Diethyl ether variation with temperature

Figure 5 Variation of the molecular weight of polyisobutene with the concentration of of catalyst in the presence of diethyl ether [2b]. Temperature -78°. Solvent ethyl chloride. [Et20] = 16.2 mM. [CH2 CMe2] and vol. of reaction mixture not given...

Okada et al. [22], used the unpolymerisable 1,3-dioxan as a model compound and let it react with Et30+BF4 in CH2C12 at 21 °C for 24 h. On the basis of the H NMR spectrum of the resulting reaction mixture and its variation with time and temperature, and other evidence, they suggested that the oxycarbenium ion (XI), solvated by diethyl ether (from the Et30+), is the propagating species ... 

FIGURE 8.4 The variation of the vapor pressure of liquids with temperature, for diethyl ether (orange), benzene (red), ethanol (green), and water (blue). The normal boiling point is the temperature at which the vapor pressure is 1 atm (760 Torr). 

An isocratic HPLC method for screening plasma samples for sixteen different non-steroidal anti-inflammatory drugs (including etodolac) has been developed [29]. The extraction efficiency from plasma was 98%. Plasma samples (100-500 pL) were spiked with internal standard (benzoyl-4-phenyl)-2-butyric acid and 1 M HC1 and were extracted with diethyl ether. The organic phase was separated, evaporated, the dry residue reconstituted in mobile phase (acetonitrile-0.3% acetic acid-tetrahydrofuran, in a 36 63.1 0,9 v/v ratio), and injected on a reverse-phase ODS 300 x 3.9 mm i.d. column heated to 40°C. A flow rate of 1 mL/min was used, and UV detection at 254 nm was used for quantitation. The retention time of etodolac was 30.0 minutes. The assay was found to be linear over the range of 0.2 to 100 pg/mL, with a limit of detection of 0.1 pg/mL. The coefficients of variation for precision and reproducibility were 2.9% and 6.0%, respectively. Less than 1% variability for intra-day, and less than 5% for inter-day, in retention times was obtained. The effect of various factors, such as, different organic solvents for extraction, pH of mobile phase, proportion of acetonitrile and THF in mobile phase, column temperature, and different detection wavelengths on the extraction and separation of analytes was studied. 

If, then, we are to explain the temperature variation of fx by means of this process of gradual uncoupling, definite relationships must hold between the absolute magnitude of the moment (as compared with the value for the ideally uncoupled state) and its temperature coefficient. This very point would seem to lead to difficulties in connexion with the results of Werner which we mentioned above. In the ideally uncoupled state quinol diethyl ether should have the moment V 2fx, where for fx the value for phenetole (i o. should be inserted. In this way we obtain 1 4. io as the limiting value for the ideally uncoupled state, i.e. a number which is smaller than the moment obtained experimentally for the di-derivative (i 7.10 at 20° C.). Now with rising temperature Werner does not obtain the anticipated tendency towards the limiting value but a... 

The sensitivity, or otherwise, of the ct-dicarbonyl substrate determines the reaction conditions. However, variations in conditions are not especially large. Although 1 equiv. of base may be used, more usually an excess is employed — sometimes 10 equiv. or more to accelerate the reaction. Studies on the reaction of hydroxides with benzil indicate that the rate depends to some extent on the cation, and it can be advantageous to use Ba(OH)2 rather than the more usual NaOH or KOH. With hydroxide ion, favored solvents are water and aqueous ethanol. Heterogeneous conditions, for example potassium hydroxide and diethyl ether or sodamide and toluene, have also been employed. The reactions are conducted at room temperature (sometimes requiring up to 4 d) or under reflux (10 min-24 h). With methoxide or -butoxide the corresponding anhydrous alcohol or benzene are employed as solvents. ... 

This complex is prepared by a variation of the published method. To potassium hexachloropIatinate(IV) [Aldrich Chemical] (4 g) and Na2HP04 (8 g) in a 500-mL flask fitted with a condenser are added concentrated aqueous ammonia (25%, 75 mL) and water (120 mL). The mixture is stirred and heated to reflux, and the temperature is maintained until the suspension turns white (—10 min). Then the mixture is cooled to or below room temperature. The white precipitate is collected on a frit, washed with methanol (2 X 25 mL), and air-dried. The precipitate is dissolved in hot (—70°) 0.1 M HCI (—200 mL). The mixture is Altered, and concentrated HCI (50 mL) is added. The colorless solution is reduced in volume to —40 mL on a rotary evaporator, during which time a white precipitate forms. After cooling, this is collected by flitration on a frit, washed with ice-cold 3 M HCI (20 mL), methanol (3 X 25 mL), and diethyl ether (25 mL), and dried in a vacuum desiccator over P40,o. Yield 3.0 g (90%). Absorption maximum in water 286 nm (e 141 M cm" ). 

For the addition reactions with simple amides, low temperatures were used (-78° C for 2 hr, then -78° - 25° C over 4 hr) and propionitrile was employed as die solvent (25). The mixtures were allowed to stir for 24-48 hr before extractive workup and subsequent column chromatography (Si02, gradients of hexane/ethyl acetate). Variations in the halonium species (e.g. C1+ or Br+), the reaction solvent (diethyl ether, THF, or DMF) or the reaction temperature gave less favorable product distributions. For the simple amides, the highest yields and greatest diasteroselectivities were obtained when benzamide was used as the nucleophile (Table 1, Entries 1-3). 

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