Preparation trihalides

A complete set of trihalides for arsenic, antimony and bismuth can be prepared by the direct combination of the elements although other methods of preparation can sometimes be used. The vigour of the direct combination reaction for a given metal decreases from fluorine to iodine (except in the case of bismuth which does not react readily with fluorine) and for a given halogen, from arsenic to bismuth. 

In addition to the trihalides, arsenic and antimony form penta-fluorides and antimony a pentachloride it is rather odd that arsenic pentachloride has not yet been prepared. 

The importance of the trihalides as industrial chemicals stems partly from their use in preparing crystalline boron (p. 141) but mainly from their ability to catalyse a wide variety of organic reactions.BF3 is the most widely used but BCI3 is employed in special cases. Thus, BF3 is manufactured on the multikilotonne scale whereas the production of BCI3 (USA, 1990) was 250 tonnes and BBr3 was about 23 tonnes. BF3 is shipped in steel cylinders containing 2.7 or 28 kg at a pressure of 10-12 atm, or in tube trailers... 

Many of the trihalides of As, Sb and Bi hydrolyse readily but can be handled without great difficulty under anhydrous conditions. AsFs and SbFs are important reagents for converting non-metal chlorides to fluorides. SbFs in particular is valuable for preparing organofluorine compounds (the Swans reaction) ... 

The trihalides of As, Sb and Bi are strong halide-ion acceptors and numerous complexes have been isolated with a wide variety of compositions. They are usually prepared by direct reaction of the trihalide with the appropriate... 

Lower oxidation states are rather sparsely represented for Zr and Hf. Even for Ti they are readily oxidized to +4 but they are undoubtedly well defined and, whatever arguments may be advanced against applying the description to Sc, there is no doubt that Ti is a transition metal . In aqueous solution Ti can be prepared by reduction of Ti, either with Zn and dilute acid or electrolytically, and it exists in dilute acids as the violet, octahedral [Ti(H20)6] + ion (p. 970). Although this is subject to a certain amount of hydrolysis, normal salts such as halides and sulfates can be separated. Zr and are known mainly as the trihalides or their derivatives and have no aqueous chemistry since they reduce water. Table 21.2 (p. 960) gives the oxidation states and stereochemistries found in the complexes of Ti, Zr and Hf along with illustrative examples. (See also pp. 1281-2.)... 

All four monohalides of gold have been prepared but the fluoride only by mass spectrometric methods. AuCl and AuBr are formed by heating the trihalides to no more than 150°C and Aul by heating the metal and iodine. At higher temperatures they dissociate into the elements. Aul is a chain polymer which features linear 2-coordinate Au with Au-I 262 pm and the angle Au-I-Au 72°. 

The anhydrous trihalides are ionic, high melting, crystalline substances which, apart from the trifluorides are extremely deliquescent. As can be seen from Table 30.4, the coordination number of the Ln changes with the radii of the ions, from 9 for the trifluorides of the large lanthanides to 6 for the triiodides of the smaller lanthanides. Their chief importance has been as materials from which the pure metals can be prepared. 

The preparation of a-iodocarboxylic acids is of particular interest, since iodide is a better leaving group as is chloride or bromide. A similar a-iodination with a phosphorus trihalide as catalyst is not known. However the iodination can be achieved in the presence of chlorosulfonic acid mechanistically the intermediate formation of a ketene 10 by dehydration of the carboxylic acid is assumed ... 

Lanthanide, yttrium and scandium trihalides preparation of anhydrous materials and solution thermochemistry. J. Burgess and J. Kijowski, Adv. Inorg. Chem. Radiochem., 1981, 24, 57-114, (320). 

Molybdenum hexafluoride. 3,1412 Molybdenum-iron-sulfur complexes, 4,241 Molybdenum oxide amino acid formation prebiotic systems, 6, 872 Molybdenum storage protein microorganisms, 6, 681 Molybdenum telluride, 3, 1431 Molybdenum tetraalkoxides physical properties, 2, 347 Molybdenum tribromide, 3,1330 Molybdenum trichloride, 3,1330 Molybdenum trifluoride, 3, 1330 Molybdenum trihalides, 3, 1330 bond lengths, 3, 1330 magnetic moments, 3,1330 preparation, 3,1330 properties, 3, 1330 structure, 3,1330 Molybdenum triiodide, 3,1330 Molybdenum trioxide complexes, 3, 1379 Molybdenum triselenide, 3, 143)... 

For single crystals, the same method is applied, using an excess of metal and of halogen. After reaction, the mixture of the sulfide halide and the halide is heated to a temperature slightly above the melting point of the respective halide. Perfect, small crystals for X-ray determination are formed. The excess of the trihalide is removed by treatment with anhydrous alcohol 92, 93, 96). CeSI may also be prepared from the sulfides 68, 93) CeSCl is formed by reaction 4 92). 

This reaction is similar to the previous one. The utility of the method is limited by the lack of availability of trihalides, though these compounds can be prepared by addition of CCI4 and similar compounds to double bonds (15-44) and by the free... 

Rowley, A. T. et al., Inorg. Chem. Acta, 1993, 211(1), 77 Preparation of metal oxides by fusing metal halides with lithium oxide in a sealed tube leads to explosions if halide hydrates are employed, particularly lanthanide trihalide hydrates. The preparation succeeds with anhydrous halides. This will be purely a question of vapour pressure above an exothermic reaction the question is whether the vapour is water, or metal halide, and the reaction oxide formation, or hydration of lithium oxide. Like other alkali metal oxides, hydration is extremely energetic. 

Although 1,3,2-diazaphospholenium cations are usually prepared from neutral NHPs or 1,3,2-diazaphospholes via Lewis-acid induced substituent abstraction or A-alkylation, respectively (cf. Sect. 3.1.2), the group of Cowley was the first to describe a direct conversion of a-diimines into cationic heterocycles by means of a reaction that can be described as capture of a P(I) cation by diazabutadiene via [4+1] cycloaddition [31] (Scheme 4). The P(I) moiety is either generated by reduction of phosphorus trihalides with tin dichloride in the presence of the diimine [31] or, even more simply, by spontaneous disproportionation of phosphorus triiodide in the presence of the diimine [32], The reaction is of particular value as it provides a straightforward access to annulated heterocyclic ring systems. Thus, the tricyclic structure of 11 is readily assembled by addition of a P(I) moiety to an acenaphthene-diimine [31], and the pyrido-annulated cationic NHP 12 is generated by action of appropriate... 

Also studied was the effect of ether, which behaves as a retarder, on the polymerization. The retardation is most marked with the di- and trihalides and least with the monohalide and Zr (allyl) 4. In fact if large amounts of ether are present from the preparation, Zr(allyl)2Br2 shows hardly any activity at all. To avoid any possibility of contamination by ether, the halides in Table XI were prepared from pure ether-free Zr(allyl)4 in toluene by reaction with propargyl bromide. 

Electric discharge in a mixture of PC13 and H2 produces P2C14, and white phosphorus dissolved in carbon disulfide reacts with I2 to produce P2I4. All of the trihalides of the group VA elements are known, and they can be prepared by reaction of the elements, although there are other preparative methods. The fluorides are prepared as follows ... 

Alkyltin trihalides with chain lengths of up to 18 carbon atoms can be prepared in the presence of trialkylantimony catalysts340 ... 

LANTHANIDE, YTTRIUM, AND SCANDIUM TRIHALIDES PREPARATION OF ANHYDROUS MATERIALS AND SOLUTION THERMOCHEMISTRY... 

The determination of many thermodynamic solution properties of these trihalides, especially enthalpies of solution, requires the use of anhydrous materials. These are by no means always readily available for this group of compounds. Therefore we precede our discussion of thermochemical results with a section on preparative methods, in which we deal summarily with many of the relevant papers published since Taylor s extensively referenced review, published in 1962 (2). 

The preparations of rare-earth trihalides can be found in various books (2-8) and in Taylor s review (2 ). This review, however, did not include the preparation of scandium and yttrium trihalides, and only covered the preparation of the trifluorides very briefly. We have reviewed the preparation of all the trihalides (including scandium and yttrium) from Taylor s review up to June 1979 and have also included some methods and references missed by Taylor. Although we have mentioned all the methods available for the preparation of the trihalides, emphasis has been placed on the methods used since Taylor s review, and these have been referenced fully, whereas for the other methods, Taylor s review is recommended as a source of references. 

The preparation of promethium trihalides has been mentioned by Scherer (9). However, the radioactive nature of these compounds has prevented any calorimetric or solubility investigations so far, and they make only one fleeting appearance in this review. 

Taylor s treatment of lanthanide trifluorides was considerably more cursory than that of the other three trihalides, but nonetheless still provides a starting point (2). More recently, the extraction, preparation, and treatment of the trifluorides have been dealt with in Gmelin (4a). 

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