Yield decrease

The use of a-bromoaldehydes, more reactive than the a-chloro derivatives, gives better results (492,512). They have permitted the yields of the cyclization to be increased from 8 to 60% in the latter case. With the higher aldehydes the yields decrease. Thus for 5-f-butylthiazole it is not higher than 7 to 20% (492, 512). On the other hand, cr-bromoaldehydes are particularly difficult to obtain. 

In the series of 2,5-dialkylthiazoles prepared by Poite and Metzger (492,512), the yields decrease from 5-methyl-2-alkylthiazoles (44 to 75%) to 5-t-butyl-2-alkylthiazoles (0 to 3%). 

DihaIogenothiazoIes (271) thus can be prepared from sodium acetylaminomethane sulfonate (270) and thionyl halide, but this reaction proceeds in low yield. With X — Cl, the yield is 20%, while with X = Br the yield decreases to 2% (Scheme 140). 

Figure 7.9 shows a schematic representation of this effect, in which the ratio of the two isotopes changes with time. To obtain an accurate estimate of the ratio of ion abundances, it is better if the relative ion yields decrease linearly (Figure 7.9) which can be achieved by adjusting the filament temperature continuously to obtain the desired linear response. An almost constant response for the isotope ratio can be obtained by slow evaporation of the sample, viz., by keeping the filament temperature as low as is consistent with sufficient sensitivity of detection (Figure 7.9). 

Properties. Results for the operation using subbituminous coal from the Wyodad mine near Gillette, Wyoming, are shown in Table 13. Char yields decreased with increasing temperature, and oil yields increased. The Fischer assay laboratory method closely approximated the yields and product assays that were obtained with the TOSCOAL process. 

Temperature and Product Yields. Most oil shale retorting processes are carried out at ca 480°C to maximize liquid product yield. The effect of increasing retort temperature on product type from 480 to 870°C has been studied using an entrained bed retort (17). The oil yield decreased and the retort gas increased with increased retorting temperature the oil became more aromatic as temperature increased, and maximum yields of olefinic gases occurred at about 760°C. Effects of retorting temperatures on a distillate fraction (to 300°C) are given in Table 6. 

Treatment of cyclic carbonates of 1,2-diols with thiocyanate ion at temperatures of 100 °C or higher yields thiiranes (Scheme 145) (66CRV297, 75RCR138). Thiourea cannot replace thiocyanate satisfactorily, and yields decrease as the carbonate becomes more sterically hindered. The reaction mechanism is similar to the reaction of oxiranes with thiocyanate (Scheme 139). As Scheme 145 shows, chiral thiiranes can be derived from chiral 1,2-diols (77T999, 75MI50600). 

As severity is increased, C5+ gasoline yields decrease, with a corresponding increase in C, to C4 products. Hydrogen yields increase with severity until the level at which no further aromatics are produced as severity is increased even further, hydrogen yields then decrease. 

It is only recently that the chloromethylation reaction, well known in the benzene series, has been extended to isoxazoles. It has been thereby found that this reaction results in 4-chloromethyl derivatives (69), their yield decreasing as follows 5-phenyl > 3,5-dimethyl > 5-methyl > 3-methyl isoxazoles > isoxazole. To prove the position of the chloromethyl group these compounds were oxidized to the known isoxazole-4-carboxylic acids (70). It is especially noteworthy that pyridine and its homologs do not undergo chloromethylation. 

By further increasing the methanol in the grafting medium, the graft yield decreases. This can be related to the lower solubility of the initiator in the grafting medium and a reduced formation of free radicals, which... 

The final conversion yield decreased when substrate concentration was increased from 2% to 4%. This was attributed to end product inhibition by the L-phenylalanine produced. Thus although faster conversion rates were observed with addition of high substrate concentrations, the product titres never exceeded 16 g l1. As already discussed the rate of yield of the conversion was proportional to the concentration of amino donor employed. Using a ratio of 1 3 substrate to amino donor, almost a 90% conversion was achieved in 3 hours. 

Heat stability The Oplophorus luminescence system is more thermostable than several other known bioluminescence systems the most stable system presently known is that of Periphylla (Section 4.5). The luminescence of the Oplophorus system is optimum at about 40°C in reference to light intensity (Fig. 3.3.3 Shimomura et al., 1978). The quantum yield of coelenterazine is nearly constant from 0°C to 20°C, decreasing slightly while the temperature is increased up to 50°C (Fig. 3.3.3) at temperatures above 50°C, the inactivation of luciferase becomes too rapid to obtain reliable data of quantum yield. In contrast, in the bioluminescence systems of Cypridina, Latia, Chaetopterus, luminous bacteria and aequorin, the relative quantum yields decrease steeply when the temperature is raised, and become almost zero at a temperature near 40-50°C (Shimomura et al., 1978). 

The effect of temperature on PIB yield was dependent on the nature and concentration of r-BuX and on solvent. For r-BuX/MeCI, yields were essentially unchanged in the range from -30° to —70°C. Except for the lowest f-BuCl concentration (4.5 x 10 4M), yield decreased slightly at and below —60 °C. For f-BuCl/MeBr, the temperature effect was insignificant from -25 °C to —55 °C. 

Initiator reactivity orders can be explained on the baas of differences in the rate of displacement of MeX from Et2AlX MeX complexes by f-BuX and/or the rate of ionization of Et2 A1X f-BuX complexes. PIB yields decrease with increase of Mel or MeBr concentration. This poisoning effect has been attributed to the formation of propagation-inactive halonium ions. 

Yield decreases on heating (the heating times and temperatures varied). 

The efficiency of extraction was observed to be inversely proportional to the corn cob particle size. This was expected because the size reduction corresponds to an increase in total particle surface area. An increase in the time of the alkaline extraction and in the NaOH concentration also improves the efficiency of xylan extraction. This happened because when the NaOH concentration was lower, the xylan present in corn cobs could not be fully dissolved in the solution. Thus, it resulted in lower efficiency of xylan extraction. However, when the NaOH concentration was higher than 2 M, the yields decreased with continuously increasing of the NaOH concentration. This is probably due to the alkaline degradation of xylan chains, proceeding at the higher NaOH concentration, which indicated that the ideal NaOH concentration in the extraction was between 1.5 and 1.8 M (Unpublished data). 

When the reaction was performed in the microreactor, the maximum conversion of 97.0 % was attained when the flow rate of Boc-AMP solution was 9 ml/min and the molar equivalents of KOH to Boc-AMP was 13 as shown in Fig. 1. Optimum operating conditions were obtained from a statistical method by using factorial design [6]. The yield decreased over the KOH equivalency of 13 in Fig. 1, since the phase separation between the t-Boc20 and the aqueous phase was observed due to the increased water content with increasing KOH equivalency. As the heat transfer performance of the microreactor was greatly improved compared with conventional reactors, higher reaction temperature could be admissible. 

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