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Author: Subject: Is a Schlenk line absolutely necessary?
nannah
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[*] posted on 24-7-2014 at 08:01
Is a Schlenk line absolutely necessary?


Hi, guys. I am a chemistry newbee thats in the process of building my first home "lab", and its been going on for about 2 years now. I has been a slow process, but i have the glassware distillation kit, plus a few other gassware items.
My goal is to have the essential basic equipment so i would be able to handle most experiments. And next thing i will add is a Schlenk line, but money is an issue right now, so what i want to know is it absolutely necessary with a Schlenk line when putting reactions under inert atmosphere or doing some other air sensitive reactions?

Thanks in advance. :)

[Edited on 24-7-2014 by nannah]
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Mailinmypocket
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[*] posted on 24-7-2014 at 09:02


I have done a few reactions which require inert atmospheres but have never had a schlenk for at home. Septums are what I find best, have one needle with inert gas going in and another one for the gas to come out. Not as perfect as a schlenk but it works! If you are really serious about doing lots of airfree reactions then a schlenk would be a better idea but for only occasional reactions it's a matter of preference I suppose...
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Burner
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[*] posted on 24-7-2014 at 10:08


There are a host of details required to answer your question. What is the degree of air sensitivity? Is it sensitive to oxygen, nitrogen, carblon dioxide, moisture? In the material pyrophoric? Or is it a case of graceful degradation of your material? What size is the reaction? If the quantities are small a large degree of oxygen exclusion (I am assuming when you say "air sensitive" you are really talking oxygen) is required.

We just need more info. Help us help you.




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nannah
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[*] posted on 25-7-2014 at 03:21


Quote: Originally posted by Burner  
There are a host of details required to answer your question. What is the degree of air sensitivity? Is it sensitive to oxygen, nitrogen, carblon dioxide, moisture? In the material pyrophoric? Or is it a case of graceful degradation of your material? What size is the reaction? If the quantities are small a large degree of oxygen exclusion (I am assuming when you say "air sensitive" you are really talking oxygen) is required.

We just need more info. Help us help you.


I dont have any specific reactions in mind at the time, but i guess i would want to be able to apply an argon or nitrogen atmosphere becouse it seems like they are mostly used.

When it comes to the scale of the reaction, i have a 24/40 kit. But i will probably keep it on a small scale.

So you say that it is possible to apply argon from a cylinder, through a hose that goes into a septum stopper thats placed on the reaction flask? Are there any members that use this kind of "technique"?
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kavu
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[*] posted on 25-7-2014 at 04:47


Most typical air/moisture sensitive reactions can be run without a Schlenk line. Assemble the apparatus while the glassware is still hot and then allow it to cool under a flow of dry argon/nitrogen. This can be supplied either with a tank + bubbler setup or balloons. Then just leave the setup under positive inert gas pressure, the least wasteful way is just to use a balloon. Typically balloons are connected either using olive adapters or cutting a syringe in half, slipping a double balloon over it and attaching it through a septa with a needle. Having double balloon instead of just one will add popping protection as well as minimize leakage in/out through the plastic.

Using the balloon method I've successfully carried out Grignard reactions and FC acetylations at home. At uni the technique has worked for me in most everything I've done (including Wittigs, DIBAL reductions, direct aldols with LDA, handling t-BuLi and so forth). True Schlenk techniques have been of use only with a few organometallic preps. Btw when running reactions at cold temperatures additional piece of electrical tape around the septum is a cheap insurance to keep condensing water out. This is not that big of a deal when doing real Schlenkin'.

Also running a real Schlenk line would call for a cold trap and a decent vacuum pump. This would involve the routine use of either dry ice or liquid nitrogen, which are both pretty much out of reach for most amateur labs.

[Edited on 25-7-2014 by kavu]
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[*] posted on 25-7-2014 at 05:52


Just a minor cautionary note - standard commercial argon and nitrogen gas can have as much as 100ppm of oxygen unless you purchase the specialty high-purity grades (which are often special order). When I need oxygen-free argon I run standard welding-grade gas through a pyrex tube packed with copper wool through my tube furnace @ 800C to ensure that all the oxygen is removed. You can do something similar with just a gas burner.



“There is a cult of ignorance in the United States, and there has always been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge.”

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Chemosynthesis
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[*] posted on 25-7-2014 at 07:29


Never used a Schlenk outside of work. I have a bubbler I can fill with oil and septa for cannula technique, but generally do not bother using any of it as I find the bubbler annoying to clean and and prefer to keep glassware out of my oven (used to have a metal trashcan lined with 60 watt bulbs that got pretty hot for curing resins). While I am sure that in some cases the yields might be affected, I have performed Grignards and FC rxns without an inert atmosphere flow at home, so I would agree that a Schlenk line/manifold, while awesome, is unnecessary.
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Dr.Bob
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[*] posted on 29-7-2014 at 06:22


The main time a Schlenk is needed is either for very hazardous reagents (pyrophoric, toxic, highly water reactive) or when the compounds being handled have issues with even traces or catalytic amounts of water or oxygen being present (like some metal complexes). In most other cases enough reagent can be used to account for small amounts of air or water being present.

For most work, a simple source of dry inert gas is fine, you can always dry glassware and syringes before use, and try to keep solvents dry. But in most reactions, just adding a slight excess of base, reducing agent, etc will account for any water and air is mostly a risk for fire, so 99% inert is good enough for most cases, as 100 ppm oxygen will not support a fire for most chemicals, although that is worse than most gases that I have seen. Putting a gas drying tube on your cylinder line is not a bad idea as well.
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[*] posted on 29-7-2014 at 06:56


Its not neceassary, it speceally at home lab. You need gas, septum, rubber pipe, and syrange needle. Thats all. In my alma mater org lab there is no schlenk line, i have been in many researc labs and i have seen that in only one, in organic research lab. And if you ask you doesnt need it, better buy more gas, nitrogen and argon. And you can always dry gass with round bottom with sulfuric acid or CaCl2. Maybe it looks great, but we dont need it at home lab.
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nannah
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[*] posted on 29-8-2014 at 14:42


Hi, sorry i havent responded sooner. I totally forgot about this thread until now. :/

I am in no real need of a Schlenk line, but some time in the future it would be cool to have one. In order to be able to handle most reactions.

And i didn´t know that you had to dry, and purify your gas for the simple reason becouse i havent thought about it any deeper. So there you taught me something new, and that i thank you for. :)

I am interested in Burners setup, with the tube furnace. I have seen a couple of them for sale on ebay, but i never did any research on them further to find out what they generally are used for. But here is one use. :)
Burner: Are your tube furnace home-made, or is it store-bought?

Anyway, thank you guys for your input. :)
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[*] posted on 30-8-2014 at 14:53


I've run several reactions that require inert atmosphere chemistry without a schlenk line or a septum. Just used two gas-inlet adapters and argon bubbled in slowly. Even ran a few low temperature reactions after only a purge of argon every 10 minutes or so. Product came out fine even without the constant positive gas.

One thing I noticed in graduate lab's was that schlenk lines are used a ton and septums to an absurd extent. People were running reactions in like THF at 50*C in a flask with a septum, no condenser, no other glass-ware. Seemed a bit sloppy to me personally but hell if it works it works I guess... I noticed when I tried the same thing the septum was completely damaged and my solvent needed replenishing frequently, not exactly a surprise given the material and THF.

[Edited on 30-8-2014 by smaerd]




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