Organic compounds coloured

If triphenylmethyl chloride in ether is treated with sodium, a yellow colour is produced due to the presence of the anionic spiecies PhsC". Alternatively, if triphenylmethyl chloride is treated with silver perchlorate in a solvent such as THF, the triphenylmethyl cation is obtained. More conveniently, triphenylmethyl salts, PhsC X", can be obtained as orange-red crystalline solids from the action of the appropriate strong acid on triphenylcarbinol in ethanoic or propanoic anhydride solution. The perchlorate, fluoroborate and hexafluoro-phosphate salts are most commonly used for hydride ion abstraction from organic compounds (e.g. cycloheptatriene gives tropylium salts). The salts are rather easily hydrolysed to triphenylcarbinol. 

The bromine test is applied first. The organic compound, if a liquid, is treated with 2-3 drops of liquid bromine or (preferably) a solution of bromine in carbon tetrachloride if the organic compound is a solid, it should first be dissolved in cold carbon tetrachloride or chloroform. The rapid absorption of the bromine (and consequent disappearance of the red colour) is a strong indication that the compound is unsaturated, and is therefore undergoing direct addition of the bromine. 

J. Berry, "Control of Volatile Organic Compound (V OC) Emissions from Painting Operations ia the United States," Polymers Paint Colour J. 181(4281), (Apr. 17,1991). 

Sulphur.—The presence of sulphur in organic compounds may be detected by heating the substance with a little metallic sodium or potassium. The alkaline sulphide, when dissolved in water, gives a violet colouration with a solution of sodium nitro-prusside. Heat a fragment of gelatine with a small piece of potassium in a test-tube until the bottom of the tube is red hot, and place it m a small beaker of water as described in the test for nitrogen (p. 2). Filter the liquid and add a few drops of sodium nitroprusside solution. 

Colour in organic compounds is also due to resonance. This also explains why a system of open conjugate double bonds containing two or more double bonds imparts colour to it. 

The reaction with permanganate constitutes a valuable and much-used test for unsaturation in an organic compound. The substance is dissolved in cold alcohol, a few drops of sodium carbonate solution are added, and then a drop.of dilute permanganate solution. Rapid disappearance of the red colour indicates the presence of a double bond. The Baeyer test can also be carried out in pure glacial acetic acid, which is stable towards permanganate. Another method of detecting double bonds is by the decolorisation of bromine. As a rule, chloroform is used as solvent. 

Theory Selenium is very toxic and its contamination is usually controlled by an absorptiometric method after destruction of the organic compound with fuming nitric acid. The latter converts selenium (Se) as selenous acid (H2Se03), which on subsequent treatment with 3,3 -diaminobenzidinc under controlled experimental parameters, results into the formation of a highly coloured compound known as 3,4-diaminophenylpiazselenol. The latter is consequently extracted with toluene after making the aqueous solution alkaline, and the colour compared with a standard prepared likewise from a known amount of selenium. The various reactions involved may be expressed as follows ... 

Metallic salts (or metallic compounds) after dissolution in appropriate solvents when introduced into a flame (for instance acetylene burning in oxygen at 3200°C), turns into its vapours that essentially contain mostly the atoms of the metal. Quite a few such gaseous metal atoms are usually raised to a particular high energy level that enables them to allow the emission of radiation characteristics features of the metal for example-the characteristic flame colourations of metals frequently encountered in simple organic compounds such as Na-yellow, Ca-brick-red Ba-apple-green. This forms the fundamental basis of initially called Flame Photometry, but more recently known as Flame Emission Spectroscopy (FES). 

The classical techniques for the solvent extraction of chemical compounds from vegetable material are based upon the correct choice of solvent and conditions e. g. heating or agitation. A range of commercially important pharmaceuticals, flavours and colourants are now derived from vegetable sources. It has been shown that the solvent extraction of organic compounds contained within the body of plants and seeds is significantly improved by the use of power ultrasound [25]. 

The photographs show the structures of coloured organic compounds. 

The prospective applications ofmolecular assemblies seem so wide that their limits are difficult to set. The sizes of electronic devices in the computer industry are close to their lower limits. One simply cannot fit many more electronic elements into a cell since the walls between the elements in the cell would become too thin to insulate them effectively. Thus further miniaturization of today s devices will soon be virtually impossible. Therefore, another approach from bottom up was proposed. It consists in the creation of electronic devices of the size of a single molecule or of a well-defined molecular aggregate. This is an enormous technological task and only the first steps in this direction have been taken. In the future, organic compounds and supramolecular complexes will serve as conductors, as well as semi- and superconductors, since they can be easily obtained with sufficient, controllable purity and their properties can be fine tuned by minor adjustments of their structures. For instance, the charge-transfer complex of tetrathiafulvalene 21 with tetramethylquinodimethane 22 exhibits room- temperature conductivity [30] close to that of metals. Therefore it could be called an organic metal. Several systems which could serve as molecular devices have been proposed. One example of such a system which can also act as a sensor consists of a basic solution of phenolophthalein dye 10b with P-cyciodextrin 11. The purple solution of the dye not only loses its colour upon the complexation but the colour comes back when the solution is heated [31]. 

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