Yield improvement

The refluxing period may be reduced to 6 hours and the yield improved slightly by mechanical stirring a tliree-necked flask should be used. 

Practically all CNDO calculations are actually performed using the CNDO/ 2 method, which is an improved parameterization over the original CNDO/1 method. There is a CNDO/S method that is parameterized to reproduce electronic spectra. The CNDO/S method does yield improved prediction of excitation energies, but at the expense of the poorer prediction of molecular geometry. There have also been extensions of the CNDO/2 method to include elements with occupied d orbitals. These techniques have not seen widespread use due to the limited accuracy of results. 

Significant differences in net photosynthetic assimilation of carbon dioxide are apparent between C, C, and CAM biomass species. One of the principal reasons for the generally lower yields of C biomass is its higher rate of photorespiration if the photorespiration rate could be reduced, the net yield of biomass would increase. Considerable research is in progress (ca 1992) to achieve this rate reduction by chemical and genetic methods, but as yet, only limited yield improvements have been made. Such an achievement with C biomass would be expected to be very beneficial for foodstuff production and biomass energy appHcations. 

The preferred route to higher purity naphthalene, either coal-tar or petroleum, is crystallisation. This process has demonstrated significant energy cost savings and yield improvements. There are several commercial processes available Sulser-MWB, Brodie type. Bets, and Recochem (37). 

The production of elfamycins is described in the references cited in Table 1. Fermentation yield improvements with aurodox (1, R = CH ) proved difficult because of feedback inhibition (48). Aurodox-resistant strains (49), however, responded positively to conventional mutagenic methods leading to yield increases from 0.4 to 2.5 g/L (50). Scale-up of efrotomycin (7, R = CH ) fermentations were found to be particularly sensitive to small changes in sterilization conditions of the oil-containing medium used (51). 

The potential usefulness of elfamycins as growth promoters and feed-conversion enhancers is now generally recognized. Low original fermentation yields and difficulties in yield improvements discouraged early attempts to develop aurodox ( 1, R = CH ) and mocimycin (kirromycin) (1, R = H) commercially. 

Raw material costs and utilisation yield improvement reduced losses... 

Manufacture. Trichloromethanesulfenyl chloride is made commercially by chlorination of carbon disulfide with the careful exclusion of iron or other metals, which cataly2e the chlorinolysis of the C—S bond to produce carbon tetrachloride. Various catalysts, notably iodine and activated carbon, are effective. The product is purified by fractional distillation to a minimum purity of 95%. Continuous processes have been described wherein carbon disulfide chlorination takes place on a granular charcoal column (59,60). A series of patents describes means for yield improvement by chlorination in the presence of dihinctional carbonyl compounds, phosphonates, phosphonites, phosphites, phosphates, or lead acetate (61). 

Work at Rhc ne-Poulenc has involved a different approach to retinal and is based on the paHadium-cataly2ed rearrangement of the mixed carbonate (41) to the aHenyl enal (42). Isomerization of the aHene (42) to the polyene (43) completes the constmction of the carbon framework. Acid-catalyzed isomerization yields retinal (5). A decided advantage of this route is that no by-products such as triphenylphosphine oxide or sodium phenylsulfinate are formed. However, significant yield improvements would be necessary for this process to compete with the current commercial syntheses (25—27) (Fig. 9). 

The majority of industrial research describes classical approaches to yield improvement (49). However, there has been some work using genetically modified organisms. In the case of these recombinant organisms, the carotenoid biosynthetic gene cluster has been expressed in noncarotegenic species such as E. coli (50) and S. cerevisiae (51). 

Valve Application Technology Functional requirements and the properties of the controlled fluid determine which valve and actuator types are best for a specific apphcation. If demands are modest and no unique valve features are required, the valve-design style selection may be determined solely by cost. If so, general-purpose globe or angle valves provide exceptional value, especially in sizes less than 3-inch NFS and hence are very popular. Beyond type selection, there are many other valve specifications that must be determined properly in order to ultimately yield-improved process control. 

In 1976, Johns, Ransom and Reese reported improvements in the previously reported syntheses of 18-crown-6 and 15-crown-5. By using tetraethylene glycol rather than triethylene glycol and the correspondingly shorter dichloride (2.5 equivalents of the latter) in concert with KOH (no water added), they were able to realize a 6% yield improvement in the synthesis of 18-crown-6 over the previously published method . The improvement in the yield of 15-crown-5 was of somewhat greater interest, being 38% compared to Liotta s previous report of 15% . ... 

Reaction times can be shonened and yields improved through the use of high pressure [40] (equation 28) Reactions may also be conducted in aqueous medium under ultraviolet irradiation [41] (equation 29)... 

Figure 16.15 shows the resulting chromatograms for the three glucan fractions obtained by previous preparative separation on Sephacryl S-200/S-1000 (Fig. 16.14). From the normalized fraction chromatograms, the elution profile of the initial mixture has been reconstructed by mixing 50% fraction 1, 40% fraction 2, and 10% fraction 3. Compared to the chromatogram of the preparative Sephacryl S-200/S-1000 system, separation with the TSK/ Superose system yields improved resolution in the low dp (high V, ) domain.

The parent TMM precursor (1) reacts with tropones (117) to give reasonable yields of the bridged [4.3.1]decanones (118) [43]. Various substituted TMMs also cycloadd to tropone with regioselectivity similar to that of the corresponding [3+2] cases [20, 43]. Addition of MesSnOAc as a co-catalyst also leads to yield improvement [16]. In the case of a phenyl-substituted tropone and a methyl-TMM, performing the reaction under high pressure favors the formation of kinetic products (119) and (120) over the thermodynamic product (121) [11]. 

Any (project yield improvements should be based on conducting a senes of operating test runs. The test runs should reflect typicar operating modes. The results should be material/heat balanced. Another test run should be performed just prior to the revamp. A comparison of the results, pre- and post-revamp, should reflect no major changes in the catalyst reformulation. 

Where biosynthesis of a product requires the net input of energy, the theoretical yield will be influenced by the P/O quotient of the process organism. Furthermore, where the formation of a product is linked to the net production of ATP and/or NADH, the P/O quotient will influence the rate of product formation. It follows that to estimate the potential for yield improvement for a given primary or secondary metabolite, it is necessary to determine the P/O quotient of the producing organism. 

Experimentally determined yields of exopolysaccharide have been found to be 70% of the theoretical. This suggests that exopolysaccharide production is an efficient process with little scope for major yield improvements. 

The chemical yield of the classical Henry reaction is not always good and depends on steric factors thus, highest yields are obtained when nitromethane is used. Performing the reaction under high pressure (9 kbar, 30 °C) with tetrabutylammonium fluoride catalysis19 enlarges the scope of the reaction dramatically. Thus, addition of nitropropane to 2-methylcyclohexanone, which is not reactive under the classical conditions, was achieved in 40 % yield. Improved yields... 

The 57-g. yield refers to the experiment in which 53 g. of starting material was recovered the percentage yield improves with increase in the amount of anthraquinone recovered. 

The first report of the use of bromine for the oxidation of sulphoxides appeared in 1966116. Diphenyl sulphone was isolated in 0.5-1% yield when the sulphoxide was treated with bromine in aqueous acetic acid for several hours. The yield was increased to about 5% by quenching the reaction with sodium carbonate. A kinetic study117 of a similar reaction involving dimethyl sulphoxide showed no significant yield improvement but postulated that the mechanism proceeds via an equilibrium step forming a bromosulph-onium type intermediate which reacted slowly with water giving dimethyl sulphone as indicated in equation (35). 

Castleberry, R.M., Crum, C.W. Krull, C.F. (1984). Genetic yield improvement of U.S. maize cultivars under varying fertility and climatic environments. Crop Science, 24, 33-7. 

According to the previous mechanism as discussed in the literature, increased loss modulus at high strain should yield improvements in abrasion resistance. Indeed in laboratory PICO abrasion experiments this result is supported. Example results are given in Table 16.1. 

Presentation of microorganism — Fungus isolated from Nature, not genetically modihed yield improvement using classical genetics. 

Finally, yield improvements were also reported for industrial process developments. For the Merck Grignard process, a yield of 95% was obtained by a micro mixer-based process, while the industrial batch process (6 m stirred vessel) had only a 72% yield (5 h, at -20 °C) [11]. The laboratory-scale batch process (0.5 1 flask ... 

Obviously, the least experience has been accumulated with monoliths, particularly in three-phase applications. They are also more expensive than the other reactors. Therefore, the use of monoliths can only be economically ju.stified for three-phase processes in which it offers a distinct advantage, like higher yield, improved. selectivity, increased throughput of a plant, or lower overall investment or operating costs. Of particular interest are situations in which a MR substantially simplifies the design or operation of a unit. 

The addition of metal ions to the mobile phase frequently yields Improved separations of solutes capable of forming complexes (conversely the addition of ligands to the mobile phase may allow the separation of metal ions based on differences in the distribution constants of the complexes between the mobile phase and, stationary phase) [353-355]. A number of important... 

In preparation for scale-up of the strigol synthesis described by Sih (8), efforts were made to improve the yield of some of the seven steps involved in the scheme. Of these steps, nine are satisfactory from the standpoint of yield and experimental conditions. For three of the steps, we have improved the yield and/or experimental conditions such that the yield of (+ )-strigol would be raised to 2.85% overall from citral rather than 1.53% based on Sih s procedure and reported yields. Improvements were developed preparation of a-cyclocitral (III), the oxidation of the hydroxyaldehyde (V) to the ketoacid (VII), and for the preparation of the hydroxybutenolide (XVII). For the remaining five steps, our attempts to change experimental conditions have failed to improve, and in most cases to even obtain, the yields reported in the literature (8). We have considered the preparation of strigol analogs and determined the conditions and limitations for the preparation of a series of alkoxybutenolides (XVI) and a butenolide dimer (XVIII). Modification of the literature procedure (11) to eliminate the use of the mesylate (XX) and the use of polar aprotic solvents gave better yields of the 2-RAS (XXI). 

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