Test for Alcohols

Test for Alcohols

Test for Alcohols

Test for Alcohols

Number of tests are available for the test of alcohol. Some of them are mentioned here-
Sodium Metal Test
Ester Test
Ceric Ammonium Nitrate Test
Acetyl Chloride Test
Iodoform test

Sodium Metal Test

When the given liquid is added to a small pieces of sodium metal and brisk effervescence appears (due to the liberation of hydrogen gas when alcohol reacts with active metals like sodium) indicates the presence of alcohol group in the given liquid.
2ROH + 2Na → 2RONa + H2

Ester Test

When the given liquid is added to carboxylic acids forms an ester indicates the presence of alcoholic group.
R-OH + R-COOH → R-COOR + H2O

Ceric Ammonium Nitrate Test

Alcohol react with ceric ammonium nitrate forms a pink or red colour precipitate due to the formation of a complex compound and ammonium nitrate. Appearance of wine red colour precipitate shows the presence of alcoholic group
(NH4)2 [Ce(NO3)6] + 3ROH → [Ce(NO3)4(ROH)3] + 2NH4NO3

Acetyl Chloride Test

Acetyl chloride when added to the given liquid results an oily layer of the ester and evolution of HCl gas indicates the presence of an OH group.
R-OH + CH3-CO-Cl → CH3-COOR + HCl

Iodoform test

Iodoform test is given by only secondary alcohols. First the compound is heated with sodium hydroxide solution and iodine. A formation of yellow precipitate of iodoform shows the presence of alcohol(secondary alcohols).
CH3-CH(OH)-CH3 + I2 + 2NaOH → CH3-CO-CH3 + 2NaI + 2H2O
CH3-CO-CH3 + 3I2 + 4NaOH → CHI3(Iodoform) + CH3COONa + 3NaI + 3H2O

Distinguish Between Primary, Secondary and Tertiary Alcohols

The organic compound which has -OH functional group are called alcohols. Alcohols are compounds containing an -OH group bonded to a sp3 hybridized carbon atom. The general formula for alcohol is R-OH. Where R is an alkyl group.
The following tests can be use to distinguish primary, secondary and tertiary alcohols from each other.

Distinguish Between Primary, Secondary and Tertiary Alcohols by Victor Meyer Test

Victor Meyer test involves in the series of reactions.
Given alcohol is converted into iodide by treatment with cold HI or red P and iodine. The iodide is then treated with silver nitrate and gives corresponding nitroalkane. The nitroalkane is finally treated with nitrous acid and the solution is made alkaline.
If the blood red color is produced in this way the original alcohol is primary, if a blue color is produced, the alcohol is secondary and if there is no color obtained, the alcohol is tertiary.
Victor Meyer Test of Alcohol

Distinguish Between Primary, Secondary and Tertiary Alcohols by Lucas Test

When given alcohol is heated with concentrated HCl containing anhydrous ZnCl2 at room temperature, following observations distinguish the different alcohols-
a tertiary alcohol produces cloudiness immediately.
a secondary alcohol produces cloudiness after 5 minutes.
a primary alcohol shows no cloudiness at room temperature and it does so only upon heating.
Lucas Test of Alcohol

Distinguish Between Primary, Secondary and Tertiary Alcohols by Oxidation

Primary alcohols on oxidation gives an aldehyde and on further oxidation gives carboxylic acid with the same number of carbon atoms.
Secondary alcohols on oxidation gives ketone with the same number of carbon atoms and on prolonged action of oxidizing agent yields mixture of acids containing fewer carbons than the original alcohol.
Tertiary alcohol is resistant to alcohol in alkaline solution but readily oxidized by dilute nitric acid to form a mixture of ketone and acid, each containing fewer number of carbons than the original alcohol.
Test of Alcohol by Oxidation

Distinguish Between Primary, Secondary and Tertiary Alcohols by Action of Hot Reduced Copper

The vapour of given alcohol are passed over reduced copper catalyst at 300°C and the product obtained is identified.
Primary alcohol dehydrogenates to give an aldehyde, while secondary alcohol dehydrogenates to form a ketone. Tertiary alcohols under the same conditions dehydrates to yield an alkene.
Test of Alcohol by Action of Hot Reduced Copper