2-Methyl-l,3 butadiene

Monomers for manufacture of butyl mbber are 2-methylpropene [115-11-7] (isobutylene) and 2-methyl-l.3-butadiene [78-79-5] (isoprene) (see Olefins). Polybutenes are copolymers of isobutylene and / -butenes from mixed-C olefin-containing streams. For the production of high mol wt butyl mbber, isobutylene must be of >99.5 wt % purity, and isoprene of >98 wt % purity is used. Water and oxygenated organic compounds iaterfere with the cationic polymerization mechanism, and are minimized by feed purification systems. 

Chonical Designations - Synonym. beta-Methylbivinyl 2-Methyl-l, 3-butadiene Chemical Formula CHj=C(CH3)CH=CHi. 

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. 

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 ... 

How might you use this reaction to prepare 2-methyl-l,3-butadiene, the starting material used in the manufacture of synthetic rubber ... 

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. 

As noted in the Chapter 7 Focus On, rubber is a naturally occurring polymer of isoprene, or 2-methyl-l,3-butadiene. The double bonds of rubber have Z stereochemistry, but gutta-percha, the E isomer of rubber, also occurs naturally. Harder and more brittle than rubber, gutta-percha has a variety of minor applications, including occasional use as the covering on golf balls. 

Reaction of isoprene (2-methyl-l,3-butadiene) with ethyl propenoate gives a mixture of two Diels-Alder adducts. Show the structure of each, and explain whv a mixture is formed. 

See Dienes, above, also 2-Methyl-l,3-butadiene Ozone Nitrogen... 

Methyl-l,3-butadiene CH2C(CH3)CHCH2. A liquid hydrocarbon of boiling point 34 °C. It is regarded as the unit molecule of natural rubber, which is polyisoprene. Synthetic polyisoprene is marketed under a variety of trade names. Isotactic... 

However, it is interesting that the corresponding reaction of 3-methyl-l,2-buta-diene affords the corresponding center attack products allylic chlorides SA/5B and 2-methyl-l,3-butadiene 6, probably owing to the strong stabilization effect of the two methyl groups on the cationic center in 4 [4]. 

Photolytic. Methyl vinyl ketone and methacrolein were reported as major photooxidation products for the reaction of 2-methyl-l,3-butadiene with OH radicals. Formaldehyde, nitrogen dioxide, nitric oxide, and HO2 were reported as minor products (Lloyd et al, 1983). Synthetic air containing gaseous nitrous acid and exposed to artificial sunlight (X = 300-450 nm) photo-oxidized 2-methyl-1,3-butadiene into formaldehyde, methyl nitrate, peroxyacetal nitrate, and a compound tentatively identified as methyl vinyl ketone (Cox et al, 1980). 

Hemellitol, see 1,2,3-Trimethylbenzene Hemimellitene, see 1,2,3-Trimethylbenzene Hemimellitol, see 1,2,3-Trimethylbenzene Hemiterpene, see 2-Methyl-l,3-butadiene Hemostyp, see 1-Butanol HEOD, see Dieldrin HEPT, see Tetraethyl pyrophosphate Heptachlorane, see Heptachlor... 

Methyldivinyl, see 2-Methyl-l,3-butadiene Methylene bichloride, see Methylene chloride Methylenebiphenyl, see Fluorene 2,2 -Methylenebiphenyl, see Fluorene l,r-[Methylenebis(oxy)]bis(2-chloroethane), see Bis(2-... 

UN 1206, see 3,3-Dimethylpentane Heptane UN 1208, see 2,2-Dimethylbutane, 2,3-Dimethylbutane, Hexane, 2-Methylpentane UN 1212, see Isobutyl alcohol UN 1213, see Isobutyl acetate UN 1218, see 2-Methyl-l,3-butadiene UN 1220, see Isopropyl acetate UN 1221, see Isopropylamine UN 1224, see 3-Heptanone, 2-Hexanone, Isophorone UN 1229, see Mesityl oxide UN 1230, see Methanol UN 1231, see Methyl acetate UN 1232, see 2-Butanone UN 1233, see sec-Hexyl acetate... 

Methyl vinyl ketone, see 2-Methyl-l, 3-butadiene Molinate sulfoxide, see Molinate Monobutyl phosphate, see Tributyl phosphate Monobutyl phthalate, see Benzyl butyl phthalate Mono-n-butyl phthalate, see Di-n-butyl phthalate Monobutyl phthalate, see Di-n-butyl phthalate Monochlorobenzidine, see 3,3 -Dichlorobenzidine Monochlorobiphenyl, see Chlorobenzene, PCB-1221, PCB-1254... 

---