Protactinium reactions

Meitnerium - the atomic number is 109 and the chemical symbol is Mt. The name derives from the Austrian physicist Lise Meitner , who had discovered the element, protactinium. The first synthesis of the element Meitnerium is credited to German physicists from the GSI (Center for Heavy-Ion Research) lab at Darmstadt, Germany under Gunther Miinzenberg, in 1982 using the nuclear reaction ° Bi ( Fe, n) Mt. The longest half-life associated with this unstable element is 0.07 second Mt. 

This article presents a general discussion of actinide metallurgy, including advanced methods such as levitation melting and chemical vapor-phase reactions. A section on purification of actinide metals by a variety of techniques is included. Finally, an element-by-element discussion is given of the most satisfactory metallurgical preparation for each individual element actinium (included for completeness even though not an actinide element), thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, and einsteinium. 

Protactinium-233 is produced by the beta decay of the short-lived thorium-233. Thorium-233 is obtained by neutron capture of natural thorium-232. The nuclear reactions are as follows ... 

Protactinium dipnictides (X = As, Sb) have been synthesized by reaction of As or Sb vapour with metal hydride at 400-700 Pa3As4 was obtained by thermal dissociation of PaAs2 at 840 °C, Pa3Sb4 from the corresponding dipnictide at 1200 °C. Monopnictides of protactinium were not obtained by thermal dissociation of higher compounds. The diantimonides of the transuranium elements Np, Pu, Am dissociate between 700-800 °C into the monocompounds. Monopnictides of the higher transuranium elements have been obtained at the pg scale with and 0 by thermal dissociation. 

To remove radium and other radioactive constituents from pitchblende, Hahn and Meitner treated pulverized pitchblende repeatedly and for long periods of time with hot concentrated nitric acid. From the insoluble siliceous residue they separated a new radioactive substance, which they called protoactinium. This name has subsequently been shortened to protactinium. When they added a little tantalum salt to a solution containing protactinium, the reactions of the new substance so closely resembled those of tantalum that Hahn and Meitner were unable to separate the two substances (118). Since tantalum is not radioactive, the protactinium could thus be obtained free from other radioelements. Since protactinium is not an isotope of tantalum, it should be possible to separate them from each other (119). By working up large quantities of rich pitchblende residues from the Quinine Works at Braunschweig, Hahn and Meitner were able to extract more active preparations of the new element (49). 

In the fall of 1934, Dr. Grosse reduced this pure oxide by two methods and obtained from it the metal protactinium, which is even rarer than radium, but much more permanent in air. In die first method, he bombarded the oxide on a copper target, in a high vacuum, with a stream of electrons. After a few hours, he obtained a shiny, partly sintered, metallic mass, stable in air. In his second method, he converted the oxide to the iodide (or chloride or bromide) and cracked it in a high vacuum on an electrically heated tungsten filament, according to the reaction ... 

The only examples of compounds of this type are the borohydrides, MIV(BH4)4 (MIV = Th-Pu) and MIV(MeBH3)4 (MIV = Th, U, Np). These compounds are conveniently prepared by reaction, for example, of the metal tetrafluoride with A1(BH4)3 in a sealed tube, followed by vacuum sublimation of the product.159 The neptunium and plutonium compounds are liquids at room temperature and are more volatile than the thorium, protactinium or uranium analogues. 

The probable existence of protactinium was predicted as early as 1871 by Mendeleev to fill up the space on his peiiodic table between thorium (at, no. 90) and uranium (at. no, 92). He termed the unconfirmed element ekatantalum. In 1926, O. Hahn predicted the properties of the element in considerable detail, including descriptions of its compounds. In 1930, Aristid v. Grosse isolated 2 milligrams of what then was termed ekatantalum pentoxide and showed that element 91 differed m all reactions with comparable amounts of tantalum compounds with exception of precipitation by NH3. However, credit for the discovery of protactinium generally is attributed to Lise Meitner and Otto Hahn in 1917,... 

Volatile protactinium pentaehloride has been prepared in a vacuum by reaction of the oxide with phosgene at 550° C or with carbon tetrachloride at 200°C. Reduction of this at 600°C with hydrogen leads to protactinium(IV) tetrachloride, Pad. which is isostructural with uranium(IV) tetrachloride, UCI4. The pentaehloride can be converted into the bromide or iodide by heating with the corresponding hydrogen halide or alkali halide... 

Thorium phthalocyanine is prepared by heating the metal (previously etched with HC1) and o-phthalonitrile, 1 25, at 270 to 300°C for 5 hr. The dark blue product is cooled to room temperature, washed with benzene, and purified twice by sublimation at 520°C and 10 4Torr. The protactinium-233 produced by w-irradiation of pure thorium phthalocyanine is separated in high purity in the residue after repeated sublimation of the thorium phthalocyanine. The thorium-231 produced by (w,2w) reaction in the thorium phthalocyanine is found to be enriched in the residue after sublimation, indicating decomposition of the phthalocyanine by irradiation. Uranyl phthalocyanine is prepared by heating a mixture of uranyl acetate and phthalonitrile at 230 to 240°C. 

Actinium and protactinium are present in uranium minerals but recovery is not generally practiced. Neptunium (237Np and 239Np) and plutonium (M9Pu) are present in minute amounts in uranium ores because they result from reaction of neutrons with uranium isotopes, not due to survival from primordial formation. All other actinides are entirely synthetic. Methods of preparation for those up to Cf are given in Table 20-2 syntheses of the other elements are noted in Section 20-18. 

The actinides are all radioactive elements. Actinium, thorium, protactinium, and uranium are the only four actinides that have been found in the environment the others are artificial, being produced through various nuclear reactions. It should be noted that at the creation of the universe some amount of Pu could have been formed however, with an 80 million year half-life, it would have fully decayed during the past 10 billion years. 

Unlike uranium pentaehloride, which is thermally unstable, protactinium pentachloride sublimes unchanged above 180°C in vacuo. It is a yellow, moisture-sensitive solid which is slightly soluble in benzene, tetrahydrofuran, and carbon tetrachloride. Visible absorption speetra have been reeorded for solutions in the last two solvents and in aleohol (110). Reactions with hydrogen, aluminum, oxygen, and silicon tetra-iodide are discussed below. It is unaffected by carbon monoxide at 350°C in a sealed tube. 

Protactinium pentaiodide was first prepared by reacting the pentox-ide with aluminum triiodide at 400°C in a vacuum (104). For large scale preparations, however, direct union of the elements or metathesis of the pentaohloride or pentabromide with an excess of silicon tetraiodide are best (40). The latter reactions take place rapidly at about 180°C in vacuo and the black crystalline product is then purified by vacuum sublimation at 400°-450°C. Silicon tetraiodide also reacts with protactinium pent-oxide, but temperatures in excess of 600°C are required with the reaction vessel completely enclosed in the furnace, and the yield is only about 70% (40). 

The protactinium(IV) fluoro complexes have been prepared either by hydrogen reduction of a pentavalent complex at 400°C or by heating together appropriate amounts of MF and PaF4 in sealed vessels. The reaction between ammonium fluoride and protactinium tetrafluoride to yield (NH4)4PaFg, the only octafluoro complex known, takes place when the component halides are ground together at room temperature (4,114). 

Although protactinium(V) chloro complexes can also be prepared using methyl cyanide as the solvent (32) (cf. PaBrg" and Pale ), the use of thionyl chloride has several advantages. Thus, it means that one can start with protactinium(V) hydroxide and not the pentachloride, thionyl chloride itself affords protection against atmospheric moisture and dry-atmosphere boxes are not necessary for the preparations, and, in addition, protactinium(V) concentrations up to 0.5 M have been obtained by dissolving the hydroxide in thionyl chloride (75). Such solutions are quite stable in contrast to the hydrolytic condensation reactions which occur in concentrated hydrochloric acid at Pa(V) concentrations as low as 10 M. 

A. A -Dimethylacetamide (DMA) forms a 1 3 complex with protactinium pentabromide (23), but its reaction with other pentahalides has not been studied. 

The results of solid state reactions of protactinium dioxide and pentoxide with other metal oxides (89, 93-96) support the view that the oxide systems of protactinium resemble those of other actinide elements rather than those of niobium and tantalum. However, when assessing results of this type one must always bear in mind the relative ionic radii of the respective M " and M + ions since they obviously play a large part in determining the structures of the complex phases. This comment applies equally well, of course, to the structural properties of other types of compound and in particular to the high coordination numbers exhibited by protactinium(V) in its chloro and nitrato complexes. 

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