December 1, 1914] 



THE INDIA RUBBER WORLD 



129 



What the Rubber Chemists Are Doing. 



THE PRODUCTION OF ISOPRENE FROM COMMERCIAL 

 I I RPENTINE. 



THE practical all synthetic rubber is the prod 



of isi md if this can be accomplished in any practical 



and cheap way the production of a synthetic rubber on a 

 competitive basis with the plantation varieties would be not only 

 possible but probable. 



Therefore anj method oi making isoprene from cheap raw 

 materials will always be of importance to the rubber industry. 



The United States is the world's greatest producer of turpen- 

 tine, and this oil has been used before to some extent as a raw 

 material for the production of isoprene, but the results have not 

 been in all cases satisfactory. 



Some experimental work on turpentine and other pine oils 

 has been done at the University of North Carolina by Cbas. H. 

 Herty and J. O. Graham, which has recently appeared in print 

 in the "Journal of Industrial and Engineering Chemistry," from 

 which we quote an abstract: "In connection with studies of 

 rubber made by polymerization of isoprene Harries and Gottlob 

 (Ann. vol. 383, p. 228) described a method for the preparation of 

 isoprene from spirits of turpentine by means of the 'isoprene 

 lamp.' In this method the spirits of turpentine is boiled in a 

 flask just below the neck of which is suspended an electrically 

 heated platinum wire coiled somewhat like the filament of a 

 tantalum electric light." 



The vapors are partly decomposed as they pass upward across 

 the heated wire. The flask is attached to an upright condenser 

 maintained at a temperature of 50 deg. C. for condensing the 

 unchanged (and polymerized) vapors of the turpentine. Beyond 

 this is an inclined condenser kept cool and a receiver surrounded 

 by a freezing mixture. Redistillation of the crude product from 

 the receiver gives the isoprene distilling between 35 and 37 

 deg. C. 



Harries and Gottlob obtained only a yield of 1 per cent, from 

 commercial pinene or American turpentine as compared with 30 

 to 50 per cent, from commercial limonene. They therefore con- 

 cluded that the production of isoprene from turpentine was due 

 solely to the presence of small quantities of limonine. 



Professors Herty and Graham, in view of the interest in their 

 section of the country in the use of turpentine, have experi- 

 mented not only on the production of isoprene from the com- 

 mercial turpentine of that section, but also have experimented 

 with the volatile oil of I'imis Serontina, or pond pine, and also 

 with refined spruce turpentine. 



Csing the Gottlob and Harries apparatus, and heating the flask 

 in a bath of cottonseed oil, a current of 2.25 amps, maintained a 

 red glow on the wires which were wound around a pipe-stem 

 triangular prism. 



The isoprene produced was redistilled through a Hempel 

 column, and the pure product, distilling between 36 and 37 deg. 

 C, was taken as isoprene. Here is the result of two of their ex- 

 periments : 



First Experiment — 200 c. c. of turpentine was boiled in the 

 isoprene lamp until no more volatile bodies came over; and on 

 purifying the distillate it was found that there was a yield of 

 18.5 per cent, of crude oil and 5.50 per cent, isoprene. The 

 residue in the flask was 103 c. c. Thus 48 per cent, distilled over 

 producing 18.5 per cent, distillate, showing 61.5 per cent, of dis- 

 tillate decomposed into incondensible gases, producing 38.5 per 

 cent, light oil, and leaving a final residue of 52 per cent, more 

 or less of polymerized oil. At present market prices this would 

 make the material cost of isoprene $1.13. allowing nothing for 

 by-products or cost of making. 



Even with a theoretical yield of rubber of first quality this 



would not be a practical process, but it is much more practical 

 than many others which have been exploited, and it points the 

 way for improvements which may give a yield that will bring 

 it within commercial possibilities. 



Second : aercial turpentine was fractionally 



distilled, and the first portion was taken oh' between 155 and 156 

 1 (.'., which would contain most of the pinene. This gave a 

 ; i i . nt. isoprene. This gives a material cost of 

 78.5 cents per pound, which is approaching commercial limits. 

 The higher boiling-point residues from tins distilled turpentine 

 gave practically no isoprene, so it is concluded that the isoprene 

 comes from the pinene in the turpentine. 



With the oil fmm pond pine, which is rich in limonene. a yield 

 of 12 per cent, isoprene was obtained. 



It appears that the oil of pond pine is an oleo resin, and that 

 it was distilled in a vacuum to produce that portion which con- 

 tained the most limonene. Owing to the expense of such an oper- 

 ation it would make the cost greater if isoprene were produced 

 from this substance than if produced from the distilled turpen- 

 tine of the second experiment. This third experiment is, there- 

 fore, of scientific and theoretical value only. 



Pine oil was also experimented on in a fourth experiment. 

 This produced 4 per cent, of isoprene. 



Pine oil is produced by the distillation of stumps or light wood 

 from the yellow pine tree of the south, and this industry has 

 assumed some importance of late years so that this pine oil ap- 

 pears on the market as a regular article of commerce. It is an 

 oil with a specific gravity of .9403. and has a higher boiling 

 point than turpentine, and is sold at a lower price. There is not 

 usually enough difference in price, however, to balance the dis- 

 advantages of the smaller yield as compared with turpentine. 

 In producing this 4 per cent, only 37.5 per cent, of the oil was 

 distilled over, the balance remaining as a residue in the still. 



The last experiment was made on spruce pine turpentine, 

 which was produced as a distillate from the wood in a digester 

 used for making soda pulp. This yielded practically no iso- 

 prene. The oil boiled between 171 and 174 deg. C. 



From the above work it would seem that it is only necessary 

 to get better conditions under which a greater yield of isoprene 

 can be obtained from distilled turpentine than were gotten in 

 these experiments to produce isoprene. and in turn synthetic rub- 

 ber on a competitive basis with the natural product. 



We note the specification of British patent No. 13,825, 

 granted to C. K. F. L. Gross, of Bevon, Soon, Norway, for the 

 manufacture of isoprene by treating the vapors of turpentine 

 oil with one or more metallic oxides at temperatures below 

 700, copper oxide being instanced as suitable. The same in- 

 ventor proposes to manufacture synthetic caoutchouc, ac- 

 cording to British patent No. 13,826, by heating isoprene 

 trioxymethylene as a polymerizing agent. 



ANOTHER ACCELERATOR. 

 Another accelerator has been put on the British market sim- 

 ilar to those described in the September issue of this journal in 

 the article entiled "The Influence of Xitrogen Compounds on 

 the Vulcanization of Rubber." This accelerator, which is called 

 "Accelerene," is said to be an invention of an English chemist 

 to whom protection has been granted. It is in the form of a 

 green powder which is added to the mixing in the proportion of 

 about one-half per cent., and which thereby reduces the time 

 of vulcanization to about one-third that required in the ordinary 

 way. Larger quantities reduce the time still further. It is 

 claimed that the use of "accelerene" makes the product superior 



