Diisopropyl ether also trivially called isopropyl ether (analogous with ethyl ether) is an important anti-knock additive for gasoline. It is an important coproduct in the preparation of isopropanol by the hydration of propylene. As a result, it is reasonably priced.
In the Research Laboratory
In the laboratory setting, diisopropyl ether must be treated with great caution because, more than almost any prospective solvent, it readily forms explosive peroxides when exposed to atmospheric oxygen. Bottles of old solvent that are left in a laboratory or storeroom slowly evaporate through inadequately seals and the peroxides concentrate. Sometimes the peroxides even crystallize. Such residues or concentrates are extremely dangerous. If one of these concentrates is discovered, it must be handled by trained personnel with special safety equipment.
The consequence is this useful solvent does not get incorporated into scaled-up processes. This is unfortunate because at scale the dangers of the solvent are drastically mitigated.
The Difference In the Plant At-Scale
In the plant, all process operations are executed under an inert atmosphere. This is part of standard operating procedures (SOPs). Vessels are closed. Transfers are made by piping liquids, solutions, or slurries. There is no pouring through the air! The possibility of exposure to oxygen in the air is remote.
In addition, in the laboratory the formation of peroxides in diisopropyl ether is made more likely because exposure to light is increased and light can catalyze peroxide formation. In the plant light is blocked by working in drums, closed metal reactors, piping, and pumps. Reactions and processing involving DIPE occur either in subdued lighting or in the dark. There is no photocatalysis possible.
Finally, at scale, batch sheets require that all chemical inputs be tested to be sure they meet their specifications and one of the requirements for DIPE use is that it passes its requirement with regard to peroxide impurities. So unlike the situation in a laboratory where an old bottle of solvent might be used in an experiment, all the inputs for working in the kilo lab or pilot plant are rigorously tested. Furthermore, the capacity for the analytical testing laboratory to do retesting for peroxides during processing is also available.
So as we can show, unlike other materials, the higher danger point using diisopropyl ether occurs in the research laboratory during process research and development. Yes- special precautions need to be implemented -in the laboratory!
These laboratory dangers can be stymied a number of ways:
- Store in the dark
- Keep bottle sealed
- Stabilize with butylated hydroxytoluene (BHT) or NaOH
- Remove peroxides by acidic iron(II) sulfate wash
- Pass through alumina (does not destroy the peroxides; merely traps them)
- A more drastic method that also removes water/oxygen is to distill from sodium/benzophenone
But Why Bother Taking Any Risk?
DIPE readily separates from water-free sulfolane.
DIPE won’t separate from totally anhydrous DMF, but adding a little water gives two layers.
DIPE does give phase separation from anhydrous DMSO. So you can do a reaction in dry DMSO and repeatedly extract the product into DIPE.
A biphasic/phase transfer catalyzed reaction can be conducted using the DIPE/DMSO system.
Diisopropyl ether (DIPE) is a clear liquid that is immiscible with water. It smells like decomposing green tea. MP: -60 °C; BP: 69 °C; Density: 0.725 g/mL . It has a reputation as a go-to solvent for recrystallizations that have failed with other solvents.
In addition to what has been established for sure, DIPE is promising in other ways. Reactions performed in dipolar aprotic solvents such as N-methylpyrollidone, dimethylformamide, N-methylformamide, dimethylacetamide and dimethylsulfoxide are often drowned out with water and then extracted to isolate organic products. No cheap and convenient method has been worked out to separate these polar organics from the bulk of the water and return the dipolar aprotic to an anhydrous condition suitable for reuse.
On the basis of the physical properties of the chemicals, the following might be workable but KiloMentor has seen no experiment to substantiate it.
Diisopropyl ether (DIPE) forms an azeotrope with water that is reported to boil at 62.2 C. This is a heteroazeotrope. The designation means that this azeotrope’s vapor is in equilibrium with two immiscible liquid phases. According to the Chemical Rubber Handbook, DIPE and water form an azeotrope that on condensation splits into a water-poor DIPE-rich upper phase and a water-rich lower phase. Thus, addition of DIPE to a mixture of one of these higher boiling solvents and water, and boiling of the ternary mixture under a Dean-Stark trap with continuous return of the top DIPE phase could be expected to gradually separate a lower water-rich phase which could be periodically drained away. The high boiling solvent that is being dried would theoretically be retained throughout in the still pot.
In the real laboratory situation, however, a small amount of the high boiling solvent as vapor entrained in the reflux stream that one is trying to free from water could be all that is needed to prevent the distillate from separating into two phases in the trap and this would scupper the procedure so this concept would need to be tested. Nevertheless, if it works and your facility has unused distillation capacity, solvent recovery could be profitably practiced.
It is crucial for a practical process that the DIPE be recycled since the distillate is 97% DIPE and only 3% water. Recycling is essential to be able to remove a large amount of water using only a small amount of DIPE.
Before recovering the DIPE by distillation in the plant it should be tested for peroxides and washed with aq. acidic iron (II) sulfate if the peroxide test is positive.
Other solvents that boil above 100 C that can potentially be separated from water and dried using DIPE are nitromethane, acetic acid, dioxane, ethylenediamine, sulfolane, and isoamyl alcohol.
After the water has been completely removed continued distillation will drive over the DIPE itself. Even if small amounts of DIPE remained in a recovered dipolar aprotic solvent it is usually unreactive. Of particular importance… it is inert towards organometallic reagents.
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