chuong 10. alcohol and phenols

7/29/2019 Chuong 10. Alcohol and Phenols

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HOA HOC HU C

Organic Chemistry

CHNG 10ALCOHOLS & PHENOLS

Mendeleev Hamilton Hartree


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GII THIEU CHNG10.1. RU10.1.1.DANH PHAP & ONG PHAN10.1.2.CAC PHNG PHAP IEU CHE10.1.3. TNH CHAT10.1.4.NG DUNG

10.2. PHENOL10.2.1. DANH PHAP & ONG PHAN10.2.2. CAC PHNG PHAP IEU CHE10.2.3. TNH CHAT10.2.4. NG DUNG


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DANH PHAP


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DANH PHAP


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CH3CHCH

2CHCH(CH

3)2

OHOH

5-methyl-2,4-hexanediol


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OH

CH2CH

2C(CH

3)2

2-methyl-4-phenyl-2-butanol


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OH

CH3 CH3

4,4-Dimethylcyclohexanol


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BrH

HOH

trans-2-Bromocyclopentanol


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LIEN KET TRONG RU


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Alcohols

IR spectrum of 1-hexanol (Fig 12.8)

O-H (free)

O-H (H bonded)

C-O

Bond IntensityFrequency, cm

-1

Medium1000 - 1250

Medium, broad3200 - 3500

3600-3650 Weak


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Example: Mass Spectrum of

Methanol (CH3OH)

m/z Rel. Abundance

12 0.33

13 0.72

14 2.4

15 13.

16 0.21

17 1.0

28 6.3

29 64

30 3.8

31 100.

32 66.

33 0.98

34 0.14

0

10

20

30

40

50

60

70

80

90

100

1 4 710

13

16

19

22

25

28

31

34

37

40

m/z

Rel.Abu

ndance,

%

15

31

CH3OH + e- CH3OH

+ + 2e-

CH3OH+ CH2OH

+ + H

CH3OH+ CH3

+ + OH

CH2OH+ H2 + CHO

+


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Chemical Properties Alcohols as acids

Sterically hindered alcohols such as tert-butylalcohol are less acidic (have higher pKavalues)

stronger acids than terminal alkynes andprimary or secondary amines

Alkoxides prepared by the reaction of an alcoholwith sodium or potassium metal


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-200

-150

-100

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0

50100

150

1 2 3 4 5 6

Period

BoilingPoint(OC),

Water

HF

Ammonia

Methane

H2O

H2SH2Se

H2Te

CH4

SiH4GeH4

SnH4

Hydrogen Bonding

1. Water, HF, andNH3 show unusually high bp.

2. Dotted lines depict bp if there were no H-bonding.

3. All others follow normal trend.

extrapolation

HF

NH3


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Hydrogen Bonding in Water

OHH

H

OH

O H

H

O HH

H

OH

Hydrogen bond,

intermolecular,

4 - 25 kJ/mol

Chemical Bond,

intramolecular,150 - 600 kJ/mol

--

++

+

+

+

+

++

+

+

--

----

--


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O RH

R

OH

O R

H

O HR

R

OH

Hydrogen Bonding in Alcohol

-

+

+

+

++ -

--

-


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Hydrogen Bonding and Boiling Point

Compound bp (oC)

Water 100

Methanol 65

Ethanol 78

Propanol 97


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Acidity & Basicity

Like water, alcohol can act as an acid or as a base.

acid oxonium ionbase

acid base

alkoxide ion

phenoxide ion

+ H ClRO

H+ Cl+

RO

H

H

+ H ClArO

H + Cl+Ar

OH

H

+RO

H HO

H + +H

OH

H

RO-

+ +H

OH

HO-


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Conversion to Alkyl Halides

Hydroxyl groups are poor leaving groups Reaction of Alcohols with HX

Tertiary alcohols: SN1Step 1

H-ClO O

H

H

Cl-

H H3O++

+

Step 2

+O

H

HO

H

H

+Cl-

Cl

Step 3


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Primary Alcohols: SN2

Use of Lewis acids

Cl-H

ClH

Step 2

Step 1H-Cl

HO

H

HO

H

H

H

Cl-

H H3O+

+ OH

H

HO

H

H

H

+

Cl-H

Cl H

Step 2

Step 1

ZnCl2

HO

H

HOH

ZnCl2

H

Cl-H

+ O

ZnCl2

H

HO

H

ZnCl2

H

+

-

- -


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Reaction of Alcohols with PBr3

Step 1PBr3R

O Br-

H

RO

H

P+

P BrBr

Br Br

Br

Step 2

Br-

R

O

H

P

+

Br

Br

RBr

OH

P Br

Br


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Reaction of Alcohols with SOCl2Step 1

SOCl2O

HO

H

S

+

S OCl

Cl Cl

Cl O-

O

H

S

+

Cl

O

Cl-

O

S

Cl

O

HCl

Step 2

Cl-

ClO

SCl

O

SO2


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Leaving Groups

Tosylates (Ts), Mesylates (Ms), and Triflates(Tf): Leaving Group Derivatives of Alcohols

-O S

O

O

-O S

O

OH

H

H -O S

O

OF

F

F

Cl S

O

OR

OH

S

O

O

RO

H

+

Base

S

O

OR

O

Cl S

O

OR

OH

ClS

O

O-

RO

H+

ClS

O

O-

RO

H+

S

O

O

RO

H

+

Base


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Sulfonates as Leaving Groups

Recall: SN2 inversion of configuration

Triflate anion is such a good leaving group that

even vinyl triflates can undergo SN1 reaction

S

O

OR

OR1

R3R2

Nu-

R

Nu R1

R3R2

S

O

O F

FO F

S

O

O F

F-O F+


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Synthesis of Ethers

Intermolecular Dehydration of Alcohol This reaction occurs at lower temperature than the

competing dehydration to an alkene

does not generally work with secondary or tertiary

alcohols (elimination competes strongly)

OH

H

H2O

H2SO4

180

o

C

OH

H

O

H2SO4

140

o

C


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Synthesis of Ethers

Mechanism

O

H HStep 1

+H

H+

O

H

H

O

Step 2

+

H

O

H

H O


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Williamson Ether Synthesis

Synthesis of unsymmetrical ethers

Recall: the alkyl halide (or alkyl sulfonate) shouldbe primary to avoid E2 reaction, Substitution isfavored over elimination at lower temperatures

O

Step 1

H NaH O

H

O

Step 2

I

O


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Alkoxymercuration-

Demercuration Markovnikov selectivity

H

H

Hg(OAc)2, ROHH

NaBH4, OH-

HH

H Hg(OAc)

OR

HHH

Hg(OAc)

ORH

HH

H

OR


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Reaction of Ethers

Acyclic ethers are generally unreactive, exceptfor cleavage by very strong acids

Step 1

+O O

H

HBrBr-

Step 2

+Br

O

H

Br-O

H

Step 3

O

H

HBr

+O H

H

Br-

Br


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Alcohol Protecting Groups

The protecting groups are used to protectprimary alcohols from reacting

Added before the reaction and removed after

Base


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Alcohol Protecting Groups

Silyl Ethers Tert-butyldimethylsilyl (TBDMS)

Base = pyridine, imidazole

Removal: fluoride ion

SiR

OSi

ClR

OH

SiRO

H

+

Base

SiR

O

Bu4N+ F-

then H2OR

OH


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Protection of Alcohol

It often happens, particularly during synthesis of complex

molecules, that one functional group in a molecule

interferes with an intended reaction on a second functionalgroup elsewhere in the same molecule. - p 682.

CH3CH

2CH

2Br

Mg

etherCH

3CH

2CH

2MgBr

HOCH2CH

2CH

2Br

Mg

etherHOCH

2CH

2CH

2MgBr


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Trimethylsilyl (TMS) ether

Chlorotrimethylsilane TMS ether

ROH is now blocked or protected!!!

ROH + SiCH

3CH

3

CH3Cl

SiCH

3CH

3

CH3O

R

(CH3CH

2)3N

+ (CH3CH2)3NH-Cl+ -

Triethylamine

Si CH3CH3

CH3

ORH3O+

ORH Si CH

3CH3

CH3

OH+


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Step 1: Adding Protection Group

HOCH2CH

2CH

2Br(CH

3)3SiCl +

(CH3CH

2)3N

(CH3)3SiOCH

2CH

2CH

2Br

+


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Step 2a: Carrying Out Reaction

(CH3)3SiOCH

2CH

2CH

2Br (CH3)3SiOCH2CH2CH2MgBr

Mg

ether


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Step 2b: Carrying Out Reaction

(CH3)3SiOCH

2CH

2CH

2MgBr

H3O+

+ CH3CH

O

(CH3)3SiOCH

2CH

2CH

2CHCH

3

OH

+


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Step 3: Removing Protection Group

H3O+

(CH3)3SiOCH

2CH

2CH

2CHCH

3

OH

HOCH2CH

2CH

2CHCH

3

OH

+ (CH3)3SiOH

+


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CAM N S THEO DOI CUA CAC BAN

CHUC MOI IEU TOT EP

chuong 10. alcohol and phenols

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