Catechols, methylation

In the case of low temperature tar, the aqueous Hquor that accompanies the cmde tar contains between 1 and 1.5% by weight of soluble tar acids, eg, phenol, cresols, and dihydroxybenzenes. Both for the sake of economics and effluent purification, it is necessary to recover these, usually by the Lurgi Phenosolvan process based on the selective extraction of the tar acids with butyl or isobutyl acetate. The recovered phenols are separated by fractional distillation into monohydroxybenzenes, mainly phenol and cresols, and dihydroxybenzenes, mainly (9-dihydroxybenzene (catechol), methyl (9-dihydtoxybenzene, (methyl catechol), and y -dihydroxybenzene (resorcinol). The monohydric phenol fraction is added to the cmde tar acids extracted from the tar for further refining, whereas the dihydric phenol fraction is incorporated in wood-preservation creosote or sold to adhesive manufacturers. Naphthalene Oils. Naphthalene is the principal component of coke-oven tats and the only component that can be concentrated to a reasonably high content on primary distillation. Naphthalene oils from coke-oven tars distilled in a modem pipe stiU generally contain 60—65% of naphthalene. They are further upgraded by a number of methods. 

For the studied catechol methylation reaction the catalyst structure and surface properties can explain the catalytic behaviour As mentioned above, the reaction at 260-350°C has to be performed over the acid catalysts. Porchet et al. [2] have shown, by FTIR experiments, the strong adsorption of catechol on Lewis acid/basic sites of the Y-AI2O3 surface. These sites control the reaction mechanism. 

MDB 2-(Ethoxy methoxy) phenol 3-Methyl catechol Methyl -MDB ... 

Catechol methyl transferases require the catechol function to be present to bind to the Mg ion. In the search for p2-adrenoceptor selectivity to produce potent bron-chodilators with low cardiovascular effects, changing the 3,4-hydroxy grouping of the catechol to 3,5- or 3-hydroxyl, 4-methyl-hydroxy, proved to be important (Figure 7.25). These compounds now have much improved bioavailability and pharmacokinetics due to their resistance to catechol methyl transferases. 

Scheme 1. Reaction scheme in catechol methylation with strongly acid catalysts.

The reaction of catechol methylation by methanol in gas-phase over modified y-alumina was studied with the aim to correlate catalytic activity and selectivity to acid/base properties of the catalysts. Catalytic activity and selectivity towards guaiacol formation (0-alkylation) was found to increase with surface acidity. A 20-fold change in the O/C-methylation ratio was achieved by varying the catalyst acid/base properties, keeping constant the other reaction parameters. 

This work intends to correlate the catalytic activity and selectivity of catechol methylation to catalyst acid-base properties under constant reaction operating conditions. The work also aims at the study of the reaction selectivity towards O- or C-alkylated product formation through suitable catalyst modification. 

During the catechol methylation under the conditions used, three parallel reactions take place (see Figure 2). The rates of these pathways (R,) can be easily calculated from the data of Table 1, since Rj = Si (-Ri), where Si is the selectivity towards the monomethylated product Ai. The rise of acidity affects differently the rates of the reaction pathways for the phosphated alumina the rate of guaiacol formation (R2, O-methylation ) doubled and the rate of C-methylation pathways simultaneously decreased 1.5 times, if compared to pure Y-AI2O3. 

The reaction of catechol methylation in gas phase at temperatures below 300°C is seen to proceed efficiently over modified y-aluminas with moderate acid sites. At low catechol conversion (X < 0.05), O- and C-methylated products are formed in parallel reaction pathways. The 0/C methylation ratio has been regulated by varying acid/base properties of the catalyst. Modification of Y-AI2O3 by phosphoric acid was observed to increase the selectivity towards guaiacol formation (O-methylation) up to 82=0.89. The catalyst Mg (7.5 at.% )/ Y-AI2O3 showed the maximum selectivity towards 3-methyl catechol formation (C-methylation) to be 3=0.65. It means that a 20-fold change in the O/C methylation ratio was achieved, when the catalyst acidity was modified, keeping constant other reaction conditions. 

Guaiacol (Catechol methyl ether, o-hydroxy-aniaole, o-methoxyphenol)... 

Ashton, P.R., Odell, B., Reddington, M.V., Slawin, A.M.Z., Stoddart, J.F. and Williams, D.J. (1988) Isostructural Alternately-charged Receptor Stacks. The Inclusion Complexes of Hydroquinol and Catechol Methyl Ethers with Bisparaquat(l,4)cyclophane Angew. Chem. Int. Ed. Engl. 27,1550. 

Fig. 4. Protected catechol-methyl ethers and methylenedioxy analogs...

Catechol methyl ether, see M-00102 Catechol sulfonephthalein, see P-00433 Catechol violet, see P-00433 4-CatecholyIazo-4 -acetylaminobiphenyl, in... 

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