Added solvent

The addition of an organic solvent to modify the mobile phase is often used to alter the selectivity of the stationary phase. Methanol, acetonitrile, ethanol and dioxane at concentrations of up to 10% are used for this purpose. The effects resulting from such an addition are similar to those observed in reversed phase HPLC and generally result in a reduction in the retention of the solutes. 

---

Chain transfer to initiator or monomer cannot always be ignored. It may be possible, however, to evaluate the transfer constants to these substances by investigating a polymerization without added solvent or in the presence of a solvent for which Cgj is known to be negligibly small. In this case the transfer constants Cjj and Cj determined from experiments in which (via... 

Paraffin wax vapor barriers are used in water rinse removers that can disperse the wax without coating the substrate. In soak tank applications, water is sometimes doated on top of an ad-solvent, neutral pH, nonwater rinse remover to prevent evaporation. Flotation devices that cover the exposed surface area may be used with other formulas. 

Solvent Process. In the solvent process, or solvent cook, water formed from the reaction is removed from the reactor as an a2eotropic mixture with an added solvent, typically xylene. Usually between 3 to 10 wt % of the solvent, based on the total charge, is added at the beginning of the esterification step. The mixed vapor passes through a condenser. The condensed water and solvent have low solubiUty in each other and phase separation is allowed to occur in an automatic decanter. The water is removed, usually to a measuring vessel. The amount of water collected can be monitored as one of the indicators of the extent of the reaction. The solvent is continuously returned to the reactor to be recycled. Typical equipment for this process is shown in Figure 2. The reactor temperature is modulated by the amount and type of refluxing solvent. Typical conditions are ... 

Figure 1 Schematic diagram depicting the partitioning of an enzymatic system into quantum and classical regions. The side chains of a tyrosine and valine are treated quantum mechanically, whereas the remainder of the enzyme and added solvent are treated with a classical force field.

If the ice bath is not removed, the mixture may solidify and must be dissolved by adding solvent and heating slightly. Mixing of the reactants at ice-bath temperature prevents discoloration. Practical grades of materials were used. 

In the absence of an added solvent, 3-alkyIpyridines, 4-alkyl-pyridines, and 3,4-dialkylpyridines all gave yields of substituted 2,2 -bipyridines that were up to three times greater than that of 2,2 -bipyridine from pyridine under similar conditions. With 3-ethyl-4-methylpyridine a marked improvement in yield was ob.served when the reaction was carried out at about 150°C in a vacuum, rather than at the atmospheric boiling point (195°C) of this base. This effect has also been observed with some other bases but the amount of 3,3, 5,5 -tetramethy 1-2,2 -bipyridine from 3,5-lutidine could not be increased in this way, and this pyridine was as unreactive as the 2-substituted pyridines. This finding is undoubtedly related to the reluctance of 3-substituted pyridines to form 3,3 -disubstituted 2,2 -bipyridines. 

Relatively few pyridines with substituents other than alkyl groups have so far been examined, and with some of these the reaction has been carried out only in the presence of added solvent. A comparison of the reactivities of these pyridines is therefore difficult. It has, however, been established that the presence of benzoyl groups in the 3- and 4-positions causes a very marked drop in the yields of the corresponding 2,2 -bipyridines. The 3- and 4-benzylpyridines were found to be more reactive but even in the absence of solvent, and in vacuo, 4-benzylpyridine gave only about one-third of the yield of the 2,2 -bipyridine compared with pyridine itself. Ethyl nicotinate in the absence of solvent and under vacuum -- gave a similar yield of biaryl but 4-phenylpyridine was found to be less reactive. 

The use of liquid salts, based on anodi-cally stable cations such as 1,2-dimethyl-3-propylimidazolium (Dmpi) without added solvent, allows the investigation of the electrochemical stability of anions [75],... 

Allow the added solvent, of volume V, to pass reversibly through a into A, against the osmotic pressure P of the solution (with the pure solvent under the pressure of its own vapour). 

The tetrahydrocannabinol carboxylic acid was extracted from the urine by means of a solid state extraction cartridge packed with a Cl 8 reverse phase (octyldecyldimethyl chains). As the urine sample was used direct, and contained no added solvent, the materials of interest were irreversibly adsorbed on the reverse phase solely by dispersive interactions. 

The straightforward formation of A-aLkylquinoxalinium halides (by dissolution of the quinoxaline in an excess of alkyl halide, with or without added solvent, at room temperature or above until complete) is now seldom, if ever, described. However, the following examples of somewhat abnormal procedures may prove useful. 

Transesterification has been carried out with phase-transfer catalysis, without an added solvent. In another procedure, RCOOR are converted to RCOOR" by treatment of the ester and an alcohol R OH with n-BuLi, which converts the R"OH to R"OLi. ... 

Krupp-Koppers (2) A process for separating butane and butene isomers from their mixtures by extractive distillation. The added solvent (Butenex) is a morpholine derivative, possibly N-formyl morpholine. 

MORPHYLANE A process for removing aromatic hydrocarbons from hydrocarbon mixtures by extractive distillation. The added solvent is N-formyl morpholine. The process was developed by Krupp Koppers in the 1960s and by 1994, 22 units had been built. See also MORPHYLEX, OCTENAR. 

You now let the trash-free solution cool and clean crystals should come out. Since you have probably added solvent to the solution, don t he surprised if no crystals come out of solution. Don t panic either Just boil away some of the solvent, let your solution cool, and wait for the crystals again. If they still don t come back, just repeat the boiling. 

Another way to prepare a solution is by diluting a more concentrated solution to a more dilute one by adding solvent. You can use the following equation ... 

In contrast with standard liquiddiquid two-phase alkylation reactions, it is possible to use iodoalkanes with only catalytic amounts of the ammonium salts in the absence of an added solvent under soliddiquid conditions [e.g. 80]. 

A detailed study of the formation of n-octyl ethers under solidrliquid two-phase conditions in the absence of an added solvent has been reported [10], Potassium alkoxides tend to produce higher yields of the ethers than do the corresponding sodium derivatives, but octene is the major product in the reaction of 1-bromooctane with potassium t-butoxide. High temperatures also tend to promote the preferential formation of octene and slightly higher yields of the ethers are obtained using n-octyl tosylate in preference to n-octyl bromide. p-Fluorinated acetals have been prepared either under basic catalytic liquidrliquid or solidrliquid conditions from the fluori-nated alcohol and dichloromethane [11] with displacement of the fluorine atoms. 

Solid-liquid phase systems with no added solvent produce esters in high yield [e.g. 2, 3] and are particularly Useful when using less reactive alkyl halides [e.g. 15], for the preparation of sterically hindered esters [16], or where other basic sites within the molecule are susceptible to alkylation, e.g. anthranilic acid is converted into the esters with minimal A-alkylation and pyridine carboxylic acids do no undergo quat-emization [17]. Excellent yields of the esters in very short reaction times (2-7 minutes) are also obtained when the two-phase system is subjected to microwave irradiation [18]. Direct reaction of the carboxylic acids with 1,2-dichloroethane under reflux yields the chloroethyl ester [19], although generally higher yields of the esters are obtained under microwave conditions [20]. 

Tetralone is readily mono- or di-alkylated at the 1-position to the exclusion of O-alky lation with a range of alkylating agents under liquiddiquid two-phase conditions without an added solvent [24], Similarly, it has been reported that anthrone undergoes mono- and di-C-alky lation at the 10-position with propargyl and allyl halides to the almost complete exclusion of O-alkylation [25]. It has been claimed that methyl-ation yields 9-methoxyanthracene [26],... 

Esters are hydrolysed under basic conditions in the presence of quaternary ammonium salts [e.g. 1-7], Microwave activation of basic soliddiquid systems without an added solvent enhances the rate of saponification and the reaction is not affected by steric factors [3], Microwave irradiation has also been used in the hydrolysis and decarboxylation of malonic esters [8] and p-keto esters [9] (>90%). Lactones... 

The stereoselective Michael addition of the anion derived from diethyl acetyl-aminomalonate with chalcone has been found to be most effective under soliddiquid two-phase conditions in the absence of an added solvent [62]. For optimum overall conversion and enantiomeric excess (56% with 60% ee), A-benzyl-V-methyl-... 

Extractive distillation is a method of rectification similar in purpose to azeotropic distillation. To a binary mixture which is difficult or impossible to separate by ordinary means, a third component, termed a solvent, is added which alters the relative volatility of the original constituents, thus permitting the separation. The added solvent is, however, of low volatility and is itself not appreciably vaporised in the fractionator. 

In the single-stage batch process illustrated in Figure 13.1, the solvent and solution are mixed together and then allowed to separate into the two phases—the extract E containing the required solute in the added solvent and the raffinate R, the weaker solution with some associated solvent. With this simple arrangement mixing and separation occur in the same vessel. 

If the two solvents are immiscible, the solvent in the raffinate streams remains as A, and the added solvent in the extract streams as S. The material balances for the solute may then be written as... 

---