Solid state reactions disproportionation

Dithiophenylbutane 66 is obtained by a radical-radical combination reaction, while 3-isopropylthiophene 67 and 3-(propen-2-yl)thiophene 68 form by a radical-radical disproportionation process. The solid-state reaction was shown to be highly temperature dependent. While irradiation of powdered samples at 20°C led to no observable product after 2 days, samples exposed to the same UV source for 24 h at ca. 45°C gave 66 as the only product in ca. 5-10% yield. Photochemical reactions were carried out with nanocrystalline suspensions of 65 in a Pyrex tube acting both as a container and a light filter (X > 290 nm). 

If calcium metal is treated with a deficiency of chlorine gas, we obtain only CaCl2, and there is no reaction between Ca and CaCl2 to yield CaCl. Could CaCl be stabilised kinetically Probably not. It is impossible to conceive of any other thermodynamically-favourable reaction whereby it might be produced (except as a molecular gas at high temperatures) and one can easily envisage a facile electron-transfer process in the solid state whereby disproportionation would take place before a crystal of CaCl reached macroscopic proportions. 

While the ion exchange with alkaline metal cations does not result in catalysts active in acid-catalysed hydrocarbon reactions and, in contrast, may be carried out to remove any residual activity [1], the incorporation of alkaline earth cations by solid-state reaction should lead to active catalysts. It was shown, however, that the solid-state ion exchange had to be followed by contact with water vapour in order to obtain calcium or magnesium mordenites which are sufficiently active in, for instance, disproportionation of ethylbenzene. This is in full agreement with the IR spectroscopic results which indeed showed that only upon interaction of the heat-treated CaCl2/H-MOR mixture with water vapour were acidic OH groups generated. 

In Figure 9 the catalytic performance of almost 100% exchanged La-Y, obtained by solid-state reaction (A) and conventional exchange (B), is illustrated. Both catalysts were, under the conditions chosen, see Figure 9, entirely selective in ethylbenzene disproportionation in that they yielded, after an induction period, benzene and diethylbenzenes in the ratio 1 1. The activity and stability of catalyst (A) were similar to or even better than those of catalyst (B). 

Fig. 4. Selective disproportionation of ethylbenzene over La,H-Y zeolites. The catalysts were prepared (a) by a solid-state reaction between LaCl3 and the corresponding zeolite and (b) by conventional ion exchange. Experimental conditions T = 182°C 1.3 vol% ethylbenzene in He, total flow 5 ml min-1, m(cat) = 0.25 g. (After...

When SiO (Patinal) was heated in pure O2, thermogravimetric analysis showed a slow weight increase above 1000 °C, but even at 1500 °C oxidation was not exhaustive. When a sample was kept at 1300 °C in air for 48 h, crystalline Si and Si02 (cristobalite) were observed by XRD. Thus, disproportionation into Si and Si02 is much faster than oxidation at this temperature. The conclusion from these experiments is that solid-state reactions of SiO must be carried out at temperatures below 1000 °C to exclude the possibility that the observed products originate from initial oxidation and/or disproportionation reactions. ... 

It was shown that solid-state ion exchange is also a suitable route to preparation of active acidic or bifunctional catalysts. Introduction of Ca or Mg into mordenite [21] or La " into Y-type zeolite, mordenite or ZSM-5 [22] by solid-state reaction yielded, after brief contact with small amounts of water, acidic zeolite catalysts which were, for instance, active in disproportionation and/or dealkylation of ethylbenzene or in cracking of n-decane [43]. The contact with water was essential to generate, after solid-state ion exchange, acidic Brpnsted centres (compare, for instance. Figure 2). In the case of solid-state exchange between LaClj and NH -Y an almost 100% exchange was achieved in a one-step procedure, and the hydrated La-Y reaction product exhibited a catalytic performance (selectivity in ethylbenzene disporportionation, time-onstream behaviour) comparable to or even better than that of a conventionally produced La-Y (96) catalyst [22,23]. In fact, compared to the case of NH -Y the introduction of La " " by solid-state reaction proceeded less easily and was frequently lower than 100% with H-ZSM-5 or H-MOR. 

Figure 9. Selective disproportionation of ethylbenzene (EB) over La,Na-Y catalysts (A) prepared by solid-state reaction between LaClg and Na-Y (for details see text) and (B) prepared by conventional ion exchange in aqueous suspension T[react]=455 K, 1.3 vol% EB in He, 5ml-min, m[cat]=0.25 g (after Ref. [23]).

An almost completely exchanged La-Y sample (0.25 g), viz., La-Y(98) with only 2% of residual Na+, was prepared via solid-state reaction of NH4-Y(98) with LaCl3 7H2O at 725 K. This process was carried out in a conventional micro-flow reactor [78], followed by cooling to 455 K, a hydroxylation step (1.2 kPa H2O vapor, 455 K, 2 h), degassing in a helium flow at 625 K and cooling to 425 K (reaction temperature). Upon admission of the feed stream of 1.3 vol. % ethylbenzene in dry helium (30 ml min )> disproportionation to benzene and diethylbenzenes was observed. The results of the conversion measurements are shown in Fig. 23 and compared with those obtained over a conventionally prepared La-Y(96) catalyst. 

Exchange of antimony-carbon bonds with antimony-oxygen bonds is reported in a thorough study of the disproportionation of arylantimony oxides, RSbO (126, 127). At moderately elevated temperatures ( 100° C) in the solid state, the reaction of Eq. (157)... 

SiO in polymeric state There is good knowledge of SiO in the gaseous state, but not in the solid state. SiO is thermodynamically unstable at room tempe rature. It disproportionates to silicon metal and Si02. Under some reaction... 

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