Hydrogenation monomeric product yields

When equal amounts of solutions of poly(ethylene oxide) and poly(acryhc acid) ate mixed, a precipitate, which appears to be an association product of the two polymers, forms immediately. This association reaction is influenced by hydrogen-ion concentration. Below ca pH 4, the complex precipitates from solution. Above ca pH 12, precipitation also occurs, but probably only poly(ethylene oxide) precipitates. If solution viscosity is used as an indication of the degree of association, it appears that association becomes mote pronounced as the pH is reduced toward a lower limit of about four. The highest yield of insoluble complex usually occurs at an equimolar ratio of ether and carboxyl groups. Studies of the poly(ethylene oxide)—poly(methacryhc acid) complexes indicate a stoichiometric ratio of three monomeric units of ethylene oxide for each methacrylic acid unit. 

A very interesting result on ruthenocene showed that when fission product ruthenium was projected into dimeric cyclopentadiene, the yield of ruthenocene was quite low, while when monomeric cyclopentadiene was used, the yield was close to 100%. This was interpreted as involving a thermal reaction between the ruthenium atom and a cyclopentadiene monomer molecule, likely the simple displacement of an acid hydrogen. 

The polymeric pyrrolic autoxidation products probably result from the oxidized monomeric systems, which are analogous in structure to those isolated from photooxidation and peroxide oxidation reactions. Thus, for example, analysis of the products of the autoxidation of 1-methylpyrrole (Scheme 47) would suggest that 1 -methyl-A3-pyrrolin-2-one (153) is initially formed from a radical reaction of the pyrrole with triplet oxygen. This reaction sequence should be compared with that proposed for the oxidation of pyrroles with hydrogen peroxide (Scheme 50), which yields (181), (182) and (183) as the major isolable products. The acid-catalyzed reaction of a pyrrole with its oxidation product e.g. 153) also results in the formation of polymeric material and the formation of pyrrole black is probably a combination of oxidation and acid-catalyzed polymerization processes. 

Brown et al. [36] attempted to approach pentalene (2) by a thermolytic ring-contraction-cyclization of 3-ethenylbenzyne 41, which, in turn, was generated by flash vacuum thermolysis of 3-ethenylphthalic anhydride 40. Indeed, the pentalene dimer 43 ( 50%) was formed along with phenylacetylene 44 ( 50%) in 80% overall yield (Scheme 6). The failure to detect monomeric pentalene (2) is in accord with the observation of de Mayo et al. that 1-methylpentalene (37) dimerizes above —140 °C [29]. The formation of phenylacetylene 44 was unexpected, and it is as yet unclear as to whether it arises by migration of two hydrogens in the aryne 41 or the intermediate carbene 42, or whether it is a secondary product formed from pentalene (2). 

We consider this reaction to be calorimetrically useful, especially given the interest in CpsUX derivatives by the thermochemical community . Like its Th analog, the reaction of Cp 2UMc2 with CO quantitatively yields dimeric 27, a Z-enediolate with a 10-membered ring. We may then ask about the enthalpies of interconversion with the respective monomer, noting that Zr and Hf form the monomeric 2-metala-l,3-dioxolenes, 27 167 j jjg corresponding carbocycles are (Z,Z)-l,6-cyclodecadiene and cyclopentene. From the enthalpy of hydrogenation of the former species and the enthalpies of formation of their saturated cycloalkane products , the conversion of 1,6-cyclodecadiene to two cyclopentenes is found to be endothermic by some 30 kJmol . 

The reaction sequence involved in the hydrogenation of aromatic nitro groups is shown in Scheme 19.1. This can be classed as a complex Type III selectivity. The end product from all paths is the aniline (10), but intermediates such as hydroxylamines (11), azo (12), azoxy (13), and hydrazo (14) compounds are present and can sometimes be isolated under the proper reaction conditions. In general, the dimeric products usually form in alkaline media, the partially reduced monomeric species form in neutral solutions, and anilines are produced in acid. The best yields of partially reduced products are obtained when the reaction is interrupted before it stops spontaneously and when it is carried out in the presence of various modifiers. ... 

In addition to dimeric isomerisation products, hydrogen bromide treatment of C-curarine yields the monomeric curare alkaloid C-fluorocurarine (C2oH2 30N2 ) in low yield. ... 

For the malonate group to be used for fatty acid synthesis, it must first be transferred from malonyl-CoA to malonyl-ACP by the 32.4-kDa monomeric malonyl-CoA ACP transacy-lase, the product of the fabD gene (Fig. 2). A stable malonyl-serine enzyme intermediate is formed during the course of the FabD reaction, and subsequent nucleophilic attack on this ester by the sulfhydryl of ACP yields malonyl-ACP. The high reactivity of the serine in malonyl-ACP transacylase is due to the active site being composed of a nucleophilic elbow as observed in alpha/beta hydrolases. The serine is hydrogen bonded to His-201 in a fashion similar to serine hydrolases. 

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