Ray E. Humphrey

Reduction of alkyl disulphides with triphenylphosphine

Abstract Alkyl disulphides are reduced to thiols by triphenylphosphine in aqueous methanol, with the phosphine being converted to the oxide. Water is believed to be the source of the hydrogen and oxygen required. The reductions are rather slow; heating for periods of several hours is necessary. Maximum yields of 70–80% are generally obtained, although some substituted alkyl disulphides, such as cystine and dithiodiglycolic acid, are quantitatively reduced. The principal analytical application of this reduction appears to be the determination of aromatic disulphides in the presence of alkyl disulphides, because the aromatic compounds are reduced at a much greater rate.

Improved spectrophotometric determination of cyanide with organic disulfides using dimethylformamide

Abstract The rate of reaction of cyanide ion with the dissulfide 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) is increased considerably with N,N -Dimethylformamide present. The time required for the spectrophotometric determination of cyanide using this procedure is decreased from 2 hours to 30 minutes or less.

Determination of sulfite by reaction with mercury(I) chloride and spectrophotometric measurement of mercury(II) complexes

Abstract Sulfite ion was determined in the 0.4 to 12-ppm range by reaction with insoluble mercury(I) chloride to form the soluble Hg(SO3)2staggered2− ion and elemental mercury. The uv absorption of the sulfite complex or an anion species, HgX4staggered2−, formed on adding an excess of KBr, KCl, KI, or KSCN is measured. The mercury(II) in solution can also be determined by lowering the pH, adding KCl, and forming the crystal violet adduct of the HgCl3staggered− ion. This adduct is extracted into benzene and the absorbance measured at 605 nm.

Colorimetric determination of fluoride employing thorium lodate and the linear starch-iodine system

Abstract Fluoride ion can be determined colorimetrically by reaction with solid thorium iodate in 1:1 ethanol-water solvent to release iodate ion, reduction of the iodate with iodide in acid solution, and formation of the starch-iodine blue complex. By using different dilutions of the reaction solution fluoride ion can be measured from approximately 0.15 to 6.0 ppm. The color system is stable and reproducibility is good. A number of common anions interfere seriously with the method.

Spectrophotometric determination of sulfite with soluble mercury(II) compounds

Abstract Sulfite ion reacts with mercury(II) ion in acid solution to form the mercury(I) ion. The reaction is rapid and quantitative. The mercury(I) ion absorbs at 237 nm with a molar 5 . Beers law Data for Sulfite Complexes of Covalent Mercury(II) Compounds SO2 (ppm) ϵHgCl2 a ϵHgBr2 ϵHg(Ac)2 b ϵHg(SCN)2 2.0 12,500 10,000 10,000 9,200 4.0 12,500 11,500 10,000 9,000 6.0 12,500 11,500 10,000 9,200 8.0 12,000 11,000 10,500 9,800 a Molar absorptivity based on sulfite ion at 230 nm. Solution was 6.86 buffer. b Mercuric acetate solutions seemed to be somewhat unstable. absorptivity of about 25,000. The absorbance is linear over a range of approximately 0.5–5.0 ppm as SO2. Covalent mercury(II) compounds form a complex with sulfite, Hg(SO3)22−, which absorbs at 230 nm and shows a linear response over a range of 1–8 ppm as SO2.

Indirect ultraviolet determination of cyanide with mercury complexes

Abstract Cyanide ion can be determined in the range of 0.50 to 10 parts per million by the decrease in ultraviolet absorption of the mercury complexes HgBr 4 2− , HgCl 4 2− , HgI 4 2− , Hg(SCN) 4 2− , and Hg(SO 3 ) 2 2− . The decrease in absorbance is linear with cyanide concentration. Reaction of cyanide with the complexes is rapid in pH 6.86 and 9.01 buffers and in water. Solutions of the complexes are reasonably stable.

Determination of silver by potentiometric titration with sodium thiosulfate

Abstract Silver can be determined in the low parts per million range by potentiometric titration with sodium thiosulfate solution. Sodium thiosulfate solutions can be standardized by potentiometric titration of silver nitrate. Some time is required to achieve a stable potential reading in the vicinity of the end point. Reduced temperatures are required to obtain a useful potentiometric titration on adding silver ion to a thiosulfate solution. Quantitative results can be obtained in this titration also.

Reduction of disulfides in the milligram range with hypophosphorous acid and organic phosphites

Abstract A number of organic disulfides in the milligram range were reduced to the corresponding thiol by reaction with hypophosphorous acid at elevated temperatures in aqueous solvents. Reduction is extensive after several hours. Aromatic disulfides were reduced by triethyl phosphite and triphenyl phosphite at room temperature. Products were deterimned by polarographic and amperometric titration techniques.

Determination of benzoyl bisulphide by desulphurisation and solvolysis

Benzoyl disulphide is rapidly and quantitatively desulphurised to the monosulphide by reaction with triphenylphosphine in aqueous methanol at 25 degrees . The monosulphide reacts with methanol to form thiobenzoic acid and methyl benzoate. Benzoyl disulphide also reacts with methanol in solutions containing ammonium acetate or sodium acetate yielding thiobenzoic acid, methyl benzoate and elemental sulphur. Benzoyl disulphide and sulphur were detected by their polarographic reduction waves. Thiobenzoic acid was detected by its polarographic oxidation wave and yields were determined by amperometric silver nitrate titrations.