In organic chemistry, functional groups play a crucial role. Alcohols are referred to as the organic compound with -OH functional group. Compounds containing a -OH group bonded to a tetrahedral carbon atom are alcohols. For alcohol, the general formula is R-OH, where R consists of an alkyl group. In this article, we will study the identification test for alcohol.
Qualitative Test For Alcohol:
To identify the present functional group (test for Alcoholic group) in a given organic compound.
Qualitative test for alcohol- there are various test to detect the alcoholic group present-
Sodium metal test
Ceric ammonium nitrate test
Acetyl chloride test
Carboxylic acids react with alcohols resulting in the formation of fruit-smelling ester. The reaction is called the esterification reaction between an alcohol and a carboxylic acid. This reaction is a concentrated sulphuric acid-catalyzed reaction.
R-OH + R-COOH → R-COOR + H2O
CH3OH + CH3-COOH → CH3-COOCH3 + H2O
Sodium Metal Test
It is based on the appearance of brisk effervescence when alcohol reacts with active metals such as sodium because of the release of hydrogen gas.
Below, the chemical reaction is given.
2R-OH + 2Na → 2R-O-Na + H2↑
2CH3-OH + 2Na → 2CH3-O-Na + H2↑
Ceric Ammonium Nitrate Test for Alcohol
Due to the formation of a complex compound and ammonium nitrate, alcohol or ceric ammonium nitrate reactions form a pink or red-coloured precipitate.
(NH4)2 [Ce(NO3)6] + 3ROH → [Ce(NO3)4(ROH)3] + 2NH4NO3
(NH4)2 [Ce(NO3)6] + 3CH3OH → [Ce(NO3)4(CH3OH)3] + 2NH4NO3
The formation of ester and hydrogen chloride results from alcohol reactions with acetyl chloride
R-OH + CH3-CO-Cl → CH3-COOR + HCl
HCl + NH4OH → NH4Cl + H2O
This test is conducted with secondary alcohols, acetaldehyde, and ketones. The compound is heated in the presence of a sodium hydroxide solution and iodine. The presence of alcohol is shown by the formation of a yellow iodoform precipitate.
CH3-CH(OH)-CH3 + I2 + 2NaOH → CH3-CO-CH3 + 2NaI + 2H2O
CH3-CO-CH3 + 3I2 + 4NaOH → CHI3(Iodoform) + CH3COONa + 3NaI + 3H2O
This test is used to distinguish between primary, secondary, and tertiary alcohols. Lucas reagent is a mixture of concentrated hydrochloric acid and zinc chloride. Tertiary alcohols on treatment with Luca’s reagent result in the formation of white ppt immediately. Secondary alcohol on treatment with Lucas reagent forms white ppt after 5 minutes. Primary alcohol on treatment with Luca’s reagent does not form white ppt at room temperature.
Ceric ammonium nitrate
Lucas reagent (zinc chloride and Con.HCl)
Test tube holder
Procedure and Observations (Identification Test for Alcohol)
The given organic compound is ___________. (primary alcohol, secondary alcohol or tertiary alcohol)
Sodium metal should be carefully treated, as it responds violently to water.
As it can cause nasal irritation, iodine should not be inhaled.
Did you Know?
The boiling points of alcohols of equal molecular weights are much higher than those of alkanes. Ethanol, for example, has a boiling point of 78 °C (173 °F) with a molecular weight (MW) of 46, while propane (MW 44) has a boiling point of −42 °C (−44 °F). Such a large difference in boiling points means that ethanol molecules are much more highly attracted to each other than propane molecules are. The ability of ethanol and other alcohols to form intermolecular hydrogen bonds results in much of this disparity. (For a discussion of hydrogen bonding, see chemical bonding: Intermolecular forces.)