Bài giảng Hoá học hữu cơ alcohol

Classification• CH3 • Primary 1o: carbon with –OH is bonded to one other carbon.. • Tertiary 3o: carbon with –OH is bonded to three other carbons.. Grignard Reagents• Formula R-Mg-X r

II.Physical Properties III.Synthesis

IV.Reaction

ALCOHOL

I.1.Structure of Alcohols

• Hydroxyl (OH) functional group

• Oxygen is sp3 hybridized

=>

I.2 Classification

• CH3

• Primary ( 1o): carbon with –OH is bonded

to one other carbon.

• Secondary ( 2o) : carbon with –OH is

bonded to two other carbons.

• Tertiary ( 3o): carbon with –OH is bonded to three other carbons.

• Aromatic (phenol): -OH is bonded to a

benzene ring.

Classify these alcohols:

I.3.IUPAC Nomenclature

• Find the longest carbon chain containing the carbon with the -OH group.

• Drop the -e from the alkane name, add -ol.

• Number the chain, starting from the end closest to the -OH group.

• Number and name all substituents

CH2 CHCH2CHCH3

OH

Common Names

• Alcohol can be named as alkyl alcohol.

• Useful only for small alkyl groups.

• 1, 2 diols (vicinal diols) are called glycols.

• Common names for glycols use the name of the alkene from which they were made.

Naming Phenols

• -OH group is assumed to be on carbon 1.

• For common names of disubstituted phenols,

use ortho- for 1,2; meta- for 1,3; and para- for

II.Physical Properties

• Unusually high boiling

bonding between

molecules

• Small alcohols are

miscible in water, but

solubility decreases as the

size of the alkyl group

increases

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Boiling Points

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Solubility in Water

Solubility decreases as the size

of the alkyl group increases

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• Syn hydroxylation of alkenes

osmium tetroxide, hydrogen peroxide

cold, dilute, basic potassium permanganate

• Anti hydroxylation of alkenes

peroxyacids, hydrolysis

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Organometallic Reagents

• Carbon is bonded to a metal (Mg or Li).

• Carbon is nucleophilic (partially negative).

• It will attack a partially positive carbon.

C - X

C = O

• A new carbon-carbon bond forms

=>

Grignard Reagents

• Formula R-Mg-X (reacts like R: - +MgX)

• Stabilized by anhydrous ether

• Iodides most reactive

• May be formed from any halide

CH3C CH2

Br + Mg ether CH3 C CH2

MgBr =>

Organolithium Reagents

• Can be produced from alkyl, vinyl, or aryl halides, just like Grignard reagents.

• Ether not necessary, wide variety of

solvents can be used

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Reaction with Carbonyl

• R:- attacks the partially positive carbon in the

carbonyl.

• The intermediate is an alkoxide ion.

• Addition of water or dilute acid protonates the

alkoxide to produce an alcohol.

Synthesis of 1° Alcohols

Grignard + formaldehyde yields a primary alcohol with one additional carbon.

C O H

CH3 CH

CH3

CH2 CH2 C

H H

C O H

How would you synthesize

Grignard Reactions with Acid

Chlorides and Esters

• Use two moles of Grignard reagent.

• The product is a tertiary alcohol with

two identical alkyl groups.

• Reaction with one mole of Grignard

reagent produces a ketone intermediate, which reacts with the second mole of

Grignard reagent.

=>

Grignard + Acid Chloride (1)

C O Cl

H3C

MgBr

CH3Cl

• Grignard attacks the carbonyl.

• Chloride ion leaves.

Grignard and Ester (1)

• Grignard attacks the carbonyl.

• Alkoxide ion leaves! ? !

Second step of reaction

• Second mole of Grignard reacts with the

ketone intermediate to form an alkoxide ion.

• Alkoxide ion is protonated with dilute acid.

C

CH3R

O

CH3R

=>

How would you synthesize

CH3CH2CCH3

OH

CH3

C OH

Grignard Reagent + Ethylene Oxide

• Epoxides are unusually reactive ethers.

• Product is a 1º alcohol with 2 additional carbons.

Limitations of Grignard

• No water or other acidic protons like

O-H, N-H, S-H, or -C—C-H Grignard reagent is destroyed, becomes an

alkane.

• No other electrophilic multiple bonds,

like C=N, C—N, S=O, or N=O

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Reduction of Carbonyl

• Reduction of aldehyde yields 1º alcohol.

• Reduction of ketone yields 2º alcohol.

• Reagents:

Sodium borohydride, NaBH4

Lithium aluminum hydride, LiAlH4

Raney nickel

=>

Sodium Borohydride

carbon, forming an alkoxide ion.

• Then the alkoxide ion is protonated by

dilute acid.

• Only reacts with carbonyl of aldehyde or

ketone, not with carbonyls of esters or

O

H3O+

=>

Lithium Aluminum Hydride

• Stronger reducing agent than sodium

borohydride, but dangerous to work with.

• Converts esters and acids to 1º alcohols.

to reduction.

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Catalytic Hydrogenation

• Add H2 with Raney nickel catalyst.

• Also reduces any C=C bonds.

O

H2, Raney Ni

OH

NaBH4OH

=>

IV.1 Reaction of alcohols with HX: (#1 synthesis of RX)

R-OH + HX  R-X + H2O

a) HX: HI > HBr > HCl

b) ROH: 3o > 2o > CH3 > 1o

c) May be acid catalyzed

d) Rearrangements are possible except with most 1o alcohols

CH3CH2CH2CH2-OH + NaBr, H2SO4, heat  CH3CH2CH2CH2-Br

n-butyl alcohol n-butyl bromide

CH3CH2-OH + HI, H + , heat  CH3CH2-I

CH3-OH and most 1o alcohols react with HX via S N 2 mechanism

3o and 2o react with HX via S N 1 mechanism

Both mechanisms include an additional, first step, protonation

of the alcohol oxygen:

R-OH + H+  R-OH2+ “oxonium ion”

Mechanism for reaction of an alcohol with HX:

CH3OH or 1o alcohols:

SN2

Mechanism for reaction of an alcohol with HX:

Rearrangements are possible (except with most 1 o alcohols):

CH3 CH3

CH3CHCHCH3 + HBr  CH3CCH2CH3

CH3CH2CH2CH2CH2-OH + HBr, H+, heat

CH3CH2CH2CH2CH2-Br

1o alcohol:

No rearrangement, SN2

In the reaction of most 1o alcohols with HX you don't have

to worry about the possibility of rearrangements The mechanism

is SN2 and does not involve carbocations.

1-pentanol

1-bromopentane

Most 1o? If large steric requirement

C – C

-H O-H

IV.5 Ester formation.

CH3CH2-OH + CH3CO2H, H +  CH3CO2CH2CH3 + H2O

CH3CH2-OH + CH3COCl  CH3CO2CH2CH3 + HCl

CH3-OH + CH3SO2Cl  CH3SO3CH3 + HCl

acetyl chloride isopropyl alcohol isopropyl acetate

acid chloride + alcohol > ester

R S

O O Cl

sulfonyl chloride

O O

O-R + HCl

Sulfonate ester

Oxidizing agents: KMnO4, K2Cr2O7, CrO3, NaOCl, etc.

Primary alcohols ONLY can be oxidized to aldehydes:

CH3CH2CH2-OH + C5H5NHCrO3Cl  CH3CH2CHO

pyridinium chlorochromate (PCC) aldehyde

or

CH3CH2CH2-OH + K2Cr2O7, special conditions

 Enzymes in the liver oxidize ethanol.

 The aldehyde produced impairs coordination.

O ||

CH 3 CH 2 OH CH 3 CH 2CO 2 + H 2 O

Ethyl alcohol acetaldehyde

Oxidation of Alcohol in

the Body

Oxidation of alcohols in liver

CH3CH2OH CH3C

O

O OH

metyl alcohol

methanol formaldehydemethanal

reacts with proteins causing denaturation great toxicity to humans

not toxic to horses and rats

HC O

OH formic acid methanoic acid acetaldehydedehydrogenase

Effect of Alcohol on the Body

Breathalyzer reaction

orange-red green

8H++Cr2O72-+3C2H5OH→2Cr3++3C2H4O+7H2O dichromate ethyl chromium (III) acetaldehyde

ion alcohol ion (from K2Cr2O7)

ethyl

alcohol

acetaldehyde

Oxidation of Thiols.

• Mild oxidizing agens remove two

hydrogen atoms from two thiol molecules.

• The remaining pieces of thiols combine to form a new molecule, disulfide, with a

covalent bond between two sulfur atoms.

The chemistry of the

“permanent” waving of hair.

• Hair is protein, and it is held in shape by disulfide linkages

between adjacent protein chains.

• The first step involves the use of lotion containing a reducing agent such as thioglycolic acid, HS – CH2 – COOH.

• The wave lotion ruptures the disulfide linkages of the hair protein.

• The hair is then set on curles or rollers and is treated with a mild oxidizing agent such as hydrogen peroxide (H2O2).

• Disulfide linkages are formed in new positions to give new shape

to the hair.

• Exactly the same chemical process can be used to straighten

naturally curly hair.

• The change in hair style depends only on how one arranges the hair after the disulfide bonds have been reduced and before the reoxidation takes place.

• Permanent Hair Wave

(http://www.elmhurst.edu/~chm/vchembook/568hairwave.html)

Highly applied alcohols

• Ethanol is made by hydration of ethylene

(ethene) in the presence of acid catalyst

H H

Production of ethanol from

grain by fermentation

• Grain seeds are grounded and cooked → mash

• Malt (the dried sprouts of barley) or special mold is

added → source of the enzyme diastase that catalyzes the conversion of starch to malt sugar, maltose

propyl alcohol is never formed

• is made commercially from carbon monoxide and hydrogen

• CO + 2H2 → CH3OH