(a) (i) Phenol to Anisole
Through williamson synthesis phenols can be converted to anisole
(ii) Ethanol to Propan-2-ol
By the use og Grignard reagent ketones can be reduced to sec- alcohols
(b) Mechanism of ethanol to ethene
The mechanism of acid dehydration of ethanol to yield ethene involves the following three steps:
Protonation of ethanol to form ethyl oxonium ion:
Formation of carbocation (rate determining step):
Elimination of a proton to form ethene:
The acid consumed in step 1 is released in Step 3. After the formation of ethene, it is removed to shift the equilibrium in a forward direction.
(c) The increased reactivity of phenols towards electrophilic substitution reactions compared to benzene is due to the lone pair of p-orbital electrons on the oxygen atom in the phenol group. The electron pair is delocalised into the ring structure, activating the ring. This increases the electron density of the molecule and hence influence electrophiles to attack over the ring. Therefore, electrophilic substitution can then take place.
(a) (i) There is intramolecular hydrogen bonding present in o-nitrophenol which is much weaker than intermolecular hydrogen bonding in p-nitrophenol. Therefore, o-nitrophenol is steam volatile due to absence of intermolecular attractions.
(ii) if the alkyl halide is primary than ether is formed through SN2 reaction mechanism.
But if the alkyl haide is tertiary then alkene is formed instead of ether E1 elimination mechanism
(ii) Friedel Crafts Alkylation of Phenols
(c) Chemical test to distinguish between phenol and ethanol
Phenols are unsaturated aromatic alcohols while ethanol is saturated aliphatic alcohol.
1. Phenol has benzene ring, it undergoes diazo coupling reaction, while ethanol doesn’t give this reaction.
2. Phenol decolourise bromine solution and therefore proves the unsaturation in phenol, ethanol doesn’t give this test.
3. Ethanol give iodoform test and forms the yellow precipitate, phenol doesn’t give this test.
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