The preparation of 2 – (2’, 4’ – dinitrobenzyl) pyridine PDF

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The preparation of 2 – (2’, 4’ – dinitrobenzyl) pyridine...

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Name: Febin Xavier

Date:15/10/20

Experiment 3 – The preparation of 2 – (2’, 4’ – dinitrobenzyl) pyridine Introduction and Safety Data Experiment involves the electrophilic aromatic substitution in which nitration occurs to 2 – benzylpyridine. This in turn raises its pH level to 11 using diluter ammonia which yields 2 – (2’, 4’ – dinitrobenzyl) pyridine. As part of the experimental aim this is then recrystallised to produce the analytical sample. Analysis is done via FT – IR spectrum, in which the yield and melting point are recorded.

Chemical

Volume (mL)

Hazard

Sulfuric acid Benzylpyridine Nitric acid Ammonia Ethyl Acetate Sodium hydroxide

15 2.4 3.0 50 – 100 40 40

Corrosive Toxic, Irritant Corrosive, Oxidiser Corrosive, Toxic Flammable, Irritant Corrosive

Experimental Method: A solution of sulfuric acid (15 mL) is placed in an ice bath along with a magnetic stirrer. Benzylpyridine (2.4 mL) is added dropwise, maintaining a temperature below 10°C. This process is then repeated for fuming nitric acid (3.0 mL), once again maintaining the temperature. After addition mixture is allowed to stand at room temperature for 30 minutes. Once completed reaction mixture is heated in an 80°C water bath for 20 minutes. Mixture is then poured into a conical flask containing crushed ice (50 cm3) which is stirred in an ice bath. Using a separating funnel aqueous ammonia is added (50 – 100 mL) until the pH rises to ~9 – 10 and filter using a Buchner funnel. Ethyl acetate (40mL) & sodium hydroxide (40mL) is added to the solid and stirred using a magnetic stirrer until dissolved. Dry the organic layer using magnesium sulfate as the drying agent which is then followed by a rotary evaporator (40°C, vacuum). Product is then washed using cold methylated spirit and left to recrystalise. The sample is then observed under UV light and IR spectrum is recorded for analysis.

Name: Febin Xavier

Date:15/10/20

Results and Discussion:

Mass (g) Vial Jar Vial Jar + Product Product

Mass (g) Mr Moles

H2SO4+ 15 98.87 0.15

45.10 46.71 1.61 HNO3+ 3.0 63.01 0.048 LIMITING REAGEN T

NH3+ 80 17.01 4.70

C12H11N+ 2.4 169.01 0.014

C12H9N3O4+ 11.67 245.02 0.048

NH4+ 18.01

Theoretical yield = 11.67g Percentage yield = (actual yield/theoretical yield) x 100 (1.61/11.67) x 100 = 13.8 Therefore, percentage yield = 13.8% IR Spectrum

Absorption (cm-1) 1340.53 1521.84 3103.46

Functional group C – N (aromatic amine) N – O (nitro compound) N – H (stretching)

Observations During the experimental colour change was observed once ammonia was added to the acid mix which turned the solution bright yellow from clear yellow solution as it was heated at 80°C. under the UV – lamp the white / clear crystals turned black. Rotavapor flask Rotavapor flask + sample

Mass (g) 60.25 71.33

Conclusion: The experiment was successful as 2-(2’,4’ -dinitrobenzyl) pyridine was synthesised accurately and recrystalised to produce an analytical sample which helped determine the species formed evident via the infra-red spectrum through the absorption it

Name: Febin Xavier

Date:15/10/20

caused. The aims of the experiment were met and an accurate nitration reaction was completed during the process in the fume cupboard.

Supplementary Questions: (a) The pyridine ring is very electron poor in comparison to benzene ring. This is due to the nitrogen present in pyridine ring being an electron withdrawing group. Hence pyridine doesn’t undergo electrophilic substitution easily. (b) Generating the electrophile:

NH4

(c)

Name: Febin Xavier

Date:15/10/20

d) Benzonitrile has an electron withdrawing group so nitration would occur in the meta positions whereas if the substrate used was methoxybenzene then it has an electron donating group shifting the electron density to the ring which favours ortho and para positions. (e) Phenol consists of an electron donating OH group whereas benzoic acid has an electron withdrawing carbonyl group attached to itself, meaning phenol is more susceptible to nitration than benzoic acid. The ring in benzoic acid has less electron density therefore less susceptible to an electrophilic attack.

Appendix: Attached Spectra...