[orgoclear]

Paragraph (Questions may have multiple answers)

Nitration reaction is classified under electrophilic substitution where the electrophile is NO2+. The reagent used in this reaction is conc. HNO3 + conc. H2SO4.

Q1. What is the role of conc. H2SO4 in this reaction?
(a) It is a good dehydrating agent so, it can remove water to form the corresponding nitro- compound
(b) In presence of it, HNO3 behaves as a base and can give OH- ion to form the electrophile NO2+
(c) conc. H2SO4, by giving H+ facilitates the formation of electrophile
(d) In its presence, the solvent becomes polar and the reaction is faster

Q2. A student A tries to nitrate phenol by taking phenol and conc. HNO3. Another student B performs the same reaction by taking phenol, conc. HNO3 + conc. H2SO4.
Which of the following is/are correct?
(a) The student A will not get any product (if he gets any it will be very less)
(b) The student B gets two products
(c) The student A gets two products
(d) None of these

Q3. Referring to the above question, which of the following is/are correct?
(a) The rate of reaction for student A is negligible
(b) The rate of reaction for student A is less than but comparable to that for B
(c) The rate of reaction for student A is more than that for student B
(d) None of these

Q4. A third student C takes the following: phenol, conc. HNO3 and heats the mixture.

(a) He obtains only one compound
(b) He doesnt obtain any product
(c) He gets two products
(d) Heating will cause explosion

the answers given were:
1. bc
2. bc
3. c
4. a

for Q2. i thought that there wont be any reaction for student A as H2SO4 is not present to generate the nucleophile but in the answer to that and the next question, it says that student A will have higher yield?. I am really confused about that

any help in this direction would be great

[nj_bartel]

acid/base reaction

phenol as the base

[orgoclear]

acid/base reaction

phenol as the base

can you please elaborate a bit more on that?

Our prof. said that the phenol will provide H+ that will help in producing NO2+
But this doesnt account for the rate of reaction for student A (higher yield)

[orgopete]

Since Q1 cannot be b, should be presume that none of those answers are correct?

[408]

Phenol will actually oxidize if attempted to be nitrated with mixed acids...

[orgoclear]

i think Q1. is (b) also.  because H2SO4 is a stronger acid than HNO3 and in its presence there will be common ion effect which will further reduce the acidity consequently increasing the basicity. In the actual mechanism too,
H+ is given by H2SO4 which adds to the -O-H in HNO3 producing -OH2+ which leaves the system, i.e. OH- has been removed from nitric acid. So, according to Lowry-Bronsted theory it acted as a base

[Arctic-Nation]

Phenol will actually oxidize if attempted to be nitrated with mixed acids...

True. While the answers given can be assumed to be correct in an entry-level chemistry course, direct nitration of phenols usually results in the formation of tars.

On top that, to say that nitric acid 'gives' OH- is very, very wrong. The dehydration of nitric acid to form nitronium ions in acidic media does not involve in any way hydroxide ions.