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3.9 Reactions of alcohols

3.9 Reactions of alcohols. 1.Combustion 2. Dehydration 3. Formation of ethers 4.Oxidation. The same as hydrocarbons undergo combustion in the presence of oxygen, alcohols burn with oxygen too. Combustion CH 3 OH + 2O 2 CO 2 + 2H 2 O + Heat.

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3.9 Reactions of alcohols

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  1. 3.9 Reactions of alcohols 1.Combustion 2. Dehydration 3. Formation of ethers 4.Oxidation

  2. The same as hydrocarbons undergo combustion in the presence of oxygen, alcohols burn with oxygen too. Combustion CH3OH + 2O2 CO2 + 2H2O + Heat

  3. Dehydration of Alcohols to form Alkenes Alkenes can add water to yield alcohols. In a reverse reaction, alcohols can lose water molecule when they are heated with an acid catalyst such as H2SO4. H OH H+, heat H-C-C-H H-C=C-H + H2O H H H H alcohol (ethanol) alkene (ethene)

  4. Dehydration of Alcohols to form Alkenes During the dehydration of an alcohol, a H– and –OH are removed from adjacent carbon atoms of the same alcohol to produce a water molecule. A double bond forms between the same two carbon atoms to produce an alkene. H OH H+, heat H-C-C-H H-C=C-H + H2O H H H H alcohol (ethanol) alkene (ethene)

  5. Saytzeff’s Rule The dehydration of a secondary alcohol can result in the formation of either of two products. Saytzeff’s rule state that the major product is the one that results when the hydrogen is removed from the carbon atom with the smallest number of hydrogen atoms. “THE POOR GET POORER” rule

  6. Saytzeff’s Rule The major product is the one that results when the hydrogen is removed from the carbon atom with the smallest number of hydrogen atoms. “The poor get poorer” 2 H 3H +H2O H+ 2-Butene (major product: 90%) Heat +H2O 1-Butene (minor product: 10%) 2-Butanol THE MOST SUBSTITUTED C=C IS THE MAJOR PRODUCT

  7. Formation of Ethers ANOTHER KIND OF DEHYDRATION Ethers form when the dehydration of alcohols occurs at lower temperatures in the presence of an acid catalyst. H+ R—OH + HO—R’ R—O—R’ + H2O Low Heat The components of water are removed from two molecules: an H– from one alcohol and the –OH from another.

  8. Formation of Ethers ANOTHER KIND OF DEHYDRATION H+ CH3—OH + HO—CH3 CH3—O—CH3 + H2O Low Heat

  9. [O] [O] 2 Bonds to O 3 Bonds to O 1 Bond to O Oxidation of Alcohols The reactions of alcohols have a central role in organic chemistry because alcohols can be converted to many of the other functional groups. • Reduction is • a gain of electrons • a less positive oxidation number • a gain of hydrogen atoms • the loss of oxygen atoms • the loss of bonds to oxygen. • Oxidation is • a loss of electrons • a more positive oxidation number • a loss of hydrogen atoms • the addition of oxygen atoms. • more bonds to oxygen Alkane Alcohol (1°) Aldehyde Carboxylic acid [O] [O]

  10. Oxidation numbers • Each C-H is a -1 • Each C-O is a +1 • Sum total C-H and C-O to determine Oxidation Number

  11. Oxidation numbers • Each C-H is a -1 • Each C-O is a +1 What are the oxidation numbers for CH3OH CH2O HCO2H Hint: Write the expanded formula to determine the number of bonds to C

  12. OXIDATION REACTIONS ALCOHOLS • Primay • Seconday • Tertiary

  13. OXIDATION REACTIONS CH3OH  CH2O  HCO2H Oxidation of Primary Alcohol [O] [O] Primary alcohol aldehyde carboxylic acid Example: oxidation of methanol

  14. [O] Double bonds forms Two hydrogen atoms removed 2° Alcohol Ketone R1, R2: alkyl groups Oxidation of Secondary Alcohol Secondary alcohol Ketone

  15. O O O H O C H 3 C C O H C H 3 C H C O H Metabolic example Lactic acid dehyrogenase Lactic acid Pyruvic acid

  16. [O] [O] Oxidation of Alcohol in the body O Breathalyzer test for suspected drunk drivers Acetic acid green orange ethanol

  17. Oxidation of Tertiary Alcohol [O] Tertiary alcohol No reaction Only one hydrogen atom, not the two required to be removed 3° Alcohol R1, R2, R3: alkyl groups

  18. a. trans-2-butene b. 2-methyl-2-butene c. trans-2-methyl-2-butene d. 3-methyl-1-butene Question What is the dehydration product when 3-methyl-2-butanol reacts with acid in the presence of heat? Answer: “b”. The alkene forms so that the carbon-carbon double bond is more substituted. This is Saytzeff's rule.

  19. a. a carboxylic acid b. a ketone c. an aldehyde d. no product forms Question What is the product of this reaction? Answer: “d”. Tertiary alcohols cannot oxidize.

  20. a. 1-methylcyclopentanol. b. 2-methylcyclopentanol. c. 3-methylcyclopentanol. d. None of these form. Question The hydration of 1-methylcyclopentene gives Answer”a”. This reaction is the addition of water to a double bond. Do you remember Markovnikov's rule? The hydrogen from water adds to the end of the double bond with the most hydrogens.

  21. Question What product forms and what type of reaction is this? a. The reaction is an oxidation and the product is b. The reaction forms ether and the product is c. The reaction is an oxidation and the product is d. The reaction forms ether and the product is Answer: “b”.

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