Phenols with ferric chloride

Some northern trees and phenolics reactions with ferric chloride. The phenolics stains are shown on cross sections of twigs in the middle two rows... 

Color Reactions.—Many of the derivatives of phenol are highly colored, especially the nitroso and nitro compounds. The formation of these compounds under qualitative conditions is often made use of in testing either for a phenol or for nitrous or nitric acid or a derivative. With ferric chloride, FeCls, phenols give characteristic colors, hlue greeny red or violet. Phenol ethers do not respond to these tests. 

Resorcinol crystallizes from water in colorless plates or prisms, which melt at 118°, and turn red in the air. It gives a deep violet coloration with a solution of ferric chloride. The phenol is not as strong a reducing agent as pyrocatechol. 

Colorations or coloured precipitates are frequently given by the reaction of ferric chloride solution with.(i) solutions of neutral salts of acids, (ii) phenols and many of their derivatives, (iii) a few amines. If a free acid is under investigation it must first be neutralised as follows Place about 01 g. of the acid in a boiling-tube and add a slight excess of ammonia solution, i,e., until the solution is just alkaline to litmus-paper. Add a piece of unglazed porcelain and boil until the odour of ammonia is completely removed, and then cool. To the solution so obtained add a few drops of the "neutralised ferric chloride solution. Perform this test with the following acids and note the result ... 

Dissolve a few crystals of phenol in water and add ferric chloride solution a violet coloration is produced. Repeat, using i 2 drops of m-cresol shaken up with about i ml. of water a violet coloration is again produced. Catechol (in dilute solution) gives a green coloration. 

Aqueous solutions (when obtainable) give no reaction with ferric chloride. This is an important distinction from ammonium salts (sec above). Salicylamide, being also a phenol, is however an exception (p. 344). 

A fairly general procedure consists in coupling a phenol or naphthol with a diazotised amine, reducing the product to an aminophenol or aminonaphthol, and oxidising the hydroxy compound with acid ferric chloride solution. This method is illustrated by the preparation of (3 (or 1 2)-naphthoquinone ... 

With more reactive substances, 2iac or ferric chlorides may be substituted as catalysts (138). More elevated temperatures and high pressure are, however, generally needed, and only very reactive substrates (such as phenols) react readily. 

Benzene Chlorination. In this process, benzene is chlorinated at 38—60°C in the presence of ferric chloride catalyst. The chlorobenzene is hydrolyzed with caustic soda at 400°C and 2.56 kPa (260 atm) to form sodium phenate. The impure sodium phenate reacts with hydrochloric acid to release the phenol from the sodium salt. The yield of phenol is about 82 mol % to that of the theoretical value based on benzene. Plants employing this technology have been shut down for environmental and economic reasons. 

Chondrofoline, CgjHgjOjNj, 2H2O, crystallises from methyl alcohol in triangular plates, m.p. about 135°, [ajffg — 280-6° (dry base N/10. HCl). It is a phenolic base, contains three methoxyl groups, does not give a Millon reaction, but in methyl alcoholic solution gives a faint, pink-purple colour with ferric chloride. The nitrate forms needles m.p. 225° (dec.). 

The hydroxy-l-thia-2,4-diazole 125 is reported to exhibit phenolic character and to give a red color with ferric chloride. Infra-rediooa.142,143 ultraviolet spectral evidence indicates that 1-thia-3,4-diazoles of type 126 exist predominantly in an oxo form,... 

Like most phenols, it gives an intense blue colour with solution of ferric chloride. By heating it with alcoholic potash and methyl iodide it is converted into methyl-chavicol or estragol, the characteristic constituent of tarragon oil. 

Constitution of the Esters of the (3-Ketocarboxylic Acids and of the P-Diketones.—Ethyl acetoacetate is taken as example. It reacts like a ketone with phenylhydrazine, bisulphite, and other ketone reagents on the other hand it shows an acid reaction, it dissolves in alkalis, and gives the colour reaction with ferric chloride characteristic of ends and also of phenols. From this double behaviour it was formerly concluded that it was either purely ketonic or purely enolic and that the reactions in the other form were to be attributed to a rearrangement caused by the reagents used. The true state of affairs was first disclosed by... 

Nor can there be any question of real tautomerism in the case of phenol. In its chemical properties phenol resembles the aliphatic enols in all respects. We need only recall the agreement in the acid character, the production of colour with ferric chloride, and the reactions with halogens, nitrous acid, and aromatic diazo-compounds (coupling), caused by the activity of the double bond and proceeding in the same way in phenols and aliphatic enols. The enol nature of phenol provides valuable support for the conception of the constitution of benzene as expressed in the Kekule-Thiele formula, since it is an expression of the tendency of the ring to maintain the aromatic state of lowest energy. In this connexion the hypothetical keto-form of phenol (A)—not yet obtained—would be of interest in comparison with... 

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