Abstract
The new possibilities of preparing the ethyl 4-nitrobenzoate by esterification of 4-nitrobenzoic acid (4-NBA) with ethanol under argon at 80°C are shown; particularly, over catalysts: on micrometric (4.8 - 7.0 μm) or ultradispersed crystallites (290 - 480 nm) of hydrogen forms of nanoporous natural zeolites H-CL, H-MOR, H-HEU-M, H-PHI and under irradiation of the reaction mixture with ultrasound (US, 37 kHz, 330 W, 2 h) or microwaves (MW, 2450 MHz, 300 W, 2 h). Ultradispersed crystallites of zeolite catalysts were prepared from hydrogen forms of parent natural zeolites by their treatment with US or MW. In the esterification, the synergism of the actions of catalysts and MW or US was revealed; wherein on the ultradispersed best catalysts H-HEU-M and H-MOR conversion of 4-NBA and yield of ethyl 4-nitrobenzoate reached up to 70% and 67%, respectively. GC/MS, FTIR, NMR methods were used in the study.
Highlights
The results show that irradiation of hydrogen forms of natural zeolites with US or MW causes a decrease in the size of their crystallites from 4.8 - 7.0 μm to 290 - 480 nm (Table 1); the catalytic activity of the prepared zeolite catalysts (H-CL, H-MOR, H-HEU-M, H-PHI), containing ultradispersed crystallites, is increased in the esterification reaction 4-nitrobenzoic acid (4-NBA) with ethyl alcohol compared to their parent forms (Figure 2)
1) The synthesis reaction of ethyl 4-nitrobenzoate was investigated by esterification of 4-nitrobenzoic acid with ethanol under argon at the boiling point of the reaction mixture; heterogeneous catalytic synthesis is carried out in the presence of acidic catalysts, hydrogen forms of natural zeolites: H-CL, H-MOR, H-HEU-M, H-PHI with ultradispersed crystallites (290 - 480 nm); and ethyl 4-nitrobenzoate was synthesized by irradiation of the reaction mixture with ultrasound (37 kHz, 330 W, 2 h) or microwaves (2450 MHz, 300 W, 2 h)
2) Zeolite catalysts with ultradispersed crystallites were prepared from hydrogen forms of parent natural zeolites with micrometric crystallites (4.8 - 7.0 μm) by their indirect treatment with ultrasound (US, 300 W, 37 kHz, 7.5 h) or by direct influence of microwaves (MV, 300 W, 2450 MHz, 2 h) on the catalysts; these irradiations cause a reduction in the size of zeolite crystallites as determined by means of the laser light scattering particle size analyzer
Summary
Many methods were described for the preparation of ethyl 4-nitrobenzoate with esterification (Fischer esterification) of 4-nitrobenzoic acid with ethanol (Scheme 1); the reaction is reversible and the catalysts for this process are sulfuric acid [7], ammonium hydrogen sulfate [8], this catalyst is not commercially available; polyfluoroalkanesulfonic acid [9], silicon tetrachloride [10]. In all these methods, the yield of ethyl 4-benzoate was 75% - 98%. In a cascade reactor at 110 ̊C - 120 ̊C in a short time (10.5 min), the conversion of 4-nitrobenzoic acid reaches 96%, while in a batch reactor; the same effect is achieved at a higher temperature (180 ̊C) and within 3 hours
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