m-Nitromethylbenzoate Synthesis: Lab Experiment on Aromatic Substitution - Prof. Anthony J, Lab Reports of Organic Chemistry

Download m-Nitromethylbenzoate Synthesis: Lab Experiment on Aromatic Substitution - Prof. Anthony J and more Lab Reports Organic Chemistry in PDF only on Docsity! Synthesis of m-nitromethylbenzoate Purpose: To synthesize a disubstituted benzene ring by electrophilic aromatic substitution Background: The addition of a nitro group to a benzene ring is indicative of a type of reaction called “electrophilic aromatic substitution”. When there is a group attached to the benzene ring in which the atom directly attached to the ring bears positive character then the second group being added to the ring will add in the meta position. In the nitration of methylbenzoate the carbon atom of the carbonyl bears positive character. The first step of this mechanism is the generation of NO2+. This takes place by reacting nitric acid HNO3 with sulfuric acid H2SO4 (Scheme 1). The addition step results from a pair of electron on the benzene ring attacking the nitro group resulting in the formation of an allylic cation. Sulfate, which was generated in the formation of the nitro group (Scheme 1), pulls off a proton from the benzene ring to rearomatize the ring (Scheme 1). HNO3 + 2H2SO4 NO2 + + 2HSO4 - + H3O + CH3CO O NO2 + CH3CO O NO2 H HSO4 - CH3CO O NO2 C OCH3O Procedure: 1. Add 0.3 mL of conc. Sulfuric acid to a large test tube immersed in an ice bath. 2. Cool in ice to 0-10 oC and then add 0.153 g of methylbenzoate. 3. Prepare a mixture of 0.1 mL of cold conc. Sulfuric acid and 0.1 mL of conc. Nitric acid (add cold sulfuric acid to cold nitric acid). 4. Stir to mix the solution completely. 5. Maintain the temperature between 5-15 oC. 6. After the addition is complete, warm to room temperature and allow to stand for 15 min. 7. Pour onto 1 g of ice in a 10 mL beaker. 8. Stir and allow the product to solidify. 9. Collect on a Hirsch funnel and wash with water (2 x 1 mL), then two .15 mL portions of ICE COLD methanol. Use Ranin pipets for this part. 10. Save a small sample of the crude and recrystallize the remainder form an equivalent weight of methanol. 11. Compare the mp of the crude to that of the recrystallized material. 12. Calculate the theoretical and Experimental yields. 13. Calculate the percent yield. 14. Interpret spectra provided. Pre Laboratory Questions 1. Explain why the nitration occurs in the meta position. 2. Why is it important to keep the reaction mixture cold? 3. What is the function of the sulfuric acid? 1. Name: Sulfuric Acid a. Molecular Formula: H2SO4 b. Formula Weight: 98.08g/mole c. bp: 330oC d. mp: 10.36 oC e. density: 1.840g/mL f. solubility: Water, alcohol g. refractive index, n, : 1.4175 h. Dangers: Highly Toxic 2. Name: Methyl Benzoate a. Molecular Formula: C8H8O2 b. Formula Weight: 136.15 g/mole c. bp: 199.5 oC d. mp: -12.1 oC e. density: 1.0933g/mL f. solubility: Alcohol, ether g. refractive index, n, : 1.5205 h. Dangers: toxic