N-Hexane oxygenation

Figure 40.1 reports the flammabihty diagrams for the ternary mixtures ammonia/oxygen/inert and n-hexane/oxygen/inert. The boundary conditions for the catalytic tests were the following ... 

Fig. 42. n-Hexane—oxygen. Molar ratio 1.25 1 cylindrical pyrex reaction vessel, volume 200 cm. (From ref. 73.)... 

Properties Colorless oily liq., char, fatty odor cryst. when cooled sol. in alcohol, chloroform, ether, acetone, benzene, cyclohexane, n-hexane, oxygenated soivs. pract. Insol. In water m.w. 158.24 dens. 0.907 (20/4 C) m.p, 10-12 C b.p, 252-253 C (756 mm) acid no. 351 flash pt. 129 C ref. index 1.433 (20 C) weakly acidic Toxicology LD50 (oral, mouse) 15 g/kg, (IV, mouse) 224 4.6 mg/kg poison by IV route mod. toxic by ing. strong irritant to skin and eyes inh. of mists may cause mild to mod. irritation to nose/throat ing. of Ig. doses may cause mild irritation, sore throat, abdominal pain, nausea, vomiting TSCA listed Precaution Combustible corrosive... 

Figure 2. Effect of n-hexane/oxygen ratio for 2.0 SLPM total flow (t = 500 jas), 30% Nj dilution, = 200°C, and P=. 2 atm.

Individual olefins as well as selectivity to all Cg olefins are shown in Figure 2c. Ethylene was by far the dominant olefin for C JO < 1.0. Propylene and 1-butene were also important they exhibited maximum selectivities at a n-hexane/oxygen ratio of unity and then fell to <5% selectivity forCgHi/Oj > 3.0. The Cg olefins, which include 1-hexene, 2-hexene, and 2-methyl-1-pentene (not shown), gradually increased to 14% selectivity at CgHi4/0, = 5.0. The isomers 1-hexene and 2-hexene were produced in nearly equal amounts until CgHig/Oj = 3.0, after which the l-CgHi2/2-CgH,2 ratio was approximately two. 

If all the oxygen containing groups are reduced, n-hexane results. This test helps establish that the glucose molecule has a chain structure. One representation of the structural formula of glucose, C6Hi206, is... 

Hydrocarbon-rich conditions imply that oxygen is the limiting reactant, due to the high oxygen-to-hydrocarbon stoichiometric ratio in n-hexane ammoxidation. Therefore, the conversion of the hydrocarbon is low this should favour, in principle, the selectivity to products of partial (amm)oxidation instead of that to combustion products. 

The feed composition chosen was 6 mol% n-hexane, 6 mol% ammonia, 12 mol% oxygen and remainder helium, with an overall gas residence time of 2.5 s. Due to the low temperature of n-hexane self-ignition (T 234°C), a relevant contribution of homogeneous, radical reactions was expected. Tests made in the absence of catalyst... 

Figure 40.3. Conversion of reactants in n-hexane ammoxidation as a function of the reaction temperature. Symbols conversion of n-hexane ( ), annnonia (A) and oxygen ( ). Catalyst SnA /Nb/Sb 1/0.2/1/3.

Bobrowski and Das33 studied the transient absorption phenomena observed in pulse radiolysis of several retinyl polyenes at submillimolar concentrations in acetone, n -hexane and 1,2-dichloroethane under conditions favourable for radical cation formation. The polyene radical cations are unreactive toward oxygen and are characterized by intense absorption with maxima at 575-635 nm. The peak of the absorption band was found to be almost independent of the functional group (aldehyde, alcohol, Schiff base ester, carboxylic acid). In acetone, the cations decay predominantly by first-order kinetics with half life times of 4-11 ps. The bimolecular rate constant for quenching of the radical cations by water, triethylamine and bromide ion in acetone are in the ranges (0.8-2) x 105, (0.3-2) x 108 and (3 — 5) x 1010 M 1 s 1, respectively. 

J. M. Thomas, R. Raja, G. Sankar, and R. G. Bell, Molecular-sieve catalysts for the selective oxidation of linear alkanes by molecular oxygen. Nature 398,227 (1999) J. M. Thomas, Designing a molecular sieve catalyst for the aerial oxidation of n-hexane to adipic acid, Angew. Chem. Int. 

Fig. 23. (—) spectrum at atmospheric pressure (—) spectrum under 100 atm of oxygen. 1-naphthaldehyde, 0.20 M in n-hexane 2-acetonaphthone, 2.00 M in chloroform 1-acetonaph-thone, 1.00 M in chloroform. Path length 8.5 cm. (From Warwick and Wells, Ref. >)... 

Figure 5. Effect of oxygen concentration on catalytic oxidation of n-hexane...

Allylation of Pyranosyl Compounds with Allylstannane [19,20]. A solution of the methyl-(p-D-galactopyranosyl chloride) onate 22 (953.5 mg, 1.8 mmol) in 30 mL of dry, oxygen-free THF, was heated to 60°C. To this solution under nitrogen, were added the tributylallyl tin 23 (5.2 mL, 14.7 mmol) and A1BN (15 mg, 0.1 mmol). After 20 h, the solvent was evaporated, and the residue was taken up in 5 mL of acetonitrile. The acetonitrile layer was extracted with 20 mL of n-hexane and then concentrated. Chromatography on silica gel (toluene-acetone, 4 1) afforded the product 24 (889 mg, 93%), containing two anomers. Nuclear magnetic resonance (NMR) spectroscopy showed a ratio of the two anomers of 1.8 1. 

Figure 20.5 Activation period for n-hexane isomerization over Mo2C-oxygen-modified at atmospheric pressure (623 K, p(C6) = 5 Torr).

Another difference between WC and Mo2C catalysts in n-hexane-H2 reactions is their selectivity-conversion relationship as shown in Figure 21.3. Isomerization selectivity over WC did not show any dependence on n-hexane conversion. It depended only on the oxygen treatment temperature. In contrast, isomerization selectivity over Mo2C showed a linear decrease with increasing -hexane conversion. 

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