Phenols ferric chloride

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 ... 

Uffelmann s reagent (gives a yellow coloration in the presence of lactic acid) add a ferric chloride solution to a 2% phenol solution until the solution becomes violet in color. 

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.). 

Reactions.—I. Make a solution of phenol in water, and to one portion add a drop of ferric chloride. A violet colouration is produced. 

Fe7-ric chloride reaclion.—Dissolve a drop of the free phenol in water and add a drop of ueutral ferric chloride. A green (catechol), blue (orcinol, pyiogallol) or purple (phenol, resorcinol) colouration is produced, which is often destroyed by acid or alkali. Quinol is o.xidised to quinone, and turns biown (p. 193). The naphthols give precipitates of dinaphthol (p. 220). 

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. 

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