Presentation on theme: "1 3.9 Reactions of alcohols 1.Combustion 2. Dehydration 3. Formation of ethers 4.Oxidation."— Presentation transcript:
1 3.9 Reactions of alcohols 1.Combustion 2. Dehydration 3. Formation of ethers 4.Oxidation
2 Combustion CH 3 OH + 2O 2 CO 2 + 2H 2 O + Heat The same as hydrocarbons undergo combustion in the presence of oxygen, alcohols burn with oxygen too.
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 H 2 SO 4. H OH H +, heat H-C-C-H H-C=C-H + H 2 O 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 + H 2 O 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” H+H+ Heat +H 2 O 2-Butene (major product: 90%) 1-Butene (minor product: 10%) 2-Butanol 2 H3H THE MOST SUBSTITUTED C=C IS THE MAJOR PRODUCT
7 Formation of Ethers lower temperatures Ethers form when the dehydration of alcohols occurs at lower temperatures in the presence of an acid catalyst. R—OH + HO—R’ R—O—R’ + H 2 O H+H+ Low Heat ANOTHER KIND OF DEHYDRATION The components of water are removed from two molecules: an H– from one alcohol and the –OH from another.
8 Formation of Ethers CH 3 —OH + HO—CH 3 CH 3 —O—CH 3 + H 2 O H+H+ Low Heat ANOTHER KIND OF DEHYDRATION
9 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. 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 AlkaneAlcohol (1°)AldehydeCarboxylic acid 1 Bond to O 2 Bonds to O3 Bonds to O [O] 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.
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 CH 3 OH CH 2 O HCO 2 H Hint: Write the expanded formula to determine the number of bonds to C
13 OXIDATION REACTIONS CH 3 OH CH 2 O HCO 2 H Oxidation of Primary Alcohol Primary alcohol aldehyde carboxylic acid Example: oxidation of methanol [O]
14 Oxidation of Secondary Alcohol Secondary alcohol Ketone [O] R1, R2: alkyl groups 2° Alcohol Ketone Double bonds forms Two hydrogen atoms removed
15 Metabolic example Lactic acid dehyrogenase Lactic acid Pyruvic acid CH3CH OH COH O CH3C O COH O
16 ethanol orange Acetic acidgreen Breathalyzer test for suspected drunk drivers O Oxidation of Alcohol in the body [O]
17 Oxidation of Tertiary Alcohol Tertiary alcohol No reaction [O] R1, R2, R3: alkyl groups 3° Alcohol Only one hydrogen atom, not the two required to be removed
18 What is the dehydration product when 3-methyl-2-butanol reacts with acid in the presence of heat? a.trans-2-butene b.2-methyl-2-butene c.trans-2-methyl-2-butene d.3-methyl-1-butene Question Answer: “b”. The alkene forms so that the carbon- carbon double bond is more substituted. This is Saytzeff's rule.
19 What is the product of this reaction? a.a carboxylic acid b.a ketone c.an aldehyde d.no product forms Question Answer: “d”. Tertiary alcohols cannot oxidize.
20 The hydration of 1-methylcyclopentene gives a.1-methylcyclopentanol. b.2-methylcyclopentanol. c.3-methylcyclopentanol. d.None of these form. Question 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 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 Question Answer: “b”.