Sulfuric acid, epoxide ring

The stmcture of the ketones produced from unsymmetrical internal perfluoroepoxides has been reported (5). The epoxide ring may also be opened by strong protic acids such as fluorosulfonic acid or hydrogen fluoride at elevated temperatures (23—25). The ring opening of HFPO by sulfur trioxide at 150°C has been interpreted as an example of an electrophilic reaction (26) (eq. 3). 

Ester functions are not saponified under these ring opening conditions. However, a trans-a-acetoxy function hinders the epoxide opening reaction and a noticeable decrease in yield is observed in comparison to the cw-a-acetoxy isomer. The ring opening reaction is also dependent on the concentration of sulfuric acid. Polymer formation results when the acid concentration is too low and the reaction is markedly slower with excessive concentrations of acid. A 0.5% (vol./vol.) concentration of acid in DMSO is satisfactory. Ring opening does not occur when ethanol, acetone, or dioxane are used as solvent. 

Under some circumstances, acid-catalyzed ring opening of 2,2-disubstituted epoxides by sulfuric acid in dioxane goes with high inversion at the tertiary center.116... 

The cause for this regioselectivity may be the influence of the sulfoxide (acceptor) which renders its proximal carbon in the epoxide ring more donor like. Furthermore, ring opening at this site would not improve the unfavorable electronic status of the molecule, while attack on the distal carbon atom gives an intermediate in which the unfavorable captodative situation is dissolved on expulsion of phenylsulfenic acid, upon contropolarization at the sulfur atom. 

The alcoholysis of a-epoxides gives hydroxy ethers in a trans opening of the ring. An example is the treatment of cyclohexene oxide with methanol under reflux in the presence of a small quantity of sulfuric acid, trans-2-methoxycyclohexanol being formed in 82% yield. The mechanism and stereochemistry of the opening of oxide rings have been reviewed. ... 

Leukotrienes are synthesized in cells by the oxidation of arachidonic acid to 5-HPETE, which is then converted to an epoxide, leukotriene A4. Opening of the epoxide ring with a sulfur nucleophile RSH yields leukotriene C4. 

Alternatively, Sepracor scientists employed the enantiomeric catalyst (R,R)-71 to epoxidize indene with NaOCl in dichloromethane to give (1 R,2S)-72. This was ring-opened with ammonia and transformed into oxazoline 74 by reaction with benzoylchloride in Schot-ten-Baumann conditions followed by addition of 80% sulfuric acid. Hydrolysis of 74 afforded 73. 

Reaction of an epoxide with cyclopentanone has been used to prepare a cyclo-pentylidene derivative on a substantial scale. Protic acids such as sulfuric acid can be used or Lewis acids such as tin(IV) chloride [Scheme 3,47]. The reaction requires nucleophilic opening of the oxirane ring by the oxygen atom ... 

As mentioned, epoxidized fatty acids, esters, and alcohols are used for polyurethanepolyols after ring opening with water or alcohols (4) (Fig. 11). However, the ring opening of internal epoxides, in contrast to those of ethylene or propylene oxide, is not trivial, and quite harsh reaction conditions (160-200°C, sulfuric acid) have to be used (39). Therefore, the direct synthesis of these epoxide derivatives is a worthy target. 

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... 

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