and HCl. PCC O H O Secondary alcohols are oxidised to ketones by chromic anhyride (CrO ). Tertiary alcohols do not undergo oxidation reaction. Under strong reaction conditions such as strong oxidising agents (KMnO ) and elevated temperatures, cleavage of various C-C bonds takes place and a mixture of carboxylic acids containing lesser number of carbon atoms is formed.
When the vapours of a primary or a secondary alcohol are passed over heated copper at K, dehydrogenation takes place and an aldehyde or a ketone is formed while tertiary alcohols undergo dehydration. Biological oxidation of methanol and ethanol in the body produces the corresponding aldehyde followed by the acid. At times the alcoholics, by mistake, drink ethanol, mixed with methanol also called denatured alcohol. In the body, methanol is oxidised first to methanal and then to methanoic acid, which may cause blindness and death.
A methanol poisoned patient is treated by giving intravenous infusions of diluted ethanol. The enzyme responsible for oxidation of aldehyde (HCHO) to acid is swamped allowing time for kidneys to excrete methanol. (c) Reactions of phenols Following reactions are shown by phenols only. .
Electrophilic aromatic substitution In phenols, the reactions that take place on the aromatic ring are electrophilic substitution reactions (Unit , Class XI). The –OH group attached to the benzene ring activates it towards electrophilic substitution. Also, it directs the incoming group to ortho and para positions in the ring as these positions become electron rich due to the resonance effect caused by –OH group. The resonance structures are shown under acidity of phenols.
Common electrophilic aromatic substitution reactions taking place in phenol are as follows: (i) Nitration: With dilute nitric acid at low temperature ( K), phenol yields a mixture of ortho and para nitrophenols. The ortho and para isomers can be separated by steam distillation. o -Nitrophenol is steam volatile due to intramolecular hydrogen bonding while p -nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the association of molecules. With concentrated nitric acid, phenol is converted