Distinction of primary, secondary and tertiary alcohol:

(a) Oxidation test

(b) Lucas test

(c) Victer meyer test (best method)

(d) Catalytic dehydrogenation by Cu/300^°C.

1. VICTER MEYER ‘S test: it involves following step,

a) Alcohol is treated with conc. HI or red phosphorous and iodide to form the corresponding alkyliodide.

b) alkyl iodide is treated with silver nitrite when nitro alkane is formed.

(a) Oxidation with sodium Dichromate (Na₂Cr₂O7)

Primary and secondary alcohols are easily oxidized by reagents containing chromium (VI). For low-molecular-weight alcohols that are water-soluble, water solutions of sodium dichromate in the presence of acid are used. .

The oxidizing solution in the above examples, an acidic solution of sodium dichromate, contains a variety of species in equilibrium. Most important of these is the acid chromate ion, HCrO₄^¯.

(b) Lucas test: Alcohols react with concentrated hydrochloric acid in presence of anhydrous zinc chloride to form alkyl halides.

[conc. HCl + ZnCl₂ (anhydrous) follow the following order:

Tertiary alcohol > Secondary alcohol > Primary alcohol

Lucas test is based on this order because formation of intermediate carbocation

The following observations are made:

(a) If cloudiness appears immediately, the alcohol is tertiary.

(b) If cloudiness appears within 5–10 minutes, the alcohol is secondary.

(c) If the solution remains clear, i.e., on cloudiness is formed the alcohol is primary.

Note:

Primary alcohols do not react with Lucas reagent at room temperature. It requires high temperature.

(c) Victor Meyer’s test:

 (iii) Nitro alkane is treated with nitrous acid (NaNO₂+ H₂SO₄) and the solution is made alkaline by addition of excess of caustic soda.

IF BLOOD RED colouration appears,it indicates a primary alcohol

IF BLUE COLOR APPEARS THEN IT’S A SECONDARY ALCOHOL

AND IT’S A TERTIARY ALCOHOL IF IT REMAINS COLOURLESS.