Cresols disproportionation

At low temperature, an almost equimolar amount of m-cresol and of DMAs were produced (selectivity of 41% and 32%, respectively), with minor amounts of DMPs. Therefore, it is likely that the primary mechanism for the transformation of 3-MA consists of the intermolecular methylation with cogeneration of m-cresol and DMA. Also, the contribution of hydrolysis of 3-MA to yield m-cresol can not be excluded. On increasing the reaction temperature, the selectivity to DMAs decreased, with a corresponding increase in the formation of DMPs and polyalkylates. This is likely due to the reactions between DMAs and m-cresol to yield DMPs, and between two molecules of DMAs (a sort of intermolecular disproportionation) to yield polyalkylates and DMPs. The selectivity to m-cresol remained approximately constant on increasing the reaction temperature. 

The w-cresol transformation was carried out on wide pore zeolites (HFAU, HBEA, HMOR and HOFF). The activity follows the sequence HFAU > HBEA HMOR > HOFF. The order of the acid strength determined by TPD-NH3 was HMOR>HOFF>HBEA>HFAU. On the HBEA. HMOR and HOFF the isomerization was the main reaction due to their pore system structure, that limits the formation of diphenylmethane intermediate of disproportionation, while on HFAU the disproportionation reaction was not impeded at low conversion. The p o selectivity is mainly function of conversion. 

Decomposition of Cured Resoles and Novolaks. Above 250°C, cured phenolic resins begin to decompose. For example, dibenzyl ethers such as 9 disproportionate to aldehydes (salicylaldehyde) and cresols (o-cresol). The aldehyde group is rapidly oxidized to the corresponding carboxylic acid. In an analogous reaction in hexa-cured novolaks, tribenzylamines decompose into cresols and azome-thines, which cause yellowing. 

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