IMPROVEMENTS IN OR RELATING TO THE FORMATION OF METAL ALKOXIDES AND METAL POWDERS BY THE USE OF MICROWAVE RADIATION

Abstract: The method of forming metal alkoxides and metal powders which consists in the formation and elimination of water or equivalent compounds and the resultant production of a metal alkoxide or metal powder in which particular metal compounds when in a solution or suspension are subjected to molecular bond excitation by microwave radiation.

Description: "IMPROVEMENTS IN OR RELATING TO THE FORMATION OF METAL ALKOXIDES AND METAL POWDERS BY THE USE OF MICROWAVE RADIATION" This invention relates to the formation and elimination of water or equivalent compound and the resultant production of a metal alkoxide from a solution or suspension of particular metal compounds 5. in a suitable polyhydric alcohol by a reaction initiated and maintained by the absorption of microwave radiation. Examples of this invention are given by the formation of metal alkoxides of propanetriol (glycerolates) 10. when particular compounds of these metallic elements such as zinc or bismuth are mixed with or dissolved in glycerol and the resultant solution or suspension is irradiated by microwave energy of a suitable wavelength. The reactions involved may be exemplified 15. by chemical equations shown the formation of zinc glycerolate (Zinc(l,2,3-propanetriolato(2-)- Dl, D2) homopolymer, stereoisomer; C-H,0_jZn) from a suspension of zinc hydroxide (or a solution of zinc acetate) in glycerol (propanetriol, C-HQO,,):- microwave K 0. Z n(OH) 2 + C 3 H 8 0 3 energy C 3 H 6 0 3 Zn + 2H 2 0 and:- microwave (CH 3 COO) 2 Zn + C 3 H 8 0 3 energy ^ C 3 H 6 0 3 Zn + 2CH 3 C00H A further example of the invention may be given by the formation of a new crystalline metal-organic 5 - compound, when say, zinc hydroxide is reacted with the polyhydric alcohol sorbitol (CH 2 0H-(CH0H)^- CH 2 OH) . The invention is not limited to the compounds of these elements or to the alcohols glycerol 5« and sorbitol but extends to and embraces any other element whose particular compounds may be reacted with a di-, tri- 3 or poly-hydric alcohol by these microwave techniques. The high temperature formation of the glycerolates 10, of zinc, cobalt, manganese and iron has already been described, (1) Australian Journal of Chemistry vol. 23 no. 10, pl963 1971, Radoslovich, E.W., Raupach, M. , Slade, P.G. and Taylor, R.M. 15 - (2) Clays and Clay Minerals vol. 18 (1970), p53-62, Fuls, P.F., Rodrique, L. and Fripiat, J.J. (3) Australian Journal of Chemistry vol. 36 (1983) p 1249-1253, Hambly, T.J. and Snow, M.R. 20. These reactions are achieved by the direct heating of particular oxides or hydroxides or other suitable compounds or salts of these metallic elements in the polyhydric alcohol, glycerol. The pharmaceutical, cosmetic and various industrial 25. applications of the zinc glycerolate, formed by the reaction of certain zinc compounds with glycerol at elevated temperatures, are the subjects of previous patents granted and applied for namely: U.K. Letters Patent No. 2101132 May 15, 1985, R.M. Taylor and A.J. Brock. Letters Patent France 81 21 914 November 23, 1981, 5 * R.M. Taylor and A.J. Brock. United States of America Patent 4,544,761 October 1, 1985, R.M. Taylor and A.J. Brock. In the first place therefore this invention specific¬ ally relates to an improved method of forming 10, these high-temperature glycerolate compounds by the use of a new technique whereby the absorption of radiated microwave energy of a suitable wavelength causes some nearby C-OH groups to condense to form C - 0 15. M linkages plus water, where M denotes a C - 0 a metal capable of taking part in such a reaction. The formation of an alkoxide or its degree of crystallinity may be limited by steric hindrances 0 « imposed by the size of the metallic cation or by other factors, such as, for example, its coordination requirements. Thus it is claimed that in the presence of particular or suitable metallic oxides, hydroxides, oxy- 5' hydroxides or metallic oxy-salts that thermally decompose to the fine-grained metallic oxide at temperatures below the boiling or decomposition temperature of the alcohol being used, the excitation of the OH groups of the polyhydric alcohol may lead to the coordination of the metal through oxygen ligands to form the alkoxide with an associated formation and elimination of water. 5. However, it is noted that a reaction which may proceed rapidly and efficiently when, say, an aqueous suspension of the metal hydroxide is used, may be inhibited if, for example the oxide or some particular oxide phase of the metal is used 10. instead. Furthermore it is known within the scope of this invention that for the same band-width of wavelengths of the incident microwave energy, particular metal alkoxides may only be induced to form or form efficiently when a suitable compound 15. of the metal, rather than its oxide or hydroxide form, is used. This invention is meant to embrace an alteration of the wavelength band-width of the incident microwave radiation where such a variation may enable the 20. formation of an alkoxide to proceed, or to proceed more efficiently, or to proceed with a desired modification of the properties of the alkoxide. The scope of this invention also includes the application of microwave energy to suspensions 25. or solutions of the compounds of certain metals in polyhydric alcohols where in some cases, as will be exemplified, the metal alkoxide is not the preferred end product of the reaction induced by the irradiation, but rather, a fine-grained, generally crystalline, precipitate of the pure metallic phase may be formed by reductive processes. Therefore the technique of this invention may be said to offer an improvement in the method of formation of some of the metal alkoxides. Moreover where a metallic alkoxide is not formed and the reaction results in the formation of metallic powders, the technique of the invention offers an improvement in the production of these metallic 10. powders from a reaction between particular metal compounds and an alcohol. Examples of the above claim for an improvement in the method of formation of an alkoxide or metallic powders by the technique of this invention are 15. given. By subjecting a suspension of zinc hydroxide in an excess of glycerol to microwave radiation in a normal domestic microwave cooking apparatus very well crystalline zinc glycerolate forms within a few minutes. The improvement in the quality 20. of the crystalline alkoxide so formed may be exemplified by the electron micrographs which form part of this invention and in which the variation in size and morphology of zinc glycerolate crystals is shown, 25. FIG. 1 showing the crystals as prepared by the conventional techniques of heating a suspension of zinc oxide in glycerol, FIG. 2 showing the result of subjecting a suspension of zinc hydroxide in glycerol to microwave radiation 0, for a few minutes. The form of crystal shown in FIG. 1 was the result of prolonged heating with constant stirring, and a similar formation resulted when the prolonged heating was carried out under reduced pressure. 5- In reference to the scanning electron micrographs, it will be of interest to note that crystals as shown in FIG. 1 which result from prior art methods of production, are of less regular form than the crystals shown in FIG. 2, produced by the method of 10. this invention, and further it is to be noted that the crystals of this invention have a more regular hexagonal shape irrespective of size, unlike the prior art crystals. It will be known that the glycerolate crystals 15. shown have a substantial extension in two planes but low thickness, and because of the regular crystalline configuration and substantial variation in extension in two planes, have high covering capacity when similarly orientated and also have 20. substantial lubricity because of the uniformity of the hexagonal crystal formation. It is believed that the microwave action of the present invention induces significant vibration in particular molecular bonds which accelerates and 25. enhances the reaction. It will be appreciated from the photomicrographs that the zinc glycerolate prepared by the conventional technique of heating zinc oxide with glycerol produces irregular crystals, whereas when microwave radiation is applied a much more uniformly crystalline structure results and regular particle production results from a suspension of zinc 5. hydroxide in glycerol. It has been found that improvements offered by the technique of this invention apply in a wide field, and an example is the reaction induced by such microwave energy between a suspension 10. of basic copper carbonate in glycerol or ethylene glycol or a solution of copper acetate in glycerol according to which the formation of micron sized hexagonal copper crystals was found to exist. Further examples of the technique are given by the 15. production of crystalline metallic bismuth by a microwave energy induced reaction between a concentrated aqueous sus.pension of BiOCl admixed with sorbitol, but reference to these examples do not in any way limit the scope of this invention to 20. the initial metallic compounds or the polyhydric materials stated in examples. Further improvements arising out of the technique of this invention are, firstly the reduction in time of formation, 25. secondly a greater measure of control of the reaction between the metal compound and the alcohol and, thirdly a reduced chance of ignition during the formation of the metal alkoxide or metallic micro- crystals. Again without limiting the scope of this invention examples are given for the formation of metal alkoxides by the technique of inducing and maintaining the reaction by the use of absorption of microwave ' energy, each of these subjecting a metal source in the presence of a glycerol to the action of microwaves. EXAMPLE 1 Manganese glycerolate was formed by the addition ■J -^* of one gram of manganese (II) acetate to ten millilitres of glycerol and one millilitre of distilled water and then reacting this solution- suspension in a domestic microwave oven (National model NE-8070, 650 watts) for six minutes at the 1 -** medium power setting of the above oven. The resulting pinkish-white precipitate in the glycerol residues was cooled, washed with ethyl alcohol and dried at 105°C. The dried, pinkish-white powder was highly crystalline and exhibited a high degree 20, of lubricity. EXAMPLE 2 Cobalt glycerolate was formed by dissolving cobalt acetate in an excess of glycerol (1:10) by gentle heating and then adding a small amount of NaOH. 2 -> * The solution was then subjected to absorption of microwave energy and a purple precipitate formed on washing and drying from ethanol, the magenta- coloured, highly lubricious crystalline precipitate was identified as the cobalt glycerolate originally 30. described. EXAMPLE 3 Bismuth glycerolate was formed by a reaction initiated by subjecting a suspension or solution of particular bismuth compounds in glycerol to microwave radiation. -> • A well crystalline alkoxide was formed by dispersing l-2g bismuth subnitrate in 20 ml glycerol and subjecting the suspension to microwave energy (3 minutes on medium setting (National model Genius). On cooling the greyish-white crystalline powder 1 . W as washed and dried from ethanol. EXAMPLE 4 Iron glycerolate was formed by subjecting a suspension of freshly precipitated ferric hydroxide (ferrihydrite) in excess glycerol (ratio approx 5' 1:10) to microwave radiation. The green crystalline powder contained both divalent and trivalent iron and the relative amounts of these two cations caused a variation in colour, the crystalline structure and the composition.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. The method of forming metal alkoxides and metal powders which consists in the formation and elimination of water or equivalent compounds and the resultant production of a metal alkoxide or 5. metal powder, characterised by subjecting particular metal compounds when in a solution or suspension to molecular bond excitation by microwave radiation. 2. The method of claim 1 wherein the solution or suspension medium is an alcohol. 10. 3. The method of claim 2 wherein the alcohol is a polyhydric alcohol. 4. The method of claim 1, 2 or 3 wherein the metal is one capable of being reacted with an alcohol of the group consisting of the di-, tri-, 15. or polyhydric alcohols. 5. The method of claim 1 wherein the metal compound is reacted with sorbitol and the suspension or solution subjected to the microwave reaction. 6. The method of claim 1 wherein metallic compounds 20. are reduced to the metallic state when suspended or dissolved in an alcohol and the suspension or solution is subjected to the microwave reaction. 7. The method of claim 1 wherein the metal compound is reacted with glycerol under microwave radiation to form a glycerolate i.e. glycerato-; propanetriolato- metal complexes. 8. The method of claim 6 or 7 wherein water is added or freed to initiate or form part of the 5. reaction caused by submitting the solution or suspension to microwave reaction. 9. The method of claim 1 for forming crystalline zinc glycerolate comprising subjecting a suspension of zinc hydroxide in an excess of glycerol to 10. the microwave radiation. 10. The method of claim 1 for forming manganese glycerolate comprising adding manganese (II) acetate to glycerol and distilled water in the general proportions of one gram of manganese acetate to 15. ten millilitres of glycerol and one millilitre of distilled water and then reacting the solution so formed to the microwave radiation. 11. The method of claim 1 for forming cobalt glycer¬ olate comprising dissolving cobalt acetate in 20. an excess of glycerol by gentle heating and adding NaOH and then reacting the solution to the microwave radiation. 12. The method of claim 1 for forming bismuth glycerolate comprising subjecting a suspension of 25. bismuth subnitrate in glycerol in the proportions of l-2g bismuth subnitrate to 20 ml glycerol and subjecting a suspension or solution of bismuth so formed to microwave radiation. 13. The method of claim 1 for forming an iron glycerolate comprising subjecting a suspension of freshly precipitated ferric hydroxide in excess glycerol to the microwave radiation. 5. 14. The metal alkoxide and metal powder when produced by the method described in any preceding claim.

Inventors: TAYLOR REGINALD MORTON, TAYLOR, REGINALD, MORTON
Applicants: HALLSWORTH & ASS PTY LTD
Application year: 1987
Main classification: C07C31
IPC codes: B22F9, C07C27, C07C29, C07C31, C07C67