Zirconium phosphonate synthesis

Layered metal IV phosphonates are widely used, particularly zirconium phosphonates, because their synthesis is versatile and their structural arrangement may be tailored to applications. Zirconium phosphonates are usually prepared by heating an aqueous solution of a metal IV salt (e.g., ZrOCl2) with a phosphonic acid at 60-80 °C synthesis in the presence of HP permits one to increase significantly the crystallinity of the final products. 

Debashis C, Vadapalli C, Manish B, Ralph K, Roesky WH, Mathias N, et al. Metal aUcoxides as versatile precursors for group 4 phosphonates synthesis and X-ray structure of a novel organosoluble zirconium phosphonate. Inorg Chem 2000 39(l) 23-6. 

FIGURE 15 Synthesis of molecular multilayers of controlled thickness using zirconium phosphonate chemistry. 

Synthesis and Study of Asymmetrically Layered Zirconium Phosphonates... 

Despite the significant work reported in the literature for these materials, there are few examples of the synthesis of zirconium phosphonates containing pendant acid groups and then-utilization as ion exchangers or as solid catalysts [refs. 5-8]. The ability to incorporate specific pendant functional groups into MELS provides opportunities for the development of several classes of novel solid acid catalysts. This paper provides an introduction to MELS materials, a description of synthetic methods used to produce solid MELS catalysts containing pendant sulfonic acid groups, and a discussion of some of the physical and catalytic properties of these materials. 

The synthesis of metal phosphonates is typically achieved via a precipitation reaction, where two soluble precursors are mixed, typically in aqueous solution, to produce an insoluble product. Any tetravalent metal ion can be utilized that can accommodate an octahedral coordination environment, such as Zr, Ti, Sn, Ce, Th, U. Most reported work employs zirconium as the metal, due to its availability, easy formation of products, and moderate cost. Other metals may be chosen for specific properties i.e., to provide larger intralayer spacing. For synthesis of zirconium phosphonates, typical precursors such as zirconium oxychloride, ZrOCl2.8H20 or zirconium sulfate, Zr(S04)2.4H2O can be used. 

In an application of the Paal-Knorr pyrrole synthesis, the synthetic equivalents 3 of 1,4-ketoaldehydes were prepared by the radical addition of ketones 4 to vinyl pivalate. Treatment of the intermediates 3 with amines gave pyrroles 5 <03SL75>. Other new extensions of this popular pyrrole synthesis include the preparation of a number of pyrroles from hexane-2,5-dione and amines under solvent-free conditions in the presence of layered zirconium phosphate or phosphonate catalysts <03TL3923>, and the development of a solid-phase variant of this reaction <03SL711>. Likewise, the preparation of iV-acylpyrroles from primary amides and 2,5-dimethoxytetrahydrofuran in the presence of one equivalent of thionyl chloride has also been reported <03S1959>. 

Snover, J.L. and Thompson, M.E., Synthesis and Study of Zirconium Viologen Phosphonate Thin-Films Containing Colloidal Platinum / Am. Chem. Soc. 1994, 116, 765. 

In 1988, it was discovered that 3-phospholenes can be prepared directly by the reaction of zirconium metallocycles with phosphonous dihalides (Equation (50)) <88JA2310>. The synthesis of only one phospholene (3,4-dimethyl-l-phenyl) has been reported so far, but the method appears to have a good chance of possessing valuable versatility. 

Tetravalent metal phosphonates, or MELS (for Molecularly Engineered Layered Structures), provide a novel class of materials that combine many of the properties of incn-ganic metal oxides with the organic functionality more commonly found in functionalized polymeric resins. Early development work on these materials was carried out by Alberti and co-woikers [ref. 1] and Dines et al. [ref. 2]. Synthesis and characterization of related zirconium phosphates that also contain phosphonate groups as pillars have been described by Clearfield [ref 3]. There is a substantial patent estate for tetravalent metal phosphonates, and exclusive rights to this estate are owned by Catalytica [ref 4]. 

Zirconium sulfophenylphosphonate can be prepared by the reaction of a water soluble zirconium salt with sulfophenylphosphonic acid. This phosphonic acid has been described in patent literature [ref. 22], but diere is no evidence of its actual synthesis. We found that sulfophenylphosphonic acid can be syndierized by the reaction of phenylphosphonic dichloride with CISO3H or SO3. The reaction of phenylphosphonic dichlmide with excess CISO3H proceeds smoothly to m-sulfophenylphosphonic dichlmide at 150 °C and to the phosphonic acid on subsequent hydrolysis. Purification of the acid requires removal of excess sulfate by barium precipitation, followed by ion exchange to remove excess barium. For a sulfate-fiee synthesis, we tried the direct sulfonation of phenylphosphonic acid with liquid SO3- The sulfonation proceeds readily at 125 °C, with excess SO3 relative to stoichiometry. We found that 1 1 ratios of S03 phenylphosphonic acid are insufficient for complete sulfonation, even under forcing conditions, due to the competitive formation of mixed anhydrides of sulfophenylphosphonic acid and SO3, depicted in fig. 4. This competitive formation results in a consumption of greater than 1 mole of SO3 per mole of phenylphosphonic acid. These anhydrides are thermally stable but may be converted to sulfophenylphosphonic acid by hydrolysis however, this method also requires sulfate removal from the final product. 

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