Ether 10

[Kassim Sin]

Oxygenis more electronegative than carbon, thus the alpha hydrogens of ethers are more acidic than those of simple hydrocarbons. They are far less acidic than alpha hydrogens of carbonyl groups (such as in ketones or aldehydes), however.

Ethers can be symmetrical of the type ROR or unsymmetrical of the type ROR'. Examples of the former are dimethyl ether, diethyl ether, dipropyl ether etc. Illustrative unsymmetrical ethers are anisole (methoxybenzene) and dimethoxyethane.

Vinyl- and acetylenic ethers are far less common than alkyl or aryl ethers. Vinylethers, often called enol ethers, are important intermediates in organic synthesis. Acetylenic ethers are especially rare. Di-tert-butoxyacetylene is the most common example of this rare class of compounds.

Polyethers are generally polymers containing ether linkages in their main chain. The term polyol generally refers to polyether polyols with one or more functional end-groups such as a hydroxyl group. The term "oxide" or other terms are used for high molar mass polymer when end-groups no longer affect polymer properties.

Some ethers undergo rapid cleavage with boron tribromide (even aluminium chloride is used in some cases) to give the alkyl bromide.[5] Depending on the substituents, some ethers can be cleaved with a variety of reagents, e.g. strong base.

When stored in the presence of air or oxygen, ethers tend to form explosive peroxides, such as diethyl ether hydroperoxide. The reaction is accelerated by light, metal catalysts, and aldehydes. In addition to avoiding storage conditions likely to form peroxides, it is recommended, when an ether is used as a solvent, not to distill it to dryness, as any peroxides that may have formed, being less volatile than the original ether, will become concentrated in the last few drops of liquid. The presence of peroxide in old samples of ethers may be detected by shaking them with freshly prepared solution of a ferrous sulfate followed by addition of KSCN. Appearance of blood red color indicates presence of peroxides. The dangerous properties of ether peroxides are the reason that diethyl ether and other peroxide forming ethers like tetrahydrofuran (THF) or ethylene glycol dimethyl ether (1,2-dimethoxyethane) are avoided in industrial processes.

Ethers serve as Lewis bases. For instance, diethyl ether forms a complex with boron trifluoride, i.e. borane diethyl etherate (BF3O(CH2CH3)2). Ethers also coordinate to the Mg center in Grignard reagents. Tetrahydrofuran is more basic than acyclic ethers. It forms with many complexes.

This direct nucleophilic substitution reaction requires elevated temperatures (about 125 C). The reaction is catalyzed by acids, usually sulfuric acid. The method is effective for generating symmetrical ethers, but not unsymmetrical ethers, since either OH can be protonated, which would give a mixture of products. Diethyl ether is produced from ethanol by this method. Cyclic ethers are readily generated by this approach. Elimination reactions compete with dehydration of the alcohol:

Acid catalysis is required for this reaction. Commericially important ethers prepared in this way are derived from isobutene or isoamylene, which protonate to give relatively stable carbocations. Using ethanol and methanol with these two alkenes, four fuel-grade ethers are produced: methyl tert-butyl ether (MTBE), methyl tert-amyl ether (TAME), ethyl tert-butyl ether (ETBE), and ethyl tert-amyl ether (TAEE).[4]

Epoxides are typically prepared by oxidation of alkenes. The most important epoxide in terms of industrial scale is ethylene oxide, which is produced by oxidation of ethylene with oxygen. Other epoxides are produced by one of two routes:

Suitable leaving groups (X) include iodide, bromide, or sulfonates. This method usually does not work well for aryl halides (e.g. bromobenzene, see Ullmann condensation below). Likewise, this method only gives the best yields for primary halides. Secondary and tertiary halides are prone to undergo E2 elimination on exposure to the basic alkoxide anion used in the reaction due to steric hindrance from the large alkyl groups.

Surprisingly, although anesthesia with ether was first used in surgery at Massachusetts General Hospital in 1846, the specific processes as to how general anesthetics act at multiple sites to produce anesthetic action remain a mystery.

The Panel on Food Contact Materials, Enzymes, Flavourings and Processing Aids of the European Food Safety Authority was requested to deliver a scientific opinion on the implications for human health of the flavouring rum ether [FL-no: 21.001] in the Flavouring Group Evaluation 500 (FGE.500), according to Regulation (EC) No 1331/2008 and Regulation (EC) No 1334/2008 of the European Parliament and of the Council. Rum ether is a complex mixture of volatile substances obtained by distillation of the reaction products of pyroligneous acid and ethyl alcohol under oxidative conditions in the presence of manganese dioxide and sulfuric acid. A total of 84 volatile constituents have been reported by the applicant. It is a colourless liquid with a rum-like odour and flavour. Its major uses are in the food categories beverages, confectionery and baked goods. The Panel decided to apply a congeneric group-based approach. The 84 reported constituents were allocated to 12 congeneric groups, based on structural and metabolic similarity. For eight of the congeneric groups, the Panel concluded that there is no safety concern at the intended conditions of use. However, the Panel concluded that substances in congeneric group 1 (ethanol and acetaldehyde) and congeneric group 12 (furan) are carcinogenic and genotoxic. The Panel also identified genotoxicity concerns for substances in congeneric group 3 (3-pentene-2-one). The exposure for congeneric group 10 (ethers of various structures) was above the Threshold of Toxicological Concern (TTC) applicable for this group, but a point of departure or health based guidance value that covers all the substances in this group could not be identified. The Panel concluded that according to the overall strategy for the risk assessment of flavouring substances, the presence of genotoxic substances as process-derived constituents of rum ether is of safety concern.

The Ether Monument is the oldest monument in the Boston Public Garden, installed in 1868. This forty-foot-tall monument commemorates a medical breakthrough: the use of ether as an anesthetic, a pivotal moment in medical history. The first public demonstration of ether anesthesia was conducted at Massachusetts General Hospital in 1846 by Boston dentist William Thomas Green Morton and Doctor John Collins Warren. Morton administered the ether, and Warren then removed a tumor from an unconscious patient. Atop the Ether monument, two figures sculpted by John Quincy Adams Ward enact a famous Biblical story about the relief of suffering: the Good Samaritan caring for an injured stranger he met on the road.

The Friends of the Public Garden (the Friends) led the most dramatic restoration of the Ether Monument and Fountain in 2006. Contributions were received from the anesthesiology community, local foundations, and the city. The marble and granite monument was restored, the fountain electrical system, motor, and plumbing were completely upgraded and lighting was added.

Outdoor monuments need to be vigilantly maintained to prevent deterioration caused by weather, pollution, tree debris, bird waste, and vandalism. Regular annual maintenance provided by the Friends to the Ether Monument includes cleaning the stonework and visits by the plumber to the fountain every other week during the warm weather to clean out debris, check the mechanical systems, and keep it in good working order. In 2018, in addition to the regular maintenance, the Friends will be providing the Ether monument and fountain with special care. The monument will be thoroughly cleaned by a combination of handwashing and power washing to remove urban grime and biological growth and the granite will be repointed with sealant to protect the seams that have contact with the water. This special intensive conservation work is done on the monument every three years to protect it and prevent future costly restoration. The current endowment is not large enough to provide for this level of ongoing care. An additional $100,000 would bring the endowment to the appropriate amount.

The Friends welcomes contributions for the Ether Endowment of any size from individuals and institutions who wish to help care for this unique, historic monument and preserve the heritage of the anesthesiology community. You may choose to make a gift in honor of a new anesthesiologist or in memory of one who has passed. The Friends will inform the appropriate person of/about your thoughtful gift.

Contributions are 100% tax-deductible to the extent provided by law and will be designated specifically for the future care of the Ether Monument. Checks made payable to the Friends of the Public Garden can be mailed to Friends of the Public Garden, 69 Beacon Street, Boston, MA 02108.

The use of DME in vehicles requires a compression ignition engine with a fuel system specifically developed to operate on DME. A number of DME vehicle demonstrations have been held in Europe and North America, including one in which a customer operated 10 vehicles for 750,000 miles.

Although DME can be produced from biomass, methanol, and fossil fuels, the likely feedstock of choice for large-scale DME production in the United States is natural gas. DME can be produced directly from synthesis gas produced from natural gas, coal, or biomass. It can also be produced indirectly from methanol via a dehydration reaction. DME is not commercially available in the United States.

Dimethyl ether has several fuel properties that make it attractive for use in diesel engines. It has a very high cetane number, which is a measure of the fuel's ignitibility in compression ignition engines. The energy efficiency and power ratings of DME and diesel engines are virtually the same.

3a8082e126