 2 detergent.  This reaction is of great importance to (x) Action of steam : petroleum industry. CH 4  H 2 O  o  CO  3 H 2 Ni / Al2O3 800 C (v) Isomerisation : Individual members of alkanes CH 3 (1) Methane : Known as marsh gas. | AlCl 3  HCl CH 3 CH 2 CH 2 CH 3     CH CHCH (i) Industrial method of preparation : Mathane o 3 3 n - Butane 200 C , 35 atm Isobutane gas is obtained on a large scale from natural gas by liquefaction. It can also be obtained by the application AlCl3  HCl    of following methods, 2-Methyl pentane heat (a) From carbon monoxide : A mixture of 2,3 Dimethyl carbonmonoxide and hydrogen is passed over a catalyst butane containing nickel and carbon at 250 o C when methane (vi) Aromatisation : is formed. Ni  C CH3 CO  3 H 2  o CH 4  H 2 O 250 C H2C CH3     Cr2 O3 / Al2 O 3 (b) Bacterial decomposition of cellulose material o +4H2 CH2 600 C / 15 atm present in sewage water : This method is being used in H2C CH2 England for production of methane. Benzene n-Hexane (C6 H10 O5 )n  nH 2 O  3nCH 4  3nCO 2 CH3 CH3 Cellulose (c) Synthesis :  By striking an electric arc H2    Cr2O3 / Al2O3  between carbon electrodes in an atmosphere of o 600 C hydrogen at 1200oC, methane is formed. o n- Methyl cyclo Toluen C  2 H 2   CH 4 1200 C Heptane Hexane e By passing a mixture of hydrogen sulphide and (vii) Step up reaction carbon disulphide vapour through red hot copper, (a) Reaction with CH 2 N 2 (Diazo methane) : methane is formed. CS 2  2 H 2 S  8 Cu    CH 4  4 Cu 2 S High temperatur e R  CH 2  H  CH 2 N 2  hv R  CH 2  CH 2  H (ii) Physical properties (b) Reaction with CHCl 3 / NaOH : (a) It is a colourless, odourless, tasteless and non-poisonous gas.  R  CH 2  H    R  CH 2  CHCl 2 CHCl 3 / OH (b) It is lighter than air. Its density at NTP is 0.71 : CCl 2 g/L. (c) Reaction with CH 2  C : (c) It is slightly soluble in water but is fairly || soluble in ether, alcohol and acetone. O (d) Its melting point is  182. 5 o C and boiling O || point is  161. 5 C. o CH  C /  R  CH 2  H   2  R  CH 2  CH 3 (iii) Uses :CH 2 /  CO (a) In the manufacture of compounds like methyl alcohol, formaldehyde, methyl chloride, chloroform, (viii) HCN formation : carbon tetrachloride, etc. 2CH 4   2 HCN  3 H 2 or N 2 / electric arc (b) In the manufacture of hydrogen, used for making ammonia. CH 4  NH 3   HCN  3 H 2 Al 2 O 3 700 o C (c) In the preparation of carbon black which is used for making printing ink, black paints and as a (ix) Chloro sulphonation/Reaction with SO2+Cl2 filler in rubber vulcanisation.  1088 Hydrocarbon (d) As a fuel and illuminant. H (2) Ethane | R  C  C  R  H 2   R  C  C  R Lindlar' s Cataly st (i) Methods of preparation Pd. BaSO 4 | (a) Laboratory method of preparation : H Zn  Cu couple C2 H 5 I  2 H    C2 H 6  HI  Poison’s catalyst such as BaSO 4 ,CaCO 3 are Ethyl iodide C2 H5 OH Ethane used to stop the reaction after the formation of alkene. (b) Industrial method of preparation : (ii) From mono halides : CH 2  CH 2  H 2   CH 3  CH 3 Ni Ethy lene 300 o C Ethane H H H (ethene) | | | (ii) Physical properties R  C  C  H  Alc. KOH   R  C  C  H  HX | | | (a) It is a colourless, odourless, tasteless and H X H non-poisonous gas. Alkene (b) It is very slightly soluble in water but fairly  If we use alc. NaOH in place of KOH then soluble in alcohol, acetone, ether, etc. trans product is formed in majority because of its (c) Its density at NTP is 1.34 g/L stability. According to saytzeff rule. (d) It boils at – 89oC. Its melting point is –172oC. (iii) From dihalides (iii) Uses (a) From Gem dihalides (a) As a fuel. (b) For making hexachloroethane X Zn which is an artificial camphor. X  (3) Interconversion of Alkanes R – CH + + CH – R    2 ZnX 2 R – CH = CH – R X Zn Ascent of alkane series, X  If we take two different types of gemdihalides (i) Methane to ethane : then we get three different types of alkenes. CH 4  CH 3 Cl  Cl 2   CH 3  CH 3 Wurtz reaction  Above reaction is used in the formation of Methane UV Heat with Na in ether Ethane symmetrical alkenes only. (ii) Butane from ethane : (b) From vicinal dihalides : C 2 H 6  C 2 H 5 Cl  Cl 2   C 2 H 5  C 2 H 5 Wurtz reaction H H H H UV Ethy l chloride Heat with Na in ether Ethane Butane | | | | (excess)  R  C  C  H  Zn dust  R  C  C  H  ZnX 2 o Descent of alkane series : Use of | | 300 C decarboxylation reaction is made. It is a multistep X X conversion.  Alkene is not formed from 1, 3 dihalides. Ethane to methane Cycloalkanes are formed by dehalogenation of it. C 2 H 6  C 2 H 5 Cl  Cl 2  C 2 H 5 OH  Aq. KOH  CH 3 CHO [O ] C H 2  CH 2  C H 2   Zn dust CH 2  ZnX 2 Ethane UV Ethy l chloride Ethy l alcohol Acetaldehyde | | (excess) X X H 2C CH 2   CH 3 COOH  [O ]  CH 3 COONa  NaOH  CH 4 NaOH / CaO Aceticacid Sodium acetate heat Methane (iv) By action of NaI on vicinal dihalide : Higher   Alkyl   Alcohol  Cl 2  Aldehyde   Aq. [O ] [O ] Br Br I I alkane UV halide KOH | | | | C C   NaI C C  CC Acid   Sodium salt of  NaOH   Lower alkane NaOH / CaO vic dihalide acetone unstable  I2 alkene heat the acid (v) From alcohols [Laboratory method] : Alkenes CH 3 CH 2 OH   CH 2  CH 2  H 2 O H 2 SO 4 or H 3 PO4 Ethyl alcohol 443 K Ethene These are the acyclic hydrocarbon in which carbon-carbon contain double bond. These are also (vi) Kolbe’s reaction : known as olefins, because lower alkene react with CH 2 COOK CH 2 halogens to form oily substances. General formula is |  2 H 2 O  | | Electroly sis  2CO 2  H 2  2 KOH Cn H 2n. Examples, C2 H 4 , C3 H 6 , C4 H 8. CH 2 COOK CH 2 Potassium succinate Ethene (1) Preparation methods (vii) From esters [Pyrolysis of ester] : (i) From Alkynes : CH 3  CO  O H CH 3  COOH Glass wool 450 o | |    CH 2  CH 2 liq. N 2 CH 2  CH 2  Hydrocarbon 1089 (viii) Pyrolysis of quaternary ammonium (i) Francis experiment : According to Francis compounds : electrophile first attacks on olefinic bond.   (C 2 H 5 )4 N OH   (C 2 H 5 )3 N  C 2 H 4  H 2 O heat CH2 = CH2 + Br – Br  4 CH2 – CCl Tetraethy l ammonium Triethy lamine Ethene hydroxide (Tert. amine) CH2 | | (ix) Action of copper alkyl on vinyl chloride : Br Br H 2 C  CHCl  H 2 C  CHR CuR   CH2 – CH2 + CH2 – CH2 NaCl 2 Viny lchloride | | | | (x) By Grignard reagents : Br Cl Br Br R Mg  X  CH  CH 2  MgX 2  R  CH  CH 2 (ii) Reaction with hydrogen : X H H H H (xi) The wittig reaction : | | | | (Ph)3 P  CH 2  CH  R (Ph)3 P  O  R  CH R  C  C  R  H 2   R  C  C R Ni || | | || O H H CH 2 O (iii) Reduction of alkene via hydroboration : || Alkene can be converted into alkane by protolysis (Ph)3 P  CH  R  CH  R (Ph)3 P  O  R  CH  CH  R H  BH 2 RCH  CH 2  (R  CH 2  CH 2 ) 3 B (xii) From  bromo ether [Boord synthesis] Br O  C 2 H 5     R  CH 2  CH 3 H / H 2O | | Br R  CH  CH  R  CH  CH  R   Zn Zn C4 H 9 OH Hydroboration : Alkene give addition reaction | O  C2 H 5 R with diborane which called hydroboration. In this reaction formed trialkylborane, Which is very (2) Physical Properties important and used for synthesis of different organic (i) Alkenes are colourless and odourless. compound (ii) These are insoluble in water and soluble in organic solvents. 3 R  CH  CH 2  BH 3  (iii) Physical state (R  CH 2  CH 2 )3 B Trialkyl borane C1  C 4  gas CH3COOH/Z NaOH/ H2O2 HI/H2O2 C 4  C16  liquid n  C17  solid wax R – CH2 –CH3 R – CH2 –CH2OH R – CH2 –CH3 (iv) B.P. and M.P. decreases with increasing The overall result of the above reaction appears to branches in alkene. be antimarkownikoff’s addition of water to a double (v) The melting points of cis isomers are lower bond. than trans isomers because cis isomer is less (iv) By treatment with AgNO3 + NaOH : This symmetrical than trans. Thus trans packs more tightly reaction gives coupling in the crystal lattice and hence has a higher melting CH 3 point. | (vi) The boiling points of cis isomers are higher 6 CH 3  CH 2  CH 2  C  CH 2    B2 H 6 than trans isomers because cis-alkenes has greater CH 3 polarity (Dipole moment) than trans one. | 2[CH 3  (CH 2 ) 2  C  CH 2 ] 3 B   Ag / NO 3 NaOH (vii) These are lighter than water. | (viii) Dipole moment : Alkenes are weakly polar. H The, -electron’s of the double bond. Can be easily CH 3 CH 3 polarized. Therefore, their dipole moments are higher | | CH 3  CH 2  CH 2  C  CH 2  CH 2  C  CH 2  CH 2  CH 3 than those of alkanes. | | (3) Chemical properties H H  1090 Hydrocarbon (v) Birch reduction : This reaction is believed to  In case of unsymmetrical alkenes proceed via anionic free radical mechanism. markownikoff rule is followed.   (ix) Reaction with sulphuric acid : R  CH  CH 2   R  C H  C H 2  Na  R  CH  CH 3 Et  O  H e  CH 2  CH 2  H  HSO 4  CH 3 CH 2 HSO 4  Ethy lene Ethy l hydrogen sulphate Et. O  H   R  C H  CH 3    Na  R  CH 2  CH 3 e  CH 3 CH 2 HSO 4  CH 2  CH 2  H 2 SO 4 (vi) Halogenation  This reaction is used in the seperation of alkene o CH 3 CH  CH 2  Cl 2   ClCH 2  CH  CH 2  HCl 500 C from a gaseous mixture of alkanes and alkenes. Propene Ally lchloride or 3-Chloro- 1- propene (x) Reaction with nitrosyl chloride  If NBS [N-bromo succinimide] is a reagent used NO | for the specific purpose of brominating alkenes at the C  C  NOCl  C  C ( NOCl is called allylic position. | CH2 – CO Cl CH3 CH=CH2 + | N – Br Tillden reagent) CH2 – CO  If hydrogen is attached to the carbon atom of Propene NBS product, the product changes to more stable oxime. NO CH2 – CO | H CH2 – CH = CH2+ | N–H C C ⇌ C  C  NOH | CH2 – CO | | | Br Cl Cl Oxime Allyl Succinimid C C bromide e  In presence of polar medium alkene form CC  NOCl  C  C (Blue colour) vicinal dihalide with halogen. C | | C H H H H NO Cl | | | | (xi) Oxidation : With alkaline KMnO 4 [Bayer’s R  C  C  H  X  X   R  C  C  H CCl 4 reagent] : This reaction is used as a test of | | unsaturation. X X Vicinal dihalide H H H H | | | | Reactivity of halogen is F2  Cl 2  Br2  I2 R  C  C  H  [O]  H  OH   R  C  C  H Alk KMnO 4 OH | | (vii) Reaction with HX [Hydrohalogenation] H HO OH gly col | CC  HX  C  C With acidic KMnO 4 : | H H O alkene X | | || Alky lhalide R  C  C  H  [O]  R  C  O  H  CO 2  H 2 O acidic KMnO 4 According to markownikoff’s rule and kharasch effect. (xii) Hydroxylation (a) Using per oxy acid : H H | | CH 3 CH 3 CH 3  CH  CH 2  HBr  CH 3  C  C  H | | | | H  C   H 2 O2 , HCOOH H  C  OH || or HCO 3 H | Br H H C HO  C  H According to Anti Markownikoff rule (Based | | CH 3 CH 3 on F.R.M.) CH 3  CH  CH 2  HBr   Peroxide 2 - Butene Trans (racemic) H H H H R H | | | | CH 3  C  C  H  CH 3  C  C  H | | | | (b) Hydroxylation by OsO4 : Br H H Br C (minor) (major) | |  OsO4  NaHSO 4  I (viii) Reaction with hypohalous acids : C R H R   Trans H OH CH 2  CH 2  H O Cl  CH 2 OH.CH 2 Cl Ethy lene Ethy lene chlorohy drin HO H R ()  Hydrocarbon 1091  3 R  CH  CH 2  BH 3  (R  CH 2  CH 2 ) 3 B   H 2 O 2 / OH Tri alky l bora ne  If per benzoic acid or peroxy acetic acid is used R  CH 2  CH 2  OH  B(OH )3 then oxirane are formed. (Anti markownikoff’s rule) R  CH  CH  R   H 2O   R  CH  CH  R  C 6 H 5 CO 3 H  (xviii) Hydroformylation : or CH 3 CO 3 H | | H H OH OH | | R  CH  CH 2  CO  H 2  R  C  C  H CoH (CO )4 R  CH  CH  R | | H C O | O H [Oxirane]  If CO  H 2 O is taken then respective acid is (xiii) Combustion : formed. 3n R  CH  CH 2  CO  H 2 O   R  CH 2  CH 2 CoH (CO )4 Cn H 2n  O 2  nCO 2  nH 2 O 2 | They burn with luminous flame and form COOH explosive mixture with air or oxygen. (xix) Addition of formaldehyde    (xiv) Ozonolysis H 2 C  O  H [H 2 C  O H  H 2 C  OH ]  HOH R  CH  CH 2   R  C H  CH 2  CH 2  OH CC   O3 H  I O O O H H 2 O / H  / Zn 2 C C   ZnO  C+C II R – C CH2  O O CH    R  CH  CH 2  CH 2 HCHO / H Ozonide O O | | C OH  Application of ozonolysis : This process is quite OH H 1, 3 diol useful to locate the position of double bond in an alkene Cyclic acetal 2 molecule. The double bond is obtained by Joining the (xx) Polymerisation carbon atoms. of the two carbonyl compounds. H H  H H H H (xv) Oxy – mercuration demercuration : With   | |  | | | |  mercuric acetate (in THF), followed by reduction with Trace O 2  Catalyst C  C       C  C  C  C  NaBH 4 / NaOH is also an example of hydration of alkene 1500 o / high pressure   according to markownikoff’s rule. | |  | | | |   H H H H H H  n (CH 3 )3 C  CH  CH 2  (CH 3 COO )2 Hg  3,3- dimethyl-1- butene Mercuric acetate  If in polymerisation zeigler- natta catalyst [(R)3 Al  TiCl 4 ] is used then polymerisation is known as (CH 3 )3 C  CH  CH 2  Hg   (CH 3 )3 C  CH  CH 3 NaBH 4 / NaOH THF | | zeigler-natta polymerisation. OCOCH 3 OH (xxi) Isomerisation : 3, 3 Dimethy l 2  butanol AlCl3 CH 3  CH 2  CH 2  CH  CH 2 (xvi) Epoxidation CH 3  CH 2  CH  CH  CH 3 (a) By O2 / Ag : The mechanism proceeds via carbocation. O (xxii) Addition of HNO3 : 1 CH 2  CH 2  O 2   CH 2  CH 2 Ag CH 2  CH 2  HO  NO 2  CH 2 OH.CH 2 NO 2 2 Ethene 2- Nitroethan ol (xxiii) Addition of Acetyl chloride : (b) Epoxidation by performic acid or perbenzoic O CH 2  CH 2  CH 3 COCl  CH 2 ClCH 2 COCH 3 acid : Ethene 4 -Chlorobuta none - 2 || C–O–O– H (4) Uses | (i) For the manufacture of polythene – a plastic O material; (ii) For artificial ripening of fruits; (