Alcohol Reactions: Oxidation, Dehydration, Esterification, Substitution Reactions

Any member of the family of organic compounds known as alcohols may be identified by the presence of one or more hydroxyl (-OH) groups linked to an alkyl group's carbon atom (hydrocarbon chain). Alcohols can be thought of as organic derivatives of water in which an alkyl group, which is commonly denoted by R in organic structures, has replaced the position of one of the hydrogen atoms. According to the degree of bonding between the hydroxyl group and the carbon of the alkyl group, alcohols can be categorised as primary, secondary, or tertiary alcohols. At room temperature, the majority of alcohols are colourless solids or liquids. High water solubility is a property of low molecular weight alcohols; as molecular weight increases, so do their boiling points, vapour pressures, densities, and viscosities. Alcohols undergo various reactions like oxidation, dehydration and esterification to yield various products.

Oxidation Of Alcohols

Ketones, aldehydes, and carboxylic acids can be produced by oxidising alcohol. These functional groups are helpful for later reactions; for instance, ketones and aldehydes can be employed in subsequent Grignard reactions, while carboxylic acids can be used for esterification. The number of bonds between carbon and oxygen is often increased during the oxidation of organic molecules while the number of bonds to hydrogen may decrease.

1. Oxidation Of Primary Alcohols

Depending on the conditions of the reaction, primary alcohols can be converted to either aldehydes or carboxylic acids. The alcohol is first converted to an aldehyde, which is then further converted to carboxylic acid in the case of the generation of carboxylic acids. If excessive alcohol is used along with the oxidizing agent like Potassium Dichromate in presence of dilute Sulphuric acid, the formed aldehyde is immediately distilled out, an aldehyde is produced.

To obtain Carboxylic acid as the final product, the oxidising agent must be taken in excess, and the mixture should contain the aldehyde produced as the halfway result. An excessive amount of the oxidising agent is used to reflux heat the alcohol. The carboxylic acid is distilled out when the reaction is finished.

2. Oxidation Of Secondary Alcohols

Secondary alcohol produces a ketone when it undergoes oxidation. Both the hydrogen linked to the carbon connected to the oxygen and the hydrogen from the hydroxyl group are lost. The leftover oxygen then joins the carbon in double bonds resulting in the formation of a ketone. The need to break an adjacent C-C bond makes ketones highly resistant to additional oxidation, although, in the presence of extreme conditions like very strong oxidizing agents, this is possible and can result in the production of esters or carboxylic acids.

3. Oxidation Of Tertiary Alcohols

Since the carbon atom that contains the -OH group is not directly connected to a hydrogen atom but is instead bound to other carbon atoms, tertiary alcohols are resistant to oxidation. A double bond between carbon and oxygen is created during the oxidation process. As a result, to create the double bond, the carbon atom carrying the -OH group must be able to release one of its bound atoms. Carbon-to-hydrogen bonds can be easily broken in an oxidising medium, but not carbon-to-carbon bonds. hence, Tertiary alcohols are therefore challenging to oxidise.

Dehydration Of Alcohols

To dehydrate alcohol, a C-O bond must typically be broken and a proton must be lost from the beta position. When secondary and tertiary alcohols are dehydrated, a species known as the carbocation intermediate is formed.

1. Formation Of Alkenes

The hydroxyl group and a hydrogen atom on the nearby carbon atom must be removed to transform an alcohol into an alkene. This process is referred to as dehydration since the components of water are being taken away. Warming the alcohol in the presence of a strong dehydrating acid, such as concentrated sulfuric acid, is the most frequent method for dehydrating alcohol.

2. Formation Of Ethers

Simple alcohols can intermolecularly dehydrate to produce ethers under precisely controlled conditions. This process is most cost-effective for producing ethyl ether (also known as diethyl ether), an essential industrial solvent, although it is only successful with methanol, ethanol, and other simple primary alcohols.

Esterification Of Alcohols

A chemical process known as esterification occurs when two reactants, often an alcohol and an acid, combine to form an ester and water as end products. Esters are often employed in organic chemistry and biological materials. They also have a pleasant fruity smell.

Alcohols and a number of other acids can combine to generate esters. The reaction of an alcohol and an acid, which is catalysed by the acid, results in the production of an ester and water, known as Fischer's esterification. Under the correct circumstances, inorganic acids may also react with alcohol to produce esters. A mixture of ethanol and ethanoic acid heated gradually in the presence of concentrated sulphuric acid yields an ester, such as an ethyl ethanoate, which is then quickly removed by distillation. By doing this, the back reaction is prevented. Several esters can be produced through esterification, a process that involves heating a carboxylic acid and an alcohol in the presence of a mineral acid catalyst to produce an ester and water. It is possible to reverse the reaction.

Substitution Reactions Of Alcohols

Alcohols are frequently converted into alkyl halides by replacing a halogen atom for the hydroxyl group. When used with tertiary alcohols, the hydrochloric (HCl ), hydrobromic (HBr ), and hydroiodic (HI ) acids provide the greatest yields for this replacement. Alkyl chlorides, bromides, and iodides may all be produced using thionyl chloride (SOCl_{2} ), phosphorus tribromide (PBr_{3}), and phosphorus triiodide (produced from phosphorus and molecular iodine, respectively).