or by reactions in molten AICI3 for example,
7 Te + TeCl4+ 4AlCl3 = 2Te42+ + 4AlCl4-
The S42+ ,Se42+, and Te42 + ions are square (19-I) and there is probably a six π-electron quasi-aromatic system. The green Se82+ ion has a ring structure (19-II). The S162+ and Se162+ ions have two M8 rings joined together.
The reaction of sulfur with the double bonds of natural and synthetic rubbers, a process called vulcanization, is of great technical importance it leads to formation of S bridges between carbon chains and, hence, to strengthening of rubber.
All reactions of S8 must involve initial ring opening to give sulfur chains or chain compounds. Many reactions involve nucleophilic reactants, for example
Such reactions proceed by a series of steps such as:
Sulfur—sulfur bonds occur in a variety of compounds, and —S— S— bridges are especially important in certain enzymes and other proteins.
COMPOUNDS OF GROUP VI ELEMENTS
19-3
Hydrides, MH2
These are obtained by action of acids on metal sulfides, selenides , or tellurides. They are extremely poisonous gases with revolting odors. The toxicity of H2S far exceeds that of HCN. The thermal stability and bond strengths decrease down the series, whereas the acidity in water increases.