Pentene time effect

Female mice have volatile components in their urine that are depressed after adrenalectomy. Six components have been detected, of which three (2-heptanone, trans-5-h. ptea-l-one., and tra 5-4-hepten-2-one) have no apparent effects either as a group or when added to the other three components. The active three components are w-pentyl acetate, m-2-penten-l-yl acetate, and 2,5-dimethylpyrazine (Fig. 8.3). If 2,5-dimethylpyrazine is painted daily on the external nares of young female mice from day 21 on, the time of the first vaginal estrus is delayed. These three compoimds act in redimdant fashion the two acetate esters delay vaginal estrus by 1.5 days, on average 2,5-dimethylpyrazine alone delays it by 2.4 days, and a mixture of all three delays it by 1.7 days. (Novotny et a /., 1986a). 

In contrast, dramatic steric effects are found, when a tert-butyl group is introduced at the position of electrophilic attack. Scheme 38 shows, that the tert-butyl-substituted compound reacts at least 103 times more slowly than the corresponding methyl-substituted compound. The determination of the accurate rate constant for 2,4,4-trimethyl-2-pentene failed, as this... 

The elementary reactions of carbocationic polymerizations can be separated into three types. Deactivation of carbenium ions with anions and transfer to counteranion are ion-ion reactions, propagation and transfer to monomer are ion-dipole reactions, and ionization is a dipole-dipole reaction [274]. Ion-ion and dipole-dipole reactions with polar transition states experience the strongest solvent effects. Carbocationic propagation is an ion-dipole reaction in which a growing carbenium ion adds electro-philically to an alkene it should be weakly accelerated in less polar solvents because the charge is more dispersed in the transition state than in the ground state [276]. However, a model addition reaction of bis(p-methoxyphenyl)carbenium ions to 2-methyl- 1-pentene is two times faster in nitroethane (e = 28) than in methylene chloride (e = 9) at - 30° C [193]. However, this is a minor effect which corresponds to only ddG = 2 kJ morit may also be influenced by specific solvation, polarizability, etc. [276,277]. 

When a stream of ozonized oxygen or air, usually under 6% ozone, is passed through a solution of an olefin, such as 2,4,4-trimethyl-2-pentene, absorption occurs as fast as the ozone is introduced and no ozone escapes through the solution until all the olefin has been converted to ozonide. If an aromatic hydrocarbon such as benzene is ozonized rather than an aliphatic olefin, absorption of ozone is not complete and several times the theoretical amount of ozone must be used to effect complete ozoniza-tion. When a molecule has both an aromatic system and an aliphatic double bond, the aliphatic bond may react selectively, with little or no reaction with the aromatic system. Anethole will absorb a mole of ozone and produce, on hydrolysis of the ozonide, a very good yield of anise aldehyde. Complete saturation of the molecule requires almost 10 moles of ozone, however. 

The order of relative reactivities of unsaturated alcohols with respect to 1-hexene was not the same (101) as that with respect to 4-methyl-2-pentene hence, the relative reactivity of various alcoholic substrates related each time to one olefinic substrate depends not only on the structure of this olefinic substrate, but also on the structure of the reference compound. This finding shows that the resulting effect (relative reactivity) is affected by mutual interactions of both reacting substrates. 

Employing a silicon micro reactor [channel dimensions = 500 or 1000 pm (width) x 250 pm (depth)], wall-coated with the acidic zeolite titanium silicate-1 (TS-1, Si Ti ratio = 17) (83) (3 pm), Gavrilidis and co-workers [52] demonstrated a facile method for the epoxidation of 1-pentene (84) (Scheme 6.23). Using H202 (85) (0.18 M, 30wt%) as the oxidant and 84 (0.90 M) in MeOH, the effect of reactant residence time on the formation of epoxypentane (86) was evaluated at room temperature. The authors observed increased productivity within the 500 pm reaction channel compared with the 1000 pm channel, a feature that is attributed to an increase in the surface-to-volume ratio and thus a higher effective catalyst loading. 

The effect of the temperature of preconditioning was investigated to test whether shorter times at higher temperatures are effective. Fresh catalyst was heated in F /F O to 450°C for 30 mins and cooled to 300°C then tested for reaction of 1-pentene in F /HgO at 300°C. The results (table 6) are compared with the previous results obtained after catalyst conditioning at 380°C for 28 hours. This high temperature activation treatment results initially in rather more disproportionation and hydrogenation. Catalyst life and ultimate product distributions were not adversely affected. 

When metathesis is effected with tra i-2-pentene, rather than cis-, and (diphenylcarbene)pentacarbonyltungsten is the initiator, the 2-butene and 2-hexene products are largely trans. The stereospecificity (73-83% trans) is not as great as for cw-olefin metathesis, but it is appreciable (63). The ratios of the stereoisomers in the products are close to the equilibrium ratios, but they probably are not determined by the products equilibrating, for in the short time the metathesis was run to determine the stereochemistry of the initial product, the precursor, tranj-2-pentene, underwent only negligible isomerization. The stereochemistries therefore are determined by the kinetics, which in turn should be affected by conformational factors similar to those in Scheme... 

The most effective solvent-catalyst systems for alkene isomerizations are hexamethylphosphoramide solutions of alkali alkylamides. For example, sodium dimethylamide in hexamethylphosphoramide is about 300,000 times as effective in catalyzing the isomerization of 2,4,4-trimethyl-1-pentene as is potassium / r/.-butoxide in dimethylsulfoxide. ... 

Table 5.3-1 summarizes the most relevant results of this early study. Although the reactants show only limited solubility in the catalyst phase, the rates of hydrogenation in [BMIM][SbFis] are almost five times faster than for the comparable reaction in acetone. However, the reaction was found to be much slower using a hexafluo-rophosphate ionic liquid. This effect was attributed to the better solubility of pentene in the hexafluoroantimonate ionic liquid. The very poor yield in [BMIM](BF4], however, was due to a high amount of residual Cl ions in the ionic liquid leading to catalyst deactivation. At that time the preparation of this tetrafluoroborate ionic liquid in a chloride-free quality was obviously a problem. 

With olefins, CO, and H2 catalytic hydroformylation takes place even at 25 and subatmospheric pressure. Rates and product distributions depend on substrate type, [S], [H2], [CO], ligand type, [L], [Rh], and temperature. Rates with selected olefins are given in Table 10. Note that 2-pentenes react about 25 times slower than 1-pentene, and that 2-methyl-1-pentene (a hindered terminal olefin) is slower still. Cyclooctene is much faster than cyclohexene, presumably because of ring strain effects on olefin coordination, t Butadiene reacts rapidly with the catalyst to form an inert (tt-crotyl)Rh(CO)L2 complex and no gas uptake occurs at 25 . 1,5-Hexadiene can be successfully hydroformylated, because the hydroformylation rate (to primarily linear dialdehyde) is fast compared to the rate of isomerization... 

ADMET polymerization has also been applied to 1,5-hexadiene, and polybutadiene (PBD) exclusively in the 1,4 mode was obtained [49]. Unlike PBD produced by ROMP, this ADMET polymer has a trans content of 75% [52]. With [W]l and [Mo]2,theAfn of these polymers was approximately 8.0 X lO gmol , witha poly-dispersity near 2.0. Attempts to polymerize 1,5-hexadiene with [Ru]l, however, resulted in oligomers of approximately 1.0 x lO gmoD, in addition to cyclics and unreacted monomer, even after extended reaction times [53]. This decrease in activity was attributed to stable intramolecular ii-complexation of the distal olefin of the 4-penten-l-ylidene complex to the metal center. Such coordination could obstruct bimolecular coordination of another diene to the metal, and thereby prevent further polymerization. The absence of this effect with Schrock s catalysts was explained in part by the steric congestion around the metal center of those catalysts and the lack of a labile ligand. A number of hydrocarbon dienes have been utilized in ADMET polymerizations [54, 55]. 

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