Bulk bases

Tool-mounted optrode (TMO). The cure-monitoring experiments described here were conducted with a "tool-mounted" optrode (TMO) arrangement (5,6) (Figure 2) which is Ideally suited for the manufacturing environment where minimum interference with the laminate layup work is desirable. The use of a tool-mounted optrode is as simple as the use of tool-mounted thermocouples currently in wide use. Indeed, the TMO provides viscosity/degree-of-cure information on the cure state of the surface layer only. However, knowledge of the cure state of the surface layer permits determination of the cure states in the bulk based on the available models (1,2). 

The finding that the use of LDA as bulk base results in non-enantioselective deprotonation indicated that bulk bases which are much less reactive toward the epoxide substrate compared with the chiral lithium amide are needed. But they should be strong enough to regenerate the chiral amide from the amine formed in the epoxide rearrangement. 

In order to further develop the field of enantioselective catalytic deprotonation, it was necessary to develop bulk bases that show low reactivity toward the epoxide but have the ability to regenerate the chiral catalyst. Thus, the bulk bases should show low kinetic basicity toward the substrate, but be thermodynamically and kinetically basic enough to be able to regenerate the chiral lithium amide from the amine produced in the rearrangement. 

Ahlberg and coworkers have found that lithiated 1-methylimidazole (21) and lithiated 1,2-dimethylimidazole (22) work as such bulk bases in the presence of catalytic amounts of a readily accessible homochiral lithium amide 20 (both enantiomers are readily available) (see Section III.C)45,46. These new bulk bases are easily accessible by deprotonation of 1-methylimidazole and 1,2-dimethylimidazole by, e.g., n-BuLi (Scheme 72). Using chiral lithium amide 20 (20 mol%) and bulk base 21 or 22 (200 mol%) in the deprotonation of cyclohexene oxide 1 gave (S)-2 with the same enantiomeric excess (93%) as under stoichiometric conditions (Scheme 15). Apparently, any background reactions of the bulk bases are insignificant. Interestingly, no addition of DBU was needed to obtain the high enantioselectivities under these catalytic conditions. 

Ahlberg and coworkers noted that in some cases the enantioselectivity was increased when running the deprotonations with equimolar amounts of the novel bulk bases and the chiral lithium amide113. This finding initiated a detailed mechanistic investigation using isotopically labeled compounds and multinuclear NMR spectroscopy and kinetics, to elucidate the nature of the reagents and transition states in the deprotonations. They discovered that mixed dimers 23 and 24 are formed in solution from monomers of chiral lithium amide 20 and bulk base 21 and 22, respectively (Scheme 73). 

Thus LDA is not needed for efficient recycling, which was demonstrated by deprotonation of cyclohexene oxide using 4 in catalytic amounts together with 102 as bulk base generated from DBU and w-BuLi, (S)-2 is formed in 79% ee (Scheme 74) (80% ee under stoichiometric conditions, Scheme 2). In contrast, when 4 was used in catalytic amounts... 

Deprotonation of 4-f-butyl cyclohexanone 28 with chiral lithium amide 39 (30 mol%) and bulk base 107 (240 mol%) in the presence of HMPA (240 mol%) and DABCO (150 mol%), under external quench conditions, resulted in 79% ee of the silyl enol ether 29 (Scheme 79)121. This stereoselectivity is only slightly lower than that of the stoichiometric reaction (81% ee). 

More recently, NEBULA catalyst has been developed jointly by ExxonMobil, AkzoNobel, and Nippon Ketjen and commercialized in 2001.103 NEBULA stands for New Bulk Activity and is bulk base metal catalyst without using a porous support. Figures 5.8-5.10 show the recent results published by AkzoNobel on relative activity of the new NEBULA and STARS catalysts compared with conventional CoMo/A1203 developed over the last 50 years.104 The NEBULA-1 catalyst is even more active than KF 848 STARS catalyst with respect to HDS and hydrodenitroge-nation (HDN) and diesel hydrotreating it has been successfully applied in several... 

Patterson, D., Amedjkouh, M. and Ahlberg, P. (2002) Improved enantioselectivity by using novel bulk bases in chiral hthium amide catalysed deprotonations mixed dimers as reagents and... 

In a lithium amide promoted deprotonation, one lithium amide molecule is consumed for each deprotonated epoxide molecule. Since chiral hthium amides are expensive reagents, there is a strong desire to develop less costly synthetic procedures for stereoselective deprotonations. Catalysis has the potential to solve the problem. What are needed are bulk bases capable of regenerating the chiral hthium amide from the chiral diamine produced in the deprotonation reaction. There have been some attempts along this line, e.g., by Asami and co-workers, who used the non-chiral hthium amide LDA as bulk base and the chiral hthium amide 4 as catalyst [9,12,39-41]. However, the stereoselectivity was considerably lower than what had been achieved in absence of the bulk base, i.e., under stoichiometric conditions. Most likely, the decreased stereoselectivity in the presence of bulk LDA is due to competing deprotonation by LDA to yield racemic product alcohol. The situation is illustrated in Scheme 9. 

Apparently there is a need for bulk bases that are kinetically much less basic than LD A but that still are capable of efficiently regenerating the chiral lithium amide. Proton transfers to and from electronegative atoms like nitrogen are usually faster than from and to carbon. Therefore, we have explored carbon-based bases for the present purpose [20-22,24]. Indeed, bases like those displayed in Scheme 10 appear to have the predicted behaviour. 

Using either the carbenoid compound 6 or the carbanionic compound 7 as a bulk base in large excess and 5 as catalyst (Scheme 11) gave the same stereoselectivity as the stoichiometric deprotonation of 2 with 5. 

These encouraging results indicate that both bulk bases are functioning as predicted. 

However, when another experiment using equimolar amounts of bulk base and 5 was carried out, to our surprise, an increased stereoselectivity was observed [20-22]. The mixture of product enantiomers now contained 98% of the (5)-alcohol and only 2% of the (/ )-alcohol. Apparently the interpretation just made needs some adjustment to account also for these new observations. 

The results led us to investigate the composition of the reagent solutions by multinuclear NMR spectroscopy. These studies revealed that under these new conditions 5 was no longer present as a homodimer, i.e., a 5 molecule is complexed with another 5 molecule. Instead the results showed new dimers -heterodimers 8 or 9, respectively. A monomer of 5 forms complex with a monomer of a bulk base and these heterodimers are the new reagents rather than homodimers of the chiral lithium amide (Scheme 12) [20-22]. 

W.J.S. Craigen and Canmet/MSL Staff, The CANMET Ferric Chloride Leach Process for the Treatment of Bulk Base Metal Sulphide Concentrates , MSL Division Report. MSL 89-67, June 1989. 

This phase has presumably mobility and therefore gas permeability properties differing from fhe bulk. Based on fhis consideration, the oxygen permeation through the confined polymer phase was tentatively assumed to be negligible with respect to the bulk one, and a modified version of the tortuous path model of Gusev and Lusti taking into account the total non permeable volume (silica plus volume of confined polymer chains) was derived (Figure 11.27). 

Diffusion- M (bulk) -based EET parameters Bulk FMN concentration 1 pM [26, 41]... 

The aqua-Ln cations may be considered reference species in several regards and for [Ln(OH2) ] + complexes, measurements of water molecule exchange between the primary coordination sphere and the bulk, based largely on NMR measurements, have established that all are extremely labile species, with exchange half-lives in the micro- to nanosecond range. Various measurements have estabhshed tiiat, in aqueous solution, [Ln(OH2)9] + (1) is the dominant species for Ln = La-Nd and [Ln(OH2)8] + and (2) for Ln = Gd-Lu, while for Ln = Pm-Eu a mixture of... 

Step 1. Preparation of Base Fluid Bulk base fluid samples were prepwed by mixing water, viscosifiers, and barite. Immediately after mixing all water-based fluids were covered and left undisturbed for a minimum of 24 hours to ensure full hydration of... 

ERF dielectric response can be appropriately described by the classical Debye circuit model (Section 4-4). The model contains 1 pF/cm bulk base oil capacitance in parallel with Tohm range base oil resistance This combination results in a circuit with a time constant on the order of 10 seconds, typical of the impedance behavior of dielectric materials with very low ionic content. The presence of 10 to 50 percent polarizable particles results in the development of a parallel bulk-solution conduction mechanism through the particles. When compared to the ions that transport current by electrophoretic mobility, the ERF particles have larger sizes and lower mobility and are capable of becoming polarized and reoriented in the external electric field. This percolation type of conduction mechanism can be represented by a series of the particle resistance and the contact impedance between the particles (Figure 12-8). As the ionic content is essentially absent in the... 

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