Alcohols, Phenols Class 12 Notes | EduRev

Chemistry Class 12

Created by: Mohit Rajpoot

Class 12 : Alcohols, Phenols Class 12 Notes | EduRev

The document Alcohols, Phenols Class 12 Notes | EduRev is a part of the Class 12 Course Chemistry Class 12.
All you need of Class 12 at this link: Class 12

Introduction 

  Alcohols, Phenols Class 12 Notes | EduRev

Physical Properties: 

 (1) Boiling point : 

(a) Alcohols show increase in boiling point with increase in molecular weight amongst homologues.

(b) Alcohols have higher boiling point than hydrocarbons of the same molecular weight. The reason for higher boiling point is the intermolecular H-bonding present in alcohols.

Alcohols, Phenols Class 12 Notes | EduRev

Intermolecular H bonds in alcohols.

(2) Solubility in water :

As molecular weight increases solubility in water decreases. The lower alcohols are miscible with water. This is due to intermolecular hydrogen bonding between alcohol and water molecules.

Alcohols, Phenols Class 12 Notes | EduRev

Intermolecular H bond between water & alcohol molecules.

Preparation of alcohols: 

(1) From alkenes 

(a) By acid catalyzed hydration of alkenes: Formation of carbocation intermediate (Markovnikov addition, rearrangement possible).

General reaction:  

Alcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRev     

e.g. 

(b) By Oxymercuration - demercuration process :

(1) Oxymercuration involves an electrophilic attack on the double bond by the positively charged mercury species. The product is a mercurinium ion, an organometallic cation containing a three-membered ring.

(2) In the second step, water from the solvent attacks the mercurinium ion to give (after deprotonation) an organomercurial alcohol.

(3) The third step is demercuration to remove the Hg. Sodium borohydride (NaBH4, a reducing agent) replaces the mercuric acetate fragment with hydrogen.

General reaction:

Alcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRev  + OH- + NaBH4Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

e.g. Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

(c) By Hydroboration-oxidation process : (Forms anti-Markovnikov alcohol, no rearrangement).

General reaction: R-Ch=CH2Alcohols, Phenols Class 12 Notes | EduRevR-CH2-CH2-OH

e.g. Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

Ex. Give the major product of the following reaction:

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Ans. Major product is

(a) Alcohols, Phenols Class 12 Notes | EduRev
because 3o carbocation is more stable.

(b) Alcohols, Phenols Class 12 Notes | EduRev

(c) Alcohols, Phenols Class 12 Notes | EduRev

(2) From alkyl halides : By nucleophilic substitution reactions. 

(a) By SN2 mechanism (second-order substitution) : It is given by primary (and some secondary) halides.

General reaction: R-CH2-Br Alcohols, Phenols Class 12 Notes | EduRev R-CH2-OH

e.g. (CH3)2CHCH2CH 2-Br Alcohols, Phenols Class 12 Notes | EduRev (CH3)2CHCH2CH 2- OH

e.g. Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

(b) By SN1 mechanism : It is given by tertiary and some secondary halides. 

General reaction : Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

e.g. Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

(3) From Grignard's reagent. 

(a) From air:

A Grignard reagent may be used to synthesize an alcohol by treating it with dry oxygen and decomposing the product with acid :

General reaction RMgX Alcohols, Phenols Class 12 Notes | EduRev RO2MgX Alcohols, Phenols Class 12 Notes | EduRev 2ROMgX Alcohols, Phenols Class 12 Notes | EduRev 2ROH

e.g. C2H5MgBrAlcohols, Phenols Class 12 Notes | EduRevC2H5O2 MgXAlcohols, Phenols Class 12 Notes | EduRev2C2H5OMgX Alcohols, Phenols Class 12 Notes | EduRev2C2H5OH MgBr(OH)

(b) From ethylene oxide:

Addition of Grignard reagent to ethylene oxide gives a primary alcohol (with two carbon atoms added).

General reaction Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev RCH2CH2OMgX Alcohols, Phenols Class 12 Notes | EduRev RCH2CH2OH MgX(OH)

e.g. Alcohols, Phenols Class 12 Notes | EduRev C2H5MgBr Alcohols, Phenols Class 12 Notes | EduRev C2H5CH2CH2 OMgX Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev MgBr(OH)

(c) From carbonyl compounds : Nucleophilic addition to the carbonyl groups by Grignard's reagent.

General reactionAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev Mg(OH)X

 

(i) Addition of formaldehyde gives a primary alcohol. 

General reactionAlcohols, Phenols Class 12 Notes | EduRev= O RMgX Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevRCH2-OH

(ii) Addition to an aldehyde (other than formaldehyde) gives a secondary alcohol. 

General reaction:

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev (sec-alcohol)

 

e.g.Alcohols, Phenols Class 12 Notes | EduRev +  Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

(iii) Addition to a ketone gives a tertiary alcohol. 

General reaction:

 Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

e.g. CH3CH2MgCl +  Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

(iv) Addition to an acid halide or an ester gives a tertiary alcohol.

Esters on treatment with Grignard's reagent first form ketones which then react with second molecule of Grignard's reagent and form tertiary alcohol.

General reaction:

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

(4) By reduction of carbonyl compounds. 

(a) Catalytic hydrogenation of aldehydes and ketones. 

General reaction: 

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

e.g. CH3CHO + 2H Alcohols, Phenols Class 12 Notes | EduRev CH3CH2OH

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev CH3CH2CH2OH

Alcohols, Phenols Class 12 Notes | EduRev + 4H Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

(b) Lithium aluminium hydride reduction of aldehydes and ketones.

General reaction:

(i) Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

(ii) Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

(iii) RCOOH+ 4H Alcohols, Phenols Class 12 Notes | EduRev RCH2OH + H2O

(iv) Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev RCH2OH+ HCl

(v) Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev R-CH2OH +R'OH

e.g.Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev CH3CH2OH

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev C2H5CH2OH +HCl

 

(c) By NaBH4 (sodium borohydride) : It is insoluble in ether and is used in aqueous ethanolic solution to reduce carbonyl compounds. It does not reduce esters and acids.

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev R-CH2-OH

e.g.Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRevCH=CHCHO +4H Alcohols, Phenols Class 12 Notes | EduRev CH3CH=CHCH2OH

(ii) Reduction of a ketone gives a secondary alcohol.

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

(d) Bouveault-Blanc reduction : The reduction of aldehydes, ketones or esters by means of excess of sodium and ethanol or n-butanol as the reducing agent.

General reaction:

(i) Aldehyde  RCHO Alcohols, Phenols Class 12 Notes | EduRevRCH2OH

(ii) Esters  R'CO2R'' Alcohols, Phenols Class 12 Notes | EduRevR'CH2OH R''OH

(iii) Ketones  R2CO Alcohols, Phenols Class 12 Notes | EduRevR2CHOH

The Bouveault-Blanc reduction is believed to occur in steps involving transfer of one electron at a time.

Mechanism:

Alcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRev

e.g. CH3CHO +2H Alcohols, Phenols Class 12 Notes | EduRevCH3CH2OH

CH3COOC2H5 +4HAlcohols, Phenols Class 12 Notes | EduRev2CH3CH2OH

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Ex. Identify (X) in the following reaction:

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevX

Ans.Alcohols, Phenols Class 12 Notes | EduRev

 

Ex. What are the product A, B, C, D and E in the following reactions?

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevA Alcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevD Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevE

Ans. A : Alcohols, Phenols Class 12 Notes | EduRev (EtOH)

B : Alcohols, Phenols Class 12 Notes | EduRev Ester part is not affected by NaBH4

C : Alcohols, Phenols Class 12 Notes | EduRev Ester part and keto parts are affected by LiAlH4

D : Alcohols, Phenols Class 12 Notes | EduRev

E : Alcohols, Phenols Class 12 Notes | EduRev

 

(5) By reaction of nitrous acid on aliphatic primary amines.

General reaction: R-NH2 + HONO Alcohols, Phenols Class 12 Notes | EduRev R-OH +N2  + H2O

Mech.

R-NH2Alcohols, Phenols Class 12 Notes | EduRev (RAlcohols, Phenols Class 12 Notes | EduRev) Alcohols, Phenols Class 12 Notes | EduRev ROH +N2 +Alcohols, Phenols Class 12 Notes | EduRev

e.g. (i) C2H5NH2 +HNO2Alcohols, Phenols Class 12 Notes | EduRev C2H5OH+ N+ H2O

 

(ii) CH3-CH2-Alcohols, Phenols Class 12 Notes | EduRev +HONO Alcohols, Phenols Class 12 Notes | EduRev CH3-CH2-Alcohols, Phenols Class 12 Notes | EduRev+ N2 +H2O

Mech.

Alcohols, Phenols Class 12 Notes | EduRev

(6) Hydroxylation : Forms vicinal diols (glycols).

Converting an alkene to a glycol requires adding a hydroxy group to each end of the double bond. This addition is called hydroxylation of the double bond.

(a) Syn hydroxylation, using KMnO/ NaOH or using OsO4/H2O2

General reaction :

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

e.g. Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

(b) Anti hydroxylation, using per acids.

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

Chemical reactions of alcohols: 

1. Reaction with hydrogen halides.

General reaction :

R - OH HX Alcohols, Phenols Class 12 Notes | EduRev R - X H2O (R may rearrange)

Reactivity of HX : Hl > HBr > HCl

Reactivity of ROH: allyl > benzyl > 3o > 2o > 1o

Mechanism R - OH Alcohols, Phenols Class 12 Notes | EduRev R-Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev R-X

 

e.g.Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

e.g.Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

e.g.Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

2. Reaction with Phosphorus trihalides: 

(1) Several phosphorus halides are useful for converting alcohols to alkyl halides. PBr3, PCl3, & PCl5 work well and are commercially available.

(2) Phosphorus halides produce good yields of most primary and secondary alkyl halides, but none works well with ter. alcohols. The two phosphorus halides used most often are PBr3 and the P/ I2 combination.
General reaction :

3R - OH + PX3 Alcohols, Phenols Class 12 Notes | EduRev 3R - X + H3PO

Mechanism:

The mechanism for the reaction involves attachment of the alcohol group on the phosphorus atom, displacing a bromide ion and forming a protonated alkyl dibromophosphite (see following reaction).

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

In second step a bromide ion acts as nucleophile to displace HOPBr2, a good leaving group due to the electronegative atoms bonded to the phosphorus.

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev RCH2X HOPX2

e.g. Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

3. Reaction with thionyl chloride

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev R-Cl SO2 HCl

 

4. Dehydration of alcohols

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev H2O (Rearrangement may occur)

Mechanism 

Step 1 :Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

Step 2 :Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Step 3 :Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Reactivity of ROH : 3º > 2º > 1º

5. Reaction with metals

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

e.g.Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

6. Ester formation

General reaction: 

Alcohols, Phenols Class 12 Notes | EduRev  + Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev + H2O

e.g. CH3CH2O - H + Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev  + H2O

Alcohols, Phenols Class 12 Notes | EduRev  + Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

 

7. Oxidation reactions 

(a) oxidation of primary alcohols

Oxidation of a primary alcohol initially forms an aldehyde. Obtaining the aldehyde is often difficult, since most oxidizing agents are strong enough to oxidize the adehydes formed. CrO3 acid generally oxidizes a primary alcohol all the way upto the carboxylic acid

(b) oxidation of secondary aldohols-

Sec. alcohols are easily oxidized to give excellent yields of ketones. The chromic acid reagent is often best for laboratory oxidations of secondary alcohols. The active species in the mixture is probably chromic acid, H2CrO4, or the acid chromate ion, Alcohols, Phenols Class 12 Notes | EduRev

(c) Resistance of tertiary alcohols to oxidation-

Oxidation of ter-alcohol is not an important reaction is organic chemistry. Ter-alcohols have hydrogen atoms on the carbinol carbon atom, so oxidation must take place by breaking C-C bonds. These oxidations require severe conditions and result in mixtures of products.

Primary

Alcohols, Phenols Class 12 Notes | EduRev

Secondary

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Tertiary

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevno reaction

e.g. 

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

Ex.Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevA

Identify A

Ans.Alcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRevAlcohols, Phenols Class 12 Notes | EduRev

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