Calculations dichloromethane

Recrystallization of this product from dichloromethane-ether (1 4) affords needles of 3-(2-piperidino-1-hydroxyethyl)-5-phenylisoxazole (701 mg, 51.3% as an overall yield calculated based on the starting material, melting point 104°C to 106°C. The product thus obtained may be reacted with citric acid to give the citrate. 

Nesmeyanov et a/.546 have also measured the effects of substituents in deuteration of ferrocene by deuterated trifluoroacetic acid in dichloromethane at 25 °C. Rate coefficients were measured for ferrocene and its derivative in a range of such acid mixtures, the composition of which was omitted, and in some cases the rate of exchange for ferrocene was calculated on the basis of a linear relationship between log and —H0. Results including the calculated knl values are given in Table 161. It should be noted that, in discussing those results, the authors quoted the incorrect partial rate factors for dedeuteration of toluene arising from the use of the incorrect data for benzene (see p. 199). This should be taken into account... 

The oxidation of sulfides to sulfoxides are occasionally found to be unsatisfactory, since the resulting sulfoxides are easily oxidized to sulfones. In order to avoid the further oxidation of sulfoxides into sulfones, several oxidizing agents have been selected. Recently, we found that BTMA Bt3 is the most effective and satisfactory oxidizing agent for this purpose. That is, the reaction of sulfides with a calculated amount of BTMA Br3 and aq. sodium hydroxide in dichloromethane at room temperature, or in 1,2-dichloroethane under reflux, gave sulfoxides in good yields (Fig. 28) (ref. 36). 

In order to go further into the experimental check we constructed Arrhenius plots of the fluorescence quantum yield of BMPC in a few solvents (methanol, ethanol, propanol, hexanol and methylene chloride), all of which showed good linearity. The activation energies and A/kp ratios, calculated from the slopes and intercepts of those plots, are collected in Table 1. The smooth increase of both parameters in the alcohol series is mainly associated with the increase of solvent viscosity. On the other hand, decrease of the solvent dielectric constant from 32.7 (methanol) to 8.9 (dichloromethane) causes a small but significant increase of the activation energy also, this increase is probably somewhat compensated by the decrease of the viscous-flow... 

The organic solvent used to elute the compound must be adequately strong (polar for the adsorbent silica gel) and a good solvent for the component. Absolute methanol should be avoided as a siugle solvent because silica gel itself and some of its common impurities (Fe, Na, SO4) are soluble iu this solvent and will contaminate the isolated material. Solvent containing less than 30% methanol is recommended, or ethanol, acetone, chloroform, dichloromethane, or the mobile phase originally used for PLC are other frequently nsed choices for solnte recovery. Water is not recommended because it is so difficult to remove by evaporation during the concentration step (removal by lyophilization is necessary). A formula that has been used to calculate the volume of solvent needed when the PLC mobile phase is chosen for elution is ... 

If clogging of the filter occurs, collect only a smaller volume of filtrate and take the portion which runs quickly through the filter-paper. Reduce the amounts of sodium chloride and dichloromethane to be added according to the volume collected, and consider the smaller volume in the calculation. 

Crude methyl diazoacetate contains up to 20% of the solvent dichloromethane. which has to be taken into account when calculating the stoichiometry. The checkers had no problems in preparing, handling, antf using undistilled methyl diazoacetate however, it must be emphasized that this compound is a potential explosive and all operations should be performed behind an effident safety shield. 

This compound was prepared as depicted in Scheme 1 using the following procedure To a 250-ml round-bottom flask was added lO.OOg (0.0170mol) of 2,2-bis[4-( 1-naphthoxy)phenyl]hexafluoropropane (1), 5.71 g (0.0360mol) of 4-fluorobenzoyl chloride, 2.3 g (0.0246 mol) of dimethyl sulfone, and 132 g of dichloromethane. The mixture was stirred under nitrogen until the solids dissolved, then cooled in an ice bath, and 14.5 g (0.109 mol) of aluminum chloride was added. The mixture was stirred for 1 h at ice-bath temperature, 24 h at room temperature, and 1 h at reflux. The mixture was allowed to cool to room temperature and poured into methanol. The resulting solid was filtered, washed with methanol and water, dried, and recrystallized from DMAc to yield 11.6 g (82% yield), m.p. = 261-263°C. Calculated for C HM04F, C, 70.67 H, 3.39 F, 18.25. Found C, 70.74 H, 3.36 F, 18.54. 

To a slurry of product 4 (13.07 g [calculated], 8.14mmol) in lOOmL DMF in the reaction flask from the last procedure was added 5.85 mL (62.1 mmol) acetic anhydride (Note 8) and 8.66 mL (62.1 mmol) triethylamine. The slurry was stirred for 3 h at room temperature. The resin was filtered and washed three times each with 50 mL portions of each of the following solvents A, A-dimcthyl acetamide, methanol, and dichloromethane. After drying the resin by allowing nitrogen to flow through the reaction... 

Resins 2 and 3 are treated with dichloromethane containg 3% and 1.5% trifluoroacetic acid (lOmL/g resin), respectively, for 18 h. The resin is filtered off and washed twice with dichloromethane (10 mL / g of resin). The filtrate is washed with saturated NaHCCL (5 mL) and brine (5 mL), and the organic phase is separated and filtered through a short path silica gel column to obtain a colourless solution. In the case of polymer-bound allyl esters giving rise to cleavage products of type 5f, the aqueous workup is omitted. The products obtained after removal of solvent under reduced pressure contain small amounts of silanol by-products (note 5), which is to be accounted for in the calculation of cleavage yields. 

A standard UV cell was filled with 3.5mL of a 3 X 10"4 M dichloromethane solution of polyether 2. The solution was then treated with 10 uL of trifluoromethanesulfon-ic acid and the changes in UV absorption of the mixture were monitored. Once the reaction was complete the molar extinction coefficient of the product at 276nm was identical to that of naphthalene, therefore conversions during acidolysis were calculated directly from absorption measurements (At/A ). 

Similar monoadducts were also obtained, when more simple chloroalkanes such as dichloromethane, chloroform, carbon tetrachloride were used (Figure 4, Table I). In the case of dichloromethane the product was a mixture of the 1,4 and 1,2 adducts. DFT calculations (B3LYP/3-21G ) showed that the 1,2 adduct is slightly more stable than the 1,4 adduct in this case, but becomes less stable when the alkyl group is bulkier, in agreement with the experimental results. 

Fig. 2 Chemical structures of fluorescent ligands (anion coordination sites are indicated in blue) and tentative reaction schemes on interaction of 6 with chloride and fluoride in dichloromethane according to the color patterns observed in [41]. The wavelengths of absorption given in brackets have been calculated for the geometry optimized species 6, 6-C1 and 6 in the gas phase by semiempirical AMI calculations (Ampac V6.55, Semichem)...

The electrostatic terms can be reasonably well handled in solvents of high dielectric constant, but problems are raised by some solvents of widespread use in spin trapping, for example dichloromethane ( ) = 8.9), chloroform (D = 4.8) and benzene (D = 2.3), in which the electrostatic terms calculated as above for acetonitrile become -24.8, -46 and —96 kcal mol-1, respectively. Already in dichloromethane the effective standard potential of Fe(CN)6 /Fe(CN)6- is increased by 1.08 V and in benzene by an absurdly high 4.2 V ... 

The competition between the OsvCl6 reaction with a neutral compound (A) and a negatively charged one (A-), respectively, which is the experimental situation in some of the spin trapping reactions mentioned above, was analysed by the Marcus treatment for some model cases in dichloromethane or acetonitrile. These data are shown in Table 7, giving the details of the calculations in order to illustrate the use of equations (20) and (21) and the importance of the electrostatic factors, particularly in dichloromethane. The assumptions behind the calculations are given in the table heading and footnotes. 

The activation of various reactions by Lewis acids is now an everyday practice in synthetic organic chemistry. In contrast, solvent effects on Lewis acid catalysed Diels-Alder reactions have received much less attention. A change in the solvent can affect the association step leading to the transition structure. Ab initio calculations on the Diels-Alder reaction of cyclopentadiene and methyl vinyl ketone in aqueous media showed that there is a complex of the reactants which also involves one water molecule119. In an extreme case solvents can even impede catalysis120. The use of inert solvents such as dichloromethane and chloroform for synthetic applications of Lewis acid catalysed Diels-Alder reactions is thus well justified. General solvent effects, in particular those of water, will be discussed in the following section. 

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