Butadiene and Isoprene

3-Butadiene and Isoprene. Butane may be transformed directly to 1,3-buta-diene on chromia-alumina (Houdry Catadiene process).144-146 172 The most significant condition is operation under subatmospheric pressure (0.1-0.4 atm), which provides an improved yield of 1,3-butadiene. Operating at about 600°C, the process produces a mixture of butenes and 1,3-butadiene. After the removal of the latter, the remaining butane-butenes mixture is mixed with fresh butane and recycled. Extensive coke formation requires regeneration of the catalyst after a few minutes of operation. 1,3-Butadiene yields up to 63% are obtained at a conversion level of 30 40%. 

Much higher butadiene yields may be obtained in a two-step process developed by Phillips in which butane is first converted to butenes with the chromia-alumina catalyst, and the butenes are then further dehydrogenated to 1,3-butadiene.144 173 The butene selectivity in the first step is about 80-85% (600°C, atmospheric pressure). The butenes recovered from the reaction mixture undergo further dehydrogenation in the presence of excess steam (10-20 mol) over a mixed 

Similar to the processes used in the manufacture of 1,3-butadiene, isoprene can be prepared from isopentane, isoamylenes, or a mixed isoC5 feed.172 176 177 The Shell process177 dehydrogenates isoamylenes to isoprene in the presence of steam with 85% selectivity at 35% conversion, over a Fe203—K2CO3—Cr2Oj catalyst at 600°C. 

Oxo-D process (Petro-Tex),180 and a technology developed by BP applying a tin-antimony oxide catalyst.181,182 The Phillips technology produces 1,3-butadiene with 88-92% selectivity at 75-80% conversion.179 A new catalyst used in the Nippon Zeon process offers improved process characteristics.183 

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Chemical Uses. In Europe, products such as ethylene, acetaldehyde, acetic acid, acetone, butadiene, and isoprene have been manufactured from acetylene at one time. Wartime shortages or raw material restrictions were the basis for the choice of process. Coking coal was readily available in Europe and acetylene was easily accessible via calcium carbide. 

Commercially, anionic polymerization is limited to three monomers styrene, butadiene, and isoprene [78-79-5], therefore only two useful A—B—A block copolymers, S—B—S and S—I—S, can be produced direcdy. In both cases, the elastomer segments contain double bonds which are reactive and limit the stabhity of the product. To improve stabhity, the polybutadiene mid-segment can be polymerized as a random mixture of two stmctural forms, the 1,4 and 1,2 isomers, by addition of an inert polar material to the polymerization solvent ethers and amines have been suggested for this purpose (46). Upon hydrogenation, these isomers give a copolymer of ethylene and butylene. 

The refined grade s fastest growing use is as a commercial extraction solvent and reaction medium. Other uses are as a solvent for radical-free copolymerization of maleic anhydride and an alkyl vinyl ether, and as a solvent for the polymerization of butadiene and isoprene usiag lithium alkyls as catalyst. Other laboratory appHcations include use as a solvent for Grignard reagents, and also for phase-transfer catalysts. 

Troublesome amounts of C and Q acetylenes are also produced in cracking. In the butadiene and isoprene recovery processes, the acetylenes in the feed are either hydrogenated, polymerized, or extracted and burned. Acetylene hydrogenation catalyst types include palladium on alumina, and some non-noble metals. 

Copolymerization of methacrylic acid with butadiene and isoprene was photoinitiated by Mn2(CO)io without any halide catalyst [28,29]. The po]ymerization system is accompanied by a Dieis-Alder additive. Cross propagation reaction was promoted by adding trieth-y]aluminum chioride. 

The chemical modification of PS with epichlorohydrin (EC), maleic anhydride (MA), acetic anhydride (AA), butadiene, and isoprene in the presence of cationic catalysis such as AICI3, FeCU, BF3 0(C2H5)2, ZnCb, TiCL, and SnCU, have been extensively studied under various conditions for the last 15 years. We have also studied their kinetics, physico-mechanical, thermal, and dielec-... 

In the chemical modification of PS with MA, AA, EC, butadiene, and isoprene using cationic catalysis caused either destruction of macromolecules or the binding of functional groups to the aromatic ring. 

When the quantity of olefinic increased from 2.5-10.0 mol% in the alkenylated PS with butadiene and isoprene, the following advantages were achieved resistance to strike, 21.0-39.0 KJ/m ) elasticity. 

When polymerizing dienes for synthetic rubber production, coordination catalysts are used to direct the reaction to yield predominantly 1,4-addition polymers. Chapter 11 discusses addition polymerization. The following reviews some of the physical and chemical properties of butadiene and isoprene. 

Diolefms are hydrocarbon compounds that have two double bonds. Conjugated diolefins have two double bonds separated by one single bond. Due to conjugation, these compounds are more stable than mono-olefms and diolefms with isolated double bonds. Conjugated diolefins also have different reactivities than monoolefins. The most important industrial diolefmic hydrocarbons are butadiene and isoprene. 

Simple conjugated dienes used in polymer synthesis include 1,3-butadiene, chloroprene (Z-chloro-l -butadiene), and isoprene (2-methyl-l,3-butadiene). Isoprene has been prepared industrially by several methods, including the acid-catalyzed double dehydration of S-methyl-l/S-butanediol. 

Copolymers of AN with diene monomers and, in particular, with butadiene and isoprene, deserve special attention. These copolymers with a predominating content of monomeric units of dienes are known to have been produced in the form of rubbers for a long time and are finding a broad application in various branches of technology. 

Emulsion polymerization is the most important process for production of elastic polymers based on butadiene. Copolymers of butadiene with styrene and acrylonitrile have attained particular significance. Polymerized 2-chlorobutadiene is known as chloroprene rubber. Emulsion polymerization provides the advantage of running a low viscosity during the entire time of polymerization. Hence the temperature can easily be controlled. The polymerizate is formed as a latex similar to natural rubber latex. In this way the production of mixed lattices is relieved. The temperature of polymerization is usually 50°C. Low-temperature polymerization is carried out by the help of redox systems at a temperature of 5°C. This kind of polymerization leads to a higher amount of desired trans-1,4 structures instead of cis-1,4 structures. Chloroprene rubber from poly-2-chlorbutadiene is equally formed by emulsion polymerization. Chloroprene polymerizes considerably more rapidly than butadiene and isoprene. Especially in low-temperature polymerization emulsifiers must show good solubility and... 

The distinction between the rates of homo- and copolymerization apparently is misapprehended by some workers. For example, a recent review 141) discusses the results of McGrath 142) who reported butadiene to be more reactive in polymerization in hexane than isoprene, whether with respect to lithium polybutadiene or polyisoprene, although the homopropagation of lithium polyisoprene in hexane was found to be faster than of polybutadiene. The miscomprehension led to the erroneous statement14l) McGrath 142) results regarding the rate constants for butadiene and isoprene place in clear perspective the bizarre assertion 140) that butadiene will be twice as reactive as isoprene (in anionic co-polymerization). 

Dienes (butadiene and isoprene) may yield polymers with high 1,4 unit contents 4S 49), when the process is initiated with butyllithium in nonpolar solvents. Small amounts of polar additives suppress steric control6). 

Many of these cobalt complexes will catalyze the reduction of organic compounds by borohydride, hydrazine, thiols, etc. Cobalt cyanide complexes will catalyze the reduction of a,j8-unsaturated acids by borohydride (105) DMG complexes the reduction of butadiene and isoprene by borohydride, but not by H2 (124) Co(II) salen, the reduction of CHCI3 and CH3CCI3 to the dichloro compounds by borohydride (116) and cyanocobalamin, the selective reduction of -CCI2- by borohydride to -CHCl- in compounds such as aldrin, isodrin, dieldrin, and endrin without... 

Propagation constants for butadiene and isoprene were determined from rate of polymerization per particle in emulsion polymerization. 

Addihon of primary and secondary amines to 1,3-butadiene and isoprene at 0 to 180°C over solid bases such as MgO, CaO, SrO, LajOj, Th02, and ZrOj has also been studied. CaO exhibits the highest achvity, while ZrOj is inachve. MejNH is the most reactive amine, giving primarily the 1,4-addihon product which undergoes iso-merizahon to the enamine N,N-dimethyl-l-butenylamine. It has been proposed that addihon of amines to 1,3-dienes on basic catalysts proceeds via aminoallyl carban-ion intermediates which result from addihon of amide ions to the dienes [169, 170]. 

Butadiene and isoprene give rise to mixtures of what are usually called telom-ers, namely 1 1 telomers between the amine and the 1,3-diene (trae hydroamination products), 1 2 telomers and even higher homologs together with oligomers of the diene as exemplified in Eq. (4.41). 

In fact, catalytic systems which effect solely the hydroamination of 1,3-butadiene and isoprene are rare and usually specific to the diene and to the amine. Thus morpholine adds to 1,3-butadiene in the presence of RhCf.lHjO to give a mixture of 1,2-(Markoviiikov) and 1,4-hydroamination products in good overall yield (Eq. 4.42) [171,172). 

Conjugated dienes are among the most significant building blocks both in laboratories and in the chemical industry [1], Especially, 1,3-butadiene and isoprene are key feedstocks for the manufacture of polymers and fine chemicals. Since the discovery of the Ziegler-Natta catalyst for the polymerizations of ethylene and propylene, the powerful features of transition metal catalysis has been widely recognized, and studies in this field have been pursued very actively [2-7]. 

Some of the important results for butadiene are summarized in Table XV. The most efficient system identified was for cis-polymerization using 1 1 molar ratio of (XXI) with trifluoroacetic acid. An even more remarkable observation, however, was the almost complete suppression of the cis-polymerization in favor of trans-polymerization processes on addition of triphenylphosphite to the mixture of (XXI) and trifluoroacetic acid. More recently (89), Durand and Dawans have synthesized the trifluoroacetates (XXIII) where R = H and C9H15, and these were shown to be catalytically active as well as exhibiting some specificity in polymerization of butadiene and isoprene. 

Ionic Polymerization. Ionic polymerizations, especially cationic polymerizations, are not as well understood as radical polymerizations because of experimental difficulties involved in their study. The nature of the reaction media is not always clear since heterogeneous initiators are often involved. Further, it is much more difficult to obtain reproducible data because ionic polymerizations proceed at very fast rates and are highly sensitive to small concentrations of impurities and adventitious materials. Butyl rubber, a polymer of isobutene and isoprene, is produced commercially by cationic polymerization. Anionic polymerization is used for various polymerizations of 1,3-butadiene and isoprene. 

Anionic polymerization can be initiated by a variety of anionic sources such as metal alkoxides, aryls, and alkyls. Alkyllithium initiators are among the most useful, being employed commercially in the polymerization of 1,3-butadiene and isoprene, due to their solubility in hydrocarbon solvents. Initiation involves addition of alkyl anion to monomer... 

As to the first route, we started in 1969 (1) in investigating unconventional transition metal complexes of the 5 and 4f block elements of periodic table, e.g., actinides and lanthanides as catalysts for the polymerization of dienes (butadiene and isoprene) with an extremely high cis content. Even a small increase of cistacticity in the vicinity of 100% has an important effect on crystallization and consequently on elastomer processability and properties (2). The f-block elements have unique electronic and stereochemical characteristics and give the possibility of a participation of the f-electrons in the metal ligand bond. 

A common feature of catalysts based on 4 and 5f block elements is that of being able to polymerize both butadiene and isoprene to highly cistactic polymers, independently of the ligands involved. Butadiene, in particular, can reach a cistacticity as high as 99% with uranium based catalysts (3) and cistacticity of > 98% with neodymium based catalysts (4). This high tacticity does not change with the ligand nature (Fig. 1) in contrast to conventional catalysts based on 3-d block elements. A second feature of f-block catalysts is that the cis content of polymer is scarcely... 

This gives rise to dual valency state (+3 and +4) (23). As to the activity of lanthanide based catalysts we confirm a singular behavior that has been already reported by Chinese scientists (22) and that is summarized in Fig. 9. The activity of lanthanides in promoting the polymerization of butadiene and isoprene shows a large maximum centered on neodymium, the only exception being represented by samarium and europium that are not active, reasonably because they are reduced to bivalent state by aluminum alkyls, as pointed out by Tse-chuan and associates (22). 

Hydrogenated Linear Block Copolymers of Butadiene and Isoprene... 

Reactions of conjugated 1,3-dienes, mainly butadiene and isoprene, catalyzed by transition metal complexes to form a number of linear and cyclic oligomers and telomers, are one of the most fascinating fields of research in the last 20 years. Extensive studies from academic and in-... 

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