Synthesis and Purification of Nitrophenols

price reduction and Purification of Nitro oxybenzenesAbstractOrtho and para-nitrophenol was synthesized using an electrophilic remindful substitution of phenol and contract nitric acid. Isolation of the crude ingathe reverberance used a dichloromethane followed by a short vortex and sodium sulfate for weewee removal. Separation of the ortho and para merchandises was completed using column chromatography to collect the eluent in ten ampoules vials 1-5 collected o- and vials 6-10 collected p-nitrophenol. Thin layer chromatography digested synthetic thinking of o-nitrophenol collected in vial 3, 4 and 5 and p-nitrophenol in vial 7.1H NMR give tongue toed o-nitrophenol being the spectrum with more than peaks, payable to the a isobilateral structural leaving creating more nuclear environments for the proton to character referenceicipate in.IntroductionPhenols, due to their rich negatron density, are highly susceptible to undergo electrophilic substitution reactions. The hy droxyl convention on the reminiscent ring of the phenol promotes charge delocalization thus, allowing for stabilization by dint of and through resonance. One such electrophilic substitution reaction is that of nitration. First, an electrophilic attack of the phenol readys place, resulting in a carbocation intermediate stabilized by resonance1. Next, the nitronium ion nitrates the phenol ring, producing p-nitrophenol and o-nitrophenol (Figure 1). The hydroxyl conference of the phenol is an ortho para director therefore, the meta isomer is non produced. However, by products such as 2,4-dinitrophenol and 2,4,6,-trinitrophenol may be present in excess amounts of nitric acid. at a time nitration is complete, the crude product basis be purified through column chromatography and monitored through tender loving care.Thin layer chromatography (tender loving care) is a chromatographic technique used to narrate the components of a mixture using a thin stationary phase. tender loving care functions on the analogous principle as all chromatography a change go out have varied affinities for the mobile and stationary phases and this affects the speed at which migrates2.After a separation is complete, individual compounds appear as drifter separated vertically. Each spot has a retention factor (Rf) which is equalize to the outper take a crap migrated over the total distance covered by the solvent. The Rf formula is2In this experiment the difference in Rf grade will allow for identification mingled with o- and p-nitrophenol. When comparing two different compounds under the same conditions, the compound with the larger Rf range is slight(prenominal) polar because it does not stick to the stationary phase as keen-sighted as the polar compound, which would have a lower Rf value2. mainstay chromatography is a useful analytical technique for small-scale separation and cultivation using similar principles as TLC3. The polar, stationary phase remains either si lica gel or alumina and the mobile phase can be dichloromethane (DCM)/hexane or DCM/ethyl acetate depending on the preindication of the sample. Therefore, the more polar isomers will adsorb to the silica gel and take longer to elute than the less polar isomers3. In the above reaction, the ortho product should elute first as it is less polar than the para product.Results jibe percent digest using mass set Table 1Table 1 Mass of fractions 1-10Vial NumberEmpty readable Vial (g)Dry Vial Weight (g)Product only (g)113.349713.46630.1166213.335713.3370.0013313.160513.16080.0003413.081913.35430.2724513.205413.31470.1093613.283813.67430.3905713.200713.51760.3169813.046413.09770.0513913.315713.46820.12251013.581813.83760.2558Table 2. 1H NMR spectrum of o-nitrophenol pinpointAtom is part of a gathering diadem multiplicity cover discovered (ppm) period calculated (ppm)Ahydroxyl radicalSinglet10.710.84BAreneDoublet7.157.07CArene tether7.06.59DAreneDoublet8.28.00EAreneTriplet7.67.22Table 3 1 H NMR spectrum of p-nitrophenolAtomAtom is part of a group power point multiplicityPeak find (ppm)Peak calculated (ppm)AAreneDoublet8.158.24BAreneDoublet6.87.0CHydroxylSinglet5.456.0Table 4 IR spectrum of o-nitrophenol utilitarian Groupmolecular(a) MotionObserved Wavenumber (cm-1)Literature Value Range2-4 (cm-1)Peak IntensityPeak Shape reminiscent alcoholO-H Stretch3240.313550-3500 worn outBroadAromatic C=CC=C Stretch1613.371600-1430Medium crispAromatic nitroNO2 Asymmetric Stretch1530.131540-1500Medium cracking Aromatic nitroNO2 symmetric Stretch1471.311370-1330MediumSharpTable 5 IR spectrum of p-nitrophenolFunctional GroupMolecular MotionObserved Wavenumber (cm-1)Literature Value Range2-4 (cm-1)Peak IntensityPeak ShapeAromatic alcoholO-H Stretch2999.353550-3500WeakBroadAromatic C-HIn planeC-H bending1259.931275-1000MediumSharpAromatic nitroNO2 Asymmetric Stretch1517.921540-1500MediumSharpAromatic nitroNO2 bilaterally symmetric Stretch1326.381370-1330StrongSharpAromatic C=CC=C St retch16001600-1430MediumSharpFigure 2 TLC plate A Figure 3 TLC plate BTable 6 Rf valuesCompoundRetention mover (Rf)Relative Polarityo-nitrophenol0.93Less polarp-nitrophenol0.07More polar word of honorIn this experiment a nitrophenol synthesis was carried out. The total percent yield is 42.7% as evident in Equation 2. Equations 2 and 3 show o-nitrophenol yield being 54.66% and p-nitrophenol being 45.34%. It could be assumed that not all of the organic matter was collected during the crude isolation phase.Two TLC analyses were performed to further determine the identity of o- and p- nitrophenols. The analysis on plate A determined that the fractions collected correspond to o-nitrophenol. This was concluded based on the distance the spots prompted up the plate. The o-nitrophenol complex is less polar than some(prenominal) the silica gel on the TLC plate and the p-nitrophenol complex. Therefore, it was expected to travel further up the plate. The fractions collected on TLC plate B co rrespond to p-nitrophenol this complex is polar and adheres to the polar silica gel of the plate. The Rf value (retention factor) obtained for o-nitrophenol is 0.93. The Rf value obtained for p-nitrophenol is 0.07. Compounds with larger retention factors are less polar as they do not stick to the polar solvent. The fractions collected on plate A are all pure as only one spot is discover per lane. Lanes 1 and 2 do not show any spots because the fractions were collected too archeozoic and no product exists. The only pure fraction collected on plate B is the one in lane 7. Lanes 8, 9, and 10 each have multiple spots suggesting that by-products are present. Lane 6 does not have any spots meaning that only solvent, not product exists.To confirm the identity of the product, 1 H NMR spectroscopy were used. The 1 H NMR spectrum of p-nitrophenol it is easily distinguishable because it contains only 3 discover peaks- A, B and C at 8.15 ppm, 6.8 ppm and 5.45 ppm accordingly. Peak A is a dou blet and belongs to the protons nigh to the deshielding nitro group. The proton check adjacent to the hydroxyl group show a doublet signal at 6.8 ppm on the spectrum. The singlet showing lack of splitting must(prenominal) belong to the hydroxyl group, provided it is far below expected values of around 10 ppm4. This is due to the intermolecular hydrogen stick toing in this compound. The spectrum for o-nitrophenol has five observed peaks. The hydroxyl group is just above 10.5 ppm, which is in normal range. Peak D which is a doublet belongs to the proton terminalst to the nitro group at 8.2 ppm. The triplet directly across the nitro group peak E has a values of 7.6 ppm. This value generally would be expected at 7.0 ppm, but the ortho and para positions are more deshielded due to the resonance structure observed in Figure 4 and 5.Comparing resonance structures of p-nitrophenol and phenol explains why pnitrophenol is more acidic (Figure 4, Figure 5). Phenol can donate an electron pair to the evocative system from the hydroxide group. P-nitrophenol has a ring deactivating nitro group that withdraws electron density from the aromatic system. This allows the hydroxyl proton to be removed because of the partial derivative positive charge on that side of the system. The conjugate base is accordingly stabilized by the nitro group taking away an electron pair from the negatively charged oxygen to form a double bond with the ring system. The stable conjugate base means that it cant form a new bond with the free proton, thus making p-nitrophenol more acidic than phenol. However with phenol, there is no electron withdrawing group, allowing oxygen to obligate its negative charge. The conjugate base formed is very unstable and will immediately bond with any available proton. Also, o-nitrophenol has the nitro group in close proximity to the hydroxyl, thus allowing for intramolecular hydrogen bonding to occur. This slightly lowers the moroseness of o-nitrophenol comp ared to pnitrophenol because the hydroxyl proton is made unavailable by the negative oxygen on the nitro substituent. Whereas in p-nitrophenol, intermolecular bonding occurs between other p-nitrophenols contributing to the overall stability of the compound.The IR spectrum of o-nitrophenol was given however, the IR spectrum of p-nitrophenol was obtained experimentally. The IR spectrum for o-nitrophenol shows the following extendes O-H alloy C=C stretch aromatic NO2 asymmetric stretch and an aromatic NO2 symmetric stretch. The O-H stretch is caused by the hydroxyl group on the phenol ring. The observed value is 3240.31 cm-1 this corresponds to the literature value range of 3550-3500 cm-1. The peak was long and exhibited strong intensity. The C=C stretch is caused by the aromatic ring of the phenol. The observed value is 1613.37 cm-1 this corresponds to the literature value range of 1370-13130 cm-1. The peak was groovy and exhibited moderate intensity. The aromatic NO2 asymmetr ic stretch is caused by a nitro group. The observed value is 1530.13 cm-1 this corresponds to the literature value range of 1540-1500 cm-1. The peak was sharp and exhibited smedium intensity. The aromatic NO2 symmetric stretch is to a fault caused by the nitro group.The p-nitrophenol IR spectrum exhibited many of the same peaks. The observed peaks are as follows O-H stretch C-H bending aromatic NO2 asymmetric stretch aromatic NO2 symmetric stretch and C=C stretch. The O-H stretch is caused by the hydroxyl group on the phenol ring. The observed value is between 3726.38 and 2999.35 cm-1 this corresponds to the literature value range of 3550-3500 cm-1. The peak was broad and exhibited spineless intensity. The C-H in plane bend is caused by the aromatic ring of the phenol. The observed value is 1259.93 cm-1 this corresponds to the literature value range of 1275-1000 cm-1. The peak was sharp and exhibited medium intensity. The aromatic NO2 asymmetric stretch is caused by a nitro group. The observed value is 1517.92 cm-1 this corresponds to the literature value range of 1540-1500 cm-1. The peak was sharp and exhibited strong intensity. The aromatic NO2 symmetric stretch is also caused by the nitro group. The observed value is 1326.38 cm-1 this corresponds to the literature value range of 1540-1500 cm-1. The peak was sharp and exhibited medium intensity.ConclusionThe synthesis of o- and p-nitrophenol was performed using an electrophilic aromatic substitution of a nitro group in charge acidic conditions. This was followed by column chromatography to separate the o- and p forms and TLC to confirm that the synthesis and purification was successful. The capture of o-nitrophenol and of p-nitrophenol was successful due to having product in vials 3,4,5 and 7 as seen on the TLC plates (Figure 2 nand 3). IR spectra of o- and p-nitrophenol also confirm a successful synthesis due to the differences in the aromatic OH streches (Table 4, Table 5). The experiment may be consider ed a success because of the differences between the IR spectra confirming the synthesis of o- and p-nitrophenol. The IR spectra may be amend by more homogenous packing of the column. Also, waiting to collect a darker yellow elute may have increased yield of o-nitrophenol due to not capturing only solvent in vials 3-4.ReferencesStawikowski, M. Experiment 5 tax deduction and Purification of Nitrophenols BlackBoard.Touchstone, Joseph C. Practice of thin layer chromatography. 2nd ed. New York Wiley, 1983.PrintSmiley RA Ullmanns Encyclopedia of Industrial Chemistry. John Wiley and Sons. Richards, S. A., and Hollerton, J. C.. Essential Practical NMR for thoroughgoing Chemistry (1). Hoboken, GB Wiley, 2010, 2.