Calixarenes for Separations - American Chemical Society

Chapter 11

CMPO-Substituted Calixarenes Volker Böhmer

Downloaded by NORTH CAROLINA STATE UNIV on December 7, 2012 | http://pubs.acs.org Publication Date: July 20, 2000 | doi: 10.1021/bk-2000-0757.ch011

Fachbereich Chemie und Pharmazie, Johannes Gutenberg-Universität Mainz, Duesbergweg 10-14, D-55099 Mainz, Germany

The synthesis of calixarenes substituted by carbamoylmethylphosphine oxide groups either on their wide rim or on their narrow rim is reviewed. Some typical results of extraction, membrane transport, and complexation studies are reported. In comparison to C M P O all CMPO-substituted calixarenes show a drastically improved extraction efficiency and also a strongly increased selectivity within the lanthanides and between actinides and lanthanides.

Carbamoylmethylphosphine oxides (1) are excellent extractants for actinides. In deed, (N,N-di-isobutylcarbamoylmethyl)octylphenylphosphine oxide ( l a , referred to as C M P O in this article) is used in the T R U E X process (7). For trivalent actinides, such as Am(III), the species extracted is believed to contain three C M P O molecules per actinide cation. Thus, it seems reasonable to attach three (or more) functional groups of the C M P O type in a suitable way on an appropriate skeleton, which would allow their si multaneous, "coordinated" action in the complexation of the metal cation.

Calixarenes represent a class of cyclic oligomers which are not only easily available in larger quantities, but offer also nearly unlimited possibilities of chemical modification (2,3). Calix[4]arenes have especially been used in numerous ways as such a basic scaf fold on which various ligating groups have been attached. Looking for improved extractants for actinides, it was therefore logical to think of calixarenes substituted by CMPO-like functions. This article gives a short survey of the results obtained so far, concentrating mainly on the synthesis. A brief discussion of typi cal results for extraction, complexation, and structure of the complexes formed is also presented. For a more detailed discussion of these latter topics, the reader is referred to the contributions from F. Arnaud-Neu and J. Desreux.

© 2000 American Chemical Society

In Calixarenes for Separations; Lumetta, G., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

135

136

Wide Rim CMPO-Calixarenes


Synthesis While many calixarene based ionophores were known, in which ligating functions are attached to the narrow rim (4) (caused probably by the fact, that the phenolic hydroxyl groups are especially prone to chemical modification), our first attempts concen trated on the attachment of CMPO-functions via amide bonds to the wide rim (5). The synthetic strategy is outlined in the following schemes.

a Y = CH

3

b Y=C H 3

7

c y =c H d Y = C H 5

u

10

21

e Y =C H 14

c

29

Λ Ph Ph

i-Butylcalix[4] arene is easily converted to tetraethers, in which the cone-conforma tion is fixed, if the residues attached to the phenolic oxygen are at least as large as a propyl group. Such tetraethers can be efficiently ipso-nitrated (room temperature, H N 0 , dichloromethane/acetic acid) in high yields (6,7) The tetranitro derivatives may then be reduced to the tetraamino derivatives in numerous ways. (For standard preparations of sufficiently soluble compounds we normally use catalytic hydrogénation with Raney-Ni at room temperature (7).) 3

For the next steps we initially planned the acylation with chloro- or bromoacetyl chloride followed by Arbouzov reaction with various esters of tri valent phosphorus.


137


Although this reaction sequence has been successfully used for the synthesis of phosphinates 7 and phosphonates 8 (see below), it failed for the preparation of phosphine oxides 6. The introduction of the desired phosphine oxide functions was possible, however, using an active ester, easily available from bromoethylacetate via Arbouzov reaction with the isopropyl ester of diphenylphosphinous acid followed by hydrolysis and esterification with p-nitrophenol (5). Br

C Il Ο

^Et

o k-P Ph II 0

C II 0

Et

ρ

^-P Ph n

n

«,Ph n

0

0

0

c

||

\=/

0

10

9

The (diphenylphosphoryl)acetic acid 9 and the active ester 10 have been structurally characterized by X-ray diffraction (Fig. 1) (8). This active ester 10 can be used as a stable and storable, crystalline reagent, to attach carbonylmethyldiphenylphosphine oxide functions via amide bonds to various amines, provided their nucleophilicity is sufficiently high. This comprises of course aliphatic amines, while kinetic studies show (9) that the reactivity of simple aromatic amines is too low, if they are not "activated" by alkoxy groups.

Figure 1. Single crystal X-ray structure of (diphenylphosporyl)acetic acid 9 (two mole cules of a centrο symmetric tetrameric arrangement) and its p-nitrophenyl ester 10 (cocrystallized with p-nitrophenol) (8). Ionophoric Properties Ligands 6 were compared in extraction and ion transport experiments with typical "standard" extractants like C M P O or TOPO (trioctylphosphine oxide) (5). Using dichloromethane as the diluent, and an organic-to-aqueous volume ratio of 1 % E (percent extracted) values >50 are reached for the extraction of Th(IV) nitrate (from 1 M H N 0 ) with a ligand concentration as low as ΙΟ" M (equal to the initial aqueousphase concentration of metal ions). These values are not obtained by C M P O even at a 4

3


138 100-fold concentration. For the extraction of Eu(III) nitrate, the concentration of C M P O must be 250-fold, to get the same % E of about 70 reached by a 10" M solution of 6. Extraction under conditions closer to the technical requirements (aqueous phase 1 M H N 0 , 4 M N a N 0 ; organic phase o-nitrophenyl hexyl ether, c = 10" M ) gave ex traction values of >99% for E u , P u , and Am, values which were not reached by C M P O with a 10-fold higher concentration. Some of the wide rim C M P O s were checked in transport studies using supported liquid membranes (o-nitrophenyl hexyl ether, c = 10" M ) . The results are shown in Table I. Again C M P O l a must be applied with a 10-fold concentration to reach perme abilities which still are generally lower ( N p , Am) or at least comparable ( Pu). 3

3

3

3

L

152

239

2 4 1

3


L

237

2 4 1

239

Table I. Transport through supported liquid membranes (NPHE) 1

Permeabilities Ρ (cm h" ) Carrier

Y

CL(M)

6c 6d 6e 11 12b' 12b" 12b'" la CMPO

C5H11

ΙΟ" ΙΟ" ΙΟ" 10

QoH i 2

3

Q4H29

3

C14H29

CH CH(C H5)C H 2

2

QoH i Ci8H

3

3

4

a) 9

10-

3

3

10"

a )

2

a )

3 7

10-

3

10-

2

237

Np

5. However, p=o since only i-butylcalix[5]arene can be fixed in the cone conformaPh Vh tion by ether groups, we have not studied larger calixarenes so far. Extraction results with calix[5]arenes 11 are in principle similar to calix[4]arenes, although an interesting selectivity for Np was observed (5). Its distribution coefficient (1 M H N 0 , 4 M N a N 0 / NPHE) is distinctly higher than for analogous calix[4]arenes 6, while the opposite trend is seen for Am. This may be due to higher oxidation states (IV - VI) possible for Np. k

N

> 5

c

=

0

1 1

/

3

3

Flexible Calix[4]arenes The basic conformations of calix[4]arenes can be completely fixed by O-alkyl groups larger than ethyl, while methyl groups can pass the annulus. Therefore mixed (yyn)alkyl/methyl ethers of calix[4]arenes do not necessarily assume exclusively the cone conformation. And even if complexation requires the cone conformation they should show slight differences in their conformational preferences, which might be used


142 to "fine tune" the complexation properties of wide rim C M P O calix[4]arenes 6. With this idea in mind we prepared a series of CMPO-derivatives bearing on their narrow rim all possible combinations of O-propyl and O-methyl groups (14). Their synthesis starts with the partial O-alkylation with propylbromide (or any other alkylating agent, if desired) followed by exhaustive methylation. This sequence is cru cial to ensure the syn arrangement of the propoxy groups. The subsequent steps are those, described already above. Among the various compounds the l,2-dipropyl-3,4-dimethylether 12c shows the highest (73%), the tetramethylether 6a the lowest (35%) extraction values for E u from 1 M H N 0 into dichloromethane at a 1:1 o/a ratio. This corresponds to a factor of five for the distribution coefficients. Differences are less pronounced for T h , where all compounds 12a-d are slightly better (66-70%) than 6b (Y = Pr) (14). In Fig. 5 the extraction abilities of the different calixarenes 12 for various actinides and lanthanides are compared for the extraction from 3 M HNO3 to o-nitrophenyl hexyl ether (extraction from highly acidic solution being technically most interesting). Again 12c shows the best results (expressed here by the distribution coefficient).


3 +

3

4+

γ

1.γ4

9

S

600

H

500

NH \ C=0

La

I

400

I Ce E l Nd Sm M Eu Ï^Z\ Am Π Cm

Η

300

200

100

0

12a

12b

12c

LLm 12d

6a

6b

phosphinate > phosphonate, as shown in Table II for the rigid com pounds 14. Phosphinates and phosphonates may be hydrolyzed, however, to the corresponding acids via the silyl-derivatives (79). In combination with phosphine oxide groups the in corporation of these potentially ionizable groups may lead to elaborate ligands able to compensate the cationic charge (completely or in part) by anionic groups, which may be favorable for the extraction.


146 The combination of CMPO-functions with malonic acid functions attached via am ide bonds (calix-NH-C(0)-CH -COOH) is another option (26). 2


Narrow Rim CMPO-Calix[4]arenes Functional groups attached to the wide rim of a calix[4]arene fixed in the cone con formation are divergently oriented, and this could well be one reason for the compli cated situation with respect to their interaction with metal cations. The situation may change, if such groups are attached to the narrow rim, having therefore primarily a more convergent orientation.

Syntheses The preparation of calix[4]arenes bearing CMPO-functions at the narrow rim (27) requires again suitable tetraamines, which in the last step can be acylated by the active ester 10 (28). The shortest inert and stable connection to the narrow rim seems to be an ether linkage (-0-(CH ) -NH ) of at least two carbon atoms length. Such aminoether derivatives 15 have been partly described before (29). In our hands O-alkylation of tbutylcalix[4]arene by N-(œ-bromoalkyl)-phthalimide followed by deprotection of the aminogroups with hydrazine gave the best results for η > 2, while for η = 2 the known ethyleneoxy tetratosylate (available in three steps from i-butylcalix[4]arene) was substi tuted by azide and the product reduced to the amine 15a (n=2) without isolation. 2

n

2

Ph \ / P=0

< /

NH

2

c=o

NH

Extraction First extraction studies with ligands 16a-c (n = 2-4) were done again from 1 M H N 0 to dichloromethane. A l l the narrow rim CMPO-calixarenes are better extractants for Th(IV) as compared to 6c, while for the extraction of lanthanides only 16c, surpri singly the compound with the longest tether, can compete with 6c. However, the % E values reveal, that the selectivity for the light over the heavy lanthanides is not so pro nounced as for 6c (27). 3


147 Fig. 8 shows in comparison typical results for the extraction of selected cations with wide and narrow rim CMPO-calixarenes as a function of the concentration of H N 0 in the source phase. In contrast to 6c no decrease of the extraction ability is observed for higher concentrations in the case of 16c. Although the reason for this remarkable differ ence is not known yet, this may be well a potential advantage of narrow rim C M P O s over wide rim CMPOs.


3

D

0

1

2

3

4

0

c (HNO,) / M

1

2

3

4

c (HNOJ / M

Figure 8. Distribution coefficient as function of c(HN0 ) for the extraction with 16c (left) and 6c (right). Organic phase NPHE, c = 10' M (27). 3

3

L

Conclusions and Outlook Calix[4]arenes bearing - N H - C ( 0 ) - C H - P ( 0 ) - P h functions, either at their narrow or at their wide rim, are excellent extractants for lanthanides and actinides. Extraction lev els comparable or even superior to those of the "classical" C M P O l a are reached with ligand concentrations of 10" M or less under conditions relevant for the treatment of technical nuclear waste streams. This high efficiency would compensate also a higher price for their synthesis. In addition, wide rim CMPO-calixarenes 6 show an interesting size selectivity within the lanthanides and between actinides and lanthanides. At present it must be stated, however, that these excellent extraction properties can not yet be convincingly explained by structural features of the complexes formed and that even the composition of the extracted species is not entirely clear. The structural modifications which are possible with these ligands, especially the construction of calix arene derivatives with mixed ligating functions, may be used to fine tune their proper ties. Simultaneously this will lead also to a better understanding of these properties and to a detailed description of the interaction between cations and ligand. 2

2

3

Acknowledgement: These studies were supported by the European Community (Con tract FI4W-CT96-0022). I am grateful to all the colleagues and coworkers who contrib uted to these results. Their names are mentioned in the respective references.


148


References 1. Horwitz, E . P.; Kalina, D . G.; Diamond, H.; Vandegrift, D . G . ; Schultz, W . W . Solv. Extr. Ion Exch. 1985, 3, 75. 2. Böhmer, V . Angew. Chem. 1995, 107, 785; Angew. Chem. Int. Ed. Engl. 1995, 34, 713. 3. Gutsche, C. D . Calixarenes Revisited in Monographs in Supramolecular Chemistry, ed. F. Stoddart, F., Ed.; The Royal Chemical Society, Cambridge, 1998. 4. For reviews on calixarene based ionophores see: a) McKervey, Μ. Α.; Arnaud-Neu, F.; Schwing-Weill, M.-J. Cation binding by calixarenes in Comprehensive Supra molecular Chemistry, V o l . 1, p. 537, Gokel, G. W., Ed.; Pergamon, Oxford, 1996 b) Ikeda, Α.; Shinkai, S. Chem. Rev. 1997, 97, 1713. 5. Arnaud-Neu, F.; Böhmer, V . ; Dozol, J.-F.; Grüttner, C.; Jakobi, R. Α.; Kraft, D . ; Mauprivez, O.; Rouquette, H . ; Schwing-Weill, M.-J.; Simon, N.; Vogt, W . J. Chem. Soc., Perkin Trans. 2, 1996, 1175. 6. Verboom, W.; Durie, Α.; Egberink, R. J. M.; Asfari, Z.; Reinhoudt, D . N. J. Org. Chem. 1992, 57, 1313. 7. Jakobi, R. Α.; Böhmer, V . ; Grüttner, C.; Kraft, D.; Vogt, W . New J. Chem. 1996, 20, 493. 8. Ugozzoli, F.; Böhmer, V . ; et al., unpublished results. 9. Klüh, U.; Vogt, W.; Böhmer, V . , unpublished results. 10. Delmau, L . H . ; Simon, N.; Schwing-Weill, M.-J.; Arnaud-Neu, F.; Dozol, J.-F.; Eymard, S.; Tournois, B . ; Böhmer, V . ; Grüttner, C.; Musigmann, C.; Tunayar, Α. Chem. Commun. 1998, 1627. 11. Lambert, Β.; Jacques, V . ; Shivanyuk, Α.; Matthews, S. Ε.; Tunayar, Α.; Baaden, M.; Wipff, G.; Böhmer, V . ; Desreux, J. F. Inorg. Chem., submitted. 12. Desreux, J. F.; Böhmer, V . ; et al., unpublished results. 13. Musigmann, C.; Böhmer, V . , unpublished results. 14. Matthews, S. E . ; Saadioui, M.; Böhmer, V.; Barboso, S.; Arnaud-Neu, F . ; SchwingWeill, M.-J.; Garcia Carrera, Α.; Dozol, J.-F. J. prakt. Chem. 1999, 341, 264. 15. For the use of cavitands as molecular scaffold for CMPO-like functions see: a) Boerrigter, H . ; Verboom, W.; Reinhoudt, D. N. J. Org. Chem., 1997, 62, 7155; b) Boerrigter, H . ; Verboom, W.; Reinhoudt, D. N. Liebigs Ann./Recueil, 1997, 2247; c) Boerrigter, H . ; Verboom, W.; De Jong, F.; Reinhoudt, D. N. Radiochim. Acta, 1998, 81, 39. 16. Arduini, Α.; Fanni, S.; Manfredi, G.; Pochini, Α.; Ungaro, R.; Sicuri, A . R.; Ugozzoli, F. J. Org. Chem. 1995, 60, 1454. 17. For an X-ray structure see: Arduini, Α.; McGregor, W . M.; Paganuzzi, D . ; Pochini, Α.; Secchi, Α.; Ugozzoli, F.; Ungaro, R. J. Chem. Soc., Perkin Trans. 2, 1996, 839. 18. For the nitration see: Arduini, Α.; Mirone, L.; Paganuzzi, D.; Pinalli, Α.; Pochini, Α.; Secchi, Α.; Ungaro, R. Tetrahedron 1996, 52, 6011. 19. Shivanyuk, Α.; Böhmer, V . , unpublished results. 20. Delmau, L. H . ; Dozol, J.-F; Böhmer, V . ; et al., unpublished results.


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21. 22. 23. 24. 25.

Garcia Carrera, Α.; Dozol, J.-F.; Böhmer, V . ; et al., unpublished results. Böhmer, V . Liebigs Ann./Recueil 1997, 2019. Paulus, E . F.; Shivanyuk, Α.; Böhmer, V . , unpublished results. Saadioui, M.; Shivanyuk, Α.; Böhmer, V . ; Vogt, W . J. Org. Chem. 1999, 64, 3774. Kalina, D . G . ; Horwitz, E . P.; Kaplan, L . ; Muscatello, A. C. Sep. Sci. Techn. 1981, 16, 1127. 26. Shivanyuk, Α.; Tunayar, Α.; Böhmer, V . , unpublished results. 27. Barboso, S.; Garcia Carrera, Α.; Matthews, S. E . ; Arnaud-Neu, F.; Böhmer, V . ; Dozol, J.-F.; Rouquette, H . ; Schwing-Weill, M.-J. J. Chem. Soc., Perkin Trans. 2, 1999, 719. 28. See also: Lambert, T. N.; Jarvinen, G. D . ; Gopolan, A . S. Tetrahedron Lett. 1999, 40, 1613. 29. e.g. Scheerder, J.; Fochi, M.; Engbersen, J. F. J.; Reinhoudt, D . N. J. Org. Chem., 1994, 59, 7815.


Calixarenes for Separations - American Chemical Society

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