Post is authored by Kasey McEvoy with an introduction by Tori Hidalgo
I currently run the Advanced Inorganic Synthesis course taught at The University of Arizona. This course consists of several teaching type experiments and ends with a “Special Project”. One objective of this project is to have the students redo an experiment from earlier in the semester with a modified “greener” procedure using at least one of the 12 Principles of Green Chemistry. Examples of changes students have made in the past are to use a greener alternative for solvents or eliminate the use of solvents all together if all the reagents are liquids. Others chose to reduce the reaction time if heat is used or use a lower temperature than suggested by the literature. The last blog entry I contributed discussed a student’s results using recycled acetone. This semester a student chose to compare a conventional synthesis to a published greener synthesis for an industrially relevant catalyst, iron(III) tris(acetylacetonate).
The procedure differences that reflected a greener reaction were primarily in replacing sodium acetate with potassium hydroxide, eliminating some solvents, and eliminating heat for portions of the reaction. The student reported that the conventional synthesis occurred at a much faster rate and produced a higher yield; however, the purities of each are comparable. Tabulated results and a brief discussion are below.
In the green synthesis reaction, the iron(III) tris(acetylacetonate) percent yield was determined to be 50.32% (Table 1), which does not compare well the literature value of 87.56%.2 This loss in product yield was likely due to sample loss during decantation (which proved tedious) and initial loss of Fe(OH)3, when filtration of flocculent proved impossible due to the small size of the precipitate and incompatible filter paper grades. The final sample of Fe(acac)3 was dark red with small, shiny crystals present. In the conventionally synthesized reaction the iron(III) tris(acetylacetonate) percent yield was determined to be 71.98% (Table 2), which compares well to the literature value of 87.03%.3 The final sample of Fe(acac)3 was bright red with shiny crystals present. The conventional synthesis reaction was a much faster and more straightforward reaction compared to the green synthesis method, which accounts for the higher yield as product was not lost through additional filtrations.
The color differences observed between the green sample and the conventional sample suggested some difference in the sample purities (Figure 1). IR spectra were taken to determine if the green sample (which was darker red) had unreacted Fe(OH)3 remaining. The IR spectra for the two samples had major peaks occurring at nearly the same wavenumbers. Both spectra matched the literature Fe(acac)3 IR spectra very closely, which indicates that both sample were pure.4
The green synthesis reaction was determined to produce a sample with comparable purity to that of the conventionally synthesized iron(III) tris(acetylacetonate) sample. The reaction was determined to be inefficient however, due to sample loss resulting in a lower product yield and additional time required for the synthesis. The overall ease and the substantially higher product yield determine the conventional reaction to be the most efficient synthesis procedure. In the future, the green synthesis reaction may be improved by modifying the reaction to use heat to drive the production of the iron(III) tris(acetylacetonate) crystals. The collection of the intermediate Fe(OH)3 could also be improved by using a Büchner funnel with smaller filter pores, thus increasing the product yield.
- M. K. Chaudhuri and S.K. Ghosh, J. Chem. Soc. Dalton Trans., 1983, 839.
- B.C Ranu, S. Chandrasekaran, M. K. Chaudhuri, et al: Monograph on Green Chemistry Experiments: Green Chemistry Task Force Committee, DST: p 48-50.
- Colored Complexes of Iron. Laboratory Manuel: University of Adelaide: School of Chemistry and Physics. South Australia. 2011.
- Ferric tris(acetylacetonate), National Institute of Standards and Technology. http://webbook.nist.gov/cgi/cbook.cgi?ID=C14024181&Mask=80#IR-Spec (assessed May 3, 2014).
- Webspectra. Table of IR Frequencies. http://www.chem.ucla.edu/~webspectra/irtable.html (accessed May 2, 2014).