Vinylcyclohexene oxidation

Other recent reports of interesting terpolymerization processes involving cyclohexene oxide and diglycolic anhydride or vinylcyclohexene oxide have appeared in the literature [66-68]. These processes are indicated in (7) and (8), and were carried out in the presence of p-diiminate zinc catalysts. The vinyl functionalized polymer was intramolecularly crosslinked by a metathesis reaction to afford nanoparticles. 

For the copolymerization of epoxides with cyclic anhydrides and curing of epoxy resins, Lewis bases such as tertiary amines are most frequently used as initiators. In this case, terminal epoxides react with cyclic anhydrides at equimolar ratios. The time dependence of the consumption of epoxide and anhydride is almost the same for curing 35-36> and for model copolymerizations 39,40,45). The reaction is specific 39,40) to at least 99 %. In contrast, the copolymerization with non-terminal epoxides does not exhibit this high specificity, probably because of steric hindrances. The copolymerization of vinylcyclohexene oxide or cyclohexene oxide is specific only to 75-80 % and internal epoxides such as alkylepoxy stearates react with anhydrides only to 60-65 %. On the other hand, in the reaction of epoxy resins with maleic anhydride the consumption of anhydride is faster 65the products are discoloured and the gel is formed at a low anhydride conversion 39). Fischer 39) assumes that the other resonance form of maleic anhydride is involved in the reaction according to Eq. (33). 

The polymerization rate depends on both the reactivity of monomers and the nature of the counter anion of the initiator salt. In the fastest case (3-vinylcyclohexene oxide), a quantitative conversion was attained at 25 °C within 1.5 minutes whereas in the slowest case (e-caprolactone), irradiation at 60 °C for 60 min was required. 

Vinylcyclohexene and terf-butyl hydroperoxide, in the presence of chromium acetylacetonate, yield exclusively 4-vinylcyclohexene oxide [217]. 

Two olefin epoxides, allylglycldylether and 4-vinylcyclohexene-oxide (VCHO), are commercially available to the extent that large scale production of their siloxane derivatives is feasiblet... 

Crivello and Lam have demonstrated the use of diaryliodonium salts as photoinitiators for polymerization of electron-rich olefins, cyclic ethers, cyclic sulfides, lactones and spiro orthoesters, but a vast majority of their published work concerns polymerization of substituted oxiranes, illustrating the potential of such systems in photocuring of epoxy resins. Such polymerizations can be quite fast in the most favorable example, a 93% yield of polymer of Mn 10,700 was obtained from 3-vinylcyclohexene oxide after only 90 seconds of irradiation at room temperature with 4,4 -di-tert-butyldiphenyliodonium hexafluoroantimonate as initiator (3). The substituted salts are often preferred to the simple unsubstituted diphenyliodonium compounds for reasons of solubility (2). The use of diaryliodonium salts in combination with various dyes allows one to initiate cationic polymerization with visible light (5). 

The hydrosilation of 4-vinylcyclohexene oxide with Tg using Wilkinson s catalyst was carried out under a variety of conditions. Even in the presence of excess epoxide, only four of the eight Si-H bonds could be successfully hydrosilated onto the Tg core (eq. 2). 

Production of styrene from butadiene has also been extensively investigated. Recentiy, Dow announced licensing a process involving cyclodimerization of 1,3-butadiene to 4-vinylcyclohexene, followed by oxidative dehydrogenation of the vinylcyclohexene to styrene (65,66). The cyclodimerization step takes place in... 

When the Diels-Alder reaction between butadiene and itself is carried out in the presence of alkah metal hydroxide or carbonate (such as KOH, Na2C02, and K CO on alumina or magnesia supports) dehydrogenation of the product, vinylcyclohexene, to ethylben2ene can occur at the same time (134). The same reaction can take place on simple metal oxides like Zr02, MgO, CaO, SrO, and BaO (135). 

The process which was developed hy DOW involves cyclodimerization of hutadiene over a proprietary copper-loaded zeolite catalyst at moderate temperature and pressure (100°C and 250 psig). To increase the yield, the cyclodimerization step takes place in a liquid phase process over the catalyst. Selectivity for vinylcyclohexene (VCH) was over 99%. In the second step VCH is oxidized with oxygen over a proprietary oxide catalyst in presence of steam. Conversion over 90% and selectivity to styrene of 92% could he achieved. ... 

Overman, Hehre and coworkers reported anti rr-fadal selectivity in Diels-Alder reactions of vinylcyclopenten 73, 74 and 4,5-dihydro-3-etliynylthiophen S-oxide 75 [38] (Scheme 31). These results are not in agreement with the Cieplak effect, at least in Diels-Alder reactions of the dienes having unsymmetrical rr-plane. Yadav and coworkers reported that the reactions between the vinylcyclohexene 76 and dienophiles favor the reactions syn to oxygen, while 77 and 78 favor the reaction anti to oxygen substituents [39], They discuss the Cieplak effect but the reactions are not suitable. 

In the absence of Aldol condensation, the only heavies forming reactions involve a butadiene Diels-Alder reaction to form 4-vinylcyclohexene and subsequent oxidative carbonylation. 

Typically, little butadiene is dimerized to 4-vinylcyclohexene under actual reaction conditionsOO,31). The butadiene used in the process, however, can contain up to. 5 weight % Diels-Alder product, and at this level oxidative carbonylation can become a significant heavies forming reaction (Equation 9.). The major product from this reaction comes from l, -dicarbonylation of the 4-vinylcyclohexene exocyclic double bond. 

The Cu+/zeolite-catalyzed cyclodimerization of 1,3-butadiene at 100°C and 7 atm was found to give 4-vinylcyclohexene [Eq. (13.12)] with high (>99%) selectivity. Subsequent oxidative dehydrogenation over an oxide catalyst in the presence of steam gives styrene. The overall process developed by Dow Chemical113 offers an alternative to usual styrene processes based on ethylation of benzene (see Section 5.5.2). 

Cyclization of butadiene catalysed by Ni(0) catalysts proceeds via 7r-allylnickel complexes. At first, the metallacyclic bis-7i-allylnickel complex 6, in which Ni is bivalent, is formed by oxidative cyclization. The bis-7r-allyl complex 6 may also be represented by cr-allyl structures 7, 8 and 9. Reductive elimination of 7, 8 and 9 produces the cyclic dimers 1, 2 and 3 by [2+2], [2+4] and [4+4] cycloadditions. Selectivity for 1, 2 and 3 is controlled by phosphine ligands. The catalyst made of a 1 1 ratio of Ni and a phosphine ligand affords the cyclic dimers 1, 2 and 3. In particular, 1 and 3 are obtained selectively by using the bulky phosphite 11. 1,2-Divinylcyclobutane (1) can be isolated only at a low temperature, because it undergoes facile Cope rearrangement to form 1,5-COD on warming. Use of tricyclohexylpho-sphine produces 4-vinylcyclohexene (2) with high selectivity. 

Fig (24) Oxidation of (198) gives o-quinone (199) which on heating with vinylcyclohexene (200) gives miltirone (197). 

Fig (25) Catechol (201) on oxidation with silver oxide generates 3-isopropyl-o-benzoquinone (199) which undergoes ultrasound-promoted cycloaddition with 6,6-dimethyl-1 -vinylcyclohexene (200) yielding the synthesis of miltirone (197). 

In route A, one electron is removed fiom cme double bond to generate a cation radical, and subsequent transannular reaction of the cation radical with the other double bond forms a new carbon-carbon tend. On the other hand, in route B, allylic substitution or oxidative addition at one double bond takes place without intramolecular interaction between the double bonds. As exemplified by the anodic oxidation of 4-vinylcyclohexene (11) in methanol (equation 16), such dienes as 4-vinylcyclohexene, limonene and 1,5-cyclooctadiene yield only products via route B. 

The first step of the process involves the cyclodimerization of butadiene to 4-vinylcyclohexene. The reaction is exothermic and can be catalyzed by either a copper-containing zeolite catalyst or an iron dinitrosyl chloride catalyst complex. Although both vapor-phase and liquid-phase processes have been studied, it appears that liquid-phase reactions are preferred because they achieve higher butadiene conversion levels. The second step is oxidative dehydrogenation of the 4-vinylcyclohexene to produce styrene. Dow has led the research effort in this area and has... 

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