508 SCIENCE PROGRESS 



(c) Ozone. — The study of the action of ozone on solutions of 

 caoutchouc by Prof. Harries of Kiel ' has been accompanied by 

 most fruitful results, so much so that our direct knowledge 

 of the constitution of indiarubber may be said to date from 

 Prof. Harries' first paper on this subject in 1904. 



When Para rubber was dissolved in chloroform, and a stream 

 of ozonised oxygen passed through the solution for several 

 hours, caoutchouc ozonide was formed. On distilling off the 

 solvent, a colourless syrup was obtained which, on drying in a 

 vacuum, solidified to a hard glass, and this on analysis proved 

 to have the formula C 10 H 10 O fi . Two molecules of ozone had 

 evidently attached themselves to the C 10 H 1G group. On decom- 

 position of the above ozonide with water, hydrogen peroxide 

 was formed, and the liquid remaining had the properties of a 

 ketone or aldehyde. When, however, the mixture with water 

 was heated for a long time, complete solution took place, the 

 hydrogen dioxide disappeared, and levulinic acid was afterwards 

 found to be present in the aqueous solution. The levulinic 

 acid was obviously the oxidation product of levulinic aldehyde — 



CH 3 -CO-CH 2 -CH 2 -CHO + H,0,-> CH 3 - CO • CH,- CH, " COOH + H,0 



Levulinic aldehyde. Levulinic acid. 



and as in the process of oxidation of unsaturated hydrocarbons 

 the oxygen is always found at the point where a double bond 

 has previously been, Harries first proposed the following 

 arrangement of carbon atoms in the indiarubber molecule — 



C\ I 



\C = CH - CH, - CH 3 - C = CH - C 



C/ I il 



CH 3 



This would give on oxidation — 



OCH - CH, - CH, - CO - CH 3 



i.e. levulinic aldehyde. 



In the aqueous solution, besides levulinic acid, there was also 

 found a crystalline substance, m.p. 195° C, which Harries dis- 

 covered to be another derivative of levulinic aldehyde, namely, 

 levulinic aldehyde peroxide. 



CH 3 - C - CH, - CH, - CH 



II II 



o = o =0 =0 

 This is formed along with levulinic aldehyde when the 



1 Ber. (36), 1903, p. 1923 1 {37), 1904, pp. 839, 2708 ; (38), 1905, p. 1195. 



