April, 1927
INDUSTRIAL A N D E,VGI;VEERING CHEMISTRY
and sodium hydroxide by titration using phenolphthalein as indicator are necessary to determine the strength of the sodium phenolate. The writer has found that sodium phenolate is titratable using phenolphthalein as an indicator up to about 85 per cent its sodium hydroxide equivalent. This should also be determined a t least daily. A very good indication of the amount of phenols in sodium phenolate may be had by measuring 50 cc. of the solution into a beaker,
53 1
boiling to expel small amounts of benzene which are sometimes present, cooling, and liberating the phenols with 25 per cent sulfuric acid in a graduate. When neutralizing sodium phenolate with sodium bicarbonate both the amount of bicarbonate necessary and the extent to which the reaction has gone toward completion can be determined by the usual double indicator method for carbonate-hydroxide and carbonate-bicarbonate mixtures.
Direct Determination of Hydrocarbon in R a w Rubber, Gutta-percha, and Related Su bstances'jz By A. R. Kemp BELL TELEPHONE LABORATORIES, N E W
YORK,
N. Y
Iodochloride in glacial acetic acid is shown to be a were much better. On the N S A T U R A T I O N is suitable reagent to determine the unsaturation of the other hand, it was practically one of the outstanding hydrocarbon in rubber or gutta-percha. The influence impossible to obtain satischemical properties of of time, temperature, sunlight, and reagent concenfactory end points owing to rubber and gutta-percha. Up tration upon the reaction is shown. the formation of emulsions, t o the present time there has Comparisons are made between iodochloride, iodoas was the case in the Lewis been no satisfactory method bromide and bromine relative to their reactions with and McAdams methode6 It for determining this property. raw rubber and some of the terpenes. was found that carbon biBromine absorption methods Results of analyses of several rubber and gutta-percha sulfide was an excellent solhave been widely used to samples are given. vent for the rubber iodoestimate the unsaturation of The effects of mastication and heat upon the unchloride and that there was organic compounds, but they saturation of raw rubber are shown. practically no tendency for have proved unsatisfactory emulsions to form with this for rubber. V a ~ b e l Kirch,~ hof,* and Schmitz5 attempted to estimate rubber volumet- solvent, thus making it possible to determine accurately rically by bromine absorption methods, but without success. the unsaturation of rubber hydrocarbon by a rapid voluSome of t'he difficulties cited were-variations of results metric procedure. Further, it was found that under proper with time, substitution with liberation of hydrobromic acid, conditions no substitution took place with the iodochloride and poor end points due to occlusion of bromine by pre- reagent, thus making it unnecessary to apply the McIlhiney? cipitation of the tetrabromide. Lewis and McL4dams6were procedure, as must be done when bromine is used. more successful in applying the McIlhiney7 modification Procedure for Raw Rubber, Gutta-percha, Balata, Etc. of the bromine absorption method. However, this method was reported upon unfavorably by Fisher, Gray, and MerlingS d O.k-gram sample of the material, from which the resins on account of the precipitation of the tetrabromide and the have been removed by extraction with acetone, or any formation of bad emulsions during titration which interfere other suitable method, is cut into small pieces and allowed with the end point, thus making it impossible to obtain to swell overnight in 75 cc. of purified carbon disulfide. concordant results. (The ordinary C. P. carbon bisulfide was purified by allowing A search of the literature failed to reveal any attempt it t'o stand in contact with solid potassium hydroxide for to apply the well-known methods of Wijs and Hanus to 48 hours and finally distilling over same.) Twenty-five rubber. I n an attempt to apply the standard Wijs method cubic centimet'ers of 0.2 N Wijs solutiong are then added to a sample of crepe rubber, very discordant values were from a pipet, and the flask is manipulated in such a way obtained which were very much less than the theoretical as to give a rotating motion to the rubber solution, thus value for rubber hydrocarbon calculated on the basi; of one preventing the formation of a precipitate. After the addition double bond for each CsHs group. It was observed, when of the TT7ijs reagent a clear dark-red solution should result. the Wijs solution was added to 0.1 gram of smoked-sheet The stoppers are then wetted with a drop of potassium rubber which had swollen overnight in 10 cc. of chloroform iodide solution to prevent escape of iodine and the flasks or carbon tetrachloride, that practically all of the rubber placed in ice water for 2 hours. A blank determination was coagulated. This two-phase condition made it im- is also prepared a t the same time. At the end of this period possible for complete reaction to take place, thus undoubtedly 25 cc. of 15 per cent potassium iodide and 50 cc. of distilled accounting for the low results. When larger amounts of water are added. The iodine liberated is then titrated with the chloroform or carbon tetrachloride (up t o 100 cc.) were 0.1 N sodium thiosulfate.1° Before the brownish color used, the precipitation was largely prevented and the results of iodine has disappeared 5 cc. of 5 per cent soluble starch solution are added as an indicator. Further addition of 1 Received December 13, 1926. The application of this method t o vulcanized rubber will be described the thiosulfate solution changes the deep blue to a brown in a later communication. and then to a yellow. At this point the solution is shaken a Gummi-Ztg., 26, 1879 (1912).
U
4 5 8 7 8
I b i d . , 27, 9 (1913). I b i d . , 27, 1342 (1913). THISJ O U R N A L , la, 673 (1920). J . ~ m Chem. . SOL., a i , 1084 (1899). THIS JOL'RXAL, IS, 1031 (1921).
g The directions given by Fryer and Weston, "Oils, Fats, and Waxes," Vol. XI, p. 93, are recommended for the preparation of the Wijs reagent. 10 The conditions recommended for standardization of the thiosulfate solution are given by Popoff and Whitman. J. A m . Chcm. SOC.,47, 2259 (1925).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
532
vigorously to remove the last trace of iodine from the carbon disulfide. When the end point has been reached the aqueous layer becomes milky white and should remain so after shaking. The difference between the blank and the sample titration is used to calculate the iodine number in the usual manner. The theoretical iodine value of rubber hydrocarbon is 372.8, calculated on the basis of one double bond for each C6Hs group. The per cent unsaturation and per cent rubber hydrocarbon in the sample are calculated from the ratio of the iodine value of the sample to the theoretical iodine value. Application of Pure Rubber Hydrocarbon and AcetoneExtracted Pale Crepe Note-The pure rubber hydrocarbon was prepared by treating acetoneextracted unmilled pale crepe a t room temperature with petroleum ether (b. p. 35' to 60' C.) without agitation, separating the insoluble portion by decantation, and precipitating the hydrocarbon from the solution with absolute alcohol. The hydrocarbon was freed from solvent by heating at 50° C.under high vacuum. The product was transparent and practically colorless. 11 The results of analysis of the rubber so prepared are: carbon 88.02, hydrogen 11.75,nitrogen and ash 0.00 per cent; ratio carbon to hydrogen 15.90 (averages of two determinations).
Figure 1 shows the effect of time and temperature on the reaction involved. The determinations were carried out in diffused sunlight, using the procedure described above. It appears evident from these results that substitution takes place slowly a t room temperatureI2 but is practically negligible a t ice-water temperature. In the case of the pure rubber hydrocarbon the agreement with the theoretical value is very close. The 95.8 per cent of rubber hydrocarbon in the sample of acetone-extracted pale crepe is very close to what would be expected if the protein and other im-
0" C. for 1 hour are shown in Figure 2. A 50 per cent excess of reagent seems to be necessary in order that the addition reaction be completed in a reasonable length of time. I n the previously outlined method the 25 cc. of 0.2 N Wijs solution provides 70 per cent in excess of the amount of iodochloride necessary to saturate completely the double bonds in 0.1 gram of rubber hydrocarbon. A very large excess, such as the addition of 25 cc. of a 0.4 N Wijs reagent, is without effect on the iodine value at ice-water temperature. It does, however, cause an increase in the iodine value at room temperature, which is probably due to increased substitution. Effect of Light
The effect of diffused sunlight upon the rubber-iodochloride addition and substitution reaction is shown in Table I. The results show that it is unnecessary to carry out the reaction in the absence of light and that substitution a t room temperature takes place appreciably in the dark. T a b l e I-Effect
of Diffused Sunlight on Iodine Values of AcetoneExtracted P a l e Crepe REACTION IODINE PERIOD NUMBER
LIGHT
Diffused Dark Dark Dark
93
2
90 ..e
Gram 0.1033 0.1024
96
Blank
94
350
SAMPLE
97
35
93
358.3 357.6 372.7 357.8
96.10 95.90 99.97 95.97
The results obtained with pure rubber hydrocarbon under the best conditions are given in Table I1 as an indication of the accuracy of the method. An absolute accuracy of k 0 . 5 per cent appears easily attainable. T a b l e 11-Iodine
0
IION
Pn cent
Hours 3 3 19 19
Ice water Ice water Room Ice water
UNSATURA-
Accuracy of Method
Y
I 0
Vol. 19, No. 4
0.1031 0.0945 Blank
0.1038 0.1001 Blank
Values of Rubber Hydrocarbon
RE-
THIO-
ACTION
SULFATE
PERIOD
TITER
Hours
Cc. 0.1 N
16.50 16.80 46.75 16.54 19.14 46.75 16.36 17.52 46.76
THIOSULFATE
USED
pfpi::R UNE:F-
ENCE
30.25 29.95
371.7 371.2
P e r cent 99.70 99.57
Pcr cenl 0.13
36121 27.61
3ii19 370.7
99:$6 99.43
0.33
30:40 29.24
3ii:7 370.8
99:io 99.46
0.24
Cc. 0.1 N
...
...
...
32 31
Comparison of Iodine Monochloride with Bromine and Iodine Monobromide Reagents
30 REACTION T I M E - HOURS
:Figure 1-Effect
of T e m p e r a t u r e a n d T i m e u p o n I o d i n e Values
purities remaining in the rubber after acetone extraction do not react with an appreciable amount of the iodochloride. Blum and Vaubell3 found that the amount of halogen fixed by the rubber protein ranges from 2 to 7 per cent, depending on the halogen used. A fixation of 10 per cent of iodochloride by the protein in the rubber is equivalent to less than 0.1 per cent when calculated as rubber hydrocarbon. Effect of Concentration of Wijs Reagent
The results obtained by using various excess quantities of Wijs reagent on a sample of unextracted pale crepe at 11 Weber, Caspari, and Feuchter, J . SOL.Chem. Ind., 19, 215 (1900); SP, 1041 (1913); KoUoidchem. Beihefre, PO, 434 (1925). 12 The term room temperature throughout this paper is taken to mean a range of approximately 20' t o 30' C. 18 Dubosc and Luttringer, English Edition by Lewis, p. 166 (1918).
Fifth-normal solutions of bromine, iodine monochloride, and iodine monobromide in glacial acetic acid and carbon tetrachloride were used in the previously outlined procedure with certain modifications to 'determine the unsaturation of acetone-extracted pale crepe rubber. The carbon tetrachloride solutions were used in order to carry out the McIlhiney7 modification of adding potassium iodate solution to determine substitution. The results in Table I11 show that at 0" C. bromine substitutes in the rubber hydrocarbon and that McIlhiney's7 method of determining this substitution is not satisfactory owing to formation 'of emulsions. With iodochloride reagent in carbon tetrachloride the tendency for formation of emulsions is much less than with bromine. The results further confirm that iodochloride does not substitute in the rubber hydrocarbon a t 0" C. The rate of addition of iodobromide is too slow to make feasible the use of this reagent in place of the iodochloride.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1927 Table 111-Iodine REAGENT
Values of Extracted Pale Crepe as Determined w i t h Various R e a g e n t s REACTION NUMBER
REMARKS
Hours ~~.
No tendency t o form
Bra in CHsCOOH
403.0
Brz in CHsCOOH B n in CClr
381.5 (424)
‘2
Brz in CClr
(387)
1/2
3
emulsions ._ __ - __ ..
Reaction in dark Bad emulsion formed; considerable I z liberated by KIOa Reaction in dark; considerable 11liberated by KIOs; emulsion formed
IC1 in CHKOOH IC1 in cc14
292,6 302.0
IBr in CHsCOOH IBr in CHsCOOH
3
1s
good end point Reaction in dark
‘89
e-3 325:
533
Iodine Values of Various Deresinated Rubber and GuttaPercha Samples and Their Extracted Resins
The results in Table V were obtained by the use of the modified Wijs method using the procedure previously outlined. T a b l e V-Analyses
of Deresinated Rubbers, G u t t a - p e r c h a , a n d Corresponding Resins RESIN IN SAMPLE
SAMPLE
Pale crepe Pale crepe resin Smoked sheet Smoked sheet resin Smoked sheet, washed 5 hours Resin from smoked sheet, washed 5 hours Pahang gutta-percha, washed Pahang gutta-percha resin Surinam sheet balata, washed Surinam sheet balata resin Caucho, washed Caucho resin Guavule. washed Gua5ule’resin African lump, washed African lump resin
IODINE UNSATURANUMBER TION
Per cent 2.99
... 3.70 ...
358.8 145.2 359.5 134.0 360.3
...
138.5 352.3 119.6 349.3 225.1 360.6 174.7 354.0 128.9 362.8 123.3
2.97 27.4
... ...
47.0 4.60
... ...
26.2 16.9
...
Per cent 96.22
9s:43
: 94 : 50
9s 64
93:70 9s: i 3
94:90 97:32
...
The rubber samples were extracted with acetone in the usual manner. The gutta-percha and balata samples were sheeted very thin and extracted a t room temperature with acetone. Petroleum ether or ethyl ether are also very suitable solvents for the extraction of resins from guttapercha or balata a t room temperature. The results on the extracted rubber, gutta-percha, and balata samples correspond closely to the theoretical value for rubber or gutta-percha hydrocarbon, and the departures accord in each case with the known protein, dirt, and humus contents. The unsaturation of the resins from the different samples shows wide variations. Whitby’s14 work on plantation Hevea resin shows the presence of unsaturated fatty acids and sterol bodies, which would account in part for the iodine values obtained. Investigations similar to Whitby’s have not been carried out on resins from other sources. Effect of Mastication and Melting on Unsaturation of Rubber
The results in Table VI show that the milling of rubber in air for 2 hours is without effect upon its unsaturation. Fisher,Is using the authorls method of analysis, found only a slight reduction in the unsaturation of pale crepe which had been milled 2 hours in air. Smoked-sheet rubber which was melted to a completely viscous and non-elastic condition by a prolonged heating a t 280” C. in a carbon dioxide atmosphere showed only a slight decrease in its unsaturation. From this result it appears possible to change extensively the physical structure or, in other words, depolymerize the raw rubber, by heating without appreciably changing its chemical unsaturation. SUBSTANCE
REAGEXP
Theoretical
IODINE~YUMBI%R Additive Substitutive
Table VI-Iodine
Values of Smoked S h e e t before a n d a f t e r Milling a n d Melting
~-
~
Pinene Dipentene a
Terpineol a
Bra IC1 IBr Br IC1 IBr Brz IBr
186 373 165
193 204 189 300 302 282 174
1711
174 95
IODINE NUMBER
SAMPLE
10
UNSATURATION
~~
58 12 12 5
Untreated (1) Untreated (2) Milled 2 hours (1) Milled 2 hours (2) Melted a t 280° C. (1) Melted a t 280’ C. (2)
n
All in, carbon tetrachloride.
The data in Table IV bring out clearly the variations which may occur in reactions of halogens with unsaturated organic compounds. The use of the different halogen reagents in connection with the McIlhiney method has proved extremely useful in determining the unsaturation of compounds about which little is known.
350.9 351.4 351.6 351.1 348.8 349.5
P e r ccnf 94.12 94.26 94.31 94.17 93.56 93.75
Acknowledgment
Much of the experimental work mentioned in this paper was conducted by T. J. Lackner. 14
J . Ckem. SOC.(London), 1926, 1448. THIS J O U R N A L , 18, 414 (1926).
