Solvent additives

Process Solvent Solvent additives and reflux conditions Operating tempera-ture, °C Contacting equipment Comments... 

Micellar properties are affected by changes in the environment, eg, temperature, solvents, electrolytes, and solubilized components. These changes include compHcated phase changes, viscosity effects, gel formation, and Hquefication of Hquid crystals. Of the simpler changes, high concentrations of water-soluble alcohols in aqueous solution often dissolve micelles and in nonaqueous solvents addition of water frequendy causes a sharp increase in micellar size. 

The natural relative volatility of the system is enhanced when the ac tivity coefficient of the lower-boiling pure component is increased by the solvent addition (Yl/Yw increases and P IPh > 1). In this case, the lower-boiling pure component will be recovered in the distillate as expec ted. In order for the higher-boihng pure component to be recovered in the distillate, the addition of the solvent must decrease the ratio Yl/Yw such that the product of the Yl/Yw nd (i- -, ( l,h) in the... 

It is not difficult to incorporate this result into the general mechanism for hydrogen halide additions. These products are formed as the result of solvent competing with halide ion as the nucleophilic component in the addition. Solvent addition can occur via a concerted mechanism or by capture of a carbocation intermediate. Addition of a halide salt increases the likelihood of capture of a carbocation intermediate by halide ion. The effect of added halide salt can be detected kinetically. For example, the presence of tetramethylammonium... 

In the case of cycloheptenone and larger rings, the main initial photoproducts are the -cycloalkenones produced by photoisomerization. In the case of the seven- and eight-membered rings, the double bonds are sufficiently strained that rapid reactions follow. In nonnucleophilic solvents dimerization occurs, whereas in nucleophilic solvents addition occurs. ... 

However, these methods suffer from their sensitivity to the punty of the solvent Addition of one equivalent of zinc dust and use of dimethylacetamide make the reaction much more reproducible [41] (equation 41) (Table 15)... 

The reaction is generally performed between 0 and 100 °C with the majority of the reactions being mn at reflux. Polar protic solvents such as methanol, ethanol, isopropanol, and water are commonly used as solvents. Addition of acid or use of acetic acid as solvent generally helps push sluggish reactions. The use of P-ketoesters as the dicarbonyl partner occasionally requires added base for cyclization to occur to form the pyrazolone. When using alkyl hydrazine salts, base may be required to deprotonate the hydrazine for the reaction to take place. 

These results were in fair agreement with the experimentally determined values for the parent compounds in nonionio solvents. Additional values for the n it transitions have been determined for pyrido[3,2-d]pyrimidine (345 mp loge 2.07) and for pyrido[4,3-d]-pyrimidine (330 mp, loge 2.49). ... 

R1 R2 R3 Reagent Solvent/ Additive (equiv) Temp. ("C) d.r. Csynjanti) Yield3 (%) Ref... 

A typical polymerization system comprises many components besides the initiators and the monomers. There will be solvents, additives (e.g. transfer agents, inhibitors) as well as a variety of adventitious impurities that may also be reactive towards the iniLiator-derived radicals. 

Different sequences of solvent addition or cleaning techniques may be required for each of the two or three most abundant minerals present. Passivation is always an essential element and mechanical repairs also may be required... 

Carboxylic acids can be converted by anodic oxidation into radicals and/or carbo-cations. The procedure is simple, an undivided beaker-type cell to perform the reaction, current control, and usually methanol as solvent is sufficient. A scale up is fairly easy and the yields are generally good. The pathway towards either radicals or carbocations can be efficiently controlled by the reaction conditions (electrode material, solvent, additives) and the structure of the carboxylic acids. A broad variety of starting compounds is easily and inexpensively available from natural and petrochemical sources, or by highly developed procedures for the synthesis of carboxylic acids. 

The function of the post-column solvent addition was not discussed but is presumably to overcome, in the early stages of the gradient elution, the need to spray a largely aqueous mobile phase. 

We first examined the lipase-catalyzed resolution of azirine-2-methanol I, which we expected to have a versatile synthetic utility. As expected for primary alcohols, the enantioselectivity obtained in the transesterification with lipase PS in ether was low (E = 17 at best) at room temperature despite considerable efforts such as screening of lipases, solvents, additives, and acylating agents. 

Because of their polymeric forms, alkylenebis(dithiocarbamates) are insoluble in water and most organic solvents. Additionally, they form strong complexes with different metal ions No extraction and chromatographic procedure has been reported for the parent compound of this chemical class. These compounds decompose readily under acidic conditions, for example by contact with the fruit or plant juice generated during sample preparation. 

The stirred batch reactors are easy to operate and their configurations avoid temperature and concentration gradient (Table 5). These reactors are useful for hydrolysis reactions proceeding very slowly. After the end of the batch reaction, separation of the powdered enzyme support and the product from the reaction mixture can be accomplished by a simple centrifugation and/or filtration. Roffler et al. [114] investigated two-phase biocatalysis and described stirred-tank reactor coupled to a settler for extraction of product with direct solvent addition. This basic experimental setup can lead to a rather stable emulsion that needs a long settling time. 

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