Low solubility

An interesting consequence of covering a surface with a film is that the rate of evaporation of the substrate is reduced. Most of these studies have been carried out with films spread on aqueous substrates in such cases the activity of the water is practically unaffected because of the low solubility of the film material, and it is only the rate of evaporation and not the equilibrium vapor pressure that is affected. Barnes [273] has reviewed the general subject. 

These are practically insoluble in water, are not hydrolysed and so may be prepared by addition of a sufficient concentration of sulphide ion to exceed the solubility product of the particular sulphide. Some sulphides, for example those of lead(II), copper(II) and silver(I), have low solubility products and are precipitated by the small concentration of sulphide ions produced by passing hydrogen sulphide through an acid solution of the metal salts others for example those of zincfll), iron(II), nickel(II) and cobalt(II) are only precipitated when sulphide ions are available in reasonable concentrations, as they are when hydrogen sulphide is passed into an alkaline solution. 

Figure 10.1-2. A four-fold toroidal KNM map for 1 293 compounds obtained by using ihe 15 input descriptors high" means compounds v ilh high solubiiity where log S is in the range -2.82 to 1.58 "middle" means compounds with medium solubility where log 5 is in the range -7.21 to -2.83 low means compounds with low solubility where log S is in the range -11.62 to -7.22.

The very low solubility of oxamide is almost undoubtedly the result of the extensively hydrogen-bonded nature of the crystalline compound (cf. E. M. Ayerst and J. R. C. Duke, Acta. Cryst. (1954), 7, 588). 

A second preparation to illustrate sulphonation is that of sulphanilic acid, NH2C4H4SO3H, a highly crystalline substance which, having a low solubility in cold water, can be readily isolated. If aniline is treated with an excess of concentrated sulphuric acid, aniline hydrogen sulphate is first formed, and... 

Dinitrophenylhydra2ones usually separate in well-formed crystals. These can be filtered at the pump, washed with a diluted sample of the acid in the reagent used, then with water, and then (when the solubility allows) with a small quantity of ethanol the dried specimen is then usually pure. It should, however, be recrystallised from a suitable solvent, a process which can usually be carried out with the dinitrophenylhydrazones of the simpler aldehydes and ketones. Many other hydrazones have a very low solubility in most solvents, and a recrystallisation which involves prolonged boiling with a large volume of solvent may be accompanied by partial decomposition, and with the ultimate deposition of a sample less pure than the above washed, dried and unrecrystal-lised sample. 

Arylarsonic acids have usually a very low solubility in cold water. They are however amphoteric, since with, for example, sodium hydroxide they form sodium salts as above and with acids such as hydrochloric acid they form salts of the type [CaHjAsCOHljlCl. Both types of salt are usually soluble in water, and to isolate the free acid the aqueous solution has to be brought to the correct pH for most arsonic acids this can be achieved by niaking the solution only just acid to Congo Red, when the free acid will usually rapidly separate. 

J Some sodium salts (particularly sodium oxalate) may be precipitated, due to their low solubility in NaOH solution. The salt should be redissolved by the addition of water before the subsequent distillatfon. 

When an amine, or a solution of its hydrochloride, is added to an aqueous solution of chloroplatinic acid, a salt of the base with the cliloroplatinic acid, of general formula BjiHiPtCle (where B is one molecule of the base) is formed and usually crystallises out, for these chloroplatinates hai e normally a rather low solubility in cold water. The chloroplatinate can be filtered off, dried, and then analysed by direct ignition, when only the metallic platinum ultimately remains. Knowing the percentage of platinum in the chloroplatinate, the molecular weight of the latter, and hence of the constituent base, can readily be calculated. 

A solution prepared by dissolving 2 g. of biomine in 100 g. of carbon tetra. chloride is satisfactory. Carbon tetrachloride is employed because it is an excellent solvent for bromine as well as for hydrocarbons it possesses the additional advan. tage of low solubility for hydrogen bromide, the evolution of which renders possible the distinction between decolourisation of bromine due to substitution or due to addition. 

Note that the reaction time in water is considerably shorter than that in organic solvents, despite the fact that the concentration of diene used for the reaction in water was less than one third of that for the reaction in the organic solvents. Contrary to the organic solvents, the reaction mixture in water is heterogeneous. It might well be that the low solubility of the Diels-Alder product (3.10c) in this solution reduces inhibition of the reaction by this compound. Consequently, product inlribition is likely to be more pronounced in the organic media. 

Although Pd is cheaper than Rh and Pt, it is still expensive. In Pd(0)- or Pd(ll)-catalyzed reactions, particularly in commercial processes, repeated use of Pd catalysts is required. When the products are low-boiling, they can be separated from the catalyst by distillation. The Wacker process for the production of acetaldehyde is an example. For less volatile products, there are several approaches to the economical uses of Pd catalysts. As one method, an alkyldi-phenylphosphine 9, in which the alkyl group is a polyethylene chain, is prepared as shown. The Pd complex of this phosphine has low solubility in some organic solvents such as toluene at room temperature, and is soluble at higher temperature[28]. Pd(0)-catalyzed reactions such as an allylation reaction of nucleophiles using this complex as a catalyst proceed smoothly at higher temperatures. After the reaction, the Pd complex precipitates and is recovered when the reaction mixture is cooled. 

A precipitation gravimetric analysis must have several important attributes. Eirst, the precipitate must be of low solubility, high purity, and of known composition if its mass is to accurately reflect the analyte s mass. Second, the precipitate must be in a form that is easy to separate from the reaction mixture. The theoretical and experimental details of precipitation gravimetry are reviewed in this section. 

In the geochemistry of fluorine, the close match in the ionic radii of fluoride (0.136 nm), hydroxide (0.140 nm), and oxide ion (0.140 nm) allows a sequential replacement of oxygen by fluorine in a wide variety of minerals. This accounts for the wide dissemination of the element in nature. The ready formation of volatile silicon tetrafluoride, the pyrohydrolysis of fluorides to hydrogen fluoride, and the low solubility of calcium fluoride and of calcium fluorophosphates, have provided a geochemical cycle in which fluorine may be stripped from solution by limestone and by apatite to form the deposits of fluorspar and of phosphate rock (fluoroapatite [1306-01 -0]) approximately CaF2 3Ca2(P0 2 which ate the world s main resources of fluorine (1). 

MetlylEsters. The addition product of two moles of TYZOR TPT and one mole of ethylene glycol, GLY—TI, can be used as a transesterification catalyst for the preparation of methyl esters. The low solubility of tetramethyl titanate has prevented the use of them as a catalyst for methyl ester preparation (488). 

Most of the naturally-occurring pyrazine hydroxamic acids appear to be derived from valine, leucine and isoleucine, and biosynthetic studies by MacDonald and coworkers (61JBC(236)512, 62JBC(237)1977, 65JBC(240)1692) indicate that these amino acids are incorporated. However, it would seem that the logical intermediates, viz. the 2,5-dioxopiperazines such as (111) and (112), are not always incorporated. This does not rule out their intermediacy, as there may be problems such as low solubility or membrane permeability which prevent their efficient incorporation. An exception to these results was reported for pulcherrimic acid (113) (65BJ(96)533), which has been shown to be derived from cyclo-L-leu-L-leu which serves as an efficient precursor. 

For lubricated plug cocks, the lubricant must have limited viscosity change over the range of operating temperature, must have low solubility in the fluid handled, and must be applied regularly. There must be no chemical reaction between the luBricant and the fluid which... 

Solvent solubility. A low solubility of extrac tion solvent in the raffinate generally leads to a high relative volatihty in a raffinate stripper or a low solvent loss if the raffinate is not desolventized. A low solubility of feed solvent in the extract leads to a high relative separation and, generally, to low solute-recovery costs. 

The way to obtain the membranes as well their composition has been optimized. The main operational criterion for the membranes is the solubility of applicable ionic pairs. The solubility should be quite low - else the substance will be outwashed from the membrane. At the same time, the ionic pairs which have very low solubility are not suitable too because of the complicated obtaining homogeneous membranes. 

Mancozeb is a dithiocarbamate pesticide with a very low solubility in organic and inorganic solvent. In this work we have developed a solvent free, accurate and fast photoacoustic FTIR-based methodology for Mancozeb determination in commercial fungicides. The proposed procedure was based on the direct measurement of the solid samples in the middle infrared region using a photoacoustic detector. A multivariate calibration approach based on the use of partial least squares (PLS) was employed to determine the pesticide content in commercially available formulations. 

Amides are stable compounds. The lower-melting members (such as acetamide) can be readily purified by fractional distillation. Most amides are solids which have low solubilities in water. They can be recrystallised from large quantities of water, ethanol, ethanol/ether, aqueous ethanol, chloroform/toluene, chloroform or acetic acid. The likely impurities are the parent acids or the alkyl esters from which they have been made. The former can be removed by thorough washing with aqueous ammonia followed by recrystallisation, whereas elimination of the latter is by trituration or recrystallisation from an organic solvent. Amides can be freed from solvent or water by drying below their melting points. These purifications can also be used for sulfonamides and acid hydrazides. 

In seawater, HCO3 ions lead to surface films and increased polarization. In aqueous solutions low in salt and with low loading of the anodes, less easily soluble basic zinc chloride [10] and other basic salts of low solubility are formed. In impure waters, phosphates can also be present and can form ZnNH4P04, which is very insoluble [11]. These compounds are only precipitated in a relatively narrow range around pH 7. In weakly acid media due to hydrolysis at the working anode, the solubility increases considerably and the anode remains active, particularly in flowing and salt-rich media. 

Because the solubility parameter of tritolyl phosphate is higher than that of dioctyl sebacate, PVC-tritolyl phosphate blends can tolerate more of a low solubility parameter extender than can a corresponding sebacate formulation. 

The solubility parameters of these extenders are generally somewhat lower than that of PVC. They are thus tolerated in only small amounts when conventional plasticisers of low solubility parameter, e.g. the sebacates, are used but in greater amounts when phosphates such as tritolyl phosphate are employed. 

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