Synthesis of 2-methylpyrazine from cyclocondensation of ethylene diamine and propylene glycol over p

Available online at www. sciencedirect.comCHINES EScienceDirectCHEMICALLETTERSEL SEVIERChinese Chemical Letters 19 (2008) 752 -755www.elsevier.com/locate/ccletSynthesis of 2-methylpyrazine from cyclocondensation of ethylenediamine and propylene glycol over promoted copper catalystFang Li Jing", Wei Chua.*, Yuan Yuan Zhang a,Ye Qiang Chenb, Shi Zhong Luoa Department of Chemical Engineering, Sichuan University, Chengdu 610065, Chinab College of Materials Science and Chemical Engineering, Zhejiang University, Hangzhou 310027, ChinaReceived 15 November 2007AbstractThe 2-methylpyrazine was synthesized by catalytic reaction of ethylene diamine and propylene glycol at 380。C. The aluminasupported copper catalysts with promoter were prepared by impregnation method, characterized by ICP-AES, BET and TPR. Theresults demonstrated that the dehydrogenation was improved by addition of chromium promoter. The selectivity of 2-methylpyr-azine reached 84.75%, while the conversions of reactants were also enhanced.C 2008 Wei Chu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.Keywords: 2-Methylpyrazine; Copper catalyst; Dehydrogenation; Ethylene diamine; Propylene glycol; Promoter2-Methylpyrazine, an important alkyl-substituted pyrazine, was investigated and applied as a key intermediate forpyrazineamide, an effective anti-tubercular drug [1,2]. Currently, 2-methylpyrazine was prepared by dehydration-cyclization and/or partial dehydrogenation of ethylene diamine (ED) and propylene glycol (PG) [1]. Catalytic systemsbased on Zn [3], Zn-Cr [4], Cu-Cr [5] and Ag [6] were patented, over which the selectivity of 2-methylpyrazine variedin the range of 60- 80%. Recently, MoO3- modified ZnO [7], Zn-modified ferrierite (FER) [8], H-ZSM-5, Zn- modifiedzeolite catalysts (including ZSM-5 and Beta) [9] were selected for the reaction, the selectivity of 2-methylpyrazinewas very low, less than 50%. Park et al. [10] reported that metal oxide-modified ZnO/SiO2 for 2-methylpyrazinesynthesis, the results demonstrated that the metallic Cu and ZnO were assigned to dehydrogenation and dehydration,respectively. The Cr-promoted catalysts were reported to be effective for dehydrogenation of piperazine to pyrazine[11]. The catalytic synthesis of 2-methylpyrazine is related with cyclization (dehydration) and dehydrogenation ofpiperazine intermediate, even though the catalysts which possess dual functional active sites have been designed, therestill remain a general problem: low 2-methylpyrazine selectivity.In this work, Cr-promoted Cu-Zn/Al2O3 catalyst was proposed for the effective preparation of 2-methylpyrazine. Thecatalyst samples were prepared by a 3-step-impregnation. Appropriate amount ofCu(NO3)2 :3H2O, Zn(NO3)2 6H2O andCr(NO3)3:9H2O were dissolved in 9 mL deionized water as the impregnating solution. One third of the solution was* Corresponding authors.E-mail addresses: chuwei65 @ yahoo.com.cn (W. Chu), luoszscu@ gmail.com (S.Z.中国煤化工1001-8417/$ - see front matter◎2008 Wei Chu. Published by EIsevier B.V. on behalMYHCNMHG,. 91 rights reserved.doi: 10.101 6/.cclet.2008.04.007FL. Jing et al./Chinese Chemical Letters 19 (2008) 752- -755753uniformly added slowly on 3 g alumina support (40- - 60 mesh, pretreated at 450。C for 4 h), aged for 10 min, and thendried at 110 °C for 20 min. Repeating above operations 2 more times, it was dried at 110 °C for 4 h and calcined at 450 °Cfor 5 h. The Cu/Al2O3 and Cu-Zn/Al2O3 catalysts were also prepared for comparison.The ICP-AES IRIS Advantage (TJA Solution, USA) was employed to determine the chemical compositions. TheBET surface area was measured by the N2 adsorption, using a Quantachrome Nova 1000e apparatus at liquid nitrogentemperature. Temperature-programmed reduction (TPR) measurements were carried out at atmospheric pressure in afixed-bed. 50 mg sample was loaded in a quartz reactor. The efluent stream was analyzed by a thermal conductivitydetector (TCD).The catalytic activity measurements of the calcined catalysts were performed at atmospheric pressure in acontinuous fixed-bed reactor (stainless steel, 8 mm i.d., 300 mm length). The catalyst was loaded at the middle of thereactor tube with a packing height of 60 mm reduced under the H2 and N2 gas mixture flow (H2/N2= 1, molar ratio) at380 °C for 2 h and then reacted at the same temperature. The aqueous liquid reactants were prepared by mixingethylene diamine and propylene glycol in the mole ratio of 1:1, and diluted with deionized water (50 wt%). The liquidreactants were injected into the top-side of reactor by a pump at 3 mL/h and the pure nitrogen (25 mL/min) wasintroduced as dilute gas. The liquid products were collected in an ice-water condenser and analyzed by gaschromatography (GC-112A) using a capillary column (cross -linked SE-30 gum, 0.33 mm x 30 m) and flameionization detector (FID). The identification of the liquid products was done by GC-MS (Agilent Technol. 6890N/Agilent Technol. 5973 Network Mass Selective Detector).The element amounts in the catalysts were measured by ICP-AES method and listed in Table 1. From ICP-AESresults, the copper content was 11.2 wt% for Cu/Al2O3 and Cu-Zn/Al2O3 and 12.4 wt% for Cr-Cu-Zn/Al2O3 sample.The zinc content in Cu-Zn/Al2O3 catalyst was 16.5 wt%, and that for Cr-Cu-Zn/Al2O3 was 16.2 wt%. The chromiumcontent in Cr-Cu-Zn/Al2O3 catalyst was 2.74 wt%. The results of metal contents were close to those of initialcalculated ones. The BET surface areas of Cu/Al2O3, Cu-Zn/Al2O3 and Cr-Cu-Zn/Al2O3 catalysts were 187.8, 126.6and 124.7 m-/g, respectively.The effects of Cu-Zn/Al2O3 catalyst promoted by chromium on the conversions of reactants and the productselectivity were studied and the results were presented in Table 2. It is clear that the Cu-Zn/Al2O3 catalyst performedbetter as a dual function active catalyst in dehydrate and dehydrogenation than Cu/Al2O3 catalyst, the details includinghigher reactant conversions and 2-methylpyrazine selectivity, lower amount of 2-methylpiperazine and by-products,were in accordance with the reported paper [10]. Especially, the catalyst containing chromium produced lower amountof pyrazine and intermediate 2-methylpiperazine, compared with those of the catalysts without chromium. Theselectivity of 2-methylpyrazine increased to 84.75% over Cr-Cu-Zn/Al2O3 catalyst compared to 68.02% on Cu-Zn/TableCompositions and BET surface area of Cu/Al2O3, Cu-Zn/Al2O3 and Cr-Cu-Zn/Al2O3 catalystsCatalystComposition (wt%)bSBEr (m/g)CuZrCrAlCu/Al2O311.288.8187.8Cu-Zn/Al2O316.572.3126.6CrCu Zn/Al2O3*12.416.22.768.7124.7a Chromium initial calculated content is 3 wt%.Calculated from ICP-AES.Table 2Effect of different catalyst on synthesis of 2-methylpyrazineED conversionPG conversionSelectivity (%)2-MPy2-MPIPOthers76.780.2中国煤化工41.6388.190.527.72Cr3-Cu-Zn/Al2O397 9100.0FYHCNM HGED: Ethylene diamine, PG: propylene glycol, 2-Mpy: 2-methylpyrazine, and 2-MPIP: 2-methylpiperazine.754FL. Jing et al./Chinese Chemical Letters 19 (2008) 752- -755292/298罢|Cr-Cu-Zn/AL2O3297Cu-Zn/Al203Cu/Al2O300200300400500Temperature (°C)Fig. 1. TPR profiles of Cu/Al2O3, Cu-Zn/AI2O3 and Cr-Cu-Zn/Al2O3 catalysts.Al2O3 catalyst. The value was higher than that of ZnO-FER, Zn ZSM- 5 and ZnO/SiO2 catalysts, 26.0, 53.1 and 61.4%[8- - 10], respectively. The chromium promoted the dispersion of active copper species and acted as a fence to separateactive species from congregating, addition of chromium as a promoter was helpful for synthesis of 2-methylpyrazine.The TPR profiles of Cu/Al2O3, Cu-Zn/AI2O3 and Cr-Cu-Zn/Al2O3 catalysts were demonstrated in Fig. 1. It wasshown that the Cu/Al2O3 catalyst had two reduction peaks detected at 251 and 297 °C, which could be assigned toCu2+→Cu+ and Cu+→Cu°[12]. Two similar TPR patterns, different from that of Cu/Al2O3 catalyst, were observedin Cu-Zn/Al2O3 and Cr-Cu-Zn/Al2O3 catalysts, both of which had two reduction peaks assigned as the reduction ofCu2+ and Cu+ as in Cu-Zn/Al2O3 catalyst with different peak area ratios and reduction temperatures.The reaction peak area was in proportion to the reducible copper content for the copper-based catalyst. Thevariation of reduction peak area indicated that the catalyst reducibility was modified by the addition of promoter. Fromthe results of the quantitative calculation, the Cr-Cu Zn/Al2O3 catalyst sample displayed the higher peak area at thehigh-temperature (~290 °C), which demonstrated that chromium improved the dispersion of active copper componenton the catalyst surface. The high-temperature peak shifted from 298 to 292 °C also indicated that the Cu2+ specieswere easily reduced to lower valent species by promotion of chromium [13- -16].The influence of reaction temperature was investigated and the results were illustrated in Fig. 2. It was shown thatthe selectivity of 2-methylpyrazine was up to the maximum 84.75% at 380 °C. At lower reaction temperature, the lowboilers were easy to form while at higher reaction temperature the low boilers could react with piperazine andpyrazine, giving alkyl pyrazine, which resulted in decrease in 2-methylpyrazine selectivity.In conclusion, the 2-methylpyrazine was synthesized by the cyclo-dehydrogenation of ethylene diamine andpropylene glycol at 380 °C over the alumina supported copper-based catalysts. Chromium, added into the catalyst as a00 t830--o- ED Conv.-“ - 2-Methylpiperazine-一 - 2-Methylpyrazine20 F04036080中国煤化工Reaction temperatureMYHCNMHGFig. 2. Infuence of reaction temperature on synthesis of 2-methylpyrazine over Cr-Cu-Zn/Al2O3 catalyst.FL. Jing et al./Chinese Chemical Letters 19 (2008) 752 -755promoter, improved the dehydrogenation activity of catalyst. The Cr-Cu-Zn/AI2O3 catalyst displayed highconversions of reactants and excellent selectivity of 2-methylpyrazine.References[1] L. Forni, P. Pollesel, J. Catal. 130 (1991) 403.[2] L. Forni, G. Stemn, M. Gatti, Appl. Catal. 29 (1987) 161.[3] K. Sato, US 4,097,478 (1978).[4] M. Subrahmanyam, G. Muralidhar, P. K. Verma, IN 185,482 (2001).[5] Y.K. Lee, S.E. Park, Y.S. Kwon, US 4,966,970 (1990)[6] T. Shoji. T. Nakaishi, M. Mikata, JP 08225543 A (1996).[7] D.S. Balpanov, LA. Krichevskii, A.D. Kagrliski, Russ. J. Appl. Chem. 74 (2001) 2125.[9] R. Anand, S.G. Hegde, B.S. Rao, C.S. Gopinath, Catal. Lett. 84 (2002) 265.[10] I. Park, Y. Rhee, J. Lee, Y. Han, Res. Chem. Intermed. 29 (2003) 575.[11] JK. Dixon, US 2.400,398 (1946).[12] x. Zhai, J. Shamoto, H. Xie, Y. Han, Fuel 87 (2008) 430.[13] L.H. Huang, W. Chu, Y. Long, Z.M. Ci, Catal. Lett. 108 (2006) 113.[15] w. Chu, T Zhang, C.H He, TY Wu, Catal. Lett. 79 (2002) 129.[16] Y. Tan, H. Xie, H. Cui, Y. Han, Catal. Today 104 (2005) 25.中国煤化工MYHCNMH G .