"December 1, 1916.] 



THE INDIA RUBBER WORLD 



131 



What the Rubber Chemists Are Doing. 



SYNTHETIC CAOUTCHOL'C. 



THE researches on the chemical constitution of caoutchouc 

 and the sources and processes available for its synthesis, 

 have been outlined by B. D. W. Lufif in the "Journal of the 

 Society of Chemical Industry'' (October 16, 1916). The author's 

 paper may be summarized as follows : 



Between 1835 and 1840 the study of caoutchouc was undertaken 

 ■on scientific lines by various investigators, including Dalton, Lie- 

 big, Himly, A. Bouchardat, and Gregory, but in all cases their 

 work was more or less disjointed. The most systematic attempt 

 to isolate and examine the various products present in the crude 

 distillate from caoutchouc was made by Greville Williams in 

 1860. He obtained (1) a liquid boiling at 37 degrees C. to which 

 he gave the name "Isoprene"; (2) a large proportion of a hydro- 

 carbon boiling at 170 to 173 degrees C. which was identical with 

 a body previously obtained by Himly, and called caoutchoucine — 

 this has since been proved to be dipentene ; (3) a fraction boiling 

 above 300 degrees C. to which he gave the name "Heveene." 



Gustave Bouchardat in 1879 undertook a detailed investiga- 

 tion of isoprene, in the course of which he examined the action 

 ■of hydrochloric acid ; he noted that an additional product was 

 formed, but under certain conditions the action of the acid re- 

 sulted in the formation of a solid mass, not containing chlorine, 

 but having, in fact, the same percentage composition as isoprene 

 itself. He described this body thus : "It possesses the elasticity 

 and other properties of rubber itself. It is insoluble in alcohol, 

 swells in ether and also in carbon bisulphide, in which it dis- 

 solves after the fashion of natural rubber." He also noted that 

 ■ on distillation it yielded the same hydrocarbons as in the case of 

 the natural product. This was an important step in the synthesis 

 ■of caoutchouc ; in fact, in order to make this complete, all that 

 was necessary was to prepare isoprene from elementary materials. 

 At that time the only source of isoprene was rubber itself. 



Bouchardat's results were confirmed in 1882 by Tilden who 

 observed the polymerization of isoprene. In discussing isoprene 

 he remarked that one of its chief characteristics was its conver- 

 sion into true caoutchouc when brought in contact with certain 

 chemical reagents. He pointed out that this was of great prac- 

 :tical interest as, if isoprene could be obtained from some other 

 and more accessible source, the synthetical production of rubber 

 could be accomplished. Two'-years later he succeeded in obtain- 

 ing isoprene by passing the-yapors of turpentine through a hot 

 tube. 



The outcome of the work of these two investigators was that 

 the caoutchouc molecule was shown to be formed by the union 

 of a number of molecules of isoprene, and this union or poly- 

 merization could be brought about by treating the isoprene with 

 suitable reagents. To them must be given the major share of the 

 credit for laying the foundation of the numerous processes since 

 suggested for preparing synthetic rubber. 



In 1887 Wallach observed that isoprene undergoes polymeriza- 

 tion on exposure to light with production of a rubber-like mass. 

 In 1892 Tilden showed that the material obtained in this manner 

 ■could be vulcanized with sulphur. The synthesis of isoprene, 

 and as a corollary, that of caoutchouc, was accomplished by Eulcr 

 in 1897. 



In 1909, owing to the rapid rise in the price of rubber, the prob- 

 lem was taken up in England in a systematic manner by Perkin, 

 Fernbach, Weizmann and Mathews and in Germany by the Bayer 

 and Badische companies. In 1884 Tilden suggested that not only 

 isoprene, but its homologues should be capable of polymerization 

 in a similar manner. This was found to be the case, and these 

 bodies, chief among them butadiene, form the basis of methods 

 for obtaining synthetic caoutchoucs. 



Among the materials available as starting points for suggested 

 syntheses are coal tar ; the low'-boiling fractions obtained in 

 petroleum distillation ; starch and cellulose. On account of the 

 colloidal nature of caoutchouc the question whether or not the 

 synthetic caoutchouc-like bodies can be regarded as true caout- 

 chouc cannot be settled by determining such physical character- 

 istics as would serve to identify a crystalline solid such as cam- 

 phor. 



Harries holds the view that caoutchouc obtained from isoprene 

 with the aid of acetic acid is identical with that occurring in 

 nature. This view is dissented from by Stemmig. The syn- 

 thetic caoutchouc obtained by polymerization of isoprene in the 

 presence of sodium, however, is not identical with the natural 

 product. In view of the rapid advance in the cultivation of 

 rubber it ' is generally assumed that unless a synthetic product 

 can be marketed at about 30 cents per pound there is little hope 

 of the natural material being superseded. 



METHODS OF ANALYSIS. 



TESTING ANILINE OIL. 

 pURE aniline boils at 360.5 degrees F. and at this temperature 

 ' 95 per cent of the sample should distil. A common method 

 of testing it is with the apparatus shown in the illustration. It 



consists of a ring stand A 

 and a piece of wire gauze 

 to support the flask; a 

 Bunsen burner B; several 

 200 cc. Lunge distillation 

 flasks C: a thermometer 

 D; a funnel for filling the 

 flask ; an 18 or 20-inch 

 condenser E, and a 100 

 cc. measuring cylinder F. 

 To make the test, lOO- 

 cc. of aniline oil are put into the flask by means of the funnel; 

 the apparatus is assembled as in the illustration, and a flow of 

 water connected from the tap to the condenser. The contents 

 of the flask are gently heated until 360.5 degrees F. is reached, 

 at which temperature it is maintained. The volume of oil col- 

 lected in the cylinder is the measure of the purity of the aniline. 



CHEMICAL PATENTS. 



THE UNITED STATES. 



Vulcanizing Process. Treating rubber for vulcanization by 

 adding vulcanizing material containing lead and sulphur and a 

 reactive substance comprising a metal and an acid radical adapted 

 to form, with the sulphur and lead, respectively, a light-colored 

 water-insoluble sulphide and a light-colored water-insoluble lead 

 salt and vulcanizing the mixture. [Harold R. Murdock, Nauga- 

 tuck, Connecticut, assignor to Rubber Regenerating Co., a cor- 

 poration of Indiana. United States patent No. 95,359 (May 4, 

 1916).] 



Purifying Isoprene. Isoprene is treated with sulphurous acid 

 in presence of hydrochloric acid which serves to facilitate the 

 formation of a crystallizable sulfoxide for the recovery by heat 

 of the pure hydrocarbon. [F. E. Matthews and E. II. Strange. 

 United States patent No. 1,196,256.] 



Rubber Comi'Ound. Rubber, dry cork flour, iron slag and 

 gelatinous rawhide, the quantity of rubber in the compound 

 being less than the combined weights of the other ingredients. 

 [Eugene Von Vargyas, Washington, D. C. United States patent 

 No. 1,202,340.] 



Agent for Treating Vulcanized Rubber. As a new agent 

 for the. treatment of vulcanized rubber, the solution of vulcanized 



