— 167 — 



respectively, which can be separated by petroleum ether. Up to the 

 present it has not yet been possible to effect a reduction of the hydroxy 

 acid into hexahydro-m-toluylic acid by heating with red phosphorus 

 and hydr iodic acid. 



With regard to p-nitrobenzyl mercaptan as a reagent on ketones, 

 see under Aldehydes, p. 151. 



Phenols and Phenol Ethers. 



Whilst up to the present diphenyl urea chloride could only be 

 employed in a few cases for the determination of the alcoholic 

 hydroxyl group, J. Herzog 1 ) recommends this reagent as specially 

 adapted for detecting phenols, as it readily forms well- crystallising 

 compounds with the latter. Tertiary alcohols do not as a rule react 

 with diphenyl urea chloride, whose behaviour therefore shows a 

 characteristic difference with the hydroxyl groups of the alcohols, and 

 the phenols. Of all the phenols and derivatives of phenols which 

 Herzog employed for the formation of urethanes, only the phenol 

 carboxylic acids do not react easily with diphenyl urea chloride, as 

 the free carboxyl group impedes the reaction. Salicylic acid, for 

 example, does not yield a urethane, but salol does. For the production 

 of the phenol urethanes Herzog gives the following directions: The 

 phenol, with four times the quantity pyridine and the molecular weight 

 of diphenyl urea chloride, is heated a in flask privided with a reflux 

 tube for an hour in boiling water; the solution is then whilst stirring 

 poured in water, when a reddish, more or less greasy crystalline paste 

 separates off, which is recrystallised from ligroin or alcohol. 



The reaction occurs probably in the following manner: the diphenyl 

 urea chloride forms first of all with the pyridine, diphenyl urea pyridine 

 chloride, which is then split up in the presence of phenols into pyridine 

 hydrochloride and phenol urethane. 



/ C1 



C 5 H 5 N<( /C 6 H 5 /CI /C 6 H 5 



X CO«N< +R.OH = C r H 5 N( +RO.CO.N( 



X C 6 H 5 \ H \C 6 H 5 



Herzog gives the following reasons for this supposition: in dissolv- 

 ing diphenyl urea chloride in pyridine, he obtained, with a vivid red 

 coloration, diphenyl urea pyridine chloride, which on recrystallisation 

 from an anhydrous mixture of alcohol and ether can be obtained in 

 colourless needles which soon acquire a red colour when exposed to 

 the light. These needles become soft at 105 , and melt at no° 

 with evolution of gas. As this product gives with phenols the corre- 



Berl. Berichte 40 (1907), 1831. 



