Cyclic acetylene polymerization

Synthesis of Cyclic Polymers Using Acetylene Polymerization. 143... 

Combination of WCl6 and EtAlCb (or Et3Al) is also effective for acetylene polymerization . This catalyst shows high activity towards linear and cyclic alkene metathesis and a metathesis propagation step is to be invoked also in this case. However, this combination is a typical Ziegler-Natta catalyst system, and it may be probable that, in this particular case, the components are acting as a simple coordinated anionic catalyst system. 

S. Ikeda and his coworkers studied a mechanism of acetylene polymerization in connection with olefin polymerization by various Ziegler-Natta catalysts. They found that polymerization yields not only highly polymerized polyacetylene but also benzene, which is a cyclic trimer of acetylene, and that the ratio of these two products depends... 

Group 10 transition metal catalysts including Ni and Pd are known as a new class of catalysts for the polymerization of substituted acetylenes, but the reports treating these catalysts are still not many. Some of the reports in an early stage displayed that the group 10 catalysts rather induce cyclic and linear oligomerizations of acetylene monomers. Thus, only fragmental information is available in some of the papers. 

CAROTHERS. WALLACE H. 0896-1937). Bom in Iowa. Carothers obtained his doctorate in chemistry at the University of Illinois. He joined the research staff of Du Pom in 1928, where lie undertook the development of polychioroprene (later called neoprene) that had been initialed by Nieuland" research on acetylene polymers. Carother s crowning achievement was the synthesis of nylon, the reaction product of hexamethylenetetramine and adipic acid. Carother s work in the polymerization mechanisms of fiber like synthetics of cyclic organic stoic-lures was brilliant and productive, and he is regarded as one of the most original and creative American chemists of the early 20"1 cenlury. 

Polyacetylene has promise as a polymeric electroconducting material [26-31]. The simplest way to obtain this polymer is by polymerisation of acetylene, although alternative methods involving the metathesis polymerisation of cyclic polyenes are also effective. 

C. Hoogzand, and W. Hubei, Cyclic Polymerization of Acetylenes by Metal Carbonyl Compounds, in Organic Synthesis via Metal Carbonyls (Eds. I. Wender and P. Pino, Wiley Interscience, New York, 1968, Vol. I, pp. 343-371). 

Beryllium chemistry includes its S-diketonate complexes formed from dimedone (9), acetylacetone and some other S-diketones such as a,a,a-trifluoroacetylacetone. However, unlike the monomeric chelate products from acetylacetone and its fluorinated derivative, the enolate species of dimedone (9) cannot form chelates and as the complex is polymeric, it cannot be distilled and is more labile to hydrolysis, as might be expected for an unstabilized alkoxide. However, dimedone has a gas phase deprotonation enthalpy of 1418 9 kJmoD while acetylacetone enol (the more stable tautomer) is somewhat less acidic with a deprotonation enthalpy of 1438 10 klmoD Accordingly, had beryllium acetylacetonate not been a chelate, this species would have been more, not less, susceptible to hydrolysis. There is a formal similarity (roughly 7r-isoelectronic structures) between cyclic S-diketonates and complexes of dimedone with benzene and poly acetylene (10). The difference between the enthalpies of formation of these hydrocarbons is ca... 

While caoutchouc was first obtained by polymerizing isoprene it has been found that other hydrocarbons containing the buta i-ydi-ene group will likewise yield caoutchouc. Such hydrocarbons have been obtained from several sources, e.g., turpentiney petroleuniy coaly acetylene. Also compounds related to succinic acid, e.g., pyrotartaric acid (methyl succinic acid) are possible of transformation into isoprene. Levulinic acid, which is aceto propionic acid, CHa—CO—CH2—CH2—COOH, yields a cyclic sulphur compound, methyl-thiophen (p. 853), which, like methyl pyrrolidine, yields isoprene. Ethyl alcohol by conversion into acetone and then by aldol condensation with ethane yields 2-methyl buta 2-ene, CHa—C = CH—CHa which may be transformed... 

As early as 1948, Reppe et al. reported the discovery of the cyclic polymerization of acetylene to cyclooctatetraene (eq. (29)) using nickel catalysts [84]. This discovery represented a true landmark in transition metal catalysis. 

Wender, I., and P. Pino, eds., Organic Syntheses via Metal Carbonyls, Wiley, Vol. 1, 1968 (cyclic polymerization of acetylenes organic synthesis via alkyl and acyl Co carbonyls reactions of nitrogen compounds). 

A number of metal complexes catalyses specific alkyne polymerizations, giving rise to four-, six- or eight-membered carbocyclic rings. The first work in this area was the nickel-catalysed formation of cyclooctatetraene (40) from acetylene by the group of Reppe ", but since then formation of cyclic systems from acetylenes has been found to be also catalysed by molybdenum, cobalt, iridium and tantalum. ... 

Metathesis-type reactions of acetylenes fall into two categories true metathesis, in which the triple bond is completely broken, and olefin-type metathesis, in which only two of the three bonds are broken. The latter results in polymerization and the formation of cyclic oligomers, especially trimers. The overall reactions are illustrated by eqns. (l)- 3). 

Synthesis of amides and peptides. The simplest compound of this type, dimethylaminopropynal (CH3)aNC=CCHO, is known, but it polymerizes within minutes at room temperature. The thermal stability is improved by introduction of bulky constituents. A whole series of these acetylenes have been prepared of these 1 and a few related compounds have been found useful for synthesis of CO—NH bonds by a push-pull mechanism shown in equation (I). The reaction of 1 with a carboxylic acid proceeds by Michael addition to give a, which rearranges by a cyclic intermediate (b) to the enol ester (2). Reaction of 2 with an amine yields an amide (3) and the water adduct (4) of 1. Yields of amides are in the range 85-95y . This sequence cannot be used for esterification of carboxylic acids. 

Although the polymerization was extensive in most cases, the analysis of the cyclic products clearly shows that in terminal acetylenes nucleophilic reaction leads mainly to exo-methylene-heterocycles, while free radical cyclization leads to unsaturated rings. 

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