Green Synthesis of C-4-Hydroxy-3-methoxyphenylcalix[4 ...

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M. Firdaus et al. Proceeding of The International Seminar on Chemistry 2008 (pp. 346-350)Jatinangor, 30-31 October 2008Solvent-free synthesis of 1The reaction was done according to the method asdescribed by Roberts et al. (2001). A mixture ofvanillin (5 mmol), resorcinol (5 mmol), and p-toluenesulfonic acid (0.3 mmol) was added together ina mortar and pestle and ground vigorously. Withinseconds, a viscous paste formed which hardened onfurther grinding. The paste was left to stand for up to1 h, during which time it solidified to yield a red solid.The solid was reground, washed with water to removeany acid, filtered, and the product was recrystallizedwith hot methanol to give pink colored solid 1. m.p.>400 °C. FTIR (KBr) ν max (cm −1 ): 3425 (OH), 1612and 1512 (ArH), 3000 – 2800 and 1373 (CH 3 ), 1427(>CH−), 1033 and 1211 (OCH 3 ). 1 H NMR (500 MHz,DMSO-d 6 ) C 2h isomer δ (ppm): 8.38 (8H, s, OH A ),7.98 (4H, s, OH B ), 5.96 – 6.40 (20H, m, ArH), 5.41(4H, s, >CH−), 3.44 (12H, s, −OCH 3 ). C 4v isomer δ(ppm): 8.47 (8H, s, OH), 7.98 (4H, s, OH), 5.96 –6.40 (20H, m, ArH), 5.58 (4H, s, >CH−), 3.44 (12H,s, −OCH 3 ).Solvent-free synthesis of 2This reaction was carried out with the same procedureand condition in mol quantity as in synthesis of 1 butvanillin was replaced by p-anisaldehyde. Yield solidm.p. >400 °C. FTIR (KBr) ν max (cm −1 ): 3402 (OH),3001, 1612, and 1512 (ArH), 3000 – 2800 (CH 3 ),1427 (>CH−), 1026 and 1242 (OCH 3 ). 1 H NMR (500MHz, DMSO-d 6 ) C 2h isomer δ (ppm): 8.43 (8H, s,OH), 5.74 – 6.60 (24H, m, ArH), 5.44 (4H, s, >CH−),3.61 (12H, s, −OCH 3 ). C 4v isomer δ (ppm): 8.52 (8H,s, OH), 5.74 – 6.60 (20H, m, ArH), 5.57 (4H, s,>CH−), 3.70 (12H, s, −OCH 3 ).Results and DiscussionC–4–hydroxy–3–methoxyphenylcalix[4]resorcinarene1 and C–4–methoxyphenylcalix[4]resorcinarene 2have been prepared by a single step direct synthesisunder solvent free condition. The reaction wasachieved by simply grinding together equimolarquantities of starting materials in the presence of p-toluenesulfonic acid as the catalyst. The methodologyis simple, energy-efficient, and relatively quick. Thismethod is significantly faster than solvent-basedmethod traditionally employed in the synthesis of 1and 2 as previously reported by Sardjono (2006). Thereaction scheme for the formation of 1 and 2 ispresented in Figure 1.Solvent-free synthesis of 1Solvent-free synthesis of calix[4]resorcinarene 1from vanillin and resorcinol gave pink colored solid in52% yield having melting point >400 °C. Regardingthe theoretical atom economy, this reaction has highatom economy (93%). Unfortunately, the experimentalatom economy is only 48%. Although theexperimental atom economy is not as high as thetheoretical atom economy, this procedure is still incorridor of the green chemistry principles. Thereduced reaction time, elimination of energy neededfor heating and/or cooling, minimum quantity ofcatalyst, elimination of solvent and subsequent wasteare all important factors in complying with theprinciples of green chemistry.Figure 1 Synthesis of calix[4]resorcinarene 1 and 2FTIR spectrum of compound 1 shows the hydroxyl(-OH) stretching as a broad absorption at 3425.3 cm −1 .Strong absorptions at 1612.4 and 1512.1 cm −1 indicatean aromatic group. Absorption band at 3000 – 2800cm -1 together with absorption at 1373.2 cm −1 expressthe existence of Csp 3 -H from a methyl group. Theabsorption of the methine group appears at 1427.2cm −1 . Absorptions at 1033.1 cm −1 and 1211.2 cm −1indicate a C–O–C bond of methoxy bonded inunsaturated group (Sharma, 2002). There is noaldehyde absorption band of the starting material(vanillin) appeared in the spectrum. This is theevidence that the reaction had taken place. All of thefunctional groups appeared in the spectrum (Figure 2)are consistent to the structure of C–4–hydroxy–3–methoxyphenyl calix[4]resorcinarene.% TransmittanceWavenumber (cm −1 )Figure 2 FTIR Spectrum of Compound 1347
M. Firdaus et al. Proceeding of The International Seminar on Chemistry 2008 (pp. 346-350)Jatinangor, 30-31 October 20081 H NMR spectrum of calix[4]resorcinarene 1shows 5 signal groups depicting 5 different types ofprotons (Figure 3). Signal of proton E is overlappingwith proton H 2 O signal. Therefore, it is difficult to beinterpreted and analyzed. However, it can still bepredicted that the signal at δ = 3.44 ppm is fromOCH 3 protons. The existence of aromatic protons areshown at δ = 5.96 – 6.40 ppm. Signals at δ = 5.41 –5.58 ppm are coming from methine bridge protons.The resonance of hydroxyl group protons occur at δ =7.98 – 8.47 ppm. All of the protons in the spectrumare very appropriate to the structure of C–4–hydroxy–3–methoxy-phenylcalix[4]resorcinarene.ABCDEChemical shift (ppm)C–4–hydroxy–3–methoxyphenylcalix[4]resorcinarene.Solvent-free synthesis of 2The synthesis of C–4–methoxyphenylcalix[4]resorcinarene2 was achieved using the same methodologyas described in the synthesis of 1 section. The startingmaterial used in previous section, vanillin, wasreplaced by p-anisaldehyde. The product was solid in63% yield having melting point >400 °C.Regarding FTIR spectrum (Figure 5) analysis,there is no aldehyde absorption band of the startingmaterial (p-anisaldehyde) appeared in the spectrum.This is the evidence that the reaction had taken place.FTIR spectrum of compound 1 shows –OH stretchingabsorption at 3402.2 cm −1 . Strong absorptions at1612.4 and 1512.1 cm −1 together with absorption at3001 cm -1 indicate an aromatic group. Absorptionband at 3000 – 2800 cm −1 express the existence ofCsp 3 -H from a methyl group. Absorptions at 1026.1and 1242.1 cm −1 indicate a C–O–C bond of methoxygroup (Sharma, 2002). Thus, the FTIR spectrum ofthe synthesized product indicates that the compoundcontains an aromatic, a hydroxyl, and a methoxygroup, which is in full agreement withcalix[4]resorcinarene 2 structure.Figure 3 1 H NMR Spectrum of Compound 1Calix[4]resorcinarenes commonly occur in twoisomeric forms, namely the cis-cis-cis (rccc) or C 4vand the cis-trans-trans (rctt) or C 2h isomers, which aredistinguishable by comparison of 1 H NMR spectra.The C 4v or ‘crown’ isomer and the C 2h or ‘chair’isomer is illustrated schematically in Figure 4(Tunstad et al., 1989 and Roberts et al., 2001). In thisresearch, the ratio of C 4v : C 2h isomer is 1 : 5.% TransmittanceHOOHHOHO OH OH OHOHC 4v isomerWavenumber (cm −1 )RRRRFigure 5 FTIR Spectrum of Compound 2C 2h isomerHOHORHOHOROHROHRFigure 4 Schematic of C 4v and C 2h isomersBased on FTIR and 1 H NMR spectral, it can beconcluded that the product obtained from solvent-freereaction between resorcinol and vanillin in thepresence of p-toluenesulfonic acid as the catalyst isOHOH1 H NMR spectrum of the synthesized product(Figure 6) shows signal at δ = 3.44 ppm from -OCH 3protons. Signals at δ = 5.44 – 5.57 ppm are comingfrom methine bridge protons. The existence ofaromatic protons are shown at δ = 5.75 – 6.60 ppm.The hydroxyl group protons resonate at δ = 8.43 –8.52 ppm. All of the protons in the spectrum are veryappropriate to C–4–methoxyphenyl calix[4]resorcinarenestructure.348
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