The first diiron thiadithiolates as active site models for the Fe-only hydrogenases were prepared. Treatment of Fe 3 (CO) 12 with excess 1,2,4-trithiolane in THF at reflux afforded parent model Fe 2 (µ-SCH 2 ) 2 S(CO) 6 (1) in 42% yield. Further treatment of 1 with Cp(CO) 2 Fe(BF 4 ) prepared in situ from Cp(CO) 2 FeI and AgBF 4 in CH 2 Cl 2 gave cationic model [Fe 2 (µ-SCH 2 ) 2 S(CO) 6 ][Cp(CO) 2 Fe](BF 4 ) (2) in 81% yield, while treatment of 1 with 2 equiv of Et 4 NCN in MeCN or with t-BuNC in CH 2 Cl 2 produced models (Et 4 N) 2 [Fe 2 (µ-SCH 2 ) 2 S(CO) 4 (CN) 2 ] (3) and Fe 2 (µ-SCH 2 ) 2 S(CO) 4 (t-BuNC) 2 (4) in 93% and 51% yields, respectively. All the new models 1-4 were characterized by elemental analysis and spectroscopy, as well as by X-ray crystallography for 1, 2, and 4. Furthermore, model 1 has been proved to be a catalyst for proton reduction of a weak acid Et 3 NHCl to give hydrogen under electrochemical conditions.

Understanding the properties and behaviors of diluted bitumen/water interfaces under stresses is important for remediating emulsion problems in bitumen production. We studied the dilational interfacial rheology of toluene-diluted mineralfree Athabasca bitumen, its n-pentane (n-C5) asphaltenes, and partially deasphalted Athabasca bitumens in a NaHCO 3 solution. n-Heptane (n-C7) added in increasing mass ratios to diluted bitumen produced the partially deasphalted bitumens. The solventfree deasphalted bitumens and the precipitated n-C7 asphaltenes were recovered for study. The number averaged molecular weight (M n ) of the samples was first measured as a function of the mass concentration in toluene. The slopes of these curves indicated that asphaltenes showed higher aggregation tendencies than the bitumens. This tendency was reduced significantly for the deasphalted bitumens. For all oscillation frequencies studied, the interfacial viscoelastic modulus of Athabasca bitumen-intoluene reached a maximum at 0.865 g•L −1 (0.1 wt%) bitumen, then declined as the bitumen concentration increased. The n-C5 asphaltenes-in-toluene made up at the same concentration at which they occur in the diluted bitumen showed higher elastic and viscous moduli than those for the diluted source bitumen, at all frequencies tested. Both systems showed direct dependence of viscoelasticity on the logarithm of frequency; the n-C5 asphaltenes showed a higher viscoelasticity gradient than that for the bitumen. Distinct differences between the interfacial properties for asphaltenes-in-toluene/water vs source bitumens-in-toluene/ water were observed. The interfacial viscoelasticity values for the partially deasphalted bitumens also show apparent dependence on the mass ratio of resins to residual asphaltenes (R/A). Different asphaltene aggregates present in the bitumens may also influence the R/As correlated with reduced elasticity. The interfacial behaviors of asphaltenes only in toluene are thus not indicative of those of bitumens.

No abstract

Bitumen films formed on water surfaces have negative consequences, both environmental and economic. CanmetENERGY has placed considerable research emphasis on understanding the structures of the bitumen films on water as a necessary step before optimization of bitumen extraction. The detailed structures of the adsorbed molecules and, especially, the role of asphaltene molecules at the interfaces are still under scrutiny and debate. In the present study, we compared bitumen and asphaltene films as they were compressed and expanded under various surface pressures in order to achieve a clearer understanding of bitumen film structures. We used a customized NIMA Langmuir trough interfaced to a Brewster angle microscope (BAM) and CCD camera (Nanofilm_ep3BAM, Accurion, previously Nanofilm Gmbh) to study images of bitumen films at the air/water interface. The bitumen film appeared uniform with high reflectivity at a surface pressure of 18 mN·m(-1) and exhibited a coarse pebblelike interface with reduced reflectivity in the liquid condensed (LC) phase at higher pressures (18-35 mN·m(-1)). During the first cycle of compression asphaltene films showed well-defined phase transitions and a uniformly smooth interface in the LC phase between 9 and 35 mN·m(-1). However, folding or buckling occurred at surface pressures from 35 to 44 mN·m(-1). On expansion, asphaltene films appeared to break into islands. The hysteresis of the pressure-area isotherm was much larger for asphaltenes than for bitumen. In both compression and expansion cycles, BAM images for bitumen films appeared to be more reproducible than those of the asphaltene films at the same surface pressures. Films for low-°API SAGD bitumen were almost identical to those for surface-mined bitumen. Films formed from partially deasphalted surface-mined bitumens showed higher compressibility and lower rigidity than the original bitumen. The BAM images illustrated significant differences between the partially deasphalted and original bitumen films. Other components in bitumen also played important roles in determining the interfacial properties of bitumen films.

No abstract