//M3//QN1//SUB//DL0

What are alcohol, phenol and ether compounds?

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Alcohol compounds: An alcohol contains one or more hydroxyl (OH) group(s) directly attached to carbon atom(s), of an aliphatic system. For example, CH 3 OH.
Phenol compounds: A phenol contains one or more hydroxyl (OH) group(s) directly attached to carbon atom(s), of an aromatic system. For example, C 6 H 5 OH.
Ether compounds: The substitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group (R-O/Ar-O) yields another class of compounds known as ‘ethers’. For example, dimethyl ether (CH 3 OCH 3).
In short, ether is a compound which is formed by substituting the hydrogen atom of hydroxyl group of an alcohol or phenol by an alkyl or aryl group.

//M2//QN2//SUB//DL0//EQ

Discuss the classification of monohydric alcohols containing C sp 2–OH bond.

//X

Compounds containing C sp 2–OH bond: These alcohols contain –OH group bonded to a carbon-carbon double bond i.e., to a vinylic carbon or to an aryl carbon. These alcohols are also known as vinylic alcohols.
Vinylic alcohol: CH 2= CH – OH
Phenols:

//M3//QN3//SUB//DL0//EQ

Discuss the classification of monohydric alcohols containing C sp 3 –OH bond.

//X

C sp 3 – OH bond: In this class of alcohols, the –OH group is attached to an sp 3 hybridised carbon atom of an alkyl group. They are further classified as follows:
Primary, secondary and tertiary alcohols:
In these three types of alcohols, the –OH group is attached to primary, secondary and tertiary carbon atom, respectively as depicted below:
–CH 2–OH CH–OH C–OH
Primary (1°) Secondary (2°) Tertiary (3°)
Allylic alcohols: In these alcohols, the –OH group is attached to an sp 3 hybridised carbon next the carbon-carbon double bond, that is to an allylic carbon. For example,
Benzylic alcohols: In these alcohols, the –OH group is attached to an sp 3 – hybridised carbon atom next to an aromatic ring. For example,
Allylic and benzylic alcohols may be primary, secondary or tertiary.

//M2//QN4//SUB//DL0//EQ

Explain the classification of alcohols and phenols on the basis of number of hydroxyl groups.

//X

Alcohols and phenols may be classified as
mono–, di–, tri– or polyhydric compounds depending on whether they contain one, two, three or many hydroxyl groups respectively in their structures as given below:

//M2//QN5//SUB//DL0

Write common name and IUPAC name of following alcohol compounds.

//X

Compound | Common Name | IUPAC Name
CH 3–OH | Methyl alcohol | Methanol
CH 3–CH 2–CH 2–OH | n-Propyl alcohol | Propan-1-ol
| Isopropyl alcohol | Propan-2-ol
CH 3–CH 2–CH 2–CH 2–OH | n-Butyl alcohol | Butan-1-ol
| sec-Butyl alcohol | Butan-2-ol
| Isobutyl alcohol | 2-Methyl propan-1-ol
| tert-Butyl alcohol | 2-Methyl propan-2-ol
| Glycerol | Propane -1,2, 3-triol

//M2//QN6//SUB//DL0//EQ

How is the nomenclature of cyclic alcohol compound carried out? Give two examples.

//X

Cyclic alcohols are named using the prefix cyclo and considering the –OH group attached to C–1.

//M3//QN7//SUB//DL0//EQ

Explain the nomenclature of phenols by giving examples.

//X

The simplest hydroxyl derivative of benzene is phenol. It is its common name and also an accepted IUPAC name. As structure of phenol involves a benzene ring, in its substituted compounds the term ortho
(1,2- disubstituted), meta (1,3- disubstituted) and para (1,4- disubstituted) are often used in the common names.
Example:
Dihydroxy derivatives of benzene are known as 1, 2-, 1, 3- and 1, 4-benzenediol.

//M1//QN8//SUB//DL0

Write IUPAC name of the following ether compounds. Also write common names wherever possible.

//X

Compound | Common name | IUPAC name
CH 3 OCH 3 | Dimethyl ether | Methoxymethane
C 2 H 5 OC 2 H 5 | Diethyl ether | Ethoxyethane
CH 3 OCH 2 CH 2 CH 3 | Methyl n-propyl ether | 1-Methoxypropane
C 6 H 5 OCH 3 | Methylphenyl ether (Anisole) | Methoxybenzene (Anisole)
C 6 H 5 OCH 2 CH 3 | Ethylphenyl ether (Phenetole) | Ethoxybenzene
C 6 H 5 O(CH 2)6–CH 3 | Heptylphenyl ether | 1-Phenoxyheptane
| Methylisopropyl ether | 2-Methoxypropane
| Phenyl isopentyl ether | 3- Methylbutoxybenzene
CH 3–O–CH 2–CH 2–OCH 3 | – | 1,2-Dimethoxyethane
| – | 2-Ethoxy- -1,1-dimethylcyclohexane

//M3//QN9//SUB//DL0//EQ

Give information about C-O-H bond angle in alcohol, phenol and ether with suitable example.

//X

In alcohols, the oxygen of –OH group is attached to carbon by a sigma (s) bond formed by the overlap of an sp3 hybridised orbital of carbon with sp 3 hybridised orbital of oxygen.
Figure depicts structural aspects of methanol, phenol and methoxymethane.
The bond angle in alcohols is slightly less than the tetrahedral angle
(109°-28’).
It is due to the repulsion between the unshared electron pairs of oxygen.
In phenols, the –OH group is attached to sp 2 hybridised carbon of an aromatic ring.
The carbon-oxygen bond length (136 pm) in phenol is slightly less than that in methanol.
This is due to (i) partial double bond character on account of the conjugation of unshared electron pair of oxygen with the aromatic ring and (ii) sp 2 hybridised state of carbon to which oxygen is attached.
In ethers, the four electron pairs, i.e., the two bond pairs and two lone pairs of electron on oxygen are arranged approximately in a tetrahedral arrangement.
The bond angle is slightly greater than the tetrahedral angle due to the repulsive interaction between the two bulky (-R) groups.
The C-O bond length (141 pm) is almost the same as in alcohols.

//M3//QN10//SUB//DL0//EQ

What is meant by hydroboration-oxidation reaction? Illustrate it with an example.

//X

By hydroboration-oxidation: Diborane (BH 3)2, reacts with alkenes to give trialkyl boranes as addition product. This is oxidised to alcohol by hydrogen peroxide in the presence of aqueous sodium hydroxide.
The addition of borane to the double bond takes place in such a manner that the boron atom gets attached to the sp 2 carbon carrying greater number of hydrogen atoms. The alcohol so formed looks as if it a way opposite to the Markovnikov’s rule. In this reaction, alcohol is obtained in excellent yield.

//M3//QN11//SUB//DL0//EQ

Explain the preparation of alcohol from alkene by acid catalyzed hydration with its mechanism.OR Write the mechanism of hydration of ethene to yield ethanol.

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By acid catalysed hydration: Alkenes react with water in the presence of acid as catalyst to form reaction takes place in accordance with Markovnikov’s rule.
Mechanism:
The mechanism of the reaction involves the following three steps:

- Step - 1: Protonation of alkene to form carbocation by electrophilic attack of H 3 O+.

H 2 O + H+ → H 3 O+
Step - 2: Nucleophilic attack of water on carbocation.
Step - 3: Deprotonation to form an alcohol.

//M2//QN12//SUB//DL0//EQ

Show how will you synthesise: (i) 1-phenylethanol from a suitable alkene. (ii) cyclohexylmethanol using an alkyl halide by an S N 2 reaction. (iii) pentan-1-ol using a suitable alkyl halide?

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(i) 1-Phenylethanol can be synthesised by the reaction between phenylethene (Styrene) and water in acidic medium.
(ii) Cyclohexylmethanol can be synthesised by hydrolysis of cyclohexyl methylchloride in presence of aqueous NaOH.
(iii) When 1-bromopentane is treated with aqueous NaOH, pentan-1-ol is obtained.

//M0//QN13//SUB//DL0//EQ

Explain the preparation of alcohol by reduction of aldehydes and ketones.

//X

By reduction of aldehydes and ketones : Aldehydes and ketones are reduced to the corresponding alcohols by addition of hydrogen in the presence of catalysts (catalytic hydrogenation). The usual catalyst is a finely divided metal such as platinum, palladium or nickel. It is also prepared by treating aldehydes and ketones with sodium borohydride (NaBH 4) or lithium aluminium hydride (LiAlH 4).
Aldehydes yield primary alcohols whereas ketones give secondary alcohols.
RCHO + H 2 RCH 2 OH
Examples:

//M2//QN14//SUB//DL0//EQ

How are alcohol compounds prepared by reduction of carboxylic acids and esters? Explain.

//X

By reduction of carboxylic acids and esters : Carboxylic acids are reduced to primary alcohols in excellent yields by lithium aluminium hydride, a strong reducing agent.
RCOOH RCH 2 OH
Example:
However, LiAlH 4 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 catalyst (catalytic hydrogenation).
RCOOH RCOOR' RCH 2 OH + R'OH

//M3//QN15//SUB//DL0//EQ

Explain the nucleophilic substitution reaction of aldehydes and ketones with Grignard reagent (R’-Mg-X) with chemical equations.OR Write only chemical reactions to obtain 1°, 2° and 3° alcohols from aldehyde and ketone compounds.

//X

Alcohols are produced by the reaction of Grignard reagents with aldehydes and ketones.
The first step of the reaction is the nucleophilic addition of Grignard reagent to the carbonyl group, forming an adduct. Hydrolysis of the adduct yields an alcohol.
The overall reactions using different aldehydes and ketones are as follows:
HCHO + RMgX → RCH 2 OMgX RCH 2 OH + Mg(OH)X
RCHO + R'MgX → + Mg(OH)X
RCOR + R'MgX →
+ Mg(OH)X
You will notice that the reaction produces a primary alcohol with methanal, a secondary alcohol with other aldehydes and tertiary alcohol with ketones.

//M2//QN16//SUB//DL0//EQ

Explain why propanol has higher boiling point than that of the hydrocarbon butane ?

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The molecules of hydrocarbon butane are attached with each other by weak Van der Waals attraction force, whereas molecules of propanol are attached with each other by strong intermolecular hydrogen bond, therefore the boiling point of propanol is much higher than that of hydrocarbon butane.

//M4//QN17//SUB//DL0//EQ

Explain the preparation of phenol compounds with chemical equations.OR Explain the preparation of phenol from chlorobenzene, benzenesulphonic acid, aniline and cumene.

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(i) From haloarenes: (Exercise Q.7.10)
Chlorobenzene is fused NaOH at 623 K and 300 atmospheric pressure. Phenol is obtained by acidification of sodium phenoxide.
(ii) From benzenesulphonic acid:
Benzene is sulphonated with oleum and benzene sulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide. Acidification of the sodium salt gives phenol.
(iii) From diazonium salts:
Dizonium salt is formed by treating an aromatic primary amine with nitrous acid (NaNO 2 + HCl) at 273-278 K. Diazonium salts are hydrolysed to phenols by warming with water or by treating with dilute acids.
(iv) From cumene:
Phenol is manufactured from the hydrocarbon, cumene. Cumene (isopropylbenzene) is oxidised in the presence of air to cumene hydroperoxide. It is converted to phenol and acetone by treating it with dilute acid. Acetone, a by-product of this reaction, is also obtained in large quantities by this method.

//M3//QN18//SUB//DL0//EQ

Explain the effect of hydrogen bond on boiling point of alcohol and phenol.

//X

The boiling points of alcohols and phenols increase with increase in the number of carbon atoms (increase in van der Waals forces).
In alcohols, the boiling points decrease with increase of branching in carbon chain (because of decrease in van der Waals forces with decrease in surface area).
The –OH group in alcohols and phenols involved in intermolecular hydrogen bonding is as
shown below:
It is interesting to note that boiling points of alcohols and phenols are higher in comparison to other classes of compounds, namely hydrocarbons, ethers, haloalkanes and haloarenes of comparable molecular masses. For example, ethanol and propane have comparable molecular masses but their boiling points differ widely. The boiling point of methoxymethane is intermediate of the two boiling points.
The high boiling points of alcohols are mainly due to the presence of intermolecular hydrogen bonding in them which is lacking in ethers and hydrocarbons.

//M2//QN19//SUB//DL0//EQ

Write a note on solubility of alcohol and phenol compounds in water.OR Alcohols are comparatively more soluble in water than hydrocarbon of comparable molecular masses. Explain this fact.

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Solubility of alcohols and phenols in water is due to their ability to form hydrogen bonds with water molecules as shown. The solubility decreases with increase in size of alkyl/aryl (hydro-phobic) groups. Several of the lower molecular mass alcohols are miscible with water in all proportions.

//M2//QN20//SUB//DL0//EQ

‘Alcohols are versatile compounds’ discuss this statement by giving suitable example.

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Alcohols are versatile compounds. They react both as nucleophiles and electrophiles. The bond between O – H is broken when alcohols react as nucleophiles.
Alcohols as nucleophiles:
(i)
(ii) The bond between C – O is broken when they react as electrophiles. Protonated alcohols react in this manner.
Protonated alcohols as electrophiles:

//M3//QN21//SUB//DL0//EQ

Explain the acidic nature of alcohols and phenols by their reaction with metals.OR ‘Alcohols and phenols are acidic in nature’ verify the truth of this statement by a reaction with metals.

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Reaction with metals: Alcohols and phenols react with active metals such as sodium, potassium and aluminium to yield corresponding alkoxides/phenoxides and hydrogen.
In addition to this, phenols react with aqueous sodium hydroxide to form sodium phenoxides.
The above reactions show that alcohols and phenols are acidic in nature. In fact, alcohols and phenols are bronsted acids i.e., they can donate a proton to a stronger base (B:).

//M3//QN22//SUB//DL0//EQ

Write a note on acidity of alcohols.

//X

Acidity of alcohols: The acidic character of alcohols is due to the polar nature of O – H bond. An electron-releasing group (–CH 3, –C 2 H 5) increases electron density on oxygen tending to decrease the polarity of O – H bond. This decreases the acid strength. For this reason, the acid strength of alcohols decreases in the following order:
Alcohols are, however, weaker acids than water. This can be illustrated by the reaction of water with an alkoxide.
This reaction shows that water is a better proton donor (i.e., stronger acid) than alcohol. Also, in the above reaction, we note that an alkoxide ion is a better proton acceptor than hydroxide ion, which suggests that alkoxides are stronger bases (sodium ethoxide is a stronger base than sodium hydroxide).
Alcohols can act as both bronsted bases as well as acids. It is due to the presence of unshared electron pairs on oxygen. which makes them proton acceptors.

//M2//QN23//SUB//DL0

Write a note on acidity of phenols.

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Acidity of phenols: The reactions of phenol with metals (e.g., sodium, aluminium) and sodium hydroxide indicate its acidic nature. The hydroxyl group, in phenol is directly attached to the sp 2 hybridised carbon of benzene ring which acts as an electron withdrawing group. Due to this, the charge distribution in phenol molecule, as depicted in its resonance structures, causes the oxygen of –OH group to be positive.
The reaction of phenol with aqueous sodium hydroxide indicates that phenols are stronger acids than alcohols and water.

//M3//QN24//SUB//DL0//EQ

Why a compound in which hydroxyl group attached to an aromatic ring is more acidic than the one in which hydroxyl group is attached to an alkyl group?

//X

The ionization of an alcohol and a phenol takes place as follows:
R – – H R – + H+
Due to the higher electronegativity of sp 2 hybridised carbon of phenol to which –OH is attached, electron density decreases on oxygen. This increases the polarity of O–H bond and results in an increase in ionization of phenols than that of alcohols.
Now let us examine the stabilities of alkoxide and phenoxide ions. In alkoxide ion, the negative charge is localised on oxygen while in phenoxide ion, the charge is delocalised.
The delocalisation of negative charge (structures I-V) makes phenoxide ion more stable and favours the ionization of phenol.
Although there is also charge delocalisation in phenol, its resonance structures have charge separation due to which the phenol molecule is less stable than phenoxide ion.

//M3//QN25//SUB//DL0//EQ

Write a note on esterification of alcohols and phenols.OR Write equation of preparing Aspirin from phenol in these steps.

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Alcohols and phenols react with carboxylic acids, acid chlorides and acid anhydrides to form esters.
Ar/RO–H + R'-COOH Ar/ROCOR' + H 2 O
Ar/R-OH + (R'CO)2 O Ar/ROCOR' + R'COOH
R/ArOH + R'COCl R/ArOCOR' + HCl
The reaction with carboxylic acid and acid anhydride is carried out in the presence of a small amount of concentrated sulphuric acid. The reaction is reversible, and therefore, water is removed as soon as it is formed. The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to neutralise HCl which is formed during the reaction. It shifts the equilibrium to the right hand side. The introduction of acetyl (CH 3 CO) group in alcohols or phenols is known as acetylation. Acetylation of salicylic acid produces aspirin.

//M2//QN26//SN//DL0//EQ

Explain the reaction of alcohols with hydrogen halides.OR Write a short note on Lucas test.

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Alcohols react with hydrogen halides to form alkyl halides.
R-OH + HCl R-Cl + H 2 O
The difference in reactivity of three classes of alcohols with HCl distinguishes them from one another.
Alcohols are soluble in Lucas reagent (conc. HCl and ZnCl 2) while their halides are immiscible and produce turbidity in solution.
In case of tertiary alcohols, turbidity is produced immediately as they form the halides easily.
Primary alcohols do not produce turbidity at room temperature.
This is how alcohols can be distinguished by Lucas test.

//M2//QN27//SUB//DL0//EQ

Write the mechanism of acid-dehydration of ethanol to yield ethene.OR Explain dehydration reaction of alcohol to form alkene.

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The mechanism of dehydration of ethanol involves the following steps:
Mechanism:
Step 1: Formation of protonated alcohol
Step 2: Formation of carbocation: It is the slowest step and hence, the rate determining step of the reaction.
Step 3: Formation of ethene by elimination of a proton.
The acid used in step 1 is released in step 3. To drive the equilibrium to the right, ethene is removed as it is formed.

//M2//QN28//SUB//DL0

Write a note on the reaction of alcohols with phosphorus trihalides.

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Alcohols react with phosphorus trihalides to give corresponded alkyl halides. This reaction is useful for preparation of alkyl halides from alcohols.
3R–OH + PX 3 → 3R-X + H 3 PO 3 (X = Cl, Br)
3CH 3 OH + PCl 3 → 3CH 3 Cl + H 3 PO 3
3CH 3 CH 2 OH + PBr 3 → 3CH 3 CH 2 Br + H 3 PO 3

//M3//QN29//SUB//DL0//EQ

Explain dehydration of alcohols with chemical equations. Also give the order for relative ease of dehydration of alcohols.

//X

Dehydration: Alcohols undergo dehydration (removal of a molecule of water) to form alkenes on treating with a protic acid e.g., concentrated H 2 SO 4 or H 3 PO 4, or catalysts such as anhydrous zinc chloride or alumina.
Ethanol undergoes dehydration by heating it with concentrated H 2 SO 4 at 443 K.
C 2 H 5 OH CH 2 = CH 2 + H 2 O
Secondary and tertiary alcohols are dehydrated under milder conditions. For example
Thus, the relative ease of dehydration of alcohols follows the following order:
Tertiary > Secondary > Primary

//M3//QN30//SUB//DL0//EQ

Write a note on oxidation reaction of alcohols.OR Explain oxidation of alcohols with chemical reactions.

//X

Oxidation: Oxidation of alcohols involves the formation of a carbon oxygen double bond with cleavage of an O-H and C-H bonds.
Such a cleavage and formation of bonds occur in oxidation reactions. These are also known as dehydrogenation reactions as these involve loss of dihydrogen from an alcohol molecule. Depending on the oxidising agent used, a primary alcohol is oxidised to an aldehyde which in turn is oxidised to a carboxylic acid.
Strong oxidising agents such as acidified potassium permanganate are used for getting carboxylic acids from alcohols directly. CrO3 in anhydrous medium is used as the oxidising agent for the isolation of aldehydes.
RCH 2 OH RCHO
A better reagent for oxidation of primary alcohols to aldehydes in good yield is pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HCl.
CH 3 – CH = CH – CH 2 OH
CH 3 – CH = CH – CHO [March 2025]
Secondary alcohols are oxidised to ketones by chromic anhydride (CrO 3).
Tertiary alcohols do not undergo oxidation reaction. Under strong reaction condition such as strong oxidizing agents (KMnO4) and elevated temperature, cleavage of various C-C bonds place and mixture of carboxylic acid containing lesser number of carbon atoms is formed.

//M2//QN31//SUB//DL0//EQ

What happens when the vapours of a primary, secondary and tertiary alcohol are passed over heated copper at 573K temperature? Explain with chemical equation.

//X

When the vapours of a primary, secondary and tertiary alcohol are passed over heated copper at 573 K, dehydrogenation takes place and an aldehyde or a ketone is formed while tertiary alcohols undergo dehydration.
RCH 2 OH RCHO

//M3//QN32//SUB//DL0//EQ

Explain nitration of phenol in detail.

//X

Nitration: With dilute nitric acid at low temperature (298 K), phenol yields a mixture of ortho and para nitrophenols.
The ortho and para isomers can be separated by steam distillation. o-Nitrophenol is steam volatile due to intramolecular hydrogen bonding while p-nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the association of molecules.
With concentrated nitric acid, phenol is converted to 2,4,6-trinitrophenol. The product is commonly known as picric acid. The yield of the reaction product is poor.
Nowadays picric acid is prepared by treating phenol first with concentrated sulphuric acid which converts into phenol-2,4-disulphonic acid, and then with concentrated nitric acid to get 2,4,6-trinitrophenol.

//M2//QN33//SUB//DL0//EQ

While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason.

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The ortho and para isomers can be separated by steam distillation. o-Nitrophenol is steam volatile due to intramolecular hydrogen bonding while p-nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the association of molecules.

//M3//QN34//SUB//DL0//EQ

Write a note on halogenation of phenol.

//X

Halogenation: On treating phenol with bromine, different reaction products are formed under different experimental conditions.
(a) When the reaction is carried out in solvents of low polarity such as CHCl 3 or CS 2 and at low temperature, monobromophenols are formed.
The usual halogenation of benzene takes place in the presence of a Lewis acid, such as FeBr 3, which polarises the halogen molecule. In case of phenol, the polarization of bromine molecule takes place even in the absence of Lewis acid. It is due to the highly activating effect of –OH group attached to the benzene ring.
(b) When phenol is treated with bromine water, 2, 4, 6-tribromophenol is formed as white precipitate.

//M2//QN35//SUB//DL0//EQ

Explain Kolbe’s reaction of phenol.

OR Explain the reaction to obtain salicylic acid from phenol. OR Expalin the following with an example

Kolbe’s reaction.

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Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive than phenol towards electrophilic aromatic substitution. Hence, it undergoes electrophilic substitution with carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is formed as the main reaction product.

//M2//QN36//SUB//DL0//EQ

Explain the Reimer-Tiemann reaction of phenol. OR Explain the reaction to obtain salicylaldehyde from phenol. OR Explain the following with an example (ii) Reimer-Tiemann reaction.

//X

On treating phenol with chloroform in the presence of sodium hydroxide, a –CHO group is introduced at ortho position of benzene ring. This reaction is known as Reimer - Tiemann reaction.
The intermediate substituted benzal chloride is hydrolysed in the presence of alkali to produce salicylaldehyde.

//M2//QN37//SUB//DL0//EQ

Explain the following with an example (i) Reaction of phenol with zinc dust. (ii) Oxidation reaction of phenol.

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Reaction of phenol with zinc dust: Phenol is converted to benzene on heating with zinc dust.
Oxidation: Oxidation of phenol with chromic acid produces a conjugated diketone known as benzoquinone. In the presence of air, phenols are slowly oxidised to dark coloured mixtures containing quinones.

//M2//QN38//SUB//DL0//EQ

Give equations of the following reactions:(i) When tertiary alcohol heated at 573K in presence of copper (Cu)(ii) Oxidation of phenol with chromic acid.

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(i) When tertiary alcohol heated at 573K in presence of copper (Cu)
(ii) Oxidation of phenol with chromic acid

//M3//QN39//SUB//DL0//EQ

State the preparation, properties and uses of methanol.

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Methanol, CH 3 OH, also known as ‘wood spirit’, was produced by destructive distillation of wood. Today, most of the methanol is produced by catalytic hydrogenation of carbon monoxide at high pressure and temperature and in the presence of ZnO – Cr 2 O 3 catalyst.
CO + 2H 2 CH 3 OH
Methanol is a colourless liquid and boils at
337K. It is highly poisonous in nature. Ingestion of even small quantities of methanol can cause blindness and large quantities causes even death. Methanol is used as a solvent in paints, varnishes and chiefly for making formaldehyde.

//M4//QN40//SUB//DL0//EQ

State the preparation, properties and uses of ethanol.

//X

Ethanol, C 2 H 5 OH, is obtained commercially by fermentation, the oldest method is from sugars. The sugar in molasses, sugarcane or fruits such as grapes is converted to glucose and fructose, (both of which have the formula C 6 H 12 O 6), in the presence of an enzyme, invertase. Glucose and fructose undergo fermentation in the presence of another enzyme, zymase, which is found in yeast.
C 12 H 22 O 11 + H 2 O +
C 6 H 12 O 6 2C 2 H 5 OH + 2CO 2
In wine making, grapes are the source of sugars and yeast. As grapes ripen, the quantity of sugar increases and yeast grows on the outer skin. When grapes are crushed, sugar and the enzyme come in contact and fermentation starts. Fermentation takes place in anaerobic conditions i.e. in absence of air. Carbon dioxide is released during fermentation.
The action of zymase is inhibited once the percentage of alcohol formed exceeds 14 percent. If air gets into fermentation mixture, the oxygen of air oxidises ethanol to ethanoic acid which in turn destroys the taste of alcoholic drinks.
Ethanol is a colourless liquid with boiling point 351K. It is used as a solvent in paint industry and in the preparation of a number of carbon compounds. 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). It is known as denaturation
of alcohol.

//M3//QN41//SUB//DL0//EQ

Explain the preparation of ethers with mechanism by dehydration of alcohols.

//X

Alcohols undergo dehydration in the presence of protic acids (H 2 SO 4, H 3 PO 4). The formation of the reaction product, alkene or ether depends on the reaction conditions. For example, ethanol is dehydrated to ethene in the presence of sulphuric acid at 443K. At 413K, ethoxyethane is the main product.
The formation of ether is a nucleophilic bimolecular reaction (S N 2) involving the attack of alcohol molecule on a protonated alcohol, as indicated below:
(i)
(ii)
(iii)
Acidic dehydration of alcohols, to give an alkene is also associated with substitution reaction to give an ether.

//M2//QN42//SUB//DL0

Discuss the classification of ethers.
OR Explain the following with an example. (iv) Unsymmetrical ether.

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Ethers are classified as simple or symmetrical, if the alkyl or aryl groups attached to the oxygen atom are the same, and mixed or unsymmetrical, if the two groups are different. Diethyl ether, C2H5OC2H5, is a symmetrical ether whereas C2H5OCH3 and C2H5OC6H5 are unsymmetrical ethers.

//M4//QN43//SN//DL0//EQ

Write short note: Williamson synthesis.OR Explain the following with an example:

(iii) Williamson ether synthesis:

//X

It is an important laboratory method for the preparation of symmetrical and unsymmetrical ethers. In this method, an alkyl halide is allowed to react with sodium alkoxide.
Ethers containing substituted alkyl groups (secondary or tertiary) may also be prepared by this method. The reaction involves S N 2 attack of an alkoxide ion on primary alkyl halide.
Better results are obtained if the alkyl halide is primary. In case of secondary and tertiary alkyl halides, elimination competes over substitution. If a tertiary alkyl halide is used, an alkene is the only reaction product and no ether is formed. For example, the reaction of CH 3 ONa with
(CH 3)3 C–Br gives exclusively 2-methylpropene.
It is because alkoxides are not only nucleophiles but strong bases as well. They react with alkyl halides leading to elimination reactions.
Phenols are also converted to ethers by this method. In this, phenol is used as the phenoxide moiety.

//M3//QN44//SUB//DL0

Illustrate with examples the limitation of williamson synthesis for the preparation of certain type of ethers.

//X

Williamson synthesis is an important laboratory method for the preparation of symmetrical and unsymmetrical ethers.
However, selection of appropriate reactants is required for the preparation of unsymmetrical ethers.
Williamson synthesis occurs via S N 2 mechanism and primary alkyl halides are more reactive towards S N 2 reaction.
Thus, better results are obtained if the alkyl halide is primary and alkoxide ion is primary, secondary or tertiary.
For example, tert-butyl ether can be prepared by treating methyl bromide with tert-butyloxide ion.
The above ether can not be prepared by the reaction between sodium methoxide and tert-butyl bromide. Because in this case elimination competes over substitution and alkene compound iso-butylene obtain as a product.
It is because alkoxides are not only nucleophiles but strong bases as well. They react with alkyl halides leading to elimination reactions.
Aryl and vinyl halides can not be used as reactant in Williamson synthesis as they are very less reactive towards nucleophilic reaction.

//M2//QN45//SUB//DL0

Preparation of ether by acid dehydration of secondary or tertiary alcohols is not a suitable method. Give reason.

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The acid dehydration method is suitable for the preparation of ethers having primary alkyl groups only.
The alkyl group should be unhindered and the temperature be kept low.
Otherwise the reaction favours the formation of alkene.
The reaction follows S N 1 pathway when the alcohol is secondary or tertiary.
However, the dehydration of secondary and tertiary alcohols to give corresponding ethers is unsuccessful as elimination competes over substitution and as a consequence, alkenes are easily formed.

//M2//QN46//SUB//DL0//EQ

Explain the fact in aryl alkyl ethers: (i) The alkoxy group activates the benzene ring towards electrophilic substitution and (ii) It directs the incoming substituents to ortho and para position in benzene ring.

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(i) The alkoxy group (– OR) is ortho, para directing and activates the aromatic ring towards electrophilic substitution in the same way as in phenol.
(ii) From the above resonance structures, we infer that the electron density on ortho and para position is more than that of meta position. Therefore, the substituent which is electrophile is directed to the ortho and para position of the benzene ring.

//M2//QN47//SUB//DL0//EQ

Write equations of the following reactions: (i) Friedel-Crafts reaction – alkylation of anisole. (ii) Nitration of anisole. (iii) Bromination of anisole in ethanoic acid medium. (iv) Friedel-Crafts acetylation of anisole.

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(i) Friedel-Crafts reaction – alkylation of anisole:
(ii) Nitration of anisole:
(iii) Bromination of anisole in ethanoic acid medium:
(iv) Friedel-Crafts acetylation of anisole:

//M4//QN48//SUB//DL0//EQ

Write products of the following reactions.

(i)
(ii)
(iii)
(iv)

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(i) (ii)
(iii) (iv)
Class 12 Chemistry (Part 2) 007