[java]

Not having done a reaction under an inert gas reflux reduction ...I'm in need for clarification of the following experimantal instructions....

Reduction of 4-methylbenzhydrol (representative reaction):
Iodine (1.00 g; 4.0 mmol), 4-methylbenzhydrol
(0.79 g; 4.03 mmol), and acetic acid (25 mL) were
stirred under nitrogen in a flask equipped with condenser.
Hypophosphorous acid (50% aq.; 2 mL; 19.3
mmol) was added and the mixture was heated to 60°C.
The mixture was stirred for 24 h, diluted with water,
and extracted with hexane. The hexane was dried over
MgSO4 and removed under reduced pressure. Analysis
by GC–MS showed only a single constituent, 4-
methyldiphenylmethane,20 produced in 100% yield. 1H
NMR (300 MHz, CDCl3: d 2.49 (s, 3H), 4.12 (s, 2H),
7.15–7.54 (m, 9H).

... now my question is does one plug the end of the condenser column or does one allow the gas to  exit and hava a continous flow of nitrogen gas into the reaction flask?..I'm familiar with hydrogenations but on this reaction nitrogen is not part of the reactio, but I suspect it keeps the reaction from getting too  violent as I'm familiar with the reaction with the Hypoposphorous acid/I2 which is a bit violent in the production of HI....java

[movies]

Typically you would split the nitrogen line so that one end runs to your reaction and the other would run to a bubbler that contains mineral oil.  Then you would have the reaction apparatus, including the condenser, "sealed," but the whole system can't get above atmospheric pressure because of the bubbler.  The bubbler also has the purpose of preventing backflow of oxygen into the system.

[java]

..well that was easy enough...thanks...java

[java]

Not clear about the situation with nitrogen environment..

 Is here a constant flow of Nitrogen into the reaction flask at what rate ? or is it just a fixed reservoir or nitrogen but again at what pressure?  also is the bubbler inserted into a container with mineral oil and the bubbler submerged?   .

[beheada]

Since this thread seems to be on topic, and seeing as how I've never done anything using a nitrogen atmosphere, I was wondering if someone with proper experience would explain the setup behind said atmosphere. Although I've taken up to organic II, in my organic I lab I've yet to come across any labs using nitrogen.

Hopefully someone can explain how it is set up? My guess is that they have a nitrogen tank with some type of regulator and pressure gauge which goes into a system (like distillation system) and then there's another line split from it going to the (bubbler flask)? which is filled with an oil to allow nitrogen to escape but not allow oxygen in? Therefore, I guess you hook up the intake of nitrogen to the vacuum adapter on your distillation set up? What about for reflux?

Just curious because I've read quite a few articles using nitrogen atmosphere or argon atmosphere and I've yet to come across a resource that really elaborates on the lab procedure.

[java]

this is a pic of a set up with the bubbler.....it's not  the best but one gets the idea...java

[movies]

Dammit.

While you were posting that pic I drew one of my own.  I'm posting it anyway.   

[lavoisier]

*** Two posts went in while I was writing this, but I think it's still worth posting it. ***

If you want your reaction to be under nitrogen only, in the first place you need to remove air or any gas that you have in the apparatus.

There are two main ways to achieve that: one is based on doing vacuum/nitrogen cycles (which has a specific name, but I don't remember it), the other is based on diffusion.

In small scale reactions, people just seal the apparatus with a special rubber stopper that can be pierced by needles. Vacuum is applied, and then a rubber balloon filled with nitrogen, connected to a needle, is inserted. Nitrogen substitutes the vacuum, and you have little or no air left. You can repeat the procedure 2-3 times to be sure.

You can do the same in larger scale apparati, you just need to use a special piece of glassware (a gas inlet with stopcock). In this case, in order to keep the pressure at about 1 atm, you use the system described in previous posts. The bubbler is just a Drechsel bottle filled with (little!) silicone oil or similar stuff, and you need the oil only for detecting the flow. Basically you have your nitrogen source connected to a T joint. One arm is connected to the bubbler, the other to your reaction vessel, and that's it. Hardly rocket science!

When it's not practical (or not possible) to apply vacuum, the usual procedure consists in having a flow of nitrogen going through the apparatus (i.e. you need an inlet and an outlet). Based on the principle of diffusion, you can assume that after some time you have almost no air left, because nitrogen carried it all away.
The major drawback of this method (especially for small scale reaction) is that nitrogen carries away your solvent too, so you may end up with a different solvent composition, different concentration, or even with a solid (I say that from personal experience...).
What you can do then is to maintain the flow at the beginning, to remove air, and then switch to the static nitrogen system as above.

To answer beheada, yes, you do need a pressure gauge, if you connected directly the big cylinder to the line you would just blow everything up; reflux doesn't make a huge difference, you just need to use a good condenser and connect the nitrogen line to the top of the condenser rather than to a sidearm of the flask (or you will see the solvent condensing in the N2 line!).

[beheada]

All very very interesting. What I find most interesting is the two answers I got in class this evening. My professor told me that alot of times they use the glove box (it has a name) and flush the inside of the box with nitrogen... or he said they'll simply line in nitrogen into a fumehood.

A previous chem-engineering grad student who happens to be in organic lab II told me he just did a lab the other day using nitrogen to dry out a compound (since dessicators aren't exactly fast) by simply running the nitrogen from a tube directly onto his target compound.

I appreciate all the set up illustrations, because I really wasn't understanding how the nitrogen was introduced to the system, but now I think I have an appreciable level of comprehension. Thanks much!

[movies]

The glove box is great because it makes handling sensitive things considerably easier, but the drawback is that it's kind of a pain to move materials in and out of the box and it's not really amenable to large scale work.  Moreover, no one wants to use a glovebox on a daily basis.  It's just so much more convenient to do chemistry on the bench.