Distinction between Primary, Secondary end Tertiary Alcohols Preparation and Properties
Distinction between Primary, Secondary end Tertiary Alcohols :
Primary, Secondary and Tertiary Alcohols can be distinguished by the following methods :
→ Lucas Test : Equimolar mixture of concentrated hydrochloric acid and anhydrous ZnCl2 is called Lucas reagent.
→ Primary, secondary and tertiary alcohol react with Lucas reagent with different rates and form respective chloride. Since the alkyl halides are insoluble in water, their formation is indicated by the appearance of white turbidity in the reaction mixture.
→ Tertiary alcohol reacts immediately with Lucas reagent and produces turbidity.
→ Secondary alcohol does not react immediately with Lucas reagent. It produces turbidity within five minutes.
→ Primary alcohol does not react at room temeperature and does not produces turbidity.
Victor Meyer Method : This method involves the following steps:
→ The given alcohol is treated with red phosphorus and iodine resulting in the formation of corresponding alkyl iodide.
- The alkyl iodide is treated with silver nitrite (AgNO2) to form corresponding nitroalkane.
- Reaction of nitroalkane with nitrous acid. (NaNO2 + HCl).
- The resulting solutions are made alkaline by addition NaOH or KOH.
- Formation of blood red colour indicates the primary alcohol.
- Formation of blue colour indicates the presence of secondary alcohol.
- If solution remains colourless then it indicates the presence of tertiary alcohol.
→ Esteritlcation : Esterification reaction is used to distinguish between primary, secondary and tertiary alcohols.
→ In this reaction alcohol reacts with carboxylic acid in the presence of acid catalyst to form ester.
Order of ease of various alcohols towards esterification is as follows:
Primary alcohol > Secondary alcohol > Tertiary alcohol
→ Oxidation Method : Primary, secondary and tertiary alcohol react with oxidising agents and form different products. hence, this method is used to ditinguish between them. Description of this method is given in chemical properties of alkanl.
→ Dehydrogenation : When vapours of alcohols are passed on red hot copper at 573 K primary and secondary alcohol get dehydrogenated to form aldehyde and ketone respectively whereas tertiary alcohol form alkene in these conditions. Description of chemical equation of the reaction is given in chemical properties of alkanol.