Classification of Alcohol, Phenol and Ether

Alcohol, phenol and ether are classes of Organic Compounds that incorporate the C⎯O bond. The alcohol, phenol and ether functional groups are found in many important naturally occurring molecules like glucose, glycerol, cholesterol. They have many applications in several domestic and industrial processes. So, let's get started with the classification of alcohol in Chemistry, classification of phenol, what are ethers, how are they classified, and their uses.

Alcohols

Alcohols contain the hydroxyl (⎯OH) functional group connected to a carbon atom by a covalent bond. Alcohols include all compounds having the general formula CnH2n+1OH. Examples – ethyl alcohol, methyl alcohol, butyl alcohol, etc.

Classification of Alcohol

Alcohols can be classified into three types depending on the number of carbon atoms directly bonded to the carbon atom containing the hydroxyl functional group. The types are:

• Primary alcohol (1°): The carbon atom carrying the hydroxyl group is attached to only one alkyl group. Example: 1-butanol, 2-methyl-1-propanol.

• Secondary alcohol (2°): The carbon atom carrying the hydroxyl group is attached to two alkyl groups, either the same or different. Example: 2-butanol.

• Tertiary alcohol: The carbon atom carrying the hydroxyl group is attached to three alkyl groups, all the same, or different. Example: 2-methyl-2-propanol.

Another classification of alcohols is based on the number of hydroxyl groups attached. The three types under this classification are:

• Monohydric Alcohol: Alcohols containing one hydroxyl group. Example: CH3-CH2-OH (Ethanol), CH3-CH2-CH2-OH (Propanol).

• Dihydric Alcohol: Alcohols containing two hydroxyl groups. Example: 1, 2-Ethanediol, 1, 3-Propandiol.

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• Trihydric Alcohol: Alcohols containing three hydroxyl groups. Example: 1, 2, 3-Propantriol, 1, 2, 3-Butantriol.

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Simple monohydric phenols are either corrosive liquids or low melting solids. The dihydric and trihydric phenols are solids.

Chemical Test used for Distinguishing Alcohols

The test used to differentiate between primary, secondary and tertiary alcohols is called the Lucas Test. Each type of alcohol gives separate results when the reactivity of alcohol is tested with the Lucas reagent in this test. Lucas reagent is a solution of anhydrous zinc chloride concentrated hydrochloric acid. 

The reaction is observed with a change in this colourless and clear solution upon reaction with alcohol. Tertiary alcohols react quickly, whereas primary alcohols do not react noticeably at room temperature. If the colourless and clear solution turns hazy/cloudy and turbid, it is a positive indication of the Lucas Test. 

Uses of Alcohol

• Ethyl alcohol is the major component of alcoholic drinks like wine and beer.

• Ethanol, combined with a small quantity of methanol, is sold as a methylated spirit with many industrial applications.

• Ethanol combustion produces energy, carbon dioxide, and water and can be used by itself or with petrol as a fuel.

• Ethanol is widely used as a solvent for dissolving Organic Compounds and is used in the manufacture of perfumes and cosmetics.

• Methanol is combined with petrol to improve combustion.

• Methanol serves as an industrial feedstock for the preparation of other compounds like aldehydes and acids.

Phenols

Phenols are compounds in which the ⎯OH group is directly attached to an aromatic ring and are designated as ArOH. Phenol differs from alcohol in that the former is slightly acidic in water and reacts with aqueous sodium hydroxide to form salts. Example: C6H5OH, the parent compound, is called phenol.

Classification of Phenol

Phenols can be classified into the following categories depending on the number of hydroxyl groups present:

• Monohydric Phenol: Contain only one hydroxyl group. Example: C6H5OH (phenol)

• Dihydric Phenol: Contain two hydroxyl groups. Example: Benzene-1, 2-diol.

• Trihydric Phenol: Contain three hydroxyl groups. Example: Benzene-1, 3, 5-triol.

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Uses of Phenol

• Phenols are widely used as an antiseptic and disinfectant.

• Phenol is a useful precursor for the synthesis of food preservatives, pharmaceuticals, resins, polymers, and adhesives.

• Phenolics are components of many biological systems and are present in naturally occurring substances like flavouring agents, neurotransmitters, and vitamins.

• Bisphenol A is a component of polycarbonate plastics.

Ethers

Ethers are the class of Organic Compounds containing the functional group ⎯O⎯. Ethers have the general formula R⎯O⎯R, where the hydrocarbon groups (R) may be either the same or different.

Classification of Ether

Ethers are classified into the following two types based on the type of alkyl or aryl groups attached to the ⎯O⎯.  functional group. The types are:

• Symmetrical ethers or simple ethers: These ethers have the same alkyl or aryl groups attached on either side of the ⎯O⎯ functional group. Example: C2H5⎯O⎯C2H5 (diethyl ether), CH3⎯O⎯CH3 (dimethyl ether).

• Unsymmetrical ethers or mixed ethers: These ethers have different alkyl or aryl groups attached on either side of the ⎯O⎯functional group. Example: C2H5⎯O⎯CH3 (ethyl methyl ether), CH3⎯O⎯C6H5 (methyl phenyl ether).

Uses of Ether

• Dimethyl ether is used as a refrigerant and as a solvent at low temperatures.

• Diethyl ether is used as a universal solvent for gums, oils, and resins.

• Diethyl ether is also a common anaesthetic ingredient in surgery.

• Due to its high boiling point, phenyl ether serves as a heat transfer medium.

• Methyl Benzenes are used in cosmetics, pharmaceuticals, and are naturally present in insect pheromones.

Differences Between Alcohol and Ether

There are differences in the chemical and physical properties of alcohols and ethers that arise due to the difference in their chemical structures. Alcohol is an Organic Compounds with a hydroxyl group (–OH) bonded to a carbon atom, whereas ether is an Organic Compounds with an oxygen atom that is bonded to two carbon atoms. 

The major difference between alcohol and ether is the absence of OH groups in the ether that are present in alcohol. The boiling point of ether is significantly lower than the corresponding alcohol as hydrogen bonds do not form between the molecules in ether. For example, the boiling point of diethyl ether is 35 °C, but the boiling point of 1-butanol is 118 °C. This comparison is between a corresponding ether and alcohol as both of them have the same molecular weight.

Alcohol with the same molecular weight is more likely to be soluble in water than ether because ethers cannot act as hydrogen bond donors. Ethers are hydrogen bond acceptors.

Ethers are inert to most chemical reactions because of the absence of an OH group, unlike alcohols. Except at high temperatures, ethers are stable to most acids and bases and do not react to most oxidising or reducing agents.

In an ether, alkyl or aryl groups replace both hydrogen atoms whereas, in alcohol, an alkyl group replaces one hydrogen atom of a water molecule. 

Relative to ethers, alcohols are generally denser. But the unreactive nature of ethers being colourless, pleasant-smelling liquids at room temperature makes them extremely useful solvents. Ethers are used in dyes, gums, resins, fats, waxes, perfumes and oils. Even vapours of particular ethers are useful. They protect crops by their use as fumigants and insecticides in soil.

Ways to Distinguish between Alcohol and Phenol

In order to distinguish between two different colourless species, chemical reactions must be carried out to observe any colour changes. To differentiate between the two, a certain reagent should be selected that remains unchanged in colour after reacting with one species and changes in colour after reacting with the other species.

For example, ethyl alcohol does not react with the neutral ferric chloride solution, whereas phenol gives a purple colour of ferric phenoxide upon reacting with the neutral ferric chloride solution. Another example is that alcohol does not react with aqueous NaOH, whereas phenol reacts to form sodium phenoxide.

Students can understand the fundamental differences in properties of phenols and alcohols in detail and in tabular form from the Vedantu website and app. Study material can be downloaded for free from the Vedantu website and app for exam preparation and revision.