Ester ions, decomposition

The o-substituted benzoic acid methyl ester of formula (CH3)2NC6H4C02CH3 has been found to lose both the ester methyl and the amine methyl in metastable ion decompositions. It has been proposed that the bond cleavage to eliminate the ester methyl is accompanied by a hydrogen transfer from one of the other methyl groups to the carbonyl oxygen in a 7-membered cyclic transition state [83]. The mechanistic proposal rests upon isotope effects observed on substituting deuterium in methyl groups. 

This chapter presents various examples of enzyme catalysis by polymers including ester hydrolysis, decomposition of hydrogen peroxide, oxidation of disubstituted phenols and hydroquinone, interfacial catalysis and other types of reaction. Because metal ions (Fe, Zn, Cu. Mn, Co, etc.) are often involved as coferments during enzyme catalysis, some examples illustrating their catalytic action are also given. The catalytic activity of polymeric coordination compounds is shown to depend on the strength of the ligand-metal bond. 

The r-butyl reactant ions are formed in the near vicinity of the electron beam, and they drift to the ion exit slit of the ionization chamber under the influence of the repeller field. Protonated ester molecules (taken as a typical example) are formed along the path of the r-butyl ions by proton-transfer reactions, and after formation the protonated ester ions drift toward the ion exit slit under the influence of the repeller field. In the process of doing this they undergo decomposition reactions which may be looked upon as a set of parallel, competing first-order reactions, that is. 

G-20 Dicarboxylic Acids. These acids have been prepared from cyclohexanone via conversion to cyclohexanone peroxide foUowed by decomposition by ferrous ions in the presence of butadiene (84—87). Okamura Oil Mill (Japan) produces a series of commercial acids based on a modification of this reaction. For example, Okamura s modifications of the reaction results in the foUowing composition of the reaction product C-16 (Linear) 4—9%, C-16 (branched) 2—4%, C-20 (linear) 35—52%, and C-20 (branched) 30—40%. Unsaturated methyl esters are first formed that are hydrogenated and then hydrolyzed to obtain the mixed acids. Relatively pure fractions of C-16 and C-20, both linear and branched, are obtained after... 

It would be reasonable to expect that the decomposition of the N,N-dimethylimino ester chlorides proceeds via a bimolecular mechanism already demonstrated for the thermal decomposition of simple imino ester salts (79). In the carbohydrate series, where an isolated secondary hydroxyl group is involved, such a process would result in chlorodeoxy sugar derivatives with overall inversion of configuration, provided that the approach of the chloride ion is not sterically hindered. Further experiments are in progress in this laboratory utilizing additional model substance to establish the scope and stereochemical course of the chlorination reaction. 

The nitrene can be generated by a variety of methods, the most popular being the thermal or photolytic decomposition of azidoformates. Other methods, particularly the base-catalyzed a-elimination of arylsulfonate ion from 7V-[(arylsulfonyl)oxy]urethanes, are useful as they avoid the use of the potentially explosive azido esters. 

A situation similar to that in acetyl phosphate is also encountered in benzoyl phosphate76 . Electron-attracting substituents on the phenyl ring accelerate the hydrolysis of the dianion (a linear relationship exists between log khydrol and the Hammett a constants with q = 1.2 and the linear log ki,j,drol./pKa relationship is the same as for the phosphoric monoaryl ester dianions65 . On the other hand, hydrolysis of the monoanion is influenced only slightly by substituents in the phenyl ring. These observations can also be rationalized in terms of the decomposition mechanism to the POf ion formulated for 116 and 117. 

The esters differ from each other in stability. To decompose the isopropyl ester, higher temperatures and higher acid strengths are needed than for decomposition of the s-butyl ester. It is claimed that the resulting carbenium ions are stabilized by solvation through the acid (25-27). Branched alkenes do not form esters. It is believed that they are easily protonated and polymerized (28). 

The impact which was made by the writer s revival of the old ester mechanism in the context of polymerisations is attested by the number of polymer chemists who set about examining the validity of the theory experimentally. For example, Bywater in Canada confirmed that during the progress of a polymerisation of styrene by perchloric acid the acid could not be distilled out of the reaction mixture, but after exhaustion of the monomer it could be. This regeneration of the initiating acid after the consumption of the monomer is an often attested characteristic of pseudocationic polymerisations with many different protonic acids it is most simply explained by the decomposition of the ester to an alkene and the acid, i.e., a reversal of the initiation, when the monomer has been consumed. Enikolopian in the USSR found that the effect of pressure on the rate of polymerisation in the same system was not compatible with the propagation step involving an ion, and... 

Explanation The ester polystyryl perchlorate is stabilised by M, but it decomposes slowly to Pn4. In the moderately pure system the [Pn+] are consumed by impurities, mainly water, and only when depletion of M leads to fast decomposition of E are enough Pn+ formed to give colour and conductivity. In the very pure system the scavenging of water, etc., by the ions is completed before all the M has been consumed, so that the Pn+ formed thereafter contribute to the rate. At the end of a typical polymerisation of this type the [Pn+] is ca. 10"7 mol l"1. If [H20] > [HClO4]0, the k1 is unaffected because the rate of reaction of E with H20 in CH2C12 is much smaller than the rate of polymerisation, but the Pn+ and/or the HC104 are hydrated so that no colour or conductivity appears. The visible and conducting ions are not polystyryl carbenium ions, but a cocktail of others in which the substituted indanyl ion is the most abundant [28]. 

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