Methyl Benzoate is electron rich and therefore undergoes electrophilic aromatic permutation. Nitration of methyl benzoate will organize a major merchandise, methyl m-nitrobenzoate that was farther purified by re-crystallization. The electrophile or the nitronium ion attached to the meta place in the benzine ring because of the carboxyl group being meta-deactivator that made the reaction took topographic point in the meta place and the ortho and parity places are destabilized. The mass of re-crystallized methyl m-nitrobenzoate was determined to be 0.257 g compared to the mass of methyl benzoate, 0.
360 g that resulted to …… % output. The runing point of the methyl m-nitrobenzoate resulted to 74 & A ; deg ; C compared to its true thaw point 78 & A ; deg ; C was computed to hold 5.13 % difference. Many side-products like different orientations in the benzine ring will be formed during chemical reactions. To see how much were formed and how pure was the merchandise was, its TLC Profile was calculated that resulted into Rf = 0.79 wherein the consequence from I vapour bespeaking that the merchandise synthesized was pure.
The consequences of the experiment are hence accurate and utile in familiarising with reactions and mechanisms that occur during nitration.
Aromatic hydrocarbons are compounds with one or more benzene rings ( 3 ) . Due to electron delocalization by its jumping dual bonds, it is characterized by being more stable compared to olefines ( 2 ) . Benzene, being aromatic, is a cyclic compound, an unsaturated compound due the presence of pi bonds. In contrast to the dual bonds doing the unsaturation of benzine, it is strong and unreactive because of its resonance construction where there is rearrangement of negatron brace. They undergo EAS or Electrophilic Aromatic Substitution reaction due to the fact that they are electron rich. The nitration of methyl benzoate, C6H8O2, undergoes such type of reaction with concentrated azotic acid and sulphuric acid to give methyl m-nitrobenzoate. From the methyl benzoate, methyl m-nitrobenzoate will be formed and will undergo purification by re-crystallizing with methyl alcohol. Thin Layer Chromatography profile and runing point of the merchandise were used in the experiment to do certain that there are no byproducts formed like compounds with o- and p- orientation ( 2 ) .
MATERIALS AND METHODS
The mass of conelike flask was determined and added with 20 beads of methyl benzoate. The mass was besides determined every bit good as the mass of methyl benzoate itself. The methyl benzoate in the flask was placed in an ice bath while added by 2 milliliters of conc. H2SO4 while twirling. Then, the nitrating agent was prepared which is a mixture of 1 milliliter conc. HNO3 and 1 milliliter conc. H2SO4 chilled in an ice bath. The nitrating agent was so added to the methyl benzoate solution utilizing a Pasteur pipet. The mixture was invariably stirred and still chilled in an ice bath. However, conc. H2SO4 must be added if cloudiness occurs to alter the mixture into its clear visual aspect. Furthermore, the reaction mixture was added 10 g of crushed ice so stirred. As the ice melted, the solid merchandise formed was separated utilizing vacuity filtration where a filter paper was folded into 1/16 large plenty to cover holes in the Buchner funnel. Then, the merchandise was washed with cold distilled H2O, followed by 5 % NaHCO3 and with cold distilled H2O until the filtrate became impersonal.
The merchandise was transferred in a ticker glass and dried over a steam bath. Methanol was used to recrystallize or solidify the merchandise and the per centum output was calculated. The runing point of the recrystallized merchandise was determined utilizing the thaw point setup. The TLC profile was determined utilizing a TLC home base. The TLC home base was drawn with a line utilizing a pencil 1 centimeter from the underside and from the top so dipped in a beaker with ethyl ethanoate. The home base was dipped in ethyl ethanoate 3 times. When the dissolver reached the other border ( the other line ) , the home base was removed from the beaker. Last, Iodine pellets were used to further find the TLC profile.
RESULTS AND DISCUSSIONS
Methyl benzoate, C6H8O2, is an aromatic hydrocarbon, a methyl ester with a colorless visual aspect and used in perfumery. With Methyl benzoate, methyl m-nitrobenzoate will be synthesized and will farther be purified by re-crystallization ( 2 ) with consequences shown in Table 1.
Table 1. Percentage Output of methyl m-nitrobenzoate
Mass of conelike flask
Mass of methyl benzoate and conelike flask
Mass of methyl benzoate
Mass of re-crystallized methyl m-nitrobenzoate
The mass of methyl benzoate was determined by difference so cooled in an ice bath so added conc. H2SO4. The solution will still be colourless because methyl benzoate is soluble in H2SO4. Therefore, it will organize a homogeneous mixture. On the contrary, it will organize a xanthous solution if the flask used is contaminated. The nitrating agent prepared in an ice bath because nitration is an exothermal that requires merely 15 & A ; deg ; C and must non increase ( 1 ) . HNO3 and H2SO4 should be added in the homogeneous solution easy while stirring to avoid side merchandises formation like compounds with o- and p- orientation. Besides, it will ensue to a low output of the merchandise desired. Likewise, fast add-on will ensue to acquiring a high temperature that must be 15 & A ; deg ; C merely. Addition of H2SO4 if cloud cover will happen is of import since methyl benzoate is soluble in sulphuric acid and will bring forth a colourless solution.
The mixture of HNO3 and H2SO4 produces nitronium ion that will attach to the benzine ring ( 5 ) . Methyl Benzoate is characterized for being negatron rich and therefore capable of responding to electrophiles and undergoes EAS or Electrophilic Aromatic Substitution with a mechanism via carbocation [ C+ ] intermediate shown in Figure 1.
Figure 1. Complete Mechanism of Nitration via Carbocation Intermediate
It follows 3 stairss that started from the coevals of electrophile which is the nitronium ion, NO2. Then, the formation of carbocation intermediate where nitronium ion will be attacked by the nucleophile will follow. The carbocation in the 2nd measure is capable of vibrating since aromatic compounds are resonance construction wherein the negatron brace can travel around the molecule. The resonance of the benzine ring makes them stable and favourable to the reaction since the more stabilize the benzine ring is, the more reaction. The last measure is the dissociation of H+ and the reformation of aromatic ring where the electrophile will replace in one of the Hs on the benzine ring. This mechanism resulted to an overall reaction shown in Figure 2.
Figure 1. Nitration of methyl benzoate
The dissolver of the nitration which is the sulphuric acid will protonate the reagent, methyl benzoate, which will make stabilised carbocation intermediate. The electrophile or the negatron hapless nitronium ion, will respond to the protonated intermediate in the meta place. The carboxyl group belongs to the e- withdrawing group that deactivates the aromatic ring. Since negatron retreating group has a meta orientation and a deactivator, the reaction will take topographic point in the meta place. Likewise, the ortho and parity places are destabilized ( 5 ) . The major merchandise now is the methyl m-nitrobenzene which has nitro and carboxyl group being both electron retreating groups oriented at the meta place.
After adding the nitrating agent, the reaction mixture was added 10 g of crushed ice until it solidified and filtrated by vacuity filtration to acquire a drier merchandise. It was so washed by cold distilled H2O and 5 % NaHCO to do extra acid neutralize that made the merchandise green-colored. The merchandise was dried over a steam bath and re-crystallized with methyl alcohol for purification. By rinsing the merchandise with methanol, byproducts or drosss like permutation on different topographic points on the aromatic ring ( ortho and para places ) , methyl-2-nitrobenzoate or possibly methy-3-nitrobenzoate formed during the old reactions should sublimate to acquire the preferable merchandise. However, the methyl alcohol is preferred cold to command loss of coveted merchandise. The re-crystallized methyl m-nitrobenzoate weighed 0.257 and had …… % output. The runing point of the re-crystallized methyl m-nitrobenzoate was determined to be 74 & A ; deg ; C that is near to its true thaw point being 78 & A ; deg ; C. The % difference was determined to be 5.13 % as shown in Table 2.
Table 2. Melting point of re-crystallized methyl m-nitrobenzoate
Melting point of re-crystallized methyl m-nitrobenzoate
74 & A ; deg ; C
True Melting point of methyl m-nitrobenzoate
78 & A ; deg ; C
To see how much merchandises were formed and to look into its pureness, the TLC profile or Thin Layer Chromatography should be done ( 6 ) . Each test as the TLC home base was dipped in the dissolver ( Ethyl ethanoate ) should hold merely 1 topographic point that is tantamount to 1 compound. If 3 musca volitanss were formed in the TLC home base on 3 tests when the dissolver moves on the top of the home base by capillary action, it merely means that 3 compounds were present in the merchandise. Therefore, doing it considered as non pure. The musca volitanss will be clealy visualized when the home base is placed in an I vapour ( 4 ) here it sublimes from solid to liquid discoloration. Besides, other compounds are capable of adsorbing I and go seeable. On the contrary, the re-crystallized m-nitrobenzene formed had been considered as a pure compound as illustrated in Figure 3 and had an Rf value of 0.79.
Rf = dspot / dsolvent forepart
Rf = 3.75 centimeter / 4.6 cmC: Documents and Settings
icolleMy DocumentsCollege Files2nd Year – 2nd SemORGCHEMLABEXPT4 NITRATION OF METHYL BENZOATETLC Plate.jpg
Rf = 0.79
dsolvent forepart = 4.7 centimeter
dspot = 3.7 centimeter
Figure 3. TLC Profile
The coveted merchandise, methyl m-benzoate, purified by re-crystallization was successfully synthesized from methyl benzoate by avoiding the formation of other side-products. However, if phenyl benzoate was used, it will besides follow EAS or Electrophilic Aromatic Substitution
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