Hydrogenation of furan

Catalytic hydrogenation of furan to tetrahydrofuran is accompHshed in either Hquid or vapor phase. Hydrogenation of the double bonds is essentially quantitative over nickel catalysts but is generally accompanied by hydrogenolysis over the noble metals. 

Similar procedures to those used for the catalytic hydrogenation of furan and thiophene can usually be applied to the functional derivatives of these heterocycles. 

Catalytic hydrogenation of furan Catalytic hydrogenation of furan with a palladium catalyst gives tetrahydrofuran, which is a clear, low-viscosity liquid with a diethyl-ether-like smell. 

The popular approach to tetrahydrofurans involves an electrophilic process and the commonly used electrophiles for the cyclization are acids, oxygen, halogen, mercury (see Section 3.11.2.2.9) and selenium. The ionic hydrogenation of furans with excess triethyl-silane in trifluoroacetic acid affords high yields, e.g. 2-methylfuran is reduced to 2-methyl-tetrahydrofuran and 2-ethylfuran to 2-ethyltetrahydrofuran (see Section 3.11.2.5). The synthesis of several dihydro and tetrahydrofurans containing natural products by chirality transfer from carbohydrates has been used successfully for total synthesis, e.g. (-)-nonactic acid. A reasonable yield of 2-alkyltetrahydrofuran was prepared from 4-alkylbut-l-en-4-ol by hydroboration followed by cyclization with p-toluenesulfonic acid. 

According to Freifelder, in most instances ruthenium catalyst is superior to nickel catalyst for the hydrogenation of furans to tetrahydrofurans the hydrogenation can be carried out at 70-100°C and 7 MPa H2.185 He refers to an example in which 2-furfu-rylamine was hydrogenated without solvent over ruthenium dioxide at 100°C and 8 MPa H2 in 10 min, compared to the temperatures of < 150°C and a reaction time of 30 h at 7 MPa H2 that were required for hydrogenation with Raney Ni. Hydrogenation of P-(2-furyl)alkylamines and an A-ethyl-2-furylalkylamine to the corresponding tetrahydro compounds was performed satisfactorily over palladium catalyst in ethanol in the presence of hydrochloric acid at room temperature and 0.62 MPa H2 (eq. 12.102)197 and over 5% Rh-C in neutral solvent at room temperature and 0.15 MPa... 

The catalytic hydrogenation of furan and its derivatives is strongly dependent on reaction conditions and catalysts employed. A review is available.188 It is possible to classify the results of these reactions into three main groups ... 

The experiments were run with a view to determining how four experimental variables influence the yield in the catalytic hydrogenation of furan over a palladium catalyst. The variables were x2, the amount of palladium catalyst x2, the hydrogen pressure x3, the reaction temperature and x4, the stirring rate. The factorial design, 24, shown in Table 2 was used to fit a second-order intraction model to the yields obtained ... 

Table 2. Experimental design and yields obtained in the catalytic hydrogenation of furan...

Fig. 4. Response surface showing the variation in yield when hydrogen pressure and stirring rate was varied in the catalytic hydrogenation of furan. The twist due to an interaction effect is clearly seen. The remaining variables were set to their upper levels...

The hydrogenation of furan may be carried out with initial pressures of only 3 atm. (45 lb.), but the reduction is slower. 

Tetrahydrofurane-cis-2,S-dkarboxylic acid. Rhodium (5%) on carbon is the catalyst of choice for hydrogenation of furane-2,5-dicarboxylic acid (1) to tetra-hydrofurane-c -2,5-dicarboxylic acid (2). 

Hydrogenation of furan, 2,3-dihy-drofuran, silvan, and furfural Methanol steam reforming Coupling of dehydrogenation of isoamylenes and hydrodemethyN ation of toluene or oxidation of hydrogen ... 

A 2-aminofuran was converted into 4,4 -bipyrazole by reaction with two molecules of hydrazine <06TL8965>. Hydrogenation of 2-amylfuran under 5 atm of H, as catalyzed by 10% Rh/Cat80 °C in water provided 2-amyltetrahydrofuran in 90% yield <06SL1440>. An advance in the area of enantioselecti ve hydrogenation of furans, as reported by Pfaltz, is the hydrogenation of... 

The hydrogenation of furan to THF is an energetically very strongly favored reaction. The enthalpy change of the reaction in the liquid phase is 153.8 kcal/mole (643.499 kJ/mole), and in the vapor phase it is 149.4 kcal/mole (625.090 kJ/mole), which is more than twice as much as for the hydrogenation of furfural to furfuryl alcohol. 

Derivation (1) Catalytic hydrogenation of furan with nickel catalyst. (2) Acid-catalyzed dehydration of 1,4-butanediol. 

The experiments were run to determine how four experimental variables influence the yield of tetrahydrofuran in catalytic hydrogenation of furan over a palladium catalyst. The variables and the experimental domain are shown in Table 5.10. 

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