July 1, 1916] 



THE INDIA RUBBER WORLD 



535 



What the Rubber Chemists Are Doing. 



\XlI.CANlZATION OF CAOUTCHOUC BV MOLECULAR OXYGEN. 

 * I 'HE researches of I. I. Ostromyslenski have shown that the 



action of ozone in vulcanizing caoutchouc flepends on the 

 preliminary formation of the caoutchouc ozonide. The 

 ready-formed ozonide has an effect similar to that of ozone, both 

 soft and hard resins being formed. The course of the process 

 is chiefly determined by the concentration of the vulcanizing 

 compound. When caoutchouc is exposed in an atmosphere of 

 dry air to the ultra-violet rays of a quartz mercury lamp, it 

 undergoes gradual vulcanization, increasing in weight at the ex- 

 pense of the oxygen. At 104 to 176 degrees F. this process takes 

 place with fair rapidity, but at 248 degrees F. no vulcanization 

 occurs. 



Vulcanization of caoutchouc by means of its ozonide takes 

 place under the same conditions as vulcanization by benzoyl 

 peroxide. 



In the presence of moisture, chemically pure caoutchouc acti- 

 vates molecular o.xygen and thus behaves like most of the 

 terpenes. Thus, moist isoprene — or erythrene, caoutchouc of the 

 normal series, when left in the air at ordinary temperature, 

 gradually becomes covered with a layer of new, less elastic 

 substance, this process being analogous to the drying of vege- 

 table oils. If normal erythrene-caoutchouc, thus coated, is milled 

 on cold rolls to render it homogeneous, and then heated in the 

 ordinary way in the absence of air, the unchanged caoutchouc 

 undergoes vulcanization. If, however, this surface is first re- 

 moved, vulcanization does not take place. Evidently this layer, 

 consisting of a product of the action of atmospheric oxygen on 

 the caoutchouc, constitutes the vulcanizing substance. 



The vulcanization of caoutchouc by its halogenides or ozonides 

 is purely a physical process and is comparable with the forma- 

 tion of celluloid. The latter process may be regarded as vul- 

 canization of cellulose esters by camphor, etc. 



The large number of known vulcanizing agents indicates that 

 the chemical nature of these plays no determining part. All 

 these agents form colloids with the caoutchouc, and it is by these 

 colloids that vulcanization is effected. 



VULCANIZATION BY NITROBENZENES. 



Dr. H. P. Stevens has endeavored, without success, to repeat 

 the results of Ostromyslenski in the vulcanization of rubber by 

 the use of nitrobenzenes (see The India Rubber World, May, 

 1916). 



His method was as follows : 



A mixture was made, in the ordinary way, of 100 parts raw 

 rubber and 2 parts of powdered dinitrobenzene. A control sample 

 of rubber alone was prepared. Both samples were vulcanized, 

 under cover, in steam for 3 hours at 275 degrees F. Comparison 

 after this treatment showed no apparent difference between the 

 samples, neither being vulcanized in the slightest degree. The 

 rubber was simply lifeless and without nerve, same as when 

 overmasticated and heated. The result seems to indicate, con- 

 trary to the announcement of Ostromyslenski, that dinitrobenzene 

 has no vulcanizing property and is unable to replace sulphur in 

 vulcanization. 



ORGANIC PIGMENTS IN VULCANIZED RUBBER. 



Most organic pigments are practically unavailable for coloring 

 hot vulcanized rubber, because at high temperature, in the pres- 

 ence of sulphur, they readily decompose with loss of color. A 

 method of special value in the manufacture of rubber articles, 

 colored with such pigments, has been devised by 1. 1. Ostromyslen- 

 ski, which permits vulcanization at the ordinary temperatures in 

 the presence of sulphur, an amine, and an oxide. Certain organic 

 pigments are not decomposed when heated either at a compara- 



tively low temperature, or even at that of ordinary vulcanization, 

 provided that the heat is maintained for only a short time. In 

 such cases the process permits acceleration of the vulcanization 

 or lowering the temperature employed. Experiments were made 

 with eosin, erythrosin alkali blue and cinnamylidene-fluorene. 

 In the case of erythrosin, a mixture of 3 parts of the dycstuff, 

 10 of caoutchouc, 2 of magnesium oxide, 0.8 of sulphur and 0.2 

 of piperidine-piperidyldithicarbamate, after cool mixing, was 

 completely vulcanized in iron molds in ten minutes at 284 de- 

 grees F. Similar results were obtained with the other dye- 

 stuffs mentioned. 



THE STRUCTURE OF CAOUTCHOUC. 

 Doctor Samuel S. Pickles in the "India Rubber Journal" (May 

 6, 1916) has briefly stated his views on the structure of 

 caoutchouc, a summary of which is that the molecule consists 

 of a large number of C, H, complexes. Natural rubber contains 

 at least eight of these units and the ring is a 32-carbon ring. 

 The simplest form to express this formula is 



(_CH,-C ( CH.) =CH— CH,-) n. 

 The chemical reasons why the ring, rather than the open chain 

 form of molecule is preferred are (1) Caoutchouc combines with 

 only two bromine atoms for every C, Hj complex which it con- 

 tains (Weber) ; (2) Caoutchouc can be so oxidized that the 

 whole of its carbon atoms appear as derivitives of levulinic- 

 aldehyde and levulic acid (Harris). Assuming the correctness 

 of these two observations, the closed ring follows as a corollary. 

 The bulk of the evidence and the weight of opinion are at present 

 strongly in favor of the large ring formula for caoutchouc. 



ANALYTIC REACTIONS OF ISOPRENE. 



THE presence of isoprene formed in a reaction of a diole- 

 fine with conjugated linkings is detected by I. I. Ostro- 

 myslenski by shaking 5 to 10 drops of the products of the 

 reaction for a short time with SO cc. of concentrated aqueous 

 sulphur dioxide solution, the mixture being then left at the 

 ordinary temperature in a hermetically sealed vessel. In the 

 course of 2 to 30 hours an abundant, colorless, amorphous 

 precipitate is formed. This consists of a compound of the 

 diolefine with sulphur dioxide possessing characteristic 

 properties. 



Isoprene may be determined quantitatively by converting it 

 into 1.3-dichloroisopentane. If a grams of the dichloroisopentane 

 compound be obtained from S grams of the crude isoprene, 

 the latter contains 3403 a X 70.49 S per cent isoprene. The 

 procedure is as follows : 200 grams of the crude isoprene, 

 containing butylenes, amylenes, benzene, etc., with boiling 

 point 86 to 104 degrees F., is energetically shaken with 1500 

 cc. of fuming hydrochloric acid for 6 hours in a mechanical 

 shaker. The black, opaque upper layer of chloro-compounds 

 is separated, washed with aqueous sodium chloride solution 

 saturated in the cold, again separated after the emulsion 

 formed has separated into two layers, dried over calcium 

 chloride and distilled. At 104 to 122 degrees F. only two or three 

 drops of hydrocarbons generally distil over, and the fraction 

 122 to 194 degrees F. contains butylene and amylene chlo- 

 rides. The fraction 194 to 266 degrees F. is collected sepa- 

 rately. From 266 degrees F. the temperature usually jumps 

 immediately to 288 degrees F.. the boiling point of the 

 1.3-dichIoroisopentane. When the crude isoprene has been 

 obtained, for example, from turpentine, the 1.3-dichloroiso- 

 pentane cannot be distilled, but it is found that the residue 

 distilling with boiling point beyond 291 degrees F. consists, 

 in spite of its black color, of almost chemically pure 1.3-di- 



