Acylation of alcohols and phenols

Jin, T.-S., Xiao, J.-C., Wang, Z.-H., Li, T.-S. Silica gel-supported phosphotungstic acid (PTA) catalyzed acylation of alcohols and phenols with acetic anhydride under mild reaction conditions. J. Chem. Res., Synop. 2003, 412-414. 

Acyloxy- and acylthiopyrazines are convenient acylation reagents for benzylamine, aniline, pyrrolidine, and related compounds (see Section 6.03.8.3). The acylthio compounds are also useful for acylation of alcohols and phenols. Pyrazinyl alkyl sulfoxides (see Section 6.03.8.4) give aldehydes and ketones by treatment with TFAA <91H(32)937>. The pyrazinium chlorochromate salt (181) is formed by addition of chromium(VI) oxide to a solution of pyrazine in hydrochloric acid, and it has proved to be more effective for the oxidation of aliphatic and allyl alcohols to the aldehydes than pcc <83H(20)2029>. 

Acylation of alcohols and phenols by acid anhydrides is often a simpler process than that with acid chlorides ... 

Moghaddam FM, Saeidian H. Controlled microwave-assisted synthesis of ZnO nanopowder and its catalytic activity for O-acylation of alcohol and phenol. Mater Sci Eng 2007 139(2/3) 265-9. 

Derivatives are prepared from the appropriate acid anhydride, or occasionally the acid chloride, usually in the presence of a base such as pyridine, triethylamine, or N,N-dimethyl-4-amlnopyridine at elevated temperatures [474-482]. Acylation of amines and phenols (not alcohols) in aqueous solution in the presence of potassium carbonate has been demonstrated (448,483,484), but does not constitute m l practice as reactions are generally performed under i Arous conditions. 

Fluoroboric acid supported on silica (HBF4-silica) has recently been found to be a highly efficient catalyst in the protection of various functional groups. Structurally diverse alcohols, phenols, thiophenols, and anilines can be acylated under solvent-free conditions at room temperature.669 Even acid-sensitive tertiary alcohols (1-alkylcyclo-hexanols) and sterically hindered compounds, such as endo-borneol, give the acylated products in high yields. A triflic acid-silica catalyst also shows high activity in the (9-acetylation with Ac20 of alcohols and phenols.359... 

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. ... 

Parameters such as solvent, basic medium and reaction time, affecting the derivatization of alcohols and phenols with benzoyl chloride, were investigated. End analysis was by GC with UVD . a sensitive method proposed for trace determination of phenols in water consists of preconcentration by SPE with a commercial styrene-divinylbenzene copolymer, acylation with pentafluorobenzoyl chloride in the presence of tetrabutylammonium bromide and end analysis by GC with either ECD or ITD-MS. LOD was 3 to 20 ngL for ECD and 10 to 60 ngL for ITD-MS, with 500 mL samples . Acylation with the fluorinated glutaric acid derivative 43 was proposed for determination of urinary phenols, as indicative of exposure to benzene and other aromatic hydrocarbons. End analysis by GC-MS shows strong molecular ions of the derivatives by electron ionization. The proto-nated ions are the base peaks obtained by chemical ionization. LOD was 0.5 mgL and the linearity range 0-100 mg L for phenol . 

The acetylation of alcohols and phenols with acetic anhydride and HSZ-360 zeolite at 60oC used no solvent. The acetate of 1-dodecanol was obtained in 98% yield, and the acetate from 1 naphthol in 100% yield.183 The acylation of anisole with acetic anhydride at 100oC without solvent using zeolite H-/8 gave 4-methoxyacetophenone (6.30) in 98%yield.184 The catalyst could be recovered, regenerated, and reused with no decrease in yield. These reactions show that not all zeolites are used at high temperatures in the vapor phase. 

Pd nanoparticles supported on PANI-NFs are efficient semi-heterogeneous catalysts for Suzuki coupling between aryl chlorides and phenylboronic acid, the homocoupling of deactivated aryl chlorides, and for phenol formation from aryl halides and potassium hydroxide in water and air [493], PANl-NF-supported FeCl3 as an efficient and reusable heterogeneous catalyst for the acylation of alcohols and amines with acetic acid has been presented [494]. Vanadate-doped PANI-NFs and PANI-NTs have proven to be excellent catalysts for selective oxidation of arylalkylsulfides to sulfoxides under nuld conditions [412]. Heterogeneous Mo catalysts for the efficient epoxidation of olefins with ferf-butylhydroperoxide were successfully synthesized using sea urchin-Uke PANI hollow microspheres, constructed with oriented PANI-NF arrays, as support [495]. Pt- and Ru-based electrocatalyst PANI-NFs—PSSA—Ru—Pt, synthesized by the electrodeposition of Pt and Ru particles into the nanofibrous network of PANI-PSSA, exhibited an excellent electrocatalytic performance for methanol oxidation [496]. A Pt electrode modified by PANI-NFs made the electrocatalytic oxidation reaction of methanol more complete [497]. Synthesis of a nanoelectrocatalyst based on PANI-NF-supported... 

As has already been pointed out in Chapter III, the acyl halides and anhydrides react readily with the hydroxyl groups of alcohols and phenols. This fact must be kept in mind in connection with tests for amines. Acid chlorides of low molecular... 

These catalysts have been tested in a variety of reactions such as acylation of alcohols and alkylation of phenols and naphthols [71,72,96,100,101,108]. The encapsulated triflate derivatives, and particularly the immobilized Lewis acid r rr-butyldimethylsilyltri-fluoromethanesulfonate, are very active catalysts in acylation of 2-methoxynaphthalene with acetic anhydride. In solvent-free conditions, the TOF is much higher than the values reported in literature for other heterogeneous catalysts. Moreover, leaching can be completely avoided when the solvent is omitted. The major product was in all cases the 1-acetylated methoxynaphthalene the isomerization to the 6-isomer was negligible even at high conversions. 

AcCl, NaOH, dioxane, Bu4N HSO, 25°, 30 min, 90% yield. Phase-transfer catalysis with tetra-n-butylammionium hydrogen sulfate effects acylation of sterically hindered phenols and selective acylation of a phenol in the presence of an aliphatic secondary alcohol. 

Carboxylic acids react with trifluoroacetic anhydride to give mixed anhydrides that are especially useful for the acylation of hindered alcohols and phenols ... 

Since the imidazolide method proceeds almost quantitatively, it has been used for the synthesis of isotopically labeled esters (see also Section 3.2), and it is always useful for the esterification of sensitive carboxylic acids, alcohols, and phenols under mild conditions. This advantage has been utilized in biochemistry for the study of transacylating enzymes. A number of enzymatic transacylations (e.g., those catalyzed by oc-chymo-trypsin) have been shown to proceed in two steps an acyl group is first transferred from the substrate to the enzyme to form an acyl enzyme, which is then deacylated in a second step. In this context it has been shown[21] that oc-chymotrypsin is rapidly and quantitatively acylated by Af-fraw.s-cinnamoylimidazole to give /ra/w-cinnamoyl-a-chymotrypsin, which can be isolated in preparative quantities and retains its enzymatic activity (see also Chapter 6). 

It must further be mentioned that the acylation of alcohols, phenols, and amines with acid chlorides (and also anhydrides) is now frequently carried out in pyridine solution instead of according to the older Schotten-Baumann method (action of acid chloride in aqueous-alkaline suspension). The hydrogen chloride is fixed by the pyridine. 

Since serine-195 is the site of acylation, a good deal of recent work has been directed towards determining the efficiency of neighboring alcohol and phenol groups as intramolecular nucleophiles in ester and amide hydrolysis. In comparison with acetamide and butyramide, the hydrolysis of 7-hydroxybutyramide [equation (17)] in the alkaline and neutral pH-range is accelerated 800-fold (Bruice and Marquardt, 1962). These reactions are attack of alkoxide ion on the neutral and protonated amide function,... 

Other authors have described the lipase-catalyzed chemoselective acylation of alcohols in the presence of phenolic moities [14], the protease-catalyzed acylation of the 17-amino moiety of an estradiol derivative [15], the chemoselectivity in the aminolysis reaction of methyl acrylate (amide formation vs the favored Michael addition) catalyzed by Candida antarctica lipase (Novozym 435) [16], and the lipase preference for the O-esterification in the presence of thiol moieties, as, for instance, in 2-mercaptoethanol and dithiotreitol [17]. This last finding was recently exploited for the synthesis of thiol end-functionalized polyesters by enzymatic polymerization of e-caprolactone initiated by 2-mercaptoethanol (Figure 6.2)... 

Both aliphatic alcohols and phenols have been immobilized as esters of support-bound carboxylic acids. The esterification can be achieved by treatment of resin-bound acids with alcohols and a carbodiimide, under Mitsunobu conditions, or by acylation of alcohols with support-bound acyl halides (see Section 13.4). 

Less reactive than acyl halides, but still suitable for difficult couplings, are symmetric or mixed anhydrides (e.g. with pivalic or 2,6-dichlorobenzoic acid) and HOAt-derived active esters. HOBt esters smoothly acylate primary or secondary aliphatic amines, including amino acid esters or amides, without concomitant esterification of alcohols or phenols [34], HOBt esters are the most commonly used type of activated esters in automated solid-phase peptide synthesis. For reasons not yet fully understood, acylations with HOBt esters or halophenyl esters can be effectively catalyzed by HOBt and HOAt [3], and mixtures of BOP (in situ formation of HOBt esters) and HOBt are among the most efficient coupling agents for solid-phase peptide synthesis [2]. In acylations with activated amino acid derivatives, the addition of HOBt or HOAt also retards racemization [4,12,35]. 

Regioselective acylation of diols.1 3-Acyl-2-oxazolones2 are useful for acylation of amines and thiols to give peptides and thioesters. They also acylate alcohols in high yield in the presence of this catalyst. With this catalyst, the reactivity for acylation of hydroxyl groups in primary >> phenolic > secondary. However, for selective acylation of primary hydroxyl groups of 1,2-diols, the Cp2ZrHCl-Mg couple is superior to Zr(acac)4. 

Li, T.-S. Li, A.-X. Montmorillonite day catalysis. Part 10. K-10 and KSF-catalyzed acylation of alcohols, phenols, thiols and amines scope and limitation. J. Chem. Soc. Perkin Trans. 1 1998, 1913-1917. 

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