Phenol acetylation reaction

Sepiolite has also been employed as support to deposit gold nanoparticles for designing catalyst for phenol acetylation reaction [95]. A gold hydrosol... 

Curvature in a Br nsted-type plot is sometimes attributed to a change in transition state structure. This is not a change in mechanism rather it is interpreted as a shift in extent of bond cleavage and bond formation within the same mechanistic pattern. Thus, Ba-Saif et al. ° found curvature in the Br nsted-type plot for the identity reactions in acetyl transfer between substituted phenolates this reaction was shown earlier. They concluded that a change in transition state structure occurs in the series. Jencks et al." caution against this type of conclusion solely on the evidence of curvature, because of the other possible causes. 

Fries rearrangement and phenol acetylation The Fries rearrangement is the acid catalysed transformation of aryl esters into hydroxyarylketones. Both this rearrangement and the two-step transformation (esterification, Fries rearrangement) in one-pot operation of phenols with carboxylic acid or anhydrides will be examined hereafter. Most studies in which acid zeolites were used as catalysts (Tables 3.6 and 3.7) deal with the synthesis of o- and p-hydroxyacetophenones (o- and p-HAP) either by the Fries rearrangement of phenyl acetate [Reaction (3.5)] ... 

Table 3.6 Gas phase Fries rearrangement of phenyl acetate and phenol acetylation over zeolite and mesoporous molecular sieves. All the reactions were carried out in fixed bed...

Aminolysis is a laborious procedure, e.g., for wood samples, a 6-7-h reaction period may be required for the aminolysis step alone. The accuracy of this method is critically dependent upon both a quantitative acetylation of phenolic hydroxyl groups and a selective deacetylation of phenolic acetyl groups. Although these requirements may not represent a serious concern in the analysis of soluble or reagent-accessible lignin preparations, they could present a problem in the case of lignocellulosic materials. 

The progress of the reaction was followed by monitoring the decrease in formaldehyde concentration with time. Previous studies used the hydroxylamine hydrochloride method of analysis (5 -55), but this was avoided in the current study as it requires tedious pH titrations. Instead, a colorimetric method was used that was first developed by Nash (55), involving formation of 3,5-diacetyl-1,4-dihydrolutidine, by reaction of formaldehyde with ammonia and acetyl acetone at neutral pH. The cyclic product absorbs at 412 nm with a molar extinction coefficient of 8,000 (55). Other colorimetric methods cannot be used as they all involve very strongly acidic or basic media (55), which would force the phenol-formaldehyde reaction to completion. 

Figure 1.6 Phenol acetylation and related Condensed Graph of Reaction. Dynamical bonds marked with green and red correspond, respectively, to formation and breaking a single bond.

For resorcinolic lipids, particularly those with long saturated side-chains, the use of polar solvents is important due to their amphiphilicity. The crude extracts in many cases are subjected to preliminary fractionation/purification either by solvent fractionation/partition or by application of chromatography. For prepurification of the material and its separation from polymerized phenolics, gel filtration on hydrophobic Sephadex or TSK gel is sometimes used. Silica gel is most frequently employed for the separation and/or purification of resorcinolic lipids, notably in some studies with Ononis species (12-14). The array of compounds reported appears partly attributable to methylation or acetylation reactions occurring during column chromatographic separation. An interesting approach for I the pre-purification and selective separation of resorcinolic lipid from phenolic lipids or resorcinolic lipids from impurities has recently been reported. A selective partitioning of different non-isoprenoid phenolic lipids... 

Compound 468 readily replaced 1-0-acetyl group for a number of alkoxy, aryloxy, and thioalkoxy groups in reactions with alcohols, phenols, or thiols in the presence of p-toluenesulfonic acid. In the case of alcohols and phenols, the reaction was stereospecific and 3-anomers (472) were formed. With thiols, both anomeric thioglycosides (473) were obtained in about equal proportions. 

Esterifications. Pyridine is a widely used catalyst for acylation reactions. Acetylation reactions are effectively carried out in the presence of hexachlorocyclophosphazatriene and pyridine. Acetylation of phenols by acetic anhydride in carbon tetrachloride is also catalyzed by pyridine. In the absence of the pyridine catalyst, at 0 °C and 25 °C, no acylation of the phenols is observed (eq 21). ... 

Although the acetylation of alcohols and amines by acetic anhydride is almost invariably carried out under anhydrous conditions owing to the ready hydrolysis of the anhydride, it has been shown by Chattaway (1931) that phenols, when dissolved in aqueous sodium hydroxide solution and shaken with acetic anhydride, undergo rapid and almost quantitative acetylation if ice is present to keep the temperature low throughout the reaction. The success of this method is due primarily to the acidic nature of the phenols, which enables them to form soluble sodium derivatives, capable of reacting with the acetic... 

Crystalline derivatives, suitable for identification and characterisation are dealt with in Section IV, 114, but the preparation of the following, largely liquid, derivatives will be described in the following Sections. When phenols are dissolved in aqueous sodium hydroxide solution and shaken with acetic anhydride, they undergo rapid and almost quantitative acetylation if the temperature is kept low throughout the reaction. This is because phenols form readily soluble sodium derivatives, which react with acetic anhydride before the latter undergoes appreciable hydrolysis, for example ... 

Other substituents which belong with this group have already been discussed. These include phenol, anisole and compounds related to it ( 5.3.4 the only kinetic data for anisole are for nitration at the encounter rate in sulphuric acid, and with acetyl nitrate in acetic anhydride see 2.5 and 5.3.3, respectively), and acetanilide ( 5.3.4). The cations PhSMe2+, PhSeMe2+, and PhaO+ have also been discussed ( 9.1.2). Amino groups are prevented from showing their character ( — 7 +717) in nitration because conditions enforce reaction through the protonated forms ( 9.1.2). 

Sulfonated styrene—divinylbensene cross-linked polymers have been appHed in many of the previously mentioned reactions and also in the acylation of thiophene with acetic anhydride and acetyl chloride (209). Resins of this type (Dowex 50, Amherljte IR-112, and Permutit Q) are particularly effective catalysts in the alkylation of phenols with olefins (such as propylene, isobutylene, diisobutylene), alkyl haUdes, and alcohols (210) (see Ion exchange). Superacids. 

Acetoiicetyliition Reactions. The best known and commercially most important reaction of diketene is the aceto acetylation of nucleophiles to give derivatives of acetoacetic acid (Fig. 2) (1,5,6). A wide variety of substances with acidic hydrogens can be acetoacetylated. This includes alcohols, amines, phenols, thiols, carboxyHc acids, amides, ureas, thioureas, urethanes, and sulfonamides. Where more than one functional group is present, ring closure often follows aceto acetylation, giving access to a variety of heterocycHc compounds. These reactions often require catalysts in the form of tertiary amines, acids, and mercury salts. Acetoacetate esters and acetoacetamides are the most important industrial intermediates prepared from diketene. 

Uses ndReactions. The Prins reaction of 3-carene with formaldehyde in acetic acid gives mainly 2-carene-4-methanol acetate, which when saponified produces the 2-carene-4-methanol, both of which are commercial products of modest usage (60). 3-Carene (28) also reacts with acetic anhydride with a catalyst (ZnCl2) to give 4-acetyl-2-carene (29) (61), which is also a commercial product. Although 3-carene does not polymerize to produce terpene resins, copolymerization with phenol has been successfully commercialized by DRT in France (62). 

Hydroxythiophene also exists mainly in ketonic forms. Electrophilic reagents react either at oxygen or at C-5. O-Methyl and O-acetyl derivatives are obtained in alkaline solution, probably through intermediacy of the anion. In acidic solution, coupling with benzenediazonium ion, a characteristic phenolic reaction, is found to take place (Scheme 72). 

Isotope labeling by derivative formation with deuterated reagents is useful for the preparation of analogs such as dg-acetonides, da-acetates, da-methyl ethers, dg-methyl esters, etc. The required reagents are either commercially available or can be easily prepared. (The preparation of da-methyl iodide is described in section IX-F. Various procedures are reported in the literature for the preparation of dg-acetone, da-diazometh-ane57.i63.i73 and da-acetyl chloride. ) These reactions can be carried out under the usual conditions and they need no further discussion. A convenient procedure has been reported for the da-methylation of sterically hindered or hydrogen bonded phenolic hydroxyl functions by using da-methyl iodide and sodium hydroxide in dimethyl sulfoxide solution. This procedure should be equally applicable to the preparation of estradiol da-methyl ether derivatives. 

Schotfev-Bauviann reaction (p. 209).—This maybe applied to tile pure phenol in order to obtain the benzoyl deiii ative, and the melting-point deteimined, or the acetyl deri -ative maybe pie-pared by boiling for a minute with acetic anhydride with the same object. 

Comforth has reviewed literature reports and independently studied the special cases of reaction of 1 with salicylaldehyde and with 2-acetoxybenzaldehyde. Coumarins (10) are afforded in the condensation of 1 with salicylaldehyde or its imine, whereas when 2-acetoxybenzaldehyde is used, acetoxy oxazolone 12 is the major product. The initial aldol condensation product between the oxazolone and 2-acetoxybenzaldehyde is the 4-(a-hydroxybenzyl)oxazolone 11, in which base-catalyzed intramolecular transacetylation is envisioned. The product 9 (R = Ac) can either be acetylated on the phenolic hydroxy group, before or after loss of acetic acid, to yield the oxazolone 12, or it can rearrange, by a second intramolecular process catalyzed by base and acid, to the hydrocoumarin, which loses acetic acid to yield 10. When salicylaldehyde is the starting material, aldol intermediate 9 (R = H) can rearrange directly to a hydrocoumarin. Comforth also accessed pure 4-(2 -hydroxyphenylmethylene)-2-phenyloxazol-5(4//)-one (13) through hydrolysis of 12 with 88% sulfuric acid. 

A -acetyl groups attached to the aniline have been shown to withstand the Conrad-Limpach reaction. Phenols and alcohols also survived unless in proximity to a reactive center. Jaroszewski reported the formation of 64 by reaction of aniline 63 with ethyl acetoacetate (5). Cyclization under thermal conditions in paraffin gave a mixture of quinolone 65 and quinoline 66. 

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