Identification of Primary, Secondary and Tertiary Alcohols

Alcohols are organic compounds that are among the most well-known because of their numerous applications and uses in everyday life. Alcohols are organic molecules that have a hydroxyl group attached to an alkyl or aryl group (ROH). A hydroxyl carbon with only one R group is referred to as a primary alcohol. It is a secondary alcohol if it has two R groups, and a tertiary alcohol if it has three R groups. Alcohols, like many other organic compounds, can be aromatic if they contain a benzene ring. Phenol is the most basic aromatic alcohol.

Define Alcohol

An alcohol is an organic compound with at least one hydroxyl functional group (OH) bound to a saturated carbon atom in chemistry. All compounds with the general formula CnH2n+1OH belong to an important class of alcohols, of which methanol and ethanol are the simplest members. An alcohol is an organic compound with at least one hydroxyl functional group (OH) bound to a saturated carbon atom in chemistry. All compounds with the general formula CnH2n+1OH belong to an important class of alcohols, of which methanol and ethanol are the simplest members. 

Types of Alcohol:

1. Primary Alcohol : Only one carbon atom is attached to the alpha-carbon in a primary alcohol. Only when the hydroxyl group is at the end of the molecule chain will this happen. Ethanol, propanol, and butanol are examples. Methanol is the primary alcohol when no carbon atoms are bonded.
2. Second Alcohol : A secondary alcohol has only one hydrogen atom attached to the hydroxyl group (-OH). This can happen anywhere along a carbon chain.
3. Tertiary Alcohol : The hydroxyl group is attached to a carbon with no hydrogen atoms attached in a tertiary alcohol. This usually indicates that the hydroxyl group is attached to the same carbon atom as the branch.

Identification of primary, secondary and tertiary alcohols:

The different properties of the various types of alcohols can be used to identify an alcohol in organic chemistry. Other qualitative tests can be used in addition to various instrumentation analysis methods like nuclear magnetic resonance (NMR). The identity of an alcohol can be determined by combining these tests in the same way that aldehydes and ketones can be identified.

• Ferric Chloride Test : Iron(III) chloride is one way to tell the difference between an aliphatic and an aromatic alcohol. The red-orange colour of the solution is due to the iron chloride compound. The chloride atoms are replaced by the aromatic alcohol in the presence of an aromatic alcohol, such as phenol, altering the coordination property of the centre iron atom. The solution will turn purple as a result of this. Iron(III) chloride does not react with aliphatic alcohols, so the solution remains red-orange.

• Oxidation Test : The alcohols are oxidised with sodium dichromate in the oxidation test (Na2Cr2O7). The rate of oxidation varies depending on whether the alcohol is primary, secondary, or tertiary. Alcohols are classified as follows based on their oxidation rates:

1. Primary alcohol is easily converted to an aldehyde, which can then be converted to carboxylic acids.
2. Secondary alcohol can easily be converted to ketone, but no further oxidation is possible.
3. In the presence of sodium dichromate, tertiary alcohol does not oxidise.

• Lucas Test : The Lucas test compares the reactivity of primary, secondary, and tertiary alcohols to hydrogen chloride. The alcohol is treated with Lucas reagent in the Lucas test (concentrated HCl and ZnCl2). The halides of the substituted alcohol are immiscible in Lucas reagent, resulting in turbidity. The time it took to achieve turbidity is recorded, along with the following observations: 

1. Turbidity does not form at room temperature in the case of a primary alcohol. When heated, however, an oily layer forms.
2. An oily layer forms in 5-6 minutes when a secondary alcohol is used. As a result, it takes some time for the reaction to produce turbidity.
3. Turbidity is immediately produced in the case of tertiary alcohol because halides are easily formed.Jones Test : In the Jones test, chromium trioxide is used as a powerful oxidising agent in the presence of sulfuric acid. A primary alcohol is converted to an aldehyde and then to a carboxylic acid in the presence of the Jones’ reagent, whereas a secondary alcohol is oxidised to a ketone. tertiary alcohols do not react with chromium, no precipitate is formed, resulting in an orange solution.

Conclusion

Any of a group of common organic compounds with one or more hydroxyl groups (OH) attached to one or more carbon atoms in a hydrocarbon chain is called an alcohol. The alcohol is classified as primary (RCH2OH), secondary (R2CHOH), or tertiary (R3COH) based on the number of other substituent groups (R) on that carbon atom. The different properties of the various types of alcohols can be used to identify alcohol in organic chemistry like, Jones Test, Oxidation Test, Lucas test etc.

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