242 REPORTS OTf THE STATE OF SCIENCE. 



This hoils at 114'-118° (10 mm.), and on treatment with hydrogen 

 chloride gas gives the same dihydrochloride as above, C|oH,b2HC1, shown 

 by Wallach to be identical with dipentene hydrochloride. The formation 

 of these compounds furnishes additional proof of the identity of caout- 

 chine with dipentene. 



We have seen that in 1882 Tilden suggested that isoprene was fi methyl 

 crotonylene, but brought forward no other experimental proof than that 

 on oxidation it yielded carbonic, formic, and acetic acids. Gadziatzky ' 

 was the first to bring forward direct experimental proof in the support of 

 this, formula for isoprene. From isoprene hydrochloride he obtained a 

 tertiary alcohol, dimethyl-vinyl carbinol — 



^g'\c(0H).CH = CH2. 



He also showed that on heating isoprene with dilate alcoholic hydro- 

 chloric acid it is transformed into dimethylallene, which change can be 

 represented as taking place by the alternate addition and elimination of 

 hydrochloric acid : — 



(1) gU»\G-CH = CH2 + HCl = ^g''^CCl-CH = OH2; 





(2) pS'^^CCl - CH = CHj - HCl = p5^\c = C = CH^ 



Mokiewsky 2 in 1895 succeeded in obtaining a solid crystalline 

 derivative of isoprene by the action of hypochlorous acid upon it. This 

 melted at 81°, and he considered it to have the formula C5Hg(OH)2Cl2 

 (isoprene dichlorhydrin), 



Ipatieff and Wittorf (1897) identified amongst the products of 

 rubber distillation the hydrocarbon trimethyl ethylene, 



?:>=' 



gJj3>C = CH.CH3, 



after Mokiewsky * had shown it to be present in the distillation products 

 of the turpentine decomposition. This occurs in the fraction SS^-SS" of 

 the rubber distillate. On treating this fraction with HBr in acetic acid 

 solution a hydrobromide was obtained, boiling-point 50°-74° (16 mm.). 

 On treatment with water and potassium carbonate this gave an oil which 

 proved to be dimethyl ethyl carbinol. Its formation from trimethyl- 

 ethylene is expressed in the following manner : — 



Ch'/^ = oh . CH3 -h H Br = ^^»\cBr - CH^ . CH3 



Trimethyethylene 



^^»"\cBr . CHj . CH3 + HjO = ^y'\c(OH) . CH, . OH,. 



Dimethylethyl carbinol. 



The chief product of the treatment of the 33°-38° fraction with 



' Wolkow, Jonrn. 0/ Russian Phys. Chem. Soc, 20, 706. 

 = Mokiewsky, CItem. Zeit, 1895, 101. 

 ' JouTii.f. Prakt. Chem., 1897, pp. 2-3. 

 ♦ Journ. Puss. Phye. Chem. Soc, 27, 516. 



