Methylation ratios

Selectivity parameters can be used to compare the catalytic performance of the different catalysts, and to find relationships between catalysts performance and physico-chemical features. Specifically, the following parameters were chosen (a) the O/C-methylation ratio, that is the ratio between the selectivity to 3-MA and that to 2,3-DMP+2,5-DMP+3,4-DMP (b) the ortho/para-C-alkylation ratio, that is the ratio between the selectivity to 2,3-DMP+2,5-DMP and the selectivity to 3,4-DMP (c) the 2,5-DMP/2,3-DMP selectivity ratio. Table 2 compares these parameters for MgO, Mg/Al/O and Mg/Fe/O catalysts. Data were reported at 30% m-cresol conversion, thus under conditions of negligible consecutive reactions. In this way it is possible to compare the ratio of the sole parallel... 

Catalyst O/C-methylation ratio ortho/para- C-methylation ratio 2,5-DMP / 2,3-DMP selectivity ratio... 

Increasing the number of acid sites, the C-methylation becomes largely preferred over the O-methylation (the QC-mcthylation ratio increased), while between the two ortho-C-methylated compounds, 2,5-DMP becomes more preferred than 2,3-DMP, in agreement with the calculated energies for the corresponding transition states. Disagreement between results obtained in gas-and liquid-phase methylation with the Mg/Fe/O catalyst (Table 2) concerns the ortho/para-C-methylation ratio (which in liquid phase was not varied when the Fe content was increased), and the 2,5-DMP/2,3-DMP ratio (which in gas phase... 

Figure 4 Effect of the Mg/Fe atomic ratio in Mg/Fe/O catalysts on the number of acid sites, as determined by pyridine adsorption (o), on the Q C-methylation ratio (v), on the ortho/para-C-methylation ratio (a), and on the 2,5-DMP/2,3-DMP selectivity ratio (/ ), in the liquid-phase methylation of m-cresol [4],...

Figure 15 Quantitative methylation analysis using MALDI-TOF MS. Cleavage reactions from the reverse strand allow for determination of methylation ratios. When mixtures of methylated and non-methylated template are analyzed. Typically, in a signal pair one signal represents the methylated and a second nearby signal represents the non-methylated template for defined CpG sites. The ratio of signal intensities reflects the ratio of methylated/non-methylated template DNA.

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. 

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. 

The former arises from a beta-pinene chain or from a dipentene initiating mer unit. Single methyl arises from a beta-pinene initiating mer unit or a dipentene chain. Typically, the gem dimethyl/ single methyl ratio is 85/15 for a beta-pinene and 15/85 for a dipentene resin. 

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