Acid-Catalyzed Ring Opening of Ethylene Oxide

Acid-Catalyzed Ring Opening of Ethylene Oxide THE OVERALL REACTION  

Ethylene oxide Water 1,2-Ethanediol (ethylene glycol) 

Step 1 Proton transfer to the oxygen of the epoxide to give an oxonium ion. 

Step 2 Nucleophilic attack by water on carbon of the oxonium ion. The carbon-oxygen bond of the ring is broken in this step and the ring opens. 

Step 3 Proton transfer to water completes the reaction and regenerates the acid catalyst. 

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The reaction of a -halocarboxylic acids with sodium nitrite has been used to synthesize ni-tromethane, nitroethane and nitropropane, although the reaction fails for higher nitroalkanes. " A number of other reactions have been reported which use nitrite anion as a nucleophile, including (1) reaction of alkyl halides with potassium nitrite in the presence of 18-crown-6, (2) reaction of alkyl halides with nitrite anion bound to amberlite resins, (3) synthesis of 2-nitroethanol from the acid-catalyzed ring opening of ethylene oxide with sodium nitrite, and (4) reaction of primary alkyl chlorides with sodium nitrite in the presence of sodium iodide. ... 

Acid-catalyzed ring opening of ethylene oxide in water -6 eu ,.,.H H ° H... 

Each year, over three million tons of ethylene glycol are produced in the United States via the acid-catalyzed ring opening of ethylene oxide. Most of the ethylene glycol is used as antifireeze. 

FIGURE 16 6 The mecha nism for the acid catalyzed nucleophilic ring opening of ethylene oxide by water... 

Nichols and co-workersstudied the formation of j8-hydroxy nitrate esters via the acid-catalyzed ring-opening of epoxides with nitrate anion. Reactions were conducted in aqueous media using solutions of ammonium nitrate is nitric acid and under nonaqueous conditions using solutions of pure nitric acid in chloroform. 2-Nitratoethanol (32) is formed in 58 % yield from ethylene oxide (30) using either of these methods. ... 

A third example is the industrial preparation of ethylene glycol (HOCH2CH2OH) by hydrolysis of ethylene oxide in dilute sulfuric acid. This reaction and its mechanism (Mechanism 16.3) illustrate the difference between the ring openings of ethylene oxide discussed in the preceding section and the acid-catalyzed ones described here. In acid, the species that is attacked by the nucleophile is not the epoxide itself, but rather its... 

The primary manufacturing method of making ethylene glycol is from acid- or thermal-catalyzed hydration and ring opening of the oxide. Nearly all the glycol is made by this process. Either a 0.5-1.0% H2SO4 catalyst is used at 50-70°C for 30 min or, in the absence of the acid, a temperature of 195 C and 185 psi for 1 hr will form the diol. A 90% yield is realized when... 

The primary manufacturing method of making ethylene glycol (ethane-1,2-diol, boiling point 197.6°C, density 1.1155, flash point 127°C) is from acid or thermal-catalyzed hydration and ring opening of the oxide. 

Arrhenius parameters (as far as available) for the ring-opening reactions of ethylene oxide, propylene oxide, and isobutylene oxide. Overall values of ftCi and fcHcl obtained for propylene oxide have been split into rate coefficients for attack at primary carbon and attack at secondary carbon, utilizing gas chromatographic product analysis data [152]. (It is interesting to note that the results for attack at primary carbon are of the same order of magnitude as the corresponding values for ethylene oxide.) First-order rate coefficients at a constant acid concentration for the acid catalyzed hydrolysis of various epoxides [153] are collected in Table 10. Rate coefficients of the uncatalyzed and acid catalyzed reactions of ethylene oxide with various nucleophiles [151, 154] can be found in Table 11. 

B-90 and B-91, respectively.390 Another route coupled with cationic ring-opening polymerizations is accomplished for polymer B-92 with the use of a hydroxyl-functionalized initiator with a C—Br terminal, where the OH group initiates the cationic polymerizations of 1,3-dioxepane in the presence of triflic acid.329 Polyethylene oxide)-based block copolymers B-93 are obtained by living anionic polymerization of ethylene oxide and the subsequent transformation of the hydroxyl terminal into a reactive C—Br terminal with 2-bromopropionyl bromide, followed by the copper-catalyzed radical polymerization of styrene.391... 

Although the reaction with ethylene oxide is quite successful, substituted epoxides often lead to mixtures. In addition to ring opening by the halide ion. isomerization of the epoxide to an isomeric aldehyde or ketone is catalyzed by the l.ewis-acidic species of the Grignard reagent 6.1471. The... 

Commercial polyethers are made from ethylene oxide and propylene oxide by high-pressure, acid- or base-catalyzed processes. Initiation by base occurs by ring opening addition to the epoxy group and subsequent attack by the alkoxide ion generated on another monomer molecule. If sodium hydroxide is the initiator, the product is a diol. If an alkoxide is the initiator, one of the chain ends is an ether group, and the other is a hydroxyl group. 

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