Research Into Alternate Syntheses

1
Research Into Alternate Syntheses of
Cr(en)3Cl3 2H2O
Objectives --Research two novel procedures for
synthesis of Cr(en)3Cl3 2H2O
--Alter significant synthetic variables
--Determine success rate vs prior syntheses
2
Literature Synthetic Procedure
J. Bray, J. Locke, J. McCleverty, and D.
Coucouvanis, Inorganic Syntheses 13, pp. 184 -
186
--CrCl3 6H2O, granular zinc in dry methanol,
reflux
--Add anhydrous en, reflux one hour
--Workup 51 yield
Notes --Zn acts as catalyst generates
Cr(II) --No reaction in the presence of water
3
Synthesis Experiment 4
"Microscale Inorganic Chemistry", Z. Szafran, R.
Pike, M. Singh., J. Wiley, NewYork 1991, p.
251.
--Wash mossy zinc with 6M HCl, methanol
--CrCl3 6H2O, mossy zinc, en in methanol at RT
--Heat to reflux, reflux one hour
--workup almost no yield
Notes --purple solution or white ZnCl2 only
products --almost universal result
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Deviations in Experiment 4 Synthesis
1) Used mossy zinc, not granular
2) en, MeOH not anhydrous
3) Used HCl to clean the Zn0 surface
4) Added en to room-temp CrCl36H2O/Zn/methanol
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New Strategies
1) Exclusion of Water and Protons
--Dried methanol
--Anhydrous en
--Omit HCl washing (Caveat! Removal of ZnO
layer? Zn grains)
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New Strategies
2) Experimentation With New Forms of Zinc
Mossy and zinc grains (not granular) --gener
ate more catalyst surface area --speed reduction
to substitution-active Cr(II)
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New Strategies
3) Accelerating Rate of En Substitution
Heat CrCl3/Zn/methanol to reflux generation of
substitution-active Cr(II)
New EP study difference in addition of en
procedure. Keep reaction mixture warm at
all times.
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New Experimental
--Heat MeOH to near-boiling in back hood sand
baths
--Add en while MeOH near-boiling in back hoods
--Quickly heat MeOH to reflux on your sand bath
--NO EXPOSURE of en vapors to lab
Cover graduated cylinder while carrying through
lab!
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Summary
--Actual research results unknown.
--New strategies helpful or harmful?
--Only discerned through results, observations,
notes.