Acetic anhydride, as acylating agent

Silica sol-gel inunobihzed La(OTf)3 (Scheme 48.2B) previously used in the acylation of a series of alcohols and activated aromatic compounds using acetic anhydride as acylating agent, showed a poor activity compared with other various sihca sol-gel inunobihzed triflate derivatives (tert-butyl-dimethylsilyl-trifluoromethane-sulfonate (BDMST), or trifhc acid (HOTf)). Acylation at the aromatic ring occurred over the BDMST and HOTf catalysts, while the La(OTl)3 catalysts only led to O-acetylated products [22]. Such behavior is characteristic... 

Tables 14.1 and 14.2 show the dramatic improvement brought by the substitution of the old technology with AICI3 catalyst and acetylchloride as acylating agent in a batch reactor by the new technology with a HBEA zeolite catalyst, acetic anhydride as acylating agent in a fixed bed reactor (12). The fixed bed reactor process constitutes a major break-through in anisole acetylation.

The reaction was carried out at 100°C with sulpholane as solvent and acetic anhydride as acylating agent [9]. The results conversion of 2MN and the ratio of the two ketone products, l-acetyl-2-methoxynaphthalene (lAC) over 2-acetyl-6-methoxy-naphthalene (2AC), are given in Table 2. The selectivity for the two products was better than 95% in all cases. 

Anhydrides and esters are routinely used as acylating agents. Anhydrides, however, are the reagents of choice for acylating alcohols. For example, acetylation of cholesterol is carried out using acetic anhydride (Z = 0C(=0)CH3), and not ethyl acetate (Z = OCH2CH3). 

Cs2.5 for the acylation. Anisole and /j-xylene are acylated with benzoic anhydride and acetic anhydride in the presence of Cs2.5 without the dissolution of this catalyst. Carboxylic acids are much less reactive as acylating agents than the corresponding anhydrides because of the liberation of water. But when the water is removed, the acylation proceeds smoothly 214). Although the reaction of benzene with acetic acid is attractive in prospect, there is no report of heteropoly compounds as catalysts for this reaction. 

Resolution of racemic alcohols by acylation (Table 6) is as popular as that by hydrolysis. Because of the simplicity of reactions in nonaqueous media, acylation routes are often preferred. As in hydrolytic reactions, selectivity of esterification may depend on the structure of the acylating agent. Whereas Candida cylindracea lipase-catalyzed acylation of racemic-Ot-methylbenzyl alcohol [98-85-1] (59) with butyric acid has an enantiomeric value E of 20, acylation with dodecanoic acid increases the E value to 46 (16). Not only acids but also anhydrides are used as acylating agents. Pseudomonasjl. lipase (PFL), for example, catalyzed acylation of OC-phenethanol [98-85-1] (59) with acetic anhydride in 42% yield and 92% selectivity (74). 

A modification of this system was also used in intramolecular MBH reactions (also called as aldol cycloisomerization) [71, 74]. In this reaction, optically active pipecolinic acid 61 was found to be a better co-catalyst than proline, and allowed ee-values of up to 80% to be obtained, without a peptide catalyst. The inter-molecular aldol dimerization, which is an important competing side-reaction of the basic amine-mediated intramolecular MBH reaction, was efficiently suppressed in a THF H20 (3 1) mixture at room temperature, allowing the formation of six-membered carbocycles (Scheme 5.14). The enantioselectivity of the reaction could be improved via a kinetic resolution quench by adding acetic anhydride as an acylating agent to the reaction mixture and a peptide-based asymmetric catalyst such as 64 that mediates a subsequent asymmetric acylation reaction. The non-acylated product 65 was recovered in 50% isolated yield with ee >98%. 

The vapor-phase acylation of pyrrole was carried out over zeolite catalysts such as HZSM-5(19.7), HZSM-5(30), HZSM-5(280), HY, and cation-promoted modified zeolites like CeHZSM-5(30), LaHZSM-5(30), and CeHY, in a fixed-bed reactor at atmospheric pressure using acetic anhydride as an acylating agent <1998CAL95>. The catalytic activity of the zeolite catalysts was dependent on the reaction temperature and the type of cation polymer used in the modification of the zeolite surface. The acylation was found to be more active on Br0nsted acidic sites available over zeolite systems. The yield of l-(l//-pyrrol-2-yl)-l-ethanone 376 with respect to the conversion of pyrrole on HZSM-5(280) at 250 °C was 75.5% (Equation 87). 

To start our investigations, we examined the conversion of 2,3-dimethyl-2-butene (1) into 3,3,4-trimethyl-4-penten-2-one (2) as a model reaction (eq. 1). The choice of acetic anhydride as the acetylating agent was made in the light of related studies on the acylation of aryl ethers. Our work in this field had shown that acetic anhydride was the most effective reagent for the Friedel-Crafts acylation of anisole in the presence of Hp zeolite. A lower degree of conversion was achieved with acetyl chloride, while hardly any reaction occurred with ethyl acetate or acetic acid [6]. 

Esters. The catalyst promotes transesterification, for example, the acetyl group from EtOAc to alcohols. Acetic anhydride can be used as acylating agent. 

The most prominent cellulose ester produced on the industrial scale is cellulose acetate. The reaction is usually performed with acetic anhydride and with sulfuric acid as a catalyst. To minimize heterogeneities, acetylation is allowed to run nearly to completion, and subsequently partial ester hydrolysis is initiated by the addition of water until a desirable solubility is achieved that corresponds to a DS of about 2.5. Such higher acyl homologues as propanoyl or butanoyl exhibit more thermoplastic properties. Many specialized esters such as chiral (-)-menthyloxyacetates, furan-2-carboxylates, or crown-ether-containing acylates have been prepared on the laboratory scale and characterized by NMR spectroscopy. Various procedures have been applied, using anhydrides and acyl chlorides as acylating agents in combination with such bases as pyridine, 4-dimethylaminopyridine (DMAP), or iV,iV -carbonyldi-imidazole. The substitution pattern of cellulose acetates has also been modified by postchemical enzymatic deacetylation. Cellulose 6-tosylates have been used as activated intermediates for nucleophihc substitution to afford 6-amino-6-deoxy, 6-deoxy, or 6-deoxy-6-halo-celluloses. ... 

Praill, having discovered the efficiency of acylium perchlorates as acylating agents, decided to examine the esterification of /err-butanol as opposed to its dehydration to isobutene. Using acetic anhydride and perchloric acid mixtures, both tert-h xty acetate and isobutene were rapidly produced and in accordance with the known alkyl oxygen fission of tertiary esters, the proportion of isobutene increased with time. In these reactions where acetic anhydride was in excess, crystalline material was deposited in the mixture. Later this was shown to be 2,4,6-trimethylpyrylium perchlorate, identified by its conversion to 2,4,6-trimethyl pyridine and its picrate. When isobutene itself was acylated using acetic anhydride and perchloric... 

Purpose. You wfll carry out one of the major synthetic routes used in the preparation of amides the method involves the reaction of ammonia, or a primary or secondary amine, with an active acylating reagent. You will also explore the use of acetic anhydride as an acylating agent. The acetanilide product (Experiment [23A]) may be used in Experiment [28]. 

The A-heterocyclic carbene precursor 49 is a photo-switchable catalyst for amidation reactions. The synthesis of this catalyst begins with two Friedel-Crafts reactions firstly, 2-melhyl-5-phenylthiophene was 3-acetylated with acetic anhydride using SnCLj, then product ketone oxidised to a glyoxal by SeOa- The glyoxal itself was used as acylating agent to react with 2-methyl-5-phenylthiophene with the assistance of SnCLj. After several further steps, the salt 49 was obtained (Scheme 51) [69]. 

Chiral n complexes of heterocycles with transition metals can serve as effective catalysts for an array of useful organic reactions.The most efficient nucleophilic catalysts previously used had planar structures, e.g., 4-(dimethylamino)pyridine, and therefore required an asymmetric environment in the vicinity of an sp -hybridized nucleophilic atom. In a recent paper, G. C. Fu et al describe a procedure, which they call a second-generation system for kinetic resolution, that employs an iron complex at a mole fraction of 2% as the chiral catalyst, and acetic anhydride as the acylating agent (Figure 9.7.1). The authors attached the 4-(dimethylamino)pyridine moiety to a chiral ferrocene analog. The lower portion of the ferrocene, coordinated to the iron atom is pentaphenylcyclopentadiene, as shown in Figure 9.7.1. 

Acylation. Aliphatic amine oxides react with acylating agents such as acetic anhydride and acetyl chloride to form either A[,A/-diaLkylamides and aldehyde (34), the Polonovski reaction, or an ester, depending upon the polarity of the solvent used (35,36). Along with a polar mechanism (37), a metal-complex-induced mechanism involving a free-radical intermediate has been proposed. 

Esters of the phenohc hydroxyl are obtained easily by the Schotten-Baumaim reaction. The reaction ia many cases iavolves an acid chloride as the acylating agent. However, acylation is achieved more commonly by reaction with an acid anhydride. The single most important commercial reaction of this type is the acetylation of sahcyhc acid with acetic anhydride to produce acetylsahcyhc acid [50-78-2] (aspirin). 

Acetic anhydride has also been used as the acylating agent. The formation of thiiranes from thiocyanatohydrins having a tertiary hydroxy group is best achieved by p-toluenesulfonic acid-catalyzed acetylation.The analogous thiocyanatohydrins with a secondary hydroxyl and a tertiary thiocyanate function give a predominance of epoxide from thiocyanatohydrin acetates since the hydrolysis rate of the secondary acetate grouping becomes competitive with that of the tertiary thiocyanate. 

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