Solvents, unsuitable

Studies of the rates of deamidation in a series of nonaqueous solvents have indicated a dependence of rate on the dielectric constant of the solvent. Although these experiments have generally involved solvents unsuitable for use in formulation, it is interesting to note a reported decrease of the rate of deamidation of N-terminal-blocked Boc-Asn-Gly-Gly in ethanol" (Boc = butoxycarbonyl). Similarly, the deamidation rate of the hexapeptide Val-Thr-Pro-Asn-Gly-Ala decreased with decrease in the dielectric constant of the solvent, an effect which was attributed to the destabilisation of the deprotonated peptide bond nitrogen anion which is involved in the formation of the cyclic imide intermediate. 

Finally there are many cases where chemical reactivity makes a solvent unsuitable for applications where materials are present which can react with them via their reactive function(s). Certainly water, but also alco-... 

If the diastereoisomeric salt can not be separated by fractionated precipitation, it is feasible to get its crystalline solvate by fractionated precipitation from a solvate forming solution.i2 When the solvent, unsuitable for separation of the diastereoisomers, contains structurally (partly) similar compound(s) to the solvate forming solution, the separation of enantiomers became feasiable by fractionated precipitation of the diastereoisomeric salt. It is particularly striking, when the wanted crystal composition is obtained by using a structurally similar (either with racemic compound or resolving agent) achiral... 

These tests are very important, since—apart from the sensitizer—other components of the device, such as the redox electrolyte or the sealing, may fail under long term illumination. Indeed, a problem emerged with electrolytes based on cyclic carbonates, such as propylene- or ethylene carbonate, which were found to undergo thermally activated decarboxylation in the presence of Ti02 rendering these solvents unsuitable for practical usage. 

White-spirits are solvents that are slightly heavier than SBP s and have boiling ranges between 135 and 205°C. A dearomatized grade exists. These solvents are used essentially as paint thinners although their low aromatic content makes them unsuitable for lacquers, cellulosic paints and resins. 

When the correct solvent for recrystallisation is not known a procedure similar to that given on pp. 15-16 should be followed, but on the semi-micro scale not more than 10 mg. of the solid should be placed in the tapered-end test-tube (Fig. 29(B)) and about o i ml. of the solvent should be added from the calibrated dropping-pipette (Fig. 30(B)). If the compound dissolves readily in the cold, the solvent is unsuitable, but the solution should not be discarded. [In this case recourse should be had to the use of mixed solvents (p. 18). For example if the substance is very soluble in ethanol, water should be added from a calibrated pipette with shaking to determine whether crystallisation will now take place, indicated by a cloudiness or by the separation of solid.]... 

The choice of solvent cannot usually be made on the basis of theoretical considerations alone (see below), but must be experimentally determined, if no information is already available. About 0 -1 g. of the powdered substance is placed in a small test-tube (75 X 11 or 110 X 12 mm.) and the solvent is added a drop at a time (best with a calibrated dropper. Fig. 11, 27, 1) with continuous shaking of the test-tube. After about 1 ml. of the solvent has been added, the mixture is heated to boiling, due precautions being taken if the solvent is inflammable. If the sample dissolves easily in 1 ml. of cold solvent or upon gentle warming, the solvent is unsuitable. If aU the solid does not dissolve, more 11,27,1. solvent is added in 0-5 ml. portions, and again heated to boiling after each addition. If 3 ml. of solvent is added and the substance... 

Styrene-butadiene (SBR) 250 Better water resistance than natural rubber. Fair to good resistance to acids, alkalies. Unsuitable with gasobue, oils and solvents. 

The concentration of acid impurities is an important indication of the quality of petroleum products and the purity of organic solvents, plasticizers, mineral oils, food fats, and polymers. Methods are used to detect organic acids in such compounds have many disadvantages the alkalimetry - low sensitivity, especially in the determination of weak acids, the extraction-photometric method is laborious, instmmental methods are expensive. In addition, most of methods are commonly unsuitable for direct analysis. 

Solvents and substances that are specified as pure for a particular purpose may, in fact, be quite impure for other uses. Absolute ethanol may contain traces of benzene, which makes it unsuitable for ultraviolet spectroscopy, or plasticizers which make it unsuitable for use in solvent extraction. 

Barium perchlorate. Expensive. Used in desiccators (covered with a metal guard). Unsuitable for drying solvents or organic material where contact is necessary, because of the danger of EXPLOSION... 

In the discussion of the relative acidity of carboxylic acids in Chapter 1, the thermodynamic acidity, expressed as the acid dissociation constant, was taken as the measure of acidity. It is straightforward to determine dissociation constants of such adds in aqueous solution by measurement of the titration curve with a pH-sensitive electrode (pH meter). Determination of the acidity of carbon acids is more difficult. Because most are very weak acids, very strong bases are required to cause deprotonation. Water and alcohols are far more acidic than most hydrocarbons and are unsuitable solvents for generation of hydrocarbon anions. Any strong base will deprotonate the solvent rather than the hydrocarbon. For synthetic purposes, aprotic solvents such as ether, tetrahydrofuran (THF), and dimethoxyethane (DME) are used, but for equilibrium measurements solvents that promote dissociation of ion pairs and ion clusters are preferred. Weakly acidic solvents such as DMSO and cyclohexylamine are used in the preparation of strongly basic carbanions. The high polarity and cation-solvating ability of DMSO facilitate dissociation... 

The chromatography literature contains a vast amount of dispersion data for all types of chromatography and, in particular, much of the data pertains directly to GC and LC. Unfortunately, almost all the data is unsuitable for validating one particular dispersion equation as opposed to another. There are a number of reasons for this firstly, the necessary supporting data (e.g., diffusivity data for the solutes in the solvents employed as the mobile phase, accurate distribution and/or capacity factor constants (k")) are not available secondly, the accuracy and precision of much of the data are inadequate, largely due to the use of inappropriate apparatus with high extracolumn dispersion. 

Solvent-borne polychloroprene adhesives are unsuitable for bonding low-energy substrates, such as PVC. However, water-borne polychloroprene adhesives display good peel adhesion to vinyl substrates. Addition of an accelerator such as zinc oxide is essential for improved hot bond strength. 

For this specific task, ionic liquids containing allcylaluminiums proved unsuitable, due to their strong isomerization activity [102]. Since, mechanistically, only the linkage of two 1-butene molecules can give rise to the formation of linear octenes, isomerization activity in the solvent inhibits the formation of the desired product. Therefore, slightly acidic chloroaluminate melts that would enable selective nickel catalysis without the addition of alkylaluminiums were developed [104]. It was found that an acidic chloroaluminate ionic liquid buffered with small amounts of weak organic bases provided a solvent that allowed a selective, biphasic reaction with [(H-COD)Ni(hfacac)]. 

Introduce a 0.30 pL portion of the solvent extract into the gas chromatograph. It is found that solutions of concentrations greater than 0.3 M are unsuitable as they deposit solid and thus cause a blockage of the 1 jj.L microsyringe used for the injection of the sample. The syringe is flushed several times with the sample solution, filled with the sample to the required volume, excess liquid wiped from the tip of the needle and the sample injected into the chromatograph. 

The fourth type was not detected in homogeneous kinetics (116) because of the unsuitable statistical treatment used, but it was known in heterogeneous catalysis (4, 5). It is the so called anticompensation, when AH and AS change in the opposite sense. It was supposed that solvent effects particularly can cause such changes (37). 

Supercritical fluid extraction (SEE) is another modern separation technology usually employed to extract lipophilic compounds such as cranberry seed oil, lycopene, coumarins, and other seed oils. Anthocyanins generally and glycosylated anthocyanins in particular were considered unsuitable for SEE due to their hydrophilic properties, since SEE is applicable for non-polar analytes. However, a small amount of methanol was applied as co-solvent to increase CO2 polarity in anthocyanin extraction from grape pomace. New applications of SEE for anthocyanin purification have been reported for cosmetic applications from red fruits. ... 

Hot splitless WCOT 0.5 ppm (FID) without preconcentration Lower injection temperature than split Trace analysis Handles dirty samples Automation Flash vaporisation Optimisation required (splitless time, oven temperature, solvent) Limited number of solvents ( solvent effect ) Thermal degradation possible Discrimination possible Poor direct quantification Unsuitable for very polar substances... 

This electrode filling is unsuitable with acetic acid or another related acid as the titration solvent, as in this medium possible leakage of sodium acetate would act as the inherent base. 

---