AROMATIC COMPOUNDS 245 



These salts are stable to water, but are decomposed by carbon dioxide. 

 It has acid properties and hence is usually termed carbolic acid. 



As an alcohol it will form esters, but owing to its acid character 

 the esters are not easily formed by the direct action of the acid. They 

 are prepared by the action of the acid chloride, or anhydride, upon the 

 phenol or its potassium salt : 



OO.OC.CH. + HC1. 



Phenyl sulphuric acid is present in mammalian urine. 

 Phenol also forms ethers ; these are prepared by the action of an 

 alkyl iodide upon potassium phenate : 



OOK /\OCH 3 



-f CH 3 I =11 + KI. 



These ethers resemble the aliphatic ethers, but also show the 

 typical aromatic reactions with nitric acid, etc. 

 Reactions and Tests. 



(1) A violet coloration is formed on adding a few drops of ferric 

 chloride solution to a solution of phenol in water. 



(2) Phenol is readily brominated. On adding bromine water 

 gradually to some phenol solution, there is first a cloudiness due to 

 mono- and dibromophenol which are characterised by a very penetrating 

 smell. The further addition of bromine water produces a precipitate 

 of tribromophenol in yellowish-white needles or flakes. Tribromo- 

 phenol is formed directly with very dilute solutions of phenol. 



(3) Phenol is also readily nitrated. On adding concentrated nitric 

 acid to a solution of phenol and warming, a yellow colour is produced. 

 On cooling and making alkaline with ammonia, the colour becomes 

 orange. Picric acid is formed : 



C 6 H 5 OH + 3HN0 3 = C 6 H 2 (N0 2 ) 3 OH + 3 H 2 O. 



(4) A deep red coloration is produced on adding Millon's reagent 

 to a solution of phenol and warming. 



Detection of Phenol in Urine (Roaf). 



I c.c. of concentrated hydrochloric acid is added to 10 c.c. of horse's 

 urine and the mixture is boiled for two minutes. The phenyl-sulphuric 

 acid is hydrolysed. The solution is cooled and extracted with ether. 

 The ethereal layer is separated and the ether evaporated. The residue 

 dissolved in water will give the reaction with Millon's reagent. 



It is better to distil the urine with dilute sulphuric acid sufficient 

 concentrated acid being added to make the mixture contain 5 per cent. 

 and collect about a quarter of the volume. The phenol can be 

 tested for in the distillate. 



