Alkyl-Substituted Ethylenes

Unhindered simple olefins are usually rapidly hydrogenated under very mild conditions over platinum metal catalysts such as platinum, palladium, and rhodium as well as over active nickel catalysts such as Raney Ni, nickel boride, and Urushibara Ni. For example, 0.1 mol of cyclohexene is hydrogenated in 7 min over 0.05 g of Adams platinum oxide in ethanol at 25°C and 0.2-0.3 MPa H2 (eq. 3.1).5 1-Octene and cyclopentene (eq. 3.2) are hydrogenated in rates of 11.5 and 8.6 mmol (258 and 193 ml H2 at STP) g Ni 1-min 1, respectively, over P-1 Ni in ethanol at 25°C and 1 atm H2.18 Hydrogenation of cyclohexene over active Raney Ni proceeds at rates of 96-100 ml H2 at STP (4.3-4.5 mmol) g Ni min-1 in methanol at 25°C and 1 atm H2 49,50 and can be completed within a short time, although usually larger catalyst substrate ratios than required for platinum catalyzed hydrogenations are employed (eq. 3.3).50 

For hydrogenation of more substituted double bonds over Raney Ni, application of elevated temperature and pressure may be advantageous to complete the reaction within a reasonable time, as seen in the hydrogenation of ethylidenecyclobutane in eq. 3.4, although the reaction time was not described.51 Hydrogenation of iso-propylidenecyclobutane at 80-100°C and 0.34-0.41 MPa H2 proceeded less readily than in the case of ethylidenecyclobutane. 

TABLE 3.2 Hydrogenation and Racemization of Optically Active Alkenes 

Optically active alkene Catalyst Solvent Additive % Racemization Ref. 

The solution was added to a suspension of catalyst prereduced in 30 ml AcOH. 

---

Notes The uncertainty in the proton affinities of the alkylenes is probably 3 kcal/mole, in those of butadiene and styrene rather greater The proton affinities of multiply alkyl substituted ethylenes probably all lie within 3 kcal/mole of that of isobutene [4c] ... 

T. Watabe, K. Akamatsu, Enzymatic Hydrolysis of Mono-n-alkyl Substituted Ethylene Oxides and Their Inhibitory Effects on Hepatic Microsomal Epoxide Hydrolase , Chem. Pharm. Bull. 1974, 22, 2155 - 2158. 

This result is similar to that obtained by Widing and Levitt for the normal alkanes and to that observed for alkyl-substituted ethylenes [171] in the latter case, linear correlations were obtained between the IPs and the sum of charges of the unsaturated carbon atoms, whereby any increase of their electron density due to substituent effects leads to a lowering of the molecular ionization potential. 

When an alkyl or aryl ketone, or an aryl aldehyde, reacts with an alkyl-substituted ethylene, or with an electron-rich alkene such as a vinyl ether, the mechanism involves attack by the (n,n triplet state of the ketone on ground-state alkene to generate a 1,4-biradical that subsequently cyclizes. The orientation of addition is in keeping with this proposal, since the major product is formed by way of the more stable of the possible biradicals, as seen for benzophenone and 2-melhylpropene (4.64). As would be expected for a triplet-state reaction, the stereoselectivity is low, and benzophenone gives the same mixture of stereoisomers when it reacts with either trans or... 

Com forth and co-workers914 employed zinc in a solution of sodium iodide and sodium acetate in acetic acid to effect reduction of several alkyl-substituted ethylene oxides to the corresponding olefins (Eq. 337). 

Among alkyl-substituted ethylene oxides known to umletrn cleavage on treatment with sodium sulfite are propylene oxide, isobutylene oxide, 1,2-epoxybutane, 1,2-epoxyoctane, and 2,3-cpow-butane.1 75 These reactions with sodium sulfite constitute the bani-, ffrail analytical method developed by Swan1875 for the estimation <[Pg.179]

Several simple alkyl-substituted ethylene oxides undergo addition of hydrogen halide to give the corresponding balohydrins. Wiilt attention, for example, has been accorded to propylene oxide, particularly in connexion with kinetic studies.148 1Mi-1490... 

With increasing alkyl-substitution, ethylene oxides tend to undergo isomerization to carbonyl compounds before condensation with ilw Organic radical of the Grignard reagent. 10. ... 

Condensation of Grignard reagents with alkyl-substituted ethylene oxides is fairly complex, particularly if the epoxides involved are asymmetric and massively substituted. The reaction course depends also on the structure of the Grignard reagent, and obviously on experimental conditions used for the condensation. 45 ... 

There is, however, other evidence that speaks for the bromonium ion concept and against competition between AdE2 and Ad3 pathways.35 We have already noted that, in polar solvents, addition of bromine to multiple bonds is first-order in bromine when bromine is present in low concentration. Moreover, as Table 7.7 shows, increasing the number of substituents on the double bond cumulatively increases the rate of bromination of nonconjugated olefins in polar solvents irrespective of whether each new substituent is on the same or on the other olefinic carbon as the last.36 Dubois has found that the bimolecular rate constants for addition of bromine to alkyl substituted ethylenes are correlated by... 

Only monosubstituted terminal alkenes, including some terminal dienes, have so far been successfully methylaluminated. Within this restriction, however, the reaction appears to be reasonably general, as shown in Table 4.1. Specifically, n-alkyl, isoalkyl, and secondary alkyl substituents can be accommodated, but tertially alkyl-substituted ethylenes, such as r-BuCH=CH2, fail to react under the same conditions. In contrast with styrene, allylbenzene reacts normally. 

The trends in the ozonolysis rates of simple olefins require further examination. The object of the present work was to obtain kinetic data on the reaction of ozone with simple alkyl-substituted ethylenes. The results will allow a discussion of the substituent effects on the reaction rates and of the mode of ozone attack on the carbon-carbon double bond. 

A comparison of the results obtained with alkyl-substituted ethylenes (Tables III and IV) indicates that krei decreases with increasing bulk of the substituents. This is also found to be true with the terminal olefins (Table V), as indicated by the lowering of krei from 1.11 to 0.407 when n-propyl is replaced by the tert-butyl group. The terminal olefins bearing an electron-withdrawing substituent also indicate a significant decrease of krei, as compared with 1-pentene, which is in agreement with Cveta-novic s observations (II). 

This is true not only for halogen-substituted ethylenes. The reactions of alkyl-substituted ethylenes (82, 83, 93) seem to follow the same reaction mechanisms. The products from the reaction of propene under various reaction conditions are summarized in Table IV. The overall picture of the reaction is illustrated in Schemes 8 and 9 (93). These reaction mechanisms seem to be generally applicable. Studies on the reactions with cyclic olefins could serve as a further evidence (61, 78). 

The correlations outlined above are empirical, that is, their applicability is proved by their success. The finding that the carrier alone or the concentration of platinum on the carrier did not change the parameters of the Taft equation to any essential degree makes possible some generalization of the results. All alkyl-substituted ethylenes are hydrogenated under the same mechanism, most likely through a simultaneous addition of both hydrogen particles to the Ti-adsorbed olefin (48, 78). 

Competition experiments between C2H4 and alkyl-substituted ethylenes for the capture of CTF show that the relative efficiencies increase by a factor of six in going from ethylene to tetramethylethylene. The temperature dependence of these relative rates indicates that the variation is almost entirely the result of differences in activation energy for monofluorocarbene addition to alkenes. 

The C=C stretching frequency near 1640 cm" in vinyl hydrocarbons is a medium intensity band which becomes inactive in the infrared region in a symmetrical trans- or symmetrical tetrasubstituted double bond compound, both of which have centers of symmetry. Even when the substituents are not exactly alike in trans-md tetrasubstituted olefins, the infrared absorption may be quite weak. These double bond vibrations all appear strongly in the Raman effect, however, where the C=C stretch vibration in all types of ethylenes gives rise to a strong Raman band in the region 1680-1630 cm The trans, tri, and tetra alkyl-substituted ethylenes appear at 1680-1665 cm which are strong in Raman but weak or absent in the infrared. The cis, or... 

Another approach to make homo- or copolymers which contain primary amino functions was developed by Maeda and coworkers.A lithium alkyl-amide catalyzed addition of mono N-alkyl-substituted ethylene diamines [34] to 1,4-divinylbenzene [33] yielded a styrene derivative [35] containing both tertiary and primary amino groups (Scheme 4). 

---