Thermal decomposition, metal iodide

The reaction of higher alkyl chlorides with tin metal at 235°C is not practical because of the thermal decomposition which occurs before the products can be removed from the reaction zone. The reaction temperature necessary for the formation of dimethyl tin dichloride can be lowered considerably by the use of certain catalysts. Quaternary ammonium and phosphonium iodides allow the reaction to proceed in good yield at 150—160°C (109). An improvement in the process involves the use of amine—stannic chloride complexes or mixtures of stannic chloride and a quaternary ammonium or phosphonium compound (110). Use of these catalysts is claimed to yield dimethyl tin dichloride containing less than 0.1 wt % trimethyl tin chloride. Catalyzed direct reactions under pressure are used commercially to manufacture dimethyl tin dichloride. 

Protactinium metal was first prepared in 1934 by thermal decomposition of a pentahalide on a hot filament 50). It has since been prepared from PaF4 by metallothermic reduction (Section II,A) with barium 26, 27, 34,102), lithium 40), and calcium 73, 74). However, the highest purity metal is achieved using the iodide transport (van Arkel-De Boer) process (Section II,D). 

VEEL spectra of surface phenyl groups have been obtained by ultraviolet photolysis of phenyl chloride on Ag(lll) at 300 K (211) and by thermal decomposition of phenyl iodide on Cu(lll) (212). The spectra are similar, and the strengths of the absorptions from the out-of-plane yCH modes, at 740 and 725 cm-1 respectively, show that the phenyl group is also more near to parallel than to perpendicular to the metal surfaces, again probably because of a combination of cr- and 77-bonding. 

---