March 1, 1920.] 



THE INDIA RUBBER WORLD 



35V 



\\^hat the Rubber Chemists Are Doing. 



IDENTIFYING ARTIFICIAL RUBBERS. 



C Harries discusses the possibility of identifying the presence 

 , of artificial or synthetic rubbers in a special contribution in 

 "Gummi-Zeitung," Volume 33, No. 16, January 17, 1919, 

 page 222,' and gives his method in detail. 



All previous methods for either qualitative or quantitative 

 examination of rubber substance are incapable of distinguish- 

 ing which kind of rubber is present because all artificial rubbers 

 yield bromides and nitrosites so similar to those of natural 

 rubber that only by tedious examination can the sources of their 

 derivation be distinguished. The only method available is 

 ozonizing. Even this affords quantitative results only indirectly. 

 First, obtain the rubber substance by the methods hitherto used 

 and then by ozonizing or by separation of the ozonate obtained 

 determine how much of the rubber can be regarded as artificial. 



The kinds of artificial rubber to be distinguished are the com- 

 mon isoprene rubber and the so-called carbonate of sodium iso- 

 prene rubber. To isolate these products and distinguish them 

 the procedure is as follows : 



The watery solution obtained in disintegrating the ozonide is 

 steamed in a vacuum until the residuum is of a syrupy consist- 

 ency. The aldehydes, diketones and formic acids go off with the 

 steam into the distillation. The residue contains the levuline 

 acids, the succinic acids, and sometimes also another crystallizing 

 product, the levuline aldehyde diperoxide, to which generally 

 no attention need be given. The succinic acid, if it is present, 

 crystallizes quickly and can be expressed. The levuline acids 

 distill in a vacuum below 10 to 12 millimeters at a temperature 

 of about 130 to ISO degrees C. and then give, with acetic acid, 

 phenylhydrazine, a well crystallizing hydrazone with a melting 

 point of 108 degrees C. 



For the quantitative estimate of the levuline aldehyde the dis- 

 tillation product is mixed with about 5 grams of acetic acid 

 phenylhydrazine and a few cubic centimeters of diluted muriatic 

 acid, when after standing for a day the levuline aldehyde derivate, 

 the phenyl-methyl-dihydro-pyridazine is set free in solid form. 

 This melts, after it has again been decrystallized with alcohol, 

 at 197 degrees C. 



To determine the acetonyl acetone the whole mass is distilled 

 with steam, without first separatin.e the pyridazine. The pres- 

 ence of the muriatic acid turns the biphenyl hydrazine derivative 

 of the acetonyl acetone, with the casting off of a molecule of 

 phenyl hydrazine, into anilino-dimethyl pyrrol which is converted 

 into crj'stal flakes of 90 to 92 degrees melting point, while the 

 phenyl-methyl-dihydro-pyridazine remains behind in slabs. From 

 the quantity of the anilidopyrrol which appears, certain infer- 

 ences may be drawn as to the deriva-tion of the isoprene rubber. 

 If some anilino-dimethyl-pyrrol is found, it is a pretty sure 

 indication of the presence of artificial isoprene rubber. 



It is to be noticed, however, that the dimethyl butadiene rub- 

 ber ozonides when disintegrated with water also yield acetonyl 

 acetone, namely, normal dimethyl butadiene rubber, in almost an 

 equal quantity, but the converted Kondakow product only 50 

 per cent of the amount that the theory calls for. With these, 

 however, no succinic acid is found in the residue. Much anilido- 

 dimethyl-pyrrol would point to the presence of the last two ma- 

 terials. If we have clean normal dimethyl butadiene rubber, 

 when its ozonide is separated, we have a watery solution which, 

 mixed with acetic acid phenylhydrazine gives at once a beauti- 

 ful yellow precipitate of the biphenyl hydrazone of acetonyl 

 acetone, which, when filtered and weighed, enables us to cal- 

 culate pretty closely the amount of dimethyl butadiene rubber. 



I'Ik- melting pomt of the biphenyl hydrazone, decrystallized out 

 of diluted alcohol is, according to Paal around 120 degrees C. 

 Pure dimethyl butadiene rubber is the easiest of all artificial 

 rubbers to detect. 



The hardest of the butadiene rubbers to investigate is that 

 whose ozonide in the disintegration yields succinaldehyde. We 

 must proceed in seeking its quality as we do with the isoprene 

 rubbers, namely, steam the watery decomposing fluid in a vacuum. 

 The succinaldehyde passes out with the steam, and gives, when 

 combined with acetic acid phenyl hydrazine, the succinbiphenyU 

 hydrazone with a melting point of 125 degrees C. This is very 

 decomposable. Treated with diluted muriatic acid it is con- 

 verted into a solid, white polymeric base, throwing off phenyl- 

 hydrazine which melts at 184 to 185 degrees C. 



In mixtures of butadiene rubbers with other kinds of rubber, 

 it is extremely hard to demonstrate the presence of succinbi- 

 phenyl hydrazone. 



With vulcanized products the procedure would be as follows: 



The sample to be investigated in the first place must be freed 

 of sulphur as much as possible. This can be brought about only 

 by rolling the sample thin, wetting the surface, and dissolving 

 it with acetone in a Soxhlet apparatus as long as sulphur is 

 taken up by the solvent. Then, after the extraction has con- 

 tinued for about eight days, the sample is rolled out again and 

 subjected to extraction once more for a like period. The sulphur 

 absorbed only coUoidally is thus pretty nearly all removed, 

 and the samples retain only the sulphur that is chemically com- 

 bined. This, when treated with ozone, is converted into peculiar 

 sulphur acids bound to carbon ; free sulphuric acid is also de- 

 veloped. In order that these, when the ozonide is boiled with 

 water, shall not harden the aldehydes and ketones that are 

 formed, a few grams of precipitated calcium carbonate are added 

 to the water beforehand in order to neutralize it. Then when 

 it is steamed in a vacuum, the aldehydes and ketones pass over 

 into the distillation, the acids partially bound to the calcium 

 (levuline acids) must be set free and etherized out of the residue 

 by the measured quantity of sulphuric acid, whereupon it may 

 he isolated by redistillation in a vacuum. The individual sub- 

 stance can then be determined as shown above. This method, 

 however, can be used for sofi rubbers only and not for hard 

 rubbers. 



In conclusion, the author stales regarding his method lor 

 identifying artificial rubbers that it is still imperfect, but there 

 seems no other possible way at present. The analytical solution 

 of the problem must be accompanied by thorough mechanical 

 tests which presupopse exact knowledge of the physical qualities 

 of the individual materials. During the past few years practical 

 results have been obtained in the identification of series of 

 artificial rubbers submitted lor test. 



DETERMINATION OF THE SOFTENING POINT OF ASPHALTUM 

 AND OTHER PLASTIC SUBSTANCES. 



The following method by D. \\'. Twi-^ and E. .\. Murphcy is 

 from a paper published in the "Journal of the Society of Chem- 

 ical Industry," December 15, 1919. page 405T. 



Substances of the asphaltum type are employed widely in chem- 

 ical industry under various names, such as gilsonite, grahamite, 

 pitch, elaterite, albertite, bitumen, "mineral rubber," and "hy- 

 dro-carbon," and as the differences in chemical composition are 

 relatively slight, physical tests become of correspondingly greater 

 importance. 



The absence of any definite point of fusion renders all the 

 so-called melting-point methods of examination really methods 



