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11
Some Important Reactions of Some Important Reactions of AlcoholsAlcohols
1. Dehydration = loss of H1. Dehydration = loss of H22O to O to form form an alkenean alkene
2. Oxidation = loss of H to form 2. Oxidation = loss of H to form a a C=O compoundC=O compound
22
Dehydration ExamplesDehydration Examples
CH3CHCH3 CH2=CHCH3 + H2OOH2-propanol --> propene + water2-propanol --> propene + water
general pattern:general pattern:
alcohol --> alkene + wateralcohol --> alkene + water
33
HH
OH
HAnother exampleAnother example
H2O +
cyclopentanol --> cyclopentanol --> cyclopentene + watercyclopentene + water
44How 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
55
Catalyst for dehydration of alcohol is usually acid =
H+ from H2SO4 (sulfuric acid) or
enzyme in living organism.
66Main thing to focus on:
C-C C-C
OH
H OH H
HH+
+
lose H+& H2OC=C
alkene
C=C forms C=C forms between C between C bonded to OH bonded to OH and adjacent C and adjacent C bonded to H lost bonded to H lost as Has H++
77
When the C-O bonds breaks to lose H2O, an adjacent C-H bond breaks to lose H+.
The result is formation of the The result is formation of the new pi (new pi () bond to make the ) bond to make the alkene.alkene.Catalyst helps OH leave as HCatalyst helps OH leave as H22O O from alcohol.from alcohol.
88When there is more than one kind of H on the C next to C-OH, more than one alkene can form:
CH3CHCH2CH3 H2O +OH
H+
heat
CH2=CHCH2CH3 + CH3CH=CHCH3
99Oxidation Reaction Examples
CH3CH2-CH-CH3
OH[O]
CH3CH2-C-CH3
O
2° alcohol2° alcohol
ketoneketone
oxidizing oxidizing agentagent
1010General reaction:
R-CH-R’ R-C-R’
OH O[O]
2° ROH + [O] ---> ketone2° ROH + [O] ---> ketone
1111Oxidizing 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].
1212Primary alcohols can be oxidized in 2 stages:
R-CH2-OH R-C-H
O[O]
aldehydealdehyde
R-C-H
O[O]
R-C-OHO
carboxylic acidcarboxylic acid
1313Aldehydes 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.
1414Tertiary alcohols are not oxidized because there is no H on the C bonded to OH:
R-C-O-H is 3° alcohol
R
RCH3-C-O-H
CH3
CH3
no H on Cno H on C
1515Phenols are benzene compounds with an OH group attached to a sp2 C in ring:
OH
““phenol” salicylic acidphenol” salicylic acid
OH
CO2H
1616Phenols & Alcohols are not alike!
* both have C-O-H* both have C-O-H* both form H-bonds, * both form H-bonds, BUT:* alcohols are neutral * alcohols are neutral
compoundscompounds* phenols are acidic* phenols are acidic
1717ETHERS have the general formula
R-O-R’ R-O-R’ (has C-O-C bond)(has C-O-C bond)
*bond angles about 109°*tetrahedral e- pairs on O*C-O-C shape is angular or
bent
1818
CHCH33CHCH22-O-CH-O-CH22CHCH33
“diethyl ether” is symmetrical
CHCH33-O-CH-O-CH22CHCH22CHCH33
““methyl propyl ether” is methyl propyl ether” is unsymmetricalunsymmetrical
both Alkyl groups can be the same or different:
1919
non-IUPAC names for ethers = “common names”
name of alkyl group 1 name of alkyl group 1 (space) name of alkyl group 2 name of alkyl group 2 (space) etherether
see previous slide for examples
2020Ethers 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
2121
R
R
O••
••
etherether
H-bond H-bond acceptoracceptor
H-OR’
alcoholalcohol
H-bond donorH-bond donor
2222Sulfur 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 Simply be able to recognize the type from structure.type from structure.