In the Laboratory edited by
Mary M. Kirchhoff American Chemical Society Washington, DC 20036
Solventless and One-Pot Synthesis of Cu(II) Phthalocyanine Complex: A Green Chemistry Experiment R. K. Sharma,* Chetna Sharma, and Indu Tucker Sidhwani Green Chemistry Network Centre, Department of Chemistry, University of Delhi, Delhi-110007, India *
[email protected] In recent years there has been a concerted effort to introduce undergraduate students to green chemistry principles (1-5) both in the classroom and in the laboratory. The new catch phrases “green chemistry” and “green engineering” intimates reaction optimization with respect to materials and energy usage, waste reduction from all sources, and overall cost minimization. Also suggested are minimization of toxicity and hazards and maximization of safety practices. When these terms are applied to the performances of individual chemical reactions, chemical processes, and chemical synthesis plans, they deal with the same issues (6). Although microwave-assisted organic synthesis has become a common and invaluable technique in recent years (7), there have been few procedures published for microwave-assisted inorganic synthesis reactions (8) in the undergraduate teaching laboratories. The advantages of microwave-assisted reactions lie not only in their speed, but also in the fact that these reactions are generally cleaner and more economical than standard reactions. When microwave-assisted reactions are conducted in the absence of solvent, the reactions become “greener” (9-11) and offer an environmentally friendly way of practicing and teaching chemistry. In this context, few published examples for undergraduate student courses (12-15) can be used with great success. The Indian International Chapter of ACS-GCI is working to popularize green chemistry education and outreach activities in India (16). Recently, the Green Chemistry Task Force created by the Department of Science and Technology (Government of India) invited one of the authors of this paper (R.K.S.) to prepare a Green Chemistry Experiment Manual for undergraduate and postgraduate students (17). In an effort to introduce green chemistry into the curriculum, synthesis of an inorganic complex, Cu(II) phthalocyanine (Scheme 1), was modified to make it greener by (i) replacing a hazardous solvent, pyridine, with a more benign solvent, N-methyl-2-pyrolidinone (18) to be used in UV-vis spectroscopy and (ii) switching from conventional thermal heating of several hours to microwave heating for 6 min (19). We believe this modified experiment will be of interest to many instructors who have used the conventional method of synthesizing Cu(II) phthalocyanine in their laboratories. Experimental Procedure The experiment is conducted over two 55 min lab periods in which the students work individually to prepare a copper phthalocyanine complex. As a safety precaution, the reaction is carried out in a fume hood using a laboratory microwave oven as a heat source, which is also located inside the fume hood. 86
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Scheme 1. Synthesis of Cu(II) Phthalocyanine Complex
The characterization of the complex is done by students in groups of two where they prepare a dilute solution of the complex (10-3-10-4 M) in N-methyl-2-pyrolidinone and the UV-vis spectrum is recorded. Phthalic anhydride, one of the reactants in the synthesis, can be prepared from phthalic acid via sublimation. To make the metal complex, anhydrous CuCl2, phthalic anhydride, urea, and ammonium molybdate are added to a clean, dry mortar. The reaction mixture is ground with a pestle until it becomes homogeneous, then transferred to a 50 mL beaker and placed in a laboratory microwave oven (1000 W model) for 6 min. After each interval of 1 min, the microwave is stopped for 5 s (without opening its door) to allow for the removal of the generated ammonia fumes. Because of the insolubility of the copper complex formed, it is washed with dilute acid and base solutions to free the product from the starting materials. The isolated yield was 90% of the theoretical amount based on phthalic anhydride. The entire process takes 30-45 min. Generally, the UV-vis spectrum of the copper complex is recorded in pyridine because of the insolubility of unsubstituted metallophthalocyanines in organic solvents or water. We made the process greener by changing the solvent to N-methyl-2pyrrolidinone. The wavelength corresponding to maximum absorbance of the copper phthalocyanine complex is 671.5 nm, which agrees with the literature values (20-22). An IR spectrum in KBr also corresponds well with the literature (23-25).
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Vol. 88 No. 1 January 2011 pubs.acs.org/jchemeduc r 2010 American Chemical Society and Division of Chemical Education, Inc. 10.1021/ed100473u Published on Web 10/08/2010
In the Laboratory
Hazards Although irritants such as hydrochloric acid and sodium hydroxide are used, their effect has been minimized by using 2% HCl and 5% NaOH solutions. CuCl2, urea, phthalic acid, and ammonium molybdate may cause irritation to skin, eyes, and respiratory tract and may be harmful if swallowed or inhaled. N-methyl-2-pyrrolidinone is hazardous in case of eye contact (irritant) and slightly hazardous in case of skin contact. Care must be taken while preparing phthalic anhydride as fumes generated during the sublimation process may be harmful if inhaled, so the funnel should be removed only after it cools down to room temperature. Because a Bunsen burner is used in the preparation of phthalic anhydride and in the dehydration of copper chloride, it should be done away from the highly inflammable organic solvents that are also present in the lab. Organic solvents should not be used until all Bunsen burner flames have been extinguished. Discussion Metallophthalocyanine complexes have attracted considerable attention owing to their impressive and useful chemical and physical properties (26). Phthalocyanines are unstable to light, heat, acids, and alkalis (27) and are important blue and green dyes that are used in inks (ballpoint pens), textiles, and coloring for plastic and metal surfaces. Recently, they have been used as photoconducting agents in photocopiers and laser printers, sensing elements in chemical sensors, electrochromic display devices, and photodynamic reagents for cancer therapy and other medical applications (28). The synthesis of metal-free phthalocyanines is more complicated than the synthesis of metallophthalocyanines. Students who are interested can perform the experiment following the same procedure but without adding the metal salt. The conventional methods of preparation of Cu(II) phthalocyanine complex, some of which are previously reported in this Journal (29-31), are highly nongreen processes that require high temperatures, heating for several hours, and use of solvents. Conclusion A simple, green, and systematic procedure for the synthesis of copper phthalocyanine has been demonstrated. This article incorporates the use of solid reactants, including the catalyst, and microwave energy. The experiment illustrates the application of several principles of green chemistry and allows students to see that green chemistry is an active ongoing process with the goal of making all reaction as environmentally benign as far as possible. Literature Cited 1. Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice; Oxford University Press: New York, 1998. 2. Matlack, A. S. Introduction to Green Chemistry; Marcel Dekker: New York, 2001. 3. Lancaster, M. Green Chemistry: An Introductory Text; Royal Society of Chemistry: Cambridge, 2002.
r 2010 American Chemical Society and Division of Chemical Education, Inc.
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4. Hjeresen, D. L.; Schutt, D. L.; Boese, J. M. J. Chem. Educ. 2000, 77, 1543–1544. 5. Collins, T. J. J. Chem. Educ. 1995, 72, 965–966. 6. Andraos, J.; Sayed, M. J. Chem. Educ. 2007, 84, 1004–1010. 7. Martin, E.; Kellen-Yuen, C. J. Chem. Educ. 2007, 84, 2004–2006. 8. (a) Filhol, J.-S.; Zitoun, D.; Bernaud, L.; Mantenghetti, A. J. Chem. Educ. 2009, 86, 72–75. (b) Ardon, M.; Hayes, P. D.; Hogarth, G. J. Chem. Educ. 2002, 79, 1249–1251. 9. Abramovitch, R. A. Org. Prep. Proced. Int. 1991, 23, 685. 10. Hayes, B. L. Microwave Synthesis: Chemistry at the Speed of Light; CEM Publishing: Matthews, NC, 2002. 11. Musiol, R.; Tyman-Szram, B.; Polanski, J. J. Chem. Educ. 2006, 83, 632–633. 12. Bari, S. S.; Bose, A. K.; Chaudhary, A. G.; Manhas, M. S.; Raju, V. S.; Robb, E. W. J. Chem. Educ. 1992, 69, 938–939. 13. Parquet, E.; Lin, Q. J. Chem. Educ. 1997, 74, 1225. 14. Hayes, J., W., II; Taylor, C. J.; Hotz, R. P. J. Chem. Educ. 1996, 73, 991–992. 15. Mirafzal, G. A.; Summer, J. M. J. Chem. Educ. 2000, 77, 356–357. 16. Sharma, R. K.ACS GCI International Chapters Spotlight on India Nexus May 19, 2009, 13-15. 17. Department of Science & Technology, Govt. of India, Monograph on Green Chemistry Laboratory Experiments. http://www.dst.gov. in/green-chem.pdf (accessed Sep 2010). 18. The need to conserve energy: Using lower amounts of energy for chemical processes. In Introduction to Green Chemistry; Ryan, M. A.; Tinnesand, M., Eds.; American Chemical Society: Washington, DC, 2002; pp 45-54. 19. Warner, M.; Hutchison, J. Metallation of tetraphenylporphyrin. In Greener Approaches to Undergraduate Chemistry Experiments; Kirchhoff, M.; Ryan, M. A., Eds.; American Chemical Society: Washington, DC, 2002; pp 32-34. 20. MacFarland, D. K.; Lieb, S.; Oswald, J. J. Chem. Educ. 2000, 77, 1482–1483. 21. Esenpınar, A. A.; Bulut, M. Dyes Pigm. 2006, 79, 249–255. 22. Liu, M. O.; Tai, C. H.; Wang, W. Y.; Chen, J. R.; Teh, Hu, A.; Wei, T. H. J. Organomet. Chem. 2004, 689, 1078–1084. 23. Kasuga, K.; Tsutsui, M. Coord. Chem. Rev. 1980, 32, 67–95. 24. Kobayashi., T.; Kurokawa., F.; Uyeda., N.; Saito., E. Spectrochim. Acta, Part A 1970, 26, 1305. 25. Kobayashi, T. Spectrochim. Acta, Part A 1970, 26, 1313. 26. Rawling, T.; McDonagh, A. Coord. Chem. Rev. 2007, 251, 1128–1157. 27. Finar, I. L. Organic Chemistry, The Fundamental Principles, 6th ed.; John Wiley & Sons, Inc.: New York, 1973; pp 899-900. € 28. Ozil, M.; Ag ar, E.; S-as-maz, S.; Kahveci, B.; Akdemir, N.; Gumrukc-uogtu, I. E. Dyes Pigm. 2007, 75, 732–740. 29. Morer, F. H.; Thomas, A. L. J. Chem. Educ. 1964, 41, 245–249. 30. Joestenl, M. D.; Higgins, M. M. J. Chem. Educ. 1986, 63, 1097– 1098. 31. MacFarland, D. K.; Hardin, C. M.; Lowe, M. J. J. Chem. Educ. 2000, 77, 1484–1485.
Supporting Information Available Student handout; instructor notes. This material is available via the Internet at http://pubs.acs.org.
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