Propadiene Compounds

The recent discovery that propadiene can be converted into a lithio compound, which is stable enough at low temperature to allow functionalization, has made it an important starting compound for the synthesis of derivatives. A fortunate circumstance is that allene can be obtained in > 30% yield in an extremely simple... 

Cumulated dienes are those m which one carbon atom is common to two carbon-carbon double bonds The simplest cumulated diene is 1 2 propadiene also called allene and compounds of this class are generally referred to as allenes... 

A mixture of propyne containing 30% of propadiene under a pressure of 3.5 bar was accidentally brought to 95°C at a spot in the storage cylinder. It then detonated. Commercial propyne becomes dangerous at 3.4 bar and at 20°C. It is lowered to 2.1 bar if the compound is heated to 120°C. Some authors think that the stability of the commercial mixture is close to that of ethylene. 

The stereoselective elimination reaction of suitably substituted allylic compounds is a reasonable approach to the construction of the propadiene framework. Central chirality at the allylic position is transferred to axial chirality of the allene by stereoselective /3-elimination (Scheme 4.53). 

In contrast to the limited success with vinyl sulfides as components of [2 + 2] cycloadditions, allenyl sulfides show wide applicability. As illustrated in Scheme 8.91, Lewis acid-catalyzed [2 + 2] cycloadditions of l-trimethylsilyl-l-methylthio-1,2-propadiene (333) with a variety of electron-deficient olefins 336 provide cycloadducts 337 with excellent regioselectivity but with moderate stereoselectivity [175c], Nara-saka and co-workers reported the first Lewis acid-catalyzed asymmetric [2 + 2] cycloaddition of C-l-substituted allenyl sulfides 319 with a,/3-unsaturated compounds 338 using a chiral TADDOL-titanium catalyst. The corresponding cycloadducts 339 were obtained with 88-98% ee, but a low level of trans/cis selectivity (Scheme 8.92) [169,175d[. 

Compound 484 was synthesized by the reaction of malonate with propadiene-tetracarboxylate in the presence of NaH [221],... 

The isomers of the simplest allene, 1,2-propadiene 1, are propyne 2 and cydopro-pene 3 (Scheme 1.2). Their isomerization engergies have been measured and calculated [2-4]. Compound 2 is clearly the most stable isomer, 1 lies 2.1 kj higher and 3 about 22.3 kj. Hence in principle, if reversible, thermodynamics of an equilibrium should favor the alkyne. However, several factors can influence this in two ways, i.e. a change of the relative thermodynamic stability, for example by substituents, or a... 

The presence of the endothermic triply-bonded acetylene (ethyne) group confers explosive instability on a wide range of acetylenic compounds (notably when halogen is also present) and derivatives of metals (and especially of heavy metals) [1], Explosive properties of butadiyne, buten-3-yne, hexatriyne, propyne and propadiene have been reviewed, with 74 references [2], The tendency of higher acetylenes to explosive decomposition may be reduced by dilution with methanol [3], The class includes the separately treated groups ... 

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). 

Allenlc Compounds are derivs of allene or propadiene, also called dtmothylenemethane, CHj C CHa. Allene was probably first prepd in 1865(Ref 2), but the hydrocarbon was not actually identified until 1872 (Ref 3). A rather general method for the prepn of allene by treating 1,2-dihalopropene with Zn dust in ale, was first used in 1838(Ref 4). Many other methods of prepn are known and some of them are described in Ref 5... 

Propadiene. See Allene under Allenic Compounds A133-R... 

Various polar and chemical compounds reportedly are capable of poisoning or deactivating disproportionation catalysts if present in the feed or allowed to contact the catalyst after activation. For example, propylene conversion over cobalt-molybdate catalyst was reduced when 300—2000 ppm of oxygen, water, carbon dioxide, hydrogen sulfide, ethyl sulfide, acetylene, or propadiene... 

Allenes are compounds that contain the C=C=C unit, with two C=C double bonds meeting at a single carbon atom. The parent compound, propadiene, has the common name allene. 

Similar photolysis of 20 in the presence of 1-trimethylsilylpropyne produces a silacyclopropene in 33% yield. In this case, small amounts of two other compounds, l-trimethylsilyl-l-(r-phenyl-2, 2, 2 -trimethyldi-silanyl)propadiene (2% yield) arising from a 1,3-hydrogen shift of the initially formed silacyclopropene and l-bis(trimethylsilyl)phenylsilylpro-pyne (2% yield), are also obtained. Formation of the latter compound can be best explained in terms of another type of photochemical migration in-... 

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). 

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