Unsaturated system butadiene

The epoxidations of propylene and isobutylene with peroxyformic acid proceed in a concerted way via slightly unsymmetrical Markovnikov-type transition stmctnres where the differences in the bond distances between the donble-bond carbons and the spiro oxygen are only 0.021 and 0.044 A at the QCISD/6-31G level. In contrast, the more polarizable natnre of the carbon-carbon double bond of o ,/ -unsaturated systems results in a highly nnsymmetrical transition structure for the epoxidation of 1,3-butadiene with an order-of-magnitnde difference in the carbon-oxygen bond distances of 0.305 A at the QCISD/6-31G level. A highly unsymmetrical transition structure has been also found for the epoxidation of acrylonitrile. 

Epoxidations of methyl-substituted alkenes and ,/j-unsaturated systems as 1,3-butadiene and acrylonitrile with peroxyformic acid follow a concerted asynchronous pathway. 

Immediately after the discovery of the cyclodecadiene synthesis by the co-oligomerization of butadiene and ethylene, the question of whether other unsaturated systems could be used in place of ethylene was investigated. Of the many variations on this theme which have been studied (92, 93), we will limit ourselves to discussing the co-oligomerization of 2-butyne, since this system became a model for all the other combinations. 

The more interesting isobutene copolymers described in Sect. A.2. contain as repeat units 1,4-di-substituted-l, 3-dienes (Table 2). The common feature of these copolymers is the prevalent trans-trans configuration of the unsaturated system (infrared band at 985 cm ), because the infrared band at 970 cm , due to the ds-trans dienic system, is very weak Since it is well known that Diels-Alder reactions of 1,4-trans-trans substituted derivatives of 13-butadiene are more humred than those of cis-trans isomers , we studied Diels-Alder reactions of the copolymers of Table 2 under mild and other conditions. Namely ... 

In molecules, the conjugation of unsaturated systems, i.e., possessing molecular orbitals built up from Ti-atomic orbitals (2p-orbitals in hydrocarbons benzene), is, in general, a planarity factor (e.g., butadiene). Nevertheless, steric hindering can oppose this tendency to make a planar system (e.g., biphenyl, cyclooctatetraen ). The same phenomena are encountered in crystals. 

As an example of the utility of this model, consider the norbomadiene molecule (see Fig. 12-7a). According to our understanding of unsaturated systems, the double bonds in this molecule should behave like isolated ethylene double bonds and not like the conjugated bonds of butadiene. But these bonds are at an orientation and proximity allowing significant overlap between AO lobes beneath the molecule. If we treat this system with our two-level model, the unperturbed MOs are the bonding... 

Table I gives the results of the polymerization of the unsaturated epoxides butadiene monoepoxide (BDME) and SO (entries 4 and 5, respectively). Surprisingly, BDME does not form any polymer but instead slowly converts exclusively to the cycloaddition by-product. SO, however, undergoes copolymerization but with low selectivity only 35% of the epoxide is converted to polycarbonate. Increasing the CO2 pressure in both systems does not improve the selectivity to polymer.

Protonated Amino Radicals. The reac.tion of hydroxyl amine with TiCl, in aqueous, acidic methanol results in the formation of the simplest protonated amino radical, NH,T. This radical added readily to butadiene and to simple olefins to form products which were the result of coupling of the intermediate B-aminoalkyl radicals ( ). The addition reactions of protonated di-alkylamino radicals were described in a series of elegant papers by Neale and his co-workers (5-10). The radicals were generated from the appropriate N-chloroamines in presence of the unsaturated system. The most effective acid solvent combination was found to be 4M sulfuric acid in glacial acetic acid, but other acid/solvent combinations were also used. The reactions proceeded by chain mechanisms, which were initiated by light or by... 

In this section, selected results for other polymers will be presented. It will be demonstrated that our method is applicable to a wide range of systems belonging to different structural classes, including the simplest polymer poly (ethylene) (PE), a bisubstituted polyolefine (poly (isobutylene), PIB), unsaturated systems (poly(butadiene), PBD and poly(isoprene), PIP), polymers with hetero atoms (poly(vinyl chloride), PVC), and extended sidegroups (poly(methyl methacrylate), PMMA). 

Aryl or alkenyl halides attack the central carbon of the allene system in the 2,3-butadien-l-ol 120 to form the 7r-allyl intermediate 121, which undergoes elimination reaction to afford the o,/3-unsaturated ketone 122 or aldehyde. The reaction proceeds smoothly in DMSO using dppe as a ligandflOl]. 

An elegant example of a system investigated by UV-visible spectroscopy is the copolymer of styrene (molecule 1) and 1-chloro-l, 3-butadiene (molecule 2). These molecules quantitatively degrade with the loss of HCl upon heating in base solution. This restores 1,3-unsaturation to the butadiene repeat unit ... 

Diels-Alder Reaction. In 1928, Diels and Alder discovered that 1,3-unsaturated organic compounds reacted with quinoid systems to give partially hydrogenated, cycHc compounds. In the course of their work, they found that 1 mol of 1,4-naphthoquinone [130-15-4] reacted readily with 1 mol of 1,3-butadiene [106-99-0] to give a partially hydrogenated anthraquinone (11) l,4,4a,9a-tetrahydro-9,10-anthracenedione [56136-14-2] which, on oxidation with chromic oxide, produced anthraquinone (43) ... 

Telomerization Reactions. Butadiene can react readily with a number of chain-transfer agents to undergo telomerization reactions. The more often studied reagents are carbon dioxide (167—178), water (179—181), ammonia (182), alcohols (183—185), amines (186), acetic acid (187), water and CO2 (188), ammonia and CO2 (189), epoxide and CO2 (190), mercaptans (191), and other systems (171). These reactions have been widely studied and used in making unsaturated lactones, alcohols, amines, ethers, esters, and many other compounds. 

The presence of acetylenic impurities or butadiene in the system can also give rise to unsaturation in the polymer backbone. 

A modified latex composition contains a phosphorus surface group. Such a latex is formed by emulsion polymerization of unsaturated synthetic monomers in the presence of a phosponate or a phosphate which is intimately bound to the surface of the latex. Thus, a modified latex containing 46% solids was prepared by emulsion polymerization of butadiene, styrene, acrylic acid-styrene seed latex, and a phosphonate comonomer in H20 in the presence of phosphated alkylphenol ethoxylate at 90°C. The modified latex is useful as a coating for substrates and as a binder in aqueous systems containing inorganic fillers employed in paper coatings, carpet backings, and wallboards [119]. 

Complexes 17-19 can be written in one valence structure as a, /3-unsaturated carbonyl compounds in which the carbonyl oxygen atom is coordinated to a BF2(OR) Lewis acid. The C=C double bonds of such organic systems are activated toward certain reactions, like Diels-Alder additions, and complexes 17-19 show similar chemistry. Complexes 17 and 18 undergo Diels-Alder additions with isoprene, 2,3-dimethyl-1,3-butadiene, tram-2-methyl-l,3-pentadiene, and cyclopentadiene to give Diels-Alder products 20-23 as shown in Scheme 1 for complex 17 (32). Compounds 20-23 are prepared in crude product yields of 75-98% and are isolated as analytically pure solids in yields of 16-66%. The X-ray structure of the isoprene product 20 has been determined and the ORTEP diagram (shown in Fig. 3) reveals the regiochemistry of the Diels-Alder addition. The C-14=C-15 double bond distance is 1.327(4) A, and the... 

A typical reaction is the formation of 2-substituted 3,6-divinyltetrahydro-pyranes (108) by the reaction of butadiene with aldehydes (97-100). In this reaction, unsaturated noncyclized alcohols 109 are also formed. The selectivity to the pyranes and alcohols can be controlled by the ratio of Pd and PPh3 in the catalyst system. When the ratio was higher than 3, pyranes were formed exclusively. On the other hand, with the lower ratio of Pd and PPh3, the unsaturated alcohols were formed as the main product. 

This field is still active today numerous recent patents [46, 63-89] and several reports [90-92] have detailed the efficiency of such types of systems for the hydrogenation of unsaturated polymers resulting from the polymerization of dienes (butadiene, isoprene, 1,3-cyclohexadiene) or the co-polymerization of dienes and styrenes (block co-polymers of butadiene and styrene SB, SBS, SBSB polymers). 

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