General procedure for the synthesis of 4-(4-nitrobenzyl)-benzoic acid from 4-nitrotoluene (CAS: 5350-47-0): Concentrated sulfuric acid (28 mL) was slowly added to a mixture of 4-nitrotoluene (20.00 g, 0.08 mol) and glacial acetic acid (150 mL) under the cooling of an ice bath, and the temperature of the reaction was controlled to be below 5°C. The reaction was carried out in the following manner. Subsequently, chromium oxide (28.00 g, 0.28 mol) was added in small batches at a temperature not exceeding 10 °C. After addition, the reaction mixture was stirred at room temperature overnight. Upon completion of the reaction, ice water (20 mL) was added to the mixture to quench the reaction. The precipitated solid was collected by filtration, washed with water and dried to give 4-(4-nitrobenzyl)-benzoic acid (22.0 g, 85% yield) as a white powder. The melting point of the product was 254-256 °C.
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