Calixarenes and their use for sequestration of metals

Details Calixarenes and their use for sequestration of metals Calixarenes and their use for sequestration of metals

1999-12-13

2001-10-02

Geist, Gary (Department: 1623)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acid esters

C562S451000, C560S061000, C528S012000, C548S518000

Reexamination Certificate

active

06297395

ABSTRACT:

The present invention relates to novel calixarenes, methods of their preparation, and uses thereof, in particular for the sequestration of metals.
European Patent Publication No. 0 432 989 describes a number of calixarene and oxacalixarene derivatives as having metal sequestering properties, and reviews some of the prior art in this field.
In a first aspect of the present invention there is disclosed calixarenes of the formula (I). The term calixarenes as used hereinafter is intended to embrace also oxacalixarenes,
wherein:
L is [—CH
2
—] or [—O—CH
2
—O—] and may be the same or different between each aryl group.
R
5
is H, halogen, or C
1
-C
10
aliphatic hydrocarbyl group, C
6
-C
20
aryl group, C
6
-C
20
hydrocarbylaryl group, any of which may optionally be substituted by one or more halo or oxo groups or interrupted by one or more oxo groups, and R
5
may be the same or different on each aryl group.
R
1
comprises a carboxy group [—COO
−
] which may or may not be protonated or protected. Suitable protecting derivatives include salts and ester derivatives of the carboxylic acid.
two groups out of R
2
, R
3
, and R
4
are H
the one group out of R
2
, R
3
, and R
4
not being H comprises an amide group.
The combination of ‘acid’ (or protected acid) and ‘amide’ in the calixarenes of the present invention is not found in the calixarenes of the prior art; this combination leads to unexpected and desirable metal sequestering properties (particularly for lanthanide and actinide cations) as will be further discussed below.
Preferably:
R
2
and R
4
are H and R
3
comprises the amide group; L is [—C
2
—]— between each of the aryl groups;
R
5
is tertiary alkyl, especially butyl.
Preferably the carboxy group R
1
conforms to the general formula (A):
[—X—COOR
10
]  (A)
wherein X is a C
1
, a C
2
or a C
3
carbon chain being a part of an aliphatic hydrocarbyl group, aryl group or hydrocarbylaryl group, any of which may optionally be substituted by one or more halo, oxo or nitro groups.
R
10
is H or a protecting group being a salt or an Ester derivative.
Salts include metal salts e.g. alkali (such as Li) or alkali earth metals, or ammonium or substituted ammonium derivatives. The choice of salt should be made such as to prevent the cation interfering with the operation of the calixarene in practice.
Ester groups may be formed with C
1
-C
10
aliphatic alkyl alcohols, C
6
-C
20
aryl alcohols, C
6
-C
20
hydrocarbylaryl alcohols, any of which may optionally be substituted by one or more halo, nitro, or oxo groups or interrupted by one or more oxo groups. Examples include benzyl, p-methoxybenzyl, benzoylmethyl, p-nitrobenzyl, methyl, ethyl, butyl, t-butyl etc.
More preferably R
1
is of the general formula (B):
[—(C.R
6
.R
7
)
n
—COOR
10
]  (B)
wherein n is 1, 2 or 3 and R
6
and R
7
are H or halogen and can be the same or different on each carbon.
Alternatively R
1
may be of the general formula (C):
wherein n is 0 or 1 and R6 and R
7
are H or halogen and can be the same or different on each carbon and wherein the phenyl ring of the benzoic acid group may be optionally substituted by one or more halo, oxo or nitro groups.
In each case it is preferable that n is 1 and R
6
, R
7
and R
10
are all H.
In unprotected acid embodiments, preferably the aliphatic hydrocarbyl group, aryl group or hydrocarbylaryl group of X in formula (A) are substituted by one or more groups which cause a reduction in the pKa of the carboxy group with respect to the unsubstituted molecule e.g. nitro.
For instance the phenyl ring of the benzoic acid of formula (C) is preferably substituted by one or more groups which cause a reduction in the pKa of the carboxy group with respect to the unsubstituted molecule e.g. nitro.
Preferably the amide group R
2
, R
3
, or R
4
of formula (I) is of the general formula (D):
wherein n is 1, 2 or 3 and R
6
and R
7
are H, halogen, or C
1
-C
10
aliphatic hydrocarbyl group, and can be the same or different on each carbon, and wherein R
8
and R
9
, which may be the same or different, are H or C
1
-C
10
aliphatic hydrocarbyl group (optionally halo substituted) including a cycloaliphatic ring formed by R
8
and R
9
together.
In certain embodiments of the invention, as described in more detail below, R
8
or R9 may form a bridge to between a calixarene of the present invention and a further calixarene in order to produce a dimer.
Most preferably, the calixarene is of the formula (II):
(5,11,17,23-tetra-tert-butyl-25-[hydroxycarbomylmethoxy]-27-[(N-diethylamino) carbomylmethoxy]-26-28-dihydroxy-calix[4]arene.)
This compound (“acid-amide”) has been found to be useful for the extraction of both divalent and trivalent metal ions such as Pb, Sr, Hg, Bi and Y; in particular Lanthanides (e.g. La) and Actinides (e.g. U).
Also embraced by the present invention are calixarenes of the general formulae (I) and (II) but wherein some or all of phenyl groups of the calixarene ring are further peripherally substituted in such a way as not to compromise the advantageous combination of the carboxy and amide groups which form the central core of the present invention. Possible substituents include halogen, nitro, C
1
-C
10
aliphatic hydrocarbyl group, C
6
-C
20
aryl group, or C
6
-C
20
hydrocarbylaryl group, any of which may optionally be substituted by one or more halo or oxo groups or interrupted by one or more oxo groups. Indeed certain substituents (e.g. nitro) may be desirable in as much as they reduce the pKa values of the two hydroxy groups of the calixarene ring, thereby modifying the metal-chelating properties of the compound.
In a second aspect of the present invention there is disclosed a method of sequestering metals comprising contacting the metals with a calixarene as described above.
Preferably the calixarene is used to complex metals at a pH of 2-6, (most preferably pH 3-6) since at higher pHs there is an increased risk of the target metal precipitating. For instance, precipitation of Lanthanides occurs at fairly low pH (7.5 for La, 6.4 for Lu).
If required, additional complexing agents (such as are well known to the skilled person) may be used to prevent precipitation of target metals. This allows the use of the calixarene at higher pHs, which will advantageously reduce protonation of the carboxy and hydroxy groups. The use of such additional complexing agents can thus raise the useful working pH range of the calixarene to the point at which the metal-calixarene complex itself precipitates e.g. around pH 11.
The use of higher pHs (e.g. pH 7 to 10, preferably pH 9) may be particularly advantageous for increasing the concentration of negative charge in calixarenes having protected acid groups or in calixarene-dimers, which may otherwise be reduced by the protecting group or steric effects respectively.
If desired the environmental pH may be adjusted using conventional methods of the art. For instance if it is desired to raise the pH, then LiOH may be added. If desired, the pH may be buffered by using an appropriate buffer such as are well known to those skilled in this art e.g. citrate.
In all cases the lower pH limit of useful operation will be dependent on the pKa of each chelating group in the calixarene, since that will dictate whether each (unprotected) carboxy or hydroxy group will be protonated at any given pH. It may therefore be desirable for each group to have a low pKa e.g. when treating acidic waste streams for which the pH cannot be readily adjusted. The pKa of the protonated carboxy and the amide group of the calixarene of formula (II) is less than 3.
Preferably the calixarene is dissolved in a hydrophobic organic solvent (e.g. dichloromethane) and this is mixed with an aqueous phase containing metal ions (e.g. in equal volumes).
The phases are then stirred or otherwise agitated, typically for around 1 hour, followed by a 2 hour separation time.
Preferably the calixarene is present in excess over the metal target e.g. 25-fold, or 250-fold. Th

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