TRANSITION METAL CATALYZED/NaBH4/MeOH REDUCTION OF NITRO, CARBONYL, AROMATICS TO HYDROGENATED PRODUCTS AT ROOM TEMPERATURE

Headnote

ABSTRACT

Reduction of nitrobenzene, 4-ethyl nitrobenzene, 4-isopropyl nitrobenzene, 4-nitro 1-phenyl acetate, acetophenone, with CuCl2/MeOH/NaBH4 provided hydrogenated products in quantitative yields. In order to evaluate the best catalytic systems various transition metal catalysts were examined for the first time and CuCl2 catalysts was superactive system. And a solvent system was also studied with methanol being the best solvent evolved. The reactions were exceedingly clean with no byproduct formation, negating the need for further purification. Most reactions provided moderate to excellent yields.

KEYWORDS: Reduction, CuCl2, NaBH4, nitrobenzene, aniline. I. INTRODUCTION

I. INTRODUCTION

The pioneering discovery by Brown describing the use of Ni borides in accelerating CuCl2-mediated reactions has resulted in widespread applications of NiCl2-NaBH4 catalysts. This combination is utilized in several reduction reactions. Due to its ability to enhance reaction outcomes, NaBH4 is the preferred reducing agent in CuCl2-mediated reactions.

Homogeneous catalysts have attracted interest for reductions reactions due its conversions and high selectivity [1,2]. H.C. Brown [3] and A. Rahman [4] co-workers have explored the use of Ni- Boride[3], Ni-Boride silica catalysts[4,5] Au complexes[6], Ni[7],Pt, Ru[8], Fe[9] for reduction of nitroaromatics, and other aromatics to hydrogenated products at room temperature and at low temperature (0-5°C) methanol co-solvents in reduction reactions.

Comparison with other reported protocols with Pd, Ni complexes, Ru, Rh[4] using raney nickel catalysts (which is pyrophoric) reveals some interesting trends were observed with longer reaction times, use of sophisticated instruments, high pressure, temperature precludes the wide use of these reagents and conditions.

The effects of water and DMPU[2] in the reduction of ketones. These additives have proven to be useful in several reactions but unfortunately do not have the broad applicability of HMPA, and as a consequence, the search for an alternative is ongoing. The major drawback of using HMPA is carcinogenic. The use of SmI2/H2O/Et3N mixture in the reduction of ketones [10,11]. The use of the above mentioned catalysts requires stringent conditions and the authors developed a new CuCl2 /NaBH4 system for these reduction reactions. These reactions are instantaneous and provide yields of reduced products. The author studied the comparison of the H2O/NaBH4 method and the NaBH4/MeOH method in reduction of ketones indicates that MeOH/NaBH4/CuCl2 is approximately 100 times faster. This method has also been applied in the reduction of nitroaromatics, ketones...