Diphenylamine reaction colors produced

The perchlorates of various secondary amines, such as diphenylamine and indole derivatives, are colorless.64 The similarity of colors produced in the presence of hydrochloric acid also attests to the non-auxochromic character of the perchlorate ion in the production of the colored derivative. Consequently, the only role attributable to the perchloric acid in this test is that with nucleic acids it leads to more effective hydrolysis and releases more 2-desoxyribose for reaction with tryptophan. This reaction leads to the production of a substance of the type represented by XV and XVI (R " = H), and the increase in the number of conjugated double bonds results in the product being colored. With ribose, which has a free hydroxyl group at carbon atom 2, a ketone of the type shown in XVII can be formed, and in this case the net result is no increase in the number of double bonds conjugated with the indole nucleus and no comparable increase in color. Hence the test will distinguish between ribose and 2-desoxyribose. 

The oxidizing agents used include gold chloride (potentiometric determination of the end point of the extremely slow oxidation) (Karrerefal, 1938) ceric sulfate (determination of the end point of the almost immediate reaction, with diphenylamine as indicator) (Kofler, 1941) lead tetraacetate (Kofler, 1941) but mostly ferric chloride in presence of a Fe -complex-forming compound, such as a,a -dipyridyl (Emmerie and Engel, 1938). The red color produced in this reaction is used for colorimetric determination. 

Such materials may interfere with the determination of hexosamines (see Chapter VIII). With the colors produced by sialic acid as a reference, Werner and Odin 100) have estimated the amounts of sialic acid in several glycoproteins, including serum glycoprotein and ovomucin. They used Bial s orcinol, the direct Ehrlich reaction, diphenylamine, and tryptophan-perchloric acid. 

The total content of RNA + DNA in tissues may be estimated from the phosphorus content or by color reactions of the sugars.37 545 These reactions depend upon dehydration to furfural or deoxyfurfural by concentrated sulfuric acid or HC1 (Eq. 4-4). Furfural formed from RNA reacts with orcinol (3,5-dihydroxy-toluene) and ferric chloride to produce a green color useful in colorimetric estimation of RNA. A similar reaction of DNA with diphenylamine yields a blue color. 

The use of certain vanadium compounds as catalysts has been increasing. Vanadium oxy trichloride is a catalyst in making ediylene-propylene rubber. Ammonium metavanadate and vanadium pentoxide aie used as oxidation catalysts, particularly in the production of polyamides, such as nylon, in the manufacture of H>S04 by the contact process, in the production of phdialic and maleic anhydrides, and in numerous other oxidation reactions, such as alcohol to acetaldehyde, anthracene to anthraquinone, sugar to oxalic acid, and diphenylamine to carbazole. Vanadium compounds have been used for many years 111 die ceramics field for enamels and glazes. Colors are produced by various combinations of vanadium oxide and silica, zirconia, zinc, lead, tin, selenium, and cadmium. Vanadium intermediate compounds also are used in the making of aniline Mack used by the dye industry... 

The test is conducted by applying melted paraffin wax to the back of a suspect s hands. With a brush, the back of the hand is coated with paraffin wax which on cooling solidifies and can be peeled off the hand. The surface of the cast that has been in contact with the skin is treated with diphenylamine/sulfuric acid reagent by dropwise addition or spraying. The reagent produces a blue color with individual particles of nitrates and nitrites. The reaction sequence is as shown in Figure 16.1.117The detection of dark blue spots was considered as indicative of the presence of nitrates and/or nitrates from FDR. 

Historically, the first color-forming reaction to be discovered which involves electron transfer is probably the photoinitiated reaction of diphenylamine with carbon tetrabromide, which forms blue colors [42]. In fact, the major path for color formation is due to radical reactions, initiated by photolysis of C—Br bonds to produce Br3C and bromine atoms. An alternative mechanistic path, possible when the light is absorbed by the diphenylamine, would involve electron transfer. MacLachlan has shown that such processes do occur durin> photolysis of aminotriarylmethanes in the presence of electron acceptors such as CBr4 and CC14 [43]. Other electron deficient species (quinones, nitroaromatics) were also demonstrated to be effective. 

Figure 10.8 The reaction with diphenylamine and nitrate to produce a blue color. 

Chlorine dioxide is produced if chlorates are warmed with concentrated sulfuric acid. Like free chlorine, this product converts diphenylamine (dissolved along with trichloroacetic acid in ethyl acetate) into a blue-green oxidation product (compare page 359). This color reaction is not shown by bromates and iodates because they are weaker oxidants than chlorates. 

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