Write preparation method of phenol and its physical and chemical properties.
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The cumene process (cumene-phenol process, Hock process) is an industrial process for developing phenol and acetone from benzene and propylene. The term stems from cumene (isopropyl benzene), the intermediate material during the process.
This process converts two relatively cheap starting materials, benzene and propylene, into two more valuable ones, phenol and acetone. Other reactants required are oxygen from air and small amounts of a radical initiator.
STEPS:
1. Cumene is formed in the gas-phase Friedel-Crafts alkylation of benzene by propylene. Benzene and propylene are compressed together to a pressure of 30 standard atmospheres at 250 °C (482 °F) in presence of a catalytic Lewis acid. Phosphoric acid is often favored over aluminiumhalides. Cumene is oxidized in air, which removes the tertiary benzylic hydrogen from cumene and hence forms a cumene radical.
2.The cumene radical then bonds with an oxygen molecule to give cumene peroxide radical, which in turn forms cumene hydroperoxide (C6H5C(CH3)2-O-O-H) by abstracting a benzylic hydrogen from another cumene molecule. This latter cumene converts into cumene radical and feeds back into subsequent chain formations of cumene hydroperoxides. A pressure of 5 atm is used to ensure that the unstable peroxide is kept in liquid state.
3.Cumene hydroperoxide is then hydrolysed in an acidic medium (the Hock rearrangement) to give phenol and acetone.
Physical properties:
1.Melting and boiling points:
It is useful to compare phenol's melting and boiling points with those of methylbenzene (toluene). Both molecules contain the same number of electrons and are a very similar shape. That means that the intermolecular attractions due to van der Waals dispersion forces are going to be very similar.
2.Solubility in water
Phenol is moderately soluble in water - about 8 g of phenol will dissolve in 100 g of water. If you try to dissolve more than this, you get two layers of liquid. The top layer is a solution of phenol in water, and the bottom one a solution of water in phenol. Phenol is somewhat soluble in water because of its ability to form hydrogen bonds with the water.
Chemical properties:
Reactions of the benzene ring :
(a) Hydrogenation
(b) Oxidation to Quionones
(c) Electrophilic Substitution
The —OH and even more so the —O(phenoxide) are strongly activating ortho ,para – directing
special mild conditions are needed to achieve electrophilic monosubstituion in phenols because their high reactivity favors both polysubstitution and oxidation.
(i) Halogenation
Monobromination is achieved with nonpolar solvents such as CS2 to decrease the electrophilicity of Br2 and also to minimized phenol ionization.
(ii) Nitrosation
(iii) Nitration
Low yields of p- nitrophenol are obtained from direct nitration of PhOH because of ring oxidation. A better synthesis method is
(iv) Sulfonation
(v) Diazonium salt coupling to form azophenols
Coupling (G in ArG is an electron – releasing group)
Hope it helps you
The cumene process (cumene-phenol process, Hock process) is an industrial process for developing phenol and acetone from benzene and propylene. The term stems from cumene (isopropyl benzene), the intermediate material during the process.
This process converts two relatively cheap starting materials, benzene and propylene, into two more valuable ones, phenol and acetone. Other reactants required are oxygen from air and small amounts of a radical initiator.
STEPS:
1. Cumene is formed in the gas-phase Friedel-Crafts alkylation of benzene by propylene. Benzene and propylene are compressed together to a pressure of 30 standard atmospheres at 250 °C (482 °F) in presence of a catalytic Lewis acid. Phosphoric acid is often favored over aluminiumhalides. Cumene is oxidized in air, which removes the tertiary benzylic hydrogen from cumene and hence forms a cumene radical.
2.The cumene radical then bonds with an oxygen molecule to give cumene peroxide radical, which in turn forms cumene hydroperoxide (C6H5C(CH3)2-O-O-H) by abstracting a benzylic hydrogen from another cumene molecule. This latter cumene converts into cumene radical and feeds back into subsequent chain formations of cumene hydroperoxides. A pressure of 5 atm is used to ensure that the unstable peroxide is kept in liquid state.
3.Cumene hydroperoxide is then hydrolysed in an acidic medium (the Hock rearrangement) to give phenol and acetone.
Physical properties:
1.Melting and boiling points:
It is useful to compare phenol's melting and boiling points with those of methylbenzene (toluene). Both molecules contain the same number of electrons and are a very similar shape. That means that the intermolecular attractions due to van der Waals dispersion forces are going to be very similar.
2.Solubility in water
Phenol is moderately soluble in water - about 8 g of phenol will dissolve in 100 g of water. If you try to dissolve more than this, you get two layers of liquid. The top layer is a solution of phenol in water, and the bottom one a solution of water in phenol. Phenol is somewhat soluble in water because of its ability to form hydrogen bonds with the water.
Chemical properties:
Reactions of the benzene ring :
(a) Hydrogenation
(b) Oxidation to Quionones
(c) Electrophilic Substitution
The —OH and even more so the —O(phenoxide) are strongly activating ortho ,para – directing
special mild conditions are needed to achieve electrophilic monosubstituion in phenols because their high reactivity favors both polysubstitution and oxidation.
(i) Halogenation
Monobromination is achieved with nonpolar solvents such as CS2 to decrease the electrophilicity of Br2 and also to minimized phenol ionization.
(ii) Nitrosation
(iii) Nitration
Low yields of p- nitrophenol are obtained from direct nitration of PhOH because of ring oxidation. A better synthesis method is
(iv) Sulfonation
(v) Diazonium salt coupling to form azophenols
Coupling (G in ArG is an electron – releasing group)
Hope it helps you
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