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THE INDIA RUBBER WORLD 



[September 1, 1915. 



What the Rubber Chemists Are Doing. 



PR] SENT STATUS OF SYNTHETIC RUBBER PRODUCTION. 



DR. F. W. HINRICHSEN in the "Zeitschrift des Vereines 

 itscher tngenieure," discusses the present situation in 

 regard to the synthetic production of rubber or caoutchouc. 

 There is not today the enthusiastic interest in the matter that 

 existed a lew years ago, although it is one of great scientific 

 importance. 



Dr. Hinrichsen in his review confines himself to the essentials 

 of the problem, observing that a complete history of its develop- 

 ment is impossible, because only a small part of the work done 

 along this line in commercial laboratories has come to the at- 

 tention of the public. 



After Harries in his basic research work in 1905 had deter- 

 mined the chemical constitution of natural rubber, CioHi«, as that 

 of a 1.5 dimethylcyclooctane of the formula 



r xj C — CH, CH, CH 



L n « CH CH, CH 2 C— CH, 



the thought occurred of taking up the synthesis of this hydro- 

 carbon on the basis of the newly acquired knowledge. Some 

 observations were already at hand. For example, Bouchardat 

 had found that the hydrocarbon isoprene CjH^, a volatile, color- 

 less liquid obtained by the dry distillation of rubber, which was 

 originally discovered by Williams, by polymerization in the 

 presence of an aqueous solution of hydrochloric acid, could be 

 converted into a rubber-like substance. Similarly it had been 

 found by Tilden that isoprene, which, in addition to being ob- 

 tainable from rubber, is also obtainable by passing turpentine 

 through red hot pipes, could be transformed into rubber by 

 means of hydrochloric acid or nitrosylchloride. But since other 

 investigators as well as Tilden did not succeed in repeating 

 this experiment with the same success, in spite of frequent at- 

 tempts under differing conditions, it was assumed that this had 

 been a pure chance observation and that the substance obtained 

 — which in the state of knowledge of the time could not be defi- 

 nitely proved to be rubber— was not rubber at all, so that the 

 statements of Bouchardat and Tilden were based on errors. 



Owing to the enormous rise in the price of rubber a few years 

 ago and the active scientific investigation of the rubber prob- 

 lem, especially by Harries, the attention of industrial circles was 

 directed toward solving the synthetic production of rubber. As 

 a result in 1909 Dr. Fritz Hofmann and Dr. Carl Coutelle, chem- 

 ists of the Elberfeld Dye Works, obtained absolutely pure iso- 

 prene process and were the first to convert it into rubber by 

 simply heating it in a closed tube separately or in the presence 

 of certain other substances. A sample of this rubber was sent 

 to Harries, who proved chemically with absolute certainty that 

 it actually was rubber. As the method of Hofmann and Cou- 

 telle was not then publicly known. Harries took up experi- 

 ments to transform isoprene into rubber. In a lecture in Vienna 

 in 1**10 he reported his observation that it was possible to con- 

 vert isoprene into rubber by heating in a closed tube in the pres- 

 ence of glacial acetic acid. Harries deserves credit for thus pub- 

 lishing a method which could be repeated by others. 



Creditable work in the technical development of the problem 

 was done by numerous individual German and other scientists, 

 by the Elberfeld Dye Works and by the Baden Aniline & Soda 

 Works. In the original patent specification of the Elberfeld Dye 

 Works the inventors did not confine themselves to the use of 

 isoprene as the basic material, but included the use of a series 

 of hydrocarbons of similar composition and behavior toward 

 polymerization, namely hydrocarbons with a so-called system of 

 conjugated double bonds, such, for example, as erythrene and 

 dimetbyltii i many other similarly constructed sub- 



Stan- 



On account of the differences in the basic material there was 

 a possibility of obtaining a series of different rubbers which 

 naturally differed in their chemical constitution. It was also 

 found that the process of polymerization was capable of various 

 modifications and that the rubbers obtained by employing differ- 

 ent methods with the same basic substance varied among them- 

 selves. 



It was thus observed independently by Harries and the Eng- 

 lish investigators, Mathews and Strange, that polymerization in 

 the presence of metallic sodium proceeds at great velocity and 

 the resulting rubber differs materially in its properties from thai 

 produced by mere heating. The chemists of the Baden Aniline 

 & Soda Works found that if polymerization by sodium is car- 

 ried on in an atmosphere of carbonic acid the results are dif- 

 ferent. A further process worked out by the same company is 

 based on the use of ozonizers on peroxide as catalizers. 



Thus various rubbers may be obtained differing from each 

 other in their properties according to the nature of the prime 

 materials and the method of polymerization. The following com- 

 pilation, according to Holt, is a concise resume of a series of such 

 differing rubber-like substances. 



RUBBERS FROM BUTANF.S. 



Standard rubber ( by heating) : Easily soluble, elastic and 

 capable of being vulcanized. 



Ozonide rubber: Insoluble, strongly inflatable, very elastic, not 

 capable of being vulcanized. 



Carbonic acid rubber; not soluble, not inflatable, moderately 

 elastic, not capable of being vulcanized. 



Sodium rubber : Easily soluble, elastic, capable of being vul- 

 canized. 



RUBBERS FROM ISOPRENE. 



Standard rubber: Easily soluble, elastic, capable of being vul- 

 canized. 



Ozonide rubber: Soluble only after calendering, strongly in- 

 flatable, elastic, capable of being vulcanized. 



Carbonic acid rubber: Insoluble, not inflatable, elastic, capable 

 of being vulcanized. 



Sodium rubber: Easily soluble, not elastic, can be vulcanized 

 incompletely and only with difficulty. 



RUBBERS FROM DIMETHYL BUTANES. 



Standard rubber : Easily soluble, not elastic, capable of being 

 vulcanized as hard rubber only. 



Ozonide rubber: Soluble only after calendering, inflatable, not 

 elastic, can be vulcanized as hard rubber only. 



Carbonic acid rubber: Insoluble, not inflatable, not elastic, can 

 be vulcanized only with difficulty and is easily oxidized. 



Sodium rubber: Soluble and insoluble modifications, inelastic 

 and incapable of vulcanization. 



This possibility of obtaining substances of varying properties 

 by changing the basic materials and the process of polymerization 

 gave rise to the hope of producing at will rubbers with properties 

 adapted to special applications, somewhat as in the dyestuffs in- 

 dustry colors are modified at will. The commercial importance 

 of rubber synthesis depends on the product equaling natural rub- 

 In in two respects, price and practical applicability. 



The price factor depends in the first instance on the manufac- 

 turing cost of the hydrocarbons of the isoprene series which are 

 used as the basic materials. 



Progress has been made in this field by the Baden Aniline & 

 Soda Works, which starts with certain fractions of petroleum. 

 Other available substances are starch, amyl alcohol, turpentine, 

 acetylene, etc. With all the processes there are such large quan- 

 tities of by-products that their removal or utilization would con- 

 stitute a problem even more difficult than that of the production 



