Propadiene, polymerization

Use of Co2(CO)8 in reactions involving 1,2-propadienes remains for the most part unexplored. It has been reported that terminal 1,2-propadienes react with Co2(CO)8 to form unidentified complexes, and that excess 1,2-propadiene is polymerized concurrently [30]. It has also been reported by Nakamura that a novel dimeric complex 54, in which a carbonyl ligand is connected to the central carbon of 1,2-propadiene, is produced by the reaction of 1,2-propadiene itself with Co2(CO)8 (Scheme 23) [31]. However, unlike the well-known chemistry of alkyne-Co2(CO)6 complexes, these 1,2-propadiene-cobalt carbonyl complexes have rarely been applied in synthetic reactions, probably due to their high activity in catalyzing the polymerization of 1,2-propadienes [32]. 

This would have results in 77 hits from l,2-[propadiene, 1,1,2,2-tetrafluoro-] with a boiling point of —38 °C, to [propane, l,l,l,2,3,3,3-heptafluoro-2-(trifluoromethyl)-] with a boiling point of 0 °C. Out of 77 hits, 49 of them contain elements that include B, Si, N, P, As, O, S, Cl, Br, and I, and perhaps too toxic to be considered as refrigerants seriously. There are 11 hits that are hydrocarbons, such as butane, which would be too flammable to be considered. Perhaps we would eliminate the six hits that have double or triple bonds, as they tend to be less stable and could polymerize. The remaining ones are all hydrofluorocarbons (HECs) without chlorine, and the prime candidates are C2H2E4, C3H3E5, and C4F10. 

Butadiene is available commercially as a liquefied gas underpressure. The polymerization grade has a minimum purity of 99%, with acetylene as an impurity in the parts-per-million (ppm) range. Isobutene, 1-butene, butane and cis-l- and Zrc//7.s-2-butcnc have been detected in pure-grade butadiene (Miller, 1978). Typical specifications for butadiene are purity, > 99.5% inhibitor (/c/V-butylcatecliol). 50-150 ppm impurities (ppm max.) 1,2-butadiene, 20 propadiene, 10 total acetylenes, 20 dimers, 500 isoprene, 10 other C5 compounds, 500 sulfur, 5 peroxides (as H2O2), 5 ammonia, 5 water, 300 carbonyls, 10 nonvolatile residues, 0.05 wt% max. and oxygen in the gas phase, 0.10 vol% max. (Sun Wristers, 1992). Butadiene has been stabilized with hydroquinone, catechol and aliphatic mercaptans (lARC, 1986, 1992). 

C4 Hydrorefining. The main components of typical C4 raw cuts of steam crackers are butanes (4-6%), butenes (40-65%), and 1,3-butadiene (30-50%). Additionally, they contain vinylacetylene and 1-butyne (up to 5%) and also some methylacetylene and propadiene. Selective hydrogenations are applied to transform vinylacetylene to 1,3-butadiene in the C4 raw cut or the acetylenic cut (which is a fraction recovered by solvent extraction containing 20-40% vinylacetylene), and to hydrogenate residual 1,3-butadiene in butene cuts. Hydrogenating vinylacetylene in these cracked products increases 1,3-butadiene recovery ratio and improves purity necessary for polymerization.308... 

Propadiene polymerisation during hydrogenation has been observed to occur, particularly with iron, cobalt and nickel. Over these metals, up to approximately 25% of the propadiene has been observed to polymerise [204], although the chemical identity of the polymeric products was not established. 

These compounds are not used as monomers. Propadiene is a strong catalytic poison in coordination polymerizations, similar to the configurationally related ketene. On the other hand, C02, with a similar bond configuration, can be copolymerized under certain conditions (see Chap. 5, Sect. 5.8). 

Carbon suboxide, C3O2, 0=C=C=C=0 , also called l,2-propadiene-l,3-dione, is an evil-smelling unstable gas, bp +6.8 °C, which is obtained by the dehydration of malonic acid with P4O10 in vacuum at 140-150 °C (equation 6). Carbon suboxide polymerizes readily at room temperature to a yellow solid, and above 100 °C to a ruby-red water-soluble solid. Photolysis of C3O2 gives C2O ( C=C=0 ) as a reactive intermediate, which reacts with alkenes by carbon atom insertion (equation 7). 

Allene (propadiene) is condensed under high vacuum into a 2-litre round-bottomed flask and, after several freeze-and-pump cycles to remove residual oxygen and volatile impurities, the reaction vessel is sealed (internal pressure at room temperature approximately 1000 mb). After 20 hours at 460° C (a high-temperature drying oven) the inner surface of the flask is covered completely by a deep-black, shiny film which can be removed in patches and whose electrical conductivity is 10 S cm. When this film is doped by treating if for 30 minutes with a saturated solution of iodine in carbon tetrachloride its appearance changes to a shiny gold. After solvent removal, the conductivity is found to have increased by a factor of 10. Several other alkynes were polymerized under above conditions and the results of these experiments are summarized in Table 3.7. 

Stereospecific polymerization of substituted conjugated dienes. Stereoregular polytactic polymers have been obtained from a number of substituted dienes, including one optically active 1,3-substituted propadiene, and various 1- or 1,4-substituted butadienes. (R)-penta-2,3-diene has been polymerized by means of 7T-allyl-Ni-iodide to an optically active polymer, to which an interesting stereoregular structure has been attributed (Scheme 26) (224). Some of the stereoregular polymers... 

This test method provides for the determination of butadiene-1,3 purity and impurities such as propane, propylene, isobutane, n-butane, butene-1, isobutylene, propadiene, fra/i5-butene-2, cu-butene-2, butadiene-1,2, pentadiene-1,4, and, methyl, dimethyl, ethyl, and vinyl acetylene in polymerization grade buta ene by gas chromatography. Impurities including butadiene dimer, carbonyls, inhibitor, and residue are measured by appropriate ASTM procedures and the results used to normalize the component distribution obtained by chromatography. 

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