Organic Chemistry II Alcohols, Phenols, Thiols

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1 06/09/22 06/09/22 Organic Chemistry II Organic Chemistry II Alcohols, Phenols, Alcohols, Phenols, Thiols Thiols Dr Seemal Jelani Dr Seemal Jelani Chem-240 Chem-240

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Organic Chemistry II Alcohols, Phenols, Thiols. Chapter Objectives. Nomenclature Properties Preparation Reaction. Alcohols and Phenols. Important solvents and intermediates Phenols contain an OH group connected to a carbon in a benzene ring - PowerPoint PPT Presentation

Transcript of Organic Chemistry II Alcohols, Phenols, Thiols

Page 1: Organic Chemistry II Alcohols, Phenols, Thiols

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Organic Chemistry IIOrganic Chemistry II

Alcohols, Phenols, Thiols Alcohols, Phenols, Thiols

Dr Seemal Jelani Chem-240Dr Seemal Jelani Chem-240

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Chapter ObjectivesChapter Objectives

• NomenclatureNomenclature

• PropertiesProperties

• PreparationPreparation

• ReactionReaction

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Alcohols and PhenolsAlcohols and Phenols

•Important solvents and intermediates•Phenols contain an OH group

connected to a carbon in a benzene ring

•Methanol, CH3OH, common name is methyl alcohol, a solvent, a fuel additive, produced in large quantities

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•Ethanol, CH3CH2OH, common name is ethyl alcohol, a solvent, fuel, beverage, produced in large quantities

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Alcohols, Phenols, Thiols, Alcohols, Phenols, Thiols, EthersEthers• Considered derivatives of waterConsidered derivatives of water

OH SH OH SH

O S

alcohol thiol phenol thiophenol

ether sulfide

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Nomenclature of AlcoholsNomenclature of Alcohols

•Derivatives of alkane with –ol suffix

•Name longest chain containing OH

•Number the chain starting nearest the carbon bearing the OH group

•Number substituents, name, and list alphabetically

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ExamplesExamples

OH

OH

OH

OH

propanol

trans-1,2-cyclopentanediol

3-ethylheptan-3-ol

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Classification of AlcoholsClassification of Alcohols•Primary – OH is attached to a carbon

bearing one carbon atom

•Secondary – OH is attached to a carbon bearing two carbon atoms

•Tertiary – OH is attached to a carbon bearing three carbon atoms

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ExamplesExamples

OH

OH

OH

primary alcohol

secondary alcohol

tertiary alcohol

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Common NamesCommon Names

OH

OH

OHOH OH

OH

OH

OH

benzyl alcohol allyl alcohol

t-butyl alcohol

ethylene glycol

glycerol

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PhenolsPhenols•Common natural source – coal tar•Found in many plants

OH

OH

CO2H

OH

CO2CH3

OH

R

OHcoal tar

willow bark

oil of wintergreen

bioactive ingredient poison ivy and oak

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PhenolsPhenolsOH

OMe

OH

OMe

OH

OMe

O O

OH

C5H11

eugenol (oil of clove) isoeugenol (oil of nutmeg)

vanillintetrahydrocannabinol

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Nomenclature of PhenolsNomenclature of Phenols

• Use “phene” (the French name for benzene) as the parent hydrocarbon name, not benzene

• Name substituents on aromatic ring by their position from OH

CH3

OH Cl

OH

OH

NO2O2N

p-methylphenol o-chlorophenol 2,4-dinitrophenol

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Common NamesCommon Names• Many common names in use

OH

CH3

OH

CH3

OH

CH3

OH

OH

OH

OH

OH

OH

o-cresol m-cresol p-cresol

catecholresorcinol

hydroquinone

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Nomenclature of ThiolsNomenclature of Thiols•Same naming system as alcohols

•Suffix is –thiol

•Sometimes named as mercaptans

SH

SH

CH3

OH

SH

isopropyl thiol cis-2-methylcycloheptane thiol

m-mercaptophenol

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Biosynthesis of EthanolBiosynthesis of Ethanol(Fermentation)(Fermentation)

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C6H12O6

glucose

CH3

O

O

OH

pyruvate

CH3

O

O

OH

pyruvate

CH3CH2OH

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PropertiesProperties

• Alcohols and phenols are similar to water form strong H-bonds

• Giving higher boiling points than the corresponding hydrocarbon

• Thiols do not form H-bonds (EN of S is low)

• Alcohols and phenols are weakly basic

• Alcohols and phenols are weakly acidic

• Phenols and Thiols are more acidic than water

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Acidity ConstantsAcidity ConstantsOH

OH

CH3

OH

O2N

OH

CH3CH2OH

H2O

CH3OH

CH3SH

pKa = 18

pKa = 16

pKa = 15.7

pKa = 15.5

pKa = 10.3

pKa = 10.2

pKa = 9.9

pKa = 7.2decreasing acidity

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Acidity of AlcoholsAcidity of Alcohols•Do not react with amines or

NaHCO3

•Limited reactivity with NaOH

•React with alkali metals Na, K

•React with strong bases like NaH or NaNH2 or RLi and RMgBr

•Forms the alkoxide (RO-1)

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Reactions with BasesReactions with BasesROH + NH3 No Reaction

ROH + NaHCO3 No Reaction

ROH + NaOH RO- + H2O

ROH + NaH RO- + H2

ROH + Na RO- + H2

ROH + RLi RO- + RH

ROH + RMgX RO- + RH

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Acidity of PhenolsAcidity of Phenols

• ArOH is more acidic than ROHArOH is more acidic than ROH• Soluble in dilute NaOHSoluble in dilute NaOH• Anion is resonance stabilizedAnion is resonance stabilized• EWG make phenols more acidic than phenolEWG make phenols more acidic than phenol• EDG make phenols less acidic than phenolEDG make phenols less acidic than phenol

OH O O

NaOH -

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Alcohols an OverviewAlcohols an Overview• Alcohols are derived from many types of

compounds

• Alkenes, alkyl halides, ketones, esters, aldehydes, and carboxylic acids can provide the alcohol

• Alcohols are among most common natural materials

• The alcohol hydroxyl can be converted to many other functional groups

• This makes alcohols useful in synthetic planning

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Preparation

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Preparation of AlcoholsPreparation of Alcohols

•Hydration of Alkenes•BH3/THF followed by H2O2 in

NaOH•Hg(OAc)2 followed by NaBH4

•OsO4 followed by NaHSO3 (cis-1,2-diols)

•RCO3H followed by aqueous acid (trans-1,2-diols)

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• From Aldehydes and Ketones• Reduction with NaBH4

– Reduces alpha beta unsaturated carbonyls as well

Reduction with LiAlH4

– Doesn’t touch alpha beta unsaturated carbonyls

• From Esters– Reduction with LiAlH4 (LAH)– No reaction with NaBH4

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Reduction of KetonesReduction of Ketones

O

OH

OH

OH

LAH

NaBH4

+

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Preparation of AlcoholsPreparation of Alcohols• From carboxylic acids

– Reduction with LiAlH4 is slow

– Reduction with NaBH4 doesn’t occur

– Reduction with BH3 is preferred method

RCO2HLiAlH4

RCH2OHslow

RCO2HNaBH4

No Reaction

RCO2H RCH2OHBH3

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From Alkyl halides•RX + Mg provides the Grignard

reagent

•Grignard reagents react with carbonyls to provide the alcohols

CH3Br + Mg CH3-Mg-Br

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Grignard Reactions

•With aldehydes or ketones

•With esters

O OH

CH3

O

H

OH

H

CH3

1. CH3MgBr

2. H3O+

1. CH3MgBr

2. H3O+

O

OMe

OH

CH3

CH3

1. CH3MgBr

2. H3O+

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Grignard Reactions

•With carboxylic acids•Grignard's are strong bases

•React with the acidic proton

O

OH

O

OH

1. CH3MgBr

2. H3O+

+ CH4

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Reactions

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Reactions of Alcohols

•Alcohols react at– the O-H bond– the C-O bond

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Alcohols to Alkyl Halides

OH Cl

OH Br

OH Cl

OH Cl

HCl

HBr

tertiary alcohols

primary or secondary alcohols

SOCl2

PBr3

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Alcohols to Alkenes

• Dehydration

• Acid catalyzed reaction

• Excellent reaction for tertiary alcohols (E1)

• Provides the Zaitsev product

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•When the substrate is asymmetric, regioselectivity is determined by Zaitsev’s rule

• The one -step mechanisms is E2 reaction and two step reaction mechanism is called E1 reaction, respectively.

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•It is the preference of one direction of chemical bond making or breaking over all other possible directions

What is regioselectivity

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•In chemistry, Zaitsev's rule, Saytzeff's rule or Saytsev's rule is a rule that states

“that if more than one alkene can be

formed during dehalogenation by an

elimination reaction the more stable

alkene is the major product”

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What is Zaitsev’s ruleWhat is Zaitsev’s rule

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•In general, the compound that has a more highly substituted C=C double bond is more stable.

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Who is then stable

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Alcohol to AlkeneAlcohol to Alkene

• Milder reaction developed

• E2 process

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Alcohols to Esters• Alcohols react with carboxylic acids

• Reaction is acid catalyzed

• Alcohols react with acid chlorides

• Reaction is base catalyzed

R

O

OH R

O

OR

R

O

Cl R

O

OR

ROH/H+

H3O+

SOCl2

ROH/pyridine

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Alcohols to Tosylate Esters • Reaction with p-toluenesulfonyl chloride

(tosyl chloride, p-TosCl) in pyridine yields alkyl tosylates, ROTos

• Formation of the tosylate does not involve the C–O bond so configuration at a chirality center is maintained

• Alkyl tosylates react like alkyl halides

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Oxidation of Alcohols • Can be accomplished by inorganic reagents, such as

KMnO4, CrO3, and Na2Cr2O7 or by more selective, expensive reagents

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Oxidation of Primary Oxidation of Primary AlcoholsAlcohols•To aldehyde: pyridinium chlorochromate

(PCC = C5H6NCrO3Cl) in dichloromethane•Other reagents produce carboxylic acids

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Oxidation of Secondary Oxidation of Secondary AlcoholsAlcohols• Effective with inexpensive reagents such as

Na2Cr2O7 in acetic acid• PCC is used for sensitive alcohols at lower

temperatures

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Preparation and Uses of Preparation and Uses of PhenolsPhenols • Industrial process from readily available cumene

• Forms cumene hydroperoxide with oxygen at high temperature

• Converted into phenol and acetone by acid

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Industrial Preparation of Industrial Preparation of PhenolPhenol

Cl OHNaOH/heat

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Laboratory Preparation of Laboratory Preparation of PhenolsPhenols• From aromatic sulfonic acids by melting

with NaOH at high temperature• Limited to the preparation of alkyl-

substituted phenols

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Reactions of PhenolsReactions of Phenols • The hydroxyl group is a strongly activating,

making phenols substrates for electrophilic halogenation, nitration, sulfonation, and Friedel–Crafts reactions

• Reaction of a phenol with strong oxidizing agents yields a quinone

• Fremy's salt [(KSO3)2NO] works under mild conditions through a radical mechanism

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