Gaseous zirconium bromides

The sublimation of solid zirconium tetrabromide to gaseous ZrBr4, as represented by Eq.(V.56)  

This value can then be combined with the selected enthalpy of formation for ZrBr4(cr) to derive the selected enthalpy of formation of ZrBr4(g)  

The enthalpy of sublimation is in very good agreement with that recommended by [85CHA/DAV] as is the enthalpy of formation of ZrBr4(g) with those values selected by both [85CHA/DAV] and [97V1S/COR]. 

There have been no studies of the enthalpies of formation of the lower gaseous zirconium bromides. Values for these parameters have been estimated by [97V1S/COR] from the bond energies of the other zirconium halides. The values estimated by [97V1S/COR] are, Af//° (ZrBr, g, 298.15 K) = (366 25) kJ-mol, Af//° (ZrBrj, g, 

The Gibbs energies of formation are then ealculated from the selected enthalpies of formation and entropies, utilising the entropy values for Zr(er) and Br2(l) (see Section V. 1.1.2.1 and Chapter IV), 

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The values for the lower gaseous zirconium bromides, ZrBr(g) to ZrBr3(g) are noted by this review but not selected due to the laek of experimental data for the enthalpies of formation. The Gibbs energy of formation for ZrBr4(g) is selected by this review. 

K. The predicted structures of the various iodides are the same as the bromides, that is Ti symmetry (tetraiodide), planar (triiodide) and linear (diiodide). From the measured data, van der Vis et al. [97VIS/COR] calculated the following heat capacity and entropy values for the gaseous zirconium iodides ... 

Dihalides of uncertain purity are prepared by the disproportionation of the trihalides. Alternate routes have also been reported. Swaroop and Flengas (549) prepared ZrCU of 95-99% purity by heating the trichloride and metallic zirconium at 675°C for 30-35 hours in an evacuated quartz tube lined with platinum foil. There is also a reference to the production of liquid dihalides by the reaction of the gaseous tetrahalides with loosely packed zirconium at 700°C for the chloride and 400°C for the bromide and iodide (270). The difluoride has been prepared (357) by the reaction of atomic hydrogen on thin layers of zirconium tetrafluoride at 350°C. New data on hafnium are lacking, although Corbett (542) has concluded that hafnium diiodide does not exist. 

The alkylation of paraSins with olefins to yield higher molecular weight branched-chain paraffins may be carried out thermally or catalyt-ically. The catalysts for the reaction fall into two principal classes, both of which may be referred to as acid-acting catalysts (1) anhydrous halides of the Friedel-Crafts type and (2) acids. Representatives of the first type are aluminum chloride, aluminum bromide, zirconium chloride, and boron fluoride gaseous hydrogen halides serve as promoters for these catalysts. The chief acid catalysts are concentrated sulfuric acid and liquid hydrogen fluoride. Catalytic alkylations are carried out under sufficient pressure to keep at least part of the reactants in the liquid phase. 

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