Lucas Test disitinction of primary, secondary and tertiary alcohols

The difference in reactivity of primary, secondary and tertiary alcohols with HCl distinguishes them from one another. This test is known as Lucas test. In this method, the alcohol is treated with Lucas reagent (a mixture of conc. HCl and anhydrous ZnCl2). The alcohol is converted into alkyl halides. Alcohols are soluble in Lucas reagent while their halides are insoluble. The formation of alkyl halide is indicated by the appearance of turbidity in the reaction mixture. As the reactivity of alcohols with halogen acids is in the order tertiary > secondary > 2primary, the time required for the appearance of turbidity will be different for primary, secondary and tertiary alcohols which helps to distinguish them from one another.

In the case of tertiary alcohols, turbidity is produced immediately at room temperature. Secondary alcohols give turbidity in few minutes while primary alcohols do not produce appreciable turbidity at room temperature, but give turbidity only on heating.

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Reaction of alcohol and phenol with carboxylic acid

Alcohols and phenols react with carboxylic acids, acid chlorides and acid anhydrides to form esters.

R-O-H + R' - COOH -----H+-----> ROCOR' + H2O
Ethanol Acetic acid Ethyl acetate(Ester)

C2-OH + CH3-COOH -----H2SO4----------> C2H5O COCH3 + H2O

Ar-OH + R'-COOH ------------------> ArOCOR' + H2O
Phenol Ester

Ar-OH/ R-OH + (R'CO)2 ---------H+----------> Ar/ ROCOR' + R'COOH


Ease of esterification of alcohol is in the order primary> secondary> tertiary .
The reaction with carboxylic acid and acid anhydride is carried out in presence of small amount of concentrated sulphuric acid. The reaction with carboxylic acid is reversible, and therefore, water is removed as soon as it is formed. The Reaction With Acid Chloride Is Carried Out In Presence Of A Base (Pyridine) so as to remove HCl. It also shifts the equilibrium to right hand side. The introduction of acetyl (CH3CO-) group in alcohols or phenols is known as acetylation. Acetylation of salicylic acid (2-hydroxy benzoic acid) produces aspirin which possesses analgesic, anti-inflammatory and antipyretic properties.

Salicylic-acid-and-acetic-anhydride-forming-acetyl-salicylic-acid (aspirin)

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Reaction of alcohol and phenol with alkali

Phenols react with aqueous sodium hydroxide to form sodium phenoxides. But alcohols are neutral to this reaction.


The above reactions show that alcohols and phenols are acidic in nature. In fact, alcohols and phenols are Bronsted acids, that is they can donate a proton to a strong base (B:)


On treating an alkoxide with water the starting alcohol is obtained.


This reaction shows that water is a better proton donor than alcohol. In other words, alcohols are weaker acids than water. Also, in the above reaction, we can see that alkoxide ion is a better proton acceptor than hydroxide ion, which shows that alkoxides are stronger bases. For example, sodium ethoxide is a stronger base than sodium hydroxide.
The acidic character of alcohols is due to the polar O-H bond. An electron releasing group increases the electron density over the oxygen atom tending to decrease the polarity of O-H bond. This decreases the acid strength of alcohols decreases in the following order.


Obviously, the basic strength of their alkoxides follows the reverse order.
Alcohols acts as Bronsted bases as well. It is due to the presence of unshared electron pairs over oxygen, which makes alcohols proton aceptors.

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