Para-nitrobenzoic acid

To overcome tbe problem of tbe bigb amount of graphite utilized and mainly to avoid tbe use of tbe expensive and pollutant acyl balides and benzene, graphite can be coupled with para-toluenesulfonic acid and utilized to activate the more ecocompatible carboxylic acids toward electrophilic acylation. i With this catalyst, not only a solvent-free process can be developed but also high yields with not activated aromatic substrates and with unactivated carboxylic acids (i.e., para-nitrobenzoic acid) can be obtained (Table 4.25). 

The C3 and C5 carbons are meta-carbons the C4 carbon is the para carbon. These three positions are abbreviated as the o, m, and p positions, respectively. Thus, the structure is called para-nitrobenzoic acid, or p-nitrobenzoic acid. 

Alcohols that can form conjugated olefins sometimes eliminate under the standard Mitsunobu conditions to provide undesired side products instead of the ester product. In the case of a protected serine derivative 35, para-nitrobenzoic acid gave preferentially the desired product 36, whereas the use of benzoic acid gave only the elimination product 37." ... 

Nishimata et al. prepared intermediate 48 during their synthetic work on the amaryllidacae alkaloids crinanine and pretazettine. The preparation of Orlistat (49), the active pharmaceutical ingredient in Xenical , involves a Mitstmobu reaction between a hydroxy- 3-lactone and A -formyl-(Z/)-leucine. A larger scale inversion involving para-nitrobenzoic acid was used in the synthesis of BILN 2061 (50), a potent HCV protease inhibitor. The alcohol... 

Note Reagents for TM 2.15a and 2.15b are available aromatic compounds, products of the petrochemical industry. Para-nitrobenzoic acid is produced by nitration of toluene to para-isomer as the prevailing product, followed by oxidation of methyl to the carboxylic group. Orf/m-dimethoxybenzene is produced from ort/to-diphenol, which in turn is available by oxidation of phenol. One technological process uses hydrogen peroxide as oxidant [25], and annual production of ort/io-diphenol reaches 20,000 tons/year, mainly intended for the production of pesticides and perfumes. 

When a proton is lost from the para-nitroanilinium ion, the electrons it leaves behind are shared by five atoms. (Draw resonance contributors if you want to see which atoms share the electrons.) In contrast, when a proton is lost from para-nitrobenzoic acid, the electrons it leaves behind are shared by two atoms. In other words, loss of a proton leads to greater electron delocalization in one base than in the other. Electron delocalization stabilizes a compound, so the difference in electron delocalization explains why a nitro substituent has a greater effect on the acidity of an anilinium ion than on the acidity of benzoic acid. 

Hammett realised that the addition of a substituent in the aromatic ring has a quantitative effect on the dissociation constant K. For para-nitrobenzoic acid the dissociation constant... 

The preparation of a number of miscellaneous acids is described. m-Nitrobenzoic acid. Although m-nitrobenzoic acid is the main product of the direct nitration of benzoic acid with potassium nitrate and concentrated sulphuric acid, the complete separation of the small quantity of the attendant para isomer is a laborious process. It is preferable to nitrate methyl benzoate and hydrolyse the resulting methyl w-nitrobenzoate, which is easily obtained in a pure condition ... 

A related problem concerns the synthesis of p nitrobenzoic acid Here two meta directing substituents are para to each other This compound has been prepared from toluene according to the procedure shown... 

The methyl group of -nitrotoluene is activated by the para nitro group. -Nitrotoluene is oxidized to -nitrobenzoic acid [62-23-7] by potassium hexacyanoferrate(III) in alkaline solution, potassium permanganate, or potassium dichromate. -Nitrotoluene is converted to -nitrobenzaldehyde... 

Jaffe (1953)52 showed that while many rate or equilibrium data conform well to the Hammett equation (as indicated by the correlation coefficient), many such data are outside the scope of the equation in its original form and mode of application. Deviations are commonly shown by para-substituents with considerable + Rot — R effect53. Hammett himself found that p-NOz (+ R) showed deviations in the correlation of reactions of anilines or phenols. The deviations were systematic in that a a value of ca. 1.27 seemed to apply, compared with 0.78 based on the ionization of p-nitrobenzoic acid. Other examples were soon discovered and it became conventional to treat them similarly in terms of a duality of substituent constants . 

Marans and co-workers used pentaerythritol trinitrate (81) to synthesize a number of aryl and alkyl esters, including the formate, propionate (84), oxalate, succinate, benzoate (85), 3,5-dinitrobenzoate (86), and ortho-, meta-, and para- (87) nitrobenzoate esters. The para-nitrobenzoate ester (87) has also been prepared from the nitration of pentaerythritol monobenzoate with mixed acid. ... 

A simple case where the general a constants in Table 8.5 do not succeed in correlating acidity constants is when the acid or base function is in direct resonance with the substituent. This may occur in cases such as substituted phenols, anilines, and pyridines. For example, owing to resonance (see Fig. 8.4), a para nitro group decreases the pKa of phenol much more than would be predicted from the o para constant obtained from the dissociation of p-nitrobenzoic acid. In such resonance cases (another example would be the anilines), a special set of o values (denoted as oJpara) has been derived (Table 8.5) to try to account for both inductive and resonance... 

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. 

A straightforward approach to the synthesis of m-nitrobenzoic acid involves preparation of benzoic acid by oxidation of toluene, followed by nitration. The carboxyl group of benzoic acid is meta-directing. Nitration of toluene prior to oxidation would lead to a mixture of ortho and para products. 

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