Cyclooctene oxygen

Another method that appears to have commercial potential is the ozonolysis of cyclooctene. Ozonolysis is carried out using a short chain carboxyHc acid, preferably propanoic acid, as solvent. The resultant mixture is thermally decomposed in the presence of oxygen at about 100°C to give suberic acid in about 60—78% yield (38—40). Carboxylation of 1,6-hexanediol using nickel carbonyl as catalyst is reported to give suberic acid in 90% yield (41). 

Alkenes strained by twist or r-bond torsion, such as E-cyclooctene, exhibit much lower barriers due to relief of strain in the TS for the oxygen transfer step. While the epoxidation of symmetrically substituted alkenes normally involve a symmetrical approach to the TT-bond, the TSs for epoxidation of E-cyclooctene and E-l-methylcyclooctene exhibit highly asymmetric transition structures. The AAE = 3.3 kcalmol" for E- versus Z-cyclooctene is clearly a reflection of the relative SE of these two medium ring alkenes (16.4 vs 4.2 kcalmol ) ". The classical activation barrier (AE ) for the highly strained bicyclo[3.3.1]non-l-ene is also quite low (Table 10, Figure 26). In these twist-strain alkenes, the approach of the peracid deviates markedly from the idealized spiro approach suggesting fliat this part of the potential energy surface is quite soft. 

Photoinduced ring cleavage also occurs readily in heterocyclic systems containing both oxygen and nitrogen. A series of dihydro-oxadiazinones, for example, undergo decomposition, and the results obtained parallel those observed on thermal decomposition cis- and Jraras-stilbene are obtained from the diphenyl derivative (71), whereas cis-cyclooctene is the major product of photolysis of the fused cyclooctane (72).62... 

In contrast to inactive iridium(TTI)-Peroxo complexes, Irm-hydroperoxo species have been shown to transfer oxygen to a coordinated alkene, for example in the slightly catalytic oxidation of cyclooctene to cyclooctanone by 02 + H2 mixtures in the presence of IrHCl2(CgH12) (equation 95). 68 Oxygen transfer presumably occurs as for palladium hydroperoxides in equations (89) and (90). 

In a 100-ml., three-necked, round-bottomed flask, 2 g. (7.7 mmoles) of rhodium(III) chloride 3-hydrate is dissolved in an oxygen-free mixture of 40 ml. of 2-propanol and 10 ml. of water. Cyclooctene (6 ml.) is added. The solution is stirred for about 15 minutes under nitrogen. The flask is then closed and allowed to stand at room temperature for 5 days. The resulting reddish-brown crystals are collected on a filter, washed with ethanol, dried under vacuum, and stored under nitrogen at —5°C. The yield is 2.0 g. (74%). Anal. Calcd. for RhC16H28Cl Rh, 28.72 C, 53.56 H, 7.81 Cl, 9.91. Found Rh, 28.55 C, 53.76 H, 7.89 Cl, 9.76. 

Phosphines may also serve as oxygen acceptors in C02 reduction. Both (Ph3P)3RhCl and [(cyclooctene)2RhCl]2 are capable of catalyzing the redox... 

Iridium Complexes. The air-stable, rose-colored monohydride HIrCl2(PCy3)2, Complex 3, may be prepared directly from a commercially available chloride, or by adding HC1 to a toluene solution containing the cyclooctene dimer [IrCl(COT)2]2 and PCy3. The six-coordinate, yellow Complex 4 containing oxygen-bonded dma, v(CO) 1628 cm-1 (28), also is isolated readily. 

Diederich et al. had postulated that the highly reactive iron-oxo species, arising from oxygen transfer from the oxidant to the Fem site [87], should be greatly stabilised by enclosure within a dendritic superstructure. The catalytic potential of the dendrimers 6 a-c was determined in the epoxidation of alkenes [83 a, 88] (1-octene and cyclooctene) and the oxidation of sulphides [83 a] ((methylsulphanyl)benzene and diphenyl sulphide) to sulphoxides - in dichloro-methane with iodosylbenzene as oxidising agent. Compared to the known metal-porphyrin catalysts, 6a-c exhibit only low TON (7 and 28, respectively, for... 

Organonitrile-functionalized mesoporous silicas such as MCM-41 and MCM-48 have been used to immobilize dioxoMo(VI) complexes such as Mo02X2(THF)2 (with X = Br or Cl) (218). The catalytic potential of these hybrid material was evaluated for the epoxidation of cyclooctene with r-BuOOH as the oxygen source. Notwithstanding the high activities claimed, pronounced Mo leakage was observed. Indeed, it was shown that cyclooctene continued to be converted after the solid catalyst was removed from the reaction mixture (218). 

In cyclic alkenes such as cyclohexene and cycloheptene trans addition was also highly stereoselective [7]. However, cis cyclooctene afforded both cis and trans adducts in the ratio 1 3 in the presence of oxygen 1,4-dichlorides were also formed [8]. In cyclodecenes, both cis and trans, the main product was the allylic chloride, with some formation of transannular dichlorides [9]. In some substrates with an exocyclic double bond, such as methylene cyclobutane, only (dichloroiodo)benzene was suitable for a clean addition [10]. 

Direct reaction between oxygen and a substrate would be expected to be more favorable when both molecules are coordinated to a metal. Indeed, hydrogen abstraction from a coordinated olefin by coordinated dioxygen was observed in the reaction of a Rh(I)-cyclooctene complex with molecular oxygen.186a,b The following mechanism was proposed ... 

Thus, the substituted heteropolyanion is stable and active even in the presence of oxidants such as /-BuOOH or PhIO. Note that the heteropolyanion is unstable with respect to hydrogen peroxide. Based on the high stability, TMSP can be used for alkane hydroxylation [67b]. Mansuy et al. have reported that P2Wn06i (Mn3+ Br)8 is oxidation resistant and more active for the epoxidation of cyclooctene with PhIO than those containing Fe3+, Co2+, Ni2+, or Cu2+ [68]. The oxygenations of cyclohexane, adamantane, and heptane and the hydroxylation of naphthalene, are also catalyzed by TMSP. 

On the basis of theoretical studies by Bach and co-workers,17 it was found that the nucleophilic 71-bond of the alkene attacks the 0-0 cr-bond in an Sn2 fashion with displacement of a neutral carboxylic acid. There are, however, some mechanistic anomalies. For example, a protonated peracid should be a much more effective oxygen transfer agent over its neutral counterpart, but experiments have shown only modest rate enhancements for acid catalysed epoxidation. Early attempts to effect acid catalysis in alkene epoxidation where relatively weak acids such as benzoic acid were employed proved unsuccessful.18 The picture is further complicated by contradictory data concerning the influence of addition of acids on epoxidation rates.19 Trichloroacetic acid catalyses the rate of epoxidation of stilbene with perbenzoic acid, but retards the rate of a double bond containing an ester constituent such as ethyl crotonate.20 Recent work has shown that a seven-fold increase in the rate of epoxidation of Z-cyclooctene with m-chloroperbenzoic acid is observed upon addition of the catalyst trifluoroacetic acid.21 Kinetic and theoretical studies suggest that the rate increase is due to complexation of the peroxy acid with the undissociated acid catalyst (HA) rather than protonation of the peroxy acid. Ab initio calculations have shown that the free energy of ethylene with peroxy-formic acid is lowered by about 3 kcal mol-1 upon complexation with the catalyst.21... 

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