Synthesis Of N-(1-ethylpropyl)-3,4-dimethyl Aniline Catalyzed By Platinum-based Catalysts

Pendimethalin is a selective dinitroaniline herbicide.It is applied widely in peanuts,corn and vegetables weed control for its properties of low toxicity and low residue.N-?1-Et-hylpropyl?-3,4-dimethylaniline?DMA?is a key intermediate in the synthesis of pendimethalin.At present,the DMA is produced mainly by 3,4-dimethyl nitrobenzene?3,4-DNB?,3-pentanone and hydrogen reaction over 5wt%Pt/AC catalyst,but the process has the shortcomings of high Pt loading and low DMA selectivity.In this paper,a systematic study is conducted on synthesis of DMA from 3,4-DNB,3-pentanone and hydrogen catalyzed by platinum-based catalysts.The results showed that the platinum precursor,preparation methods,particularly the AC support had great influence on performance of platinum-based catalysts for a pot synthesis of DMA.The0.5wt%Pt/AC-3 catalystpreparedfrompotassiumchloroplatinateprecursor,commercial AC support?AC-3?and by impregnation and sodium formate reduction,showed excellent performance for synthesis of DMA from 3,4-DNB,3-pentanone and hydrogen.Higher temperatures,H₂ pressure and long reaction time are favorable for3,4-DNB,3-pentanone and hydrogen reaction over the 0.5wt%Pt/AC-3 catalyst.The structures of AC supported platinum catalysts were characterized by N₂adsorption-desorption,X-ray diffraction and Transmission electron microscope.It was found that the AC has large specific surface area and pore diameter,which may be responsible for better catalytic performance of the 0.5wt%Pt/AC-3 catalyst for synthesis of DMA from 3,4-DNB,3-pentanone and hydrogen.Because the large specific surface area and pore diameter of AC-3 were more beneficial to Pt dispersion and inlet of the reactant and outlet of the product.The 0.5wt%Pt/AC-3 showed a low stability for synthesis of DMA from 3,4-DNB,3-pentanone and hydrogen.Therefore,nitrogen-doped activated carbon?NAC?supported Pt was investigated for synthesis of DMA from 3,4-DNB,3-pentanone and hydrogen.It was found that Pt is highly dispersed on NAC.The 0.5 wt%Pt/NAC-3catalyst shows higher catalytic activity and stability compared with the 0.5 wt%Pt/AC-3,which may be caused by strong interaction between N and Pt on the surface of NAC.The stability of Pt/NAC catalyst can be further improved by increasing Pt loading.