Auxiliary extraction

The biocatalytic reduction step B in synthetic route B demands more raw materials (mass index S , see equation (5.1)) and generates more waste (environmental factor , see equation (5.2)) as compared to reduction step C (Figure 5.1). Solvents used to perform the extraction of the product from the aqueous phase in reduction step B are denoted as auxiliaries in Figure 5.1. These solvents and the aqueous phase dominate the mass balances as well as the environmental scores in Figure 5.2 (M4, M8). 

When an auxiliary ligand is added to a chelate extraction system and it enhances the extractability and extraction rates, such a phenomenon is termed synergism. A typical... 

Cost of solvent extraction auxiliaries Cost of absorbtion and distillation column packing, supports and distributors Cost of tanks (surge, etc.)... 

The utility of a new fluorine supported chiral auxiliary was established in a series of catalyzed and uncatalyzed 1,3-dipolar cycloaddition reactions with diphenylnitrone (637b) (Scheme 2.281) (797). The yields and selectivities of the cycloadducts (645a—d) compare favorably with those obtained with conventional Evans-type auxiliaries (798). Purification of the products was greatly improved by using fluorous solid phase extraction (FSPE). 

The main disadvantages of Evans auxiliaries 22 and 23 are that they are expensive to purchase and inconvenient to prepare, as the preparation involves the reduction of (5 )-valine 24 to water-soluble (b )-valinol, which cannot be readily extracted to the organic phase. The isolation of this water-soluble vali-nol is difficult and requires a high vacuum distillation, which is not always practical, especially on an industrial scale. Therefore, an efficient synthesis of Evans chiral auxiliary 25 has been developed, as depicted in Scheme 2-1930 ... 

For WTW analysis, it is a sufficiently accurate assumption, that natural gas mainly consists of methane (CFI4). Compressed natural gas is also referred to as CNG . Natural gas is extracted, processed, transported and distributed via pipeline to the filling stations, where it is compressed to about 25 MPa. Natural gas sources may vary for different countries. Depending on the source (natural gas quality) and the transport distance (e.g., 4000 km or even 7000 km from Russia, depending on the relevant gas fields) the auxiliary energy needs or energy losses, and hence the GHG-relevant emissions can vary. For the calculation of the energy requirement and GHG emissions for the supply of natural gas, a transport distance of 4000 km is assumed. 

Our starting point is a generic constmction for the extraction of work from a flow of heat (cf. Fig. 4). The auxiliary system—for example, a Brownian motor— performs work, W = Fx, against an external force F, where x is the corresponding variation of the thermodynamically conjugated variable. The system is at a temperature T and we introduce the corresponding thermodynamic force, Xi =F/T, and flux J = x (the dot referring to the time derivative). 

The fractions containing the diol auxiliary and those containing borate derivatives were concentrated, and treated with a solution of THF (2 mL), 1 N NaOH (1 mL), and H2O2 (1 mL of a 30% aqueous solution) for 16 hours. The resulting mixture was diluted with water (5 mL) and extracted with LtOAc (3 x 10 mL). The combined organic layers were dried over anhydrous MgS04, filtered, and concentrated. Flash chromatography (5% EtOAc/hexanes) afforded 891 mg of recovered (lR,25, 3R,45 )-2-phenyl-l,7,7-trimethylbomanediol (75% yield). 

I. 4-methoxyacetophenone (30 //moles) was added as an internal standard. The reaction was stopped after 2 hours by partitioning the mixture between methylene chloride and saturated sodium bicarbonate solution. The aqueous layer was twice extracted with methylene chloride and the extracts combined. The products were analyzed by GC after acetylation with excess 1 1 acetic anhydride/pyridine for 24 hours at room temperature. The oxidations of anisyl alcohol, in the presence of veratryl alcohol or 1,4-dimethoxybenzene, were performed as indicated in Table III and IV in 6 ml of phosphate buffer (pH 3.0). Other conditions were the same as for the oxidation of veratryl alcohol described above. TDCSPPFeCl remaining after the reaction was estimated from its Soret band absorption before and after the reaction. For the decolorization of Poly B-411 (IV) by TDCSPPFeCl and mCPBA, 25 //moles of mCPBA were added to 25 ml 0.05% Poly B-411 containing 0.01 //moles TDCSPPFeCl, 25 //moles of manganese sulfate and 1.5 mmoles of lactic acid buffered at pH 4.5. The decolorization of Poly B-411 was followed by the decrease in absorption at 596 nm. For the electrochemical decolorization of Poly B-411 in the presence of veratryl alcohol, a two-compartment cell was used. A glassy carbon plate was used as the anode, a platinum plate as the auxiliary electrode, and a silver wire as the reference electrode. The potential was controlled at 0.900 V. Poly B-411 (50 ml, 0.005%) in pH 3 buffer was added to the anode compartment and pH 3 buffer was added to the cathode compartment to the same level. The decolorization of Poly B-411 was followed by the change in absorbance at 596 nm and the simultaneous oxidation of veratryl alcohol was followed at 310 nm. The same electrochemical apparatus was used for the decolorization of Poly B-411 adsorbed onto filter paper. Tetrabutylammonium perchlorate (TBAP) was used as supporting electrolyte when methylene chloride was the solvent. 

To recover the chiral auxiliary, the aqueous phases are made basic with 2 M sodium hydroxide. After extraction with dielhyl ether, the amino alcohol is recycled in >80% yield. 

A mixture of 1.5-3.5 mmol of the a-alkylated benzylimino product and 10-25 mL of0.5 M hydroxylamine acetate in anhyd ethanol is stirred at 25 C for 4-10 h. concentrated, the residue is dissolved in 30-50 mL of benzene, the solution is washed with sat. aq NaHC03 and then NaCI, concentrated, acidified with 10-20 mL of 5% aq hydrochloric acid, the mixture is stirred for 0.5 h and extracted with six 10-mL portions of diethyl ether. Concentration of the ethereal layer gives the oxime. The aqueous layer is basified with Na2C03, extracted with six 10-mL portions of diethyl ether, dried over potassium carbonate. Concentration and distillation (bulb-lo-bulb) gives the product. The chiral auxiliary can be recovered and recycled39. 

After use of this cleavage method, the chiral auxiliary may be partially recycled by neutralization and extraction of the aqueous layer. In this way a mixture of methylated hydrazine, the SAMP-hydrazone of formaldehyde and SAMP (1 7 2) is obtained, which is subjected to air oxidation and hydrolysis8. 

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