Perchloric acid reaction with epoxides

Epoxides. Epoxy compounds react with the carboxyl groups of CTPB to form polyesters. The reaction rates and extent of reaction of a number of epoxides have been determined with the model compound hexanoic acid (6). It was found that most epoxides undergo side reactions (as evidenced by the more rapid consumption of epoxide species) but that at least one difunctional epoxide, DER-332 (Dow Chemical Co.) (Table IV), exhibits a clean reaction with carboxylic acids, even in the presence of ammonium perchlorate. 

The most intriguing epoxide reaction involving participation of remote bonding electrons is the m s-annular hydride shift observed when the pjS.ii -epoxide (i) was treated with perchloric acid or hydrogen fluoride in non-polar solvents [37 3 ] The A 3.4).structure (3) of the product is reliably established [38], and separate experiments have confirmed... 

In exploring, as a model case, the conversion of A -cholestene-3-one (3) into cholestane-3,6-dione (7), a Merck group" converted 750 mg. of the 3-ethyleneketal (4) into the 5a,6a-epoxide (5) by reaction with perbenzoic acid and treated a solution of (5) in tetrahydrofurane with 3 N aqueous perchloric acid solution at room temperature to effect hydrolysis of both the ethyleneketal group at Cd and the 5a,6o -epoxide group. Treatment of (6) with base effected dehydration and isomerization to the... 

In another procedure, a halogen acid is generated by the reaction of an ionic halide salt, eg, tetraethylammoniiun bromide in acetic acid with perchloric acid with subsequent formation of a halohydrin the epoxy group is determined by back-titration with perchloric acid nsing crystal violet indicator (83). The end point can be determined visually or potentiometrically. A monograph on epoxide determinations was published in 1969 (84). This is the method adopted by ASTM and is currently used by most resin producers. 

The aforementioned epoxidation has been also performed using imidazolidinone 58 in combination with perchloric acid and (nosylimino)iodo benzene as hyperva-lent iodine oxidant. In this manner, several a,P-unsaturated aliphatic aldehydes were epoxidized in high yields and enantioselectivities (72-93%, 87-97% ee) [65], with only enals possessing an electron-withdrawing group being unreactive under these reaction conditions. 

In analogy with the peracid attack on steroidal double bonds, the formation of the bromonium ion, e.g., (81a), occurs from the less hindered side (usually the a-side of the steroid nucleus) to give in the case of the olefin (81) the 9a-bromo-l l -ol (82). Base treatment of (82) provides the 9 5,1 l S-oxide (83). Similarly, reaction of 17/3-hydroxyestr-5(10)-en-3-one (9) with A -bromosuccinimide-perchloric acid followed by treatment with sodium hydroxide and sodium borohydride furnishes the 3, 17 5-dihydroxy-5a,l0a-oxirane. As mentioned previously, epoxidation of (9) with MPA gives the 5, 10 -oxirane. °... 

Alcohols with organoelement groups listed in Table 13 gave with one exception only small amounts of olefine. But with hydroxyalkyl-selenides (35a, G = -SePh or -SeCHs) stereospecific frans-elimination can be achieved in acidic (for instance excess of perchloric acid ether at room temperature) or basic media to give olefines in good yield So we can state that preparatively useful carbonyl olefination reactions in which epoxides are not a by-product, are allowed not only with phosphorus and silicium containing regents but are possible in the wide area of the periodical table marked in Scheme 55c with little lines. 

The reaction of epoxides with carboxylic acids in the presence of ammonium perchlorate can be very slow. The search for a catalyst to accelerate the cure rate for a particular formulation can be particularly rewarding. The slowness of the reaction can lead to a disadvantage of the system if not carefully investigated. If cure is stopped before all of the epoxide groups have been consumed, cure will continue at a rate which depends on storage temperature. The epoxide can continue to react with carboxyl groups rapidly at elevated temperatures, or very, very slowly at ambient temperature, to yield highly crosslinked propellant systems with low strain capability. 

The hydrolysis of epoxides is a convenient method for the preparation of vie-diols. The reaction is catalyzed by acids or bases (see discussion of the mechanism on p. 369). Among acid catalysts the reagent of choice is perchloric acid, since side reactions are minimized with this reagent.500 Dimethyl sulfoxide is a superior solvent for the alkaline hydrolysis of epoxides.501 OS V, 414. 

Finally, fluorinated carboxylic acids react with epoxides (trimethylaluminum-catalyzed).- and conveniently with diazo conipounds. Cycloaddition is observed with diazo-methane. Reaction of compound 7 with trifluoroacetic acid alone is relatively slow (Freon 113, reflux, 12 h, for completion of reaction) however, catalytic amounts of copper(ll) perchlorate increase the rate of formation of ester 8 (rt, 5 min). ... 

A curious reaction was observed when epoxy derivatives of certain exo-methylene groups e.g. i) were treated with BFs or perchloric acid [34,35]. The products are believed to be five-membered cycHc ethers 2.). The exact mechanism of the ring expansion process is uncertain, but it has been represented as epoxide cleavage concerted with two stereospecific hydride... 

In studies with cis and tram isomers of 2-butene epoxide,26 it was found that in aqueous perchloric acid solution the cis isomer gave the dl glycol whereas the meso glycol was formed from the tram isomer. Consequently, inversion must have occurred during the reaction and the carbonium ion could have had no completely separate existence. For the cis isomer this transformation can be illustrated as follows ... 

Medium and large rings can be made via cationic intermediates which are usually generated by treatment of suitable precursors with acid. Reactions of this class are perchloric acid catalyzed rearrangements of bicyclo[n.l.0]alkan-2-ols (n > 5), solvolysis of the corresponding esters, boron trifluoride-diethyl ether complex catalyzed cleavage of epoxides, and tri-fluoroacetic acid catalyzed reactions of 7-(methylsulfanyl)bicyclo[n.l.0]alkanes. 

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