Molecular eliminations esters

It combines a complex polymer system with a high molecular weight ester to form a synergistic union that is unsurpassed in reducing or eliminating cracks and abrasion problems in processing filament yarns. 

Kinetic results for the decompositions of formate esters are shown in Table 5. The reported Arrhenius parameters are supposed to apply to the ordinary uni-molecular elimination reactions... 

D(C1-C02R) = 56 kcal.mole" would satisfy the observed kinetics. This value (which seems too low by about 5-lOkcal.mole" ) is certainly a lower limit because surface initiation reactions are undoubtedly also important. The Arrhenius /4-factors observed for the normal elimination reactions to olefin, HCl, and CO2 fluctuate around the transition state estimates and do so probably as a result of experimental errors and reaction complexities. Note that the chloroformic acid, which is the primary elimination product, is very unstable at reaction temperatures and rapidly decomposes, probably by a 4-center transition state, to give HCl -I- CO2 (ref. 159). The experimental reaction rates of the chloroformate ester eliminations are two powers of ten faster than those for the corresponding formate and acetate esters. This is reasonable since electron withdrawing substituents at the (C-1) position accelerate the decompositions. It seems likely, then, that the normal uni-molecular eliminations and the free radical chain decompositions are competitive processes in these chloroformate ester reactions. 

Photochemical intra- and inter-molecular elimination of HC1, HBr, and HI, arising in most cases by initial carbon-halogen bond cleavage, has again been widely described. The syntheses of various alkaloids144 145 147 148 and of pyrazolo-[l,5-/]phenanthridine149 have been achieved in this way. Irradiation of the chloroacetamide (226) gave the tetracyclic lactam (227).150 The alkylation of the enamino-esters (228) has been accomplished by sensitized irradiation with... 

Blooming is the phenomenon of the formation of a white residue of cured adhesive near a bond line. It is the result of the evaporation of a small amount of the adhesive monomer from where it was applied onto the adjoining surfaee and its subsequent polymerization. The use of higher molecular weight monomers, such as the alkoxy esters, eliminates this problem. 

It is important to note that in methanol as the solvent the reaction is much slower and also the molecular weight is much lower. Apparently a major part of the palladium complex occurs in an inactive state and the termination reaction is relatively accelerated by methanol. This suggests that ester formation is the dominant chain transfer mechanism in methanol, although P-hydride elimination will still occur. 

Part of the great efficiency of the intramolecular reactions of [26] and [27] is undoubtedly due to the correct alignment of the rigidly held nucleophile and carbonyl group. Molecular models show that in one of the conformations of [27] in which steric interactions are minimized, the phenoxide ion is immediately adjacent to the carbonyl group and in an excellent position for perpendicular attack (Bender, 1960) but other factors must also be important. Correct orientation would not explain why anionic nucleophiles are superior to neutral nucleophiles. Extensive studies have not been carried out with nitrogen nucleophiles in carbamate ester hydrolysis, but Hegarty and Frost (1972) found that carbamate [29] underwent elimination to an isocyanate. This can be contrasted with the... 

Polycondensation of diols with dicarboxylic acids is often performed in the melt. However, it does not always lead to high-molecular-weight polyesters. Sometimes, the starting materials or the resulting polyester are thermally unstable at the high condensation temperatures. If the reactants and the polyester are well soluble, one can carry out the polycondensation in solution (see Example 4-2). The elimination of water from diols and dicarboxylic acids frequently occurs rather slowly. In such cases suitable functional derivatives of the diols and dicarboxylic acids (esters or anhydrides) can be used instead of the direct condensation, as described in Sect. 4.1.1.3. 

Esters of Aromatic Acids The molecular ion peak of methyl esters of aromatic acids is prominent. As the size of the alcohol moiety increases, the intensity of the molecular ion peak decreases rapidly to practically zero at C5. The base peak results from elimination of... 

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