Flask Chemistry

The bromine-lithium exchange reaction of o-dibromobenzene is usually carried out at — 110°C or below in flask chemistry because the elimination of LiBr to form benzyne is very fast even at — 78 °C. However, by reducing the residence time using a microflow system, the reaction can be conducted at —78°C and o-bromophenyllithium can be effectively trapped with an electrophile before decomposition. Figure 6.23 shows a schematic diagram of the microflow system, in which reactions using methanol as an electrophile are conducted with varying temperatures and flow rates. 

Researchers will be freed from the limitations posed by the flask chemistry and will develop, with great anticipation, synthetic reactions that have been impossible with flasks, and will reveal the true values of flow reactions in the near future. Considerations needed in developing such flow reactions by taking advantage of characteristic features of flow microreactors will be discussed in the following chapters. 

Some people may think that flask chemistry is powerful enough and reactions that are complete in hours fit well for human beings. Why is flash chemistry needed The most appropriate answer to this question is because we can just do it. Reaction times at the molecular level are generally several hundred femtoseconds or picoseconds. Although the reaction times in flash chemistry are much longer than the... 

Multi-necked flasks. Fig. II, 1, 8, a, illustrates a typical threenecked flask. This has numerous applications in organic chemistry for many operations, the central aperture carries a mechanical stirrer, and the two side apertures a dropping funnel and a reflux condenser respectively. 

A common operation in practical organic chemistry is for stirring, refluxing, and addition of a liquid from a dropping funnel to be carri on simultaneously. The most convenient apparatus for this purpose is a three-necked flask, fitted as in Fig. 11, 7, 11, a. If a three-necked flask is not available, the three-way adapter inserted into a bolt-head flask (Fig. 77, 7, 11, 6) may be used. A further simplification, suitable for elementary students, is to employ a two-way adapter as in Fig. 77, 7, 11, c the stirrer passes through a closely-fitting glass sleeve which is extended... 

In molecular weight determinations it is conventional to dissolve a measured mass of polymer m2 into a volumetric flask and dilute to the mark with an appropriate solvent. We shall use the symbol Cj to designate concentrations in mass per volume units. In practice, 100-ml volumetric flasks are often used, in which case C2 is expressed in grams per 100 ml or grams per deciliter. Even though these are not SI units, they are encountered often enough in the literature to be regarded as conventional solution units in polymer chemistry. 

Organic chemistry by robot means no spilled flasks ... 

Heating mantles are particularly designed for the heating of flasks and find wide application in distillation operations. For details of the distillation procedure and description of the apparatus employed a textbook of practical organic chemistry should be consulted.9... 

Fig. 3.11 Conventional flasks for microdeterminations (a) air leak design (A) stopper design (c) filter paper for wrapping sample. Reproduced by permission from A. M. B. Macdonald, in Advances in Analytical Chemistry and Instrumentation, C. N. Reilly (Ed.), Vol. 4, Interscience, New York, 1965, p. 75.

Combinatorial Chemistry. Figure 2 Chemical libraries are prepared either by parallel synthesis or by the split-and-recombine method. In the latter case, coupling m building blocks in m separated reaction flasks through n synthetic cycles on a beaded polymer carrier generates a combinatorial library with nf individual compounds and one compound per bead. 

Over the years of evolution, Nature has developed enzymes which are able to catalyze a multitude of different transformations with amazing enhancements in rate [1]. Moreover, these enzyme proteins show a high specificity in most cases, allowing the enantioselective formation of chiral compounds. Therefore, it is not surprising that they have been used for decades as biocatalysts in the chemical synthesis in a flask. Besides their synthetic advantages, enzymes are also beneficial from an economical - and especially ecological - point of view, as they stand for renewable resources and biocompatible reaction conditions in most cases, which corresponds with the conception of Green Chemistry [2]. 

The submitters and the checkers prepared the sodium ethoxide in the conventional manner. However, sodium eth-oxide and sodium methoxide are very conveniently prepared by the inverse procedure, as described by Tishler in Fieser, Experiments in Organic Chemistry, 2nd Ed., 1941, D. C. Heath and Company, New York, p. 385 (bottom) The metal is placed in the flask, and the alcohol is added through the condenser at such a rate that rapid refluxing is maintained. It is necessary, as a precautionary measure, to clamp the flask and not to trust to the friction between a rubber stopper and the flask to hold the flask in place. When this precaution is taken, a cooling bath may be used with safety. It is necessary to cool the flask the metal must not be allowed to melt, as this will result in the formation of one large mass with a greatly decreased metallic surface. (Private communication, C. F. H. Allen.)... 

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