Unit-17 Aliphatic Hydrocarbons Alkanes General Methods of preparations:- Alkanes can be obtained by the fractional distillation of petrolium and matorral gas. @By Hee hystro geration of unsaturated bystreerituns Alkanes and alkynes are heated with hyotrogen to presence of finely divided pt, pod, or Ni to got the Corresponding alkane. R-CH=CH-R+H₂ alkene Pol →R-CH2-CH2-R (alkone) CH-CH=CH2 + H2. 7- butone CH3-CH2-CH2-CH3 -Butane Mechanism- pol CH3-CH2-CH=CH2 CH3-CH2-CH-CH2 + ↓(TS) H-H CH3-CH2-CH2-CH3 ex- R-C=C-RP, R-CH2-CH2-P' Pel CH3-CEC-BH3R-CH2-CH2-CH3 Comparatively hish Temp. (423-473k) b Nequired when nickel is used al Catalyst. a Ni GX-CH-CH=CH2 + H2", CH3-CH2-CH3 Propone Propane 2. Weertz Reacton In this neaction, two Motecules of alkyl halide neact with sodium metal presence of dry ether. A Single alud halide ased in this neaction gives better yield of alkone Containing even no. of Cerbon atoms. Ethor xXx-CH3-Br + 2Na+ Br-CH3- Methyl bromide C2H6+2 Nabr Etiane CH-Br+na+ Br-CHS- Ethyl bromide Other →CyHio + 2 NaBr propane 17 Cure et moo dift? allen Galides à cesed, @mis? of three alleome nesults. in poor Nalethor Ex-C3-Bo+2Nla + Br-CQAS C3H8 +2 NaBi Metinyl bromide. etul bromide Propane Mechanism Q 2Na + R-X R Na + Na NR R+R-X R-R+Nax G CH₃ Na + No -NaBr CH3-CH3 + NaBr @thane ex. Na + CH3-Br Na CH3 + CH3 Br- Kolbe's Synth cats: - Ethane is prepared by the electrolysis of the cone. Son of Sodium acetate. CH₃ Coola CH₃ COO + Na sod. acetate H2O H Cathode Anode At anode Cuzco-> CH3C00 → + OH 1-C02 (methone) CH2 + CH3 CH3-CH3 (Ethane) At Cathode Due 10 greater reduction Potential, Hions discharged in profesome to Na joις. 2H+20