Sulphur compounds, solvent effects

The anomalous photophysical properties of sulphur compounds continue to attract interest. Quenching studies of the luminescent S2 state of a number of aromatic thioketones show a range of lifetimes between 10 and 10 s. A variety of solvents shows the role of transient interactive effects and environmental viscosity. In the case of the S2 state of thiophosgene in perfluoro-solvents, molecular dissociation is found to be the most... 

A mixture which is to be examined is broken down into its constituents as far as possible by treating it with various substances, which either dissolve certain constituents of the mixture as such or convert them into soluble compounds. In effecting such solutions the following substances are frequently used Water, which removes from the mixture substances soluble in water a solution of hydrochloric acid, which removes basic substances insoluble in water a solution of sodium hydroxide, which dissolves acids insoluble in water concentrated sulphuric acid, which separates many oxygen compounds from hydrocarbons and certain halogen derivatives and organic solvents which, in certain cases, may dissolve certain constituents of the mixture and not others. 

By far the most evidence for electrophilic sulphur is found in the sulphenyl halides (RSCl, RSBr) Although these compounds may in theory react either as sources of RS or X (X = halogen), none of the observed reactions of the sulphenyl halides indicate the latter mode of heterolysis. Kharasch et have presented good evidence for the existence of the 2,4-dinitrobenzene-sulphenium ion (Ar ) in strongly acidic media evidence has also been presented of a strong solvent effect upon the rate of reaction of 2,4-dinitroben-zenesulphenyl chloride and cyclohexene - and of a definite substituent effect in the reaction of this sulphenyl chloride with some substituted styrenes in acetic acid . Such observations are entirely consistent with an electrophilic heterolytic ad tion mechanism involving attack by the sulphenyl chloride in the sense iC -Cl. 

Shankaranarayana has recorded and studied the electronic absorption spectra of a series of derivatives of diselenocarbonic, diselenocarbamic, and diselenothiocarbonic acids and made assignments to (w, ir ), (tt, tt ), and in, a ) transitions on the basis of the observed hetero-atom and solvent effects, and by comparison of the spectra with those of the corresponding thiocarbonyl compounds. The author found that his results supported the view that the nature of the arrangement of electrons in the selenium atom is similar to that of sulphur, although the electrons in the former are apparently more weakly bound. The electronic spectra of a series of metal AW-diethyldiselenocarbamates have been described recently. ... 

Investigations of the solubilities of aromatic compounds in concentrated and aqueous sulphuric acids showed the activity coefficients of nitrocompounds to behave unusually when the nitro-compound was dissolved in acid much more dilute than required to effect protonation. This behaviour is thought to arise from changes in the hydrogenbonding of the nitro group with the solvent. 

Substituted amides suffer hydrolysis with greater difficulty. The choice of an acid or an alkaline medium vill depend upon (a) the solubility of the compound in the medium and (b) the effect of the reagent upon the products of hydrolysis. Substituted amides of comparatively low molecular weight (e.g., acetanilide) may be hydrolysed by boiling either with 10 per cent, sodium hydroxide solution or with 10 per cent, sulphuric acid for 2-3 hours. Other substituted amides are so insoluble in water that little reaction occurs when they are refluxed with dilute acid or dilute alkali for several hours. These include such substances as benzanilide (C(H(CONHC,Hg) and the benzoyl derivative of a naphthylamine (C.HjCONHCioH,) or a toluidine (C gCONHCjH,). For these substances satisfactory results may be obtained with 70 per cent, sulphuric acid this hydrolysis medium is a much better solvent for the substituted amide than is water or more dilute acid it also permits a higher reaction temperature (compare Section IV 192) ... 

For general purpose tracer work, however, and particularly in polymer chemistry, the liquid scintillation counter surpasses all other instruments in its sensitivity and adaptability. There is no question on the author s mind that at the present time such an instrument would be the first choice, particularly where tritium, carbon-14 or sulphur-35 were involved. Samples for assay are dissolved in a phosphor whose major solvent usually consists of toluene, toluene-alcohol, or dioxan. Many polymers and low molecular weight compounds are readily soluble in these solvents. Prospective users should not be deterred by alleged complications due to "variable quench effects" as these effects are readily corrected for via internal or external standards or the channels ratio method (7, 46, 91). Dilution quench corrections, though valid, are tedious and unnecessary. Where samples are insoluble in phosphor they may be suspended (e.g. as gels or as paper cut from chromatograms, etc.) or they can be burnt and the combustion products absorbed in a suitable phosphor solution. A modification of the Schoniger flask combustion technique is particularly suitable for this purpose (43—45). 

Another method of preparation is as follows 1 33 parts of fluorescein are dissolved in 5 parts of ether and treated with 25 parts of selenium chloride in the same solvent. A yellowish-red precipitate separates, and after long stirring at the ordinary temperature the ether is distilled off. The residue is stirred with water, the mixture filtered and the residue now dissolved in sodium hydroxide. After further filtration the filtrate is treated with hydrochloric acid, which precipitates seleno-fluorescei n. Further purification is effected by solution in alkali and reprecipitation. A reddish-brown powder is obtained, soluble with fluorescence in alcohol, but insoluble in water. In concentrated sulphuric acid it dissolves to give an orange solution. Its alkali salts are very soluble in wrater, giving red solutions. This process may also be applied to phthalins, which are obtained by the reduction of phthaleins and their halogen derivatives. If the selenium chloride is replaced by the oxychloride similar products are obtained.2 In place of the phthalins specified in the patents quoted, their O-acetyl compounds or O-acetyl compounds of the phthaleins may be used in indifferent solvents. The products are different from those obtained by the action of selenium on fluoresceins in aqueous alkali solutions.3... 

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