132 



REPORT^ — 1902. 



And when these di- or tetra-hydro-compounds are oxidised with potassium' 

 permanganate, the ring is broken at the double bonds, just as in the- 

 case of unsaturated fatty compounds. 



A further analogy is to be found in the gradual reduction by nascent- 

 hydrogen of A, . 3-dihydroterephthalic acid and muconic acid. 



of 

 Thiele's theory of partial saturation. ^ Baeyer states * that all A ,. 3 or 

 A, . 5 dihydro-acids — that is, those containing two double bonds in the above 

 positions — form only dibromides, whereas other dihydro-acids form tetra- 

 bromides, and a similar case has been noticed in dimethyl- Aj . 4-dihydro- 

 benzene,^ for only two atoms of bromine or one molecule of hydrogen 

 bromide can be directly added to this substance, the addition taking 

 place, as in the case of hydrogen, to A, .3-dihydroterephthalic acid, witk 

 rearrangement of the bonds, 



CH = CH 



/ \ 



(CHsX.C CH 



\ // 



CH„ - CH 



besoming 



/ 



CH.. 



(CH3),C 



\ 



CH, 



, CH 



CH 



/ 



CHBr 



Various hexahydro-dicarboxylic acids have also been synthetically 

 prepared ; for example, when methylpentamethylene dibromide is con- 

 densed with ethyl sodiomalonate there results the ethyl salt of l-methyl- 

 hexahydrobenzent-l : \-dicarboxylic acid,* 



CH, . CH • CHjj 



/ \ 



CH. C (COOH), 



\" / 



CH„ . CH„ 



• Annalen, 1899, 306, 87. 



' Crossley and Le Sueur, J.C.S., 1902, 81, 823. 



• Perkin and Freer, J.C.S., 1888, 53, 202. 



Ibid., 1890, 258, 2. 



