Hydrogenation cydohexene

FIGURE 11 2 Heats of hy drogenation of cydohexene 1 3 cydohexadiene a hypo thetical 1 3 5 cydohexa triene and benzene All heats of hydrogenation are in kilojoules per mole... 

Cycloalkene Hydrogenation Investigated in Micro Reactors Cas/liquid reaction 16 [CL 16] Catalytic hydrc enation of cydohexene... 

In a 500 ml. three-necked flask, equipped with a mechanical stirrer, thermometer and dropping funnel, place 300 ml. of 88-90 per cent, formic acid and add 70 ml. of 30 per cent, hydrogen peroxide. Then introduce slowly 41 g. (51 ml.) of freshly distilled cydohexene (Section 111,12) over a period of 20-30 minutes maintain the temperature of the reaction mixture between 40° and 45° by cooling with an ice bath and controlling the rate of addition. Keep the reaction mixture at 40° for 1 hour after all the cydohexene has been added and then allow to stand overnight at room temperature. Remove most of the formic acid and water by distO-lation from a water bath under reduced pressure. Add an ice-cold solution of 40 g. of sodium hydroxide in 75 ml. of water in small portions to the residual mixture of the diol and its formate take care that the tempera-... 

The effect of microwave irradiation on the catalytic hydrogenation, dehydrogenation, and hydrogenolysis of cydohexene was studied by Wolf et al. [81]. Optimum conditions for benzene formation were a hydrogen flow, N-CaNi5 catalyst, atmospheric pressure, and 70 s irradiation time. Cydohexane was the main product when the irradiation time was 20 s, or in a batch/static system. 

The overall course of reaction depends on the relative rate constants for the various secondary radical processes. Aliphatic ketones are often photoreduced to secondary alcohols (4.121, but although there are interesting features in the stereochemistry of the reduction, the method is not a worthwhile alternative to thermal reduction using hydride reagents, except in cases where the substrate is sensitive to basic conditions. Photoaddition of methanol is promoted in the presence of titaniurnfiv) chloride, both for acyclic and cyclic (4.33) ketones the titanium involvement probably starts in the early steps of the reaction, but the detailed mechanism is not known. Addition may also be a major pathway when cyclohexene is used as hydrogen source (4.341 unlike many other simple alkenes, cydohexene does not readily give oxetanes by photocycloaddition (see p. 126). 

Attention may be called, in conclusion, to the observatioin of Brunei that cydohexene oxide fails to eondonee with hydrogen cyanide This is again compatible with tho weakly Tmeleoplul i-cbaracter of the CN ion and the low dissociation constant of its conjugate acid. 

Cyclohexane is rly easily dehydrogenated into benzene, and even at very low extents of reaction, stoichiometry reaction (6) can be replaced by the secondary stoichiometry reaction (12). For cyclohexane, the constituents are (apart from cyclohexane) hydrogen, methane, ethane, ethylene, acetylene, propene, 1-butene, 1,3-butadiene, cydohexene, and benzene [3]. However, one can check that the equations written are independent, using the Jouguet [IS] criterion, (t.e., if/ = n-o)). In this criterion, the number of the independent constituents, 1//, for a chemical system is equal to the required constituents. n, (i e., H3, Cl, C3, CsHe, Q, C4, Cj. c-Q, CaJ, subtracting the number of independent stoichiometric equations. q>. 

Two variants are currently employed for the synthesis of Ol/One (i) the hydrogenation of phenol to cydohexanol and cyclohexanone and (ii) the hydration of cyclohexene to cydohexanol cydohexene is synthesized by the selective hydrogenation of benzene. Cydohexanol is then oxidized to AA using the same process as that employed for the nitric acid oxidation of the KA Oil. 

Figure 7.2 Simplified flow sheet of the Asahi process for benzene hydrogenation to cydohexene.

Hydrogenation of simple alkenes often serves as a test reaction to characterize the catalytic performance of new hydrogenation catalysts, and only in relatively few cases was it employed for straightforward synthetic purposes. In aqueous solutions the most widely employed substrates for catalyst characterization are unsaturated carboxylic acids (such as maleic, fumaric, crotonic, and itaconic acids), alcohols (i.e., allyl alcohol) and sodium 4-styrenesulfonate, while in two-phase hydrogenations a-alkenes (1-hexene, 1-octene), cydohexene, and styrene are the conventional targets of catalytic reduction. These reactions will not be discussed here in detail. 

The bromine atom has replaced an atom of hydrogen and so this is a substitution reaction. The reagent is electrophilic bromine and the molecule is aromatic so the reaction is electrophilic aromatic substitution and that is the subject of this chapter. We can compare the bromination of cydohexene and of benzene directly. 

Scheme 12.8. Reaction of cydohexene in SCCO2/H2. In a continuous SCF flow reactor a high throughput with high space-time yields may be achieved. Cydohexene may be hydrogenated with a flow rate of substrate as high as 20 mt min with conversions to cyclohexane over 95 %.

A comparison of the heats of hydrogenation of cydohexene, 1,3-cydohexadlene, and benzene. Benzene is 150 k /mol (36 kcal/mol) more stable than might be expected for "cyclohexatriene."... 

Transfer hydrogenation of aromatic nitro compounds. Aromatic nitro compounds are reduced to anilines when refluxed in excess cyclohexene in the presence of ordinary commerical 10% Pd/C catalyst. The method is very useful for selective reduction of polynitrobenzenes. Halogen, if present, is eliminated. Cydohexene is superior to cyclohexa-1,3-diene as hydrogen donor. The reaction is usually successful, but slower, with sulfur-containing substrates. 4-Methoxy-2,S-dinitroanisole is reduced to 2,5-dimethoxy-4-nitroaniline in 10 min. in the steam bath under these conditions. 

The supported nanoparticle catalyst system was used for solvent-free hydrogenation reactions of cydohexene, 1-hexene, and 1,3-dicydohexadiene, respectively, and compared with a similar biphasic ionic liquid system and with a heterogeneous supported nanocatalyst (Table 5.6-6). 

The supported ionic hquid nano[Pg.552]

The hydrogenation kinetics of cydohexene catalyzed by Pt2(dba)3 dispersed in BMI.PFg, BMI.BF4 and BMl,OTf are shown in Fig. 6.3. The kinetics curves were treated using the pseudo-elementary step and fitted (Eq. (6.1) by the following integrated rate equation for metal-salt decomposition (A —> B, hi) and autocatalytic nanoduster surface growth (A + B — 2B, 2). For a more detailed description of the use of the pseudo-elementary step for the treatment of hydrogenation kinetic data and derivation of the kinetic equations see elsewhere [81-83]. 

The project started in November 1995. The first reaction involved the hydrogenation of cydohexene in SCGO2 [Eq. (1)]. The results were striking, with a quantitative conversion being observed. The reaction proceeded with a very high linear hourly... 

The rate law in Equation 15.18 quantitatively accounts for the observed rate behavior for the hydrogenation of cydohexene. Since the migratory insertion reaction k is the slowest step in the catalytic cycle, under conditions of constant H, pressure, high olefin concentrations (> 1 M), and no added phosphine, the rate reaches a limiting value determined by the rate of the migratory insertion step. 

The product of the Diels-Alder reaction is usually a structure that contains a cydohexene ring system. If the substituents as shown are simply alkyl groups or hydrogen atoms, the reaction proceeds only under extreme conditions of temperature and pressure. With more complex substituents, however, the Diels-Alder reaction may proceed at low temperatures and under mild conditions. The reaction of cyclopentadiene with maleic anhydride (Experiment 47) is an example of a Diels-Alder reaction carried out under reasonably mild conditions. 

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