P-Nitro benzoic acid

Upon acidification of the sodium carbonate washings, 4-5 g. of p-nitro benzoic acid, m.p. 242-243°, are recovered. 

F5SOOSF5 is difficult, after the initial publication in 1962 this chemistry has, unfortunately, not been explored further. Physicochemical studies on p-pentafluoro-sulfuranyloxybenzoic acid (p/Q = 5.04 for comparison, benzoic acid 5.68, p-nitro-benzoic acid 4.55) show the p-OSFj group has a relatively large ffp , , value of +0.44 (for comparison, p-F +0.062, p-COOEt +0.45), indicating a strong inductive electron-withdrawing (-/) effect. 

SOCl2 added to a soln. of p-nitrobenzoie aeid and dry pyridine in alcohol-free chloroform, and worked up after 5 min. —p-nitro-benzoic acid anhydride. Y 82%.—Similarly Benzylpenieillin anhydride. Y 71%. (F. e. s. F. H. Carpenter, Am. Soc. 70, 2964 (1948).)... 

In aprotic solvents, the allylic carbonium ion and carboxylic acid molecule produced by acid-catalyzed heterolysis of an allylic ester may recombine to form the starting material and its allylic isomer. Kinetic studies show that a-phenylallyl p-nitrobenzoate undergoes concurrent uncatalyzed and p-nitro-benzoic acid-catalyzed isomerization to cinnamyl benzoate in chlorobenzene solutions containing p-nitrobenzoic acid . Similarly, benzoic acid catalyzes the isomerization of a-phenylallyl benzoate in chlorobenzene. When this reaction was carried out using 0-labeled benzoic acid, appeared in both the starting material and its allylic isomer under the conditions used, only about a quarter of the isomerization reaction is intramolecular. 

Eq. (a) shows the oxidation ofp-nitrotoluene by sodium dichromate in an acidic medium (with H2S0 ) to yield p-nitro benzoic acid (I) whereby the methyl function in the starting material gets oxidized to the corresponding carboxylic moiety due to the evolution of 3-moles of nescent oxygen as given in Eq. (a) iii). 

Osawa, M. and M. Ikeda (1991). Surface-enhanced infrared absorption of p-nitro-benzoic acid deposited on silver island films. Contributions of electromagnetic and chemical mechanisms. J. Phys. Chem. 95, 9914. 

Enhancement of absorption bands in the IR spectra of ultrathin films in the presence of discontinnons (islandlike) nnder- and ovemanolayers of Ag and An was discovered by Hartstein et al. [356] in the early 1980s. Although these researchers believed that they observed an increase in the vCH band intensities for p-nitro-benzoic acid (p-NBA), benzoic acid, and 4-pyridine-COOH films, it was recently shown [350] that the spectra reported are in actual fact due to fully saturated hydrocarbons (possibly vacuum pump oil). In any case, this discovery has stimulated various research activities and led to the development of surface-enhanced IR absorption (SEIRA) spectroscopy. To date, the SEIRA phenomenon has been exploited in chemical [357] and biochemical IR sensors (see [357-360] and literature therein), in studying electrode-electrolyte interfaces [171, 361-365], and in LB films and SAMs [364, 366-370]. Other metals that demonstrate this effect are In [371] and Cu, Pd, Sn, and Pt [372-375]. The metal films can be prepared by conventional metal deposition procedures such as condensation of small amounts of metal vapor on the substrate, spin coating of a colloidal solution, electrochemical [388], or reactive deposition [299] (see also Section 4.10.2). 

Brown needles from AcOH. M.p. 173°. Distils undecomp, above 360°. Mod. sol. toluene. Spar. sol. hot EtOH. CrOg —> p-bromo- and p-nitrO benzoic acids. 

---