BENZENE SERIES. AROMATIC COMPOUNDS. 583 



Hydroxy-acids of the benzene series. 



These derivatives, which are known also as phenol-acids, contain 

 the (OH) and (COOH) groups in the benzene nucleus, and accord- 

 ingly possess the properties of phenols and acids. The hydrogen of 

 the (OH) group as well as that of the (COOH) group can be replaced 

 by a metal or hydrocarbon radical. The radical introduced into the 

 (COOH) group is easily removed by saponification, as in the case of 

 any ethereal salt, whereas that introduced into the (OH) group is not. 



The simplest hydroxy-acids are those containing one (OH) group 

 and one (COOH) group. There are three such acids, namely, ortho-, 

 meta-, and para-hydroxy-benzoic acid. Of these, the ortho acid, 

 known better as salicylic acid, is the most important. 



Salicylic acid, Acidum salicylicum, HC 7 H 5 O 3 or C 6 H 4 OH.CO 2 H 

 = 137. Derived from benzene by introducing one hydroxyl and 

 one carboxyl radical. It is found in several species of violet, and in 

 the form of methyl salicylate in the wintergreen oil (oil of Gaul- 

 theria procumbens). May be obtained by fusing potassium hydroxide 

 with salicin. 



Nearly all salicylic acid used medicinally or otherwise is obtained by syn- 

 thesis. The first step is the conversion of phenol into sodium pheiiolate by 

 treatment with sodium hydroxide, thus : 



C 6 H 5 OH + NaOH = C 6 H 5 ONa + H 2 O. 



Sodium phenolate is next dried and treated with carbon dioxide, when direct 

 combination takes place and sodium phenol carbonate is formed, thus : 



C 6 H 5 ONa + C0 2 -a NaC 6 H 5 C0 3 . 



Sodium Sodium phenol 



phenolate. carbonate. 



Sodium phenol carbonate is isomeric with sodium salicylate and is actually 

 converted into the latter compound by being heated to 130 C. (266 F.), in 

 tightly closed vessels, or in vessels through which carbon dioxide passes. 



Salicylic acid is a white, solid, odorless substance, having a sweet- 

 ish, slightly acrid taste, and an acid reaction ; it is soluble in 308 parts 

 of water and in 2 parts of alcohol ; it fuses at about 157 C. (315 F.), 

 and sublimes slowly at 100 C. (212 F.) and rapidly at 140 C. 

 (281 F.). It is a valuable antiseptic. 



By the action of the alkali hydroxides on salicylic acid, the various 

 salts may be obtained, as, for instance, sodium salicylate, NaC 7 H 5 O 3 , 

 ammonium salicylate, NH 4 C 7 H 5 O 3 > and lithium salicylate, LiC 7 H 5 O 3 > 



