Q.How are primary, secondary and tertiary alcohols identified by Victor Meyer's test?

Victor Meyer's test distinguishes 1 degree, 2 degree and 3 degree alcohols by converting each to its nitroalkane and observing the colour produced with nitrous acid followed by sodium hydroxide.

The test proceeds through three steps for each alcohol:

Step 1: The alcohol is converted to the corresponding alkyl iodide by treating it with red phosphorus and iodine.

R-OH --(red P + I2)--> R-I

Step 2: The alkyl iodide is converted to the nitroalkane by heating with silver nitrite (AgNO2).

R-I + AgNO2 -> R-NO2 + AgI

Step 3: The nitroalkane is treated with nitrous acid (HNO2, generated from NaNO2 + dil. HCl), and the resulting solution is then made alkaline with NaOH. The colour observed depends on the class of the original alcohol:

• Primary alcohol: its nitroalkane still has an alpha-hydrogen (attached to the same carbon as the nitro group), so it reacts with HNO2 to form a nitrolic acid, which dissolves in NaOH to give a blood-red colour. …