Nucleophilic Acyl Substitutions of Esters with Protic Nucleophiles Mediated by Amphoteric, Oxotitanium, and Vanadyl Species

Abstract

[reaction: see text] A diverse array of oxometallic species were examined as catalysts in nucleophilic acyl substitution (NAS) reactions of methyl (or ethyl) esters with protic nucleophiles. Among them, oxotitanium acetylacetonate (TiO(acac)(2)) and vanadyl chloride (VOCl(2)-(THF)(x)()) served as the most efficient and water-tolerant catalysts. Transesterifications of methyl and/or ethyl esters with functionalized (including acid- or base-sensitive) 1 degrees and 2 degrees alcohols can be carried out chemoselectively in refluxed toluene or xylene in a 1:1 substrate stoichiometry using 1 mol % catalyst loading. The resultant products were furnished in 85-100% yields by simple aqueous workup to remove water-soluble catalysts. The new NAS protocol is also amenable to amines and thiols in 74-91% yields, albeit with higher loading (2.5 equiv) of protic nucleophiles. Representative examples of commercial interests such as Padimate O and antioxidant additives for plastics were also examined to demonstrate their practical applications. A 1:1 adduct between TiO(acac)(2) and a given 1-octadecanol was identified as (C(18)H(37)O)(2)Ti(acac)(2) and was responsible for its subsequent NAS of methyl esters.

Organocatalysis: Fundamentals and Comparisons to Metal and Enzyme Catalysis

“…Transesterification (Scheme 2), reactions producing esters by catalytical alcoholysis of other esters, also play an important role in the industry, for instance in the manufacture of glycerol esters in fat chemistry (e.g., biodiesel), the transesterification of dimethyl carbonate to diethyl carbonate, or the production of polyethylene terephthalate from dimethyl terephthalate. For these reactions, the usual catalysts are Brønsted mineral acids (H 3 PO 4 , H 2 SO 4 , HCl) [24][25][26], and organic acids such as MeSO 3 H and p-toluenesulfonic acid (TsOH) [27], alkoxides such as NaOR, KOR, ROMgBr [28][29][30][31][32], Lewis bases such as 4-dimethylaminopyridine (DMAP) [33,34], 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU) [35], Lewis acids such as BX 3 [36], or AlCl 3 [37], amphoteric Catalysts 2016, 6, 128 5 of 65 compounds (compounds able to react either as acids or bases) such as Bu 3 SnOR [38][39][40][41], perfluorotin oxides [42], Al(OR) 3 [43,44], titanium oxides chlorides [45][46][47][48] or palladium oxides [49,50]. More recently, diaminocarbenes have been introduced as catalysts as well [51][52][53][54].…”

“…Other oxometallic species catalyze nucleophilic acyl substitution reactions with protic nucleophiles. Examples are TiO(acetylacetonate) 2 , vanadyl dichloride VOCl 2 (THF) n , [48] and Y 5 (O-i-Pr) 13 O [76], all being water-tolerant catalysts.…”

Transesterification Kinetics Investigation of R‐Substituted Phenyl Benzoates with 4‐Methoxyphenol in the Presence of K2CO3 in DMF

“…Acyl transfer reactions have been intensively studied due to their great importance both in biological processes and in synthetic applications . Recently, we have kinetically studied the substituent effect in a nonleaving group on the reactivity of 4‐nitrophenyl benzoates with 4‐chlorophenol and with benzenethiol in the presence of potassium carbonate in DMF .…”

In-Water and Neat Batch and Continuous-Flow Direct Esterification and Transesterification by a Porous Polymeric Acid Catalyst

“…Yamamoto and Ishihara et al reported highly efficient and direct ester condensation in hydrocarbons by using hafnium(IV) salts such as an HfCl 4 ·(THF) 2 catalyst under azeotropic reflux conditions. Transesterification of various esters with alcohols using heterogeneous and homogeneous acidic catalysts has also been reported 28 29 30 31 32 33 34 35 36 37 38 .…”