Case studies yield

Data gathered in the lessons were used to produce case studies for each of the groups of students because such case studies yield rich descriptions of events that are presented in a chronological narrative that incorporates the researcher s observations. Due to the possible inclusion of such an interpretation of the data, case studies go beyond simple descriptions of the situation and support the analysis of the phenomenon being studied (Cohen, Manion, Morrison, 2000). In order to discuss the research questions, we browsed the original case studies to identify evidence of how the students dealt with the levels of representation. Whenever it is appropriate, such evidence is included in the later sections of this chapter. 

More recently, it has been found that MTO absorbed in NaY zeolite allows the selective oxidation of silanes to silanols in the presence of H2O2 (85 %) in excellent yield [lOe]. No oxidation was found in the absence of MTO. In most cases studied, yields of disiloxanes were low (< 6 %). 

An entirely different method for effecting, overall, an jp - p -coupling of aryl Grignard reagents is by reaction of the latter with pyridazine A-oxide (Scheme 20). In the simple cases studied, yields of enynes were 52-77%. The possibility of applying this approach to more highly substituted substrates does not appear to have been examined. 

The above discussion represents a necessarily brief simnnary of the aspects of chemical reaction dynamics. The theoretical focus of tliis field is concerned with the development of accurate potential energy surfaces and the calculation of scattering dynamics on these surfaces. Experimentally, much effort has been devoted to developing complementary asymptotic techniques for product characterization and frequency- and time-resolved teclmiques to study transition-state spectroscopy and dynamics. It is instructive to see what can be accomplished with all of these capabilities. Of all the benclunark reactions mentioned in section A3.7.2. the reaction F + H2 —> HE + H represents the best example of how theory and experiment can converge to yield a fairly complete picture of the dynamics of a chemical reaction. Thus, the remainder of this chapter focuses on this reaction as a case study in reaction dynamics. 

Recovery nd Purifica.tion. The production of EH Lilly s human insulin requires 31 principal processing steps of which 27 are associated with product recovery and purification (13). The production process for human insulin, based on a fermentation which yields proinsulin, provides an instmctive case study on the range of unit operations which must be considered in the recovery and purification of a recombinant product from a bacterial fermentation. Whereas the exact sequence has not been pubUshed, the principle steps in the purification scheme are outlined in Figure la. 

There is evidence from a detailed study of the photolyses of 2-alkyl-substituted aryl azides 40 in diethylamine that A3,7V-diethyl-1 //-azepin-2-amines are formed as oxygen-sensitive, meta-stablc intermediates that can give rise to a variety of byproducts, including 5-acyl- A%V-diethyl-pyridin-2-amines and 6-alkyl-7-(diethylamino)-2//-azepin-2-ones 11 however, formation of these oxidation products can be avoided by refluxing the photolysate mixture with methanol prior to exposure to oxygen, in which case practicable yields of the /V,/V-diethyl-3W-azepin-2-amines 41 result. 

In some cases, the changes in the recipe from pilot to operation scale are substantial. In Case study 4, the introduction of a second solvent is accompanied by a better yield, at the expense of a five-fold higher sewage production. Consequently, raw material demand to produce one kilogram of product is diminished, and the introduction of a second... 

These findings support the general usefulness of efforts to increase yield and solvent recycling rates, as documented in Case study 4 (see also Geisler et al. [9]). However, producing an LCA requires a substantially higher effort for data acquisition as compared to mass balancing. 

Our case studies prove that optimization objectives generally followed in synthesis design and during scale up show a high potential for increasing resource efficiency. These objectives are, for example, increases of yield and the recycling efficiency of solvents and auxiliary materials. 

Ayscough and coworkers studied the ESR spectra of y-irradiated sulfones and polysulfones. Irradiation at 77 K leads mainly to alkyl radicals R formed by rupture of the C—S bonds. Small amounts of RS02 were also observed in some cases as well as radicals formed by loss of an a-hydrogen from the parent molecule—R". On warming the irradiated samples the simple alkyl radicals disappear first. At room temperature only the RS02 radicals have any appreciable stability. In some cases the yield of RS02 radicals increases on warming of the sample. 

Table 4.4 is the summary of the mathematical model and the results obtained for the case study. The model for scenario 1 involves 637 constraints, 245 continuous and 42 binary variables. Seventy nodes were explored in the branch and bound algorithm. The model was solved in 1.61 CPU seconds, yielding an objective value (profit) of 1.61 million over the time horizon of interest, i.e. 6 h. This objective is concomitant with the production of 850 t of product and utilization of 210 t of freshwater. Ignoring any possibility for water reuse/recycle, whilst targeting the same product quantity would result in 390 t of freshwater utilization. Therefore, exploitation of water reuse/recycle opportunities results in more than 46% savings in freshwater utilization, in the absence of central reusable water storage. The water network to achieve the target is shown in Fig. 4.14. 

The authors work demonstrated that even samples as small as 2.5 mg could be studied yielding data with s/n > 5 1. They further demonstrated for samples with aromatic rings that 60 Hz optimization of the experiment was beneficial and that correlations to aliphatic carbons with smaller LJcc couplings did not experience a serious adverse impact due to the larger optimization but the reverse was not true. Correlations to aromatic carbons were not amenable to optimization biased toward aliphatic carbons (e.g. 40 Hz). Correlations observed in the 1,1-ADEQUATE spectrum of retrorsine (22) are shown on the structure. Complete 1,1-ADEQUATE correlations were not shown for delcosine (23) but the authors noted that the key correlations shown on the structure that were observed in the 1,1-ADEQUATE data were not observed in the H2BC spectrum acquired. The impact of the availability of the 1,1-ADEQUATE data on the Structure Elucidator CASE program is discussed in Section 7. 

Loupy and Soufiaoui described a comparative study of the reactivity of diphenylnitri-limine 200 with several dipolarophiles under microwave irradiation in the absence of solvent using a solid mineral support or phase-transfer catalysis (PTC) conditions (Scheme 9.62) [30b]. The results showed that the best yields of adducts were achieved upon impregnating KF-alumina with a mixture of the hydrazynoyl chloride 199 and the dipolarophile followed by irradiation of the mixture in a focused oven. Reaction of this mixture under solid-liquid PTC conditions with KF-Aliquat under microwaves afforded lower yields of cycloadducts, perhaps owing to the partial decomposition of Aliquat at the reaction temperature (140 °C). In all cases, worse yields were obtained by classical heating under comparable reaction conditions (time and temperature). 

As already noted, the carbonylation of bis(pentamethyl-cyclopentadienyl) actinide hydrocarbyls is irreversible in the cases studied thus far. Thus, thermolysis does not result in CO loss, but rather in interesting chemical reactions. Thermolysis of 1 ( 5) in toluene solution results in hydrogen atom migration to yield an enolate (eq.(5)). NMR studies establish that eq.(5) is essentially quantitative, and that the stereochemical course... 

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