Aluminum, elemental halogens

Zirconium tetrabromide [13777-25-8] ZrBr, is prepared direcdy from the elements or by the reaction of bromine on a mixture of zirconium oxide and carbon. It may also be made by halogen exchange between the tetrachloride and aluminum bromide. The physical properties are given in Table 7. The chemical behavior is similar to that of the tetrachloride. 

Zirconium tetraiodide [13986-26-0], Zrl, is prepared directly from the elements, by the reaction of iodine on zirconium carbide, or by halogen exchange with aluminum triiodide. The reaction of iodine with zirconium oxide and carbon does not proceed. The physical properties are given in Table 7. 

Other f-transition metal catalysts have been described by von Dohlen (4) and Throckmorton (5) as well as by Chinese (6, 7) and Italian (8-10) scientists. They generally consist of a rare earth compound, an aluminum alkyl, and a halide, the halogens being bound to the rare earth element or aluminum. 

The halogenation of a wide variety of aromatic compounds proceeds readily in the presence of ferric chloride, aluminum chloride, and related Friedel-Crafts catalysts. Halogenating agents generally used are elemental chlorine, bromine, or iodine and interhalogen compounds (such as iodine monochloride, bromine monochloride, etc.). These reactions were reviewed554 and are outside the scope of the present discussion. 

Boron Trichloride. Boron trichloride is prepared commercially by the chlorination of boron carbide (equation 15). Direct chlorination of boric acid or a sodium borate in the presence of carbon is an alternative method. Most of the boron trichloride produced is converted to filaments of elemental boron by chemical vapor deposition (CVD) on tungsten wire in a hydrogen atmosphere. Numerous laboratory preparations of boron trichloride have been reported. One of the most convenient is the halogen exchange reaction of aluminum chloride with boron trifluoride or a metal fluoroborate. 

In contrast to the heterogeneous catalyst, the soluble catalysts appear to have well-defined structures. For example, the soluble catalyst system generated from triethyl aluminum and bis(cyclopentadienyl)titanium dichloride has been shown by elemental and x-ray analysis to have a halogen-bridged... 

Elements in Group 3A, particularly boron and aluminum, also tend to form compounds in which they are surrounded by fewer than eight electrons. Take boron as an example. Since its electron configuration is ls 2s 2p, it has a total of three valence electrons. Boron reacts with the halogens to form a class of compounds having the general formula BX3, where X is a halogen atom. Thus, in boron trifluoride there are only six electrons around the boron atom ... 

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