Sublimation small quantities

C4H6N2O2. Sublimes 260"C sparingly soluble in water hydrolysed by alkalis or mineral acids to glycylglycine. It and substituted dike-topiperazines are formed by the condensation of amino-acids, and are obtained in small quantities on the hydrolysis of proteins. 

Until 1990, some flaked iodine and iodine-containing wastes were sublimed to obtain an especially high grade product. This process has been dropped because of quaUty improvements in the standard operations. Sublimed iodine is produced only in small quantities by specialized companies that... 

Scientific research in the field of phosphors is almost 140 years old. In 1866, the young French chemist Theodore Sidot prepared, by a sublimation method, tiny ZnS crystals that manifested phosphorescence in the dark.4 After the experiment was repeated and confirmed it was presented in a note to the Academy of Sciences of Paris the note was then published by Becquerel.5 From present knowledge of phosphors it seems likely that Sidot s ZnS contained a small quantity of copper as an impurity, and was the precursor for ZnS-type phosphors. 

Decalin Hydroperoxide Very stable can be sublimed in small quantities at atm pressure R. Criegee, Ber 77, 22 (1944)... 

The purification of iodine.—Crude iodine contains from 75 to 90 per cent, of iodine, some iodine chloride, iodine cyanide, water, and different salts. The iodine of commerce is purified by washing it with cold water, drying by press., and subliming from heated iron retorts into udells.13 The following is a convenient way of purifying small quantities of iodine for analytical purposes 14... 

The analysed value predicts 2.5 atoms of chlorine per anthracene molecule which indicates the solid to be a dimer with an empirical formula of CscHl7Cl6. When a small quantity of the white residue is sublimed under the reduced pressure of a filter pump with the help of a small open flame, it sublimes giving vapours acidic to litmus. The absorption curve of the sublimate is identical with that of anthracene. The most plausible structure that could be assigned to this white solid seems to be... 

Sulphur thus produced is almost pure. It is true that the sublimed sulphur in powder—that is, the flowers of sulphur—contains a small quantity of sulphurous acid, which for some purposes it is necessary to remove by washing with water, hut this is pretty nearly the only body it is oontaminatod with the roll sulphur is free from sulphurous acid. 

Selenium boils at about 690° C.,4 forming a vapour the colour of which is intermediate between that of chlorine and that of sulphur. The element can be sublimed and distilled at a much lower temperature under very low pressure.5 When selenium is heated on charcoal the vapour has an odour resembling that of rotten radishes this has been attributed to the formation of a small quantity of selenium suboxide, but it is more probably due to the formation of carbon diselenide.8... 

Small quantities of selenium in solution may be detected by the test described by Meunier,1 which is similar to Marsh s test for arsenic. If there is a relatively large amount of selenium present it is readily detected by its red colour, but if the amount of the element be small the deposit closely resembles that of arsenic, and in this case the following process may be adopted to detect the selenium. A current of hydrogen sulphide is passed into the hot solution containing a little sulphurous acid. The precipitate of finely divided sulphur carries down with it any selenium present and arsenic as arsenious sulphide, and it is clotted by stirring. In the presence of selenium the clots are brown they may be dried and the sulphur and selenium separated by careful sublimation in a closed tube. 

Note.—If it is desired to use sublimed oxalic acid for standardizing solutions for alknlimetric or oxidimetric determinations, it must be heated to dryness at a temperature of 60 to 70° C., in small quantities at a time. 

Niobium Trichloride, NbCl3, is prepared by leading the vapour of niobium pentachloride through a heated tube.4 It is also formed in small quantity by the action of carbon tetrachloride vapour on niobium pentoxide contained in a hard-glass tube, and has probably been prepared in solution by the electrolytic reduction of the pentachloride.4 It forms a black, crystalline crust with an almost metallic lustre, which closely resembles the appearance of a film of sublimed iodine. It is not decomposed by water or ammonia, but is readily oxidised by dilute nitric add to niobium pentoxide. On being heated to a red heat in an atmosphere of carbon dioxide, a sublimate of niobium oxytrichloride, NbOCl3, is produced, the carbon dioxide undergoing reduction to the monoxide. 

About a gram of trinitrotoluene or of picric acid is heated in a porcelain crucible. The substance first melts and gives off combustible vapors which burn when a flame is applied but go out when the flame is removed. A small quantity of trinitrotoluene, say 0.1 gram, may actually be sublimed if heated cautiously in a test tube. If heated quickly and strongly, it decomposes or explodes mildly with a "zishing sound and with the liberation of soot. 

The sterically most congested CH-alkoxides Ln(tritox)3 is thermally labile and decomposes to Ln(ditox)3 by loss of isobutene [29, 38]. In addition, a small quantity of di-terf-butylketone indicates the formation of a Ce(III) hydride species. Ln(ditox)3 can be obtained in analytically pure form via sublimation. Scheme 44 describes the mechanistic scenario which was suggested for the Ce(tritox)3 system [29]. 

---