Sciencemadness Discussion Board


Chem Science - 23-6-2019 at 16:11

Hi everyone !
So i was working on the synthesis of Dimethyl Dioxane from Propylene Glycol and Phosphoric acid, and have a very unpleasant result. In one of the purification steps it is recommended to react the dioxane with Sodium Hydroxide solid, and then distill the product, here is the RISK .. Dioxane and dimethyl dioxane can dissolve sodium hydroxide and during distillation some product splashes to the ground glass joint and leaves Sodium Hydroxide .. and yes you know what these means.. it welds the joint and you can say goodbye.i think using grease or PTFE in these cases is the best way to protect your glassware, honestly i will make sure to do these from here on. For me these means some months until i can replenish glassware especially ground glass glassware. The last picture you see is the bottom of the fractionation column in warm dilute HCl solution .. tomorrow i will tell you if i could get my column back ... Fingers crossed
I will also, in a couple of weeks after i finish my experiments, publish my results with yields and how phosphoric acid works. But i felt like these needed to be known known

SAM_5952.JPG - 1.3MB SAM_5953.JPG - 1.7MB SAM_5954.JPG - 1.9MB SAM_5956.JPG - 1.6MB

[Edited on 24-6-2019 by Chem Science]

XeonTheMGPony - 23-6-2019 at 16:18

warm joint, add slightly acidic water, allow to cool, rinse and repeat till free, or soak, start with hot water then allow to cool while submerged.

Naturally befor you try yarding it off!

[Edited on 24-6-2019 by XeonTheMGPony]

Chem Science - 23-6-2019 at 18:06

I did warm it,low heat and hi heat, add acid yes, add oil, let it cool in between attempts ... all fail .. If it separates after the overnight warm acid bath .. then i know i FU*** SHOULD HAVE DONE THAT FIRST :( :( ... :) Love that flask ... So F**** (-_-) ... but well sometimes you just gotta let go :(

Sulaiman - 23-6-2019 at 23:58

If you are unable to separate the flask and column, then I'd

use a blowtorch or similar to rapidly heat the outer joint whilst tapping and wriggling the joint ... if I had a blowtorch.
hold the column in your (gloved) hand,
start tapping around the flask at the top of the joint with a metal rod/bar,
as multiple sharp taps can often loosen a frozen joint,
keep increasing the strength of the taps until either the flask and column separate,
or the flask neck breaks and hoefully you can keep the column.
This is a last resort action as you could loose both the flask and column.

or, probably better,

consider the column and flask as a single unit, use it as it is.
I doubt that the NaOH in the joint will significantly contaminate refluxing or distillations,
and maybe with repeated use the joint may free itself ?
For a simple siezed joint I applied WD40 silicone lubricant, waited one day, then tap-tap-wiggle-wiggle.

Keras - 24-6-2019 at 00:23

Attached is the 1,4-Dioxane purification process as suggested in the book Purification of Laboratory Chemicals, it doesn’t mention NaOH, but Na metal.

Attachment: Dioxane.pdf (193kB)
This file has been downloaded 149 times

[Edited on 24-6-2019 by Keras]

Ubya - 24-6-2019 at 01:46

the title is a bit clickbaity, the problem is not really about dioxanes, it's about a stuck ground glass joint.
@sulaiman using heat and tapping would work for a normal stuck joint (just friction), but in this case sodium hydroxide attacked the glass, dissolving part of it forming sodium silicate, a good high temperature binder.
letting the joint sit in a warm water bath for a prolonged period of time should dissolve any NaOH and sodium silicate, than is a matter of whatyou said, gently tapping and heating to free the joint. warm acidic water should be better, but now that i'm thinking any sodium silicate formed will turn into silicon dioxide (silica gel), trapped in the joint, i thounght it could be a problem, but using acidic water is the normal protocol for this situation so probably i'm overthinking

Pumukli - 24-6-2019 at 02:43

I could successfully disconnect stuck joints with the help of a heat gun - similar method as Sulaiman suggested, though somewhat less drastic. It required some beating around/ knocking the joint on the edge of a WOOD table though.

(In my case the joint was stuck because a little NaOH got there when I tried to dry pyrrolidine on NaOH in the flask.)

Chem Science - 24-6-2019 at 03:30

No it's literally weld together, overnight in an acid bath and it's dry in between the joints.These is a sad day. I don't have sodium metal, cannot yet make it (Hi temp. Hot-plate broken, still waiting the part i ordered).I Did try the fast heating method but with a nice bunsen burner and not a blowtorch. But now i think a blowtoch wasn't going to help either.
I did debate of using both as it is but for my particular situation was not possible.
Sorry for the Tricky Title i just wanted everyone to know so they can take precautions.
Ill let you know if i did get them separated :) Thanks for the suggestions

XeonTheMGPony - 24-6-2019 at 04:22

Do you have a dremmel? under flowing cold water with the diamond bit cut it off to recover the column

Keras - 24-6-2019 at 04:38

Unfortunately, this is a good remainder that distilling a product over NaOH should really be avoided.

Were you using NaOH to get a dry product? Maybe calcium chloride or magnesium sulfate would have been enough?

Chem Science - 24-6-2019 at 04:50

My intention was to ger rid of the aldehydes in the prep of the dimethyl dioxane. Unfortunately .. test with basic KMnO4 suggest presence of something .. hydrolysis of dimethyl dioxane ? mm .. By-Products ? probably :( I fail in EVERYTHING :( :(

Keras - 24-6-2019 at 04:54

Come on. I know it’s a pretty bad blow to lose a column, but it’s still better than the whole glassware blowing up in your face (so to speak). You lose money, but you’re fine.

And also, as the signature of someone else mentions, “He who has never made a mistake has made nothing new.”

So, take heart and learn from it! I’m sure very honourable chemists have made bigger mistakes in the past.

Chem Science - 24-6-2019 at 17:35

Well you are Right :) I did lear something, and yeah my comments are exaggerated hehe, Having replies is nice =) I will move on :D !!

happyfooddance - 24-6-2019 at 20:36

Glasses (esp. silicates) are a funny material. Have fun and good luck getting that loose, and maybe wear some gloves!

Keras - 24-6-2019 at 22:09

Quote: Originally posted by XeonTheMGPony  
Do you have a dremmel? under flowing cold water with the diamond bit cut it off to recover the column

IMHO, the ground glass joint of the column must be badly eroded too. The column would be fine, but with a damaged joint, it is useless anyway.

fusso - 25-6-2019 at 00:41

Dioxane can dissolve NaOH? Maybe someone can use this to make Na using electrolysis...