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Some Important Reactions of Alcohols 1. Dehydration = loss of H 2 O to form an alkene 2. Oxidation = loss of H to fo

Some Important Reactions of Alcohols 1. Dehydration = loss of H 2 O to form an alkene 2. Oxidation = loss of H to form a C=O compound. Dehydration Examples CH 3 CHCH 3 CH 2 =CHCH 3 + H 2 O. OH. 2-propanol --> propene + water. general pattern: alcohol --> alkene + water.

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Some Important Reactions of Alcohols 1. Dehydration = loss of H 2 O to form an alkene 2. Oxidation = loss of H to fo

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  1. Some Important Reactions of Alcohols 1. Dehydration = loss of H2O to form an alkene 2. Oxidation = loss of H to form a C=O compound

  2. Dehydration Examples CH3CHCH3 CH2=CHCH3 + H2O OH 2-propanol --> propene + water general pattern: alcohol --> alkene + water

  3. Another example H H H OH H2O + cyclopentanol --> cyclopentene + water

  4. How does reaction occur? * Loss of water from alcohol alone has high activation energy = alcohols dehydrate very, very, very slowly by themselves * speed up reaction by lowering Eact with catalyst

  5. Catalyst for dehydration of alcohol is usually acid = H+ from H2SO4 (sulfuric acid) or enzyme in living organism.

  6. Main thing to focus on: C-C C-C H+ H + H O O H H H lose H+& H2O C=C forms between C bonded to OH and adjacent C bonded to H lost as H+ C=C alkene

  7. When the C-O bonds breaks to lose H2O, an adjacent C-H bond breaks to lose H+. The result is formation of the new pi (p) bond to make the alkene. Catalyst helps OH leave as H2O from alcohol.

  8. When there is more than one kind of H on the C next to C-OH, more than one alkene can form: CH3CHCH2CH3 H2O + H+ heat OH CH2=CHCH2CH3 + CH3CH=CHCH3

  9. Oxidation Reaction Examples CH3CH2-CH-CH3 OH [O] 2° alcohol O oxidizing agent CH3CH2-C-CH3 ketone

  10. General reaction: R-CH-R’ R-C-R’ O OH [O] 2° ROH + [O] ---> ketone

  11. Oxidizing agents remove H and e- from the grouping H-C-O-H that makes up the alcohol group to form C=O. Many reagents can do this: common ones are Cr or Mn compounds. Even household bleach (NaOCl) can be [O].

  12. Primary alcohols can be oxidized in 2 stages: R-CH2-OH R-C-H O [O] aldehyde O O [O] R-C-H R-C-OH carboxylic acid

  13. Aldehydes are easier to oxidize than 1° alcohols, so it is sometimes difficult to stop the reaction at the aldehyde stage. Special reagents have been developed to make it possible to get aldehydes by oxidizing a 1° alcohol.

  14. Tertiary alcohols are not oxidized because there is no H on the C bonded to OH: R-C-O-H is 3° alcohol R CH3 R CH3-C-O-H no H on C CH3

  15. Phenols are benzene compounds with an OH group attached to a sp2 C in ring: OH OH CO2H “phenol” salicylic acid

  16. Phenols & Alcohols are not alike! * both have C-O-H * both form H-bonds, BUT: * alcohols are neutral compounds * phenols are acidic

  17. ETHERS have the general formula R-O-R’ (has C-O-C bond) *bond angles about 109° *tetrahedral e- pairs on O *C-O-C shape is angular or bent

  18. both Alkyl groups can be the same or different: CH3CH2-O-CH2CH3 “diethyl ether” is symmetrical CH3-O-CH2CH2CH3 “methyl propyl ether” is unsymmetrical

  19. non-IUPAC names for ethers = “common names” name of alkyl group 1 (space) name of alkyl group 2 (space) ether see previous slide for examples

  20. Ethers do not provide a H for a hydrogen bond, but can provide the electron pair of O. So: ethers are H-bond acceptors, they donate :O: to the H of another O-H or H-N

  21. • • R O • H-O • R R’ ether H-bond acceptor alcohol H-bond donor

  22. Sulfur Analogs of Alcohols and Ethers R-S-H thiol or mercaptan R-S-R’ thioether R-S-S-R’ disulfide Simply be able to recognize the type from structure.

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