Ether Reactions

3 Key excerpts on "Ether Reactions"

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  eBook - ePub

  Chemical Technologies and Processes

  • Katarzyna Staszak, Karolina Wieszczycka, Bartosz Tylkowski, Katarzyna Staszak, Karolina Wieszczycka, Bartosz Tylkowski(Authors)
  • 2020(Publication Date)
  • De Gruyter

    (Publisher)

  Each pair of alcohol molecules loses a molecule of water. The course of the dehydration reaction towards the formation of ethers, not alkenes, is regulated by the selection of appropriate reaction conditions.

  Many symmetrical ethers containing shorter alkyl groups are obtained on a large scale. They are mainly used as solvents. The most important is diethyl ether – known as an anaesthetic and a solvent used for extraction and for obtaining Grignard compounds.

  An interesting example of ether are epoxides [1 ]:

  Epoxides are a class of organic compounds that contain an oxirane ring in their structure (ethylene oxide), which gives them exceptional properties. Ethylene oxide is obtained on an industrial scale from the catalytic oxidation of ethylene with molecular oxygen in air. The C–O bond in epoxy is more readily broken down under the influence of alkalis and catalytic acids than the C–O bond present in the structure of larger cyclic ethers. This is due to the presence of stresses in the three-part ring. Epoxy-specific reactions are those where the product is a compound containing two functional groups. The reaction of epoxies with water produces diols, while the reaction with alcohols produces compounds that are both ethers and alcohols. Epoxides also react with Grignard compounds [2 ].

  Another interesting example of ethers are crown ethers [3 ]. Crown ethers are molecules in which the oxygen atom combines with two carbon atoms to form molecular rings resembling the shape of a crown, which play a very important role in the so-called supramolecular chemistry, where there are host–guest molecular complexes. In such complexes, guest molecules and ions can be placed inside the host molecules (in this case, in the rings of ethers) [5 ].

  Recent research on the properties of crown ethers has led to a radical increase in the strength of bonds and the selectivity of corona ethers molecules, placing them in a flat graphene structure. Valuable properties such as high selectivity and solubility in almost all solvents and the ability to “curl” and “develop” many times make crown ethers widely used, e. g. in accelerating chemical processes involving ions, purifying water from heavy metal ions, transporting ions through cell membranes, etc. [5

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  eBook - ePub

  BIOS Instant Notes in Organic Chemistry

  • Graham Patrick(Author)
  • 2004(Publication Date)
  • Taylor & Francis

    (Publisher)

  N 1 reaction resulting in formation of an alcohol and an alkene. Trifluoroacetic acid can be used in such situations in place of HX. Most ethers react slowly with atmospheric oxygen to produce peroxides and hydroperoxides which can prove to be explosive. Epoxides Epoxides are more reactive to nucleophiles than ethers since an SN 2 reaction relieves ring strain by opening up the ring. Hydrolysis under acidic or basic conditions converts epoxides to 1,2-diols which are trans to each other in cyclic systems. Treatment with hydrogen halides produces 1,2-halohydrins and treatment with Grignard reagents allows the formation of C–C bonds with simultaneous formation of an alcohol. Nucleophiles will attack unsymmetrical epoxides at the least substituted carbon when basic reaction conditions are employed. Under acidic reaction conditions, nucleophiles will prefer to attack the most substituted carbon atom. Thioethers Thioethers are nucleophilic. The sulfur atom can act as a nucleophilic center and take part in an SN 2 reaction with alkyl halides to form a trialkylsulfonium salt (R2 SR′+ ). This in turn can be treated with base to form a sulfur ylide (R2 S+ -CR2 − ) where the sulfur can stabilize the neighboring negative charge. Sulfur ylides can be used to synthesize epoxides from aldehydes or ketones. Thioethers can be oxidized to sulfoxides and sulfones, and can be reduced to alkanes. Related topics (L2) Nucleophilic substitution (N2) Properties of ethers, epoxides, and thioethers (L4) Elimination (M4) Reactions of alcohols

  Ethers

  Ethers are generally unreactive functional groups and the only useful reaction which they undergo is cleavage by strong acids such as HI and HBr to produce an alkyl halide and an alcohol (Figure 1 ). The ether is first protonated by the acid,

  Figure 1. Cleavage of an ether to an alkyl halide and an alcohol. Figure 2. Mechanism for the cleavage of an ether.

  then nucleophilic substitution takes place where the halide ion acts as the nucleophile. Primary and secondary ethers react by the SN 2 mechanism (Section L2 ) and the halide reacts at the least substituted carbon atom to produce an alkyl halide and an alcohol (Figure 2 ). The initial protonation is essential since it converts a poor leaving group (an alkoxide ion) into a good leaving group (the alcohol). Primary alcohols formed from this reaction may be converted further to an alkyl halide (Section M4 ). Tertiary ethers react by the SN 1 mechanism to produce the alcohol and alkylhalide. However, an alkene and alcohol may also be formed due to E1 elimination (Section L4 ) and these may be the major product (Figure 3

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  BIOS Instant Notes in Chemistry for Biologists

  • J Fisher, J.R.P. Arnold, Julie Fisher, John Arnold(Authors)
  • 2020(Publication Date)
  • Taylor & Francis

    (Publisher)

  Substitution reactions are those that involve the replacement of part of a molecule (an atom or group of atoms), with an incoming group. In some instances, it is necessary to activate the potential leaving group to make it a better leaving group and thus promote the substitution reaction. Substitution reactions are a feature of carboxylic acid chemistry and aromatic chemistry.

  Elimination reactions

  Elimination reactions occur with the loss of (generally) a small neutral molecule, from a larger molecule. These reactions are common with alkyl halides and alcohols, leading, in each case, to the formation of alkenes.

  Oxidation and reduction processes

  In organic systems oxidation and reduction reactions are those that involve the gain or loss of oxygen, respectively. Reduction reactions can also involve the gaining of hydrogen; equivalent to the loss of oxygen. In many instances these processes involve free radicals. Oxidation and reduction reactions are features of the chemistry of almost all organic compounds, and are of great significance in biology.

  Related topics

  (A1) The periodic table (A2) Electron confguration

  Addition reactions

  An addition reaction is said to have occurred when a molecule has combined with another, without the loss of any part (atom or groups of atoms) of either molecule. There are two general classes of addition reaction that may be considered, nucleophilic and electrophilic addition (Section I1). For either type of addition reaction to occur one or more units of unsaturation

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