High-temperature transformation acidic conditions

The mechanism inevitably involves the loss of water and, remarkably, methane. The yields are usually low due to the high temperatures required for this transformation to occur. If the 1,2-dihydroquinoline is isolated the aromatization can be performed in a separate step under acidic or basic conditions. ... 

These results indicate that, during thermolyses of fructose-containing saccharides, di-D-fructose dianhydrides are formed readily, but subsequent isomerization is extremely slow—even in the presence of added acid. However, under these conditions, the protonating power of any acid is moot. At the high temperatures used, residual water would be driven off rapidly, unless the reaction vessel is pressurized therefore, reaction occurs in the anhydrous melt. It is presumably protonation of one of the ring oxygen atoms in the dianhydrides that constitutes the first step in isomerization, followed by scission of a C-O bond to yield one of the oxocarbenium ion intermediates postulated in Refs. 31 and 80. Such ions have also been postulated as intermediates in the isomerization of spiroketals to a more-stable product. This latter isomerization can be extremely facile 104 dilute aqueous acid,120 or non-aqueous Lewis-acid conditions121 have been used to effect such transformations. 

The c-BN phase was first obtained in 1957 [525] by exposing hexagonal boron nitride phase (h-BN) to high pressures and low temperatures. A pressure of more than 11 GPa is necessary to induce the hexagonal to cubic transformation, and these experimental conditions prevent any practical application for industrial purposes. Subsequently, it has been found that the transition pressure can be reduced to approximately 5 GPa at very high temperature (1300-1800°C) by using catalysts such as alkali metals, alkali metal nitrides, and Fe-Al or Ag-Cd alloys [526-528]. In addition, water, urea, and boric acid have been successfully used for synthesis of cubic boron nitride from hexagonal phase at 5-6 GPa and temperature above 800-1000°C [529]. It has been... 

Sulfonic acids may be subjected to a variety of transformation conditions. Sulfonic acids may be hydrolytically cleaved, using high temperatures and pressures, to drive the reaction to completion. 

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