Autoclave-induced reaction

Because of its high penetrating power, gamma radiation induced reactions can be carried out in opaque vessels and metal autoclaves. Consequently, the temperature range within which a chain reaction can be studied in a given solution, extends from its freezing point to its critical temperature. Thermally induced reactions can also be studied in autoclaves. However, the tempe-... 

Dextrose is widely used as an isotonic media in parenteral formulations. Sterilisation using autoclaving has been reported to induce the formation of fructose via an isomerisation reaction, with the resultant formation of 5-hydroxymethyl-furfural [90]. 

The hydrogenations catalyzed by rhodium/24a are not fast at 1 bar pressure. However, at 5 bar in a well-stirred autoclave TOFs of 200-600 h 1 were reached, which is quite satisfactory even for industrial applications. Even faster reactions can be induced by further increasing the pressure. At elevated pressures the amount of catalyst can be substantially reduced to 0.01-0.1mol%. In all these hydrogenations, the enantioselectivity was not affected in any way by pressures up to 60 bar, in contrast to the deterioration of ee that occurs with increase of pressure when using bisphoshines.31... 

If the iron- and tin-based catalyst Indeed acts to inhibit radical propagation reactions then two major consequences of this effect can be tested in coal reactions. Firstly, and most importantly, the rate of the thermally Induced breakdown of the coal should be reduced in the initial minutes of the coal reaction. This has recently been demonstrated when iron catalysts were used in a series of short residence time studies ( v l2 minutes to temperature then autoclave quenched). The results, summarized in Table 2, show that the conversion of acid washed coal after rapid heating to 450 C had a conversion of 55% (daf coal) while the conversion of acid washed coal that had been re-exchanged with 240 mmol of iron kg (dry coal) had a conversion of only 46%. A similar trend was found for the reaction of as mined coal (39% conversion) and the same coal that had been treated with a solution of iron(II) acetate (300 mmol kg dry coal) and had a conversion of 33%. It is interesting to note that the natural Inorganics of the as-mlned coal had a very strong inherent activity to slow the rate of thermal decomposition. 

This natural tendency for thermal racing is accentuated by these implicated energy densities which are usually different from those used with a water or oil bath, particularly for sealed vessels and autoclaves as used by organic chemists. The temperature and, especially, the thermal path T(t) seems to be a crucial variable. The authors have shown theoretically and experimentally that strong heating rates (up to 5° s ) can induce selectivity or inversion between two competitive reactions [141]. 

More recently, Hayashi et have observed an efficient rate enhancement in the 3-HQD-catalyzed MBH reaction under high pressure induced by freezing water in a sealed autoclave. In most cases, moderate to good yields were obtained for the MBH reaction between various aldehydes with acrylates under 200 MPa pressure (Scheme 2.31). 

While high-pressure reactions typically require specialized equipment, a Bayliss-Hillman reaction between p-bromohenzaldehyde and methyl acrylate has been induced by the pressure created as water freezes (2 kbar). The reaction is performed in a test tube placed in a water-filled sealed autoclave in a household refrigerator at -20°C. An 86% yield was obtained in this manner compared to 65% yield at 1 atm [17]. 

It is undesirable to use higher pressures in autoclave testing, because this induces secondary reactions. This can be seen from the higher yields of cracking residue with an Engler viscosity of 80 at 50° = 80) and... 

---