Notes on scientific research. 101 



subsequent saponification of the unsaturated dicarboxylic acid they further prepared 

 the a-methyl-/?'-isopropylpimelic acid (XI), an amorphous, viscous mass and from this, 

 by distillation of its lead salt or by condensation of the ester with sodium, tetra- 

 hydrocarvone (m. p. 90° [11 mm.]) as only product. It would therefore appear, in 

 confirmation of Wallach's 1 ) researches, that the derivatives of pinene and pinonic 

 acid, having a double bond semicyclically attached to the four-member-ring, are 

 scarcely stable, and that they become stabilised by an intramolecular rearrangement 

 or ring-scission. 



(3) From the chloroacetic ester and the ester of pinonic acid the glycide ester of 

 the formula (XII) was prepared in the presence of sodamide. The authors will later 

 report on the further researches. 



According to J. Schindelmeiser 2 ) the pyrogenesis of pinene yields, in addition to 

 other products, in the gaseous portion propylene which was identified by its bromide 

 (b. p. 141 to 143°, diso 1.93; bromine percentage 80.47). The heating was effected 

 in an electric furnace fitted with a wide silica tube which was loosely packed with 

 fragments of porous silica. 



Camphene. — The supposition that tricyclene (I) formed an intermediate product 3 ) 

 of the conversion of isoborneol into camphene had recently been refuted by P. Lipp 4 ). 

 H. Meerwein and K. van Emster 5 ) come to the same conclusion. These authors maintain 

 that under the conditions which effect an almost complete conversion of isoborneol 

 into camphene — heating for several hours to 100° with 33 per cent, sulphuric acid — 

 tricyclene is practically not affected at all. It was further demonstrated that the 

 Tiffeneau's explanation 6 ), who suggests a compound with a bivalent carbon atom as 

 intermediate product, is not applicable to these reactions. For the compound (II), 

 which is produced by the action of mercuric oxide on camphor hydrazone and which 

 is not capable of existence, was almost exclusively isomerised into tricyclene. An 

 unsaturated hydrocarbon, probably camphene, was found only in a very small quantity. 



/CH2 /CH 2 



C 8 H 14 < I -> C 8 H 14 < I + N 2 + H 2 + Hg 



X C:N:NH-HgOH X C < 



Mercuric compound of camphor hydrazone. Not capable of existence. 



That tricyclene cannot be an intermediate product of the isoborneol — camphene 

 conversion was further proved by the inverted reaction — transformation of camphene 

 into isoborneol or into its ester. For this purpose the authors compared the reaction 

 velocities at which monochloroacetic acid unites with camphene and with tricyclene. 

 This union leads to esters of isoborneol, as had long been known 7 ). It was ascertained 

 in this connection that the acid forms an additive compound with camphene much 

 more rapidly than with tricyclene. 



The authors further prove that the trimethylene-ring of tricyclene would appear to 

 be most easily split, quite generally, between the carbon atoms 1:2 or 1:6. Thus 

 tricyclene was, in the reduction with hydrogen and nickel, easily converted at 180 to 

 200° into isocamphane (III), the reduction being probably preceded by an isomeration 

 of tricyclene into camphene. In any case tricyclene was quantitatively transformed into 

 camphene when it was passed in a slow current of nitrogen over nickel at 180 to 200°. 



J ) Liehig's Annalen 360(1909), 85. — 2 ) Ghem. Ztg. 45 (1921), 7. — 3 ) Cf. Report 1919, 115. — *) Cf. Report 

 1920, 129. — *) B( , rL Berichte 53 (1920), 1815. — 6 ) Rev. gen. des sciences pares et appliquees 18 (1907), 583. 

 — ') Luting's Annalen 340 (1905), 25. 



