4-nitrophenylacetate

The acid is conveniently prepared by the reduction of p-nitrophenylacetic acid with ammonium sulphide (hydrogen sulphide in ammoniacal solution). 

The reduction of o-nitrophenyl acetic acids or esters leads to cyclization to oxindoles. Several routes to o-nitrophenylacetic acid derivatives arc available, including nitroarylation of carbanions with o-nitroaryl halides[2l,22] or trif-late[23] and acylation of o-nitrotoluenes with diethyl oxalate followed by oxidation of the resulting 3-(u-nitrophenyl)pyruvate[24 26]. 

Thionyl chloride (11.5g, 96.4 mmol) was added to 2-nitrophenylacetic acid (8.72g, 48.2mmol) and the suspension was warmed to 50°C and stirred until gas evolution was complete. The resulting solution was concentrated in vacuo and the residue dissolved in CHjClj (30 ml). This solution was added dropwise to a stirred solution of Meldrum s acid (6.94 g, 48.2 mmol) in CH2CI2 (200 ml) under nitrogen at 0 C. The solution was stirred at 0" C for 1 h after the addition was complete and then kept at room temperature for an additional hour. The reaction solution was then worked up by successively washing with dil. HC1, water and brine and dried (MgSOJ. The dried solution was concentrated in vacuo and abs. ethanol (200 ml) was added to the residue. The mixture was... 

Bromo-2-nitrophenylacetic acid (26 g, 0.10 mol) was dissolved in a mixture of 50% HjSO (400 ml) and ethanol (600 ml) and heated to 90°C. Over a period of 1 h, zinc dust (26.2 g, 0.40 mol) was added. slowly and then heating was continued for 2 h. The excess ethanol was removed by distillation. The solution was cooled and filtered. The filtrate was extracted with EtOAc. The filtered product and extract were combined, washed with 5% NaCOj and brine and then dried (MgSO ). The solvent was removed in vacuo and the residue recrystallized from methanol to give 20.5 g (97% yield) of the oxindole. 

The intermediacy of an aci-nitro compound has been proposed for the sulfuric acid cyclization of o-nitrophenylacetic acid to yield a mixture of 2,1-benzisoxazole and 2,1-benzisoxazole-3-carboxylic acid. The acid does not decarboxylate under the reaction conditions. The proposed aci-nitro intermediate cyclized to an A/ -hydroxy compound which decomposed to the products (Scheme 179) (70JCS(C)2660). 

B A E Y E R Oxindole Synthesis Synthesis of oxindole from o-nitrophenylacetates. 

Nitrophenylacetic acid [3740-52-1] M 181.2, m 120 , pK 3.95. Crystd from EtOH/water and dried over P2O5 under vacuum. 

FIGURE 16.12 Catalysis of nitrophenylacetate hydrolysis by imidazole—an example of general base catalysis. Proton transfer to imidazole in the transition state facilitates hydroxyl attack on the substrate carbonyl carbon. 

FIGURE 16.14 All example of proximity effects in catalysis, (a) The imidazole-catalyzed hydrolysis of j nitrophenylacetate is slow, but the corresponding intramolecular reaction is 24-fold faster (assuming [imidazole] = 1 Min [a]). 

In the chymotrypsiii mechanism, the nitrophenylacetate combines with the enzyme to form an ES complex. This is followed by a rapid second step in which an acyl-enzyme intermediate is formed, with the acetyl group covalently bound to the very reactive Ser . The nitrophenyl moiety is released as nitrophenolate (Figure 16.22), accounting for the burst of nitrophenolate product. Attack of a water molecule on the acyl-enzyme intermediate yields acetate as the second product in a subsequent, slower step. The enzyme is now free to bind another molecule of nitrophenylacetate, and the nitrophenolate product produced at this point corresponds to the slower, steady-state formation of product in the upper right portion of Figure 16.21. In this mechanism, the release of acetate is the rate-llmitmg step, and accounts for the observation of burst kinetics—the pattern shown in Figure 16.21. 

Wright and Collins reduced o-nitrophenylacetic acids (37) with zinc and sulfuric acid and obtained a mixture of the hydroxamic acid (38) and lactam (39)... 

Shimidzu etal.111 studied the catalytic activity of poly (4(5)-vinylimidazole-co-acrylic add) 60 (PVIm AA) in hydrolyses of 3-acetoxy-N-trimethylanilinium iodide 61 (ANTI) and p-nitrophenylacetate 44 (PNPA). The hydrolyses of ANTI followed the Michaelis-Menten-type kinetics, and that of PNPA followed the second-order kinetics. Substrate-binding with the copolymer was strongest at an imidazole content of 30 mol%. The authors concluded that the carboxylic acid moiety not... 

Supemucleophilic polymers containing the 4-(pyrro-lidino)pyridine group were synthesized from the corresponding maleic anhydride copolymers and also by cyclopolymerization of N-4-pyridyl bis(methacryl-imide). The resulting polymers were examined for their kinetics of quaternization with benzyl chloride and hydrolysis of pj-nitrophenylacetate. In both instances, the polymer bound 4-(dialkylamino)pyridine was found to be a superior catalyst than the corresponding low molecular weight analog. 

Kinetic Studies. The pioneering work of Hierl et al. (8) and Delaney et al. (9) had established that hydrolysis of jr-nitro-phenylcarboxylates was an excellent means of observing the nucleophilic catalysis by 4-(dialkylamino) pyridine functionalized polymers. Hydrolysis of p-nitrophenylacetate in a buffer at pH 8.5 showed that the polymer was a slightly better catalyst than the monomeric analog PPY (Table II). However, preliminary results indicate that the polymer bound 4-(dialkylamino) pyridine is more effective as a catalyst than the monomeric analog in the hydrolysis of longer carbon chain p-nitrophenylcarboxylates, such as p-nitrophenylcaproate. 

Figures I and II show a comparison of the reaction profile for PPY and polymer catalyzed hydrolysis for p-nitrophenylacetate and p-nitrophenylcaproate monitored by the appearance of p-nitro-phenoxide absorption by UV-VIS spectroscopy. These results confirm the effectiveness of the interactions between the hydro-phobic polymer chain and the hydrocarbon portion of the substrate, as it was previously mentioned, in accordance with the observations of Overberger et al (20).

Figure 1. Absorbance at 400 nm vs. time for the poly(4-pyrrolidi-nopyridine) and 4-pyrrolidinopyridine catalyzed hydrolysis of p-nitrophenylacetate at pH 8.5.

---