Isoprene dioxide

A mutagenic metabolite, isoprene dioxide, was tentatively identified in all examined tissues following exposure to isoprene. It is believed that the formation of reactive epoxides following exposure to isoprene results in tumor induction. 

Mechanisms depending on carbanionic propagating centers for these polymerizations are indicated by various pieces of evidence (1) the nature of the catalysts which are effective, (2) the intense colors that often develop during polymerization, (3) the prompt cessation of sodium-catalyzed polymerization upon the introduction of carbon dioxide and the failure of -butylcatechol to cause inhibition, (4) the conversion of triphenylmethane to triphenylmethylsodium in the zone of polymerization of isoprene under the influence of metallic sodium, (5) the structures of the diene polymers obtained (see Chap. VI), which differ. both from the radical and the cationic polymers, and (6)... 

In one mechanism, Pd° generated by reduction of Pd2+ with formic acid forms hydridoformatopalladium complex 102, which reacts with isoprene to form formato(methylbutenyl)palladium complex 103. Then, insertion of the second molecule of isoprene takes place. Finally, reductive elimination and evolution of carbon dioxide give the dimers ... 

In the second mechanism, coupling of two moles of isoprene on Pd° forms a dimethyloctadienediylpalladium complex (104) which is then reduced by formic acid with evolution of carbon dioxide ... 

The earliest mention of the polymerization of isoprene was also made by Williams in 1860 (33). He noted the formation of a "white, spongy mass" when isoprene was left in a bottle with oxygen. Afterwards G. Bouchardat observed that isoprene could be converted to a sticky mass by the action of either carbon dioxide or cold aqueous hydrochloric acid (34). Tilden in 1882 (35) and independently Wallach in 1887 (36) were the first to prepare elastomers of isoprene, but little else was known of their structures. Gladstone and Hibbert (37)... 

The product 303 from disulfur dichloride and 2,3-dimethylbuta-l,3-diene rearranges spontaneously to the tetrahydrothiophene 304 (equation 159)150. The reaction of liquid sulfur dioxide with conjugated dienes 305 (e.g. butadiene, isoprene) results in cyclic sulfones which dissociate into their components on heating (equation 160)151 152. 

Isoprene, 2,3-dimethylbuta-l,3-diene and other dienes (but not butadiene itself) readily furnish analogous 2,5-dihydroselenophene 1,1-dioxides, e.g. 306, on treatment with selenious acid in chloroform at room temperature (equation 161)153. 

The route for the cyclization was easier to determine than the identification of the very reactive isoprene unit, and was understood in outline by 1960. Studies of labeled compounds detected within 10 min. of 14C-acetate addition to intestinal preparations showed label in squalene, lanosterol, and a further, unidentified ring compound, all with higher specific activities than cholesterol. By 75 min cholesterol was the main labeled compound. Clayton and Bloch then confirmed that lanosterol, previously known from sheep s wool, was converted to cholesterol with the extra three (methyl) carbon atoms being lost as carbon dioxide. 

The gas-phase reactivity of various terpenes has been measured. Stephens and Scott were the first to include two terpenes (pinene and a-phel-landrene) with their study of the relative reactivity of various hydrocar ns. Both monoterpenes showed the high reactivity predicted by their olefinic structure. Conversion of nitric oxide to nitrogen dioxide in e presence of isoprene is at a rate intermediate between those for ethylene and trans-2-butene, and Japar et al, reported rate constants for the a-pinene and terpinolene-ozone reactions. Grimsrud et a/. measured the rate con-... 

For the Diels-Alder reaction between isoprene and methyl acrylate (see fig. 6.4) in supercritical carbon dioxide at 323 K, the solubility parameter of the activated complex was determined in order to study the nature of the complex and the effect of the solvent on the reaction (Ikushima et al., 1994). 

Methylthiophene has been prepared by the dry fusion of a salt of methylsuccinic acid and phosphorus trisulfide. 4 This reaction was later investigated quite completely in respect to ratio of reactants, rate of heating, carbon dioxide atmosphere, and dilution of reactants with sand.6 An excellent technical method for preparing methylthiophenes has been described which involves a vapor-phase reaction of preheated sulfur with pentanes.6 3-Methylthiophene has also been prepared by adding 50% crude isoprene (amylenes) to molten sulfur at 350°.7... 

Isoprene — Fire Hazards Flash Point (deg. F) -65 CC Flammable Limits in Air (%) 2 - 9 Fire Extinguishing Agents Dty chemical, foam, or carbon dioxide Fire Extinguishing Agents Not To Be... 

The reaction of phenol with isoprene dibromide and sodium affords ( )-2-isopropenyl-2,3-dihydrobenzofuran (219) in high yield (78CL253) an additional formylation reaction led to fomannoxin (220), a toxin isolated from Heterobasidion annosum (77TL651). ( )-Tremetone (221) was synthesized by the same route and oxidized by selenium dioxide in acetic anhydride to give ( )-5-acetyl-2-(l-acetoxymethylvinyl)-2,3-dihydrobenzofuran. 

Dichlorothiophene-l,1-dioxide undergoes Diels-AIder reactions with butadiene and isoprene to give mixtures of 115a and 116a and... 

As Barr et al. (2003) pointed out, the importance of such emissions is determined mainly by their impact on the three processes taking place in the atmosphere. The first consists in that such NMHCs as isoprene form in the course of carboxylization in plants and contribute much thereby to the formation of biospheric carbon cycle. The second process is connected with NMHCs exhibiting high chemical activity with respect to such main oxidants as hydroxyl radicals (OH), ozone (03), and nitrate radicals (N03). Reactions with the participation of such components result in the formation of radicals of alkylperoxides (R02), which favor efficient transformation of nitrogen monoxide (NO) into nitrogen dioxide (N02), which favors an increase of ozone concentration in the ABL. Finally, NMHC oxidation leads to the formation of such carbonyl compounds as formaldehyde (HCHO), which stimulates the processes of 03 formation. Finally, the oxidation of monoterpenes and sesquiterpenes results in the intensive formation of fine carbon aerosol with a particle diameter of <0.4 pm... 

Table II. Prediction of the Activation volume of the Diels-Alder reaction between isoprene and maleic anhydride in supercritical carbon dioxide at 35 C...

The best-studied were two film systems the chlorination reaction in a solid solution of Cl2 in BC and the copolymerization reaction of sulfur dioxide with isoprene. Under the above-described conditions of cooling, the liquid films in both systems vitrified. 

The molecular weights for water, carbon dioxide, methane and isoprene are 18,44,16 and 68, respectively. 

The numerical value of the molecular weight expressed in grams (e.g. 16 g in the case of methane) is often used to represent the quantity of a substance. The gram molecular weight comprises the same number of molecules of any substance (18 g of water, 44 g of carbon dioxide or 68 g of isoprene contain the same number of molecules of the respective compounds). This number... 

Further calculations were performed on 2,3-diaza-1,3-butadiene with different heterodienophiles such as ethene, formaldehyde and formaldimine showing the same exo oxygen or nitrogen lone pair preference [49] as well as on the nitro-soethene/ethene system [50]. Recently, ab initio studies have also been performed for the Lewis acid catalysed hetero Diels-Alder reaction of isoprene and sulfur dioxide by Sordo [51]. 

Several ab initio studies of these reactions including an investigation of Lewis acid catalysis and solvent effects have been published by Sordo et al. [464-466]. Their results concerning regio- and stereoselectivity in the hetero Diels-Alder reactions of sulfur dioxide to isoprene are in good agreement with the experimental findings mentioned above. 

Sterols are synthesized in nature from squalene and, therefore, ultimately from isoprene. Mevalonic acid is the immediate precursor of the isoprene unit, and the carboxylic acid group is lost as carbon dioxide when two mevalonic acid molecules combine head to tail. Thus, if the a carbon of mevalonic acid is labeled, then this carbon is always adjacent to the carbon bearing a side-chain methyl group. Examination of the way in which six isoprene units are linked in squalene (Example 6.2) shows that they are not all linked head to tail there is a point of symmetry in the structure of squalene (marked in the structure below). At this point a set of three isoprene units, linked head to tail, is joined head-to-head to a similar set of three isoprene units, to give the labeling pattern shown. 

Sulphur Dioxide. Benzene. Isoprene. Iron Carbonyl. 

Details of the preparation of methyl (-)-cis-chrysanthemate from (+)-car-3-ene have appeared (Vol. 5, p. 15 is misleading).159 Both ( )-cis- and (+)-trans-chrysanthemic acids are again reported from (+)-car-3-ene via ozonolysis 160 this work is very similar to that reported (Vol. 5, p. 15) by Sukh Dev and illustrates the lamentable delay from receipt to publication in some journals. The decomposition of ethyl diazoacetate in 2,5-dimethylhexa-2,4-diene in the presence of the chiral copper complex (72) leads to cis- and frvms-chrysanthemic acids in 60—70% optical yield the degree of asymmetric induction is dependent upon the steric bulk of R1 and R2 in (72).161 cis-Chrysanthemic acid has also been prepared from 3,3-dimethylcyclopropene, isoprene, and 2-methylpropenylmagnesium bromide followed by treatment with carbon dioxide.162... 

Some diverse VOCs (halocarbons, isoprene (CH2C(CH3) CH2CH2), monoterpenes, ethanol, and methyl tert-butyl ether, (CHslsCOCHs)) were found to be photooxidized efficiently on solid aerosols. Solid photocatalyst particles, such as Ti02, ZnO, and Fe20s, were here of special importance, but the VOC oxidation was photoassisted also by dessert sand, volcanic ash, or even by chalk particles (23-25). Similarly, sulfur dioxide was found to... 

Theoretical calculations have also permitted one to understand the simultaneous increase of reactivity and selectivity in Lewis acid catalyzed Diels-Alder reactions . This has been traditionally interpreted by frontier orbital considerations through the destabilization of the dienophile s LUMO and the increase in the asymmetry of molecular orbital coefficients produced by the catalyst. Birney and Houk have correctly reproduced, at the RHF/3-21G level, the lowering of the energy barrier and the increase in the endo selectivity for the reaction between acrolein and butadiene catalyzed by BH3. They have shown that the catalytic effect leads to a more asynchronous mechanism, in which the transition state stmcture presents a large zwitterionic character. Similar results have been recently obtained, at several ab initio levels, for the reaction between sulfur dioxide and isoprene. ... 

ISOPRENE CYCLIC SULFONE (Thiophene, 2,5-dihydro-3-methyl-, 1-dioxide)... 

A 600-ml. steel reaction vessel (Note 1) is precooled before loading by filling it between one fourth and one half full of methanol and Dry Ice. After removal of the methanol and Dry Ice, the autoclave is charged with 120 g. (176 ml., 1.76 moles) of isoprene (Note 2), 113 g. (80 ml, 1.76 moles) of liquid sulfur dioxide, 88 ml. of methanol, and 4 g. of hydroquinone. The vessel is sealed, heated slowly to 85°, and maintained at that temperature for 4 hours. It is then cooled, the sulfone removed, the bomb rinsed with methanol, and the combined product and washings are treated hot with 5 g. of Norite. The filtered solution is concentrated to a volume of 250-300 ml., and the sulfone is allowed to crystallize. The material is filtered and washed with 50 ml. of cold methanol. Recrystallization from methanol (20 ml. per 25 g. of sulfone) yields 140-150 g. of thick, colorless plates. Concentration of the mother liquors raises the total yield to 182-191 g. (78-82%) (Note 3), melting at 63.5-64° (Note 4). 

Isoprene cyclic sulfone has been prepared only from isoprene and sulfur dioxide. ... 

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