The role of the differences in the internal cavity of cucurbituril rings in complexation of acid, reactive and disperse dyes, respectively

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1 The role of the differences in the internal cavity of cucurbituril rings in complexation of acid, reactive and disperse dyes, respectively András Víg*, Péter Sallay**, enrietta J. agy**, Mihály L. Varga**, István Rusznák**, Péter Bakó** * Research Group of the ungarian Academy of Sciences Budapest University of Technology and Economics Department of rganic hemistry and Technology, 1521 Budapest, ungary **Budapest University of Technology and Economics, Department of rganic hemistry and Technology, 1521 Budapest, ungary Introduction ew types of compounds producing inclusion complexes [1] have been delivered and widely used as well in the science as in the industry in the last decades. Inorganic complexes have already been used earlier as industrial catalysts and as the well known metal complex dyes in the textile industry. General characteristic of the inclusion complex forming organic compounds is their cavity-type structure. Guest molecules could be combined by the complex forming (host) molecules in side the mentioned cavities. The formed complexes are known as cavitands (Fig.1). yclodextrines are world wide used well known representatives of such compounds. alixarenes and cucurbiturils are the most promising future useful members of the host molecules (Fig. 2) [2,3,4]. Figure 1. Formation of inclusion complex 1

n 2 n R 2 R 2 n n = 6: α-yclodextrin n = 7: β-yclodextrin n = 4: tert-butyl-calix[4]aren n = 6: tert-butyl-calix[6]aren n = 5: R = ucurbit[5]uril n = 8: γ-yclodextrin R = 3 Decamethylcucurtit[5]uril

Removal of dyes from the waste water of dye houses [5] are among the research projects where cucurbiturils might hopefully well be used.

2 n 2 n R 2 R 2 n n = 6: α-yclodextrin n = 7: β-yclodextrin n = 4: tert-butyl-calix[4]aren n = 6: tert-butyl-calix[6]aren n = 5: R = ucurbit[5]uril n = 8: γ-yclodextrin R = 3 Decamethylcucurtit[5]uril n = 6: R = ucurbit[6]uril Figure 2. Up-to-date host molecules types ylodextrins have already been used in appropriate textile finishing and as research tasks in textile dyeing. Removal of dyes from the waste water of dye houses [5] are among the research projects where cucurbiturils might hopefully well be used. ucurbiturils are cyclo-oligomer molecules built up of glycoluril units. Their monomers are bound together by methylene bridges. Preparation of ucurbiturils Activities for preparation and use of such molecules are the targets of the present paper. The basic molecule of cucurbiturils has already been synthesized at the beginning of the last century [6], but its structure could not be clarified at that time. early 80 years had to be passed to have the appropriate analytical equipment and methods to clear up the structure [7]. The origin of the expression of cucurbituril goes back to ucurbita maxima the Latin name of pumpkin, because the rod type molecule model of cucurbituril is comparable shape with that of pumpkin (Fig. 3). Figure 3. The model of ucurbit[6]uril The production of glycoluril from glyoxal and urea is the first step of the synthesis of cucurbituril. 2

3 + l 2 2 ucurbituril is the product of the reaction between glycoluril and formaldehyde in the presence of a mineral acid. The first step of this last reaction is -hydroxymethylation (addition). Followed by an acid catalysed condensation reaction and as a consequence of that the glycoluril units will be connected with each other by methylene bridges S n n = 5,6,7,8,10 Similar reactions are well known by textile chemists too. The example might be the reaction of urea and formaldehyde. The first step of this reaction is the formation of methylol urea [8]. This product has the capacity for another reaction with urea in the production of chain molecules Due to the twice 2 hydrogen atoms in one urea molecule there remains the ability of formation three dimensional networks in the course of multiple hydroxymethylation. Subsequent to hydroxymethylation in the production of cucurbituril two types of reactions can be realised. The first one is the formation of chain molecules under oligomerisation of glycoluril methylol monomers 5-8. The second step is the formation of cucurbiturils under ring closure of the respective chain molecules. The mentioned first reaction is series of consecutive reactions, while the second one is competitive with the formers. The number of units (n) in the cucurbituril rings has been established by the ratio between the rate constants of the above mentioned two reactions. k p is the rate constant of chain propagation while k rc is that of ring closure. If k p is much higher than k rc than n is high (6-8) if however k rc is higher than k p than n is rather small (4-5). The ratio k p :k rc is primarily depending on the quality of the applied acid and on the temperature of the reaction. It is well known that no uniform molecules are produced by competitive-consecutive reactions but the mixture of different homologues (in our case U[5] U[6] U[7] and U[8]). A method for synthesis could be elaborated based upon Behrend s [6] and Buschman s [5] in which the yield of 90% could be achieved for the mixture of U[5] U[6] U[7] and U[8] in two processes: 1. polymerization, 2. ring closure (Table 1). 3

4 Table 1. Technical data of the synthesis of ucurbiturils Glycoluril [mol] Formaldehyd [mol] Water/glycoluril (mol/mol) o. of operations Acid Temperature [ ] Yield [%] U[5]- U[8] U[6] l 2. 2 S The cucurbituril homologues were separated according to their solubility s (Fig. 4). U[8] Figure 4. Separation of cucurbiturils from each other After aqueous extracting the fractions of U[5] and U[7] the U[6] fraction has been dissolved in 0.1 M a 2 S 4 solution (and precipitated thereafter with acetone (54%)) and U[8] (15%) fraction remained undissolved. omplexation of different dyes by ucurbiturils omplex formation of 3 disperse (anthraquinone, azo and nitro) and methyl orange as well as 3 hetero bifunctional reactive azo dyes with different cucurbiturils has been studied Table 2). Table 2. Dyes and auxiliary Typ ode.i. Generic ame Structure Disperse Disperse Red I Disperse Red

5 Disperse range I Disperse range 30 2 l l Disperse Yellow I Disperse Yellow 42 2 S Sumitomo A S 3 a l S S 3 a a 3 S S 3 a Reactive Dyes Sumitomo B 3 S 3 a a 3 S l 2 5 l S S 3 a Sumitomo S 3 a S S 3 a S 3 a a 3 S S 3 a Acid Dye Methyl range Acid range 56 a 3 S 3 3 RAMEB Reactive and acid dyes partly remain in the dye bath after dyeing. Disperse dyes however remain in much smaller proportion in the waste water. Dissolved dyes have been complexated by cucurbiturils from distilled water. Prior to study with cucurbituril disperse dyes have been made water soluble by complexation with randomly methylated β-cyclodextrin (RAMEB). It had to be decided weather the complex forming capacity of cucurbituril exceeded that of RAMEB. 5

Experimental conditions ucurbituril has been added to the dye solution and suspension was stirred at different temperatures for different durations.

2 mm) has been studied at p 2.2 and 6.7 respectively. Dye complexation was - in accordance with the respective literature higher in neutral than in acid medium, in our case 98% at p 6.

6 Experimental conditions ucurbituril has been added to the dye solution and suspension was stirred at different temperatures for different durations. Dye complexation has been calculated from changes of λ max in the UV-VIS spectra of the dye solutions. Results and discussion The complexation of methyl orange by U[5]-U[8] mixture (particle size < 0.2 mm) has been studied at p 2.2 and 6.7 respectively. Dye complexation was - in accordance with the respective literature higher in neutral than in acid medium, in our case 98% at p 6.7 whereas only 71% at p 2.2 (Fig. 5). This observation has been generalised in our further experiments and therefore they have been performed at neutral p. Figure 5. The impact of p in the complexation of methyl orange by cucurbiturils If the average particle size of the cucurbituril mixture was higher than 1 mm its complexation effect was rather poor. Medium effect occurred in the range of particle size from 0.2 through 1 mm. Very much better complexation occurred if the average particle size was less than 0.2 mm (Fig. 6). Figure 6. The impact of particle size of cucurbiturils on the complexation of methyl orange After separation of different cucurbiturils from each other the difference in efficiency and rate of their reactive dye complexation could be studied. Most efficient and most rapid was the complexation by U[8] Fig. 7, Fig. 8). early the some impact occurred with the mixture very probably due to the presence of U[8]. Definitely les efficient was the impact of U[6]. 6

7 Figure 7. omplexation of Sumitomo dye by U[6]; U[8]; and U[5]-U[8] mixture (U) Figure 8. Rate of complexation of Sumitomo dye by U[6]; U[8]; and U[5]-U[8] mixture (U) It could also be demonstrated for A and B dyes, what has been observed earlier for dye, that the complexation by U[8] was more efficient than by U[6]. This observation goes back to remarkable difference between the internal cavity of U[8] (47.9 nm 3 ) and U[6] (16.4 nm 3 ). Efficiency of complexation depends also on the structure of the studied dyes. Figure 9. omplexation of Sumitomo A, B and dyes by U[6] and U[8] respectively 7

8 The efficiency of complexation has nearly been equal for A and B dyes but significantly higher for dye (Fig. 9). If the cucurbituril: dye ratio has been very high (100:1) in the systems the difference in the complexating efficiency between U[6] and U[8] disappeared. Three equilibriums (1,2,3) can be assumed in the system in which cucurbituril has been added to the aqueous solution of disperse dye RAMEB complex (Fig. 10) two pathways are possible for the formation of the cucurbituril disperse dye complex (DU). a) Direct transfer of the dye molecule from the disperse dye ciklodextrin complex (DD) into cucurbituril in formation of DU complex shifting equilibrium 3 towards latter formation. b) Beside the DD complex there is always a small amount of free dye molecules in the solution. U combined the dissolved dye molecules shifting equilibrium 1 towards the uncomplexed dye formation which will continuously combined by U shifting equilibrium 2 towards DU complex formation. The direction of shifting of the equilibriums has been determined by the ration between the stabilities of the two complexes. It can be concluded that in the studied case the stability of the DU complex exceeded that of DD complex. Figure 10. Equilibriums in the cucurbituril, disperse dye, RAMEB system in water (D = disperse dye, D = RAMEB, U = cucurbituril) Results of experiments are in Fig. 11. U[6] complexated 16% of red, 30% of orange and 49% of yellow dye whereas U[8] complexated 60% of red, 61% of orange and 79% of yellow dye. It can be concluded that also in complexing disperse dyes U[8] has been markedly more efficient than U[6]. The efficiency of complex formation sensitively depends also on the structure of the disperse dye. Figure 11. ne by one proportion of the three studied dissolved disperse dyes after their complexation for 4 dyes by U[6] and U[8] respectively 8

The industrial water unfortunately usually contains more or less certain dissolved inorganic salts bringing about its hardness. According to S.

9 The industrial water unfortunately usually contains more or less certain dissolved inorganic salts bringing about its hardness. According to S. Karcher and co-workers [10] the sorption of reactive dyes from tap water by U was dramatically more efficient than from deionised water. We have also carried out reactive dye complexation as well in distilled as in tap water (14.6 German ardness) (Fig. 12) and our observation have been in good agreement with theirs. We have mentioned already that the efficiency of complexation of reactive dye with U[8] markedly exceeded that with U[6]. This difference became even much less in tap water, attributed to increased dye complex forming efficiency of both U-s in the presence of inorganic salts. Figure 12. omplex formation of reactive dyes by U[6] and U[8] in distilled and in tap water respectively Efficiency of a reactive dye complexation by U[8] has been studied in the one be one presence of a +, K +, Mg 2+ and a 2+ cations (Table 3). Table 3. Impact of selected cations on reactive B dye complexation by U[8] ation Removed dye [%] a Mg K a The impact of a + has been just detectible, that of K +, Mg 2+ ions was definite one and that by a 2+ ion was the highest. Possible explanation: the compression of the diffuse electric double layer by the studied cations. This phenomenon enables the easier approach of the U dye by the dye anions. Abstract omologue mixture of basic molecules of cucurbiturils has been synthetised and cucurbituril[6] (U[6] and cucurbituril[8] (U[8]) have been isolated by means of solvent-extraction. omplex derivatives of different acid, reactive and disperse dyes have been produced by them. U8] has been definitely more efficient in complex formation with all the studied dyes than U[6]. 9

10 ompetitivity in complex formation between randomly methylated ß-cyclodextrin (RAMEB) and the respective cucurbiturils with disperse dyes has been studied and superiority of U8] could be demonstrated. If in water salts of a, Mg, K and a respectively have been dissolved the complex forming efficiency of the cucurbiturils with acid and reactive dyes have markedly been increased. References 1. IUPA ompendium of hemical Terminology, 2nd Edition, Izatt, R. M.; Bradshaw, J. S.; ielsen, S. A.; Lamb, J. D.; hristensen, J. J.; Sen, D. hem. Rev. 85, 271 (1985). 3. Izatt, R. M.; Pawlak, K.; Bradshaw, J. S.; Bruening R. L. hem. Rev. 91, 1721 (1991). 4. Izatt, R. M.; Pawlak, K.; Bradshaw, J. S.; Bruening R. L. hem. Rev. 95, 2529 (1995). 5. Buschmann,. J.; Schollmeyer, E. J. Incl. Phenom. 29, 167 (1997). 6. Behrend, R.; Meyer, E.; Rusche, F. Liebigs Ann. hem. 339, 1 (1905). 7. Freeman, W. A.; Mock, W. L.; Shih,.-Y. J. Am. hem. Soc. 103, 7367 (1981). 8. onner, A.. Urea-Formaldehyde Adhesive Resins. In Salamone, J.. (ed.), Polymeric Materials Encyclopedia, Vol. 11, R Press, 1996, p Lagona, J.; Mukhopadhay, P.; hakrabarti, S.; Isaacs, L. Angew. hew. Int. Ed. 44, 4844 (2005). 10. Karcher, S.; Kornmüller, A.; Jekel, M. Wat. Res,. 35, 3309 (2001). 10

Study on the Complexation of Macromolecule Cucurbituril with Metals and Acetamide

Study on the Complexation of Macromolecule Cucurbituril with Metals and Acetamide International Journal of Chemistry and Applications. ISSN 0974-3111 Volume 4, Number 3 (2012), pp. 219-226 International Research Publication House http://www.irphouse.com Study on the Complexation of