Disulphides, purification

A solution of sodium methoxide, prepared from sodium (23 g) and dry methanol (500 mL), was added drop-wise at 0 °C to a stirred suspension of aminoacetonitrile hydrochloride (18, 100 g, 1.08 mol) in dry methanol (100 rnL). After stirring for 2 h at rt the precipitated sodium chloride was filtered off and the filtrate concentrated in vacuo. EtOAc (20 mL) was added and evaporated under reduced pressure to remove all traces of methanol. The oily residue was dissolved in dry EtOAc (100 mL) and anhydrous sodium sulfate added. After cooling, the precipitate was filtered off. The solution of crude aminoacetonitrile was used without further purification. This solution was added drop-wise during a period of 1 h to a vigorously stirred, ice-cooled solution of carbon disulphide (100 mL, 1.66 mol) in dry EtOAc (100 mL) under an N2 atmosphere. Continued mechanical stirring and water-free conditions were essential. The mixture was stirred at 0 °C for 1 h. The resultant precipitate was filtered off, washed with EtaO and dried, giving the product 50 as yellow crystals (99 g, 75 % on amount of sodium), m.p. 131 °C dec. IR (KBr) v max 1630, 1500 cm. ... 

Thiotelluration of 1-styrylcyclopropane In a Pyrex glass tube were placed 1-styrylcy-clopropane (0.2 mmol, 28.8 mg, 0.4 M), diphenyl disulphide (0.2 mmol, 43.7 mg, 0.4 M), diphenyl ditelluride (0.2 mmol, 81.9 mg, 0.4 M) and CDCI3 (0.5 mL). The tube was filled with Ar, and the mixture was irradiated at 40°C for 7 h through a filter (hv >400 nm) with a tungsten lamp (500 W). The solvent was evaporated in vacuo. Purification by a recycling preparative HPLC (CDCI3) yielded 77 mg (84%, E/Z= 14 86) of 2-phenyl-l-(phenylthio)-5-(phenyltelluro)-2-pentene as a pale yellow oil. 

Carbon dioxide, 184, 358, 359 solid see Dry Ice Carbon disulphide, 767 purification of, 175 Carbon monoxide, 185, 1003, 1004 Carbon, decolourising, 127, 128 Carbon tetrachloride, 733, 815 drying of, 734 purification of, 176 Carbonyl chloride, 185 Carborundum chips, 4 Carboxylic acids, equivalent weights of, 1071 ... 

Di-n-butylaniline, 572 Di-n-butyl cadmium, 935, 936 Di-n-butyl carbinol, 248, 256 Di-n-butyl cyanamide. 414, 419 Di-n-butyl disulphide, 496, 498 Di-n-butyl ether, 309,311 purification of, 165 as a solvent in the Grignard reaction, 254... 

The iron oxide used in the purification of coal gas gradually becomes richer in sulphur and can repeatedly be revivified by exposure to air until the sulphur amounts to about 40 per cent., of the whole the mixture is then of greater value as a source of sulphur. The spent oxide, as it is commonly termed, is frequently applied to the production of sulphur dioxide or sulphuric acid, but the extraction of its sulphur by carbon disulphide has been effected as a successful commercial process using the system of counter-currents the mass is exhausted of sulphur, whilst a saturated solution of sulphur is obtained, from which the solvent can be distilled and returned to the extraction process. 

Purification may also be effected by oxidation to selenious acid, e.g. by heating with dilute nitric acid. On evaporation the solid selenium dioxide may be obtained, and this can be purified by repeated sublimation in a current of dust-free dry air.3 It may then be redissolved in water, the solution acidified with hydrochloric acid, and the selenium precipitated by passing in sulphur dioxide.4 For further purification the element can be sublimed in a current of carbon dioxide, and after heating for some time at 100° C. to convert it into the crystalline condition, it may be heated with carbon disulphide to extract any traces of residual sulphur. 

Recently, active recombinant a-LTX has been generated using bacteria in which both thioredoxin reductase and glutathione reductase are inactivated to improve the formation of disulphide bonds in expressed proteins (Li et al. 2005). The toxin is expressed as a fusion with glutathione-S-transferase (GST), which is used for affinity purification of the recombinant toxin and can be subsequently removed by selective proteolysis. Considering the relative ease of generating recombinant proteins in bacteria, this approach will facilitate structure-function studies of a-LTX. 

To a stirred suspension of IOB (110 mg, 0.5 mmol) in dichloromethane (20 ml) was added triflic acid (0.044 ml, 0.5 mmol) at 0°C. After 2 h at room temperature, a solution of diphenyl disulphide (238 mg, 1.09 mmol) in dichloromethane (6 ml) was added dropwise at 0°C. After 2 h at room temperature, the alkene (5 mmol) was added at 0°C and the mixture was stirred for 12 h. The reaction mixture was poured into water and extracted with ether. The organic layer was washed with water, dried and concentrated to an oil from which iodobenzene was removed in vacuo at 70-80°C. Purification was effected using preparative centrifugal TLC yields of bis phenylsulphides were near 90%. 

The bulk of the concentrate separated from molybdenite ore by flotation is further processed to produce molybdenum. A typical extraction and purification procedure is outlined in Figure 2.1. The concentrate is roasted to convert the moiybdenum disulphide to molybdic oxide. The product is called roasted concentrate, and about 30% is marketed as Technical Oxide, mainly for alloy manufacture. A typical range of compositions is shown in Table 2.6. 

Carlsson J, Axen R, Brocklehurst K, and Crook EM. Immobilization of urease by thiol-disulphide interchange with concomitant purification. Eur. J. Biochem. 1974 44 189-194. 

Ultra-violet and visible spectrophotometry can be effectively used for the control of purification and specification of purity of compounds. If a compound is transparent in the near ultra-violet and the visible regions, the purification is continued until the absorbancy is reduced to a minimum (e < 1). Traces of impurities present in pure transparent organic compounds can be readily detected and estimated, provided the impurities themselves have fairly intense, absorption bands. Before a liquid is used as a spectroscopic solvent, it should be tested for spectrophotometric purity. For example, commercial absolute alcohol usually contains benzene as impurity. The absence of benzene in the Alcohol should be confirmed spectrophoto-metrically by using sufficiently large cells (4 or 10 cm cells), before using the alcohol as a solvent. The presence of carbon disulphide in carbon tetrachloride may be detected by the presence of the disulphide absorption tend at 318 mytt. The detection of the characteristic benzenoid absorption in the spectra of many organic compounds (e.g. diethyl ether, cyclohexene) showed that the bands attributed to these compounds earlier were only due to the contamination by benzene1. 

Another peptide derivative of MTX was prepared [362] with the aim of covalently attaching it to antibodies. Condensation of oxidized glutathione tetraethyl ester with 4-amino-4-deoxy-A °-methylpteroic acid with the aid of diethyl phosphorocyanidate afforded the tetraethyl ester (VIII.262) (47% yield). Hydrolysis of the ester groups with Ba(OH)2 followed by ion-exchange chromatography in the presence of 2-mercaptoethanol gave a crude product which was assumed to be the reduced tripeptide. On further purification by gel filtration without 2-mercaptoethanol, this compound underwent spontaneous oxidation to disulphide (VIII.263). In a model experiment, an IgG, monoclonal antibody directed against human transferrin receptor was activated by reaction with A-succinimidyl-3-(2-pyridyldithio)propionate, and con-... 

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