CHAPTER II SYNTHESIS AND CHARACTERIZATION OF HEXASULFONATO CALIX(6)ARENE p p * % * 1 (88)
ABSTRACT The synthesis and characterization of p-tert-butyl callx(6)arene [p-t-bc(6)j and hexasulfonato.caiix(6)arene [HSC(6)] are described. These were synthesized by the base catalysed reaction of p-tert~butyl phenol and paraformaldehyde. The corresponding HSC(6) was then prepared by sulfonation of p-t-bc(6). These compounds are characterised by melting point, eiementai analysis, ir, NMR and Mass spectra. 81 1 (89)
INTRODUCTION The chemistry of cyclodextrins and cyctophanes has occupied central interest in host-guest chemistry for the last three decades, and many functionalized host molecules which can mimic the in-vivo catalytic activity of 1 -S enzymes have led chemists to give increasing attention to compounds that contain cavities of sufficient diameter and depth to exist as porous monolayer,0 superuranophiles7,8 and metal complexing agents. These versatile characteristics rendei chemistry. them a promising future in supramolecular Since calixarenes have a cylindrical architecture similar to that of cyclodextrins, they are expected to be useful to design enzyme mimics in 9.10 totally synthetic systems. Gutsche stated in a recent review that there are no published data in support of solution complexes of calixarenes. 10-12 This is in sharp contrast to cyclodextrins, which can form a variety of host-guest type solution complexes. The difference would stem mainly from the poor solubility of calixarenes since they are sparingly soluble in several organic solvents but insoluble in aqueous solutions. Therefore, the experimental efforts should be directed toward solubilization of calixarenes, which eventually would lead to the exploitation of calixarene-based host molecules. 82 1 (90)
In the present investigation, new water soluble HSC(6) represented by the formula (I) was synthesized. rt OH /«CH2 Hexasulfonato calix(6)arene (I) 83 1 (91)
EXPERIMENTAL Chemicals: AnalaR grade of B.D.H. and E.Merck chemicals were used throughout, unless otherwise specified. Apparatus: Melting points were taken in a sealed capillary tube using a melting point apparatus. 1H NMR spectra were obtained on a Perkin Elmer EM-360 MHz NMR spectrometer. The FAB mass spectra were recorded on a JEOL 3X 102/DA 6000 mass spectrometer using Xenon as the FAB gas. Infrared spectra were obtained on a Shimazdu 402 spectrometer. Synthesis of 5,11,17,23,29,35ÿ0X3-ÿÿ1x1-37,38,39,40,41,42-hexahydroxy calix(6)arene [p-t-bc(6)]: It is a known compound however in brief its synthesis is described. Into a 250-ml round bottom flask equipped with Dean and Stark apparatus a slurry of 10.Og (0.066 mol) of p-tert-buty! phenol, 4.0g (0.133 mol) of paraformaldehyde and 6 ml of 5N rubidium hydroxide in 100 ml of xylene were added. The mixture was refluxed for 4 h in an inert atmosphere of nitrogen with efficient stirring. The cooled reaction mixture was filtered, the solid thus obtained was suspended in 300 ml of chloroform and shaken with 100 ml of 1N) HCl. The organic layer was separated, washed with water, dried over anhydrous Na2S04, a nd concentrated to 100 ml. The methanol s was added to precipitate the solid. It was filtered, washed with methanol and dried. Yield of the colourless product was 73% and m.p. 380-381 C. 84 1 (92)
Debutylation of 5,11,17,23,29,35-Hexa-tert:butyl-37,38,39,40f41,42-hexa hydroxy cafix(6)arene: Into a 500-ml round bottom flask, mixture of 10.54g(11 m mol) of >tert-butyl calix(6)arene, 6.19g of phenol, 11,75g (88 m mol) of anhydrous AICI3 in 125 ml of toluene was stirred for 1h in N2 atmosphere at room temperature. The reaction mixture was quenched by addition of ice-cold 100 ml water. The organic phase was separated and toluene was distilled off under vacuum. The residue was triturated with 70 ml of MeOH and contents were filtered. The product so obtained was recrystallised from MeOH-CHCI3 to a white powder. Yield 63%, m.p. 417-418 C, Preparation of 5,11,17,23,29,35jHexasulfonato-37,38,39,40,41,42- hexahydroxy calix(6)arene [HSC{6)]: Into a 100-ml round bottom flask, 7.78 g (12.2 m mo!) calix(6)arene and 60 ml of cone. H2S04 were taken. The mixture was heated at 80 C for 3h. An aliquot was withdrawn from the solution and poured into water to determine H the progress of the reaction. The reaction was completed when no water-insoluble material was detected. After cooling, the precipitate was recovered by filtration. The precipitate was dissolved in water and the solution was neutralised with BaC03. The BaS04 was removed by filtration and Na2C03 was added to the filtrate till the ph reached to 8-9. The solution was treated with active charcoal. The filtrate was concentrated in vacuum. The white powder thus obtained was dissolved in water and an insoluble material (if any) was removed by filtration. The filtrate was treated with active charcoal once again and solution was concentrated. The ethanol was added to the remaining solution. The hexa sodium salt of calix(6)arene-phexasulfonate was obtained as white precipitate. A small amount of the product was recovered by the similar treatment of H2S04 filtrate. The yield of the resultant product was 75% and m.p. > 320 C. 85 1 (93)
CH CM 3 8 CH3 C CM3 C- CH 3 CH 3 is ParaFornaldehyde RbOH 1 Xylene, 4h 1 \ CH 2 OH p-tert-butyl phenol F V OH 4 p-tert-butyl ROOM tenp. HICl 3 phenol toluene calix(6)arene 7 is ( H2SQJ I is 8a k I 3, "ÿ* CH2 CH2 OK 6 OH /6 Hexasulfonato calix{6)arene Calix(6)arene Fig. 1: Synthesis of hexasulfonato calix(6)arene 86 1 (94)
RESULTS AND DISCUSSION Preparation: The synthetic procedure employed for the preparation of hexasulfonato calix(6)arene is very simple and of general applicability. Properties: The properties and salient features of the synthesized hexasulfonato calix(6)arene are discussed below. Colour andnature: Synthesized hexasulfonatocalix(6)arene is white in colour and amorphous in nature. Stability: The calixarenes are stable to heat, light and air, Infrared Spectra: The characteristic absorption bands associated with the p-t-bc(6) and Calix(6)arene are due to (O-H) stretching vibrations while in HSC(Q) due to (O-H) and <S03) stretching vibrations are assigned. In p-t-bc(6) adsorption bands due to (O-H) stretching vibrations were observed at 3400 cm'1 and 3750 cm. Because of strong intramolecular hydrogen bonding calixarenes and H t-vderivatives show (O-H) stretching vibrations at unusually low frequencies in the IR spectra. The same can be explained for the low frequency band of (O-H) group in the HSC(6). In HSC(6) adsorption bands due to S03 stretching were observed at 1060 cm 1 and 1040 cm'1. 87 1 (95)
mm Spectra: The NMR spectra of the p-t-bc(6), calix{6)arene and HSC(6) were recorded in the range of 1-125 with offset in CD2CI2, CDCI3 and D20-Me2S0-d6 media, respectively. Chemical shifts are expressed on the 8 scale. The H NMR spectra of p-t-b C(6) show a pair of doublets around 63.88 and 5 0.9 due to CH2 axial protons and equatorial protons respectively. The singlet of OH proton also appears around 610.2 because of intramolecular hydrogen bonding. Aromatic proton shows singlet around 57.1. The singlet of C(CH3)3 proton appears around 81.25, In the 1H NMR spectra of calix(6)arene and HSC(6), a similar pattern of singlet, doublet and multiplet are observed. The values are shown in Table (2). Mass Spectra; The mass spectra of p-t-bc(6) and calix{6)arene were recorded. The molecular ion peaks for the above two compounds are found at 972 (m/e) and 636 (m/e), respectively. 88 1 (96)
Table -1 Physical Properties of Calixarenes No. Name of compound Molecular formula Molecular weight Melting point( C) Yield Colour Analysis (%) {%) C H S 1 (97) CO CO 1 p-tert-butyl calix(6)arene C66HS4O6.CHCI3.CH3OH 1125 380-381 73 White 71.79 (72.25)* 7.64 (8.11) 2 Calix(6)arene 637 417-418 63 White 78.57 5.68 (78.52) (5.78) 3 Hexasulfonato calix(6) 1255 >320 75 White 40.19 arene (40.24) 2.81 15.33 (3.01) (15.21) Values in Parentheses represent the calculated values
Table - 2 Spectral Properties of Calixarenes S.No. Name of the compound -1 NMR (ppm) IR (cm ) voh vs03 50H 5CH2 8C(CH3)3 5ArH to o 10.2 (s) 3.88 (d) 1 (98) p-tert-butyl calix(6)arene 3150 1.25 (s) 7.19 (s) 0.90 (d) 2 Calix(6) arene 3300 10.4 (s) 4.0 (d) 0.9 (d) 7.4 (m) 3 Hexasulfonato calix(6) arene 3440 1160 10.4 (s) 4.32 (d) 1040 0.90 (d) 6.7-7.4 (m)
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