tag:blogger.com,1999:blog-51846086760422068.post8673732895140781676..comments2024-03-28T08:37:08.964-07:00Comments on Open Flask: New BalloonsBaranLabhttp://www.blogger.com/profile/01806245988209508968noreply@blogger.comBlogger8125tag:blogger.com,1999:blog-51846086760422068.post-25548301971264225882014-03-09T05:59:00.056-07:002014-03-09T05:59:00.056-07:00when you make inert balloon, you probably not do 3...when you make inert balloon, you probably not do 3 times vacuo-inert steps, so when you get a inert balloon, it must with a little atmosphere, and the trace oxygen will damage your reaction esp. micro-scale reaction.openmindhttps://www.blogger.com/profile/04856685879172720228noreply@blogger.comtag:blogger.com,1999:blog-51846086760422068.post-23433989242802619302013-11-24T21:38:51.632-08:002013-11-24T21:38:51.632-08:00Diffusion is fast enough maybe in gases at normal ...Diffusion is fast enough maybe in gases at normal pressure, but not quite so in slightly viscous liquids. In reality if you don't stir your reaction you will get concentration gradients, with heavier stuff or more concentrated stuff sitting on the bottom or floating at the top. Newly-formed predicipitate can deposit over your (poorly-soluble) starting material as a poorly permeable gummy layer and make it unavailable. So whatever you learned in freshman calls is worth crap if you don't employ common sense - for example, what happens when you put few sugars into your coffee and then you drink it without stirring it firstmilkshakehttps://www.blogger.com/profile/08188961610554710616noreply@blogger.comtag:blogger.com,1999:blog-51846086760422068.post-73076902226646889362013-11-20T18:55:00.144-08:002013-11-20T18:55:00.144-08:00I can think of a few reasons to still stir them th...I can think of a few reasons to still stir them that aren't psychological...<br />1. Heat transfer (in particular for large reactions), keeping them at exactly the temperature you want<br />2. If it becomes heterogeneous while you're not watching (product crashes out)<br /><br />But yea... you shouldn't have to... maybe I'll stop too.Danehttps://www.blogger.com/profile/11311595395566607034noreply@blogger.comtag:blogger.com,1999:blog-51846086760422068.post-51752773999615162842013-11-20T17:26:42.377-08:002013-11-20T17:26:42.377-08:00Yeah, so why can't we get over stirring hetero...Yeah, so why can't we get over stirring heterogenous reactions? I learned early on in undergrad PChem that stirring heterogenous mixtures is pointless because diffusion is so fast. What is this psychological need to stir them? Theoretically, the stirbar could be a source of contamination.<br /><br />I vow to do my heterogenous reactions without stirbar from now on.Anonymoushttps://www.blogger.com/profile/14317458142143534994noreply@blogger.comtag:blogger.com,1999:blog-51846086760422068.post-34411813743728121092013-10-30T12:22:01.573-07:002013-10-30T12:22:01.573-07:00Balloons are also my black magic ritual for air-fr...Balloons are also my black magic ritual for air-free conditions. Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-51846086760422068.post-29572450346370138882013-10-06T19:08:01.081-07:002013-10-06T19:08:01.081-07:001) doubling the balloons (balloon within a balloon...1) doubling the balloons (balloon within a balloon) not only saves the reaction but also helps to prevent hydrogenation-related fire, should one of the balloons rupture in the middle of the night. I suppose this doubling also slows down the oxygen penetration by a factor of 2<br />2) balloon - assisted sparge of reaction mix works best with Ar rather than N2 because it blankets better, with buzzing the flask on ultrasonic bath, with two needles through the septa - this is fast (5-10 min) but adequate for most Pd-catalyzed couplings<br />3) since hydrogen is extremely leaky, for large-scale hydrogenation it is better not to use the needle-through septa balloon hookup but use a 3-way stopcock with a joint at the bottom, and replace the H2 balloons dailymilkshakehttps://www.blogger.com/profile/08188961610554710616noreply@blogger.comtag:blogger.com,1999:blog-51846086760422068.post-81050511277791564332013-10-05T10:37:08.408-07:002013-10-05T10:37:08.408-07:00You're probably right, I suspect there is some...You're probably right, I suspect there is some hypothetical covering, but is it worth it? Schlenk equipment is pretty expensive - although, once you have it, its a sunk cost and easy to use.<br /><br />I guess I should mention that balloons (in my experience) aren't immediately permeable to oxygen. I backfill reactions with argon from a fresh, double balloon with no issue. However, on multiple occasions I left balloons in Ni(0) reactions overnight, only to have the nickel oxidized by morning; so there is an equilibrium across the balloon. (I guess I should note that this is all observational, I never did all of the proper controls to prove it was O2, however, I've heard others echo this opinion independently of mine, notably Dave Collum.)Danehttps://www.blogger.com/profile/11311595395566607034noreply@blogger.comtag:blogger.com,1999:blog-51846086760422068.post-55648927867069806132013-10-05T09:51:42.036-07:002013-10-05T09:51:42.036-07:00I imagine there must be some way to obtain a ballo...I imagine there must be some way to obtain a balloon made of a material that would prevent O_2 from entering the system. A standard balloon could perhaps be sprayed down with some sort of inert resin or silicon grease that would at the very least make O_2 entering the balloon a non-issue. Ask a fellow material chemist and see what they have to say. I bet they would find this an interesting challenge.Alexander Irvinehttps://www.blogger.com/profile/18325210177571357093noreply@blogger.com