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HYDROXY COMPOUNDS (ALCOHOLS)

HYDROXY COMPOUNDS (ALCOHOLS)

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INTRODUCTIONAlkane with hydroxyl group (–

OH)General formula for aliphatic

alcohol, CnH2n+1OHAromatic alcohol – phenol (-OH

attached to the benzene rings)

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CH3CH2-OH

OH CH2-OH

ALIPHATIC ALCOHOL (–OH group attached directly to the alkyl group)

INTRODUCTION

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OH

AROMATIC ALCOHOL (–OH group attached directly to the aryl group)

INTRODUCTION

OHOHCH3

Br

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CLASSIFICATION

Methyl alcohol CH3-OH

10 Alcohols R-CH2-OH

20 Alcohols R-CH-OH

30 Alcohols R-C-OH

R

R

R

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NOMENCLATUREStructure General name IUPAC name

CH3-OH

CH3CH2-OH

CH3CH(OH)CH3

OH

methyl alcohol methanol

ethyl alcohol ethanol

isopropyl alcohol 2-propanol

cyclohexyl alcohol

cyclohexanol

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Naming the alcohol

1.The suffix ‘–e’ in the alkane parent name is replaced by ‘–ol’

2.The location of the –OH on the longest chain is given by the smallest possible number

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IUPAC rules for naming alcohols

1.Determine parent name

2.Give the lowest number to the carbon bearing the –OH group

3.Identify substituent groups and their position

4.Name the alcohol

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Naming Alcohols, R-O-H:

CH3 CH3

CH3CHCH2CHCH3 CH3CCH2CH2CH3

OH OH4-methyl-2-pentanol

2-methyl-2-pentanol

2o 3o

CH3

HO-CHCH2CH3 CH3CH2CH2-OH

sec-butyl alcohol n-propyl alcohol 2-butanol 1-propanol

2o 1o

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Naming Alcohols

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For phenol, C attach to the –OH group is C 1

OH OHCH3

OH

BrCH2CH3

3-ethylphenol 3-bromophenol 2-methylphenol

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Alcohol with 2 hydroxy groupsStructure General name IUPAC name

CH2(OH)CH2-OH

CH3CH(OH)CH2-OH

HO-CH2CH2CH2-OH

OH-CH2CHCH2-OH

OH

ethylene glycol 1,2-ethanediol

propylene glycol 1,2-propanediol

trimethyleneglycol

1,3-propanediol

glycerol 1,2,3-propanetriol

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Benzene derivatives with 2 –OH groups are name as benzenediol

OH OHOHOH

OHOH

1,4-benzenediol

(hydroquinone)

1,3-benzenediol

(resorcinol)

1,2-benzenediol

(catechol)

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EXCERCISE

1. Name the following compounds using IUPAC nomenclature

(a)-CH2CH(CH3)CH2-OH

(b)-OH

NO2

(b)-OH

Br

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PHYSICAL PROPERTIES

Most simple alcohols are liquids MeOH & EtOH are volatile liquids, b.p.

65oC & 78oC respectively Mr , b.p. ROH with C > 12 are solids

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No. of –OH , b.p.b.p. ROH > alkane & RX because

of H-bondingb.p. ROH straight chain > ROH

branchb.p. 1o ROH > 2o ROH > 3o ROH

PHYSICAL PROPERTIES

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(ii) Boiling point As molecular weight increase, van der

Waals forces increase, boiling point will increase too.

For isomeric alcohol (same molecular formula)

increase in boiling point with increasing carbon number.

decrease in boiling point with branching. boiling point in descending order:- 1° alcohol 2° alcohol 3° alcohol

PHYSICAL PROPERTIES

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PHYSICAL PROPERTIES(Solubility)

Alcohols and water have the ability to form inter-molecular H-bonding

Methanol, ethanol & propanol are completely soluble in water

Solubility decreases with relative Mr because of the bigger hydrophobic area

Solubility increases with the no. of -OH groups

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O

Hδ+

δ-

HO δ+δ-

H

R

O

Hδ+δ-

OHδ+

δ-H

R

R OH

Hydrophilic area

Hydrophobic area

Hydrogenbonding


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Phenol is not completely soluble in water below 66oC, but completely soluble above this temp.

Phenol is a colourless crystalline solid which is hygroscopic

4-nitrophenol is more soluble in water than 2-nitrophenol because can form H-bonding with water molecules


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ON

H

O

O

δ+δ- N

O O HO

H

OH

HO

H

δ-

δ-

δ-

δ-

δ+ δ+

δ+δ+

δ+

δ-

Intramolecular H-bonding

Intermolecular H-bonding


2-nitrophenol 4-nitrophenol

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Acidity of phenol & alcohol

phenol > water > alcohol Ethanol, very weak acid & only can

react with strong base such as Na or K to produce a conjugate base (ethoxide ion)CH3CH2-OH CH3CH2-O- + H+

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CH3CH2O- is e- richer than OH-, thus H2O > acidic than CH3CH2OH

Phenol > acidic than H2O & CH3CH2OH because phenoxide ion formed is more stable

The phenoxide ion formed is stabilised by resonance effect


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O Hrelease proton

O

+ H+

-

Phenoxide ion


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Phenoxide ion stability

O - O

-

O

-

O

-

Oδ-

δ-

δ-

δ-

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Example:

OH CH2CH2-OH CH2-OH OH

acidity increase

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Example:

COOH OH

CH3CH2-OH>>ACIDITY DECREASE

Na2CO3

NaHCO3

KOH

NaOH

K, Na

NaH

Very strong basesWeak bases Strong bases

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EXCERCISE

1. Arrange the following compounds in the order of increasing

boiling point. Explain your answer.

1,2-ethanediol , n-butane , 1-propanol , 1,3-propanediol

2. Predict which of the compound is more soluble in water.

Briefly explain your answer.

(a) propane & 1-propanol

(b) 1-propanol & 1,2-propanediol

(c) 2-propanol & 2-pentanol

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PREPARATION OF ALCOHOLSPREPARATION OF ALCOHOLS

1. Fermentation of carbohydrate

-fermentation of sugars by yeast to form ethanol

C6H12O6 2CH3CH2OH + 2CO2

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2. Hydration of Alkenes follows Markovnikov’s rule Example:-

CH3CH=CH2H2O / H2SO4 CH3CH-CH3

OH


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CH3CH=CH2 + H+ CH3CH-CH3 2o carbonium

+

CH3CH-CH3

OH-

Mechanism

●●

OH●●

●●


●●

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3. Hydrolysis of Haloalkanes

RX + OH- (aq) ROH + X-

CH2Cl

+ NaOH(aq)

CH2OH


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4. Addition of Grignard reagent to carbonyl compounds

10, 20 & 30 alcohols can be prepared by addition of Grignard reagent with carbonyl compounds followed by hydrolysis


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(a) Formation of 1o alcohols (Grignard reagent + methanal)

CH3CH2-MgCl + H2C=O CH3CH2CH2-OMgCl

CH3CH2CH2-OH

+ Mg(OH)Cl

H3O+

methanal

1o Alcohol


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(b) Formation of 2o alcohols (Grignard reagent + aldehyde)

CH3CH2-MgCl + HC=O CH3CH2CH-OMgCl

CH3CH2CH-OH

+ Mg(OH)Cl

H3O+

ethanal

2o Alcohol

CH3 CH3

CH3


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(c) Formation of 3o alcohol (Grignard reagent + ketone)

CH3-MgCl + CH3-C-CH3 CH3-C-CH3

H3O+

O O-MgCl

CH3

O-H

CH3

CH3-C-CH3 + Mg(OH)Cl

propanone

3o Alcohol


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EXCERCISE

1. Write the chemical equation for the following reaction:

i. tert-butyl alcohol from an alkene

ii. isopropyl alcohol from an alkyl halide

i.

CH3-C-MgCl +

CH3

CH3

-C-H

O

ii.

-CH=CH-CH3

H2O / H+

B + C

A

2. Draw the structure of A, B and C:

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REACTIONS OF ALCOHOLREACTIONS OF ALCOHOL

In an aqueous solution alcohol reacts as a very weak acid

ROH + H2O RO- + H3O+

(a) As an acid

Reacts with Na or NaH & form a very strong base alkoxide ion

CH3CH2OH + Na CH3CH2O-Na+ + 1/2H2

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With the presence of lone pair of e- at the O atom, alcohol can accept proton from an acid

(a) As a base

CH3CH2-O-H + HA CH3CH2O+-H + A-

H●●

●● ●●


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Alcohol reacts with carboxylic acid under reflux & is catalysed by mineral acids (H2SO4 or HCl) to form ester.

General reaction:-

(1) Esterification

acid alcohol ester water

R-C-OH + R’-OH R-C-OR’ + H-O-HO O

H+,


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Example:-

CH3C-OH + CH3-OH CH3C-OCH3 + H-O-H

O O

ethanoic acid methanol methyl ethanoate

(1) Esterification

H+,


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Alcohol reacts with acyl chloride to form ester

CH3C-Cl + CH3-OH CH3C-OCH3 + HCl

O Obase

ethanoil chloride methanol methyl ethanoate

(1) Esterification


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(2) Dehydration of alcohol

propanol propene

CH3CH2CH2OH CH3CH=CH21800

C

H2SO4(con.)

•Involve formation of carbocation

•Possible of rearrangement


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(3) Formation of haloalkane

•ROH reacts with HX to form RX

•The reaction rates are in the order

HI > HBr > HCl (HF non-reactive)

•Reactivity of alcohols

3o ROH > 2o ROH > 1o ROH > phenol


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ROH + HX RX + H2O

CH3CH2CH2OH + HBr CH3CH2CH2Br + H2O

Example:-


General Reaction

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•ROH reacts with PX3, PX5 , SOCl2

General reaction:

(i)3ROH + PX3 3RX + H3PO3

(ii)ROH + PCl5 RCl + POCl3 + HCl

(iii)ROH + SOCl2 RCl + SO2 + HCl

(3) Formation of haloalkane


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(4) Oxidation of alcohols

• Common oxidising agents are potassium permanganate (VII), (KMnO4/H+) and potassium dichromate (K2Cr2O7/H+)

• Oxidation product depends on the class of alcohol used


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(4) Oxidation of 1o alcohol

• 1o R-OH can be oxidised to give an aldehyde. Further oxidation would give a carboxylic acid

RCH2OH RC-H RC-OH

O O[O] [O]

1o alcohol aldehyde carboxylic acid


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Example:-

CH3CH2OH CH3C-H CH3C-OH + Cr 3+

O OK2Cr2O7/H+ K2Cr2O7/H+

orangegreen



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• Sarett-Collins reagent is a special oxidation agent to change a 1o alcohol to an aldehyde

• CrO3 is added to excess pyridine to form pyridinium chlorochromate (PCC)

CH3CH2CH2OH + PCC CH3CH2C-H

O

propanol propanal



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• form ketone which cannot be oxidised further under normal conditions

R’CH-OH R’C=O + H2O

[O]

2o alcohol ketone

R R

CH3

CH3CH-OH CH3C=O + H2O

KMnO4/H+

2-propanol propanone

CH3



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• Does not undergo oxidation under normal condition

R’-C-OH no reaction [O]

3o alcohol

R

R’’



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Chemical test for R-OHChemical test for R-OH

Lucas test

• Lucas reagent : HCl(con.) + ZnCl2

• 3o R-OH + Lucas reagent – reacts immediately to form cloudy haloalkane

• 2o R-OH + Lucas reagent –takes about 5-10 minutes to form cloudy

• 1o R-OH + Lucas reagent – no visible changes unless heated

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Example:

CH2OH

HCl / ZnCl2Does not turn cloudy

OBSERVATIONS :

1o

OH

HCl / ZnCl2 Turn cloudy within 5 minute

2o

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OBSERVATIONS :CH3

OHHCl / ZnCl2

Turn cloudy immediately

3o

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Haloform ReactionHaloform Reaction Methyl carbinol cleavage to give Carboxylic

acids and Haloform

CH3 C

OH

H

HX2

OH-

, H+

H C

O

OHHCX3 +

CH3 C

OH

H

RX2

OH-

, H+

HCX3+ C

O

OHR

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base (OH-)CH3CH2CCH3 + 3I2

2-butanolCH3CH2COO- + CHI3↓

IODOFORM TESTIODOFORM TEST

OH

yellow precipitate (iodoform)

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PHENOLPHENOLManufacture of phenol by Cumene process

(a) Friedel-Crafts reaction

CH3-CH-CH3

+ CH3CH=CH2

AlCl3

Isopropylbenzene

(cumene)

Isopropylbenzene

(cumene)

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(b) Oxidation of Cumene

Cumene

hydroperoxide

CH3-C-CH3

+ O2

1200C

CH3-CH-CH3

O -OH

(c) Decomposition & rearrangement

-C-O-OH

CH3

-OH + CH3CCH3

CH3

H2SO4

O

PHENOLPHENOL

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Reactions of Phenol Reactions of Phenol

1. Reaction at functional group -OH

(a) Reaction with Na

OH

+ Na

O-Na+

+ ½ H2

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(b) Reaction with NaOHOH

+ NaOH

O-Na+

+ H2O

CH3CH2OH + NaOH no reaction

1. Reaction at functional group -OH


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2. Electrophilic substitution reactions(a) Halogenation (Bromination)

-OH is ortho-para director

in Br2, aqueous solution, white precipitate 2,4,6-tribromophenol will form

OH

+ 3Br2 / H2O

OH

+ 3HBr

Br

BrBr


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(a) Bromination to get monobromination (catalyst: FeBr3 or CS2)

OH

+ Br2

OH

+ HBr

Br

CS2 50C

OH

Br+

2. Electrophilic substitution reactions


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(b) Nitration

OH

OH

NO2

OH

NO2

+

OH

NO2

NO2O2NConcentrated HNO3

Dilute HNO3 Room temp.

Yellow precipitate

2. Electrophilic substitution reactions


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3. Esterification phenol is a weaker nucleophile than alcohol

since the lone pair e- of O atom are delocalised to the benzene ring

reacts with an acid derivative such as acid chloride to form an ester

OH

+ CH3-C=O

ClO-C=O

CH3

+ Cl-


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4. Identification test for phenols phenol reacts with aqueous solution of iron (III)

chloride giving a light purple complex

Purple complex

OH

+ FeCl3 (aq)

OH

FeCl3


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EXERCISE 1

Suggest a chemical test to differentiate the following pairs of compounds. State the reagents, observations and write chemical equations involved.

(a) methanol from ethanol

(b) 2-methyl-1-propanol from 2-methyl-2-propanol

(c) cyclohexanol from cyclohexane

(d) phenol from benzyl alcohol

(e) o-methylphenol from 2-methylcyclohexanol

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EXERCISE 2

Compound A (C4H10O) undergoes oxidation to

form compound B (C4H8O). Oxidation of B gives

compound C (C4H8O2). Reaction of A with hot

concentrated sulphuric acid yields compound D

(C4H8). Hydration of D gives compound E

(C4H10O) which cannot be oxidised. A and E are

isomeric. Suggest the structure of A, B, C, D

and E. Rasionalise your answer.

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Common Used Of Alcohol And Phenol

Common Used Of Alcohol And Phenol

Ethyl alcohol is a poison. LD50 = ~10g/Kg orally in mice.- Nausea, vomiting, flushing, mental excitement or depression, drowsiness, impaired perception, loss of coordination, stupor, coma, death may occur. (intoxication)

Phenol is an important industrial chemical. Major use is in phenolic resins for adhesives and plastics.

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Phenols in Medicine Many phenols are used as antiseptics and

disinfectants.OH

OH

OH OH

OH

CH2CH2CH2CH2CH2CH3

Resorcinol 4-Hexylresorcinal(antiseptic) (antiseptic)

Phenol

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Derivatives of Phenol Compounds of phenol are the active ingredients in the

essential oils of cloves, vanilla, nutmeg, and mint.

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