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This is a classic experiment that has been revised and updated numerous times over the years. The experiment can be found in Girolami, Rauchfuss and Angelici, 3rd edition, but that edition removed some purification steps that were present in the earlier edition which has plagued generations of my students with poor resolution of the enantiomers. Marion Cass published a J. Chem. Educ. article in 2015 that included a pH determination and added back in the recrystallization step. This allowed my students to achieve higher yields and greater resolution in Spring 2020.
I have gone back and taken videos of the synthesis for our virtual offering of inorganic lab for Spring 2021 and I am pleased to report excellent yields and optical purity of all four isolations of Co(en)3I3. A variety of data (IR, UV-Vis, NMR, MS, polarimetry, and single crystal X-ray diffraction) is provided for students to analyze. I also include a few instructor notes and thoughts.
| Attachment | Size |
|---|---|
| student handout | 122.54 KB |
| data (pdf) for Co(en)3Cl3 | 745.81 KB |
| data (pdf) for Co(en)3(tart)Cl | 102.59 KB |
| data (pdf) for Co(en)3I3 | 1.27 MB |
| Co(en)3Cl3_cifreport.html | 14.3 KB |
| Co(en)3Cl3_exp_311_tables.html | 23.93 KB |
| Co(en)3Cl3_exp_311.cif | 1.93 MB |
| Co(en)3Cl3_exp_3117.jpg | 99.46 KB |
| Co(en)3(tart)Cl_checkcif.pdf | 129.74 KB |
| Co(en)3(tart)Cl_exp_123 (2)_tables.html | 41.04 KB |
| Co(en)3(tart)Cl_exp_123 (2).cif | 628 KB |
| Co(en)3(tart)Cl_exp_1235.jpg | 94.5 KB |
| Co(en)3I3_exp_324_cifreport.html | 16.4 KB |
| Co(en)3I3_exp_324_tables.html | 30.02 KB |
| Co(en)3I3_exp_324.cif | 5.92 MB |
| Co(en)3I3_exp_3243.jpg | 99.49 KB |
Students will learn to calculate yield and optical purity from mass, volume and polarimetry data
Students will be able to interpret data such as IR, MS, UV-Vis, and NMR of cobalt complexes
the ability to read pdfs, watch YouTube videos, and if evaluating the crystal structures, a visualization program like CrystalMaker or Mercury.
I will be implementing this experiment during February and March of 2021 as a 100% virtual laboratory experience. Wish me luck!
Note added after experiment began: I forgot the YIELD video for the product from the filtrate and the (-) tartaric acid. it has been added to the Youtube channel as "yield of 2nd minus product"
Evaluation
This is a classic laboratory, but now that I have instructor data (and you do too) I have decided that forever forward, a student's grade on the lab will be based on their yield·optical purity divided by /my/ yield·optical purity :)
For 2021, students will be evaluated on their correct interpretation of the videos (balanced equations, yields, etc), interpretation of the data provided (for identity and purity).
I will provide results after our spring 2021 offering here.