THE CHEMICAL HISTORY OF THE TERPENES 49 



Victor Meyer and Janny, it was shown by Goldschmidt and 

 Ziirrer 1 that the nitroso-hesperidene obtained by Tilden and 

 Shenstone from the nitrosochloride of the terpene contained in 

 orange oil was identical with carvoxime, C 10 H H : N . OH. Diffi- 

 culties, however, still remained, as the nitrosopinene obtained 

 by a similar process from turpentine oil could not be similarly 

 identified. Fortunately about this time Baeyer had begun those 

 researches into questions connected with the constitution of 

 benzene which were destined later to shed much light on these 

 obscure problems. The products of the reduction of terephthalic 

 acids were shown to have properties very different from those 

 of ordinary benzene derivatives and to approximate closely to 

 those of fatty compounds. The di- and tetra-hydro derivatives 

 combine directly not only with bromine but with hydrogen 

 bromide, while the hexhydro derivatives are saturated. The 

 difficulties involved in the acceptance of Oppenheim's formula 

 for the terpenes were thus partly dispelled, as it appeared that 

 the addition of two atoms of hydrogen to cymene was capable 

 of modifying profoundly its chemical behaviour. Nevertheless 

 the formula, while suggesting the para constitution since found 

 to be so prevalent among the terpenes and the compounds 

 naturally associated with them, was manifestly not equally 

 applicable to both the principal classes of terpenes then known 

 possessing different physical and chemical properties. 



In 1889 a further important step forward became possible as 

 a consequence of the discovery by G. Wagner 2 that the first 

 product in the oxidation of many and perhaps all unsaturated 

 compounds by means of neutral or alkaline permanganate is a 

 hydroxy compound, which is formed by the addition of hydroxylic 

 groups at the double bond, where rupture occurs on further 

 oxidation. Thus the defines yield the corresponding glycols, 

 and alcohols of the allyl series yield glycerols under the action 

 of this agent, and the number of double linkages in a molecule 

 could, in fact, be determined by studying the products of oxida- 

 tion under the prescribed conditions. It was found, for example, 

 that camphene yields a glycol C 10 H 16 (OH) 2 and limonene a 

 tetrahydric alcohol C 10 H 18 (OH) 4 . The oxidation of pinene by 

 acid agents is misleading owing to the isomeric change which is 

 brought about by contact with aqueous acids, so that dipentene 

 derivatives alone are formed. Wagner at this time suggested for 

 1 Berichte, 18, 2220. 2 Ibid. 21, 1230 ; 21, 3347 ; 23, 2307. 



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