Sealed tube method

Dissolve 1.000 g Rh by the sealed-tube method described under iridium. 

Storage under vacuum in a sealed tube (Method II). Substances that are extremely oxygen-sensitive, such as the fluorescent compound F of euphausiids and dinoflagellate luciferin, have to be stored in an evacuated sealed container at a low temperature. For long-term storage, they must be fuse-sealed in an evacuated glass vial using the method outlined below. 

If any of the reactants are volatile or air sensitive, then this simple method of heating in the open atmosphere is no longer appropriate, and a sealed tube method will be needed. 

Sealed Tube Method. No evidence for compound formation was observed when mixtures of iron and uranium oxides were heated in air to temperatures as high as 1200°C. Substituting ferric and uranyl nitrates for the oxides as starting materials also proved unsuccessful. Ferric oxide and UO2.64 were the only product phases, thus giving an empirical formula of FeU04.i4 in the 1 1 mixture, and FeU309.42 in the 1 3 mixture. Unlike the situation encountered in the other double oxide systems, the iron uranates do not appear to have sufficient thermodynamic stability to be synthesized at ambient oxygen pressure. 

Care should also be taken to avoid volatile or air-sensitive compounds, if possible. In cases where there is no alternative, sealed tube methods (Section 4.3) can be used. 

Lithium titanate could be prepared by using a sealed tube method. As the alkali metals can react with glass, the tube must be coated with graphite by decomposition of an organic solvent on the surface. Then a mixture of lithium oxide and titanium dioxide could be weighed out in a glove box, placed in the tube and the tube evacuated. Once sealed off, the whole tube could be heated in a furnace. Alternatively, a mixture of lithium carbonate (in excess) and titanium dioxide could be pressed into pellets and heated. The required excess of lithium carbonate would have to be determined by trial and error. 

Furthermore, closed reflux methods are preferred because fewer reagents are used, and therefore less hazardous wastes are generated. The methods are equivalent to ISO 15705-Determination of the chemical oxygen demand index (ST-COD) - Small-scale sealed-tube method. 

ISO 15705 (2002) Water Quality - Determination of the Chemical Oxygen Demand Index (ST-COD) - Small-scale Sealed-tube Method. 

The vapor pressure of Hg has been neglected in these calculations. Discuss the significance of this assumption in the open-tube method and in the sealed-tube method at higher temperatures. 

The only disadvantage is that the procedure does not give accurate results if the compound sublimes the capillary tube method should be used in such cases, and it may be necessary to employ a sealed capillary tube. This apparatus should find a place in every laboratory. It is... 

It is believed that the red phosphorus is the true reducing agent and the iodine (or iodide) functions as a hydrogen carrier. This proc ure replaces the obsolete method of heating with red phosphorus and concentrated hydriodic acid in a sealed tube. 

Qualitative Analysis. Several quaUtative analyses can be employed. For example, in the oxamide method (59), oxaUc acid is first heated at approximately 200°C with concentrated aqueous ammonia in a sealed tube. When thiobarbituric acid is added and heated to 140°C, a condensed compound of red color forms. The analysis limit is 1.6 pg. In the diphenylamine blue method (59,60), oxaUc acid is heated with diphenylamine to form a blue color, aniline blue. The analysis limit is 5 pg. 

Protein Hydrolysis. Acid hydrolysis of protein by 6 MHQ in a sealed tube is generally used (110°C, 24-h). During hydrolysis, slight decomposition takes place in serine (ca 10%) and threonine (ca 5%). Cystine and tryptophan in protein cannot be deterruined by this method because of complete decomposition. 

The more traditional methods of phenazine synthesis falling into the type A synthesis are altogether less satisfactory than the application of the Beirut reaction. Traditionally, Ris prepared phenazine in low yield by heating o-phenylenediamine and catechol in a sealed tube at 200 °C (1886CB2206) however, the method appears to be unsatisfactory at best and gives, in addition to phenazine, 5,10-dihydrophenazine in varying amounts (Scheme 53). Several variants of this procedure exist o-benzoquinone has been used in condensation with 0-phenylenediamine and yields as high as 35% have been reported, and 1,2,3,4-tetrahydrophenazine has been prepared by condensation of o-phenylenediamine with cyclohexane- 1,2-dione. 

The earliest preparation of cellulose acetate is credited to Schiitzenberger in 1865. The method used was to heat the cotton with acetic anhydride in sealed tubes at 130-140°C. The severe reaction conditions led to a white amorphous polymer but the product would have been severely degraded and the process difficult to control. Subsequent studies made by Liebermann, Francimont, Miles, the Bayer Company and by other workers led to techniques for controlled acetylation under less severe conditions. 

Chlorophenylacetic acid has been prepared from mandeloni-trile and hydrochloric acid in a sealed tube, from mandelic acid and hydrochloric acid in a sealed tube/ from a-nitrostyrene and hydrochloric acid in a sealed tube, from phenylglycine, hydrochloric acid, and sodium nitrite, from mandelic acid and phosphorus pentachloride (to give the acid chloride which is then hydrolyzed), and, in poor yield, from mandelic acid and thionyl chloride. In the method described, ethyl mandelate is prepared according to Fischer and Speier. The conversion to the chloroester and the acid hydrolysis step are modifications of a preparation described by McKenzie and Barrow. ... 

The most general preparative route to phosphides (Faraday s method) is to heat the metal with the appropriate amount of red P at high temperature in an inert atmosphere or an evacuated sealed tube ... 

Unsubstituted quinazoline 3-oxide was prepared in an attempt to react quinazoline with hydroxylamine. This reaction gave a product of variable composition, but when an acetone solution was heated in a sealed tube it gave quinazoline 3-oxide. The oxide is more conveniently prepared, in excellent yield, from o-aminobenzaldehyde oxime and ethyl orthoformate. This method appears to be of general use and has been used for the preparation of 4-methylquinazoline... 

These quinazolines are obtained in high yields by heating o-acyl (and formyl) anilides in a sealed tube with saturated alcoholic ammonia for a few hours (see 4a). A variant of this method... 

Dehydrogenation is a rarely used method for the production of fully unsaturated azepines, and there are no examples of its use for the formation of simple monocyclic systems, although 3-hydroxy- and 3-methoxy-2//-azepin-2-ones can be obtained by dehydrogenation of the corresponding l,5-dihydro-2//-azepin-2-ones with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in benzene in a sealed tube at 100 48-51-52-67... 

The capillary tube method initially involves packing a powdered sample into a glass capillary tube of uniform diameter and length, carefully sealed at one end so that it forms a rounded tube of uniform thickness. The tube is then attached to a standardized thermometer so that the end of the tube reaches the middle of the thermometer reservoir bulb. This assembly is then inserted into a vessel contg a suitable liq which is uniformly heated so that the temp rises at a rate of about 1° per minute. Ref 1 discusses in detail equipment design and thermometer calibration. It should be noted that this technique is the method most widely used by organic chemists... 

Dinitrophenol sealed tube with coned HC1 at 170—80° for 5—6 hrs, or by other methods. Very sol in ale or eth, sol in chlf or benz, si sol in w or petr eth. Its expl props have not been examined... 

Nitric acid is also useful as an oxidant for the formation of sulphate from sulphones. Two such methods have been developed, firstly the established AOAC method which involves oxidation with a mixture of nitric acid and bromine221, and secondly the Carius method222. The latter is probably the oldest method used for the determination of sulphones as sulphate. This oxidation procedure involves heating the sulphone with concentrated nitric acid and sodium chloride at 280-300 °C in a sealed tube. The traditional method as described is prone to explosions. This problem may be alleviated by using less nitric acid whilst employing an oxygen atmosphere2 23,224. The Carius method is slower than the other oxidation methods described above but it usually yields the best results. 

---