Selectivity in dehydration of isopropyl alcohol to diisopropyl ether

Can isopropyl alcohol be dehydrated by sulfuric acid to diisopropyl ether in a similar way as to how ethanol can? Is there a way to avoid or at least minimize the inevitable dehydration to propylene?




The acid catalyzed dehydration of secondary and tertiary alcohols to give corresponding ethers at room temperature and atmospheric pressure is unsuccessful as elimination competes over substitution and as a consequence, alkenes are easily formed.


However, in the presence of specific conditions such as low temperature and additional catalysts, isopropyl alcohol can get converted to diisopropyl ether.


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> Secondary alcohols are converted to symmetrical secondary alkyl ethers in high selectivity. The method employs acidic solid metallosilicate catalyst particles to accomplish the etherification in the presence of sulfuric acid by selective intermolecular dehydration of secondary alcohol to form di-secondary alkyl ethers. Preferably, the catalysts are solid shape selective aluminosilicate particles, especially zeolite such as ZSM-5, zeolite HY and zeolite Beta.
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2. Another resource which talks about the preparation of diisopropyl ether is the following research <https://www.researchgate.net/publication/251456024_The_mechanism_of_diisopropyl_ether_synthesis_from_a_feed_of_propylene_and_isopropanol_over_ion_exchange_resin>


What I have inferred from these is that at standard conditions, a secondary alcohol like isopropyl alcohol will get dehydrated in the presence of $\ce{H2SO4}$ to propylene. But in the presence of an acid along with a metallosilicate catalyst such as zeolite beta or ZSM-5 and at highly specific conditions, we can minimize the inevitable dehydration to propylene.


Also, another method to synthesize diisopropyl ether from excess isopropyl alcohol is by simple dehydration and elimination at high temperatures to obtain propylene(step 1). The propylene is then separated and is subjected to indirect hydration. In the indirect-hydration process, propylene is further reacted with sulfuric acid to produce mono- and diisopropyl sulfates(step 2). The diisopropyl sulfates will then subsequently get hydrated to obtain diisopropyl ether(step 3). Step 2 and 3 occur at high sulfuric acid concentration (> 80% wt) and low temperature (e.g. 20–30 °C). It might appear that in this entire process, we are first dehydrating and and then rehydrating but the reaction conditions in step 1 are different from those in step 2 and 3 which results in the product being different from the compound we began with.


**References**


1. "Process for the production of symmetrical ethers from secondary alcohols", author = Brown, Stephen H. (Princeton, NJ), 1995 August
2. The mechanism of diisopropyl ether synthesis from a feed of propylene and isopropanol over ion exchange resin, Studies in Surface Science and Catalysis, F.P Heese, M.E Dry, K.P Moller


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