[dolphinsea14]

Thank you very much, everyone, for all the good advice, I really appreciate your help.
I guess I will try some of these solutions, and I hope everything will turn out well.

[Enthalpy]

If supplying from party balloons, just make sure their helium isn't mixed with hydrogen. It's often done to save cost. As long as the mix isn't flammable in air, it saves precious helium.

[dolphinsea14]

Ok, thank you Enthalpy

[billnotgatez]

As for Helium

My understanding ( and it may be wrong)
The party balloon cylinders are mixed with air as a safety precaution because people have been known to inhale from those cylinders to get Donald Duck voice .
Although some new reserves have been found, industrial Helium source have become more pricey since the deregulation of prices and the loosening of the requirement to extract from natural gas.

I have often thought that there was a slight bit of some kind of oil or impurities in various gas cylinders that were used for industrial purposes and not medical.

I was going to price check the difference between Argon and Nitrogen but lost patience.

In any case [not to hijack this thread]
Why use nitrogen rather than Argon?
Is it just price?

[OrganicDan96]

what about CO₂ you can make that really easily in the lab. or might it be too reactive?

[rolnor]

You can remove oxygen from air by bubbling it through a alkaline solution of pyrogallol.

[Borek]

You can remove oxygen from air by bubbling it through a alkaline solution of pyrogallol.

Traces of oxygen, yes, but if one needs a lot of gas the idea is way too costly. Bubblers make sense when you want to clean technical argon or nitrogen from oxygen impurities, not when you deal with the normal air.

[rolnor]

You can remove oxygen from air by bubbling it through a alkaline solution of pyrogallol.

Traces of oxygen, yes, but if one needs a lot of gas the idea is way too costly. Bubblers make sense when you want to clean technical argon or nitrogen from oxygen impurities, not when you deal with the normal air.

But how much does he need, is it not sufficient to fill the apparatus?

[zarhym]

I have done this reaction before at about several hundred grams scale. I didn't use nitrogen since the reaction/distillation was done at reduced pressure. The cracking temperature of was around 180°C to 220°C. The strategy of this reaction is very simple.  Once the dimer was cracked into monomer, the desired product goes into gas phase at this temperature under reduced pressure, then being collected in the condenser. The reaction and separation happens simultaneously.

Since the apparatus of this approach is always under reduced pressure, there is very limited amount of oxygen is the gas phase. This oxygen can react with diene. But it only generate very small amount of impurities, which was not a problem to me.

You can add small amount of polymerization inhibitor such as tert-butyl catechol. It was good for this reaction.

The diene (with trace amount of TBC stabilizer) was stable in freezer for several days (tested with HNMR) in my case.

[pgk]

This is a convenient and rather safe technique. The addition of an antioxidant such as BHT, BHA, TBC (this one), etc. is a smart idea, too.
But even so, vacuum must be slowly broken, otherwise atmospheric oxygen will violently penetrate into the glassware.

[dolphinsea14]

I did it that way too, zarhym, without nitrogen, and it went well.
I didn't need much, I collected few mililiters. I was performing microsynthesis of ferrocene so I needed 0,3mL.
I got some orange particles floating in the beaker, but after vacuum filtration, the precipitate was completely brown (I guess impurities are present) What do you think?  The filtrate was dark blue, that means it contains ferrocenium ion, doesnt't it? How can I recover ferrocene from filtrate? Should I use SnCl2(as a reducing agent) or do you have other suggestions?

[dolphinsea14]

And is it necessary to remove filter paper before sublimation (using petri dish and beaker with ice on the top)? The temperature should be less than 100 degrees Celsius.

[zarhym]

The attachment is the HNMR spectrum of cyclopentadiene I obtained.
Without inert gas protection, my next step synthesis using cyclopentadiene at this purity is still messy.

There are simply too many side reactions of cyclopentadiene under air, which are competitive to your ferrocene synthesis. Beside, iron(II) ion can be oxidized into iron(III), which may be a problem to your reaction. Although synthesis cyclopentadiene may not need nitrogen protection, I highly recommend that you use cyclopentadiene under nitrogen atmosphere.

I also have no idea if ferrocene is stable in air. It looks like the orange particles you have is not very stable. The color change may indicate oxidization since there is large amount air being pulled through the filtration cake.

To avoid this oxidization, I may try the filtration in a glovebox (nitrogen atmosphere). This will eliminate the influence from oxygen and water.
Also, I may try recrystallize the ferrocene. If the ferrocene is in its crystalline form rather than amorphous solid, it should be more robust in the air.

Good luck.

[wildfyr]

Ferrocene is pretty stable in air whenever I've used it. Also, https://www.sciencedirect.com/topics/chemistry/ferrocene.