Electron spin resonance studies on ziegler catalyst systems: Part II. The system titanium tetrachloride‐aluminium ethyl dichloride

Abstract

Electron spin resonance was measured in a mixture of TiCl4 and (Al(C2H5)Cl2)2 in heptane, mainly at room temperature and at various concentrations of the titanium and aluminium components. Normally, two different particles to be called S1 and S2, carrying an unpaired electron are produced after some time. The concentration of S2 is always lower than the concentration of S1. Some time after the components have been brought together, the concentration of S1 reaches a maximum value equal to about 1.8 × 10−2 times the initial concentration of the aluminium dimer compound; this value may remain constant for some hours. At first the rate of formation of the particle S1 is proportional to the 3/2th power of the aluminium dimer concentration and to the root of the titanium concentration. The k‐value amounts to (14.0 + 0.5) × 10−3 mole−1·l·min−1 at 20°. From experiments conducted at various temperatures an activation energy of 12.8 + 0.8 kcals/mole was found. The concentration of unpaired electrons proves to be influenced by solid TiCl3, ethanol and oxygen. Three types of mechanisms, that may account for the formation of S1 are discussed. These mechanisms all yield complexes of a “TiCl3‐radical” and the dimer of aluminium alkyl chloride (S1). An ion‐complex mechanism is presented as the most probable one. As to the particle S2 a complex of the “TiCl3‐radical” and the monomer of aluminium alkyl chloride is suggested.

Electron paramagnetic resonance study of the TiCl4/Al(i-C4H9)3 system

“…These isolated Ti(III) ions could be located on the paramagnetic defect sites of the TiCl 3 particles formed by the reaction between and triisobutyl alumin ium. EPR studies of the TiCl 4 /AlR 3 systems [9][10][11][12][13] revealed the presence of the TiCl 3 species as a result of the dissociation of alkylated titanium complexes. For instance, the change of the signal from g = 1.925 to g = 1.933 in the TiCl 4 /Al(Et) 2 Cl and TiCl 4 /(Al(Et)Cl 2 ) 2 systems at room temperature was associated with the formation of a titanium trichloride solid phase [11][12][13].…”