Sciencemadness Discussion Board

Dimethyl Dioxane Synthesis (Alternative catalyst) [HELP !!]

Chem Science - 10-7-2019 at 17:56

Hello !!
So i was looking at the synthesis of Dimethyl-Dioxane from Propylene Glycol and a dehydrating acid catalyst, to save you time, best yield was 43% using Phosphoric acid.[Assuming is Dimethyl-Dioxane]

a quantity of propylene glycol [PEG] (Tech Grade) is placed in a erlenmeyer flask and a catalyst is added along with a stir bar, A simple distillation apparatus is assembled and distill these until yellow color distillate starts coming off or tarr starts forming in the erlenmeyer(1).The distillate consist of 2 leyers, an equal volume of water is added and the uper Dimethyl Dioxane leyer is seperated,wash with water 2 times these is Crude Dimethyl Dioxane
Here are Yields for my experiments with the general procedure of above

100ml PEG + 10ml H3PO5 (85%) = 29,5%
100ml PEG + 15g. NaHSO4 = 36,5%
200ml PEG + 30ml H3PO4 (85%) = 43%
400ml PEG + 60ml H3PO4 (85%) = 29,5%

After i finish these experiences i had collected around 250 ml of crude. To purify these i reflux it with Concentrated NaOH (4M) (2) wash with water 3 times (3) and fractionate it.
First to come was 10 ml of liquid boiling at 79°C ( ??)
Last 168 ml came at 111°C ( Dimethyl Dioxane ??? )
To be honest i can't say i have Dimethyl Dioxane. here are some reactions i did, im going to abbreviate the Product as DMD

A)DMD + Bromine = Exothermic violent reaction with release of HBr
B)PEG + Bromine = No reaction
C)DMD + KMnO4 (Basic Medium) = Reaction (Room Temp)
D)DMD + K2Cr2O7 (Acidic Medium) = Reaction (Room Temp)
E)PEG + KMnO4 (Basic Medium) = Reaction (Room Temp)
F)PEG + K2Cr2O7 (Acidic Medium) = Reaction (Room Temp)
G)DMD + I2 = No Reaction
H)DMD + NaDCCA (Anh FeCl2) = No Reaction (Boiling)

The suspected dimethyl dioxane could not be solidify to obtain melting point even at -15°C.
Density is 0,917 g/ml

I can't say these is Dimethyl Dioxane, it doesn't boil at The literature temperatura, i cant freeze it.I can understand the more reactive nature but i didn't expect these to be so very different from Dioxane. if anyone can suggest what it might be happening it will bi nice.

(1):For the phosphoric acid at the end there's a violent exothermic run away reaction with the liberation of very smelly aldehydes and formation of tarr,but in the bulk of the distillation colorless distillate is collected. Be sure to stop the reaction as soon as you see brown color appearing in the distillation flask,There's no problems with the Sodium Bisulfite catalyst, only tarr appears but doesn't go in run away reaction
(2):I have very little sodium or potassium metal to purify, so to destroy aldehyde ( Somewhat ) i reflux with base,use sodium if available
(3):If you reflux with NaOH solution, these washing steps are very important, here a post of what happens if you dont do it []

Mabus - 4-9-2019 at 08:35

Check out Nurd Rage's video on the synthesis of this compound.

Also, unlike in the case of dioxane, the preparation of this cyclic ether is sensitive to impurities. You should distill your PG first.

Chem Science - 4-9-2019 at 09:47

Hello Mabus :D !!
Well .. my PG is very pure, crystal clear. Phosphoric acid is Food Grade crystal clear. The problema es in the reactivity is weird, and the Boiling point on the wrong temperature :/
I did inspire my self in NurdRage video but it don't have access to Sulfuric Acid :( so i tried with alternatives. The liquid does behave like Dimethyl Dioxane, in the sense that it doesn't mix with water and hase lower density, but from there on .. it just doesn't feel right :/

Mabus - 4-9-2019 at 10:12

Given how reactive dimethly dioxane tends to be, especially during the synth, I wonder if it didn't form some compound/complex with the phosphoric acid.
Have you tried some other desiccant, like anhydrous calcium chloride or magnesium sulfate? These two should be available in most hardware and vet pharmacies (though you'll have to dry the latter to obtain the anhydrous form).

[Edited on 4-9-2019 by Mabus]

Chem Science - 4-9-2019 at 10:38

I'll make some test and Reply :)