54 SCIENCE PROGRESS 



above has been completely established by the brilliant synthe- 

 tical researches of W. H. Perkin, jun. 1 



Perkin's synthesis proceeds as follows : In the first place, 

 the esters of /3 iodopropionic and sodiocyanacetic acid are 

 caused to interact and the product is hydrolysed ; pentane-ave- 

 tricarboxylic ester is thus obtained, from which 8 ketohexhydro- 

 benzoic acid is formed by its treatment with acetic anhydride 

 and distillation, carbon dioxide and water being eliminated. 

 The ester of this acid, in contact with magnesium methyl iodide, 

 yields a product from which 8 hydroxy hexhydro-/-toluic acid is 

 obtained by hydrolysis. 



CH, C H, CH a CH, CH 2 



oc/ \:h . CO,H -> /\ ^> CH • C0 ^ H 



CHl CH, HO CU 2 CH, 



Hydrogen bromide converts this toluic acid into the corre- 

 sponding bromo-derivative, which when treated with weak 

 alkalis or pyridine loses hydrogen bromide and yields A ! tetra- 

 hydro-/>-toluic acid. 



CH CH, 



The ester of this unsaturated acid is converted by magnesium 

 methyl iodide in ethereal solution into inactive terpineol. 



CH..C 



This is Wagner's formula for terpineol and since dipentene 

 (limonene) is obtained from terpineol by a simple operation of 

 dehydration the position of the second A or ethylenic bond in 

 the hydrocarbon is determined. 



Optically active d and / terpineols were afterwards prepared 

 by Fisher and Perkin. 2 



It now becomes obvious that the formulae of some of the 

 other natural terpenes may be sought first of all among the 



1 Trans. Chem, Soc. [1904], 654. 



2 Ibid. [1908], 1 87 1. 



