THE STUDY OP HYDRO-AROMATIC SUBSTANCES. 83 



dioxide with formation of 3-ethoxy-l : 1-dimethyl- A 3 -cyclohexeny- 

 lidene-5-acetonitrile (VII). 



(CH 3 ),.C/^^ C ^ H ^CII (CH 3 ).,CX CH ^ I C ^ II ^CH 



~~~~ ' II "" II " 



CN.C.COOH CN.CH 



(VI) (VII) 



Although somewhat stable towards alkali this nitrile is readily hydro- 

 lysed by acids with formation of 1:1: 5-trimethyl- A 4 -cyclohexen-3- 

 one (II). When chlorodimethylcyclohexenone is condensed (a) with 

 the sodium derivative of ethyl methylcyanoacetate, the product is 

 hydroxydimethylcyclohexenylidenepropionitrile 



(CH 3 ) 2 C< C gg^° H >CH 



II 

 CH 3 .C.CN 



the carbethoxy group being eliminated as ethyl carbonate ; (b) with 

 ethyl sodioacetoacetate, the product is the same as with ethyl 

 malonate, namely, ethyl dimethylcyclohexenoneacetate, ethyl acetate 

 appearing as a by-product. The elimination in these reactions of ethyl 

 carbonate and ethyl acetate respectively is probably governed by 

 spatial considerations. 



3: 5-Dichloro-o-xylcnc and 3: 5-dichlorophthalic acid. 1 — The 

 main product arising from the action of phosphorus pentachloride on 

 dimethyldihydroresorcin (I) is 3 : 5-dichloro-l : 1-dimethylcyelohexa- 

 diene (II), but a by-product is also formed which was thought to be 

 3 : 5-dichloro-o-xylene (III). 



(CH 3 ) 2 < CH2 2 C(OH) >CH (CH 3 >,< CH ~ CC1 >CH 



(i) (i') 



(CH 3 ).,^ CH ^ CC) ^>CH 

 (III) 



This structure was assigned to the latter substance because there did 

 not appear to be any reason to presume that, in the conversion of the 

 hydroaromatic into the aromatic dichloro-derivative, the chlorine atoms 

 would alter their positions. During the reaction, however, a methyl 

 group must have wandered, and this was shown to have migrated to 

 the ortho-position, because on oxidation an acid (3 : 5-dichlorophthalic 

 acid) was obtained which readily gave an anhydride, and also the 

 fluorescein reaction. 



In a recent number of the ' Berichte ' - Villiger described the 

 preparation of three of the four possible dichloro-o-phthalic acida 

 (CI: CI, 3 : 6, 3 : 4, 4 : 5) by the direct chlorination of phthalic anhy- 

 dride. Villiger points out (ibid., p. 3532) that a fourth isomeride was 



1 Crossley and Wren, J.C.S., 1910, 97, 9S. 2 Ben> 2909, 42, 3529 



g2 



