Rudolf Pummerer

The Preparation and Molecular Size of Isorubber Nitrone. (8th Communication)

Abstract Continuing earlier experiments of Angeli, Alessandri, and Pegna, of Alessandri and of Bruni, the latter and Geiger have recently studied the action of aromatic nitroso compounds on rubber, and have obtained notable results. The earlier experimentors succeeded only in obtaining from nitrosobenzene a compound of the composition C58H61N5O9. It has recently been proved that one molecule of the nitroso compound for each isoprene nucleus enters the rubber molecule. However, as the earlier investigators have shown, three molecules of nitroso compound react with each C5H8 group when the rubber is warmed in benzene on a water bath for 15 minutes. The solution changes from green to dirty green and finally to brown-red. After cooling it is poured into petroleum-ether, whereupon yellow flakes of the composition [C11H11ON]x, decomposing at 135–140°, separate, the yield being 94–98%. This product is evidently formed by the reaction of one molecule of nitrosobenzene with C5H8 with loss of 2 atoms of hydrogen. T...

The Purification and Fractionation of Rubber. (7th Communication)

Abstract I—The Alkali Purification of Concentrated Latex. Nitrogenous Impurities in Latex Preserved with Ammonia It has already been shown that in the purification of latex by alkali, fresh and ammonia-preserved latex behave differently toward alkali. The former is changed even in the cold through decomposition of the proteins (as shown independently by de Vries and Beumee-Nieuwland), whereas the latter first shows evidences of changes at 50°, at which point it creams. Furthermore, experiments with “Revertex”, a concentrated latex, have shown that ammonia-preserved latex is changed in a still different way. Pummerer and Pahl consider the “total rubber”, obtained by them from ammonia-preserved latex by the action of alkali, to be free proteins and nitrogen. This view is, however, open to correction. Total rubber is probably fairly free of proteins, but contains nitrogen. The nitrogen content, which is still appreciable even after prolonged treatment with alkali at 50??, varies from 0.15 to 0.4%. This nitro...

Rubber. XVIII. Various Ozonides of Rubber and the Problem of the Existence of the Primary Ozonides of Harries

Abstract A permanently valuable service was rendered by Harries when he introduced the ozone cleavage of unsaturated compounds as a general method of investigation in organic chemistry. By analogy with other addition reactions of double bonded carbon atoms he derived the formula (a) for the ozonides which are first formed, but to support the existence of which he was able to obtain only scant experimental data. Harries relied above all on two observations, first, that mesityl oxide ozonide reverts to mesityl oxide when heated by itself, and, secondly, that fumaric acid is supposed to combine loosely with ozone and then readily split off again. Both of these suppositions have remained undisputed up to the present time. Harries reported that it was not possible, with any of a wide variety of reducing agents, to reduce the ozonides to the original compounds or to 1,2-glycols, as would be expected from their structure. Staudinger has laid great stress on this fundamental objection, and he considers that most ...

Rubber. XVII. Detection of Methylglyoxal and the Ozone Cleavage of Rubber

Abstract Since the work of Harries, the question whether methylglyoxal is found in the ozone cleavage of rubber has played an important part in explaining the constitution of this hydrocarbon. Since Harries found no methylglyoxal, he assumed a cyclic formation of isopentene, —CH2.C(CH 3):CH.CH2—, residue sand the absence of a corresponding —CH:C(CH3).CH:CH2 end group, which would necessarily yield methylglyoxal. Nevertheless, in view of the probability that a very long open chain is present in the rubber molecule, the necessity again arose of trying to identify methylglyoxal as n product of the ozone cleavage. This involved the problem of detecting extremely small quantities, since the length of the chain might be very great. Provided that no secondary reaction takes place, the yield of methylglyoxal, if formed, should give information about the length of the chains. If, for example, in the cleavage 0.1 per cent of the carbon skeleton were to appear as methylglyoxal, it might be concluded from the three c...

Rubber. XVIth Communication. The Method of A. R. Kemp for the Determination of the Iodine Number of Rubber

Abstract In a communication of Pummerer and Mann in 1929 on the determination of the iodine number of rubber by means of iodine chloride in chloroform solution, Fisher and Gray were erroneously mentioned as the originators of the method, because of the fact that these authors were the first to publish the method in accessible form. The fact was overlooked that Fisher and Gray state in a footnote that the method was not their own but was that of A. R. Kemp of the Bell Telephone Laboratories. We are greatly indebted to Kemp for calling to our attention the error, which also appears in our XIVth Communication. The first paper of Kemp on the subject appeared a year later, and contains precise information. Kemp worked with a solution of iodine chloride in glacial acetic acid and a solution of rubber in carbon disulfide at 0° C., and as long ago as 1927 he showed that rubber obtained by extraction of crepe with petroleum ether (b. p. 35–60° C.), and precipitation with alcohol according to the method of Weber, C...

Rubber. XVth Communication. The Polymerization of Rubber, Isoprene, and Styrene by Light in the Presence of Sensitizing Agents

Abstract Although according to Bernstein, exposure of rubber solutions to light in the absence of air diminishes the viscosity of the solutions, it is the conviction of the present authors that this change takes place only when there is air over the solutions. In 1920 Porritt observed that a rubber solution sealed off from contact with air gelatinized on exposure to light. Kirchhof however found this to be true only with small quantities of rubber solutions in quartz tubes exposed to ultra-violet light. This reaction was of particular interest to the present authors because of its possible relation to the vulcanization reaction, which can be regarded as an increase in molecular size, and as the formation of chains of rubber molecules with and without sulfur. Irradiation is perhaps an effect similar to vulcanization, but is brought about by polymerizations. It was also of interest to compare irradiated and gelatinized sol rubber with gel rubber. All the experiments described in the present paper were carri...

Rubber. Part XII. Levulinic Acid Peroxide from Rubber

Abstract The so-called levulinic aldehyde diperoxide, which has already been described by Harries and which we call more correctly “levulinic acid peroxide,” is formed not only by “over-ozonization” of the rubber ozonide, but always when rubber ozonide solutions are kept sealed up for a long time, for example, in an ice box. While frequently at first there is only a very slight precipitation after the ozonization, in the course of eight to fourteen days it increases greatly. After filtering and after washing with ether, the yield may reach from 15–20% of the carbon skeleton of the rubber, and it is therefore a decomposition product of the rubber ozonide, which is formed in the neutral medium, perhaps by traces of moisture. Since it is also especially easy to isolate beforehand and is a suitable weighing substance for levulinic acid, we have attempted to confirm for ourselves that the substance still contains the unchanged carbon skeleton of levulinic acid.

Rubber. Part XIV. The Behavior of Rubber with Iodine Chloride and with Dithiocyanogen

Abstract 1. The Determination of the Iodine Number of Rubber The investigation of carotinoids has shown us that a large excess of iodine chloride must be employed if conjugated systems of double bonds are to be completely attacked. If, for example, with isoprene 150% of the calculated quantity of iodine chloride is used, then the reaction reaches after one day and after one week only 1.77 and 1.80 double bonds, respectively. 200% of iodine chloride must be used in order to obtain the correct number of double bonds. A still greater excess of iodine chloride does not then change the results any further. Such isoprene systems, which have added a halogen atom on every carbon atom in the chain, are obviously stable to substitution by iodine chloride. The frequently discussed question of whether in rubber a pair of conjugated double bonds is present as a terminal group, therefore a true isoprene system, has been proved by Pummerer and Mann by means of iodine chloride. At that time, however, the results did not ...

Cryoscopic Measurements of Rubber Solutions and the Separation of Mixed Phases from Benzene Solutions of Rubber. [9th Communication]

Abstract We consider the separation of mixed phases in cryoscopic investigations of colloidal systems and of rubber mixtures in particular as a dangerous source of error. Therefore we place no importance on the great variations in the depressions which occur with sol-rubber in benzene. The menthol values vary less, but nevertheless more than usual. The depressions of camphor fusions proceeded strictly stoichiometrically and led to almost the same value (about 1200) as the cryoscopic menthol measurements. In both the latter instances the composition (rubber content) of the crystallized phase has not yet been studied, since the experimental difficulties involved in the separation of the crystals from the viscous fusion liquid have not yet been overcome.

The Preparation of Pure Rubber from Latex by Means of Alkali, and Its Separation into Sol-Rubber and Gel-Rubber

Abstract The protein in an ammonia-preserved latex was hydrolyzed with alkali for two days at 50° C. Creaming took place, and the cream was separated, treated twice with alkali, finally washed, dialyzed to remove the remaining alkali, and coagulated with acetic acid. The coagulum was extracted with acetone. The remaining highly purified product, “total rubber,” contains an ether-soluble and an ether-insoluble (or difficultly soluble) portion. It is probably a combination of this sol- and gel-rubber that gives rubber its important physical characteristics. The gel-rubber can slowly be transformed into the sol-rubber by means of certain solvents. The hydrochlorides were prepared and the reactions of the pure rubber hydrocarbon with tetranitromethane were studied. The purified rubber can be vulcanized to a soft and a hard rubber, and the latter was found to have exceptionally good electric insulating power.