Hexenes, addition

Water-soluble l,3-bis(di(hydroxyalkyl)phosphino)propane derivatives were thoroughly studied as components of Pd-catalysts for CO/ethene (or other a-olefins) copolymerization and for the terpolymerization of CO and ethene with various a-olefins in aqueous solution (Scheme 7.17) [59], The ligands with long hydroxyalkyl chains consistently gave catalysts with higher activity than sulfonated DPPP and this was even more expressed in copolymerization of CO with a-olefins other than ethene (e.g. propene or 1-hexene). Addition of anionic surfactants, such as dodecyl sulfate (potassium salt) resulted in about doubling the productivity of the CO/ethene copolymerization in a water/methanol (30/2) solvent (1.7 kg vs. 0.9 kg copolymer (g Pd)" h" under conditions of [59]) probably due to the concentration of the cationic Pd-catalyst at the interphase region or around the micelles which solubilize the reactants and products. Unfortunately under such conditions stable emulsions are formed which prevent the re-use... 

Hexene addition also caused the appearance of significant amounts of internal unsaturation when the catalyst was Cr/AIPO4. Shown in Table 52, this result suggests that increased 2,1-insertion occurs, followed by elimination (Scheme 34C). Phillips catalysts are not known for chain walking, and therefore 2,1-insertion probably stops polymerization until the chain can be eliminated. This pathway may account for the fact that 1-hexene tends to inhibit the activity of Cr / AIPO4 but not that of Cr/silica. 

Alumina can be treated with phosphoric acid to produce the same effect, and as more phosphate is added, the MI sensitivity grows. Even silica can be impregnated with phosphoric acid, or a phosphate, to increase its sensitivity [332,640,641], Figure 165 shows the extreme change in polymer MW distribution that can be caused by 1-hexene addition to the reactor. There is a strong shift to the low-MW region. The degree of the shift is dependent on the amount of phosphate in the support. The catalyst with a P/Al atomic ratio of 0.9 produced a major shift, whereas the shift from the catalyst with a P/Al ratio of 0.2 was more like that of Cr/silica. 

Scheme 2.2.9 demonstrates these different options for a Ce-carbocation that carries its positive charge at carbon number 3 (C3). While the reaction with the nucleophile HO leads to 3-hexanol, abstraction of a proton will produce 3-hexene. Addition of ethylene or any alkene would result in an addition reaction forming a new, very reactive carbocation. As a consequence, cationic polymerization would... 

SASOL. SASOL, South Africa, has constmcted a plant to recover 50,000 tons each of 1-pentene and 1-hexene by extractive distillation from Fischer-Tropsch hydrocarbons produced from coal-based synthesis gas. The company is marketing both products primarily as comonomers for LLDPE and HDPE (see Olefin polymers). Although there is still no developed market for 1-pentene in the mid-1990s, the 1-hexene market is well estabhshed. The Fischer-Tropsch technology produces a geometric carbon-number distribution of various odd and even, linear, branched, and alpha and internal olefins however, with additional investment, other odd and even carbon numbers can also be recovered. The Fischer-Tropsch plants were originally constmcted to produce gasoline and other hydrocarbon fuels to fill the lack of petroleum resources in South Africa. 

In laser-impulse experiments with chlorophenyldiazirine the carbene could be observed by UV spectroscopy. On addition of defined amounts of alkene the rate of cyclopropanation was measured directly. The rate constants with various alkenes were (lO moF s ) 1-hexene, 1.3 ( )-2-pentene, 34 2-methyl-2-butene, 77 2,3-dimethyl-2-butene, 130 (80JA7576>. 

A careful study of the photoinitiated addition of HBr to 1-hexene established the following facts. (1) The quantum yield is 400, (2) The products are 1-bromohexane, 2-bromohexane, and 3-bromohexane. The amounts of 2- and 3-bromohexane formed are always nearly identical and increase from about 8% each at 4°C to about 22% at 63°C, (3) During the course of the reaction, small amounts of 2-hexene can be detected. Write a mechanism that could accommodate all these facts. 

Two different routes to PCs via bicyclo[3.1.0]hexane intermediates are shown. In route 1 stereo- and position-specific addition of dichloroketene to a bicyclo[3.1.0]hexene provided the framework for elaboration to prostanoids. Route 2 featured stereospecific internal cyclopropanation and stereospecific Sn2 displacement of carbon to establish the prostanoid nucleus. 

Similarly complex is the fluorination of the Ihtes methylpyridines (a-, ()-, and 7-picolmes) with cesium tetrafluorocobaltate. 2-Methylpyridme was fluorinated at 270 °C for 180-200 mm, 3- and 4-methylpyridmes were fluorinated at 330 to 340 °C for 150 min All of them afforded the respective polyjluorinated pyridines and perfiuoro-1,2-, 1,3-dimethyl-, and 1-ethylpyrrolidine In addition, perfluoro-2-aza-2-hexene and bis(tnfluoromethyl)amine were isolated m variable yields [27] All the isolated products of the fluorination of 3-methylpyridme (3-picoline) are shown in equation 9. 

In conclusion, it may be said that a lot of literature has been published that favors the Frye and Horst mechanism of stabilization. Most of this is based on studies done on low-molecular weight model compound for al-lylicchlorines in PVC, i.e., 4-chloro-2-hexene. Although the large contribution of these studies toward understanding the mechanism of stabilization of PVC cannot be denied, the extrapolation of these results to the processes involved in the actual stabilization of the polymer should be done with extreme care. The polymer represents a complex mixture of macromolecules, which in the melt is not only physically a very different system compared to the low-molecular weight model compound, but invariably contains, apart from stabilizers, other additives, such as plasticizers, lubricants, processing aids, etc., that further complicate the situation. The criticism of the Frye and Horst mechanism is also based on solid experimental evidence, and hence, the controversy is still very much alive. 

Figure 9.16 Stereochemistry of the addition of H20 to the chiral alkene, (fl)-4-methyl-1-hexene.

Phenylsulphine prepared in situ from phenylmethanesulphinyl chloride and triethyl-amine reacted with 1 -morpholinocyclohexene to form the addition product 169 having the enamine structure218. A similar experiment with phenylsulphine and 2-pyrrolidinocyclo-hexene gave only 2-phenylmethanesulphinyl cyclohexanone 170. The latter is most probably formed by hydrolysis of the corresponding enamine sulphoxide upon isolation. The reaction of sulphines with enamines is apparently a stepwise process involving the transient formation of the dipolar intermediate 171 which is stabilized by proton transfer, giving the enamine sulphoxide. 

---