Isoprene 1,3-Butadiene, 2-methyl

Isoprene 1,3-Butadiene, 2-methyl- Palmitic acid Hexadecanoic acid... 

Gutta percha is a natural polymer of isoprene (3-methyl-l,3-butadiene) in which the configuration around each double bond is trans. It is hard and horny and has the following formula ... 

Dimerization of Isoprene. Isoprene is becoming an increasingly important raw material for the production of terpenes. For example, myrcene (7) can be produced by the dimerization of isoprene (2-methyl-1,3-butadiene) (42—44) and myrcene is very useful for synthesizing a number of oxygenated terpenes important in the flavor and fragrance industry. 

Isoprene (2-methyl-1,3-butadiene) can be telomerized in diethylamine with / -butyUithium as the catalyst to a mixture of A/,N-diethylneryl- and geranylamines. Oxidation of the amines with hydrogen peroxide gives the amine oxides, which, by the Meisenheimer rearrangement and subsequent pyrolysis, produce linalool in an overall yield of about 70% (127—129). 

Benzoic acid 140 C,H,0, Isoprene 2-Methyl-1,3-butadiene 44 C5H8... 

FIGURE 8.16 The structure of isoprene (2-methyl-l,3-butadiene) and the structure of head-to-tail and tail-to-tail linkages. Isoprene itself can be formed by distillation of natural rubber, a linear head-to-tail polymer of isoprene units. 

HCl addition to unsymmetrical dienes can be even more complicated. For example, HCl addition to isoprene (2-methyl-1,3-butadiene) might give four different 1,2-addition products and three different 1,4-addition products. 

Condensation of isoprene (2-methyl-1,3-butadiene) either leads to a polymer in which all double bonds are trans ( natural rubber ) or in which they are cis (gutta-percha). 

Isoprene (2-methyl-1,3-butadiene) is a colorless liquid, soluble in alcohol but not in water. Its boiling temperature is 34.1 °C. 

Unlike polyethylene and other simple aikene polymers, natural rubber is a polymer of a diene, isoprene (2-methyl-l,3-butadiene). The polymerization takes place by addition of isoprene monomer units to the growing chain, leading to formation of a polymer that still contains double bonds spaced regularly at four-carbon intervals. As the following structure shows, these double bonds have Z stereochemistry ... 

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. 

Electrophilic addition of Br2 to isoprene (2-methyl-l,3-butadiene) yields the following product mixture ... 

Natural rubber may be considered as a linear polymer of isoprene (2-methyl-1, 3-butadiene) and is also called as cis -1,4-polyisoprene. 

Formally, isoprenoids are derived from a single common building block, isoprene (2-methyl-l,3-butadiene), a methyl-branched compound with five C atoms. Activated isoprene, isopentenyl diphosphate, is used by plants and animals to biosynthesize linear and cyclic oligomers and polymers. For the isoprenoids listed here—which only represent a small selection—the number of isoprene units (1) is shown. 

The polymerization of conjugated dienes is of special interest. Two different types of polymerization reactions occur with 1,3-dienes such as 1,3-butadiene, isoprene(2-methyl-... 

Penultimate effects have been observed for many comonomer pairs. Among these are the radical copolymerizations of styrene-fumaronitrile, styrene-diethyl fumarate, ethyl methacrylate-styrene, methyl methacrylate l-vinylpyridine, methyl acrylate-1,3-butadiene, methyl methacrylate-methyl acrylate, styrene-dimethyl itaconate, hexafluoroisobutylene-vinyl acetate, 2,4-dicyano-l-butene-isoprene, and other comonomer pairs [Barb, 1953 Brown and Fujimori, 1987 Buback et al., 2001 Burke et al., 1994a,b, 1995 Cowie et al., 1990 Davis et al., 1990 Fordyce and Ham, 1951 Fukuda et al., 2002 Guyot and Guillot, 1967 Hecht and Ojha, 1969 Hill et al., 1982, 1985 Ma et al., 2001 Motoc et al., 1978 Natansohn et al., 1978 Prementine and Tirrell, 1987 Rounsefell and Pittman, 1979 Van Der Meer et al., 1979 Wu et al., 1990 Yee et al., 2001 Zetterlund et al., 2002]. Although ionic copolymerizations have not been as extensively studied, penultimate effects have been found in some cases. Thus in the anionic polymerization of styrene t-vinylpyri-dine, 4-vinylpyridine adds faster to chains ending in 4-vinylpyridine if the penultimate unit is styrene [Lee et al., 1963]. 

Natural rubber (Hevea brasiliensis) is as-poly-2-methyl-1,4-butadiene, and gutta-percha (Palaquium oblongi/olium) and balata (Minusops globosa) are polymers of isoprene (2-methyl-1,4-butadiene) with trans configurations. Neoprene is a polymer of 2-chloro-1,3-butadiene (chloroprene). 

Caution. Isoprene (2-methyl-1,4-butadiene) is a low-boiling (bp 34°C), flammable liquid which is suspected to be carcinogenic. Isoprene must therefore be handled in a well-ventilated hood and care must be taken to avoid overpressurizing glass containers. 

A number of plants and some trees contain a white, milky liquid that is released when the stem or bark is cut. The liquid is called a latex from the Latin meaning liquid. Common sources include dandelions, milkweed, goldenrod, and potted rubber plants. Rubber trees, from which substantial quantities of latex can be harvested, grow in some tropical areas of the world. A major constituent of this latex is a homopolymer of isoprene (2-methyl-1,3-butadiene), called polyisoprene. Polyisoprene, as well as a number of other elastomers, has a carbon-carbon double bond in every repeat unit. The properties of polyisoprene are the result of the presence of these double bonds. Just as stereochemistry plays a critical role in both proteins and polysaccharides, we will see its importance here. 

Benzoic acid 140 C,He02 Isoprene 2-Methyl- 1,3-butadiene 44 C5H3... 

Isoprene (2-Methyl-l, 3-butadiene) Peroxide, Polymeric. (No formula given). Resinbus substance decomp slightly above 0°. Reported in Ref 2 as a highly explosive substance. May be prepd by the. reaction of isoprene with molecular oxygen... 

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