hcl + bacl2

Introduction

Oximes have many applications in organic synthesis ¹. These compounds have antimicrobial, antioxidant, antitumor, anti-depressive, antiviral agents, and anticonvulsant properties ^2-7. Some oximation methods have been reported ⁸. However our ongoing attentions to tướng the development of new modified methods in organic synthesis ^8-15,we have investigated the oximation of a variety of carbonyl compounds with NH₂OH·HCl in the presence of BaCl₂.

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Results and Discussions

For finding optimization reaction conditions bezaldehyde and acetophenone have been used as model compounds. Experiments showed that using NH₂OH.HCl (1.2 mmol) and BaCl₂ (1 mmol) in C₂H₅OH (3 ml) was the best conditions for the oximation of benzaldehyde. The reaction was completed within 30 minutes in reflux conditions with the excellent yield (95%) of the product as shown in scheme 1

A variety of aldehydes were ground with NH₂OH·HCl/BaCl₂ system under optimized reaction conditions. In this approach, the corresponding Z-aldoximes were obtained in quantitative yield (93-98%). The results have been reported in table 1.

^aYields refer to tướng isolated pure products (±2%)

Then, the oximation of ketones was also performed well by NH₂OH·HCl/BaCl₂ system. Experiments showed the oximation of ketones requires higher molar amounts of NH2OH·HCl (1.5 mmol) and BaCl₂ (1 mmol) vs. 1 mmol of the substrates. The reaction of acetophenone was completed in 65 minutes with the excellent yield (93%) as shown in scheme 2.

A variety of acetophenones were ground with NH₂OH·HCl/BaCl₂ system under optimized reaction conditions. In this approach, the corresponding E-acetophenonoximes were obtained in quantitative yield (87-95%). The results have been reported in table 2.

^aYields refer to tướng isolated pure products (±2%).

Experimental

All substrates and reagents were purchased from commercially sources with the best quality. IR and ¹H NMR spectra were recorded on PerkinElmer FT-IR RXI and 300 MHz Bruker spectrometers, respectively. The products were characterized by their ¹H NMR or IR spectra and comparison with authentic samples (melting points). All yields referred to tướng isolated pure products. The purity of products was determined by TLC and ¹H NMR. Also, reactions were monitored by TLCs utilizing plates cut from silica gel 60 F₂₅₄ aluminum sheets.

A typical procedure for the oximation with NH₂OH·HCl/BaCl₂ system

In a round-bottomed flask (10 mL) equipped with a condenser, a mixture of benzaldehyde (0.106 g, 1 mmol), NH₂OH·HCl (0.084 g, 1.2 mmol) and BaCl₂ (0.2 g, 1 mmol) in ethanol (3 mL) was prepared. The mixture was stirred under reflux conditions for 30 min. The progress of the reaction was monitored by TLC. After completion of the reaction, H₂O (10 mL) was added and the reaction mixture was continued to tướng stirring for 5 min. The product has been extracted with CH₂Cl₂ (3х15 mL).The mixture was dried over anhydrous Na₂SO₄. Evaporation of the solvent and a short column chromatography of the resulting crude material over silica gel (eluent; CCl₄/Et₂O: 5/2) afforded the pure benzaldoxime (0.115 g, 95 % yield, table 1, entry 1).

Conclusion

The oximation of a variety of aldehydes and ketones was carried out efficiently with NH₂OH·HCl/BaCl₂ system. The reactions were performed in ethanol under reflux conditions. Excellent yields (93-98%) of products in appropriate times (30-100 min) have been achievement.

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Acknowledgements

The authors gratefully appreciated the financial tư vấn of this work by Islamic Azad University branch of Mahabad.