Ethyl-p-nitrobenzoate

Method 2. Ethyl p-nitrobenzoate. Place 21 g. of p-nitrobenzoic acid (Section IV,154), 11-5 g. of absolute ethyl alcohol, 3 8 g. of concentrated sulphuric acid, and 30 ml. of sodium-dried A.R. benzene in a 250 ml. round-bottomed flask, fit a reflux condenser, and heat the mixture under reflux for 16 hours. Add 50 ml. of ether to the cold reaction mixture, wash the extract successively with sodium bicarbonate soiution and water, dry with anhydrous magnesium sulphate or calcium chloride, and distil off the solvent on a water bath. Remove the last traces of benzene either by heating in an open evaporating dish on a water bath or in a bath at 100-110°. The residual ethyl p-nitrobenzoate (21 g.) solidifies completely on cooling and melts at 56°. 

Ethyl p-nitrobenzoate [99-77-4] M 195.2, m 56 . Dissolved in diethyl ether and washed with aqueous alkali, then the ether was evaporated and the solid recrystd from EtOH. 

Figure 6-7. Log Ar-pH plot for the alkaline hydrolysis of ethyl p-nitrobenzoate.

This behaviour is that expected if the positive effect of the dipolar aprotic solvent on the activity of the hydroxide ion is superimposed on the normal negative effect of an organic solvent, and should be observed also for other dipolar aprotic solvents. In fact this type of behaviour is found for the alkaline hydrolysis of ethyl p-nitrobenzoate in mixtures of water and acetone, which is less polar than dimethyl sulphoxide. Other esters show intermediate behaviour in this solvent259 (Fig. 16). It should be stressed that this represents special... 

Fig. 16. Effects of added acetone on the alkaline hydrolysis of substituted ethyl benzoates. Data for ethyl p nitrobenzoate ( ) and benzoate ( ) at 25°C (from ref. 259). The central curve...

The rates of solvolysis of 4- and 5-substituted l-(2-thienyl)ethyl p-nitrobenzoates in 80% EtOH at 25° are correlated by a p value of —6.79,265 to be compared with —5.7 for the benzenoid reaction. Using o+ values calculated by the Dewar-Grisdale approach [Eq. (2)] incorporating q parameters derived from CNDO/2 or INDO molecular orbital procedures (which give closely similar results) gives a value of p of —7.14. For the equivalent 4-substituted l-(2-furyl)ethyl systems,266 267 however, the correlation with o is poor, p being —8.5. In this case Eq. (2) yields o+ values providing a close fit to experimental determinations with a p value that is appropriate for the benzenoid reaction. 

Ethyl o-nitrobenzoate Methyl o-nitrobenzoate Ethyl m-nitrobenzoate Methyl m-nitrobenzoate Ethyl p-nitrobenzoate Methyl p-nitrobenzoate... 

For a-chymotrypsin, the procedure of active-site titration for the calculation of active enzyme concentration and thus of the catalytic constant kcat is long established. The original active-site titration experiment on a-CT by Hartley and Kilby (Hartley, 1954) was performed with ethyl p-nitrobenzoate (Figure 9.2). 

Interest in the kinetics of alkaline hydrolysis of esters in DMSO + water mixtures was stimulated by the observation that the rate constant often increased gradually as x2 increased. This is observed, for example, in the alkaline hydrolysis of ethyl acetate. For higher esters, e.g. ethyl p-nitrobenzoate, the rate constant drops slightly at low x2 but then rises again until k/k x2 = 0) > 1 (Tommila, 1964). The rate of alkaline hydrolysis of esters of benzoic acid is accelerated when DMSO is added (Tommila and Palenius, 1963), as also is the rate of alkaline hydrolysis of 2,4-dinitrofluorobenzene. In the latter case the effect is less dramatic because the rate constant for spontaneous hydrolysis also increases (Murto and Hiiro, 1964). The rate constants also increase when DMSO is added to aqueous solution for reactions between hydroxide ions and benzyl chloride (Tommila... 

Rate Factors (Relative to the 2-Position of the Heterocycle) for Solvolysis of Substituted 1-(2-Aryl)ethyl p-Nitrobenzoates at 25°C"... 

The ethyl p-nitrobenzoate should be freed from acid and recrystallized from alcohol until it melts at 57°. 

In an endeavor to study the transmission of substituent effects in imidazoles Noyce (73JOC3762) examined the solvolysis rates of a series of l-(l-methylimidazolyl)ethyl p-nitrobenzoates (75-77 OPNB = p-nitrobenzoate). The relative rates (75 76 77 = 1 13 15) parallel the relative electron densities in 1-methylimidazole as deduced from chemical shift data. By comparison with other heteroarylethyl p-nitrobenzoates the effective replacement constants, crXr, were determined as a-2-im = —0.82, o-J-im = —1.01 and <7-5.1 = —1.02. The effects on the 2-substituted compound of alkyl, aryl and halogen substituents at the 4- and 5-positions were examined, but though the rates for the 5-substituents could be represented satisfactorily by cTp, substituted compounds. It is not surprising that the distorting effects of annular heteroatoms make it difficult to superimpose the substitution behavior of benzenoid compounds into this series. 

Connors KA, Bender ML. Kinetics of alkaline hydrolysis and 39. N-Butylaminolysis of Ethyl p-Nitrobenzoate and Ethyl p-Nitro-thiolbenzoate. J. Org. Chem. 1961 26 2498-2504. 

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