ON THE PRESENT POSITION OF THE CHEMISTRY OF RUBBER. 243 



HBr, however, is /3 dimethyl trimethylene bromide ; specific gravity, 

 1-696 at 0° 



which was shown to be identical with the bromide obtained from 

 ft dimethyl allene (Gadziatzky). Assumiog that isoprene possrsses an 

 open chain, these results are best explained by supposing that isoprene 

 has the formula proposed by Tilden, and which Ipatieff called methyl 

 divinyl. 



Ch!^^ - CH = CHj + 2HBr = ^h /'^E'" • ^^2 • CH.Br. 



/3 methyl crotonylene (Tilden), 



or isopropenyl ethylene (Gadziatzky), 



or as-merhyl divinyl (Ipatieff). 



The preparation from /3 dimethyl allene is expressed — 



^^sXc = = CH. + 2HBr = ^g'^CBr . CH^ . CH^Br. 



The question of the constitution and formula of isoprene was, how- 

 ever, settled beyond doubt by the synthesis, in 1897, of ft methyl 

 crotonylene by Euler \ who found it to be identical in properties with 

 isoprene. Euler started with ft methyl pyrollidine, 



Cxig . CH — OH.^v 



I >NH, 



CHj-CH/ 



which, on treatment with methyl iodide and potassium hyrdoxide, was 

 converted into/3 methyl-dimethyl-pyrollidyl-ammonium-iodide : — 



CHg . CH CHgV /CHg 



I '>N^CH3 



ch,-ch/ m 



On distillation with solid potash this is converted into one of two 

 bases, both yielding the same end results : — 



(1) CHg.CH-CHj-N/p^' 



CH = CH, 

 or (2) CH3.C = CH, 



CH,-CH,.N<;^CH3 



On again treating with methyl iodide these bodies yield respectively 

 the compounds : — 



^CH, 



(1) CHj . OH-CHj-N r pS' 



I \i ^ 



CH = CH2 



or (2) CH3 . C = CH„ pry 



I /'PH 



CH, . CH3 . N C ch' 



\I ' 



Ber., 30 (1897), pp. 1989-91. 



u 2 



