Diethyl ether seems to be in short supply in North America these days. Suppliers have customers under allocation constraints. Yes Virginia, people still use Et2O in certain kinds of chemical processing. Sometimes Et2O is prized for its solvent effects and sometimes for its volatility. Sometimes the only way to solubilize some inorganic compounds is as the metal etherate. Solvent residues in fine chemicals are often a problem and volatile process solvents can be a big help in ameliorating that issue. You can purchase 5,000 gallon tanker loads of Et2O if the supplier has qualified you. Another reason not to swerve in front of trucks on the highway.
Part of the problem with Et2O availability is the considerable reduced demand for it these days. Many companies have banned the use of Et2O on their site for any purpose. It is easy to understand why. The insane vapor pressure and low autodecomposition temperature are problematic for plant safety. The low boiling point of Et2O means that plant utilities can heat a vessel of ethereal soln rapidly and blow a rupture disk at reasonably low pot temps. Naturally, the safetly department gets surly about this kind of thing.
Tetrahydrofuran is not always a suitable process stand-in for Et2O. Reactivity behaviors may be quite different from Et2O solns. THF’s sensitivity to butyllithium, for instance, forces one to keep the processing conditions at low temp with a chiller. Lower pot temperatures increase the thermal margin of safety, but may have a deleterious effect on activation of a transformation once BuLi has done its job.
I have studied the decomposition of methyl tetrahydrofuran with BuLi and have determined that it decomposes in the low 30’s °C range, somewhat higher than THF. MeTHF is not an exact stand-in for THF or Et2O either. But it is definitely worth having in the stockroom for development work. It will surprise you in regard to how different it can be from THF.
While MeTHF is touted for its ability to phase separate with water, it will hold appreciable amounts of water.