Charring

Fig. XVII-29. Nitrogen isotherms the volume adsorbed is plotted on an arbitrary scale. The upper scale shows pore radii corresponding to various relative pressures. Samples A, Oulton catalyst B, bone char number 452 C, activated charcoal F, Alumina catalyst F12 G, porous glass S, silica aerogel. (From Ref. 196).

For this preparation, it is particularly necessary that the sodium acetate should be free from traces of water. The anhydrous material can be prepared by gently heating the hydrated salt (CHsCOONa,3HjO) in an esaporating-basin over a small Bunsen flame. The salt dissolves in its water of ciystallisation and resolidifies as this water is driven off further heating then causes the anhydrous material to melt. Stir the molten anhydrous material to avoid charring, and then allow it to cool in a desiccator. Powder the cold material rapidly in a mortar, and bottle without delay. 

Cane sugar.—Melts, darkens, then chars, and finally burns, with a marked odour of burnt sugar. Typical of the changes given by mono- and di-saccharides. 

Tartaric acid and tartrates also swell up, blacken and give an odour resembling burnt sugar. Citrates and lactates also char, and give off odours resembling burnt sugar. 

A large variety of organic compounds char without melting, e.g., starch, oxamide, sulphonic acids, uric acid, etc. 

Sulphuric add test. Warm 0 5 g. of tartaric acid or a tartrate with i ml. of cone. H2SO4. Heavy charring takes place, CO and SOj being evolved. 

Sulphuric add test. Heat 0 5 g. of citric acid or a citrate with 1 ml. of H2SO4 CO and COg are evolved and the mixture turns yellow, but does not char. Acetone dicarboxylic acid, OC(CH2COOH)g, is also formed, and is tested for after heating the mixture for 1 minute cool, add a few ml. of water and make alkaline with NaOH solution. Add a few ml. of a freshly prepared solution of sodium nitroprusside and note the intense red coloration (see Test 4 a) for ketones, p. 346). 

Action of heat. Heat about 0 2 g. of uric acid in a hard-glass test-tube. Note the charring and also the formation of a white sublimate on the cooler parts of the tube. 

After some experience, an able student will find that it is frequently unnecessary to carry out all the Tests A—L. If, for example, the substance is found to contain only carbon and hydrogen, and chars on ignition giving a smell of burnt sugar, then confirmatory tests (given in... 

Cone. H,SO, CO — co+co. darkens on strong heating black- ens. effer- vescence chars, effer- vescence yellow. effer- vescence — darkens slightly — —... 

Evidence of the organic nature of the substance may, be provided by the behaviour of the compound when heated on porcelain or platinum or other comparatively inert metal (e.g., nickel) the substance is inflammable, burns with a more or less smoky flame, chars and leaves a black residue consisting largely of carbon (compare Ignition Test above). 

Group V. This group includes all the water-insoluble hydrocarbons and oxygen compounds that do not contain N or S and are soluble in cold concentrated sulphuric acid. Any changes—colour, excessive charring, evolution of gases or heat, polymerisation and precipitation of an insoluble compound— attending the dissolution of the substance should be carefully noted. 

Solubility in concentrated sulphuric acid. Place 3 0 ml. of pure concentrated sulphuric acid in a dry test-tube and add 0 -10 g. of a solid or 0 -20 ml. of a liquid. If the compound does not dissolve immediately, agitate for some time but do not heat. Observe any change in colour, charring, evolution of gaseous products, polymerisation accompanied by precipitation etc. 

Fuming sulphuric acid test. Place 2 ml. of 20 per cent, fuming sulphuric acid in a dry test-tube, add 0 -5 ml. of the hydrocarbon and shake vigorously. Only the aromatic hydrocarbon dissolves completely heat is evolved, but excessive charring should be absent. 

The residue (5) in the distilhng flask may stUl contain a water-soluble, non-volatile acid. Cool the acid solution, neutralise it with dilute sodium hydroxide solution to Congo red, and evaporate to dryness on a water bath under reduced pressure (water pump). Heat a httle of the residual salt (G) upon the tip of a nickel spatula in a Bunsen flame and observe whether any charring takes place. If charring occurs, thus... 

Step 3. The non-steam-volatile compounds. The alkaline solution (82) remaining in the distiUing flask from Step 2 may contain water-soluble, non-volatile acidic, basic or neutral compounds. Add dilute sulphuric acid until the solution is just acid to Congo red, evaporate to dryness, and extract the residual solid with boiling absolute ethyl alcohol extraction is complete when the undissolved salt exhibits no sign of charring when heated on a metal spatula in the Bunsen flame. Evaporate the alcoholic solution to dryness and identify the residue. 

Polonium is readily dissolved in dilute acids, but is only slightly soluble in alkali. Polonium slats of organic acids char rapidly halide amines are reduced to the metal. 

Speculation about the stability of Ceo centered on the extent to which the aromaticity associated with its 20 benzene rings is degraded by their non planarity and the accompanying angle strain It is now clear that Ceo is a relatively reactive substance reacting with many substances toward which ben zene itself is inert Many of these reactions are char acterized by addition to buckminsterfullerene converting sp hybridized carbons to sp hybridized ones and reducing the overall strain... 

FIGURE 13 15 The 200 MHz H NMR spectrum of ethyl bromide (BrCH2CH3) showing the char acteristic triplet-quartet pattern of an ethyl group The small peak at 8 1 6 is an impurity... 

The NMR spectrum of isopropyl chloride (Figure 13 17) illustrates the appearance of an isopropyl group The signal for the six equivalent methyl protons at 8 1 5 is split into a doublet by the proton of the H—C—Cl unit In turn the H—C—Cl proton signal at 8 4 2 IS split into a septet by the six methyl protons A doublet-septet pattern is char acteristic of an isopropyl group... 

Notice that (Z) 5 tetradecen 4 olide IS a cyclic ester Recall from Section 19 15 that cyclic esters are called lactones and that the suffix olide is char acteristic of lUPAC names for lactones... 

Elimination unimolecular (El) mechanism (Section 5 17) Mechanism for elimination characterized by the slow for mation of a carbocation intermediate followed by rapid loss of a proton from the carbocation to form the alkene Enamine (Section 17 11) Product of the reaction of a second ary amine and an aldehyde or a ketone Enamines are char actenzed by the general structure... 

In the first place, the calculated values of specific surface are often improbably high. A particular Saran char, for example, had a calculated area of 3000m g". This figure is actually slightly greater than the area... 

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