264 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



CH 3 

 Cresols, C 6 H 4 <; 



X OH. 



The three cresols are contained in the acid fraction of coal tar with 

 phenol. Their separation is difficult to effect and they are prepared 

 from the toluidines, or toluene sulphonic acids, by the methods given 

 under aniline and diazonium salts and phenol. 



p-Cresol occurs in urine in combination with sulphuric acid and is 

 isolated together with phenol by the methods given on p. 245. It is 

 also a product of the putrefaction of proteins and arises from the 

 amino acid, tyrosine. The cresols are crystalline solids; o-cresol 

 melts at 31, m-cresol at 5, p-cresol at 36. They resemble 

 phenol very closely in properties. 



As phenols they react 



(1) with ferric chloride ; 



(2) with bromine water; 



(3) with nitric acid ; 



(4) with Mil Ion's reagent 



/CH, 

 Toluic Acids, C 6 H / 



X COOH. 



These three acids result by oxidising the xylenes with dilute nitric acid. 

 The o- and p-acids are most readily prepared from the toluidines by Sand- 

 meyer's reaction with cuprous cyanide (p. 250). 



They are solids resembling benzoic acid. 



NH 2 



Anthranilic Acids, C 6 H C 



X COOH. 



The o-acid was first obtained by oxidising indigo and is a colourless 

 crystalline solid melting at 144; it loses carbon dioxide on heating and 

 yields aniline. 



X3 

 Sulpho- Benzoic Acids, C 6 H 4 <^ 



X COOH. 



The o-acid is of interest as saccharin is prepared from it. o-Sulpho- 

 benzoic acid is prepared by oxidising o-toluene-sulphonic acid. The am- 

 monium salt on heating loses ammonia and gives the imide, saccharin : 



/CH 8 /COOK /COONH 4 /CO \ 



C.H/ -*C 6 H 4 / ->C b H 4 / ->C,H 4 < \NH 



X SO,H \SO,H X SO 3 NH 4 \SO/ 



Saccharin. 



/ C0 \ 

 ->C 6 H,( >N.Na 



\gQ / 



Sodium Salt. 



Sacchariri is a white crystalline solid melting at 224 and it is only slightly 

 soluble in water. It forms a sodium salt, which dissolves easily in cold 

 water. The sodium salt, containing 2H 2 O and crystallising in large plates, 

 is generally used as sweetening agent. The sweetness of saccharin is about 

 500 times greater than that of cane sugar. 



