Sulfur liberation

The sulfur liberated is involved in a complicated sequence of reactions which lead to almost complete removal of copper from the matte as very insoluble CuS(S).101-103... 

The crude diethylthiocarbamyl chloride need not be distilled if sulfur does not interfere in the reaction for which the chloride is to be used and if sulfur can be readily separated from the product. At approximately 105° all the sulfur liberated by the chlorination of tetraethylthiuram disulfide will dissolve in the diethylthiocarbamyl chloride, forming a homogeneous product which may be used on the basis of 100% conversion of the disulfide to the chloride. 

The reaction is carried out at low temperature in aqueous medium and then allowed to stand overnight (221). Ammonium thiocarbamate is prepared from a cold saturated solution of ammonium thiocyanate, which is gradually added to dilute sulfuric acid at 25°C. The liberated carbonyl sulfide is passed into a saturated solution of alcoholic ammonia at about 10°C (221). The fairly low yield indicates that the reaction has not been greatly developed. 

A number of simple, standard methods have been developed for the analysis of ammonium compounds, several of which have been adapted to automated or instmmental methods. Ammonium content is most easily deterrnined by adding excess sodium hydroxide to a solution of the salt. Liberated ammonia is then distilled into standard sulfuric acid and the excess acid titrated. Other methods include colorimetry (2) and the use of a specific ion electrode (3). 

Assay of beryUium metal and beryUium compounds is usuaUy accompHshed by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryUium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryUium content of the sample is calculated from the titration volume. Standards containing known beryUium concentrations must be analyzed along with the samples, as complexation of beryUium by fluoride is not quantitative. Titration rate and hold times ate critical therefore use of an automatic titrator is recommended. Other fluotide-complexing elements such as aluminum, sUicon, zirconium, hafnium, uranium, thorium, and rate earth elements must be absent, or must be corrected for if present in smaU amounts. Copper-beryUium and nickel—beryUium aUoys can be analyzed by titration if the beryUium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

After refluxing with 10% acetone for lOh, aniline was acidified with HCl (Congo Red as indicator) and extracted with Et20 until colourless. The hydrochloride was purified by repeated crystn before aniline was liberated by addition of alkali, then dried with solid KOH, and distd. The product was sulfur-free and remained colourless in air [Hantzsch and Freese Chem Ber 27 2529, 2966 1894]. 

Bis-(trimetbylsilyl) sulfide (bexametbyldisilatbiane) [3385-94-2] M 178.5, b 65-67 /16mm, 162.5-163.5 /750mm corr, 164 /760mm, d 0.85, n 1.4598. Dissolve in pet ether (b ca 40°), remove solvent and distilled. Redistilled under atmospheric pressure of dry N2. It is collected as a colourless liquid which solidifies to a white solid in Dry-ice. On standing for several days it turns yellow possibly due to liberation of sulfur. Store below 4° under dry N2. [J Chem Soc 3077 1950.]... 

The alcoholic filtrate is evaporated to 50 cc., and 50 g. of barium hydroxide and 150 cc. of distilled water are added (Note 4). The mixture is refluxed for two hours and the excess barium hydroxide is precipitated with carbon dioxide. The barium carbonate is removed by filtration and washed with hot distilled water. A slight excess of sulfuric acid is added to the filtrate to liberate the amino acid from its barium salt, and an excess of barium carbonate is added to remove sulfate ion. The mixture is digested on the steam bath until effervescence ceases, and it is then filtered and the precipitate is washed with hot distilled water. The filtrate and washings are concentrated on the steam bath to a volume of 100 cc., decolorized with i g. of active carbon, filtered, and concentrated to the point of crystallization (about 25 cc.). The amino acid is precipitated by the addition of 150 cc. of absolute alcohol and the product is collected and washed with absolute alcohol. 

Direct conversion processes use chemical reactions to oxidize H2S and produce elemental sulfur. These processes are generally based either on the reaction of H2S and O2 or H2S and SO2. Both reactions yield water and elemental sulfur. These processes are licensed and involve specialized catalysts and/or solvents. A direct conversion process can be ii.scd directly on the produced gas stream. Where large flow rates are encoLui tered. ii is more common to contact the produced gas stream with a chemical or physical solvent and use a direct conversion proce.ss on the acid cas liberated in the regeneration step. 

The simplest NHIP is rubredoxin, in which the single iron atom is coordinated (Fig. 25.9a) to 4 S atoms belonging to cysteine residues in the protein chain. It differs from the other Fe-S proteins in having no labile sulfur (i.e. inorganic sulfur which can be liberated as H2S by treatment with mineral acid sulfur atoms of this type are not part of the protein, but form bridges between Fe atoms.)... 

There is no apparent reaction between the disulfide and dilute acids at room temperature, but with more concentrated acids liberation of nitrogen takes place and the solution becomes turbid due to the formation of sulfur. 

The formyl derivative is then hydrolyzed by refluxing with 50% sulfuric acid for about 4 hours, after which the hydrolysate is extracted with ether to remove the acid-insoluble material and the aqueous solution made strongly alkaline with any suitable alkalizing agent, for example, sodium hydroxide, to liberate the amine. 

The method described differs from that given in Org. Syn. 3, 53 mainly in the use of hydrochloric acid in place of sulfuric acid, in the liberation of the cyanoacetic acid from the sodium salt and in the simplified esterification process. These are slight but very important differences and make the procedure much easier to carry out in the laboratory. Moreover, the yields are higher. 

The first step in the manufacture of H2SO4 is to burn sulfur to sulfur dioxide. Sulfur burns spontaneously in air, liberating heat. 

This results in a concentrated sulfuric acid solution that contains 98% HzSO,. It is a viscous, colorless liquid. When it is mixed with water, so much heat is liberated that the operation must be carried out very cautiously. The sulfuric acid... 

Proteins have been hydrolyzed by treatment with sulfuric acid, hydrochloric acid, barium hydroxide, proteolytic enzymes, and other hydrolytic reagents, but no condition has been found which avoids some destruction or incomplete liberation of tryptophan, cystine, and some other amino acids. The early work on this problem has been reviewed by Mitchell and Hamilton (194). The literature and their own excellent experiments on the hydrolysis problem in relation to the liberation and destruction of tryptophan have been presented recently by Spies and Chambers (269). 

One of the least expensive and popular techniques for the quant detn of bound N in energetic materials is that of titrimetry. There are currently three basic titrimetry systems used aq acid-base, redox and non-aqueous (involving both acid-base and redox systems in which there is association, not ionization of the re-actants). The simple aq acid-base titrimetry system has been shown, earlier in the article, being used in the Kjeldahl, De varda and Ter-Meulen procedures to detn liberated NH3. It is also utilized, for example, to detn nitrosyi-sulfuric acid in mixed acids, total acidity in nitric acid, NG in exp] oils, and the N content of... 

It has been generally assumed that thermal decomposition of thiirane oxides proceeds stereospecifically to the corresponding olefins by elimination of sulfur monoxide, possibly through a concerted nonlinear chelatropic reaction96 with retention of configuration of the liberated olefin. 

---