What are Alcohols?
Alcohols are a group of molecules containing one, two, or more hydroxyl (-OH) groups linked to a single-bonded alkane. These substances have the general formula ROH.”
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By way of oxidation, alcohols are transformed into aldehydes and ketones. This is one of the most significant reactions in organic chemistry.
Oxidation of Alcohols to Aldehydes and Ketones
Alcohols are a class of chemicals with one, two, or more hydroxyl (-OH) groups connected to an alkane by a single bond. These substances have the generic formula ROH. They are of utmost importance in the study of organic chemistry since they may be altered or transformed into other compounds, such as aldehydes and ketones, etc. The reactions to alcohol fall into two distinct groups. These reactions can leave either the R-O bond or the O-H bond.
The oxidation of alcohols to aldehydes and ketones is a crucial reaction in synthetic organic chemistry. These reactions occur in the presence of catalysts, and the most effective oxidants necessary for these conversions contain high-valent ruthenium, which serves as the catalyst for this type of reaction. It is crucial to have comprehensive information and comprehension of the components and mechanisms that influence oxidation reactions.
1. Mechanism of conversion Alcohols into Aldehydes and Ketones
In organic chemistry, the catalytic conversion of primary alcohols into aldehydes and secondary alcohols into ketones is essential for the synthesis of numerous synthetic intermediates.
The outcome of the alcohol oxidation reaction depends on the types of substituents present in the carbonyl carbon. For the oxidation reaction to occur, the carbonyl carbon must contain a hydrogen atom.
In these types of reactions, the oxidizing agents or catalysts are often solutions of sodium or potassium dichromate(VI) acidified with diluted sulphuric acid. During oxidation, the orange solution containing dichromate(VI) ions is converted to the green solution containing chromium(III) ions.
2. Making of Aldehydes
Aldehydes are produced by oxidizing the main alcohols. Utilizing an acidified potassium dichromate(VI) solution as an oxidizing agent, the generated aldehyde can be further oxidized into carboxylic acids. The oxygen atom of the oxidizing agent destroys the hydrogen atom from the alcohol’s hydroxyl (-OH) group, as well as one carbon atom connected to it.
Here, R and R’ are alkyl or hydrogen groups. If these groups contain the hydrogen atom, aldehyde will result. These aldehydes are produced by primary alcohols.
3. Making of Ketones
Ketones are produced through the oxidation of secondary alcohols. Consider, for instance, heating the secondary alcohol propane-2-ol with a sodium or potassium dichromate(VI) solution acidified with dilute sulphuric acid; this results in the formation of the ketone propanone.
The reaction occurs as shown below:
The Ketones obtained cannot be further oxidized since doing so would need an excessive amount of energy to break the C–C bond.
What are the Different Types of Alcohol?
Alcohols are split into three types according to the chemical groups connected to the carbon atom:
- Primary alcohol: is a form of alcohol in which the carbon atom linked to the hydroxyl group is bound to a single carbon atom.
- Secondary alcohol: An alcohol that is covalently bound to two carbon atoms.
- Tertiary alcohol: An alcohol that is bound to three carbon atoms is known as tertiary alcohol.
Each of the three alcohol kinds (primary, secondary, and tertiary) has distinct physical and chemical properties.
Identification of Alcohols
For the identification of primary, secondary, and tertiary alcohols, several tests are conducted. Some of these exams include:
1. Lucas Test
The Lucas test is based on the distinction between the reactivity of primary, secondary, and tertiary alcohols with hydrogen chloride. Alcohol is treated with Lucas reagent in the Lucas test (concentrated HCl and ZnCl2). As the halides of the modified alcohol are incompatible with the Lucas reagent, turbidity is created. The time required to produce turbidity is recorded, along with the following observations:
- At room temperature, turbidity is not formed with primary alcohols. On heating, however, an oily film forms.
- In 5 to 6 minutes, an oily coating forms when secondary alcohol is added to water. Thus, it takes some time for the reaction to cause turbidity.
- As halides are easily generated from tertiary alcohol, turbidity is produced immediately.
The rate of turbidity generation upon the interaction of alcohol with the Lucas reagent enables us to distinguish between primary, secondary, and tertiary alcohols.
2. Oxidation Test
In the oxidation test, sodium dichromate is used to oxidize the alcohols (Na2Cr2O7). The oxidation rates of primary, secondary, and tertiary alcohols vary. On the basis of their rates of oxidation, alcohols can be classified as:
- The primary alcohol is readily oxidized to an aldehyde and is also oxidizable to carboxylic acids.
- It is simple to convert secondary alcohol to ketone, but further oxidation is impossible.
- Tertiary alcohol is not oxidized when sodium dichromate is present.
Thus, the rate of oxidation following oxidation with sodium dichromate aids in distinguishing between primary, secondary, and tertiary alcohols.
To know the physical and chemical properties of alcohols. For a detailed discussion on the types of alcohol and the identification of primary, secondary, and tertiary alcohol, please visit Utopper.com.
Frequently Asked Questions – FAQs
Q.1 What is ethanol oxidation?
Alcohol oxidation is oxidation in terms of hydrogen conversion. The alcohol is oxidized as a result of the decomposition of hydrogen. Hydrogen transfer frequently involves oxidation and reduction in hydrocarbon chemistry. Sodium dichromate (Na2Cr2O7) acidified in diluted sulphuric acid oxidizes ethanol to produce ethanal, an aldehyde.
Q.2 Why are tertiary alcohols not oxidized?
A solution of sodium or potassium dichromate(VI) that has been acidified does not oxidize tertiary alcohols. There is no reaction whatsoever. Tertiary alcohols lack a hydrogen atom linked to the carbon atom. To form the carbon-oxygen double bond, it is necessary to delete these two distinct hydrogen atoms.
Q.3 What do secondary alcohols oxidize to?
The oxidation of secondary alcohols to ketones is a major organic chemistry oxidation reaction. A ketone is formed when secondary alcohol is oxidized. Hydrogen from the hydroxyl group is lost together with the hydrogen linked to the second carbon.
Q.4 Can alcohol be oxidized?
The oxidation of alcohol is an important process in organic chemistry. Primary alcohols can be oxidized to produce aldehydes and carboxylic acids, while secondary alcohols can be oxidized to produce ketones. In contrast, tertiary alcohol cannot be oxidized without disrupting the C-C bonds inside the molecule.
Q.5 How does alcohol oxidation work?
Primary alcohols may be oxidized into aldehydes or carboxylic acids, depending on the reaction conditions. During the formation of carboxylic acids, the alcohol is first oxidized to an aldehyde and then further oxidized to the acid.
