Experiment 18-Nitration of Methyl Benzoate

Topics: Electrophilic aromatic substitution, Sulfuric acid, Benzene Pages: 5 (1068 words) Published: February 4, 2015
Title: Nitration of Methyl Benzoate
Objective: To prepare methyl-3-nitrobenzene from nitration of methyl benzoate. Results and calculations:
Density =
1.094 g/ml =
Mass of methyl benzoate = 1.094 g/ml x 2.8 ml
= 3.0632 g
no. of mol of methyl benzoate =
= 0.022499 mol 1 mol of methyl benzoate produced 1 mol of methyl m-nitrobenzene. Therefore, 0.022499 mol of methyl benzoate produced 0.022499 mol of methl m-nitrobenzene. Theoretical mass of methyl m-nitrobenzene: 0.022499 mol x 181.14 g/mol = 4.0755 g Actual mass of methyl m-nitrobenzene: 2.9226 g

% yield: x 100%
= 71.72 %
72 %
melting point of methyl m-nitrobenzene: 78-82oC
Discussion:
Methyl m-nitrobenzoate is formed in this reaction rather that ortho or para isomers because of the ester group of the starting product of methylbenzoate. All strongly electron-withdrawing groups give predominantly the meta-isomer as product while the weakly deactivating halogens give predominantly give ortho- and para- isomers as products. The functional group of ester is an electron withdrawing group causing nitrobenzene (NO2) to become in the meta position. Thus NO2 is a deactivating group causing itself to be a meta director. Basically when look at the substituents that are attached to the starting benzene ring in order to figure out whether the reaction with be ortho or para directors or meta directors. If the substituents are electron withdrawing groups then it will be left with meta as the product but if the substituents are electron donating groups then the product will be ortho or para. It is much easier for a molecule such as a phenol to undergo nitration if compared to other molecules, where the hydroxyl group is an ortho-para director and an activator of the benzene ring. In this experiment, The nitration of methyl benzoate is a typical electrophile aromatic substitution that is done by adding methyl benzoate with nitric acid and sulphuric acid. From the reaction of nitric acid and sulphuric acid, nitronium ion was produced as an electrophile. The nucleophile in the reaction is methyl benzoate, which is the reactant in the reaction. The equation for producing nitronium ion is: HNO3 + 2 H2SO4  NO2+ + 2 H2SO4- + H3O+

The equation for producing methyl m-nitrobenzoate from methyl benzoate is:

As methyl benzoate is the electron rich nucleophile, it reacts with the electron deficient electrophile, which is the nitronium ion, NO2+, this process is named as nitration. As benzene has an extra electron, it can donate that electron to nitronium ion, given that the electron is given to the nitrogen atom, not the oxygen atom. The whole benzene ring has a total of three π- bond. After donating one of the electron to nitronium ion, one of the π- bond does not exist in the benzene ring anymore, therefore the other two π- bond are free to move around the benzene ring.

Nitronium ion, NO2+, which is the electrophile, is obtained from the nitric acid. When nitric acid and sulphuric acid reacts with each other, nitric acid which is the base was protonated by the strong sulphuric acid. The purpose of this reaction is only to produce nitronium ions, because sulphuric acid was only acts as a catalyst in the reaction as it was reformed as an ion at the end of the reaction. The function of sulphuric acid is only to protonate the methyl benzoate, thus forming an intermediate, which is arenium ion. The resonance stabilized arenium ion intermediate then transfers a proton to the basic bisulphate ion to give the final product, which is methyl-3-nitrobenzoate.

The equation that shows few possible outcomes of the nitration of methyl benzoate is:

The experiment was carried out after cooling the methyl benzoate solution concentrated sulphuric acid, and concentrated nitric acid to almost 0◦C to make sure...


References: EXPERIMENT 3 (Organic Chemistry II): Nitration of Aromatic Compounds: Preparation of methyl-m-nitrobenzoate. Available from:
< http://swc2.hccs.edu/pahlavan/2425L3.pdf>
Nitrating Methyl Benzoate: Electrophilic Aromatic Substitution. Available from:
< http://www.franklincollege.edu/pwp/lmonroe/Organic%20Chem/Methyl%20Benzoate.pdf>
Pavia, D.L., 2003, Nitration of Methyl Benzoate, Introduction to Organic Laboratory Techniques: A Small Scale Approach, Brooks/Cole, USA, pp. 352-357.
Schoffstall, A.M., Gaddis, B.A., Druelinger, M.L., 8 July 2003, Nitration of Methyl Benzoate, Microscale and Miniscale Organic Chemistry Laboratory Experiments, McGraw-Hill, pp. 304-309.
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