Electrophilic aromatic substitution essay

lectrophilic Aromatic Substitution(1) Nitration of Methyl Benzoate(2) Synthesis of just one, 4-Di-t-butyl-2, 5-dimethoxybenzene byFriedel-Crafts Alkylation of 1, 4-DimethoxybenzenePurpose1)To carry out the nitration of methyl benzoate, and then determine the major product formed (position at which nitro-group substitution usually takes place) by simply thin-layer chromatography (TLC), the percent produce and the shedding point range.

2)To synthesize 1, 4-Di-t-butyl-2, 5-dimethoxybenzene simply by Friedel-Crafts Alkylation of 1, 4-Dimethoxybenzene, and then decide the percent yield and melting point range.

Procedure*Please refer to the lab handout six and Macroscale and Microscale Organic Trials (Williamson, 2003).

* Part 2 of the research (Synthesis of 1, 4-Di-t-butyl-2, 5-dimethoxybenzene by Friedel-Crafts Alkylation of 1, 4-Dimethoxybenzene) was carried out by Ashley and me. Part We (nitration of methyl benzoate) was carried out by Jenny.

Physical Quantity TableType of substanceMolecular FormulaMolecular Weight (g/mol)Density(g/cm3)M. G. (oC)B. L. (oC)Methyl benzoateC8H8O2136. 161. 094-15198-200Methyl 2-nitrobenzoateC8H7NO4181. 141. 289-13104Methyl 3-nitrobenzoateC8H7NO4181. 14-78-80289Methyl 3, 5-dinitrobenzoateC8H6N2O6226. 14544-106-109-Methyl 4-nitrobenzoateC8H7NO4181. 15-94-96-1, 4-DimethoxybenzeneC8H10O2138. 161. 0555-582131, 4-Di-t-butyl-2, 5-dimethoxybenzeneC16H26O2250. 37-104-105-2-methyl-2-propanolC4H10O74. 12-25. 482. 4Hazard Centered sulfuric chemical p and nitric acid are quite corrosive.

ObservationPart II Friedel-Crafts AlkylationThe centered sulfuric acidity used was yellow. one particular, 4-Dimethoxybenzene is at white very form. The t-butyl liquor solidified in room temperature, so it took a while to temperature it up and return to the liquid form. Following concentrated sulfuric acid was added to the t-butyl alcoholic beverages, acetic acid and 1, 4-Dimethoxybenzene mixture, the solutionbecame mild brown in color. Following warming for some time, white precipitate could be seen at the bottom from the tube. After water was added, the white medications dissolved as well as the solution turned milky. The crystals received after recrystallization are in form of significant slides. They may be grinded in to powdery or perhaps smaller lentigo for burning point test.

DataPart IMass of methyl benzoate sama dengan 0. 30gMass of recrystallized product = 0. 28436gMelting Point Selection of nitration product = 75 oC ” 83 oCChemical CompoundsDistance by B to spots (cm)Distance from N to SF(cm)Distance from M to locations (cm)/Distance via B to SF (cm)Retention FactorRfMethyl benzoate1. 684. 501. 68/4. 500. 37(ortho) Methyl 2-nitrobenzoate1. 304. 521. 30/4. 520. 29(meta) Methyl 3-nitrobenzoate1. 804. 501. 80/4. five-hundred. 40Methyl a few, 5-dinitrobenzoate1. 304. 401. 30/4. 400. 30(para)Methyl 4-nitrobenzoate1. 804. 301. 80/4. 300. forty two

Unknown Product1. 804. 301. 80/4. 300. 42Table a single showing the Retention component of unfamiliar nitration item with assessment to normal valuesB sama dengan baselineSF = solvent frontDrawing of TLC PlatesPlate #1: Platter #2: Key1 = Methyl benzoate2 = Methyl 2-nitrobenzoate3 = Methyl 3-nitrobenzoate5 = Methyl three or more, 5-dinitrobenzoate4 sama dengan Methyl 4-nitrobenzoateP = Unknown nitration ProductPart IIMass of just one, 4-Dimethoxybenzene = 0. 1220gMass of recrystallized product (1, 4-Di-t-butyl-2, 5-dimethoxybenzene)= 0. 085gMelting Point Array of alkylation item = 97oC -102 oCResult &CalculationPart IBased on data from equally melting level test and TLC, the nitration product is probably methyl 3-nitrobenzoate (details in discussion part).

Theoretical Mass1 mole of methyl benzoate produced 1 mole of methyl 3-nitrobenzoate: Mole of methyl benzoate = zero. 3g/136. of sixteen g mol-1 = installment payments on your 20 by 10-3 molðMole of methyl 3-nitrobenzoate sama dengan 2 . twenty x 10-3 molMass of methyl 3-nitrobenzoate = (2. 20 by 10-3 mol) x (181. 15g mol-1) = 0. 3991gPercent YieldPercent yield = 100% (actual mass/theoretical mass) = 100% (0. 28436g/0. 3991g)= 71. 2%Part IITheoretical Mass1 skin mole of 1, 4-Dimethoxybenzene produced 1 mole of just one, 4-Di-t-butyl-2, 5-dimethoxybenzene: Mole of 1, 4-Dimethoxybenzene = 0. 1220g/138. 16 g mol-1 sama dengan 8. 83 x 10-4 molðMole of1, 4-Di-t-butyl-2, 5-dimethoxybenzene = 8. 83 x 10-4 molMass of 1, 4-Di-t-butyl-2, 5-dimethoxybenzene= (8. 83 times 10-4 mol) x (250. 37 g mol-1) sama dengan 0. 2211gPercent YieldPercent yield = totally (actual mass/theoretical mass) = 100% (0. 085g/ zero. 2211g)= 37. 4%

DiscussionIn this research, two types of electrophilic perfumed substitutions were studied”nitration and Friedel-Crafts alkylation. Aromatic substitution involves the substitution of just one (or more) aromatic hydrogens with electrophiles. Monosubstitution is achievable only if the monosubstitution system is less reactive than the unique reactant. In case the reactivity with the monosubstitution item equals or exceeds that of the original reactant, the monosubstitution product(s) can proceed to polysubstitution goods. There are two reasons why the monosubstitution products might be less reactive: a)Electronic reasons: in case the E group that added is electron withdrawing, it will make the item aromatic diamond ring less electron rich and subsequently much less reactive toward subsequent electrophile addition.

b)Steric reasons: Replacing a small L with a significant E group will make the monosubstitution product more crowded, which may hinder the subsequent addition of additional electrophiles.

The existing substituent attached to benzene, which could both be ortho-para directing or meta leading, determines the positioning of the fresh substituent that could attach to the benzene ring. Electron donating (activating) groupings such as alkyl and carbonyl groups happen to be ortho-para directors while electron withdrawing (deactivating) groups except Br and Cl, happen to be meta company directors.

In part one, the hydrogen atom over a substituted benzene (methyl benzoate) was replaced with a nitro group (-NO2) to see the directing effect of the ester group. The product was then reviewed by equally thin part chromatography (TLC) and burning point check.

The burning point selection determined was 75 occitan ” 83 oC. Assessing this worth to the common melting details in the physical quantity table, it was identified that the product was most likely to be methyl 3-nitrobenzoate, with theaccepted melting points of 78 occitan 80oC. Using TLC, the retention factor calculated to get the product was 0. 42. By comparison, the closet preservation factors with the standards had been 0. 40 (for methyl 4-nitrobenzoate) and 0. 45 (for methyl 3-nitrobenzoate). Considering that the product location was a little bit large, this suggested the possibility of overlapping and the product could be methyl 4-nitrobenzoate and/or methyl 3-nitrobenzoate. Combining the two benefits (melting level and retention factor) jointly, it was concluded that the major item was methyl 3-nitrobenzoate. This kind of made feeling because the -COOCH3 substituent for the benzene engagement ring of methyl benzoate features two results on the effect that would be described below.

1st, because of the partial positive impose on the carbonyl carbon, -COOCH3 is a band deactivator, and therefore nitration of methyl benzoate occurs reduced than nitration of unsubstituted benzene. This ring deactivation is due to an electron-withdrawing result by the substituent. Since the electrophile NO2+ can be seeking a concentration of electron density to react with (the professional indemnity cloud in the benzene ring), electron-withdrawing substituents that take away some electron density from your ring associated with ring significantly less electron-rich and, therefore , fewer reactive toward the NO2+ ion.

The deactivation of methyl benzoate by the -COOCH3 group is usually not a significant problem because the NO2+ ion is a powerful electrophile that the response occurred by ice-bath temperatures anyway. Actually it was essential to make sure the effect mixture would not get also warm or the nitrated methyl benzoate would react which has a second NO2+ to form dinitro-methyl benzoate. Nevertheless , the dinitro-methyl benzoate could possibly be removed simply by recrystallization.

The second effect which the -COOCH3 substituent has on the reaction is that of directing the inbound NO2+ ion to replace specific hydrogens around the benzene engagement ring. Specifically, the -COOCH3 group is a meta-director, which means that the H’s coto to that are the most reactive plus the most likely to be replaced. Meta-directing, like ring deactivation, is due to the electron-withdrawing effect of the -COOCH3 substituent. The simplest justification is as comes after: The oxygens bonded to the carbonyl co2 of the -COOCH3 substituent will be electronegative and so induce an incomplete positive charge on that carbon. Reverberation delocalization with the pi electrons of thering distributes the partial great charge to other co2 atoms inside the molecule. Because the NO2+ is searching for an electron-rich co2, not one having a partial positive charge, the carbons in meta positions are the most ones pertaining to the NO2+ to respond. This leads to the expected meta substitution (mechanism attached).

The percent yield was determined to be 71. 2%, which was reasonably substantial. The TLC results mentioned that there could be some ortho-para isomers present in the product as impurities although there was zero dinitro-methylbenzoate. The merchandise yield would venture down after recrystallization and due to mechanical loss.

Simply two, you, 4-Di-t-butyl-2, 5-dimethoxybenzene was synthesized by responding 1, 4-dimethoxybenzene with tertiary butyl alcoholic beverages in the occurrence of sulfuric acid as a Lewis acid solution catalyst. The response occurred via the Friedel-Crafts alkylation mechanism, and involved the attack in the aryl group at the electrophilic trimethylcarbocation. The resulting product was recrystallized using methanol and characterized by testing the melting level.

The -OCH3 is ortho-para directing and activating, so that it put the t-butyl cation in the proper site during the response. This was for the reason that positively recharged electrophile (t-butyl cation) was more likely to behave at a center that is more negatively charged and substitution occurs on the ortho and para positions. The recognized melting point for you, 4-Di-t-butyl-2, 5-dimethoxybenzene is 104-105oC, and each of our determined burning point was 97 oC -102 oC. The slight depression in melting level could because of impurities within the product.

The percent produce was determined to be 32. 4%. The percent yield and burning point in the final merchandise achieved inside the experiment demonstrated that the item was the preferred 1, 4-Di-t-butyl-2, 5-dimethoxybenzene. The melting stage was off by about three degrees. This kind of slight depressive disorder in burning point could have been the result of a modest amount of water in the crystals or an erroneous thermometer studying due to heating the crystals a bit too quickly. The latter was likely to be true because the burning point rangeobtained was also wide. The percent produce was decreased due to physical loss during handling (leaving crystals within the surfaces or not totally collected through the flasks because they got stuck).

To improve the experiment, the second recrystallization could possibly be performed to improve the purity of the transparent product (though the percent yield might be compensated). More careful shifting of the recrystallized product was necessary to reduce product damage and more cautious monitoring of power level was important in melting level test so that the melting level range has not been widened as a result of rapid temperature rise. Furthermore, the TLC could be performed again with product recognizing on equally plates (instead of only one) to remove differential migration effect of each plate on the overall preservation factor.

Solution to the questionsP. 3711. Methyl benzoate dissolves in targeted acid to boost the rate in the reaction by increasing the concentration in the electrophile, the nitronium ion (NO2+), while shown in the equation under: 2 . I would personally expect the structure of the dinitro ester to be methyl 3, 5-dinitrobenzoate because of meta-directing effects of the ester as well as the first nitro group within the addition with the second nitro group (both ester and nitro group are electron withdrawing and for that reason lead to ring deactivation).

a few. The positive demand is delocalized to the carbon with the NO2 attached; discuss it adjacent to the positive impose on the nitrogen, which is incredibly destabilizing. Hence the electrophile (NO2+) prefers to add the meta-position. (resonance set ups attached)4. Peaks at 3101cm-1: C=H stretch (of benzene ring)Peaks at 1709cm-1: C=O stretch (of ester group)Peaks at 1390cm-1: N-O stretch (representing the nitro group)P. 3854. System attached.

a few. 1, 4 isomer is definitely the major product in alkylation of dimethoxybenzene and non-e of the other isomers listed had been very unlikely to form because the methoxy groups by 1, some positions will be electron- donating and therefore are ortho-para-directing. The electrophiles (electron-seeking) hence would attackat the positions near the methoxy groups. Likewise, more resonance structures could be written for the arenium ions resulting from ortho and para strike than from meta attack, which suggests the fact that ortho- and para- replaced arenium ions should be more stable. The transition declares leading to the ortho- and para-substituted arenium ions take place at unusually low totally free energies. Consequently, electrophiles behave at the ortho and em virtude de positions extremely rapidly.

6. The carbocation can be made from several starting components such as a great alkene, alcohols or alkyl halides. In place of t-butyl alcoholic beverages, one could employ t-butyl chloride. However , this kind of reaction is usually not near do in the lab (HCl would become generated). 2-methylpropene could also be employed. Both of these yield the same carbocations as the reaction that was performed inside the experiment, and so yield precisely the same product when ever reacted with 1, 4-dimethoxybenzene.

References1)

Williamson, Macroscale and Microscale Organic and natural Experiments, 4th Edition, the year 2003, Chapter 28 & twenty nine, P. 367 ” 3852)Solomons and Fryhle, Organic Chemistry, 8th edition, 2004, G. 669 ” 680

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