BENZENE SERIES. AROMATIC COMPOUNDS. 569 



nucleus. This substance has basic properties due to the NH 2 groups, and 

 therefore unites with acids ; it also has acid properties due to the (OH) groups, 

 and forms salts with alkalies just as phenol does. 



Salvarsan is a lemon-yellow powder, which comes in sealed tubes. It is 

 soluble in water with a decided acid reaction, due to hydrolysis and liberation 

 of hydrochloric acid. The sodium salt gives an alkaline reaction in solution, 

 due to hydrolysis and liberation of sodium hydroxide. The free base is insolu- 

 ble in water and is precipitated by the cautious addition of alkali to the solu- 

 tion of the hydrochloride, or of acid to the solution of the sodium compound. 

 For injections, either a suspension of the free base or a solution of the mono- 

 or di-sodium salt is prepared from salvarsan. 



Hydroxyl derivatives of the benzene series. 



Phenols are hydroxyl derivatives of benzene. The name is a gen- 

 eral one for all such compounds. Phenols are allied to the tertiary 

 fatty alcohols, as they contain the characteristic grouping = C OH. 

 According to the number of hydrogen atoms replaced by hydroxyl, 

 we find mono-, di-, and tri-hydroxy phenols, corresponding to the 

 similarly constituted alcohols. Phenols differ from common alcohols 

 in not yielding aldehydes or acids by oxidation. 



Phenols are either liquid or solid, and often have a peculiar odor. Most of 

 them can be distilled without decomposition, and are readily soluble in alcohol 

 and ether ; some are readily soluble in water. Many are antiseptic, for example, 

 phenol, cresol, resorcin, thymol, etc. Many individual phenols are found in the 

 vegetable and animal kingdoms. Destructive distillation of complex carbon 

 compounds usually results in the formation of phenols among the products; 

 thus, wood-tar and coal-tar are rich in phenols. 



Phenols act like weak acids, forming salts with caustic alkalies, which are 

 soluble in water and far more stable than the alcoholates. But they do not 

 decompose carbonates. 



Phenols can be obtained readily by first preparing sulphonic acids, and fusing 

 the alkali salts of these with caustic soda or potash. The actions are shown in 

 the following equations, which relate to synthetic phenol : 



C 6 H 6 + H 2 S0 4 C 6 H 5 S0 3 H + H 2 0. 



Benzene 

 eulphonic acid. 



C 6 H 5 SO 3 Na + NaOH C 6 H 5 OH. + Na 2 SO 3 . 



Phenol. 



The phenol is liberated from its alkali salt by an acid, and is purified by 

 further appropriate treatment. 



Phenol, C 6 H 5 OH = 93.34 ( Carbolic acid, Phenyl hydroxide). Crude 

 carbolic acid is a liquid obtained during the distillation of coal-tar 

 between the temperatures of 170-190 C. (338-374 F.), and con- 

 taining chiefly phenol, besides cresol, C 7 H 7 OH, and other substances. 



