Alcohol, Phenols and Ethers

Define Alcohols:

Alcohol are derivatives of hydrocarbons whose functional group is -OH as -OH has replaced a hydrogen atom. Depending on the presence of hydroxyl groups in the compound  there are different types of alcohol i.e primary alcohol, secondary alcohol, tertiary alcohol. Functional group of alcohol is known as -OH( Hydroxyl group). Nature of alcohol is mainly covalent in nature as the -OH group is attached to the carbon by covalent bond. Ethyl alcohol is considered as primary alcohol or one of the main alcohol and ethyl alcohol is also considered as ethanol. General formula of alcohol is CnH2n + 1OH.


Chemical and Physical Properties of Alcohol:

Physical Properties of Alcohol are:

  1. Boiling points of alcohol are generally higher when compared to other hydrocarbons having the same molecular mass. Concept behind higher boiling point of alcohols is presence of intermolecular hydrogen bonding between hydroxyl groups of alcohol molecules. With increase in carbon chain of aliphatic alcohol boiling point increases whereas with increase in branching of alcohol boiling point decreases.

  2. Solubility property of alcohol is determined by the presence of hydroxyl groups. Hydroxyl groups help in formation of intermolecular hydrogen bonding as the hydrogen bond formed between water and alcohol molecules make them soluble in water, where the alkyl group is hydrophobic in nature. Thus solubility is directly related to the size of the alkyl group.

  3. Alcohol reacts with metals to form corresponding alkoxide. Example ethanol reacts with sodium metal to form Sodium ethoxide. This reaction shows the acidic property of alcohol as -OH bond shows polarity of alcohol. Their acidic property decreases when the electron donating group is attached to the hydroxyl group.


Chemical Properties of Alcohols:

  1. Oxidation of Alcohol: Alcohol undergoes oxidation reaction in the presence of oxidising agent and they form aldehydes and ketone as a product which further undergoes oxidation process to give carboxylic acid.

  2. Dehydration of Alcohols: In this process alcohol is treated with protic acids to form alkenes.


Preparation of Alcohols:

There are several methods for preparation of alcohols, some of these methods are given below:

  1. Hydrolysis of Halides: When alkyl halide is boiled with an aqueous solution of an alkali hydroxide, they form alcohol as due to nucleophilic substitution mechanism. Under this reaction primary and secondary alcohols are formed.

Reaction:

R-X + KOH → R-OH + KX

  1. Hydration of Alkanes: Under this reaction there occurs direct hydration of alkanes in the presence of a catalyst. 

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  1. Hydroboration of Alkenes: Under this reaction alkene is treated with diborane to form alkyl boranes, further alkyl boranes on oxidation with alkaline hydrogen peroxide to give alcohol as a final product. 

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Define phenol:

It is an aromatic compound. It consists of phenyl groups attached to each other. Phenol is crystalline in nature having white color.


Physical and Chemical Properties of Alcohol:

Some of the physical and chemical  properties of phenol are:

  1. Pure phenol is crystalline in nature.

  2. Their crystalline form is mainly wet and discolored.

  3. Phenol is moderately soluble in water.

  4. Acidity of phenol: When phenol reacts with active metals such as sodium, potassium, etc. to from phenoxide. This reaction shows the acidic property of phenols. Due to delocalisation of negative charge in the benzene ring, phenoxide ions are more stable than alkoxide ions.


Preparation of Phenols:

There are several methods for the preparation of phenols some of these reactions are:

  1. From Sulphonic Acids: This reaction is the very first commercial step of phenol synthesis. In this process sodium benzene sulphonate is fused with sodium hydroxide to form sodium phenoxide, which further undergoes acidification to yield phenol.

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  1. From Diazonium Salts: When a diazonium salts solution is treated with steamed distilled or is added to boiling dil.H2SO4, it forms phenol as a final product.

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Define Ether:

They belong to organic compounds that have an oxygen atom attached to two same or different alkyl or aryl groups. General formula of ether is R-O-R, R-O-Ar or Ar-O-Ar.


Physical and Chemical Properties of Ether:

  1. There is presence of net dipole in ether molecules. This is the reason behind polarity of C--O bonds.

  2. It has a much lower boiling point in comparison to alcohols.

  3. Dissolving capacity of ether is the same as alcohol.

  4. Electrophilic substitution reaction: Ether undergoes electrophilic substitution reaction. Some of the electrophilic substitution reactions are halogenation and Fridel craft’s reaction etc. 

  1. Halogenation of Reaction: Aromatic ethers undergo halogenation, for example, bromination, upon the addition halogen in the presence or absence of a catalyst.

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  1. Friedel Craft Reaction: Aromatic ethers undergo Friedel Crafts reaction for example addition of alkyl or acyl group upon the reaction with alkyl or acyl halide in the presence of a Lewis acid as catalyst.

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Preparation of Ether:

There are several methods for the preparation of ether, some of these methods are given below:

  1. Preparation of Ether by Dehydration of Alcohol: This reaction takes place in the presence of protic acid i.e sulphuric acid alcohol undergo dehydration to produce alkenes and ether as their minor and major products. This reaction occurs at approx 443K. This is the ideal method of preparation of ether.

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  1. Williamson’s Synthesis: Under this reaction alkyl halide reacts with sodium alkoxide and ether is formed as a main product. This reaction generally follows SN2 mechanism for formation of primary alcohol.

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FAQ (Frequently Asked Questions)

1. Define Alcohol?

Ans: Alcohol are derivatives of hydrocarbons whose functional group is -OH as -OH has replaced a hydrogen atom. Depending on the presence of hydroxyl groups in the compound  there are different types of alcohol i.e primary alcohol, secondary alcohol, tertiary alcohol. Functional group of alcohol is known as -OH( Hydroxyl group). Nature of alcohol is mainly covalent in nature as the -OH group is attached to the carbon by covalent bond. Ethyl alcohol is considered as primary alcohol or one of the main alcohol and ethyl alcohol is also considered as ethanol. General formula of alcohol is CnH2n + 1OH.

2. Explain Preparation of Alcohol?

Ans: There are several methods for preparation of alcohols, some of these methods are given below:

  1. Hydrolysis of Halides: When alkyl halide is boiled with an aqueous solution of an alkali hydroxide, they form alcohol as due to nucleophilic substitution mechanism. Under this reaction primary and secondary alcohols are formed.

  2. Hydration of Alkanes: Under this reaction there occurs direct hydration of alkanes in the presence of a catalyst. 

  3. Hydroboration of Alkenes: Under this reaction alkene is treated with diborane to form alkyl boranes, further alkyl boranes on oxidation with alkaline hydrogen peroxide to give alcohol as a final product.