1 / 12

Preparation of Alkyl Halides from Alcohols and Hydrogen Halides

Preparation of Alkyl Halides from Alcohols and Hydrogen Halides. ROH + HX  RX + H 2 O. Reaction of Alcohols with Hydrogen Halides. Hydrogen halide reactivity HI HBr HCl HF most reactive least reactive. R OH + H X  RX + H OH.

cynthia-salinas
Download Presentation

Preparation of Alkyl Halides from Alcohols and Hydrogen Halides

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Preparation of Alkyl Halides fromAlcohols and Hydrogen Halides ROH + HX  RX + H2O

  2. Reaction of Alcohols with Hydrogen Halides Hydrogen halide reactivity HI HBr HCl HFmost reactiveleast reactive ROH + HX  RX + HOH

  3. Reaction of Alcohols with Hydrogen Halides Alcohol reactivityR3COH R2CHOH RCH2OH CH3OHTertiary Secondary Primary Methanolmost reactiveleast reactive ROH + HX  RX + HOH

  4. OH + HBr Br Preparation of Alkyl Halides 25°C (CH3)3CCl + H2O (CH3)3COH + HCl 78-88% 80-100°C + H2O 73% 120°C CH3(CH2)5CH2OH + HBr CH3(CH2)5CH2Br + H2O 87-90%

  5. Preparation of Alkyl Halides A mixture of sodium bromide and sulfuric a cid may be used in place of HBr. NaBrH2SO4 CH3CH2CH2CH2Br CH3CH2CH2CH2OH heat 70-83%

  6. Mechanism of the Reaction of Alcohols with Hydrogen Halides

  7. + R R C R Carbocation The key intermediate in reaction of secondary and tertiary alcohols with hydrogen halides is a carbocation. A carbocation is a cation in which carbon has6 valence electrons and a positive charge.

  8. + R R C R Carbocation The key intermediate in reaction of secondary and tertiary alcohols with hydrogen halides is a carbocation. The overall reaction mechanism involves threeelementary steps; the first two steps lead to thecarbocation intermediate, the third step is the conversion of this carbocation to the alkyl halide.

  9. + H3C CH3 C CH3 Example 25°C (CH3)3COH + HCl (CH3)3CCl + H2O tert-Butyl alcohol tert-Butyl chloride Carbocation intermediate is: tert-Butyl cation

  10. .. + : H Cl .. H .. – + + : : : O Cl (CH3)3C .. H Mechanism Step 1: Proton transfer from HCl to tert-butyl alcohol (CH3)3C .. : O H fast, bimolecular tert-Butyloxonium ion

  11. H + : O (CH3)3C H H : : O H Mechanism Step 2: Dissociation of tert-butyloxonium ion slow, unimolecular + + (CH3)3C tert-Butyl cation

  12. .. – : : Cl .. .. : Cl (CH3)3C .. Mechanism Step 3: Capture of tert-butyl cation by chloride ion. + + (CH3)3C fast, bimolecular tert-Butyl chloride

More Related