Alcohols Phenols and Ethers

Riemer Tiemann Reaction : -
When phenol is treated with chloroform in presence of aqueous sodium or potassium hydroxide at 340K followed by hydrolysis of the resulting product gives 2-hydroxybenzaldehyde as the major product. This reaction is called Reimer-Tiemann reaction.

Mechanism of Riemer Tiemann reaction

Hydroboration Oxidation Reaction: -

Diborane (B2H6) is an electron deficient molecule. Therefore it acts as an electrophile and reacts with alkenes to form trialkylboranes which upon subsequent oxidation with alkaline H2O2 give alcohols.

B2H6 ⟶ 2BH3

Acidic Character Sequence Compiled for JEE Advanced & Neet

-water is a stronger acid than alcohol (reciprocate - alkoxide is stronger base than hydroxide)

-acidic strength of alcohols = 3° < 2° < 1° (Primary alcohols are strongest amongst 1° 2° 3°)

-acidic strength of Phenols, Carboxylic acids and carbonic acids (Alcohols<Phenols<Carbonic Acids<Carboxylic Acids)

-Electron withdrawing group increases acidic character of Phenols (EWG - NO2, -CN, -X)

-Electron donating group decreases acidic character of Phenols (EDG - NH2, -OR (alkoxy), -R (alkyl) )

acidic character sequence : v important (lower pKa value higher will be the acidic character)

2,4,6 -Trinitrophenol 0.71 > 2,4 - Dinitrophenol 4.0 > 4-Nitrophenol 7.15 > 2-Nitrophenol 7.23 > 3-Nitrophenol 8.40 > m-Methoxyphenol 9.65 > m-Aminophenol 9.87 > Phenol 9.98 = o-Methoxyphenol > m-Cresol 10.08 > p-Cresol 10.04 > p-Methoxyphenol 10.21 > o-Cresol 10.28 >

o-Halophenol > m-Halophenol > p-Halophenol

o-Chloropheno > o-Bromophenol > o-Iodophenol > o-Fluorophenol

Main Sequence : - 2,4,6 -Trinitrophenol (pKa0.71) > 2,4 - Dinitrophenol (pKa4.0) > 4-Nitrophenol (pKa7.15) > 2-Nitrophenol (pKa7.23) > o-Chlorophenol (pKa8.11) > o-Bromophenol (pKa8.39 > 3-Nitrophenol (pKa8.40) > o-Iodophenol (pKa8.48) > o-Fluorophenol (pKa8.81)> m-Methoxyphenol (pKa9.65) > m-Aminophenol (pKa9.87) > Phenol (pKa9.98) = o-Methoxyphenol (pKa9.98) > m-Cresol (pKa10.08) > p-Cresol (pKa10.04) > p-Methoxyphenol (pKa10.21) > o-Cresol (pKa10.28)

Q.Arrange the following compounds in increasing order of their acid strength: propan-1-ol, 2,4,6-trinitrophenol, 4-nitrophenol, 3-nitrophenol, 3,5-dinitrophenol, phenol, 4-methylphenol (p-cresol), 4-methoxyphenol.

Ans. propan-1-ol < 4-methoxyphenol < 4-methylphenol < phenol < 3-nitrophenol < 4-nitrophenol < 3,5-dinitrophenol < 2,4,6-trinitrophenol.

Reaction with carboxylic acids:

Alcohols react with carboxylic acids, in presence of a few drops of conc.H2SO4 or dry HCl gas as catalyst, to form esters. This reaction which is slow and reversible is called esterification. When HCl gas is used as a catalyst, the reaction is usually referred to as Fischer-Speier esterification.