Add-catalyzed hydrolysis

The variation in the add-catalyzed hydrolysis of aliphatic carboxylic esters RCOOEt is mostly subject to the steric effect intramolecularly exerted by the substituent R on the formation of the tetrahedral reaction intermediate. Taft4) defined the steric parameter E, as Eq. 3,... 

Acetoxyandrost-5-en-l 7-one (59) is converted into the ethylene ketal (60) by treatment with ethylene glycol, triethylorthoformate and p-toluenesulfonic acid. The ketal is brominated with pyridinium bromide perbromide in THF and then treated with sodium iodide to remove bromine from the 5 and 6 positions. This gives the 16a-bromo compound (61) which is hydrolyzed in methanol to the free alcohol (62). Dehydrobromination is effected with potassium /-butoxide in DMSO to give the A15-compound (63). Add catalyzed hydrolysis of the ketal in aqueous acetone gives the title compound... 

Reactions of Vinyl Ethers. Vinyl ethers undergo the typical reactions of activated carbon-carbon double bonds, A key reaction of VEs is add-catalyzed hydrolysis to the corresponding alcohol and acetaldehyde, i.e., addition of water followed by decomposition of the hemiacetal. MVE is a reactive flammable gas and must be handled safely... 

The fact that the hydrolysis is second order overall, first order in TMMS, and first order in water suggests that the rate-determining step of the hydrolysis reaction is the nucleophilic attack of water on the silicon atom. The data also indicate that the reaction is acid-catalyzed. One possible mechanism for add-catalyzed hydrolysis of TMMS begins with the rapid protonation of the methoxy group to form a better leaving group. The protonation is followed by the... 

Cyclopentanones may also be synthesized from a,/ -unsaturated ketones and diiodo-methane. The ketone is converted to the O-silyl enol, and carbene is added to the enol double bond using the Simmons-Smith reaction (see p. 74f.). Thermal rearrangement of the resulting 1-siloxy-l-vinylcydopropane and add-catalyzed hydrolysis of the silyl enol ether leads to cyclopentanones in excellent yields (C. Girard, 1974). Very high temperatures, however, are needed, and this obviously limits the generality of this rearrangement reaction. 

The butylated /3-ketoester C of Figure 10.23 is not the final synthetic target of the acetoacetic ester synthesis of methyl ketones. In that context the /3-ketoester C is converted into the corresponding /3-ketocarboxylic add via add-catalyzed hydrolysis (Figure 10.24 for the mechanism, see Figure 6.19). This /3-ketocarboxylic acid is then heated either in the same pot or after isolation to effect decarboxylation. The /3-ketocarboxylic add de-carboxylates via a cyclic six-membered transition state in which three valence electron pairs are shifted at the same time. The reaction product is an enol, which isomerizes immediately to a ketone in general and to phenyl methyl ketone in the specific example shown. In general, alkyl methyl ketones are obtained by such acetoacetic ester syntheses. 

Sakurada et al. (57) have investi ted the influence of chain stereo-regularity on the rate of the polysulphonic-add-catalyzed hydrolysis of simple alkyl esters. They suggest, on the basis of limited data, that the... 

Problem 17.1S TMS ethers can be removed by treatment with fluoride ion as well as by add-catalyzed hydrolysis. Propose a mechanism for the reaction of eyclohexyl TMS ether with LiF. Fluorotrimethylsilane is a product. 

Cteov lgt of oxetOMes In the presence of Znli. oxctancs ace opened by cyuioiritnethylsilaDe r ]k electively to y-bydraxy isocyanides, which undergo add-catalyzed hydrolysis to T-amino alcohols. 

The [l,4,5]oxadiazepane dihydrochloride 25 is obtained in three steps. Refluxing hydrazine hydrate in ethyl acetate [83] generates N,N -diacylhydrazine 22. A cyclocondensation with ether 23 in DMSO [84] followed by the add-catalyzed hydrolysis of 24 provides the oxadiazepane 25. 

Add-Catalyzed Hydrolysis of an Acyl Chloride via a Tetrahedral Intermediate THE OVERALL REACTION ... 

The mechanism involves a Michael reaction followed by a Dieckmann reaction (intramolecular Claisen), all base promoted. Loss of the ester group begins with an add-catalyzed hydrolysis, followed by decarboxylation of the resulting carboxylic acid. Finally, a Robinson annulation with methyl vinyl ketone affords the final product. 

This is a thermod)mamically favored reaction, hut because of its high energy of activation, it occurs only very, very slowly when no catalyst is present. In the presence of strong adds, however, the reaction occurs more rapidly. In this add-catalyzed hydrolysis, different intermediates with lower activation energies are formed. The sequence of steps in the proposed mechanism is shown at the bottom of this page. 

The add-catalyzed hydrolysis of diaziridines yields ketones and hydrazines ... 

Although the above mentioned add catalyzed hydrolysis is the main cause for the deterioration of cellulose and the connected loss of permanence, the influence of oxidation cannot be neglected. The oxidative damage is much more complex in its... 

The add-catalyzed hydrolysis of the amide group takes place after protonation of the oxygen atom [7]. The rate-determining step is the attack of water and the formation of a tetrahedral intermediate then, rapid N-protonation and C-N bond deavage occur ... 

It has been proven that the polyreaction occtrrs mainly at amine end groups and the reaction can be catalyzed by the carboxyl groups. In reaction [9], a tetrahedral intermediate, similar to that occurring in the add-catalyzed hydrolysis, is involved (see Seaion 4.14.5.1.1, Scheme 7). Intermediate amidine groups may also be generated. As a matter of fact, amidines are reported to be present in the polymerization of CL and tl-caprylolactam initiated by the corresponding amino adds. ... 

The second type of chemically amplified depolymerization resist mechanism depends upon the incorportation of C-O bonds into the polymer backbone which can be cleaved by either hydrolysis or addolysis. This concept was first advanced by Crivello, who proposed that polymers such as polycarbonates and polyesters could undergo photo-induced add catalyzed hydrolysis reaction in polymeric film (9, 76). Although polymers could be designed to undergo catalytic chain cleavage in the presence of add, such an approach depends upon the inclusion of stoichiometic amounts of water in the polymer film. Uttle further work was reported on this concept until recently, when a new system for dissolution inhibition was described based upon the hydrolysis of polysilyl ethers in a novolac resin (24). 

Fragmentational cleavage of C5 of 128 was reported to take place through rupture of the N4-C5 and C5-N6 bonds upon add-catalyzed hydrolysis to give 70 (65JOC3601 93MI1 94JHC1503) (Scheme 49). 

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