Talk:Cryptand

Uses for phase-transfer?

The current article refers to the use of cryptands in phase transfer catalysis. Such an application is certainly conceivable, but why would anyone do this and what is the reality behind the commnet? I have never heard of this application and cannot imagine why anyone would do this instead of something cheap like quat salts or crowns or the N(C2H4OC2H4OMe)3 thing. The "Encyclopedia for Reagents for Organic Synthesis" lists zero applications for cryptands in organic synthesis. Cryptands are mentioned zero times in "Organic Syntheses". It will be nice to find "uses" for cryptands, but, their loveliness aside, I suspect that applications are few.--Smokefoot 00:34, 7 August 2006 (UTC)[reply]

I am familiar with cryptands from the lab, but I will find an article concerning their use as phase transfer catalysts. There are key difference between cryptands and crown ethers being strength of binding and specificity. Sometimes a crown ether or quaternary salts won't accomplish the same task. Consider that if it is being used as a catalyst then only a small amount is needed for the reaction so cost is less of an issue. All loveliness aside if they allow you to do something that no other compound can then they are indeed quite practical. The Nobel Prize release mentions that they allow the extraction of “radioactive strontium or toxic cadmium and lead ions without affecting other ions.” http://nobelprize.org/nobel_prizes/chemistry/laureates/1987/press.html These compounds, although more expensive than crown ethers, are commercially available because people really do use them. They are actually available in many different types. I think that what is need for this page is a comparison of the specificity and strength of binding between crown ethers and cryptands. Cryptand[2.2.2] is 10^5 more stable than the corresponding crown ether macrocyle. For a very good summary of cryptands check out: Cryptates: the chemistry of macropolycyclic inclusion complexes Jean Marie Lehn Acc. Chem. Res.; 1978; 11(2); 49-57. --M_stone 22:03, 7 August 2006

My point is more in the spirit of reality. No doubt someone somewherehas used cryptands for PT catalysis. But if such a use is rare then, then its inclusion in a list of "uses" is dubious and possibly misleading. Certainly dont want naive student running out and buying 2,2,2-cryptand for their reaction. Nobel verbage is often hyped because the Nobel Comm, like Lehn, is marketing their product. But I am pretty sure that recorded history reveals a different reality. No doubt that cryptand make more stable complexes, no one is disputing that. Like I say, look up 2,2,2-crypt in your favorite organic methods manual - you wont find it. Again, it is a lovely stuff and super important. But cryptands have not proven as important in a direct practical sense as many people expected. Like I say, go ask your local organic syn group. Hence Lehn's most recent mini-review on cryptands cites the electride work as being the most prominent app. --Smokefoot 22:23, 7 August 2006 (UTC)[reply]

I think that evaluation of reality is more of a philosophical question. I do take your point that it is probably not the first or even second phase transfer catalyst that you would reach for, however I think that it is worth noting because it does have better selectivity. Perhaps it would be good to put a modifier on it saying because of cost that it would be used for highly specialized purposes. There are a lot of practical things not listed in organic methods manuals. Also many of the catalysts are based on metals and ligands, such as ruthenium based Grubb’s catalyst, are very, very expensive. I don’t really see the harm in listing phase transfer catalysis as a use if it has been demonstrated. I think that if someone is interested in phase transfer catalysis then they would go to the wiki there first anyways. --M_stone 07:45, 8 August 2006 Well we've probably beaten this horse until it is quite dead, but one more comment - Grubbs catalyst is used widely and is or soon will be in all manuals. But like you say, readers should know that cryptands have lots of potential. Best wishes and hopefully we can discuss something again in the future.--Smokefoot 13:25, 8 August 2006 (UTC)[reply]