The Journal of; Industrial a n d Engineering Chemistry Published by T H E AMERIGAN GHEMIGAL SOGIETY
Volume 111
MAY, 1911
No. 5
B O A R D OF EDITORS.
Editor: M. C. Whitaker. Associate Editors : Geo. P. Adamson, E . G. Bailey, H. E. Bamard, G. E . Barton, Wm. Brady, Wm. Campbell, F. B. Carpenter, Virgil Coblentz, Francis I. Dupont, W. C. Ebaugh, Wm. C. Geer, W. F. Hillebrand, W. D. Home, Karl Langenbeck, A. D. Little, P. C. McIlhiney, E. B. McCready, Wm. McMurtrie, J. Merritt Matthews, T. J. Parker, J. D. Pennock, W. D. Richardson, Geo. C. Stone, Ernst Twitchell, Robt. Wahl, Wm. H. Walker, W. R. Whitney. Published monthly. Subscription price to non-members of the -4meriw.n Chemical Society, $6.00 yearly. Foreign postage, seventy-five cents, Canada, Cuba and Mexico excepted. Entered at the Post-Office, Raston. Pa., as Second-class Matter.
EDITORIALS THE SYNTHESIS OF INDIA RUBBER.
The synthesis of rubb’er dates back to the observations of Bouchardat (1879) and of Tilden (1882)that isopren, a definite compound C,H, (boiling point 3 7 - 3 8 O C.) isolated from the products of the dry distillation of india rubber, was the only substance thus obtained, which could be polymerized again into india rubber. According t o these investigations isopren undergoes such a change after treatment with hydrochloric acid followed b y distilling off the volatile by-products of the reaction with steam. These experiments, however, have never been duplicated and the products obtained have never been satisfactorily examined so as to furnish positive proof that they were in fact india rubber. On the contrary Harries, one of the greatest authorities in this field of chemistry, after years of research, stated emphatically that the above results could not be confirmed by him and his pupils. I n order to al.lot impartially t o each of the various investigators his proper share, we quote from a n interview granted in 1908 by Prof. Tilden to a representative of the India Rubber Journ.lzI,i and from a lecture delivered March 1 2 , 1910,b y Prof. Harries,a leaving it t o the reader to draw his own conclusions from these authoritative publications as to the part which the different investigators had in the historical development of the solution of the problem of the synthetic production of rubber. The interview states : “ The writer recently had a n .opportunity of talking the subject over’ with Prof. Tilden (now Dean of the Royal College of Science, London) who, as everybody knows, achieved some success in the synthetical production of rubber. An account of what he really did in days gone b y will not be out of place a t this
’ India Rubber Journal, October 5 , 1908. Gummi-Ztq., March 1 8 . 1910.
juncture. The details can be seen and studied by our readers in the transactions of Scientific Societies and records of chemical journals.” “Prof. Tilden’s first note on the spontaneous conversion of isopren into caoutchouc was read before the Birmingham Philosophical Society, May 18, 1892. He then explained t h a t ‘isopren’ is a hydrocarbon which was discovered by Greville Williams many years ago among the products of the destructive distillation of india rubber. Later, in 1884, it was observed b y myself among the more volatile compounds obtained by the action of a moderate heat upon oil of turpentine and other terpenes. I t is a very volatile liquid boiling a t about 36O.” ‘‘ Bouchardat observed that when isopren is heated to a temperature near 300’ it gradually polymerizes into a terpene, which he called di-isopren, but which is now called di-pentene. This compound boils a t 1 7 6 ~ .A4quantity of colophene similar t o that which is produced by the action of heat upon turpentine is formed a t the same time. When isopren is brought into contact with strong acids, aqueous hydrochloric acid, for instance, a small portion of it is converted into a tough, elastic solid, which has been examined by G. Bouchardat and by myself. I t appears t o be true india rubber.” “ Specimens of isopren were made from several terpenes in the course of my work, and some of them I have preserved. I was surprised a few weeks ago a t finding the contents of the bottles containing isopren In from turpentine entirely changed in appearance. place of a limpid, colorless liquid, the bottle contained a dense syrup in which were floating several large masses of a solid of a yellowish color. Upon examination, this turned out to beindia rubber. The change of isopren b y spontaneous polymerization has not, t o my knowledge, been observed before. I can only account for
280
T H E J O U R N A L OF I N D U S T R I A L A N D EIVGINEERING C H E M I S T R Y .
May, 1911
i t b y the hypothesis t h a t a small quantity of acetic go over, some of them beginning t o boil a t 2 5 ’ , and or formic acid had been produced by the oxidizing some of them boiling a t 300’ C. and even above. action of the air, and t h a t the presence of this com- Only two fractions of these products of distillation pound had been the means of transforming the rest. have been studied more carefully, namely, the one The liquid was acid t o test paper, and yielded a small boiling a t 30-40°, and the one boiling a t 160-170’. According t o Wallach the latter fraction contains portion of unchanged isopren.” “The artificial india rubber, like natural rubber, dipentene while the former consists of isopren, diappears t o consist of two substances, one of which is methylallene and dihydroisopren. These constituents more soluble in benzine or carbon bisulphide than the were mainly investigated b y Ipatieff, who showed t h a t pure isopren can only be produced in a most other. ’ ’ “ A solution of the artificial rubber in benzine leaves circumstantial way. The constitution of isopren on evaporation a residue which agrees in all char- was proven b y Euler and Ipatieff. Isopren was acteristics with a similar preparation from para-rubber.” known for a long time, although i t is obtained only in “The artificial rubber unites with sulphur in the small quantities on distilling caoutchouc. I ascersame way as ordinary rubber, forming a tough, elastic tained t h a t I I / ~kg. of good caoutchouc furnished only compound. I t is obvious t h a t compounds such as 35 grams of a n isopren fraction boiling a t 33-34’. these, containing doubly-linked carbon, may polym- Although only so little is obtained the bold conerize in a variety of ways; and, in the present con- clusion was arrived a t already a t a n early date t h a t dition of our knowledge even of isopren, i t would be isopren not only stands in near relation t o caoutchouc, idle t o speculate as to which out of the numerous but was more closely related t o i t than all the other possible arrangements would correspond t o the con- products of distillation.” “W. A. Tilden in 1882 was the first t o observe t h a t stitution of caoutchouc.’’ I n a letter once published in the Kew Bulletin, Prof. isopren can be polymerized. By saturating the india Tilden stated t h a t : “ A s you may imagine, I have isopren fraction with hydrochloric acid gas tried everything I can think of as likely t o promote rubber-like masses ” w e r e F a i d t o separate. Later the change, b u t without success. The polymerization Tilden found that isopren, which he had3btained b y proceeds very slowly, occupying, according t o my ex- conducting turpentine through tubes heated t o a perience, several years, and all attempts to hurry i t glow, also polymerized and furnished substances result in the production, not of rubber, but of ‘colo- which he declared were caoutchouc. He attributed phen,’ a thick, sticky oil, quite useless for the purpose this reaction t o the presence of a small quantity of t o which rubber is applied.” acid, which had been formed during the pyrogenous Professor Tilden further states: The conversion process. Wallach and also Ipatieff remarked briefly of isopren into rubber occurs, so far as observed, t h a t isopren polymerized when exposed t o light. Later Klages in a lecture in Heidelberg declared t h a t under two conditions.” according t o his experience i t was excluded t o trans‘ I ( I) When brought into contact with strong aqueous form isopren into caoutchouc.” hydrochloric acid or moist hydrogen chlorid gas. “(2) By spontaneous polymerization. “During a period of seven years with the cooperation “ I n the former case the amount of rubber produced of many of my collaborators, I tried t o duplicate the is small, as i t is only a by-product attending the for- reactions of Tilden, but have never been able t o conmation of the isopren hydrochlorides, which are both firm his results. Other investigators also advised me liquid. I n the latter case the process occupies several t h a t they had never been able to obtain the products years. Of course, many attempts were made by me described by Tilden. I show you here a substance t o hasten the process, but i t was found that contact prepared three months ago by saturating isopren with any strong reagent, such as oil of vitriol, penta- with hydrochloric acid gas. Apart from its brownish chloride of phosphorus, and others of a milder char- color, it has remained unchanged. If isopren is acter, led only t o the production of a sticky “colo- treated with a n organic acid and allowed to stand, no phene ” similar t o the substance which results from the material changes are observed even after many months; polymerization of the terpenes, and after a course of formic acid however acts a t once, but produces only a experiments which were carried on for about two resin. I t is therefore evident t h a t Tilden must have years, I was reluctantly obliged to abandon the encountered quite accidentally conditions under which subject. It is, however, a question whether the polymerization of isopren was effected, but-what did not process could be made commercially productive even of course is of the utmost importance-he if a suitable reagent could be found to effect the trans- adduce proofs t h a t he had actually produced caoutformation, because the yield of isopren from turpentine chouc; for as I am going t o show later, isopren is very small, probably not exceeding I O per cent. furnishes all kinds of substances on polymerization, under favorable conditions. I n my experience i t was and many products may be characterized as “india less. If isopren were obtainable at a low cost from the rubber-like,” which bear only very little relation to other sources it might be found possible t o utilize the caoutchouc. As a matter of fact isopren, on standing hydrochloric acid process, though I doubt it.” for a long time in the presence of air, becomes thick, Prof. Harries states: “Caoutchouc even in a high but this is not due t o polymerization. A peroxide vacuum cannot be distilled without decomposition. is formed, which on heating is very explosive. For a If it is heated in a retort, the most varied products long time my experience was the same as t h a t of ‘I
May, 1911
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y .
Klages. A new incentive to take up again the study of the subject came last summer, when upon the recommendation of Prof. Hempel a large English house sent me a sample with the request t o ascertain whether i t was real. caoutchouc. The substance had been prepared according to a patented process of a Dr. Heinemann, in England, consisting in conducting, simultaneously through a glowing tube acetylene, ethylene and chlormethyl. I n this way isopren was first produced and immediately converted into caoutchouc by polymwization. I did ascertain as a matter of fact that the substance was caoutchouc, it furnished a levulinaldehyde with ozone and a nitrosite with nitrous acid, and its appearance was that of para-rubber. This result was communicated t o the firm with the caution however t o ascertain whether the material tested had been really made according to the process of Heinemann." "For some time I experimented according to the directions of the patent, but neither myself nor any other chemist could reproduce the results described. I f , by following this process, isopren and .caoutchouc can really be produced it must be done under specific conditions which should have been described in the specification, and should any one actually ascertain the character of these conditions, I would consider him a n independent inventor. I t is my belief, however, that the process is inoperative. At any rate, these experimen.ts caused me t o take up again the synthesis of isopren and its polymerization, when in the beginning of November, 1909, the Elberfelder Farbenfabriken a t the request of Prof. Duisberg sent me some samples of artificial caoutchouc obtained from isopren acc:ording t o a process discovered b y Dr. Fritz Hofmann. I could prove beyond a shadow of a doubt t h a t these samples were real caoutchouc and therefore the examined substance was the first synthetic caoutchouc ever obtained." From the above data, it becomes obvious that the problem of synthesizing india rubber is identical with that of th.e synthesis of isopren and its polymerization into india rubber. Under the circumstances, the constitution of isopren becomes of paramount importance and may be advantageously discussed a t some length. Tildenx already concluded that isopren had the constitutional formula of CH, = C(CH,)-C.H = CH,, giving i t the name of beta-methylcrotonylene. But he did not support his theory b y experiments, and it was Gadziatzky' who carried out the first researches which partially confirmed the Tilden formula. This author prepared from the monochlorhydrate of isopren a tertiary alcohol, dimethylvinylcarbinol,
CH8 CH,= CH - C/ +HCl=CH, \CH, CH3 CH, = CH - C/
I \ CH,
\CH,
c1
I. CH,.CH.CH, I I
>NH
+
2
~
L/
+ KOH = ~
,
~
CH,.CH, Beta-methylpyrollidine.
cH8'(?rc?>N+ + CH8
KI
+H,o
Beta-methyldimethylpyrollidylammonium iodide.
11. CH3.CH.CH, I
CH,.CH, CH,.C = CH,
I
CH,
+ H,O
C H , . C H , . N < ~ 8~ Beta-methyldimethylpyrollidine.
111. .C = CH, Cj H , . C H , . NCH8 < ~ ~ CHJ
+
\C - CH = CH,.
47, 168. Chem. AVe"vkms, 46, 129. J o t r r . Russ. C h e m Ges.. 20, I , 706.
CH,
- HC1= CH, = C = C/
These experiments, however, furnished only liquids which were liable to decomposition on distillation, and altogether did not possess sufficiently definite properties. Mokiewskyx produced the first crystalline body by the action of hypochlorous acid upon isopren. Ipatiev and Hittorfz experimented with dihydrobromides of the formula C,H,,Br, and contributed largely t o the experimental proof of the constitution of isopren, which however was finally supplied b y Eulers who produced beta-methyldivinyl svnthetically and showed i t t o be identical with isopren. Basing his experiments on the reaction published by Ciamician and Magnaghi4 who prepared divinyl from dimethylpyr ollidyl-ammonium iodide on treatment with caustic potash, he transformed beta-methylpyrollidine into beta-methyldivinyl as follows :
3
CH,/
' Bull. SOC. chim.. [2]
C" C/ ('CH,
= CH-
c1
CH3
Subsequently3 he found t h a t isopren is converted into a n isomeric dimethyl-allene if i t is heated with weak alcoholic hydrochloric acid.
281
CH,.C = CH, 1
CH,.CH,.N I
'
