Phenol mechanism

One of the interesting properties of PBPCP [187] was its fast heat dissipation characteristics and so it was tested by the well-known oxy-acetylene panel test (ASTM 285-70) for ablative materials. Figure 13 shows the survival of a flower for 100 s. kept on the 6.35-mm asbestos fiber-reinforced hexamine-cured panel. The ablation rate value of this material was 3.2 x 10 in/s in comparison with 3.6 x 10 in/s for asbestos-phenolic. As the char content of PBPCP was only 27% compared with 60% for conventional phenolics, mechanisms involving transpiration processes rather than heat blocking by char formation might be playing a greater role in this case [188]. 

Casella L, Poli S, Gullotti M, Selvaggini C, Beringhelli T, Marchesini A (1994) The Chloroperoxidase-Catalyzed Oxidation of Phenols. Mechanism, Selectivity, and Characterization of Enzyme-Substrate Complexes. Biochemistry 33 6377... 

Finally, Sotelo et al. [179], while studying the ozonation of resorcinol and phloroglucinol, two precursors of trihalomethanes (THM) during water chlorination, found some polar intermediates that confirmed the proposed phenol mechanism reported elsewhere [42]. From the identified intermediates it was deduced that ozonation of phenols yields more oxygenated compounds that eventually could be removed in biological steps. 

Two-colour photoionization spectroscopy of aniline cooled in a supersonic jet. Strong propensity for vertical (An = 0) ionization allows vibrational frequencies of CgHgNH2 ( B,) to be determined Two-colour photoacoustic and MPI spectra of aniline, determined as a function of time delay between the two laser pulses. Observed both ionization and dissociation t MPI/TOF mass spectrometric study of phenol. Mechanism of ionization and ion fragmentation t MPI/TOF mass spectrometric study of fragmentation patterns in benzaldehyde. Strong wavelength dependence observed at 266 and 355 nm. Results show operation of two different mechanisms at these excitation wavelengths... 

Scheme 2. Nitrous acid catalysed nitration of phenol, mechanism proposed in literature...

The use of vanadium(V) salts in oxidative coupling reactions was prompted by the work of Funk et al. who recognized the ability of vanadium oxytrichloride to form phenoxyvanadium complexes with phenols [llO]. As it was shown by Schwartz et al., such complexes can be isolated and used for oxidative couplings [111]. Vanadium oxytrifluoride, a superior reagent [112] was found to be effective not only with free phenols but also with phenol ethers revealing the non-phenolic mechanism of this oxidation [113]. The method was successfully adapted to the oxidative macrocyclisation of a vancomycin subunit [114]. 

Polishchuk, V.R. German, L.S. Interaction of perfluoropiperidine with phenols. Mechanisms of ortho- and para-fluorination. Tetrahedron Lett. 1972 (51), 5169-5172. 

This mechanism is similar to the Sorokin and Shode acidic phenol mechanism. However, a somewhat different transition state, Ci, is encountered. In the main reaction, the phenol and the amine associate instantaneously and form an ion pair,... 

Subclass or Properties Modification Cord Filled Cellulose Filled Unfilled Cast Phenolic, Mechanical and Chemical Grade... 

Ren, S. J. (2003). Phenol mechanism of toxic action classification and prediction a decision tree approach. Toxicology letters, 144, pp. 313. 

Dimethyl sulphate is of particular value for the methylation of phenols and sugars. The phenol is dissolved in a slight excess of sodium hydroxide solution, the theoretical quantity of dimethyl sulphate is added, and the mixture is heated on a water bath and shaken or stirred mechanically (compare Section IV, 104). Under these conditions only one of the methyl groups is utilised the methyl hydrogen sulphate formed in the reaction reacts with the alkali present. -... 

Equip a 500 ml, three-necked flask with a separatory funnel, a mercury-sealed mechanical stirrer and a reflux condenser. Place a solution of 21 g. of sodium hydroxide in 200 ml. of water and also 47 g. of pure phenol in the flask, and stir the mixture cool the warm mixture to about 10° by immersing the flask in an ice bath. Place 63 g. (47 ml.) of dimethyl sulphate in the separatory funnel. 

This reaction, applicable only to the preparation of hydroxy-aldehydee, is alternative to the Gattermann aldehyde reaction (or the Adams modification of it) given under 4. The yields are usually smaller, but a large quantity of the phenol may be recovered. The following mechanism is consistent with the known facts ... 

P-Hydroxy-a-naphthaldehyde, Equip a 1 litre three-necked flask with a separatory funnel, a mercury-sealed mechanical stirrer, and a long (double surface) reflux condenser. Place 50 g. of p-naphthol and 150 ml. of rectified spirit in the flask, start the stirrer, and rapidly add a solution of 100 g. of sodium hydroxide in 210 ml. of water. Heat the resulting solution to 70-80° on a water bath, and place 62 g. (42 ml.) of pure chloroform in the separatory funnel. Introduce the chloroform dropwise until reaction commences (indicated by the formation of a deep blue colour), remove the water bath, and continue the addition of the chloroform at such a rate that the mixture refluxes gently (about 1 5 hours). The sodium salt of the phenolic aldehyde separates near the end of the addition. Continue the stirring for a further 1 hour. Distil off the excess of chloroform and alcohol on a water bath use the apparatus shown in Fig. II, 41, 1, but retain the stirrer in the central aperture. Treat the residue, with stirring, dropwise with concentrated hydrochloric acid until... 

In contrast to its effect upon the general mechanism of nitration by the nitronium ion, nitrous acid catalyses the nitration of phenol, aniline, and related compounds. Some of these compounds are oxidised under the conditions of reaction and the consequent formation of more nitrous acids leads to autocatalysis. 

Under the same conditions the even more reactive compounds 1,6-dimethylnaphthalene, phenol, and wt-cresol were nitrated very rapidly by an autocatalytic process [nitrous acid being generated in the way already discussed ( 4.3.3)]. However, by adding urea to the solutions the autocatalytic reaction could be suppressed, and 1,6-dimethyl-naphthalene and phenol were found to be nitrated about 700 times faster than benzene. Again, the barrier of the encounter rate of reaction with nitronium ions was broken, and the occurrence of nitration by the special mechanism, via nitrosation, demonstrated. 

The evidence outlined strongly suggests that nitration via nitrosation accompanies the general mechanism of nitration in these media in the reactions of very reactive compounds.i Proof that phenol, even in solutions prepared from pure nitric acid, underwent nitration by a special mechanism came from examining rates of reaction of phenol and mesi-tylene under zeroth-order conditions. The variation in the initial rates with the concentration of aromatic (fig. 5.2) shows that mesitylene (o-2-0 4 mol 1 ) reacts at the zeroth-order rate, whereas phenol is nitrated considerably faster by a process which is first order in the concentration of aromatic. It is noteworthy that in these solutions the concentration of nitrous acid was below the level of detection (< c. 5 X mol... 

The most widely used industrial synthesis of phenol is based on isopropylbenzene (cumene) as the starting material and is shown m the third entry of Table 24 3 The eco nomically attractive features of this process are its use of cheap reagents (oxygen and sulfuric acid) and the fact that it yields two high volume industrial chemicals phenol and acetone The mechanism of this novel synthesis forms the basis of Problem 24 29 at the end of this chapter... 

Q The mechanism of the Claisen rearrangement of other allylic ethers of phenol is analogous to that of allyl phenyl ether What is the product of the Claisen rearrangement of C6H50CH2CH CHCH3 /... 

You learned in Section 17 8 of the relationship among hemiacetals ketones and alcohols the for mation of phenol and acetone is simply an example of hemiacetal hydrolysis The formation of the hemiacetal intermediate is a key step in the synthetic procedure it is the step in which the aryl—oxygen bond is generated Can you suggest a reasonable mechanism for this step" ... 

Although the anionic polymerization mechanism is the predominant one for the cyanoacryhc esters, the monomer will polymerize free-radically under prolonged exposure to heat or light. To extend the usable shelf life, free-radical stabilizers such as quinones or hindered phenols are a necessary part of the adhesive formulation. 

Bromination can be conveniently effected by transfer of bromine from one nucleus to another. As the Friedel-Crafts isomerization of bromoaromatic compounds generally takes place through an intermolecular mechanism, the migrating bromine atom serves as a source of positive bromine, thus effecting ring brominations (161,162). 2,4,6-Tribromophenol, for example, has been prepared by bromination of phenol with dibromobenzene. 

Synthetic phenol capacity in the United States was reported to be ca 1.6 x 10 t/yr in 1989 (206), almost completely based on the cumene process (see Cumene Phenol). Some synthetic phenol [108-95-2] is made from toluene by a process developed by The Dow Chemical Company (2,299—301). Toluene [108-88-3] is oxidized to benzoic acid in a conventional LPO process. Liquid-phase oxidative decarboxylation with a copper-containing catalyst gives phenol in high yield (2,299—304). The phenoHc hydroxyl group is located ortho to the position previously occupied by the carboxyl group of benzoic acid (2,299,301,305). This provides a means to produce meta-substituted phenols otherwise difficult to make (2,306). VPOs for the oxidative decarboxylation of benzoic acid have also been reported (2,307—309). Although the mechanism appears to be similar to the LPO scheme (309), the VPO reaction is reported not to work for toluic acids (310). 

However, a second mole of alcohol or hemiformal caimot be added at the ordinary pH of such solutions. The equiUbrium constant for hemiformal formation depends on the nature of the R group of the alcohol. Using nmr spectroscopy, a group of alcohols including phenol has been examined in solution with formaldehyde (15,16). The spectra indicated the degree of hemiformal formation in the order of >methanol > benzyl alcohol >phenol. Hemiformal formation provides the mechanism of stabilization methanol is much more effective than phenol in this regard. 

Alkaline catalysts are also effective in the polymeri2ation—depolymeri2ation of methylene glycol. The mechanism of the formaldehyde addition to the phenolate is still not completely understood. The most likely mechanism involves the contribution of phenol hemiformals (10) (5). 

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