Question

the weight if the initial product was 3.4 grams of methyl benzoate.

Who |o yald foR 3.91SSg st prodoct nd product 2.14143 EXPERIMENTAL PROCEDURE SAFETY WEAR nitrile gloves for this experiment. The nitrating moture of sulfuric acidnitric acid (1:1) is a very strong acid system. Do not allow it to come in contact with your skin or clothing. It will cause acid burns if it comes in contact with your skin (and holes an your clothes). Wash any affected area immediately with cold water and apply 0.6 M sodium bicarbonate solution (this works for clothes, too). Even short exposure to nitric acid will cause the protein in vour skin to turn vellow; the color willl eventually wear off (consider it to be a non-permanent tattoo). Concentrated acid can cause permanent scarring if not removed from skin immediately Methanol and methyl benz0ate are volatile irritants. Methyl meta-nitrobenzoate, is a strong irritant; avoid contact with your product. Wash your hands with soap and water after any contact. Methyl para-nitrobenzoate, even though it is expected to be d minor product, is a cancer suspect agent. You can minimize your exposure to this by placing a piece of transparent tape over your TLC plate after you have marked it. You will be using a low-power UV lamp to visualize your TLC plates. Even though the hazard is low, do not stare into the lamp, as prolonged exposure can cause eye and vi- sion damage. The powder on the TLC plate is an abrasive (also used in sandblasting); wash your hands after handling the plate, This powder is an irritant and can scratch your corneas should it get into your eves. Use of tape to cover the TLC plate will also minimize your exposure to the abrasive silica gel. Half-fill your 150-mL and 250-mL beakers with ice for use later. Use the auto-pipettor to add 7 mL of concentrated sulfuric acid to a dry 50-mL. Erlenmeyer flask containing a large stir bar, and cool the flask in the larger ice-water bath (make sure this flask does not tip over). Transfer, using the other auto-pipettor, 5 ml. of the sulfuric acid-nitric acid (1:1) mixture to a medium test tube and place it in the smaller ice-water bath. Measure and add 3.4 g (d = 1.09 g/mL) of methyl benzoate to the Erlenmeyer flask con- taining sulfuric acid with swirling. Now use a pipet to add dropwise the cooled, mixed acids to the methyl benzoate solution over about three minutes. Swirl the mixture in the ice-water bath during the addition. Place the flask on the small stirrer and allow the reaction mixture to stir and warm to room temperature. Continue stirring at room temperature for about 10 minutes. While the reaction is stirring, begin warming the heater-stirrer, set at the very back of the mini-hood, at a setting of 4-5. DO NOT PLACE YOUR REACTION MIXTURE ON THE HEATER-STIRRER. Also, place about 6 mL of methanol in a 25-mL Erlenmeyer flask and cool it in ice placed in a 100-mL plastic beaker. After completion of the stirring of the reaction mixture at room temperature, slowly pour it into about 25 g of ice in the 150-ml beaker. (Note: If the ice machine produces large cubes, you will need to break these into smaller pieces.) Mix the slurry with a plas- tic stir rod, breaking up any large clumps of organic product, until the ice has melted. Collect the solid product by vacuum filtration (after all ice has melted). Crush the col- lected crystals carefully with a spatula before washing. Wash the crystals four to five E the exeeriment, you do wenr an of KT UNT 2 Experimental Proceddares and Laboratory Reports Electrophilic Aromatic Subtitution The Nitration of Methyl Benoate NOTES NOTES nem ompaaack - c OCH oCH H Desblied resonance stchure Resonance delocaliaon of charge Figure 2-3. Figure 2-1 As previously stated, the presence of any electron-withdrawing group on the benzene ring makes a compound less reactive toward electrophilic aromatic substitution. Methyl benzoate is less reactive than benzene. After nitration, methyl nitrobenzoate contains two electron-withdrawing groups. Therefore, the product is much less reactive than the starting material, and little or no dinitration is observed. If you performed the allkyla- tion of p-xylene, you would find that polysubstitution could be a problem because the product is actually more reactive than the starting material Remember, athough "protonation" and "loss of a proton" are used as shorthand de- scriptions of the utimate outcome, an isolated proton 01) does not exist in solution 40 ONO Nitronium lons Figure 2-2 Electrophilic aromatic substitution of substituted benzenes may give rise to a mixture of positional isomers. Carbonyl, sulfonyl, nitrile, or nitro-substituted benzenes pro- dace a preponderance of meta-products when they undergo electrophilic substitution. These substituents on the benzene ring act as strong electron-withdrawing groups. This redaces the electron density of the aromatic ring and dramatically lowers its reactivity Moreover, an examination of the resonance structures for the intermediate carbocation formed by addition of a nitronium ion to methyl benzoate provides an explanation of why methyl m-nitrobenzoate is the major product (Figure 2-3). The addition of the dectrophile at either the ortho or the pana positions prodaces a carbocation intermedi- ate that bears a positive charge on the carbon directly attached to the electron-with- drawing group. This significantly raises the energy of the intermediate. Therefore, the addition of the nitronium ion at the meta position (producing resonance intermediates hat are destabilized less th ocHs CH No2 M-Nite LecP -ocH3 Nor P-NiTvO Methanol and methyl benzoate are volatile irritants. Methyl meta-nitrobenzoate, is a strong irritant; avoid contact with your product. Wash your hands with soap and water after any contact. Methyl para-nitrobenzoate, even though it is expected to be a minor product, is a cancer suspect agent. You can minimize your exposure to this by placing a piece of transparent tape over your TLC plate after you have marked it. You will be using a low-power UV lamp to visualize your TLC plates. Even though the hazard is low, do not stare into the lamp, as prolonged exposure can cause eye and vi- sion damage. The powder on the TLC plate is an abrasive (also used in sandblasting);: wash your hands after handling the plate. This powder is an irritant and can scratch your corneas should it get into your eyes. Use of tape to cover the TLC plate will also minimize your exposure to the abrasive silica gel. Half-fill your 150-mL and 250-mL beakers with ice for use later. Use the auto-pipettor to add 7 mL of concentrated sulfuric acid to a dry 50-mL Erlenmeyer flask containing a large stir bar, and cool the flask in the larger ice-water bath (make sure this flask does not tip over). Transfer, using the other auto-pipettor, 5 mL of the sulfuric acid-nitric acid (1:1) mixture to a medium test tube and place it in the smaller ice-water bath. Measure and add 3.4 g (d = 1.09 g/mL) of methyl benzoate to the Erlenmeyer flask con- taining sulfuric acid with swirling. Now use a pipet to add dropwise the cooled, mixed acids to the methyl benzoate solution over about three minutes. Swirl the mixture in the ice-water bath during the addition. Place the flask on the small stirrer and allow the reaction mixture to stir and warm to room temperature. Continue stirring at room temperature for about 10 minutes. While the reaction is stirring, begin warming the heater-stirrer, set at the very back of the mini-hood, at a setting of 4-5. DO NOT PLACE YOUR REACTION MLXTURE ON THE HEATER-STIRRER. Also, place about 6 mL of methanol in a 25-mL Erlenmeyer flask and cool it in ice placed in a 100-mL plastic beaker. After completion of the stirring of the reaction mixture at roo pour it into about 25 g of ice in the 150-ml beaker. (Note: If the ice machine produces large cubes, you will need to break these into smaller pieces.) Mix the slurry with a plas- tic stir rod, breaking up any large clumps of organic product, until the ice has melted. om temperature, slowly Collect the solid product by vacuum filtration (after all ice has melted). Crush the col- lected crystals carefully with a spatula before washing. Wash the crystals four to five -cH -ocH3 OR-O No2 M-Nite Nor P-NITVO

Answer 1

Initial mass of methyl benzoate = 3.4 gms

Molar mass of methyl benzoate = 136.15 g/mol

No. of moles of methyl benzoate = Mass/molar mass = 3.4 g/136.15 g/mol = 0.02497 moles

We can observe in the above nitration reaction the molar ratio of methyl benzoate and meta nitro methyl benzoate is 1:1

Similarly the molar ratio of methyl benzoate and para nitro methyl benzoate is 1:1

Molar mass of meta nitro methyl benzoate / para nitro methyl benzoate is 181.15 g/mol

Hence moles of meta nitro methyl benzoate / para nitro methyl benzoate = 0.02497 moles

Theoretical Mass of meta nitro methyl benzoate / para nitro methyl benzoate = moles x molar mass = 0.02497 mol x 181.15 g/mol = 4.524 g

Percentage yield of product 1 (meta nitro methyl benzoate) = (actual yield/theoretical yield) x 100 = (3.9155g/4.524 g) x 100 = 86.5 %

Percentage yield of product 2 (para nitro methyl benzoate) = (2.1999 g/4.524 g/mol) x 100 = 48.6 %