Alchohols, Phenols and Ethers

Alcohols and Phenols

Alcohols and Phenols

Alcohols and phenols are formed when a hydrogen atom in a hydrocarbon, aliphatic and aromatic respectively, is replaced by –OH group.

Name a substance that can be used as an antiseptic as well as a disinfectant

Phenol : 0.2% solution of phenol is an antiseptic while 2% solution is used as disinfectant.

Classification
i) Based on Number of OH groups

• Monohydric Alcohols/Alkanols

• Dihydric Alcohols/Diols

• Polyhydric Alcohols

ii) Based on Molecular Structure

• Alkyl Alcohols

  Both α and β carbon are single-bonded

  R-CH₂OH

• Allyl Alcohols

  β carbon is double-bonded

  CH₂=CH-C(R)(R’)-OH

• Benzyl Alcohols

  α carbon is attached to the benzene ring/β carbon is part of the benzene ring
  C₆H₆-CH₂OH

• Vinyl Alcohols

  α carbon is double-bonded

  CH₂=CH-OH

• Anyl Alcohols

  OH is attached to benzene

  C₆H₅OH

Common and IUPAC Names of Some Alcohols

Preparation of Alcohols

1. From alkenes

2. From carbonyl compounds

3. From Grignard reagents

1.1) From Alkenes - acid catalysed hydration

i) How do you convert Propene to propane-2-ol?

ii) How do you convert 2-methyl-1-pentene to 2-methyl pentan-2-ol?

iii) Show how will you synthesize 1-phenylethanol from a suitable alkene.

markonikov’s addition

1.2) From Alkenes - By hydroboration–oxidation

insert how last step works

From Carbonyl Compounds (compounds with C=O) and Carboxylic Acids

i) How do you convert Primary alcohol to carboxylic acid?

ii) How do you convert Butan-2-one to Butan-2-ol?

iii) How do you convert ethanol to ethanal?

iv) Draw the structure and name of the product formed if the following alcohols are oxidized:
a) CH₃CH₂CH₂CH₂OH b) 2-butenol c) 2-methyl-1-propanol
Assume that an excess of oxidising agent is used.

1° Alcohol → [O (removal of hydrogen)] Aldehyde → [O (addition of oxygen)] Carboxylic Acid

R-OH → [O] R-CHO → [O] R-COOH

Carboxylic Acid → [H (removal of oxygen)] 1° Alcohol and Aldehyde → [H (addition of hydrogen)] 1° Alcohol

R-COOH → [H] R-OH and R-CHO → R-OH

carboxylic acids cannot directly be reduced to aldehydes

2° Alcohol → [O (removal of hydrogen)] Ketone

R-CH(OH]-R’ → [O] R-C(O)-R’

Ketone → [H (addition of hydrogen)] 2° Alcohol

R-C(O)-R’ → [H] Ketone

2) From Carbonyl Compounds

i) By reduction of aldehydes and ketones:

RCHO → [H-Pd] RCH₂OH

RCOR’ → [NaBH₄] R-CH(OH)-R’

ii) By reduction of carboxylic acids and esters:

RCOOH → [LiAlH₄,H₂O] RCH₂OH

However, LiAlH4 is an expensive reagent, and therefore, used for preparing special chemicals only. Commercially, acids are reduced to alcohols by converting them to esters, followed by their reduction using hydrogen in the presence of a catalyst (catalytic hydrogenation).

reaction in image
insert explanation here

3) From Grignard Reagents

i) Give the structure and IUPAC name of the product formed when propanone is reacted with methyl magnesium bromide followed by hydrolysis.

ii) How are the following alcohols prepared by the reaction of a suitable grignard reagent on methanal

a) 2-Methly Propanol b) C6H5CH2OH

Formaldehyde → [Grignard Reagent, H3O+] 1° Alcohol

Aldehyde → [Grignard Reagent, H3O+] 2° Alcohol

Ketone → [Grignard Reagent, H3O+] 3° Alcohol

4) From Alkyl Halides (Nucleophilic Substitution SN2 Mechanism)

i) Show how will you synthesize:(i) cyclohexylmethanol using an alkyl halide by an SN2 reaction

(ii) pentan-1-ol using a suitable alkyl halide?

R-Cl + NaOH → R-OH + NaCl

Preparation of Phenols

1. From haloarenes

2. From benzenesulphonic acid

3. From diazonium salts

4. From cumene

1) From Haloarenes (Dow’s Process)

i) How do you convert chlorobenzene into phenol?

note has simpler reaction

2) From Benzenesulphonic Acid

i) You are given benzene, conc. H2SO4 and NaOH. Write the equations for the preparation of phenol using these reagents.

Oleum - fuming sulphuric acid

H2S2O7 (or) H2SO4(SO3) (or) H2SO4 heating

3) From Diazonium Salts

i) How do you convert Aniline to phenol?

note has simpler reaction

4) From Cumene

note has simpler reaction

Physical Properties

• The boiling point of alcohols and phenols increases with the increase in molecular mass due to an increase in van der Waal’s forces

• Isomeric alcohols show a decrease in boiling point with an increase in branching. This is because branching decreases surface area which in turn decreases van der Waal’s forces

• Alcohols have higher boiling points than ethers, haloalkanes and hydrocarbons of comparable masses due to the presence of intermolecular hydrogen bonding

• Alcohols are soluble in water as they form hydrogen bonds with the water molecules. Their solubility decreases with an increase in molecular size. This is due to an increase in the size of the hydrophobic alkyl group.

Order of Boiling Point

carboxylic acids > alcohols > amines }- Hydrogen Bonding

> ketones > aldehydes}- Strong dipole dipole interactions

> ethers > haloalkanes }- Weak dipole dipole interactions

> hydrocarbons }- Van der waal’s forces

always write answers for B.P questions in terms of the one with higher B.P

Acidic Character of Alcohols and Phenols

i) Give two reactions that show the acidic nature of phenol. Compare acidity of phenol with that of ethanol.

• Alcohol is less acidic than water due to the presence of an electron-donating alkyl group (+I effect), the electron density of oxygen increases which decreases the ability to donate a proton

• The acidic nature of alcohols is due to the polar nature of O-H bond

• Phenols are more acidic than water because phenoxide ion is stabilized by resonance.

ROH < H₂O < C₆H₅OH

• Among 1°, 2°, and 3° alcohols, 1° alcohol > 2° alcohol > 3° alcohol because 3° has more +I = more electron density.

• Among substituted phenols or phenol derivatives, phenols with electron-withdrawing groups are more acidic than phenols with electron-donating groups.

  phenol (e.w.g) > phenol > phenol (e.d.g)

• The acidic strength of phenol is more pronounced when an e.w.g is present at ortho and para positions. This is due to the efffective delocalisation of negative charge in phenoxide ion when substituent is at ortho or para position

  para > ortho > meta

Order of Acidic Character

3° Alcohol < 2° Alcohol < 1° Alcohol < H₂O < phenol (e.d.g) < phenol < phenol (e.w.g)

Chemical Properties of Alcohols
a) Reactions involving cleavage of O–H bond

1. Reaction with metals

2. Reaction with Alkali

3. Reaction with Grignard Reagent

4. Esterification

1) Reaction with Metals

2) Reaction with Alkali

R-OH + NaOH → No reaction

3) Reaction with Grignard Reagent

R-OH + R’MgX → R-H +Mg(X)(OR)

4) Esterification (Preparation of Esters)

i) How do you convert Propan-1-ol to 1-propoxypropane? (i think it comes under this topic)

Model 1: Alcohol + Carboxylic Acid → [conc.H₂SO₄] Ester + Water

• R-OH + R’COOH → [conc.H₂SO₄] R’-C(O)-OR +H₂O

• CH₃CH₂-OH + CH₃COOH → [conc.H₂SO₄] CH₃-C(O)-O-CH₂CH₃ +H₂O

Model 2: Alcohol + Acid A

Acetylation of Salicylic Acid

Reactions involving cleavage of carbon – oxygen (C–O) bond

1. Lucas Test

2. With Chlorinating Agents

3. Dehydration

4. Test for Phenol

5. Haloform Reaction

6. Catalytic Dehydrogenation

1) Lucas Test (Reaction with Hydrogen Halides)

i) Give a chemical test to distinguish between 2-Pentanol and 3-Pentanol

ii) Give a chemical test to distinguish between 1-Propanol and 2-Propanol.

• Test is used to distinguish 1ᵒ, 2ᵒ and 3ᵒ alcohols

• Depends on order of reactivity ( 3ᵒ>2ᵒ>1ᵒ )

Turbidity → Formation of precipitate

General Formula:

ROH + HX → R–X + H₂O

Reactions:
1ᵒ Alcohol:

R-CH₂-OH + HCl → [ZnCl₂] R-Cl + H₂O

No turbidity at room temperature

2ᵒ Alcohol:

R-CH(R)-OH + HCl → [ZnCl₂] R-CH(R)-Cl + H₂O

Turbidity after 5-10 minutes

3ᵒ Alcohol:

R-CH(R)(R)-OH + HCl → [ZnCl₂] R-CH(R)(R)-Cl + H₂O

Immediate Turbidity

2) With Chlorinating Agents

1. ROH + PCl₅ → RCl + POCl₃ + HCl

2. ROH + SOCl₂ → RCl + SO₂ + HCl

3. 3ROH + PCl₃ → 3R-Cl + H₃PO₃

3) Dehydration

i) How do you convert Propan-2-ol to propane?

ii) How would you convert ethanol to ethene?

Mechanism of Dehydration of Alcohol

use note

Step 1: Protonation

Step 2: Elimination of water

Step 3: Deprotonation

4) Test for Phenol (neutral FeCl₃ Test)

i) Give a chemical test to distinguish between Benzoic acid and Phenol

ii) Give a chemical test to distinguish between Ethanol and Phenol

C₆H₅OH + FeCl₃ → (C₆H₅O)₃Fe violet precipitate + 3HCl

5) Haloform Reaction (Iodoform Test)

i) Give a chemical test to distinguish between 2-Pentanol and 3-Pentanol

ii) Give a chemical test to distinguish between 2-propanol and 2-methyl-2-propanol.

iii) Give a chemical test to distinguish between 1-Propanol and 2-Propanol.

The test only identifies alcohol with (CH₃-CH(OH)-)

CH₃-CH(OH)-R → [NaOI, NaOH + I₂] CHI₃ yellow precipitate + R-COONa

6) Catalytic Dehydrogenation (Oxidation)

i) How do you convert Propan-2-ol to propanone?

ii) How do you convert Hexan-1-ol to hexanal?

R-CH₂OH → [Cu,573K] R-CHO

R-CH(R’)-OH → [Cu,573K] R-C(R’)=O

(CH₃)C(CH₃)(CH₃)(OH) → [Cu, 573K] CH₃-C(CH₃)=CH₃

Chemical Properties of Phenol

1. Oxidation

2. Reduction

3. Bromination

4. Nitration

5. Reimer Tiemann Reaction

6. Kolbe’s Reaction

7. Acetylation of Salicylic Acid

1) Oxidation

i) How do you convert Phenol to Benzoquinone?

2) Reduction (Reaction Of Phenol With Zinc Dust)

i) How do you convert Phenol to Benzene?

ii) How is toluene obtained from phenol?

iii) How would you obtain acetophenone from phenol?

C₆H₅OH → [Zn dust] C₆H₆

3) Bromination

i) How to convert Phenol to 2, 4, 6-tribromophenol?

4) Nitration

i) How do you convert Phenol to 2,4,6-trinitrophenol(picric acid)?

ii) Which of the following isomers is more volatile: o-nitrophenol or p-nitrophenol?

• It is named picric acid because of its bitter taste

• Picric acid is used to make explosives

• o-Nitrophenol is more steam volatile than p-Nitrophenol due to the presence of intramolecular

  H-bonding.

• p-nitrophenol shows intermolecular H–bonding.

5) Reimer Tiemann Reaction

C₆H₅OH → [CHCl₃, NaOH, H₃O⁺] C₆H₄OH CHO

6) Kolbe’s Reaction

C₆H₅OH → [CO₂, NaOH, H₃O⁺] C₆H₄OH COOH

Commercially Important Alcohols

1. Methanol

   • aka wood spirit bc it was produced by destructive distillation of wood

   • Can cause blindness and large quantities causes even death

2. Ethanol

   • Glucose and fructose undergo fermentation in the presence of another enzyme, zymase, which is found in yeast to form ethantol

   • The commercial alcohol is made unfit for drinking by mixing in it some copper sulphate (to give it a colour) and pyridine (a foul smelling liquid).

• 100% pure ethanol is called absolute alcohol

• 95% ethanol is called rectified spirit/surgical spirit/rubbing alcohol

• Methylated spirit - Mixture of methanol and ethanol

Ethers

R-O-R

OR - Alkoxy group

Simple ethers - Symmetric (R-O-R)

Mixed ethers - Asymmetric (R-O-R’)

Preparation of Ethers

1. By Dehydration of Alcohols

2. Williamson Synthesis

Preparation of Ethers
1) By Dehydration of Alcohols

• Can only make simple/symmetric ethers, mixed ethers cannot be prepared

• The reaction follows the SN₂ mechanism (substitution) and not the elimination

• Branched alkyl ethers cannot be prepared since this reaction follows SN₂ mechanism and branched alkyl ethers show more steric hindrance

• Aromatic ethers cannot be prepared as they are less reactive towards nucleophilic substitution due to partial double bond character by C-O bond resonance

Preparation of Ethers
2) Williamson Synthesis

R-O-Na + R’-X → R-O-R’ + NaX

CH₃-CH₂-O-Na + CH₃-Cl → CH₃-CH₂-O-CH₃ + NaCl

• Can make both simple and mixed ethers

• Better results are obtained if the alkyl halide is primary. In case of secondary and tertiary alkyl halides, elimination competes over substitution.

Physical Properties of Ethers

• The large difference in boiling points of alcohols and ethers is due to the presence of hydrogen bonding in alcohols.

• The miscibility of ethers with water resembles those of alcohols of the same molecular mass.

Chemical Properties of Ethers

1. Reaction with HX

2. Electrophilic Substitution

Chemical Properties of Ethers

1) Reaction with HX

Phenol to Anisole

Chemical Properties of Ethers

2) Electrophilic Substitution

i) How do you convert Anisole to p-bromoanisole?