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chapter 9-10 Alcohols


Chapter 9-10: Alcohols , Phenols and Ethers

1

Alcohols and Phenols
Alcohols contain an OH group connected to a saturated C (sp3) They are important solvents and synthesis intermediates Phenols contain an OH group connected to a carbon in a benzene ring Ethanol, CH3CH2OH, called ethyl alcohol, is a solvent, fuel, beverage Phenol, C6H5OH (“phenyl alcohol”) has diverse uses

2

Ethers
An ether has two organic groups (alkyl, aryl, or vinyl) bonded to the same oxygen atom, R–O–R′ ′ Diethyl ether is used industrially as a solvent Tetrahydrofuran (THF) is a solvent that is a cyclic ether

3

8.1 Naming Alcohols
General classifications of alcohols based on substitution on C to which OH is attached Methyl (C has 3 H’s), Primary (1° (C has two H’s, one R), ) secondary (2° (C has one H, two R’s), ) tertiary (3° (C has no H, 3 R’s) )

4

IUPAC Rules for Naming Alcohols
Select the longest carbon chain containing the hydroxyl group, and derive the parent name by replacing the -e ending of the corresponding alkane with -ol Number the chain from the end nearer the hydroxyl group Number substituents according to position on chain, listing the substituents in alphabetical order

5

Many Alcohols Have Common Names
These are accepted by IUPAC

6

Naming Phenols
Use phenol as the family name Name substituents on aromatic ring by their position from OH

7

Common names
COOH

COOH

OH

O

COCH3

Salicylic acid reducing fevers, analgesic anti-inflammatory but too acidic, corrosive to stomach

acetylsalicylic acis Aspirin same potent less cotrrosive to stomach

8

Naming Ethers
Simple ethers are named by identifying the two organic substituents and adding the word ether

9

8.2 Properties of Alcohols and Phenols, and ethers: Hydrogen Bonding
The structure around O of the alcohol , phenol or ether is similar to that in water, sp3 hybridized Alcohols and phenols have much higher boiling points than similar alkanes and alkyl halides

10

Alcohols Form Hydrogen Bonds
A positively polarized ?OH hydrogen atom from one molecule is attracted to a lone pair of electrons on a negatively polarized oxygen atom of another molecule This produces a force that holds the two molecules together These intermolecular attractions are present in solution but not in the gas phase, thus elevating the boiling point of the solution

11

8.3 Properties of Alcohols and Phenols: Acidity
Weakly basic and weakly acidic Alcohols are weak Br?nsted bases Protonated by strong acids to yield oxonium ions, ROH2+

12

Alcohols and Phenols are Weak Br?nsted Acids
Can transfer a proton to water to a very small extent Produces H3O+ and an alkoxide ion, RO?, or a phenoxide ion, ArO?

13

Br?nsted Acidity Measurements
The acidity constant, Ka, measure the extent to which a Br?nsted acid transfers a proton to water [A?] [H3O+] Ka = ————— and pKa = ?log Ka [HA] Relative acidities are more conveniently presented on a logarithmic scale, pKa, which is directly proportional to the free energy of the equilibrium Differences in pKa correspond to differences in free energy
14

pKa Values for Typical OH Compounds

15

Generating Alkoxides from Alcohols
Alcohols are weak acids – requires a strong base to form an alkoxide such as NaH, sodium amide NaNH2, and Grignard reagents (RMgX) Alkoxides are bases used as reagents in organic chemistry

16

酸性: 酸性:ROH < H2O

;

碱性: 碱性:RONa > NaOH

RONa + H2O

ROH + NaOH

判断下列化合物的碱性大小: 判断下列化合物的碱性大小 NaOH, NaOR(1?), NaOR(2?), NaOR(3?) 共轭酸的酸性: 共轭酸的酸性 酸的离解方程式

17

Phenol Acidity
Phenols (pKa ~10) are much more acidic than alcohols (pKa ~ 16) due to resonance stabilization of the phenoxide ion Phenols react with NaOH solutions (but alcohols do not), forming soluble salts that are soluble in dilute aqueous A phenolic component can be separated from an organic solution by extraction into basic aqueous solution and is isolated after acid is added to the solution

18

Substituted Phenols
Can be more or less acidic than phenol itself An electron-withdrawing substituent makes a phenol more acidic by delocalizing the negative charge Phenols with an electron-donating substituent are less acidic because these substituents concentrate the charge

19

OH

OH

OH

OH

pka 10.0

CH3 10.26

Cl 9.38

NO2 7.15

20

比较下列各组化合物的相对酸性: 试比较下列各组化合物的相对酸性:

Cl 1) HO a
O _ _ _
21

HO b
O O

Cl

HO c
O _

8.4 Preparation of Alcohols: an Overview
Alcohols are derived from many types of compounds The alcohol hydroxyl can be converted to many other functional groups This makes alcohols useful in synthesis

22

Review: Preparation of Alcohols by Regiospecific Hydration of Alkenes

H C H

H2SO 4(Cat.) H C CH3CH2OH + H2O 250 °C H

23

Alcohols from Reduction of Carbonyl Compounds
Reduction of a carbonyl compound in general gives an alcohol Note that organic reduction reactions add the equivalent of H2 to a molecule

24

Reduction of Aldehydes and Ketones
Aldehydes give primary alcohols Ketones give secondary alcohols

25

Reduction Reagent: Sodium Borohydride
NaBH4 is not sensitive to moisture and it does not reduce other common functional groups Lithium aluminum hydride (LiAlH4) is more powerful, less specific, and very reactive with water Both add the equivalent of “H-”

26

Reduction of Carboxylic Acids and Esters
Carboxylic acids and esters are reduced to give primary alcohols LiAlH4 is used because NaBH4 is not effective

27

8.4 Reactions of Alcohols
Two general classes of reaction At the carbon of the C–O bond At the proton of the O–H bond

28

1. 取代反应(生成卤代烷 Chin. P344) 取代反应(生成卤代烷, ) 1) 与氢卤酸反应

R

OH + HX

R

X + H2O

HX活性:HI > HBr > HCl 活 醇活性顺序:3o > 2o > 1o > CH3OH

酸催化使羟基质子化,减弱 酸催化使羟基质子化,减弱C-O键,然后以水的形式离去。 键 然后以水的形式离去。
29

SN1机制:(多数 2o 3o醇) 机制:( 机制:(多数
CH3 CH3 C OH + HX CH3 CH3 CH3 C OH2 CH3
+

CH3 CH3 C
+

X

-

CH3 CH3 C X CH3

CH3

SN2机制:(多数 1o醇 ) 机制:( 机制:(多数 δ+
ROH
H

δ+
R OH2 ] X R + H 2O

ROH2

+

X-

[

X

下面的反应能否顺利进行


CH3CH2CH2CH2Br
30

CH3CH2CH2CH2OH + NaBr

鉴别不同类型的醇(六个碳以下的醇) 鉴别不同类型的醇(六个碳以下的醇)

Lucas试剂:浓HCl — 无水 试剂: 无水ZnCl2 试剂
ROH + HCl R C l + H 2O

3o 醇 、烯丙醇、苄醇 2o醇 1o醇

室温下反应液立即 混浊、分层; 2 ~ 5 min. 反应液混浊、分层; 加热 ,反应液混浊、分层;
31

反应按S 历程 有碳正离子重排。 历程, 反应按 N1历程,有碳正离子重排。

CH3 CH3C-CHCH3 H OH
HCl

CH3

CH3

CH3 CH3C-CH2CH3
+

+ CH3C-CHCH3 -H 2O CH3C-CHCH3 重排 H +OH2 H Cl-

ClCH3 CH3C-CH2CH3 Cl

CH3 CH3C-CHCH3 H Cl

32

2)与 PX3 (Chin. P347) 、SOCl2 (Chin. P347)反应 ) 反应
PBr3 PBr2 SN 2

3 (CH3)2CHCH2OH RCH2OH + Br Br + RCH2
-

3(CH3)2CHCH2Br + H3PO3 RCH2OPBr2 + HBr RCH2Br + -OPBr2

OPBr2

ROH + SOCl2

RCl + SO2 + HCl

反应不发生重排。 反应不发生重排。
33

3. 成酯反应 (Chin. P 336)

CH2OH CHOH + 3HONO2 CH2OH

CH2ONO2 CHONO2 + 3H2O CH2ONO2
甘油三硝酸酯

O CH3OH + H2SO4 CH3OSOH O
硫酸氢甲酯 CH3OH

O CH3OSOCH3 O
硫酸二甲酯
34

? 与磺酰氯作用生成磺酸酯

O CH3 对 甲苯 磺 酰 氯 S O Cl + CH3OH
吡啶 -HCl

O CH3 对 甲苯 磺 酸甲 酯 S-OCH3 O

O Nu:- + RCH2 O S O R’ Nu
CH2R + O

O S O
35 好的离去基团

R’

Dehydration of Alcohols to Yield Alkenes Eng. P253
The general reaction: forming an alkene from an alcohol through loss of O-H and H (hence dehydration) of the neighboring C–H to give π bond Specific reagents are needed

36

Acid- Catalyzed Dehydration
Tertiary alcohols are readily dehydrated with acid Secondary alcohols require severe conditions (75% H2SO4, 100° - sensitive molecules don't survive C) Primary alcohols require very harsh conditions – impractical Reactivity is the result of the nature of the carbocation intermediate (reading Figure 8.4, P. 254)

37

CH2OH

[discussion]

H+ 170 C
o

?

CH2OH H+

CH2OH2 -H2O

+

+ CH2

+

重排

-H+

H

38

Oxidation of Alcohols
Can be accomplished by inorganic reagents, such as KMnO4, CrO3, and Na2Cr2O7 or by more selective, expensive reagents

39

Oxidation of Primary Alcohols
reading Eng. P 255-256

To aldehyde: pyridinium chlorochromate (PCC, C5H6NCrO3Cl) in dichloromethane Other reagents produce carboxylic acids

40

Oxidation of Secondary Alcohols
Effective with inexpensive reagents such as Na2Cr2O7 in acetic acid PCC is used for sensitive alcohols at lower temperatures

41

Conversion into Ethers: The Williamson Ether Synthesis reading Eng. P257
Reaction of metal alkoxides and primary alkyl halides and tosylates Best method for the preparation of ethers Alkoxides prepared by reaction of an alcohol with a strong base such as sodium hydride, NaH

42

(Ar)RONa + R'X

SN 2

(Ar)ROR' + NaX

(混合醚) 混

Practice:
(CH3)3C O CH2CH3 a. (CH3)3CX + CH3CH2ONa b. (CH3)3CONa + CH3CH2X

a. OCH2CH3

ONa + CH3CH2X X
43

b. CH3CH2ONa +

8.6 Preparation and reactions of Phenols

44

Laboratory Preparation of Phenols
(Eng. 258) From aromatic sulfonic acids by melting with NaOH at high temperature

45

(2) 从芳卤衍生物制备 (Chin. P326)

Cl NO2 NaOH,140~155℃
450~530kPa,5.5h

ONa NO2
H2SO4

OH NO2

(~90%)

46

Reactions of Phenols (Eng. 259)
The hydroxyl group is strongly activating, making phenols substrates for electrophilic halogenation, nitration, sulfonation, and Friedel–Crafts reactions

47

芳环上的反应
OH Br2 CS2 Br OH Br Br2 H2O Br Br

OH

什么邻硝基苯酚的沸点、 为什么邻硝基苯酚的沸点、水溶性比相应的异构体低?
48

硝化、磺化、 硝化、磺化、F-C反应 反应

Chin. p 352-355, 了解

与FeCl3的显色反应 Chin. P343

3-

6C6H5OH + FeCl3

Fe(OC6H5)6

+ 6H+ + 3Cl-

OH C C

OH

用于定性分析

49

Reaction of a phenol with strong oxidizing agents yields a quinone

50

Quinones in Nature
Ubiquinones (辅酶) mediate electron-transfer processes involved in energy production through their redox reactions

51

Synthesis and Reactions of Ethers
Eng. P261

1. The Williamson Ether Synthesis

52

2. 醇分子间失水 Chin. P249

2 CH3CH2OH

H2SO4 ~ 130 C
o

CH3CH2OCH2CH3 (简单醚)

分子内脱水生成什么? 分子内脱水生成什么

53

Reactions of Ethers: Acidic Cleavage
Ethers are generally unreactive Strong acid will cleave an ether at elevated temperature HI, HBr produce an alkyl halide from less hindered component by SN2

54

tertiary ethers undergo SN1 P. 262, practice problem 8.5, what products will be obtained if 2 mol of HBr is added? HI > HBr > HCl

55

(CH3)3C O CH3 + HI

(CH3)3C O CH3 + IH

+

+

(CH3)3C O CH3 H

SN1

(CH3)3C+ + CH3OH I(CH3)3CI
过量

HI

CH3I + H2O

CH3I + AgNO3

CH3CH2OH

AgI

甲氧基定量测定法 Zeisel法 法
56

醚的自动氧化

醚分子中的a-H容易发生自由基取代反应 容易发生自由基取代反应 醚分子中的 容易发生

醚和O 反应生成可爆炸的过氧化物。 醚和 2反应生成可爆炸的过氧化物。
OOH 例: R CH O CH2 R

为什么醚蒸馏前必须纯化? 为什么醚蒸馏前必须纯化?
57

醚的碱性
R R O R' + BF3 R'
lewis碱 碱 lewis酸 酸

O BF3

R O R + HCl

R O R + ClH

+

58

Cyclic ethers
Eng. P 262-263, read text
benzopyrene

59

4. 1, 2-环氧化合物的开环反应 环氧化合物的开环反应

怎样制备增加两个碳原子的伯醇?( 怎样制备增加两个碳原子的伯醇?(p.372) ?(

10.6.4 环氧乙烷与格氏试剂的反应

60

Summary -Alcohols
Synthesis Reduction of aldehydes and ketones Addition of Grignard reagents to aldehydes and ketones Reactions Conversion to alkyl halides Dehydration Oxidation

61

Summary - Phenols
Much more acidic (pKa ≈ 10) than alcohols Substitution of the aromatic ring by an electronwithdrawing group increases phenol acidity Substitution by an electron-donating group decreases acidity Oxidized to quinones Quinones are reduced to hydroquinones

62

Ethers
Synthesis: Williamson ether synthesis Reaction: acidic cleavage with HBr or HI

63


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