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Synthesis of 3-bromo-3-methyl-2-butanol from 2-methyl-2 …
It is likely that 2-butanol, like ethanol (Mezey, 1976), inhibits oxidative pathways of drug metabolism and thus inhibits the hydroxylation step leading to 3-hydroxy-2-butanone.
Most solutions are relatively diluted (~5 %) and their density is not much different from that of water (i.e., 5 % HCl: 1.02 g/cm3, 5 % NaOH: 1.055 g/cm3). Thus, the density of a solid i.e., sodium hydroxide (2.1 g/cm3 in the solid) does not provide the information sought. The density is determined by the major component of a layer which is usually the solvent. About 5 % of a solute does not change the density of the solution much. However, this can change if very concentrated solutions are used (see table in the back of the reader)! Thus, diethyl ether and ethyl acetate, which are both less dense than the dilute solutions that are usually used for extraction, form the top layer, while dichloromethane and chloroform form the bottom layer (currently both of them are not used in Chem 30BL or Chem30CL due to safety concerns!).
It is not uncommon that a small amount of one layer ends up on top of the other. Mixing with a stirring rod or gentle shaking usually takes care of this problem. Small amounts (compared to the overall volume of the layer) should be discarded here.
This would usually happen if the mixture was shaken too vigorously. Subsequently, an emulsion is formed instead of two distinct layers. In such an event, the mixture can be stirred slowly with a glass rod to bring the small droplets together a little faster, which ultimately leads to the formation of a new layer. In some cases, a careful draining of the existing lower layer can also be helpful because it pushed the bubbles together in the smaller part of the extraction vessel. In cases, where the phases have similar polarity or density, the addition of more solvent can assist the separation. Sometimes, the addition of a salt (or salt solution) can also lead to a better phase separation (“salting out”). In many cases, centrifugation or gravity filtration works as well. When it is known, through experience, that some mixtures may form emulsions, vigorous shaking should be avoided. Instead, gently rocking the separatory funnel back and forth for 2-3 minutes will accomplish sufficient degree of mixing while minimizing the formation of emulsions.
Strictly speaking, hardly ever all of the solute will be extracted since there is finite distribution coefficient for the compound (see also Extraction II). As a general rule, multiple extractions with small quantities of solvent or solution are more efficient than one extraction using the same amount of solvent (see below). The amount of material left behind after two or three extractions is usually very small (less than 5 % in most cases) and does not justify the effort and resources (solvent and time to perform the extractions and to remove the solvent later on). Excessive washing will also lower the yield of the product, if the desired compound dissolves noticeably in the other phase.
This phenomenon will often be observed if sodium bicarbonate is used for the extraction in order to neutralize or remove acidic compounds. The reaction affords carbon dioxide (CO2), which is a gas at ambient temperature. Pressure builds up that pushes some of the gas and the liquid out. The container should be vented immediately before the pressure build-up can cause an explosion, an ejection of the stopper on the top or excessive spillage upon opening. A similar observation will be made if a low boiling solvent is used for extraction. The shaking of the mixture increases the surface area, and therefore the apparent vapor pressure of the solvent. In addition, many extraction processes are exothermic because they involve an acid-base reaction.
Often times the cap is either the wrong cap in the first place or it is not properly placed on the top. If NaHCO3 is used for extraction, the centrifuge tube has to be vented more frequently.
Before using the separatory funnel, the user should check if the stopcock plug and the stopcock fit together well. In addition, the stopper on the top has to fit into the joint on the top to prevent leakage there (for more details at the end of this chapter).
The conical shape of these pieces of equipment makes it easier to collect the solution on the bottom using a Pasteur pipette because of the smaller interface. The task of getting a clean phase separation will be more difficult if the liquids are spread out over a large, flat or curved surface.
The bottom layer is always removed first independently if this is the one of interest or not because it is much easier to do. If a centrifuge tube or conical vial was used, the bottom layer should be drawn using a Pasteur pipette. From this point of view, a solvent with higher density than water would be preferential, especially when very small quantities are used. This will allow to minimize the number of transfer steps required.
This highly depends on the quantity of a compound that has to be removed. For most washing processes, 10-20 % of the volume of the solution to be washed will do an adequate job. If a large amount of a compound has to be transferred or neutralized, more concentrated solutions and larger quantities might be needed. Multiple extractions with smaller quantities are preferred over one extraction with the same quantity of solution/solvent. If solutions with higher concentrations are used, extra caution is advised because neutralization reactions are exothermic. This can pose a serious problem when using low boiling solvents i.e., diethyl ether, dichloromethane, etc. because a pressure build-up will be observed in the extraction container.
Help with Organic Chemistry? | Yahoo Answers
Since MEK and 2,3-butanediol disappear from blood and urine and there is no evidence for accumulation elsewhere in the body, the above data suggest that the bulk of MEK absorbed by mammals enters the general metabolism and is eliminated from the body as simple compounds like carbon dioxide and water whose source is not readily identifiable.
Olefin to epoxide in one step requires a peracid ..
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