Martin Høj

Nitrene-Carbene-Carbene Rearrangement. Photolysis and Thermolysis of Tetrazolo[5,1-a]phthalazine with Formation of 1-Phthalazinylnitrene, o-Cyanophenylcarbene, and Phenylcyanocarbene

1-Azidophthalazine 9A is generated in trace amount by mild FVT of tetrazolo[5,1-a]phthalazine 9T and is observable by its absorption at 2121 cm(-1) in the Ar matrix IR spectrum. Ar matrix photolysis of 9T/9A at 254 nm causes ring opening to generate two conformers of (o-cyanophenyl)diazomethane 11 (2079 and 2075 cm(-1)), followed by (o-cyanophenyl)carbene (3)12, cyanocycloheptatetraene 13, and finally cyano(phenyl)carbene (3)14 as evaluated by IR spectroscopy. The two carbenes (3)12 and (3)14 were observed by ESR spectroscopy (D|hc = 0.5078, E|hc = 0.0236 and D|hc = 0.6488, E|hc = 0.0195 cm(-1), respectively). The rearrangement of 12 ⇄ 13 ⇄ 14 constitutes a carbene-carbene rearrangement. 1-Phthalazinylnitrene (3)10 is observed by means of its UV-vis spectrum in Ar matrix following FVT of 9 above 550 °C. Rearrangement to cyanophenylcarbenes also takes place on FVT of 9 as evidenced by observation of the products of ring contraction, viz., fulvenallenes and ethynylcyclopentadienes 16-18. Thus the overall rearrangement 10 → 11 → 12 ⇄ 13 ⇄ 14 can be formulated.

Deactivation behavior of an iron-molybdate catalyst during selective oxidation of methanol to formaldehyde

An iron molybdate/molybdenum oxide catalyst (Mo/Fe = 2) was synthesized by a hydrothermal method and the catalysts performance and compositional changes were followed during selective oxidation of methanol to formaldehyde for up to 600 h. The activity was continuously measured for a series of experiments performed in a laboratory fixed-bed reactor with 10, 100, 250 and 600 h on stream under reaction conditions (5% MeOH, 10% O2 in N2, Temp. = 384–416 °C, W/F = 1.2 gcat h molMeOH−1). The structural and compositional changes of the catalyst were investigated by a number of techniques including: XRD, Raman spectroscopy, XPS, SEM-EDS and STEM-EDS. Methanol forms volatile species with molybdenum at reaction conditions, leading to depletion of Mo from the catalyst. Excess MoO3 was shown to volatilize and leave the catalyst during the first 10 h on stream, leading to an initial loss in activity of 50%. From 10 to 600 h on stream leaching of molybdenum from the remaining iron molybdate phase (Fe2(MoO4)3, Mo/Fe = 1.5) leads to iron rich phases (FeMoO4 and Fe2O3, Me/Fe < 1.5) and simultaneously an increase in activity to approximately 1.5 times the initial activity. Even at high degrees of molybdenum loss (Mo/Fe = 0.49) the formaldehyde selectivity remained above 92%, and the combined CO/CO2 selectivity was below 4%. This is likely due to a surface layer of MoOx on the catalyst at all times due to segregation and a surface in equilibrium with the gaseous molybdenum compounds. After 600 h on stream formation of β-MoO3 was observed, indicating that this molybdenum oxide phase is stable to some extent under reaction conditions.