Organics - More Perchlorates in Organic Synthesis
The subtle effects of Lewis acid catalysts in organic syntheses are frequently not reflected in the title of a journal article or promotional piece. Consider the following:
“Contrasting Effects of Mg(ClO4)2 and CeCl3:7H2O in Reaction Schemes Involving t-Butyl Ethers.”
Creative chemists know that many important organic “name” reactions require the effects of key inorganic agents. With that in mind, we think it’s noteworthy that a reaction scheme such as that shown below features two core GFS technologies – Perchlorate and Rare Earth chemistries. This synthetic route1 to t-butyl ethers is but one of a multitude of methodologies that use Mg(ClO4)2 or LiClO4 to promote unusual mechanisms or dramatically enhance reaction conditions for organic preparations.2
While the protection of alcohols via the t-butyl blocking group was unexpected, even less expected was the realization that the action was promoted not only by “anhydrous” magnesium perchlorate but also by zinc perchlorate (hexahydrate).3 While the zinc perchlorate was described as usually more active in this type of reaction, that catalyst is not normally available as a dried salt as is magnesium perchlorate. Since the presence of water diminishes the yield of desired product, the magnesium salt was preferred (even though it typically contains at least 5% moisture) over the zinc salt. Even so, the zinc salt was cited as superior to more expensive triflate catalysts in this general and chemoselective reaction.
New Perchlorate Formulations
But….what if a stable, less hydrated zinc perchlorate salt were commercially available? Such a compound (and similar common metal perchlorates), properly characterized and validated, could allow the safe and effective determination of much broader catalytic effects. For that reason, GFS is excited about the prospect of offering a selection of new, “dehydrated” perchlorate salts, each having half or fewer waters of hydration normally associated with common commercial grades. For example, use of a zinc perchlorate salt of dihydrate composition reduces the water content of the catalyst from 29% to 12%.
Testing according to DOT recommendations confirms the suitability of these materials
for shipment as Div. 5.1/Class II oxidizer. This is the same classification as the fully hydrated compounds now available in research and bulk quantities from GFS.
See the alphabetical section of this catalog for the full specifications on the following reduced-moisture perchlorate salts:
Moles Typical (Comparison with
GFS # Metal H2O % H2O Common Reagent)
3718 Al 3 14.2 (nonahydrate has 33% water)
3722 Cd 3 14.8 (hexahydrate has 25.8% water)
3723 Ca <2 <10 (tetrahydrate has 23% water)
5168 Sr <2 <10 (hexahydrate has 27% water)
3792 Cr 3 13.4 (hexahydrate has 23.5% water)
Mn(II) 3(?) 17.5 (developmental item, deliquescent)
3973 Fe(II) 2 12.4 (hexahydrate has 29.8% water)
3924 Fe(III) 2 9.2 (hexahydrate has 23.4% water)
3793 Co 2 12.2 (hexahydrate has 29.5% water)
5155 Ni 3 17.3 (hexahydrate has 29.5% water)
3794 Cu 2 12.1 (hexahydrate has 29.2% water)
5184 Zn 2 12.0 (hexahydrate has 29% water)
This list complements the currently available anhydrous perchlorate salts of NH4, Li, Na, K, Rb, Cs, Mg, Ba, and Ag. The ferric perchlorate described in the GFS catalog as “non-yellow” (item 40) contains <5% water but features perchloric acid entrained within the crystal to account for its color and other useful properties. In addition, see the section on GFS Rare Earth products (p. ---) to learn more about our developmental work on crystalline reduced-moisture rare earth perchlorates.
Also in connection with the study of this mechanism, the deprotection of t-butyl ethers was also studied, and it was discovered that hydrated cerous chloride, CeCl3:7H2O, combined with sodium iodide to effectively catalyze the conversion of the ether back to the alcohol. Learn more about the use of cerium salts on organic synthesis in the Rare Earth Product section.
The GFS commitment to the development and production of perchlorate and rare earth products began over 50 years ago and continues to this day. We welcome your feedback on new product ideas as well as opportunities to find new applications for specialty perchlorate salts.
References:
- Bartoli, G. et al., Organic Letters, 7 (2005), 427.
- See GFS Publication No. 495, Practical Use of Anhydrous LiClO4 and Mg(ClO4)2 in Organic Synthesis, 2002.
- Bartoli, G. et al., Eur. J. Org. Chem. (2003), 4611.
Organics - More Perchlorates in Organic Synthesis
