GB2145077A - Chelating compounds - Google Patents

Abstract

A compound of the formula <IMAGE> in which the groups X are the same or different and are each <IMAGE> wherein R<1> and R<2> are each H or hydrocarbyl and R<3> is H, hydrocarbyl or a positive ion, provided that at least one of the groups X contains a group R<1>, R<2> or R<3> which is unsaturated hydrocarbyl, containing one or more olefinic or acetylenic bonds. These EDTA derivatives can be polymerised or incorporated into other polymer structures.

Description

SPECIFICATION Chelating compounds Ethylenediaminetetraacetic acid (EDTA) and its sodium salt are widely used as chelating agents to inactivate metal ions. EDTA is a particularly effective chelating agent because it is hexadentate and has four carbonyl groups and two nitrogens in close proximity, all of which will form complexes. Although a metal complex formed by chelation is usually soluble in water, the metal ion is effectively sequestered and loses its characteristic chemical behaviour. For example, water can be "softened" by complexing the calcium and magnesium ions therein, and this avoids the precipitation of calcium salts derived from soap, but it does not allow the complete removal of the metal ions from the system by, for example, precipitation.

Physical removal of ions from solution may be accomplished by using certain resins such as poly(vinylpyridine) or ion-exchange resins based on polystyrene with isolated nitrogen chelating groups. Although less effective than EDTA as sequestering agents, these polymers have the advantage of being insoluble so that metal ions may be physically removed from aqueous solution by the simple process of percolation through a resin bed.

There is a need for a polydentate ligand in polymeric form combining high chelating power with the advantages of a convenient physical form. To our knowledge, this has not so far been achieved.

A compound according to the present invention is an unsaturated derivative of EDTA. Such compounds can be polymerised or incorporated into other polymer structures, e.g. by copolymerisation or grafting, to form polymers according to the invention. The derivatives have the formula:

in which the groups X may be the same or different and where each group X is

where R' and R2 are each H or a hydrocarbon group, where R3 is H (forming an acid) or a hydrocarbon group (forming an ester) or a positive ion (forming a salt) and where at least one group X contains a group R1 or R2 or R3 which is an unsaturated hydrocarbon group containing one or more olefinic or acetylenic bonds.Preferably only one or two of the groups X contains an unsaturated group R' or R2 or R3 so that undue cross-linking is avoided if the derivative is polymerised.

Examples of unsaturated R groups are: -CH = CH2 -CH2-CH = CH2 -CH2-CMe = CH2 CH2C=CH -CH2-CH = CH-CH3 -CH2-CH = CH-CH = CH2 -CH2-(CH2)7-CH = CH-(CH2)7-CH3 The unsaturated derivatives of the invention may be prepared by a number of different procedures such as: (a) reaction of a mono- or di-sodium salt of EDTA with an alkenyl chloride such as methallyl chloride or allyl chloride; (b) by partial esterification of EDTA itself with an unsaturated alcohol such as allyl alcohol; (c) by partial transesterification of the tetramethyl ester of EDTA; (d) from ethylene diamine, methyl vinyl ketone and hydrogen cyanide, to give the intermediate::

which is then reacted with formaldehyde and hydrogen cyanide and subsequently hydrolysed to give

(A derivative containing two unsaturated groups may be prepared by a similar procedure); and (e) from ethylene diamine, formaldehyde and hydrogen cyanide, to give the intermediate: (NCCH2)2N-CH2CH2-N(CH2CN)2 which is then wholly hydrolysed with an unsaturated alcohol or, preferably, hydrolysed partly with such an alcohol and partly with water.

The unsaturated derivatives of this invention may be used as such but they are usually first polymerised on their own or with other monomers, or they are grafted onto a preformed polymer. In these forms, they can be cast into beads, extruded as sheets or tubes, formed into membranes or used as surface coatings.

Uses of the novel polymers include all the normal uses of chelating agents with the major advantages of the polymeric form of the product. They include the recovery of metals from solution, the removal of trace components from effluents and the softening of water.

In addition, they can be employed, for example, for the support of metal ions to be used as catalysts, or in surface coatings where powerful adhesion to the metal is of great importance.

By way of example, the mono-allyl ester of EDTA, formed by reaction of allyl chloride and the mono-sodium salt, can be polymerised to form a homopolymer which can be extruded in a multitubular form for water softening; The divinyl ester of EDTA may be copolymerised with styrene and used in bead form for extracting heavy metal ions from effluents; The diallyl ester (as monomer) of EDTA may be used for the surface treatment of glass fibres to improve their adhesion in glass-reinforced polyester; The dimethallyl ester of EDTA may be grafted onto polyethylene sheet and used to provide a catalytically active surface of chelated metal ions; The vinyl methyl derivative of EDTA

as a homopolymer may be used in granular form for the removal of metallic ion catalysts from process streams.

The mono-allyl ester of EDTA may be copolymerised with vinyl acetate and used as a coating for thin sheet steel; and The monovinyl trimethyl ester of EDTA (prepared by ester exchange) may be copolymerised with vinyl acetate and used in combination with vinyl dihydrogen phosphate for coating oxidised steel.

Claims (3)

1. A compound of the formula

in which the groups X are the same or different and are each

wherein R' and R2 are each H or hydrocarbyl and R3 is H, hydrocarbyl or a positive ion, provided that at least one of the groups X contains a group R1, R2 or R3 which is unsaturated hydrocarbyl, containing one or more olefinic or acetylenic bonds.

2. A compound as claimed in claim 1, wherein one or two of the groups X have an unsaturated group R', R2 or R3.

3. A polymer derived from monomers including a compound according to either preceding claim.