Methyl nitrobenzoates, hydrolysis

Hydrolysis of methyl m-nitrobenzoate to m-nitrobenzoic acid. Place 90 -5 g. of methyl m-nitrobenzoate and a solution of 40 g. of sodium hydroxide in 160 ml. of water in a 1-htre round-bottomed flask equipped with a reflux condenser. Heat the mixture to boiling during 5-10 minutes or until the ester has disappeared. Dilute the reaction mixture with an equal volume of water. When cold pour the diluted reaction product, with vigorous stirring, into 125 ml. of concentrated hydrochloric acid. Allow to cool to room temperature, filter the crude acid at the pump and wash it with a httle water. Upon drying at 100°, the crude m-nitrobenzoic acid, which has a pale brownish colour, weighs 80 g. and melts at 140°, Recrystalhsation from 1 per cent, hydrochloric acid afibrds the pure acid, m.p. 141°, as a pale cream sohd the loss of material is about 5 per cent. 

Coates cation [51], originally proposed to account for the exceptionally rapid stereospecific hydrolysis of the />-nitrobenzoate [59] (Coates and Kirkpatrick, 1970), joins the ranks of the well-established trishomoaro-matics. Proton and l3C NMR observations on [51] (and a methyl and phenyl derivative) supported the symmetrical delocalized nature of this ion (Coates... 

After the hydrolysis of the methyl m-nitrobenzoate it is essential that the solution of the sodium salt be poured into the acid. If acid be added to the salt in the usual way, a less soluble acid salt separates and as this cannot be entirely removed from the w-nitrobenzoic acid even on long digestion with hydrochloric acid, a product is obtained which does not dissolve completely in ether. 

Esters show similar behaviour. Hantzsch found the /-factor for ethyl acetate to be close to 2, and accurate determinations by Leisten also gave values close to 2 for ethyl and methyl benzoate and p-nitrobenzoate. In a solvent containing sufficient water, hydrolysis of the ester occurs. The reaction of methyl benzoate has a time of half-change of a few hours at 25°C in sulphuric acid containing about 0.07 M water, and Leisten actually used the increase in the / -factor, from 2 to 3, to follow the hydrolysis reaction, viz. 

If we compare the acid strengths Ka) of a series of substituted benzoic acids with the strength of benzoic acid itself (Table 26-4), we see that there are considerable variations with the nature of the substituent and its ring position, ortho, meta, or para. Thus all three nitrobenzoic acids are appreciably stronger than benzoic acid in the order ortho para > meta. A methoxy substituent in the ortho or meta position has a smaller acid-strengthening effect, and in the para position decreases the acid strength relative to benzoic acid. Rate effects also are produced by different substituents, as is evident from the data in Table 26-5 for basic hydrolysis of some substituted ethyl benzoates. A nitro substituent increases the rate, whereas methyl and methoxy substituents decrease the rate relative to that of the unsubstituted ester. 

The usual procedure for the preparation of benzo[6]thiophene- 2,3-quinones, which involves acidic hydrolysis of an anil obtained from a thioindoxyl and an aromatic nitroso compound (usually p-nitroso-iV,iV-dimethylaniline), has been used to prepare 5-methyl-,625 5-chloro-,117 and 5- and 6-nitrobenzo[h]thiophene-2,3-quinone.626... 

Recently, Putman and Hassid have confirmed93 the structural formula given by Colin and Gueguen. Methylation of floridoside, followed by hydrolysis, gave 2,3,4,6-tetra-O-methyl-D-galactose and 1,3-di-O-methyl-glyceritol (identified by its lack of optical rotation, and by mixed melting point of its p-nitrobenzoate with the authentic ester). Periodate-oxidation studies on floridoside also confirmed the earlier formula. 

IM-IM cooperation. It is difficult to establish the IM-IM" cooperation in poly(4(5)-vinylimidazole), since pK2 value is more than 14.5 (74). The IM-IM" cooperation can be observed in hydrolyses of PNPA(5) and 4-acetoxy-3-nitrobenzoic acid [n = 0 in (8)] by poly(5(6)-vinylbenzimidazole), of which pK2 value is estimated to be 12.7 (26). The hydrolyses rates increase sharply as the pH approaches the pK2 value of the polymer. In contrast, such a drastic enhancement in the rate is not observed in the benzimidazole-catalysed hydrolysis, nevertheless, pK2 value of the benzimidazole being 12.7. N-Alkylated polymers such as poly(N-vinylimidazole), poly(NIM), and poly(2-methyl-N-vinylimidazole), poly(2MIM), which have no anionic form in imidazole moieties, show the hydrolytic activities slightly less than that of poly(4(5)-vinylimidazole). In cases of low molecular weight analogues, such as N-methylimidazole and imidazole, the hydrolytic activity of the former is about 75% of the activity of imidazole (75, 76). These phenomena appear to support the IM-IM" cooperation in poly(4(5)-vmylimidazole) indirectly. In the hydrolyses of NABS(l) and NABA(3) by poly(5(6)-vinylbenzimidazole), the activity enhancement is about 50-fold compared with the activity of benzimidazole, in spite of these anionic substrates being used (23, 26). 

Low-molecular-weight a- and /3-amino esters are easily hydrolyzed merely by boiling with water. Also, aqueous barium hydroxide is employed in the preparation of several amino acids, e.g., /3-aminopropionic acid (72%) and a-methyl-y-dimethylaminobutyric acid (90%). m-Nitrobenzoic acid (96%) is best prepared from the corresponding methyl ester by boiling for 10 minutes with 20% sodium hydroxide. Longer heating gives a colored product, and the use of a more dilute base is unsatisfactory. y-Nitrovaleric acid is obtained from its methyl ester by hydrolysis with concentrated hydrochloric acid. ... 

Acid hydrolysis of tetraacetyldidesoxydihydrostreptobiosamine - yielded N-methyl-n-glucosamine and crystalline didesoxydihydrostrep-tose. The latter substance yielded a di-p-nitrobenzoate. This compound was the first derivative in which the difficultly esterifiable hydroxyl group in the streptose portion of streptomycin was acylated. A branched carbon skeleton was established therefore for streptose and streptose was shown to be a hexose containing two aldehyde groups. 

Example 3.3 The p value for alkaline hydrolysis of methyl esters of substituted benzoic acids is 2.38, and the rate constant for hydrolysis of methyl benzoate under the conditions of interest is 2 x 10 " s f Calculate the rate constant for the hydrolysis of methyl m-nitrobenzoate. 

In protic solvents, the allylic carbonium ion formed by acid-catalyzed alkyl carbon-oxygen bond fission can recombine either with the carboxylic acid molecule or with a solvent molecule. The electrostatic attraction between the carbonium and carboxylate ions, which is a major factor in isomerization of allylic esters by ion-pair internal return during solvolysis, is absent in the acid-catalyzed reaction. The more numerous, usually more nucleophilic, solvent molecules in the solvation shell of the carbonium ion should compete effectively with the departed carboxylic acid molecule and solvolysis rather than isomerization should be the predominant reaction. For example, in the presence of 0.05 M perchloric acid, solvolyses of cis- and //- //7.s-5-methyl-2-cyclohexenyl p-nitrobenzoates are not only very much faster than in the absence of the acid, but polarimetric and titrimetric rates of solvolysis of optically-active esters were identical within experimental error. For these esters, the acid-catalyzed solvolysis was not accompanied by a detectable amount of isomerization. Braude reported, on the basis of indirect evidence, that isomerization accompanies acid-catalyzed hydrolysis of a-ethynyl-y-methylallyl acetate in aqueous dioxane. It was shown that, under some experimental conditions, the spectrophotometrically determined rate of appearance of the rearranged 1 -yne-3-ene chromophore exceeds the titrimetrically determined rate of hydrolysis,... 

One feature of the reactions of these strained substrates is their reluctance to form strained products. The cationic intermediates usually escape to elimination products in preference to substitution products. Rearrangement reactions are common. 2-Methyl-2-adamantyl p-nitrobenzoate gives 82% methyleneadamantane by elimination and 18% 2-methyl-2-adamantanol by substitution on hydrolysis in 80% acetone. Elimination accounts for 95% of the product from 2-neopentyl-2-adamantyl p-nitrobenzoate. The major product (83%) from 2-tert-butyl-2-adamantyl p-nitrobenzoate is the rearranged alkene 6 ... 

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