Acetylations phenols, pyridine

The difficulty of acetylating phenolic groups which have carbonyl groups in the para position, for example, vanillin without the use of pyridine as a catalyst (Neilson et al. 1988) ... 

These can be prepared as for the benzoates using either acetic anhydride with 3N NaOH or acetyl chloride in pyridine. They are hydrolysed as described for the benzoates. This hydrolysis can also be carried out with aqueous 10% NaOH solution, completion of hydrolysis being indicated by the complete dissolution of the acetate in the aqueous alkaline solution. On steam distillation, acetic acid also distils off but in these cases the phenols (see above) are invariably solids which can be filtered off and recrystallised. 

In a related procedure, even benzene and substituted benzenes (e.g., PhMe, PhCl, xylenes) can be converted to phenols in good yields with sodium perborate F3CS020H. " Aromatic amines, N-acyl amines, and phenols were hydroxylated with H2O2 in SbFs—HF. Pyridine and quinoline were converted to their 2-acetoxy derivatives in high yields with acetyl hypofluorite AcOF at -75°C. ... 

The reaction with carboxylic acid and acid anhydride is carried out in the presence of a small amount of concentrated sulphuric acid. The reaction is reversible, and therefore, water is removed as soon as it is formed. The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to neutralise HCl which is formed during the reaction. It shifts the equilibrium to the right hand side. The introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation. Acetylation of salicylic acid produces aspirin. 

OSL Impurities. It was also of interest to determine the impurities removed from crude OSL by reslurry in aqueous sodium bicarbonate, which was done to improve its usefulness in phenolic resins (Cook, P. M., Eastman Kodak at Kingsport, TN, personal communications, 1987). Extraction and acetylation procedures, involving methylene chloride, acetic anhydride pyridine... 

Acetates of fatty [1] and polyhydric [2] alcohols, phenols [3] and chlorophenols [4] have been studied. Fell and Lee [3] described a GC method for the determination of polyhydric phenols in urine, which, having been extracted, were acetylated with acetic anhydride in the presence of 4-dimethylaminopyridine. According to these authors this substance shows much stronger catalytic effects than does the usually used pyridine. The derivatives are formed rapidly and quantitatively even in very dilute solutions. In the absence of the catalyst, bifunctional phenols provide more than one GC peak. Slightly polar OV-210 is recommended for the separation of phenol acetates, but analysis on nonpolar OV-101 leads to tailing, probably as a consequence of insufficient deactivation of the column. 

Phenoxy-substituted 2H, 8 -naphtha [l,2,3-de]-benz[/j]-2,8-quinolinedione (IIIC, R2 = hydrogen, R3 = CH3) was synthesized by cyclization of TV-chloro-acetyl-6-aminonaphthacenequinone in pyridine to the corresponding naphthacenepyrido-nyl-3-pyridinium chloride, with the subsequent reductive elimination of the pyridi-nium residue.39 The 3-acetyl derivative was obtained by the interaction of 6-amino-ll-chloro-5,12,naphthacenequinone with acetic anhydride in phenol in the presence of anhydrous sodium carbonate.39... 

In general, the aliphatic hydroxyl content of a lignin preparation is determined by subtraction of the phenolic hydroxyl content (see Chap. 7.2) from the total hydroxyl content of the lignin. The total hydroxyl content of lignin (partial structure H) can be determined by acetylation with acetic anhydride-pyridine reagent (10) followed by saponification of the acetate (partial structure 12) and titration of the resulting acetic acid (14) with a standard 0.05 N sodium hydroxide solution (Roth 1953). 

DCC is also used in nucleotide chemistry to esterify a sugar hydroxyl group with a phosphate group in another nucleotide or oligonucleotide unit. Also p-styrene based polymers with a pyridyl-2-ethanol end group are reacted in pyridine with 3 -0-acetyl-desoxythimidine-5 -phosphate in the presence of DCC." The reaction of mono esters of phosphoric acid with alcohols or phenols, in the presence of DCC, affords phosphoric acid diesters in high yield." This reaction is widely used in nucleic acid chemistry. 

All types of alcohols and phenols are acylated by anhydrides. The reaction is catalyzed by a small amount of sulfuric acid, zinc chloride, acetyl chloride, sodium acetate, or pyridine. r-Butyl alcohol gives /-butyl acetate in 60% yield. Acetylation of phenols may be accomplished in an aqueous alkaline solution, the acylation proceeding more rapidly than the hydrolysis of the anhydride. The yields are above SX)%. Phenol, dihydroxybenzenes, naphthols, and phenols carrying nitro, amino, halo, carboxyl, or carbomethoxyl groups are acetylated by this procedure. ... 

As mentioned earlier, meso-inositol, and indeed all the inositols, are readily converted to aromatic compounds by oxidation. Posternak found that inosose has the tendency to form phenolic compounds under very mild conditions. On attempted acetylation of inosose with acetic anhydride in the presence of either pyridine or sodium acetate the expected pentaacetate was not obtained the product was 1,2,3,5-tetra-acetoxybenzene (XXXVII). Similarly, the treatment of inosose pentaacetate with boiling acetic anhydride and pyridine or sodium acetate gave the same product. Inosose pentabenzoate was prepared by the use of benzoyl chloride and zinc chloride. Under the influence of pyridine or sodium acetate in acetic acid the pentabenzoate lost two molecules of benzoic acid to give l-hydroxy-2,3,5-tribenzoxybenzene (XXXVIII). 

Phenarsazine oxide crystallises from nitrobenzene or pyridine in colourless plates, which soon become yellow, M.pt. 350° C. It is sparingly soluble in most solvents, and when boiled with alcohols yields ethers, and with phenols, phenyl ethers. Boiling with acetic acid transforms it into 10-acetyl-S lO-dikydrophenarsazine, which occurs in greenish, shimmering plates, M.pt. 228° to 224° C. The corresponding 10-n-butoxy-compound forms pale yellow needles, M.pt. 158° to 160° C., and the lO-hemsyhtxy-denvaiive, colourless needles, M.pt. 178° to 175° C. 

Values of molar Kerr constants and dipole moments of nitrogen azoles and their complexes with phenols have been obtained. " These complexes are formed by an intermolecular hydrogen bond between the pyridine-type nitrogen of the azole and the phenolic proton. " The use of dipole moments in conformational studies has shown that A-aryl- and C-aryl- and A-furyl- and C-furyl imidazoles (and benzimidazoles) are nonplanar, but l-(a-furyl)-4,5-diphenylimidazoles do have a planar bicyclic fragment. The dipole moments and conformations of azolides (A-acylazoles) have been studied. In the 1-arylimidazoles the dipole is toward the aryl group. In 4,5-di-t-butylimidazole the molecule is essentially planar, but the C-4—C-5 bond is slightly stretched. Among other imidazole derivatives which have been studied by X-ray are histidine hydrochloride, 4-acetyl-amino - 2 - bromo - 5 - isopropyl -1 - methylimidazole, 4- acetyl - 5 - methyl - 2 -phenylimidazole, and imidazole-4-acetic acid hydrochloride. 

Aromatic acid chlorides (ArCOCl) are considerably less reactive than the aliphatic acid chlorides. With cold water, for example, acetyl chloride reacts almost explosively, whereas Benzoyl chloride reacts only very slowly. The reaction of aromatic acid chlorides with an alcohol or a phenol is often carried out using the Schotten-Baumaiin technique the acid chloride is added in portions (followed by vigorous shaking) to a mixture of the hydroxy compound and a base, usually aqueous sodium hydroxide or pyridine (an organic base, Sec. 31.11). Although the function of the base is not clear, it seems not only to neutralize the hydrogen chloride that would otherwise be liberated, but also tp catalyze the reaction. 

Pyridine-catalyzed acylation of phenols using benzoyl chloride and benzoyl bromide was reported . Acylation of phenols using acetyl chloride or benzoyl chloride can be achieved using triflic acid as the catalyst in nonpolar solvents snch as methylene chloride. The role of pyridine in these reactions seems to be the intermittent formation of the benzoylpyrimidinium ions as the reactive species. The activated phenolic componnds snch as resorcinol, on the other hand, could be acylated in near-supercritical water (250-300 °C) without using any external Lewis acid catalysts (equation 47) . The equilibrium conversions in water, however, are to the extent of about 4%. Running the same reactions in neat acetic acid causes a tenfold increase in yield. 

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