XYLENES. 283 



alcohol, less in cold. Combines directly with bromine, 

 forming a crystalline substance, stilbene bromide, 

 C 14 H 12 Br 2 , which is also produced when bromine is al- 

 lowed to act on dibenzyl, no care being taken to keep 

 the substances cool; treated with alcoholic potassa, it 

 yields monobromstilbene, C 14 H u Br (colorless crystals, 

 fusing point 25), and tolan. When treated with 

 hydriodic acid, stilbene is converted into dibenzyl. 



Tolan, C 14 H 10 . Is produced by heating stilbene 

 bromide with alcoholic potassa. Large, transparent, 

 colorless crystals. Yery easily soluble in ether and hot 

 alcohol ; melts at 60. Combines with bromine, form- 

 ing a crystalline substance, tolan dibromide C^H^Br 2 . 

 The tetraehloride, C 14 H 10 C1 4 , is produced by heating 

 chlorobenzyl with phosphorus pentachloride. Sodium- 

 amalgam reduces it to tolan. 



3. Hydrocarbons, C 8 H 10 . 



a. Dimethylbenzenes (Xylenes, Xylols). 

 C 6 H 4 (CH 3 ) 2 . 



The three modifications, the possibility of the exist- 

 ence of which is indicated by the theory, are all 

 known. That portion of light oil that boils between 

 136-139 consists essentially of a mixture of rneta- 

 and paraxylene, which cannot be separated from each 

 other. Metaxylene forms the largest portion of this 

 mixture. 



1. Orthoxylene. Is obtained by distilling a mix- 

 ture of paraxylylic acid with lime. Colorless liquid, 

 boiling at 140-141. Oxidized with nitric acid, it 

 yields orthotoluic acid. Chromic acid burns it up 

 completely. 



2. Metaxylene (Isoxylene). Is obtained in a pure 

 state by distilling a mixture of xylylic acid, or mesi- 

 tylic acid with lime. Liquid boiling at 137. Dilute 



