Excessive reaction

Poor distribution Implement appropriate procedures and training of solids or liquid charge. Potential for excessive reaction rates due to localized over-concentrations of reactants. CCPS G-22... 

In each example used in this section, a number of moles of NaOH was added to 0.100 liter of 1.00 M HQ with one or the other constituent in excess. Reaction between H+(aq) and OH-(aq) consumes almost all of the constituent not in excess. Let us now consider the case in which there is excess of neither HQ nor NaOH. 

Antagonists of TLR-4 have been developed to prevent an excessive reaction to infection in the body. TAK-242 and Eritoran are both in phase III trials to help combat... 

Attainment of abnormal reaction conditions, e.g. overpressure, over-temperature, segregation of reactants, excessive reaction rate, initiation of side reactions. 

Further optimization of this reaction was carried out with TFE as an achiral adduct, since reaction with TFE is much faster than that with neopentyl alcohol. We found that dimethyl- and diethylzinc were equally effective, and the chiral zinc reagent could be prepared by mixing the chiral modifier, the achiral alcohol and dialkylzinc reagent in any order without affecting the conversion and selectivity of the reaction. However, the ratio of chiral to achiral modifier does affect the efficiency of the reaction. Less than 1 equiv of the chiral modifier lowered the ee %. For example with 0.8 equiv of 46 the enantiomeric excess of 53 was only 58.8% but with 1 equiv of 46 it was increased to 95.6%. Reaction temperature has a little effect on the enantiomeric excess. Reactions with zinc alkoxide derived for 46 and TFE gave 53 with 99.2% ee at 0°C and 94.0% ee at 40°C. 

The appearance of a brown to black precipitate indicates either oxidative or thermal decomposition of the cuprate. If such decomposition has occurred, it is best to prepare the reagent again with greater care to avoid molecular oxygen and/or excessive reaction temperatures. 

The suggested incubation times should be adhered to. In the case of a long template (more than about 2 kb), an excessive reaction time may cause precipitation. In this case, mRNA will not be collected. To avoid this problem I shorten the reaction time to 20 min, II decrease the quantity of DNA template to 70-80%, III use a PCR-generated DNA template. 

Available from United Mineral and Chemical Corp., 129 Hudson Street, NY 10013. Foil should be avoided because of the excessive reaction time required. 

The hydroxides are decomposed below 600°C to finally yield the pure YBa2Cus07 x phase around 800°C, but reactivity is increased compared to organic precursors. This is demonstrated in Figure 11. The phase forms in a short time (20 min). It should therefore be very interesting to obtain homogeneous gels (53). They would allow the synthesis of thin films without excessive reaction with the substrate. 

Notwithstanding all its advantages, the principle of solid-phase synthesis cannot be applied to all kinds of chemical reactions. Although reactants are used in excess, reaction is not always quantitative. The resulting impurities cannot be separated on the solid phase, giving rise to separation problems particularly in multi-step systems. Moreover, only limited use can often be made of conventional analytical methods (NMR, MS). Recent methods of 13C-NMR spectroscopy on solid phases [21] or in gel phases [22] are ideally suited for solid-phase synthesis, but are not universally available owing to the expensive instrumentation. 

The rate of reaction is a function of the efficiency of the contact between the reactants, i.e., stirring mechanism and mixing of the reactants. In fact, mixing efficiency has a vital influence on the yield and purity of the product. Insufficient or inefficient mixing may lead to uncondensed reactants or to excessive reaction on heated surfaces. 

The reaction error is thus expressed as a percentage of the total ion concentration. Positive reaction errors indicate cation excess negative errors indicate anion excess. Reaction errors are caused by the analytical errors of the individual parameters and the fact that not all possible ions are commonly measured. 

Although WLs due to biological attack decreased in treated MDF blocks, the results were unsatisfactory when compared with those of solid wood (Tables 5 and 6). Excessive reaction time (24 h) caused a rather detrimental effect on dimensional stability and on biological resistance of treated boards. This can possibly be explained by a thermal degradation of urea-formaldehyde resin as an adhesive. 

The reader should note that the tubular SOFC at 1000 °C is too hot (excessive reaction rates) for successful reform at the anode, so that separate reformers must be employed. The MCFC of Chapter 5 at 600 °C can use anode reform, without high anode thermal stress, such as would occur in the SOFC of Figure 4.2. 

The MTU MCFC provides catalysed 600 °C anode reform capability, with flat anode temperature distribution. In contrast the 1000 °C SOFC encounters difficulties with anode reform, in which excessive reaction rates lead to unacceptable, thermally stressed, local anode cool zones. The title direct fuel cell (DFC) is used, to highlight the absence of a separate combustion-heated 800 °C reformer and its pre-reformer. The balance of plant flow sheet is shown in Figure 5.3. 

Catalytic hydrogenation is performed in alcohol solution over Raney nickel at 25° to 100° and 30 atm. or over platinum oxide at room temperature and 1 to 2 atm. The reaction is highly expthermic therefore, precautions should be taken against excessive reaction temperatures. Typical illustrations are found in the preparations of 2-amino- -cymene (90%) and 3,4-diethylaniline (90%). Heterocyclic nitro compounds in the quinoline and dibenzothiophene series also respond favorably to catalytic hydrogenation. 

This extremely exothermic reaction is successively suppressed in favor of Eq. (33) as the temperature increases, ft should be possible to use a simple autothermal reactor for the slightly exothermic reaction of Eq. (33). Proper design and an appropriate catalyst are required to avoid excessive reaction via Eq. (34) at the entrance to the reactor, causing a hot spot. The ratio H2/CO = 2 is more convenient for downstream processes than that obtained by steam reforming ... 

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