zero
Harmless
Posts: 18
Registered: 14-9-2022
Member Is Offline
|
|
Acetone Acetal
Attempting to make acetone ethylene acetal (2,2-Dimethyl-1,3-dioxolane) to create thioacetone (procedure here https://www.sciencemadness.org/whisper/viewthread.php?tid=79...).
Procedure:
Loosely based on https://doi.org/10.3390/molecules25071723 which is for 2,2,4-trimethyl-1,3-dioxolane
200g acetone
100g ethylene glycol
1ml sulfuric acid drain cleaner
30g MgSO4 anhydrous
Check strong acid to wet pH paper
Stir 24h
All MgSO4 clumped, add 5g more
Stir 24h
Clumped again, 10g more
Stir 24h
Add 5g of sodium carbonate
Stir 10 minutes
Check basic to wet pH paper
Separate drying agent+base
Fractional distillation with vigreux column
Fraction 1: 120ml acetone at 57-63
Fraction 2: 50ml ? at 63-87
Distillation slows, heat is increased
Fraction 3: 4.5g product at 88-93
Temperature quickly increases to 100 and water beads seen in column so heat is cut
After heat is cut temperature increases to 113, probably not much water
Discussion:
Yield is very bad (about 3%), maybe more product is in fraction 2? Will try to redistill for better separation.
This is second try, first was with molar ratio 6 acetone:1 ethylene glycol, no drying agent and the yield was about half and more water came over at
end which is not very soluble in the product.
Any idea how to tell if product is in fraction 2 other than redistill more carefully?
|
|
|
Fery
National Hazard
Posts: 990
Registered: 27-8-2019
Location: Czechoslovakia
Member Is Offline
|
|
You did not heat the reaction, right? At reflux temperature it would proceed much faster.
The MgSO4 consumed all the H2SO4 catalyst into MgHSO4. The pKa2 of H2SO4 for the second deprotonation tells how much weaker it is. But maybe it is
still strong enough for the reaction to proceed.
Couldn't the reaction be performed with dean-stark to remove the reaction water so avoiding MgSO4 completely?
Cannot the product form an azeotrope with acetone or ethylene glycol?
There should not be any water during your distillation although you wrote "water beads seen in column".
|
|
|
zero
Harmless
Posts: 18
Registered: 14-9-2022
Member Is Offline
|
|
No heat because it will cause the desiccant to release water. Should be complete reaction in 12h at room temp so no need to reflux.
Does MgHSO4 exist? Few results when looking it up. In literature, acetone acetals made using desiccant used HCl instead of H2SO4 so maybe you are
right?
See:
https://patents.google.com/patent/US4136124A/en
https://sci-hub.se/https://doi.org/10.1002/cber.19200530903
It can be done with dean-stark but is complicated by acetone's low boiling point, few solvents work as entrainer. Chloroform probably barely works.
Low boiling pet ether works but is complicated by needing a fractionating column before the dean-stark:
https://www.orgsyn.org/demo.aspx?prep=CV3P0502
One of the pentanes in the pet ether works to entrain the water. Could be obtained by distilling petrol, but rather avoid this route.
Similar products do not form azeotropes with the starting materials such as glycerine acetone acetal and propylene glycol acetone acetal. I think the
separation was bad because significant amounts of fraction 2 were collected well above acetone's boiling point. It was rising the whole time slowly
with no stable temperature, doesn't that indicate bad separation?
Water was only seen at the bottom of the column at the end of the distillation. The acetal is stable with water under basic conditions so could have
added water + sodium carbonate before distilling.
Thanks for the ideas.
|
|
|
Fery
National Hazard
Posts: 990
Registered: 27-8-2019
Location: Czechoslovakia
Member Is Offline
|
|
The acid is only a catalyst, it does not matter whether you use H2SO4 or HCl gas. HCl gas is easier to remove than H2SO4 (applying vacuum or heating)
but harder to handle or even produce. If using dean-stark you can use few drops of 37% HCl as the reaction water is going to be removed anyway. I
successfully used low boiling petrol ether few dozen times when synthesizing esters. We have plenty of it in my job under name pharmaceutical benzine.
There are various such products but we use hydrogenated fraction boiling in range 60-65 C = mixture of isohexanes. If you cannot find the word
"hydrogenated" on the label, then it is better to remove all possible unsaturated hydrocarbons as they can react into undesired alcohols (catalyzed by
mineral acid in presence of water, this is also used to get rid of them).
|
|
|
zero
Harmless
Posts: 18
Registered: 14-9-2022
Member Is Offline
|
|
Some patents say HCl works best because it has other effect not only catalyst. Could use HCl (aq) with desiccant since the water will be removed.
Dean-stark will be difficult because acetone boils low, pet ether-water azeotrope is too close so will need good column which I don't have.
Won't add water, that was a bad idea. Heat + water will hydrolyze the acetal in the column where there is no base.
Found patent that says dimethyl acetal can be separated by washing with 15% NaOH solution. That would be easier than distillation.
https://patents.google.com/patent/US2827495A/en
If no yield from redistilling fraction 2, will try dimethyl acetal instead.
|
|
|
zero
Harmless
Posts: 18
Registered: 14-9-2022
Member Is Offline
|
|
Redistilled fraction 2 with aluminium foil insulated column. Pinch of sodium carbonate added to distillation flask. Most came over between 58-63. Very
slow distillation needed to get good separation. Got 11.3g of product at 88-93. Nothing came over above 93, distilled to dry.
Bad yield, but enough material for microscale thioacetone experiments.
|
|
|
zero
Harmless
Posts: 18
Registered: 14-9-2022
Member Is Offline
|
|
Dimethoxypropane (acetone dimethyl acetal)
110g acetone
120g methanol
1ml 30% HCl
40g MgSO4
Stir for 6h
Filter into 400ml of 15% NaOH in separatory funnel
Yellow fluffy precipitate (phorone from acetone condensation?)
Leave for few hours for layers to separate
Take oily yellow top layer
Simple distillation
Fraction 1: azeotrope hell 40-80C
Fraction 2: 4.5g DMP 80-90C
Bottoms: heavier acetone condensation products (tar)
Azeotrope hell contains methanol-acetone at 56C, methanol-DMP at ~62C and probably DMP by itself due to bad separation
Mistakes were: Using the fresh hot NaOH solution. Should wait for cool first. Also filtered MgSO4 from solution into hot NaOH solution and took 1h,
bad mixing with base caused lots of loss of product. First filter, then quickly add to cold NaOH solution and thoroughly mix. Waited too long for
layers to separate, acetone condensed in this time and darkened. Could use fractional distillation for better separation of fraction 1, likely had
product.
I think the acetone ethylene acetal is easier since no massive quantity of dilute NaOH is needed. Might try to optimize that process for better yield.
|
|
|
zero
Harmless
Posts: 18
Registered: 14-9-2022
Member Is Offline
|
|
Triacetone mannitol (mannitol acetone triketal)
Carried out according to Fischer https://doi.org/10.1002/cber.189502801249
200g acetone
20g mannitol
2 ml concentrated sulfuric acid
Stirred in round bottom flask for 24 hrs.
Initially, mannitol is not dissolved. Slowly, over time all dissolves / reacts.
Isolation was fail. Fischer mentioned 2 methods:
Pour into ice water to precipitate crystals
Neutralise acid then evaporate acetone on water bath. Resulting oil can be purified by recrystallizing from alcohol by adding water.
Attempted to pour into 1L ice water. Was not enough, only some clear oil separated. In portions added 200ml to 1L more of water and more oil
separated. Oil density was too close to the ice water, some floated and some sank. Lost most product when discarding ice water. If tried again should
try other method of isolation.
Yield 2g of impure oil. Even if contains diketal and monoketal it could still be used for thioacetone experiment.
Advantage over other ketals is that it seems more stable on contact with water and forms easier even in somewhat wet conditions. Fery is probably
correct that on distillation other ketals were decomposing from the heat, this process does not require such temperatures.
Additional english reference for Triacetone mannitol: https://doi.org/10.1039/JR9460000013
Can also be tried with sorbitol: https://doi.org/10.1039/JR9520001408
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
