4-Dimethylaminopyridine esterification catalyst

Dimethylaminopyridine [1122-58-3] (DMAP) (24) has emerged as the preferred catalyst for a variety of synthetic transformations under mild conditions, particularly acylations, alkylations, silylations, esterifications, polymeri2ations, and rearrangements (100). POLYDMAP resin [1122-58-3], a polymeric version of DMAP, is available, and is as effective as DMAP as a catalyst for acylation reactions. Furthermore, it can be recycled without regeneration more than 20 times with very Htde loss in activity. POLYDMAP is a trademark of Reilly Industries, Inc. 

However, this method is appHed only when esterification cannot be effected by the usual acid—alcohol reaction because of the higher cost of the anhydrides. The production of cellulose acetate (see Fibers, cellulose esters), phenyl acetate (used in acetaminophen production), and aspirin (acetylsahcyhc acid) (see Salicylic acid) are examples of the large-scale use of acetic anhydride. The speed of acylation is greatiy increased by the use of catalysts (68) such as sulfuric acid, perchloric acid, trifluoroacetic acid, phosphoms pentoxide, 2inc chloride, ferric chloride, sodium acetate, and tertiary amines, eg, 4-dimethylaminopyridine. 

AC2O, AcCl, Pyr, DMAP, 24-80°, 1-40 h, 72-95% yield. The use of DMAP increases the rate of acylation by a factor of 10. These conditions will acylate most alcohols, including tertiary alcohols. The use of DMAP (4-N,N-dimethylaminopyridine) as a catalyst to improve the rate of esterification is quite general and works for other esters as well. 

During the first decade when solid-phase synthesis was executed using Fmoc/tBu chemistry, the first Fmoc-amino acid was anchored to the support by reaction of the symmetrical anhydride with the hydroxymethylphenyl group of the linker or support. Because this is an esterification reaction that does not occur readily, 4-dimethylaminopyridine was employed as catalyst. The basic catalyst caused up to 6% enantiomerization of the activated residue (see Section 4.19). Diminution of the amount of catalyst to one-tenth of an equivalent (Figure 5.21, A) reduced the isomerization substantially but did not suppress it completely. As a consequence, the products synthesized during that decade were usually contaminated with a small amount of the epimer. In addition, the basic catalyst was responsible for a second side reaction namely, the premature removal of Fmoc protector, which led to loading of some dimer of the first residue. Nothing could be done about the situation,... 

Protection of an alcohol function by esterification sometimes offers advantages over use of acetal or ether groups. Generally, ester groups are stable under acidic conditions. Esters are especially useful in protection during oxidations. Acetates and benzoates are the most commonly used ester derivatives. They can be conveniently prepared by reaction of unhindered alcohols with acetic anhydride or benzoyl chloride, respectively, in the presence of pyridine or other tertiary amines. 4-Dimethylaminopyridine (DMAP) is often used as a catalyst. The use of A-acylimidazolides (see Section 3.4.1) allows the... 

Esterification of succinic anhydride in dimethylformamide with 4-dimethylaminopyridine gives O-succinoylated inulin (Vermeersch and Schacht, 1985), which can be used as a drug carrier. Esterification of alkenyl succinic anhydrides having chain lengths of C8 to C20 in dimethylformamide, with or without a catalyst, produces potential deflocculating agents for use in detergents... 

Esterification. DCC has been satisfactory only for esterification of phenols and thiophenols because of variable yields. However, if 4-dimethylaminopyridine (3, 118-119 5, 26) or 4-pyrrolidinopyridine (this volume) is added as catalyst, alcohols and thiols are csterified readily at rm temperature in satisfactory yields. Sterically... 

Polymeric counterparts of 4-dimethylaminopyridine have been prepared by several groups. Reilly Industries sells one as Reillex PolyDMAP (5.32a).141 When used in esterifications, the polymeric catalyst offers easy separation, reduced toxicity and the ability to use it in excess. It can be reused. The monomeric reagent is highly toxic. The two other polymeric analogues of 4-dimethylaminopyridine (5.33) are based on other chemistry.142 The first is a polyamide, the second, a polyurethane. In the second case, glycerol was also sometimes added to produce an insoluble product. 

Applying dodecanoyl chloride under microwave conditions, Krausz et al. demonstrated that the esterification of cellulose can be achieved within 6-9 min (Fig. 34) [126]. In a general procedure, a mixture of cellulose, acid chloride and catalyst (4-dimethylaminopyridine) was irradiated in an open vessel placed in a... 

Poly(ethylene-octene) Copolymer/PLA Blends Poly(ethylene-octene) copolymer, a thermoplastic polyolefin elastomer (TPO), was melt blended with PLA at a ratio of 20/ 80 wt% [10]. The difference in polarities of the two polymers led to thermodynamic immiscibility and phase separation of the final blends as determined by the Molau test. Therefore, a copolymer of TPO-gra//-PLA (TPO-PLA synthesized via functionalization of TPO and MA with benzoyl peroxide (BPO), followed by esterification of the MA-functionalized TPO (TPO-MAH) with PLA using 4-dimethylaminopyridine (DMAP) as a catalyst) was introduced to improve the compatibility of the TPO/PLA blends. The use of 5 wt% TPO-... 

Trifluoroacetaldehyde, generated from l-ethoxy-2,2,2-trifluoroethanol (4 mmol) by treatment with polyphosphoric acid (PPA), was passed into a toluene solution of (Ry BIN0L-Ti(0-/-Pr)2 (1 mmol) at -78 °C in the presence of 2-propanol (2 mmol) coproduced during the preparation of the catalyst from Ti(0-/-Pr)4 and (i )-binaphthol (BINOL). The resulting hemiacetal was treated with benzoyl chloride, triethylamine and 4-dimethylaminopyridine (DMAP) at -78 °C to afford 2,2,2-trifluoro-l-isopropoxyethyl benzoate (80% ee) in 85% yield. When the esterification was carried out at higher temperatures, % ee of the product considerably decreased due probably to racemization of the intermediate hemiacetal. 

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