1. Experimental

a. MoO₂dtc₂

The reaction starts with the reaction of sodium molybdate (Na₂MoO₄* 2 H₂O) with Nadtc*3 H₂O in a solution of sodium acetate. Because the solution is basic at this point, the product does not precipitate.

The addition of the 1 M HCl (How can this solution be prepared from concentrated HCl? Does the exact concentration matter here?) should be done slowly. The pH should not be allowed to drop below pH=5.5, because the compound starts to decompose then (How can you detect that?).

The crude product is filtered, washed with 95 % ethanol and dry diethylether, and then dried in vacuo.

The recystallization should be done from warm toluene (=50-60 ^oC and not boiling toluene!). If the temperature is too high during the extraction, the product will decompose (How can you detect that?).


b. MoOdtc₂

The synthesis of compound B has entirely be conducted under inert gas, because the product is extremely air sensitive (color change from pink to dark purple). The purple color originates from the Mo(V) compound. (Mo₂O₃dtc₄)..

The reaction starts with the reaction of sodium molybdate (Na₂MoO₄) with Nadtc in the presence of sodium dithionite (Na₂S₂O₄). Initially a dark purple precipitate is formed that will turn pink after about two hours if the reaction conducted properly.

It might make sense to start this reaction first because it usually takes two hours. The use of deaerated water is advisable because it speeds up the reaction (Why?).

The filtration has to be performed using a Schlenk frit. The final product has to be stored under inert gas.

Deaerated water is obtained using the freeze-pump-thaw procedure. Make sure that the flask is less than half-filled here!


2. Characterization

a. FTIR spectrum (YH 6076, YH 1033)

- Acquired using ATR setup (>450 cm^-1) and as Nujol mull in between CsI plates (250-500 cm^-1)
- Read the chapter on how to acquire infrared spectra (Appendix A and B, p. 145-154)

3. Catalysis experiment

The student will have to prepare dry DMF for this part of the experiment as well as dry the molecular sieve.

You will have to set up three reactions:

a. using MoO₂dtc₂ as catalyst without molecular sieve
b. using MoO₂dtc₂ as catalyst with molecular sieve
c. using MoOdtc₂ as catalyst without a molecular sieve

The reactions should be run using 0.05 mmol of the catalyst, 1 mmol of benzoin and 25 mL of dry DMF. The 250 mL round-bottomed flask should be closed during the reaction. Take one sample two hours into the reaction and the other one after approximately 24 hours. It is important that the setups are identical in terms of flask size and availability of oxygen.

When using a drying agent like MgSO₄, it is crucial to use a small amount. Why?

To determine the efficiency of the catalyst, HPLC samples are prepared of the individual products from the reaction. For the standardization, five standards are prepared containing a total amount of 1 mg/mL of benzoin and benzil in the solution (i.e., 0.10 mg/mL benzoin:0.90 mg/mL benzil). Please inform the instructor the meeting prior the HPLC sample submission that you need HPLC vials.

It might be a good idea to use the rotary evaporator to remove the solvent from the samples.


4. Hints to questions

ad 1: How many 'ligands' do you have in those compounds? Which coordination figures are possible for this number of ligands?

ad 3: What determines if a compound X is able to oxidize or reduce compound Y? Which technique can be used to evaluate these properties?

ad 7: What determines the activity of molecular sieves?


5. Problems to be considered

a. What is the function of sodium acetate in the synthesis of compound A?
b. If the synthesis of compound B is not properly carried out, a dark-pink to purple compound is observed. How can this be explained?
c. What is the product of the oxidation of S₂O₄^2- in the synthesis of compound B?
d. Why is it important to prepare HPLC samples in a concentration range of 0.1-1 mg/mL?