How do ethers split in mass spectrometry?

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Ethers are organic compounds that possess an ether group, which is an oxygen atom that is connected to either two alkyl or two aryl groups. They have a C-O-C linkage and a fairly low boiling point. Most people have heard of diethyl ether, known as ether, which was used as a general anesthetic for more than a century. Ethers are widely found in organic chemistry and have many uses. Some widely used ethers are: dimethyl ether, which is commercially used as an aerosol spray propellant; diethyl ether, which is now used as a starting fluid for diesel engines; dimethoxyethane, a high boiling solvent; methoxybenzene, which is an aryl ether and an important ingredient in the essential oil of anise seed; crown ether, used as a phase transfer catalyst; and polyethylene glycol, which is used in cosmetics and pharmaceuticals. There are a variety of ways to prepare ether in the laboratory, such as by dehydrating alcohol or using Williamson ether synthesis or Ullmann condensation.

Why would scientists be interested in splitting ether? Mass spectrometry is used to determine which elements are present in a sample and thus identify the unknown compound exactly. It does this by creating charged particles (ions) from the molecules of the sample and obtaining information about the compound’s molecular weight and chemical structure. The procedure is as follows: A sample is put into the mass spectrometer and is vaporized. The vapor is ionized, and the speed of the charged ions is increased via an electric field. When the mass to charge ratio (m/z) of these mystery particles is computed, based on their speed of travel, the composition of the sample can be identified. Each element has its own unique molecular weight, and this “fingerprint” is what leads to its unmasking, when matched with the database library.

Although there are different types of mass spectrometers, they all have three regions, namely, the ionizer, the ion analyzer and the detector. There are two main types of ionizers: one that does electron impact ionization and another that performs chemical ionization. Each process has its advantages and disadvantages. As ethers are split by chemicals, it could be that chemical ionization should be used when dealing with them. In the analyzer region of the spectrometer, there are electric and magnetic fields. The ions that pass through these fields have their velocity and direction changed during their travel, depending on the m/z ratio mentioned above. For example, a light ion will find itself flung around more than a heavier one. On a windy day in New York City, a page of the morning’s discarded newspaper will be swirling and dancing in the air, while the sanitation worker’s long-handled blue dustpan might get blown over only once. The sorted ion continues from the analyzer to the detector, which transcribes how much of each ion type is in the sample. As the prior paragraph mentioned, this is the information that helps to determine exactly what the original sample is.

As ethers are resistant to being split through the addition of water, chemical (and particularly mineral) acids are used to break the molecular bonds. The cleavage of the C-O bond via strong acids is one of the most common reactions of ethers, which are usually so relatively nonreactive that they are used as solvents. Hydrobromic acid, hydrochloric acid, boron tribromide and sometimes aluminum chloride are used to cleave ethers. Hydrogen chloride can be used, but it will take some time to split the ether, as it works slowly.

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