Synthesis and reactivity

4 Jan 2008

student choice experiment

Submitted by Adam R. Johnson, Harvey Mudd College
Evaluation Methods: 
I typically have this assignment as one of 6 to 7 lab experiments that take place during the semester.  I grade on purity, yield, the proposal written by the student, and quality of presentation (when done).
Description: 

The students prepare a short proposal outlining their desired target and why they want to make it.  Chemicals are ordered, and during the last 3-4 weeks of the semester, the students carry out their synthesis.  The writeup is as a paper submtited to the journal Inorganic Chemistry using the template from the journal web page.

This is a favorite lab at HMC.  I increased the length of the experiment to 4 weeks from 2 weeks during 2007, allowing more time for exploration, optimization, and characterization of their products.  Past targets have inlucded Wilkinson’s catalyst, ionic liquids, Zr(ebthi)Cl2 (challenging), siloxane polymers (difficult to characterize).

 I highly recommend that students submit proposed syntheses early to get them approved.  The students are often either way too ambitious, or too tentative and want to make some simple thing from another lab manual.  I like them to do two linear steps (more for stronger students.)


Course Level: 
Prerequisites: 
Equipment needs: 
varies widely!
Implementation Notes: 
The lab is chaos.  Hire a TA for this experiment.  Students are running you ragged for the first 2 weeks in the lab, but it is a lot of fun. 
Time Required: 
3-4 weeks, more if student presentations are included
4 Jan 2008

Buchwald/Hartwig amination

Submitted by Adam R. Johnson, Harvey Mudd College
Evaluation Methods: 

I would normally grade on purity and yield of the isolated compound, as well as experimental technique, but since we are still optimizing the conditions, I give students the benefit of the doubt.

Description: 

I wanted a modern organometallic experiment showing the utility of Pd for coupling reactions.  Students attempted a variety of reaction conditions during the spring of 2007 and 2008.  Eventually,  we were able to get the reaction to work with a variety of primary amines (linear, cyclohexylamine) and t-butylamine.  Yields are not great (40-80%) and this experiment needs some optimization.  However, products were observed by GC-MS and NMR.

Corequisites: 
Topics Covered: 
Course Level: 
Prerequisites: 
Subdiscipline: 
Equipment needs: 

This experiment is air-sensitive, but not enormously so.  The most sensitive reagent is the NaOtBu, which could be weighed in air in a pinch.  We use a glove box since we have one.  We store the Pd complexes under N2 after use.

 

Schlenk line, Ar balloons or glove box

Schlenk glassware, standard organic glassware

temperature controlled oil bath or heating mantle and thermometer.

Related activities: 
Implementation Notes: 

I usually turn off the students reactions after 18-24 hours, let them cool down, quench them with ether and store them in the 2-neck flasks until the following week where students work up the reaction and analyze by NMR and GC-MS.  We don't purify the compounds by column chromatography, but that could be added easily.

Time Required: 
1 to 2 3-4 hour lab sessions
17 Nov 2007

How to Read an Inorganic Paper for Synthesis Information

Submitted by Hilary Eppley, DePauw University
Evaluation Methods: 

I typically have this assignment worth about 25 points. I typically use the class when this is turned in as a discussion (could even have them bring two copies of answers to class) to get at some of the topics covered in this assignment. I always like to talk about some definitions, where to find certain information in the paper, sample answers to other questions (funding, productivity of author, types of characterization, etc.). Students turn in a copy of the paper with their assignment so that the instructor can check answers. Alternatively, you could assign one or two papers to the entire class. I just like talking about the differences in the discussion.

Evaluation Results: 

Most students do quite well on this assignment, generally earning 20-25 out of 25 on the assignment.   Things sometimes missed include not knowing what to do with solvents in writing the reactions, not identifying all of the characterization methods, or missing special conditions because they are described in the General Experimental Methods section at the beginning of the Experimental Section.   

Description: 

This assignment takes students through the process of learning how to find and read a paper from the primary literature, specifically to get experimental details (synthesis, characterization).  It also focuses on how to use a variety of chemical information resources.  It could be combined with the questions from Chemical Information Assignment to create a longer assignment.  

Prerequisites: 
Corequisites: 
Learning Goals: 

A student will analyze an inorganic paper to determine the goal of the research and analyze the experimental and discussion section of a paper to extract the following information:

  • Chemical reactions (with appropriate stoichiometric ratios)
  • Special conditions for reactions (such as air sensitivity, hydrothermal conditions)
  • Experimental techniques used to identify and characterize compounds
  • Special equipment needed

The discussion resulting from the assignment will allow the instructor to address terms that students did not understand and perhaps relate the discussion to future topics that will be covered in the class.  When  combined with the Chemical Information Assignment, it could also be used as an introduction to both finding structures, what else the author has written, and other chemical information.     

Course Level: 
Topics Covered: 
Time Required: 
about 1 1/2 hours for the students, 50 min in class
17 Nov 2007

Manganese Carbonyl experiment

Submitted by Adam R. Johnson, Harvey Mudd College
Evaluation Methods: 

Students write a brief abstract/discussion (~1 page) and then a full experimental report including their characterization data, written up as if it were part of a publication. Students are graded on yield and purity;  there is time during the semester to repeat work for improved yield. A grading rubric is attached.

 

 

Evaluation Results: 

The synthesis of dppm is not particularly challenging but careful addition of the reagents (as specificed in the student notes) is important. Students should obtain a 31P, and 1H NMR spectrum of dppm, as well as melting point.  IR and UV-Vis are significantly less informative and can be omitted. For the Mn carbonyl complexes, 1H NMR is complicated, and  typically only required for the fac-complex for completeness. However, IR is very informative.  For the writeup, I like to see some discussion of analysis of the MO diagram to explain the rearrangement of the complex upon oxidation/reduction.  Students have no problems acquiring the IR (and the NMR if they choose to do it) but usually gloss over the MO analysis.

 Typical yields:  dppm yields are low, less than 40%, and it often must be recrystallized before use.  yields of the first two Mn complexes are in the 40-80% range, and for the third, about 20-40%.  Yields are generally much higher for the Mn complexes when using commerical dppm.

Description: 

This experiment has been modified and expanded from the J. Chem. Ed. article linked below (J. Chem. Ed., 1988, 65, 1020) and includes four syntheses, that of dppm, and then three Mn complexes of dppm.  Students must select appropriate characterization methods for their molecule, chosen from a list of available instrumentation including NMR (1H, 13C, 31P), IR, UV-Vis, melting point and optical rotation.  Students are graded on yield and purity;  there is time during the semester to repeat work for improved yield.  Students write a brief abstract/discussion (1/2-1 page) and then a full experimental report including their characterization data, written up as if it were part of a publication.

Subdiscipline: 
Corequisites: 
Learning Goals: 

A student will use liquid ammonia as a solvent

A student will carry out a carbonyl substitution reaction under an inert atmosphere

A student will write up synthetic results in an experimental format

Course Level: 
Equipment needs: 

Triphenylphospine
NH4Br
Triphenylphosphite
Hydrazine monohydrate
Sodium Sulfate
1-propanol           
Hexanes
Methylene Chloride
Ether
Toluene
MnBr(CO)5
[NO][BF4]               
Sodium metal               

Glassware/Equipment required
24/40 Gas Inlet Adapter
100 mL Schlenk Flask with 24/40 joint
Glass-covered Stirbar        
Syringe filled with grease
Dry Ice Condensor with 24/40 joint
Oil Bubbler               
Blast shield (recommended in case of vigorous liquid ammonia boiling during reagent addition;  careful work behind hood sash is ok)

Implementation Notes: 

My junior level laboratory course is a synthesis and characterization course. Students select 6 syntheses (from a total of 12 in the lab manual) during an 8 week period and carry out their preparation.  This laboratory is in 2 parts, synthesis of dppm in liquid ammonia in one week (can be omitted, just use commercial dppm), and synthesis of Mn complexes, done over a 2 week period.

Time Required: 
Two or three 3-4 hour laboratory periods

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