NITRATION OF METHYL BENZOATE (ELECTROPHILIC AROMATIC SUBSTITUITION)

Objectives

1)    To prepare and calculate the percentage yield of methyl m-nitrobenzoate by electrophilic aromatic substituition.

2)    To get the melting point of the product.

Introduction

            Aromatic substituition is electrophilic, due to high density in benzene ring.Benzene ring is one of components in most important natural products and other useful products. The species reacting with the aromatic ring is usually a positive ion or the end of a dipole.

            Nitration is one of the most important examples of electrophilic substituition.The electrophile in nitration is the nitronium ion which is generated from nitric acid by protonation and loss of water , using sulphuric acid as the dehydrating agent.The reaction is shown below :

HNO₃ + 2H₂SO₄              NO₂⁺ + H₃O⁺ + 2HSO₄^-

In this experiment we will put nitro group on a benzene ring which already has ester group attached to it.The actual electrophile in the reaction is the nitronium ion , which is generated in the reaction mixture using concentrated nitric acid and concentrated sulphuric acid.The equation has been shown below:

In this experiment , a cool solution of the aromatic ester that has been dissolved in sulphuric acid and nitric acid . This highly exothermic reaction is kept under control by cooling then the mixture is poured into ice.The solid product is isolated by filtration is isolated by filtration and recrystallizationfrom methanol which is very soluble. This is the mechanisms of for nitration of methyl benzoate:

Result and observation

Melting point for 1st= 75˚C - 78˚C

                           2nd= 76˚C - 78˚C

From the literature boling point which is melting point for methyl m-nitrobenzoate whic is 78-80˚C, we can conclude that the product that we get is methyl m-nitrobenzoate.

Mass of methyl benzoate=3.0500g

Mass  product=39.2225 g

Mass filter paper = 0.6963 g

Mass final product = 2.6996 g

The chemical equation :

C₆H₅CO₂CH₃ + H₂NO₃             C₆H₄CO₂CH₃NO₂ + H₂O

Number mole of C₆H₅CO₂CH₃

Molar mass of C₆H₅CO₂CH₃ = 136.1487

Mass of C₆H₅CO₂CH₃ = 3.0500g

Number of mole = 3.0500g / 136.1487

                          = 0.022 mol

1 mol of C₆H₅CO₂CH₃ needed to produce 1 mol of C₆H₄CO₂CH₃NO₂

0.022 mol of C₆H₅CO₂CH₃ needed to produce 0.022 mol of C₆H₄CO₂CH₃NO₂

Molar mass of C₆H₄CO₂CH₃NO₂ = 181.1463

The theoretical yield of C₆H₄CO₂CH₃NO₂ = 0.022 mol x 181.1463 g/mol

                                                                 = 3.9852 g

Actual yield = 38.5262 g

Percentage yield of product = (2.6996 g / 3.9852 g) x 100%

                                             = 67.74%

Discussion

            Nitration is an introduction of nitrogen dioxide into a chemical compound acid . In the process the methyl benzoate was nitrated to form a methyl m-nitro benzoate . The reagents were added very slow to avoid a vigrous reactions and the temperature was maintained low to avoid formation of dinitro product .

            In this experiment , electrophilic aromatic substituitions involved the replacement of a proton on an aromatic ring with an electrophile that becomes substituent. The solvent sulphuric acid protonates the methyl benzoate , creating the resonance stabilized arenium ion intermediate . The electron deficient nitronium ion reacts with the protonated intermidiate meta position . The ester group is the meta deactivator and the reaction takes place at the meta position because the ortho and para positions are destabilized by adjacent positives charges on the resonance structure .The major product is the meta product due to carboxyl and nitro groups both being powerful electron withdrawing groups.

            The actual yield methyl – 3- nitrobenzoate crude product is 2.6996 g while the theoretical yield is 3.9852 g  .The percentage yield that we get is 67.74%.The melting point is 75˚C - 78˚C and 76˚C - 78˚C , the value is closed to the literature value which is 78˚C .

            As we know sulphuric acid are extreamly corrosive and can cause severe burns while nitric acid is one of the strong oxidizing agent so we need to wear gloves while doing an experiment. Methanol is toxic and we need to use in well – ventiled space only for example fume board . All of the chemical material should be discarded properly in the container provided.

Conclusion

The methyl m-nitrobenzoate was prepared. The theoretical yield is 3.9852 g  while tha actual yield is 2.6996 g so we get the percentage yield is 67.74%. The melting point of our product is 75˚C - 78˚C and 76˚C - 78˚C. From the given physical constant we know that the literature melting point of methyl m-nitrobenzoate is 78 - 80˚C , so we can conclude that the product we get is methyl m-nitrobenzoate.