Benzyloxy phenol

Figure 1 Hydrogen uptake curves of 3%Pd/CPS4 and 5%Pd and 10%Pd on CPS1, CPS2 and CPS4. The reaction conditions are 10 g 4-(benzyloxy) phenol in 100 methanol, hydrogen pressure 1.1 bar, agitation rate 200 rpm, temperature 35°C, catalyst loading 3wt%.

The aromatic phenol was varied to explore the scope of the O-to-C conversion with mannosyl phosphates. Using phosphate 9, the a-C-mannosides of 2-naphthol and 3-benzyloxy phenol (23 and 25, Table 1) were synthesized in excellent yield. O-Mannosides were obtained exclusively with less nucleophilic aromatic systems, such as 3-acetoxy phenol. Several non-phenolic aromatic systems were unsuccessful in the formation of C-aryl or O-aryl glycosides. Reaction of 9 with furan, thiophene, trimethoxybenzene, and indole in the presence of TMSOTf did not result in any product formation. Interestingly, activation of 9 in the absence of any aromatic nucleophiles gave 26 as the major product via an intramolecular C-glycosylation (Figure 1) (79). 

Commercially supplied analytical grade substrates, benzyl ether, N-phenyl ben-zylamine and 4-(benzyloxy) phenol and the solvents (tetrahydrofuran, methanol, octanol, cyclohexane, acetone and methyl ethyl ketone) were used in this study. 

Scheme C Debenzylation of 4-(Benzyloxy) phenol or hydroquinone monobenzyl ether... 

Catalyst filtration rate was measured by the time required for filtration of 350 ml of debenzylation product containing 10% 4-benzyloxy phenol in methanol and 1.2g of catalyst using a 55 mm diameter, 42 Whatman filter paper under 24 Hg vacuum. 

Similar activities (based on catalyst weight) were similarly observed on 3%Pd/CPS4 and 5%Pd/CPS3 for 4-benzyloxy phenol when other solvents, e.g., n-octanol, THF, acetone, and acetic acid were employed. 

It is of interest to evaluate the inpact of catalyst pre-activation on performance. Catalyst manufacturers supply both pre-reduced and unreduced noble metal catalysts for a variety of applications. In order to assess the effect of Pd reduction, we evaluated unreduced and pre-reduced catalysts. Table 3 shows the reaction rate constants of debenzylation of 4-(benzyloxy) phenol on reduced and unreduced 3%Pd/CPS4 and 5%Pd/CPS4 under identical reaction conditions. These data clearly demonstrate the superior performance of unreduced catalysts over their pre-reduced counterparts. The reaction rate constants are significantly reduced when pre-reduced catalysts are used. 

Several Pd/CPS catalysts were also evaluated for 0-debenzylation using 4-(benzyloxy) phenol substrate with methanol, n-octanol and THE as solvents. Substitution of n-octanol and THE for methanol resulted in lower hydrogenation activity. 

The debenzylation reaction was found to be very sensitive to feedstock impurities. Eigure 8 illustrates the hydrogen uptake of debenzylation reaction of 4-(benzyloxy) phenol from two different feedstock lots. As shown in Figure 8 that the hydrogen uptake was completed in 6000 seconds on a pure feed stock how-... 

Figure 8 Effects of the feedstock impurity on the reaction rate for debenzylation of 4-(benzyloxy) phenol. Reaction conditions methanol solvent, 35°C, 1.1 bar hydrogen, 2000 rpm, 3% catalyst loading (5%Pd/CPS3).

Based on hydrogen uptake curves, the reaction rate constant is 8.7 x 10 moles/g cat./min on the higher-ptnity feed stock, but only 3.3 x 10 moles/g cat./min on the lower-quality feedstock. Although only 0.5% 2-phenylmethyl, 4-(benzyloxy) phenol is contained in the feed stock, the reaction rate has been reduced by more than 50%. 

Figure 9 Hydrogenolysts reaction of 4-(benzyloxy) phenol impurity 2-phenylmethyl, 4-benzyloxy phenol to 2-phenylmethyl 1,4-benznediol and toluene...

Synonyms Agerite alba monobenzone 4-(phenylmethoxy)phenol p-(benzyloxy)phenol hydroquinone benzyl ether p-hydroxy-phenyl benzyl ether benzyl hydroquinone monobenzyl hydroquinone Depigman Pigmex Benzoquin PBP Benoquin Uses antidegradant added to rubber products inhibitor in acrylic resins A... 

Hydroquinone and the 4-methoxyphenol-, 3-ethoxyphenol-, and 4-benzyloxy-phenol ethers were extracted fiom cosmetic formulations and analyzed on a phenyl column (A = 295nm) using a 45/55 THF/water mobile phase. Elution was complete in 9 min. Baseline resolution and excellent peak shapes were obtained. This is an interesting result since THF is known to produce peak splitting at elevated levels for some analytes. Standard curves ranging fiom 50 to 400 mg/L were used. Detection limits of 2 mg/L were reported [800]. 

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