1.1.1- Trihalides 1.1.1- trichlorides

Reaction with phosphorus trihalides (Section 4 13) Phosphorus trichloride and phosphorus tribromide convert alcohols to alkyl halides... 

The most stable product of the action of fluorine on metallic palladium is actually Pd [Pd Fg], and true trihalides of Pd do not occur. Similarly, the diamagnetic trichloride and tribromide of Pt... 

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)... 

A. Synthetic Methods.—Electrophilic addition of P compounds to olefinic compounds is a well-established route to phosphonic acids, although yields are often disappointing. With phosphorus pentachloride it has been found that yields are greatly improved when phosphorus trichloride is added to the reaction mixture. Since the orientation of the addition implies that electrophilic addition to phosphorus rather than chlorine is the initial step, it seems likely that the trihalide participates by decreasing the free concentration of chlorine rather than by a more active role. This... 

Bismuth salts, 4 25 Bismuth sesquisulfide, 4 24 Bismuth subcarbonate, 4 36 Bismuth subgallate, 4 36 Bismuth subhalides, 4 19 Bismuth subnitrate, 4 36 Bismuth subsalicylate, 4 1, 36 medical applications of, 22 11-12 Bismuth(III) sulfate, 4 25 Bismuth(III) sulfide, 4 24 Bismuth sulfides, 4 24-25 Bismuth thiolates, 4 25 Bismuth-tin alloy waterfowl shot, 4 15 Bismuth triacetate, 4 25 Bismuth tribromide, 4 21 physical properties of, 4 20t Bismuth trichloride, 4 19-20 physical properties of, 4 20t Bismuth trifluoride, 4 19 physical properties of, 4 20t Bismuth trihalides, 4 19 Bismuth triiodide, 4 21-22 physical properties of, 4 20t Bismuth trinitrate pentahydrate, 4 25 Bismuth trioxide, 4 23-24 physical properties of, 4 20t Bismuth triperchlorate pentahydrate, 4 25... 

Gallium tribromide, 72 356 Gallium trichloride, 72 356 Gallium trihalides, 72 356, 357-358 Gallium triiodide, 72 356 Gallopamil, 5 121-122 molecular formula and structure, 5 119t Galvanic corrosion, 7 804-806 as failure mechanism, 26 983 in industrial water treatment,... 

Organotin trichlorides, 24 811 Organotin trihalides, physical properties of, 24 824t... 

First, the methods that apply to all three trihalides are reviewed then other specific methods are mentioned. Far fewer methods have been perfected for preparing anhydrous lanthanide tribromides than for the trichlorides, though most of them are similar. The triiodides are the most difficult to prepare, as the iodine analogs of several useful chloro and bromo sulfur and carbon compounds are not known. Reaction temperatures for preparation of triiodides have to be carefully controlled, as Sml3 and Ybl3, for example, decompose easily at elevated temperatures to diiodides. The existence of Eul3 is questionable, with EuI2 formed even at room temperature. 

Undoubtedly, the best method for the production of pure anhydrous lanthanide trihalides involves direct reaction of the elements. However, suitable reaction vessels, of molybdenum, tungsten, or tantalum, have to be employed silica containers result in oxohalides (27). Trichlorides have been produced by reacting metal with chlorine (28), methyl chloride (28), or hydrogen chloride (28-31). Of the tribromides, only that of scandium has been prepared by direct reaction with bromine (32). The triiodides have been prepared by reacting the metal with iodine (27, 29, 31, 33-41) or with ammonium iodide (42). 

Before the availability of high-purity lanthanide metals, the most popular starting material was the oxide, readily available pure. Because of their high stability, the oxides cannot readily be converted into the respective trihalides simply by reaction with chlorine or hydrogen chloride as oxochlorides are formed nevertheless, Templeton and Carter (45) have prepared pure trichlorides using this method. 

One of the oldest methods is to pass HX gas over the heated hydrated trihalide. Thus, hydrated trichlorides (61, 88-92) are heated initially to 105°C, and then when most of the water has been removed the temperature is raised to 350°C. This method works well for trichlorides, but it does not produce pure tribromides (93-95) or triiodides better results are obtained when the triiodides are heated in a flow of HI and... 

A better method involves evaporating a solution of LnX3 containing NH4X (in a mole ratio of 1 6 for chlorides and 1 12 for iodides) to dryness. The product is transferred to a vacuum line and is slowly heated to 200°C to drive off all the water. The temperature is then raised to 300°C to sublime off the ammonium halide. This method has been used extensively to produce pure trihalides and has proved to give very good results for trichlorides (52, 78, 79, 98-105), tribromides (100-103, 106-108), and triiodides (39,40,49,100,102,103,106,107,109-111). 

The methods discussed produce trihalides of varying purity however, if very pure trihalides are required, they can be sublimed at high temperature from any oxide or oxohalide impurities. The trichlorides can usually be obtained pure, but the tribromides and triiodides tend to be contaminated with oxides and oxoiodides. The various methods of preparing triiodides are compared by a few authors 39, 40, 49, 132), and they recommend their preferred route, which generally is the direct reaction between the metal and iodine. 

Fig. 1. Enthalpies of solution of lanthanide trihalides in aqueous media ( ) anhydrous trichlorides (183) and trichloride hexahydrates (189) in water (A) trichloride hex-ahydrates in dilute hydrochloric acid (190) ( ) trichloride hexahydrates in aqueous magnesium chloride solution (191) ( ) anhydrous triiodides in water (192). Values for the trichlorides refer to 25°C, for the triiodides to 20°C. Filled symbols represent experimental determinations, open symbols represent estimates.

Hproblems associated with all the trihalides of this review of the presence of small amounts of hydrates or oxochlorides. While on the matter of possible impurities, it may be recalled that in Bommer and Hohmann s early work there is a discrepancy between enthalpies of solution of anhydrous trichlorides and of respective metals in hydrochloric acid. Here the more likely impurity to be responsible is unreacted potassium metal in the lanthanide metal used in the hydrochloric acid dissolution experiments. 

Comparisons of solubilities of trichlorides, tribromides, and triiodides of the lanthanides in a variety of nonaqueous solvents can be found in a Russian review (310). Perhaps the widest range of solubilities of lanthanide(III) salts in nonaqueous media refers not to the trihalides but to the nitrates, whose solubilities in 31 solvents have been measured (312). Unfortunately, these measurements were carried out on the hexahydrates rather than anhydrous materials. 

In principle, Gibbs free energies of transfer for trihalides can be obtained from solubilities in water and in nonaqueous or mixed aqueous solutions. However, there are two major obstacles here. The first is the prevalence of hydrates and solvates. This may complicate the calculation of AGtr(LnX3) values, for application of the standard formula connecting AGt, with solubilities requires that the composition of the solid phase be the same in equilibrium with the two solvent media in question. The other major hurdle is that solubilities of the trichlorides, tribromides, and triiodides in water are so high that knowledge of activity coefficients, which indeed are known to be far from unity 4b), is essential (201). These can, indeed, be measured, but such measurements require much time, care, and patience. 

The reactivity of aryltellurium trihalides decreases on going from the chlorides to the iodides, the same trend occurring for hydrolysis. Aryltellurium trichlorides are very sensitive to water and moisture and are easily hydrolysed, the tribromides being more stable, while the triiodides are unaffected by cold water and can be prepared even by aqueous procedures. Diaryltellurium dihalides are stable in water, and ionic exchange reactions allow the conversion of dichlorides into dibromides and diiodides. 

Tellurium tetrachloride and aryltellurium trichloride, as well as tellurium tetrabro-mide" and aryltellurium tribromides add to acetylenes to produce, respectively, 2-halovinyl tellurium trihalides and dihalides, which can be submitted to further manipulations. 

Alkylmercury anions, 11 370-371 Ai-Alkyl-A-nitrosohydroxylamine, 34 355-356 Alkylphosphazo trihalides reactions of, 14 70-77 spectral properties of, 14 78-80 syntheses of, 14 59-77 X-ray studies on, 14 80-81 Alkylphosphonofluoridous esters, 13 4(K), 401 Alkylphosphorimidic trichloride, nomenclature of, 14 3, 4... 

Crystalline indium trihalides are readily prepared from the reaction of the metal and halogen9 (sometimes in the presence of solvent), from metal+ HX, or by the electrochemical oxidation of the metal in a non-aqueous solution of X2.20 Indium trichloride and tribromide have indium octahedrally coordinated by halide in the solid state, whereas the triiodide exists as the dimer I2lnl2InI2 in the solid or in solution all three halides are dimeric in the vapor phase.9 The many adducts of these compounds with neutral donors have been extensively reviewed previously.5,7... 

Products that formally derive from the trihalides by solvolysis have been obtained (i) by metathesis of MUI trichloride adducts (ii) from reactions of [TaCl2(dmpe)2] (23) and (iii) by... 

Bismuth Halides. The bismuth trihalides are the best known. Bismuth does form a single pentahalide, BiF5, and subhalides that approximate the composition BiX, the best characterized of these being BiCl11(57. Vapors above solutions of a bismuth trihalide in molten bismuth contain the species BiX and/or (BiX)w, where X = Cl, Br, or I (9). At temperatures below 323°C, a black, diamagnetic, orthorhombic solid of the overall composition BiCl1 7 may be isolated from solutions of bismuth trichloride in molten bismuth (10). 

Triarylbismuthines have been synthesized by means of the Nesmeyanov reaction that employs an arenediazonium salt such as the tetrafluoroborate, a bismuth trihalide, and a reducing agent (51). The decomposition of iodonium salts in the presence of bismuth trichloride and metallic bismuth also leads to the formation of triarylbismuthines, Ar3Bi (52) ... 

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