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How does sulphuric acid affect isomer ratio in nitrating...
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How does sulphuric acid affect isomer ratio in nitrating...
The main purpose of using sulfuric acid in nitration of aromatic compounds is the production of the electrophile nitronium ion (+NO2) by the reaction: H2SO4 + HNO3---> +NO2 + HSO4- + H2O However, when the benzene ring has an activating group (e.g. –CH3), then dinitration or polynitration occurs. One way to control such reaction is to use proper number of moles (i.e. one reactant is limiting & the other reactant in excess). If the benzene ring contains strongly activating group (e.g. –OH), then the use of H2SO4 is cancelled & one doesn't use conc. or fuming acid. Instead, dilute nitric acid is used & it can produce the electrophile by the reaction: 2HNO3 ---> +NO2 + NO3- + H2O In such case, there will be, e.g., dinitration but one product "usually the para-" derivative will have more % yield than the other "usually the ortho-" derivative.
The main purpose of using sulfuric acid in nitration of aromatic compounds is the production of the electrophile nitronium ion (+NO2) by the reaction: H2SO4 + HNO3---> +NO2 + HSO4- + H2O However, when the benzene ring has an activating group (e.g. –CH3), then dinitration or polynitration occurs. One way to control such reaction is to use proper number of moles (i.e. one reactant is limiting & the other reactant in excess). If the benzene ring contains strongly activating group (e.g. –OH), then the use of H2SO4 is cancelled & one doesn't use conc. or fuming acid. Instead, dilute nitric acid is used & it can produce the electrophile by the reaction: 2HNO3 ---> +NO2 + NO3- + H2O In such case, there will be, e.g., dinitration but one product "usually the para-" derivative will have more % yield than the other "usually the ortho-" derivative.
About concentrate H2SO4―HNO3 mixed aq. solutions: Nitronium ion generation reaction occurs between both acids: (i) H2SO4 + HNO3 ⇌ HSO4- + NO2+ + H2O. The nitronium cation can combine with the bisulfate anion to to yield nitrosulfuric acid (nitronium hydrogen sulfate); a strong oxidizing agent: (ii) NO2+ + HSO4- ⇌ NO2HSO4. The nitronium ion can also combine with the nitrate anion, while dinitrogen pentoxide gas can evolve from the solution ― more intensely if heated: (iii) NO2+ + NO3- ⇌ N2O5(aq) ⇌ N2O5(g)↑. This gas can react in gas phase with water vapour: (iv) N2O5(g) + H2O(g) ⇌ 2HNO3(g). Nitronium hydrolysis, and that of N2O5(aq), also occurs: (v) NO2++ 3H2O ⇌ NO3- + 2H3O+; (vi) N2O5(aq) + H2O ⇌ 2HNO3.
About concentrate H2SO4―HNO3 mixed aq. solutions: Nitronium ion generation reaction occurs between both acids: (i) H2SO4 + HNO3 ⇌ HSO4- + NO2+ + H2O. The nitronium cation can combine with the bisulfate anion to to yield nitrosulfuric acid (nitronium hydrogen sulfate); a strong oxidizing agent: (ii) NO2+ + HSO4- ⇌ NO2HSO4. The nitronium ion can also combine with the nitrate anion, while dinitrogen pentoxide gas can evolve from the solution ― more intensely if heated: (iii) NO2+ + NO3- ⇌ N2O5(aq) ⇌ N2O5(g)↑. This gas can react in gas phase with water vapour: (iv) N2O5(g) + H2O(g) ⇌ 2HNO3(g). Nitronium hydrolysis, and that of N2O5(aq), also occurs: (v) NO2++ 3H2O ⇌ NO3- + 2H3O+; (vi) N2O5(aq) + H2O ⇌ 2HNO3.
in case of o-xylene nitration, increasing acidity substantially increases the proportion of reaction at C4, and to a smaller degree that at C3, both at the expense of ipso-nitration. The estimated possible percentage of initial attack at Cipso, C3 and C4 are 64, 11and 25 with 50%; 55, 15 and 30 with 60% and 45, 18 and 37% with 70% H2SO4. Barnett et al observe that above the acidity of 72% H2SO4 at which wheland intermediate rearranges rapidly it favours the formation of 3-nitro-o-xylene. Hence the ratio of 3-nitro-o-xylene to 4-nitro-o-xylene can change depending upon the acidity at that instant,
in case of o-xylene nitration, increasing acidity substantially increases the proportion of reaction at C4, and to a smaller degree that at C3, both at the expense of ipso-nitration. The estimated possible percentage of initial attack at Cipso, C3 and C4 are 64, 11and 25 with 50%; 55, 15 and 30 with 60% and 45, 18 and 37% with 70% H2SO4. Barnett et al observe that above the acidity of 72% H2SO4 at which wheland intermediate rearranges rapidly it favours the formation of 3-nitro-o-xylene. Hence the ratio of 3-nitro-o-xylene to 4-nitro-o-xylene can change depending upon the acidity at that instant,
Dear Yachita, Inside the answer you will get the information needed. If the reactant is benzene or monosubstituted benzene, we will use nitric acid/sulfuric acid. If there is a strongly activating group (e.g. -OH, -OR, -NH2), there is no need for sulfuric acid, and just diluted nitric acid is used. I DO NOT ADVICE USING TOLUENE. Take for example, nitrobenzene (the nitro is deactivating group): carry out nitration using nitric acid/sulfuric acid, then conc. nitric acid, then dil.nitric acid & you will observe a change in the rate of the reaction. The mechanism is the same(i.e. electrophilic aromatic substitution) & the electrophile in all 3 cases is the nitronium ion.
Dear Yachita, Inside the answer you will get the information needed. If the reactant is benzene or monosubstituted benzene, we will use nitric acid/sulfuric acid. If there is a strongly activating group (e.g. -OH, -OR, -NH2), there is no need for sulfuric acid, and just diluted nitric acid is used. I DO NOT ADVICE USING TOLUENE. Take for example, nitrobenzene (the nitro is deactivating group): carry out nitration using nitric acid/sulfuric acid, then conc. nitric acid, then dil.nitric acid & you will observe a change in the rate of the reaction. The mechanism is the same(i.e. electrophilic aromatic substitution) & the electrophile in all 3 cases is the nitronium ion.
Nitration radical +NO2 can exist only in sulfuric acid which concentration is 85% or greather. Belov that concentration some reaction may occur bat dis reaction is not reaction of nitration. You don’t need use fume nitric acid. Use only water solution of KNO3. You can’t obtain only one isomer.
Nitration radical +NO2 can exist only in sulfuric acid which concentration is 85% or greather. Belov that concentration some reaction may occur bat dis reaction is not reaction of nitration. You don’t need use fume nitric acid. Use only water solution of KNO3. You can’t obtain only one isomer.
The main purpose of using sulfuric acid in nitration of aromatic compounds is the production of the electrophile nitronium ion (+NO2) by the reaction:
H2SO4 + HNO3---> +NO2 + HSO4- + H2O
However, when the benzene ring has an activating group (e.g. –CH3), then dinitration or polynitration occurs. One way to control such reaction is to use proper number of moles (i.e. one reactant is limiting & the other reactant in excess).
If the benzene ring contains strongly activating group (e.g. –OH), then the use of H2SO4 is cancelled & one doesn't use conc. or fuming acid. Instead, dilute nitric acid is used & it can produce the electrophile by the reaction:
2HNO3 ---> +NO2 + NO3- + H2O
In such case, there will be, e.g., dinitration but one product "usually the para-" derivative will have more % yield than the other "usually the ortho-" derivative.
The main purpose of using sulfuric acid in nitration of aromatic compounds is the production of the electrophile nitronium ion (+NO2) by the reaction:
H2SO4 + HNO3---> +NO2 + HSO4- + H2O
However, when the benzene ring has an activating group (e.g. –CH3), then dinitration or polynitration occurs. One way to control such reaction is to use proper number of moles (i.e. one reactant is limiting & the other reactant in excess).
If the benzene ring contains strongly activating group (e.g. –OH), then the use of H2SO4 is cancelled & one doesn't use conc. or fuming acid. Instead, dilute nitric acid is used & it can produce the electrophile by the reaction:
2HNO3 ---> +NO2 + NO3- + H2O
In such case, there will be, e.g., dinitration but one product "usually the para-" derivative will have more % yield than the other "usually the ortho-" derivative.
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About concentrate H2SO4―HNO3 mixed aq. solutions:
Nitronium ion generation reaction occurs between both acids: (i) H2SO4 + HNO3 ⇌ HSO4- + NO2+ + H2O. The nitronium cation can combine with the bisulfate anion to to yield nitrosulfuric acid (nitronium hydrogen sulfate); a strong oxidizing agent: (ii) NO2+ + HSO4- ⇌ NO2HSO4. The nitronium ion can also combine with the nitrate anion, while dinitrogen pentoxide gas can evolve from the solution ― more intensely if heated: (iii) NO2+ + NO3- ⇌ N2O5(aq) ⇌ N2O5(g)↑. This gas can react in gas phase with water vapour: (iv) N2O5(g) + H2O(g) ⇌ 2HNO3(g). Nitronium hydrolysis, and that of N2O5(aq), also occurs: (v) NO2++ 3H2O ⇌ NO3- + 2H3O+; (vi) N2O5(aq) + H2O ⇌ 2HNO3.
About concentrate H2SO4―HNO3 mixed aq. solutions:
Nitronium ion generation reaction occurs between both acids: (i) H2SO4 + HNO3 ⇌ HSO4- + NO2+ + H2O. The nitronium cation can combine with the bisulfate anion to to yield nitrosulfuric acid (nitronium hydrogen sulfate); a strong oxidizing agent: (ii) NO2+ + HSO4- ⇌ NO2HSO4. The nitronium ion can also combine with the nitrate anion, while dinitrogen pentoxide gas can evolve from the solution ― more intensely if heated: (iii) NO2+ + NO3- ⇌ N2O5(aq) ⇌ N2O5(g)↑. This gas can react in gas phase with water vapour: (iv) N2O5(g) + H2O(g) ⇌ 2HNO3(g). Nitronium hydrolysis, and that of N2O5(aq), also occurs: (v) NO2++ 3H2O ⇌ NO3- + 2H3O+; (vi) N2O5(aq) + H2O ⇌ 2HNO3.
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in case of o-xylene nitration, increasing acidity substantially increases the proportion of reaction at C4, and to a smaller degree that at C3, both at the expense of ipso-nitration. The estimated possible percentage of initial attack at Cipso, C3 and C4 are 64, 11and 25 with 50%; 55, 15 and 30 with 60% and 45, 18 and 37% with 70% H2SO4. Barnett et al observe that above the acidity of 72% H2SO4 at which wheland intermediate rearranges rapidly it favours the formation of 3-nitro-o-xylene. Hence the ratio of 3-nitro-o-xylene to 4-nitro-o-xylene can change depending upon the acidity at that instant,
in case of o-xylene nitration, increasing acidity substantially increases the proportion of reaction at C4, and to a smaller degree that at C3, both at the expense of ipso-nitration. The estimated possible percentage of initial attack at Cipso, C3 and C4 are 64, 11and 25 with 50%; 55, 15 and 30 with 60% and 45, 18 and 37% with 70% H2SO4. Barnett et al observe that above the acidity of 72% H2SO4 at which wheland intermediate rearranges rapidly it favours the formation of 3-nitro-o-xylene. Hence the ratio of 3-nitro-o-xylene to 4-nitro-o-xylene can change depending upon the acidity at that instant,
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Dear Yachita,
Inside the answer you will get the information needed. If the reactant is benzene or monosubstituted benzene, we will use nitric acid/sulfuric acid. If there is a strongly activating group (e.g. -OH, -OR, -NH2), there is no need for sulfuric acid, and just diluted nitric acid is used. I DO NOT ADVICE USING TOLUENE. Take for example, nitrobenzene (the nitro is deactivating group): carry out nitration using nitric acid/sulfuric acid, then conc. nitric acid, then dil.nitric acid & you will observe a change in the rate of the reaction. The mechanism is the same(i.e. electrophilic aromatic substitution) & the electrophile in all 3 cases is the nitronium ion.
Dear Yachita,
Inside the answer you will get the information needed. If the reactant is benzene or monosubstituted benzene, we will use nitric acid/sulfuric acid. If there is a strongly activating group (e.g. -OH, -OR, -NH2), there is no need for sulfuric acid, and just diluted nitric acid is used. I DO NOT ADVICE USING TOLUENE. Take for example, nitrobenzene (the nitro is deactivating group): carry out nitration using nitric acid/sulfuric acid, then conc. nitric acid, then dil.nitric acid & you will observe a change in the rate of the reaction. The mechanism is the same(i.e. electrophilic aromatic substitution) & the electrophile in all 3 cases is the nitronium ion.
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thank you for your kind reply, but here I an talking about same reactant, same reaction condition, varying just nitrating agent.
thank you for your kind reply, but here I an talking about same reactant, same reaction condition, varying just nitrating agent.
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Nitration radical +NO2 can exist only in sulfuric acid which concentration is 85% or greather. Belov that concentration some reaction may occur bat dis reaction is not reaction of nitration. You don’t need use fume nitric acid. Use only water solution of KNO3. You can’t obtain only one isomer.
Nitration radical +NO2 can exist only in sulfuric acid which concentration is 85% or greather. Belov that concentration some reaction may occur bat dis reaction is not reaction of nitration. You don’t need use fume nitric acid. Use only water solution of KNO3. You can’t obtain only one isomer.
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