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JULES V. HALLUM AND HARRY V. DRUSHEL
Vol. 62
structure, reversible breaking of polymeric link- cresol in peptization of aluminum soap-toluene ages, and micelle alignment in flow are affected in gels is in modification of the length of soap polyvarying degrees by peptization, then values of meric micelles and blocking off of attractive forces E v i q the activation energy for flow, calculated a t ends of the soap polymers. Such action refrom n = A eEvisIRT, should vary with the amount duces the amount of network structure, with the of peptizer present. This should be especially major effect of reducing the low rate of shear vistrue a t lower rates of shear a t which structural eleTABLE I1 ments have not been as completely destroyed as under higher flow rates. ENERGY OF ACTIVATION FOR VISCOUSFLOW 1 .84T0BY WT. Some values of Evis are shown in Table 11, ALUMINUM DILAURATE IN TOLUENE cal. EVh,cal. Moles cresol D X 10-8, calculated from flow data on 1.84% aluminum 25-50' dyne cm.-* -Evil, 17.8-25' mole soap dilaurate-toluene gels with various amounts of m1900 4200 0 1 cresol. Over the temperature interval of from '/2 1 1000 -17.8 t o 25", the value of E ~ is8 lowered with 0 1 800 increasing peptization, especially a t the lower shear 2 1 720 rate. The low values of Evi,are consistent with the 1700 4400 0 4 remarkably small changes in apparent viscosity '/a 4 1800 of the gels below 25". Between 25 and 50°, the 1 4 1800 gels studied lost much of the structural viscosity, 1200 2 4 becoming comparatively free flowing at low shear rates. This is reflected in the changed values of cosity and shear modulus and the critical shear Eviawhen calculated over the higher temperature stress a t which shear rate sensitive flow sets in. interval. It is indicated that a t some point be- The action of m-cresol is similar in important tween 25 and 50" the temperature is high enough features to dilution or to critical increase in temso that thermal forces largely disrupt the inter- perature. micellar structure, corresponding to a sort of gelAcknowledgment.-Acknowledgment is made t o sol transformation. While the equation r] = Dr. Huntington Jackson8 for use of data on which d e E v i s / R T clearly is not applicable over the range of temperatures, calculations of are useful in temperature calculations of Eviswere based, and pointing out the changing mechanism of flow with to Wladimir Philippoff for helpful advice and sugpeptization, and further study of temperature gestions. This work was conducted under contract between the Chemical Corps, U. s. Army, effects on flow rates should be valuable. and Rensselaer Polytechnic Institute. Conclusions (8) Huntington Jackson, Ph.D. Dissertation, Rensselaer Polytechnic It is concluded that the primary action of m- Institute, Troy, N. Y.,1951.
THE ORGANIC NATURE OF CARBON BLACK SURFACES' BY JULES V. HALLUM AND HARRY V. DRUSHEL Contribution from the Colzimbian Carbon Fellowship, Mellon Insliliitc of Industrial Research, Pitlsbzirgh, Pa. Receiued October 4, 1967
Evidence is presented for the existence of quinone groups and aromatic hydroxyl groups on the surface of carbon black particles. This evidence is based largely upon polarographic analyses of slurries of carbon blacks. A mechanism for the chemical interaction of carbon blacks with elastomers is proposed on the basis of these functional groups.
Introduction A recent paper by Garten and Weiss2has shown that some of the reactions of the surfaces of carbon black particles can be explained as reactions of hydroquinone and quinone structures. Most recently, Studebaker, Huffman, Wolfe and Nabors3 have shown by analysis with diazomethane and other reagents that as much as 18% of the oxygen found on carbon blacks may be present in a 1,4quinone form. Independently, by the use of infra' red and polarographic analyses, the same qualitative conclusions have been reached in these laboratories. These techniques were used to identify (1) Presented i n part a t t h e 130th National Meeting of ACS, Atlantic City, N. J., Sept. 20, 1956. (2) V. A. Garten a n d D. E. Weiss, Australia?~J . Chem., 8, 6 8
(1955). ( 3 ) M. L. Studebaker, E. W. D. Huffman, A. C. Wolfe a n d L. C . Nabors, Ind. Eng. Chsm., 48, 102 (1956).
functional groups on the carbon black particle surface. On the basis of the presence of these functional groups, a mechanism for the chemical in6eraction of carbon blacks with elastomers is proposed. Discussion of Results Evidence from Infrared Spectra.-In general, infrared analyses were unsuccessful, perhaps due to absorption and scattering of the radiation by the particles. However, in the case of a channel black of 8-10 mp particle diameter and which had a high percentage of chemisorbed oxygen the method proved t o be practical. Curve A in Fig. 1 shows the infrared spectrum obtained from a Nujol mull of this black. The baiid at 6.3 p is attributable to either condensed aromatic ring systems or t o hydrogen-
.
ORGANIC NATUREOF CARBON BLACKSURFACES
Jan., 1958
bonded, conjugated carbonyl groups. Treatment of this black with diazomethane, which would react with groups containing an active hydrogen and thus render these groups incapable of hydrogen bonding, caused a shift of this band to the normal carbonyl wave length of 5.7-5.9 p as shown on curve B in Fig. 1. A very weak band can also be noted on curve B a t about 8 p which could conceivably be attributed t o aromatic methoxy groups. If this assignment is correct, the band indicates indirectly the presence of aromatic hydroxyl groups, and that the hydrogen bonding to the conjugated carbonyl group was through phenolic hydroxyl groups. Because infrared analysis was not generally successful, these data could only be taken as indications of what types of groups to look for in other carbon blacks, especially those which did not show an interpretable infrared spectrum. Evidence from Polarographic Analyses.-In order to determine whether or not carbonyl groups were generally present on carbon black surfaces, as well as the nature of these carbonyl groups, a series of blacks were submitted to polarographic analysis. The initial results apparently were successful, since most of the blacks studied gave a large wave in the range corresponding t o quinone reduction as shown in Fig. 2. However, three obvious possibilities for misinterpretation had to be eliminated before these results could be accepted. These possibilities were: (1) that the method was intrinsically unsuited for analysis of slurries of blacks; i.e., the customary current-concentration relationship might not be observed; (2) that a reaction between the black surfaces and the supporting electrolyte, tetra-n-butylammonium iodide might be occurring to form a product which could then be reduced a t the dropping mercury electrode; (3) that the solvent employed, dimet hylf ormamide , might be extracting smaller molecules from the particles which then being in true solution could be available for reduction. Table I shows the results of varying the concentration of a given furnace black in the same slurry.
111
100
t N u j o l Bond
Fig. 1.-A, infrarea spectrum of untreated channel black of 8-10 mp diameter; B, infrared spectrum of the same black after treatment with diazomethane.
porting electrolyte and the black surfaces, is presented in Table 11. TABLE I1 EFFECTOF CHANGING THE SUPPORTING ELECTROLYTE ON HALF-WAVE POTENTIALS AND WAVE HEIGHT OBSERVEDIN SLURRIES OF THE SAME ISAF BLACK Slurry of 1.00 g . furnace black in 0.1 Y
Tetra-n-butylammonium iodide Tetmn-butylammonium bromide Lithium chloride a Corrected for ohmic potential.
Ei/za (v. u s . Hg
Wave
Pool)
height (pamp.)
-0.73
3.2
-0.79
3.8
-0.58
2.9
TABLE I The use of a different supporting electrolyte WAVEHEIGHTS A N D HALF-WAVE POTENTIALS OF THE SAME would be expected to cause the wave t o be elimiISAF TYPEOF FURNACE BLACKIN 0 1 M TETRA-%-BUTYLnated entirely or to shift radically if it were caused AMMONIUM IODIDE IN DIMETHYLFORMAMIDE Wt. of black in 25 ml. slurry,
Wave height
g.
(rainp.)
1 00 0 50 0 10 1 ooa 1 oo=
Previous runs.
E d (v. us Hg pool)
3 2 -0 73 1 5 -0 68 0 3 indistinct 3 4 -0 69 3 6 -0 69 Coirected for ohmic potential.
Since the height of the wave is directly proportional to the amount of black used, while the halfwave potential remains constant, it is possible to conclude that the polarographic method is not impractical for the analysis of these solids, assuming the other possibilities for error are not operating. The results of changing the supporting electrolyte in order to eliminate the second possibility of misinterpretation, a reaction between the sup-
by a reaction of the iodide ion with the carbon black surface. Since, as seen in Table 11, no significant shifting occurred beyond the amount expected due to a change in the system, the conclusion is drawn that the electrolyte is not responsible for the observed wave. The higher value shown for the lithium chloride solution is perhaps due to the poorly defined wave obtained with this electrolyte. The wave was not as sharp as in the case of the bromide or iodide solutions. The time elapsing between mixing the slurries and pouring them into the polarographic cell apparently had no effect on either the height or position of the wave, even when this varied from a few minutes t o three days. However, to ensure that dimethylformamide was not extracting reducible materials from the black particles, a sample of a furnace black was extracted with this solvent for
JULES V. HALLUM AND HARRY V. DRUSHEL
112
Vol. 62 I l
I
I
I
I
I
I
I
I
I
-1.10 -1.30 -I 0 Minus Volts. Fig. 2.-A typical polarogram obtained from an ISAF black in dimethylformamide using tetra-n-butylammonium iodide a8 i0
-0.70
690
supporting electrolyte.
one week in a Soxhlet extractor. The extracts were made 0.1 ill with respect to the supporting electrolyte and a polarogram was measured. The current-voltage curve obtained was indistinguishable from the residual current curve. With the elimination of these three possibilities for misinterpretation of the data, it is concluded that the waves observed are due to functional groups on the surface of the carbon black particles. The polarogram shown in Fig. 2 has only one wave. While some of the blacks showed two waves, the general case was for a single wave to appear. At first this would appear to be incongruous with the data obtained by Wawzonek, Berkey, Blaha and Runner4 on the polarographic analysis of quinones. However, since these quinone carbonyl groups are a part of the surface of a relatively large particle, the second quinone carbonyl, if it exists a t all, must be buried within the bulk of the particles themselves, and thus is not available for reduction as such. However, the valency requirements must be satisfied as will be discussed later. Those blacks exhibiting a second wave (see Table 111) could have an additional type of functional group on the surface which need not be related structurally to the quinone types of groups. A somewhat similar phenomenon has been re(4) 9. Wawzonek, R. Berkey, E. W. B l a h a n d M. E. Runner, J . Electrochem. SOC.,108, 456 (1956).
ported by M i ~ k a . An ~ activated carbon was found to depolarize a dropping mercury electrode only in a stirred system. Since in all cases reported in this paper no stirring was used, it is felt that the differences lie either in type of material used by Micka or differences in the solvent action of water and dimethylformamide upon the particles. It is possible that the failure of water to suspend a significant fraction of the particles was overcome by stirring in Micka’s experiments. The results obtained by polarographic analysis of some typical blacks are set forth in Table 111. An analysis was made on the wave occurring between -0.6 and -0.8 v. in order t o determine the number of electrons involved in the reduction and the nature of the electrode process involved. A plot of log i/(& - i) us. E indicated that two electrons are transferred in the reaction. Wawzonek, et al.,4 found that a two electron reduction of quinone carbonyl groups is to be expected if the carbonyl groups were hydrogen bonded. I n the mechanism proposed, the hydrogen would be transferred to the carbanion free radical formed and give a free radical which would reduce immediately. A plot of log i vs. log P (where P represents the mercury pressure in centimeters corrected for back pressure) for the same black gave a slope of 0.44, indicating that the electrode process is predoml(6) K, Mioka, CoZZ. Ciechoslov. Chbm. Communs., 21, 647 (1956).
ORGANICNATURE OF CARBON BLACKSURFACES
Jan., 1958
113
indicating that the reagents had converted the quinone groups t o groups not reducible in this potential range (-0.6 to -0.8 v.). Not all of the blacks studied gave a wave in the region of quinone reduction. Several blacks (see Table 111) showed waves in the region -1.54 to - 1.63 v. It is possible that this wave is due to the reduction of carboxyl groups. However, this possibility has not been investigated as yet. An analysis of the wave occurring in the area of -1.5 to -1.6 v. was carried out in the same manner as for the wave previously discussed. The plot of log i / ( i d - i) vs. E suggested that in this case, the reaction was irreversible, the value a(%,) being 0.84. The electrode process involved in this wave was likewise shown to be largely diffusion controlled since a plot of log i 9s. log P had a slope of 0.41. 1 h il :I CH3 000 A large number of the blacks studied either gave no wave a t all or gave a maximum which was, Fig. 3.-Model of carbon black particle. interestingly enough, in the range -0.G to -0.8 v. At the present time, no sound explanation can be TABLE I11 advanced for this phenomenon. However, the HALF-WAVE POTENTIALS A N D WAVE HEIGHTSOBSERVED I N SLURRIESOF TYPICAL CARBON BLACKSIN 0 . 1 M TETRA- possibilities that the presence of hydroquinone n-BUTYLAMMONIUM IODIDE I N DIMETHYLFORMAMIDE groups might affect the polarographic behavior of quinones as a result of hydrogen bonding, or that a Ei/P Wave Type of blaok b (v. us. height competing reaction may be occurring a t the mer(1.00 9.) Hg pool) (ramp.) cury pool are being investigated. Some typical 1. ISAF -0.76 3.3 blacks which display this type of behavior are listed 2. ISAF - .73 3.2 in Table IV. 3. ISAF - .71 2.8 4. 5. 6. 7. 8. 9. 10. 11. 12.
ISAF SAF ISAF
FF
-
.77 .82 - .75 -1.54 -1.56 1 0 . 7 7 , -1.69 - .78 - .57 - .62, - 1.43
2.7 2.8 3.3 6.4 1.5 2.0,0.6 127.0 1.6 56.0,23.0
ISAF ISAF High color black Lamp black Intermediate color Black (Channel) Corrected for ohmic potential. * The designafions used throughout this paper are standard rubber industry classifications of carbons. These designations usually refer to the intended uses of the final rubber stock, although the method of manufacture is sometimes implied. For example, ISAF means intermediate super abrasion furnace; SAF, semi-abrasion furnace; FF, fine furnace; HAF, high abrasion furnace; MPC, medium process channel; F T , fine thermal; HMF, high modulus furnace; EPC, easy process channel.
nantly diffusion controlled. A value t o this slope of 0.5 would indicate that the process was probably controlled only by diffusion. Deviations of the value of the exponent, z, in the relationship i = kPZ from 0.5 were not sufficiently large to suggest that either kinetic or catalytic processes are operative .6 For additional evidence that these observed waves were due to quinone reduction, it was considered necessary to cause the wave t o disappear by means of suitable chemical treatment of the blacks. The reagents chosen were lithium aluminum hydride and methylmagnesium iodide. Both of these reagents reacted vigorously with the blacks studied. I n both cases the treatment resulted in the complete disappearance of the wave, (6) J.
H. Karohmer and M. J. Walker, Anal. Cham.,26, 277 (1954).
TABLE IV DESCRIPTION OF POLAROGRAMS OF SOME TYPICAL CARBON A WAVE ON POLAROBLACKSWHICH DID NOTEXHIBIT QRAPHIC ANALYSES Position of max. (v. us. Hg pool)
T y p e of black (1.00 g.)
Height
of
max.
(pamp.)
1. ISAF -0.67 (maximum) 1.2 2. ISAF .86 (maximum) 2.6 3. ISAF - .73 (maximum) 1.5 4. HAF .74 (maximum) 1.5 No wave or maximum 5. HAF No wave or maximum 6. H M F No wave or maximum 7. LiAlHa treated ISAF" No wave or maximum 8. LiAIH4 treated MPC" 9. Grignard treated No wave or maximum MPC" No wave or maximum 10. FT a Each of these carbon blacka had shown a wave in the region -0.6 to -0.8 v. before the indicated treatment.
-
Since the few interpretable infrared spectra obtained indicated the possibility of the presence of phenolic groups on the surface, it was hoped that anodic polarography could be used to establish this group in the same manner with which quinone groups were studied with cathodic polarography. Practically all of the blacks examined gave a wave a t about f1.00 v. This wave disappears upon treatment with hydrogen peroxide or diazomethme. Both this wave, which is assumed to be due to a hydroquinone group, and the quinone wave disappear upon heating the blacks to temperatures of 1950". Table V lists some typical results from
114
JULES V. HALLUM AND HARRY V. DRUSHEL
Vol. 62
A + R-H
-
(Polymer Chai?] Step 1
"Reduced
-
Step 3 R-H
+
Secondary Alkylation
R
M 0 0 0 0 0 0 Fig. 4.-Mechanism A: proposed scheme for the ini,eraction of carbon blacks with saturated molecules.
polarograms measured in a sodium nitrate solution (0.1 M ) in dimethylformamide.
proposed that the hydroxyl and quinone groups occur on the edges of aromatic rings of these crystallites which occasionally j u t out from the average TABLE V surface of the particle. Hydrogen-bonding could HALF-WAVE POTENTIALS AND WAVEHEIGHTS OF SLURRIES then be established from a hydroxyl group to a OF SOMETYPICAL CARBONBLACKB IN 0.1 M SODIUM quinone group whether the functionalities are on NITRATEIN DIMETHYLFORMAMIDE USING A PLATINUM the same plane of a crystallite or an adjacent plane. ELECTRODE The distance is too great in the case of adjacent Wave planes (usually about 3.55 A.) to permit hydrogenEl/ I height Type of black (1.00 9.) (V. 218. SCE) (cramp.) bonding in its most effective form, but the hydrogen 1. ISAF" $0.96 9.2 atom in the hydroxyl group would undoubtedly be 2. ISAF" .95 10.5 rendered more acidic than normal. 3. ISAF" .97 11.0 Interaction of Carbon Black with Elastomers.4. ISAF" .96 10.0 Before a scheme for the interaction of carbon blacks 5. ISAF" .95 11.5 with elastomers could be proposed, it was con6. ISAF" .97 16.0 sidered necessary to determine whether or not the 7. ISAF .95 9.0 presence of these functional groups was a mere 8. EPC +1.02 3.0 triviality. T o test this possibility, a furnace black 9. EPC f1.02 3.0 in wide use in the rubber industry was chosen which 10. High Color +0.88 19.0 had both quinone and hydroquinone waves. In 11. H A F +1.05 7.2 one case, this furnace black was treated with 12. SAF +o. 98 4.0 gasesous peroxide-free butadiene. Upon polaroa Experimental carbon blacks ill the fineness range of graphic analysis, it was observed that while the ISAF. quinone wave had not been affected in any way, A. Model Carbon Black Particle.-For con- the hydroquinone wave had completely disapvenience in presenting a mechanism for the inter- peared. In a second case, the same black was action of carbon black and elastomers based on the heated to reflux temperature in 2,2,4-trimethylfunctional groups indicated by the preceding data, pentane (b.p. 99.3'); the quinone wave disappeared the model carbon black particle as shown in Fig. 3 while the hydroquinone wave remained unis first constructed. As described by Biscoe and changed. These results are summarized in Table Warren,' the internal portions of the particles are VI. occupied chiefly by graphitic crystallites. It is That this type of reaction is possible was shown by heating benzoquinone itself under reflux with (7) J. Biecoe and B. E. Warren, J . A p p l . P h ~ s .13, , 364 (1942).
+ + + + + +
ORGANIC NATURE OF CARBON BLACKSURFACES
Jan., 1958
115
t R-CH=CH-R‘ Step 1 Proton Donation
-
0
0 0
2 [R-CH-CHI-R’] 4
Step 2 Alkylot ion
w
R‘-cH~-FH R
Fig. 5.--Mechanism B: proposed scheme for the interaction of carbon blacks with unsaturated molecules.
2,2,4-trimethylpentane for three days. After removing of the solvent at reduced pressure to prevent decomposition of the benzoquinone, a polaro-
and hydroquinones exist on the carbon black surface. The following two reaction schemes are proposed t o account for the total interaction of carbon black TABLEV I and elastomers. WAVEHEIQHTS AND HALF-WAVE POTENTIALS OF A CARBON Figure 4 shows the proposed mechanism for the BLACKAFTER TREATMENTS WITH SATURATED AND UNreaction of branched, saturated molecules with SATURATED HYDROCARBONS carbon black. This scheme, mechanism A, is deEl/ z ISAF type Eli a Wave Wave (v. us. carbon black height (v. u a . height scribed using a simplified version of the model in (1.00 9.) (parnp.) He Pool) SCE) (ramp.) Fig. 3 as the quinone. Mechanism A is composed Untreated -0.72 2.80 f1.02 8.0 of three distinct steps, although all three of them Treated with -0.72 2.80 No wave . . . may be occurring simultaneously a t different porButadiene tions of the particle. The first step depends upon Treated with No wave ... +1.02 8.0 the ability of the quinone group t o abstract a 2,2,4-trimethylpentane hydrogen from the saturated chain. This would gram was run on the residue. This polarogram undoubtedly take place on the most highly substiclearly showed the presence of an oxidizable group tuted carbon atoms from which the hydrogen atoms in that a wave was observed at +O.GG v. This are more easily abstractable. In this process, the wave could not be found in either of the reactants, quinone groups are reduced to hydroquinones and while pure hydroquinone showed a wave at +OX2 the aromatic rings are attacked by the radical v. Further work is in progress to determine the resulting from the removal of a hydrogen from the chain. The product obtained as a result of this generality of both of these reactions. On the basis of this experiment it is proposed first step is referred to as the “reduced, alkylated,” that any scheme for the total interaction of carbon particle. This reduced, alkylated particle is perblack with elastomers must include the possibility haps similar to the “benzene insoluble gel” that either a branched, saturated portion of an described by Sweitzer, Goodrich and Burgess.* Obviously, the hydroquinone groups could not elastomer can react with the quinone portions of the carbon black surface or an unsaturated portion of enter into this type of a reaction scheme since they the elastomer could react with the hydroquinone are already in a reduced form and thus are inportion. That both of these routes may be taken capable of removing a hydrogen from the chain. simultaneously is a distinct possibility if both types (8) C. W. Sweitzer, W. C. Goodrich a n d K. A. Burgess, Rubber of sites occur in the elastomer and both quinones Age ( N . Y , ) ,66, 651 (1949).
116
JULES V. HALLUM AND HARRY V. DRUSHEL
However, in the presence of oxidizing agents such as sulfur or peroxides these functionalities can be converted into quinone groups for further reaction as shown in step 2 with the formation of the "oxidized, alkylated " particle. This oxidized, alkylated particle can then participate in a secondary alkylation according to step 3 to give the fully alkylated particle. This step is identical to step 1. The entire series could be repeated over and over again as long as alkylatable sites exist or as long as the oxidizing agent persists in a useful form in the neighborhood of the reaction. Even after all of the oxidizing agent is used up or removed from effective sites the reaction could proceed following air oxidation of hydroquinones to quinones. Figure 5 shows the corresponding reaction scheme proposed for the reaction of unsaturated molecules with carbon black particles. I n this scheme, mechanism B, the first step is suggested as the donation of a hydrogen ion t o the double bond of the elastomer. The formation of a carbonium ion in the elastomer is accompanied by the formation of a negative charge on the carbon particle which could shift into the ring if at all possible. Alkylation of the particle by the carbonium ion is proposed as the second step. Since it is not known whether C-alkylation or 0-alkylation takes place, both are shown. Notice that, only the hydroxyl groups which are written next to a quinone group are shown to participate in the reaction. Preliminary data, taken on rubber indicate that this is SO.^ I n the few samples tested at this date, both modulus and amount of gel decrease, if the black used in the rubber compounding mixture has been reduced, either with lithium aluminum hydride or methylmagnesium iodide. Modulus and amount of gel may be interpreted as measures of the degree of interaction of carbon black with rubber. Both of the reagents used have been shown above to be capable of reducing a quinone group on carbon black. Thus it must be concluded that the quinone groups are necessary for a complete reaction of the black surface with unsaturated elastomers, and that a hydroquinone surface alone is not enough to permit the reaction to occur. However, it is assumed that only those hydroxyl groups which are near enough to a quinone group to establish hydrogen bonding, thus making the hydrogen atoms more acidic, can donate hydrogen ions to the double bond. Further studies on these and other rubber property changes with additional blacks is in progress and will be reported at a later date. Experimental Infrared Analyses.-The infrared analyses were carried out using a Nujol mull of the black under investigation. A Baird model A infrared spectrophotometer with rock salt optics was used throughout. Polarographic Analyses.-For measuring reduction potentials, the slurries were prepared by placing 1.00 g. of a carbon black in a 25-ml. volumetric flask and diluting to the mark with a solution of N,N-dimethylformamide made 0.1 M with respect to the supporting electrolyte. Tetra-nbutylammonium iodide, tetra-n-butylammonium bromide (9) C. W. Sweitzer, Coluinbian Carbon Co., New York, private communication.
Vol. 62
and lithium chloride were used as supporting electrolytes. After shaking, the slurry was poured into a polarographic cell and the oxygen removed by bubbling high-purity, dry nitrogen through the slurry for 20 minutes. For measuring oxidation potentials, 0.1 M sodium nitrate in dimethylformamide was used. The polarograms were taken on a Leeds and Northrup Electrochemograph, Type E, using a dropping mercury electrode or a platinum electrode in the case of anodic polarograms. A mercury pool electrode was used as a reference electrode for cathodic polarograms and a saturated calomel electrode for anodic polarograms. For the capillary used, t = 2.72 see. and m = 2.895 m sec.-l yielding a value of 2.400 mg.% sec.-'/z for These values were determined for the electrode immersed in the solvent-electrolyte described above with the electrical circuit open. The dimensions of the platinum wire electrode were : area = 0.138 cm.*, radius = 0.0314 cm. This latinum electrode was mounted vertically, and a small glass ead was sealed onto the tip to reduce end effects. Grignard Treatment of the Blacks.-Methylmagnesium iodide was prepared in the usual manner and added dropwise to a stirred slurry of the black in ether. The vigorous reaction which ensued was controlled by the application of an ice-bath. After all of the reagent had been added, the mixture was stirred a t room temperature for two hours and then heated under reflux overnight. Subsequent heating to reAux temperature for an additional two hours completed the treatment. The excess Grignard reagent was decomosed by treatment with a solution of ammonium chloride. he black was collected on a filter and washed thereon with distilled water. The black was then re-slurried in distilled water with high speed stirring and filtered. This process was repeated three times. The black was then stirred with methyl alcohol, collected on a filter and washed again with methyl alcohol. After drying in air, the treated black was dried overnight in a vacuum oven at 70'. The preparation of a control black was carried out using every step in the above except the addition of methylmagnesium iodide solution. Treatment of Blacks with Diazomethane.-An ether solution of N methyl - N nitroso p toluenesulfonamide was treated with 0.015 mole of cold alcoholic potassium hydroxidel0 and the resulting solution distilled on a steam-bath directly into a test-tube containing the carbon black covered with dry ether and cooled in an ice-bath. The distillation was continued as long as a yellow color persisted in the distillate. The yellow color persisted for about two hours in the solution over the carbon black. After the color had disappeared, the ether was evaporated and the black was dried overnight in a vacuum oven a t 70". The control black was prepared by evaporating ether from a sample of the carbon black. Lithium Aluminum Hydride Treatment of Blacks .Lithium aluminum hydride was Dlaced in the thimble of a Soxhlet extractor and added coniinuously to a stirred BUSpension of carbon black in dry ether. The reaction was rather violent during the first few deliveries of the extractor. The reaction was allowed to proceed in this manner for one week. Considerable amounts of lithium aluminum hydride remained in excess. This was decomposed by the addition of wet ether. The treated black was collected on a filter and washed with ether. The black was then re-slurried in distilled water with high speed stirring and filtered. This process was repeated three times. The black was then stirred with methyl alcohol, filtered, washed again with methyl alcohol and dried in air. After drying overnight in a vacuum oven at 70", the treatment was complete. The control black was prepared by heating the black to reflux for the same length of time as above and washing and drying in an identical manner. Butadiene Treatment.-This work is a part of an unpublished study carried on in the laboratories of/Columbian Carbon Company, New York. The method consists of passing butadiene onto carbon black contained in the bulbs of a nitrogen adsorption apparatus. The difference between the measured volume of butadiene added to the sample and that desorbed by pumping the sample while heated by boiling water is taken as the volume of butadiene which reacted with the carbon black. The rcsults of this study will be reportcd in a later paper.
. d/d.
E
,
5
-
-
- -
(IO) H. J. Baker and J. de Boer, P'roc. Koninlcl. Nedsrland Akad' Wetenschap, 54B, 191 (1951).
t
NOTES
Jan., 1958 Acknowledgment.-This investigation was supported by the Columbian Carbon Corporation. The infrared spectroscopy was done in the labora-
117
tory of Dr. Foil A. Miller. The rubber measurements and the butadiene adsorption was done in the laboratories of the Columbian Carbon Corporation.
NOTES T H E 0-H BOND LENGTH AS A FUNCTION OF T H E 0 . .. . .O DISTANCE IN HYDROGEN BONDS BY HANSFEILCHENFELD Petrochemistry Laboratory of the Research Council of Israel and the Department 01Physzcal Chemibtry, Hebrsiu University, Jerusalem, Israel Received Auoust 13, 1967
Recently it has been proposedl that the energy of the different C-C bonds is related t o their length by the equation
0-H distance is about 2% and the distance enters equation 2 in the third power. For large 0. . .O distances (E' -t 0) the actual error is even smaller than it might seem. F o r instance, in the casea of Crt(0H)z La.0 = 3.333 A. and LO-= = 0.984 A. The second term of equation 2 becomes therefore 7 kcal./ mole. The error in taking E' as 6 kcal./mole instead of 0 is automatically compensated for by the fact that even though no hydrogen bonding occurs, the distance of a hydrogen atom to the nearest oxygen atom of an adjacent molecule is finite.
Inserting the above numerical values for E 4-
which holds also for the C-H bond though with different k . It would be interesting to investigate whether the 0-H bond length is not connected to the 0-H bond energy in a similar way. In a normal 0-H bond E
=
E' and IC, equation 2 becomes 1
1 + (LO..O
- LO-H)a
=
1.20
'4.-
(3)
T o test the correctness of the equation, LO-H is plotted against LO. .O in Fig. 1. The experimental
110 kcal./mole 1.20 -
and
LO-= e 0.958 A. which leads t o k = 96.7
A.8
1.15
kcal./mole.
Since the 0-H bond length is practically constant except in hydrogen bonded molecules, equation 1 can only be tested by application t o the latter case. Fortunately a number of measurements of 0-H. .O distances have been made recently for linear hydrogen bonds. Using equation 1 both for the 0-H bond and the H. .O hydrogen bond leads t o the equation
-
'\ 'I
I
od1.10 d
d
bJ
1.05
1.0
where IC is given above and E and E' are the 0-H and H . . 0 bond energies, respectively. Though both E and E' vary with the 0. . . .O distance, the sum E E' remains virtually unchanged. Actually what is usually termed hydrogen bond energy is the energy increment of the hydrogen bonded over the not hydrogen bonded structure. This increment amounts in the case of the 0-H. .O system on the average to 6 kcal./mole12 i.e.
+
+
.
E E' = 116 kcal./mole The error introduced by this simplification will in general not be greater than 3 kcal./mole. This is bearable since anyhow the error in the experimental determination of the (1) H. Feilohenfeld, THISJOURNAL, 61, 1133 (1957). (2) C. A. Coulson, Research, 10, 149 (1957).
'
0.95 2.25
I
2.50
3.0
3.5
L o . . . .ol A. Fig. 1.-Plot of the 0-H bond length against the 0. .O distance: 0,experimental data$ -.-.-., curve due to Welsh;' - - -, curve due to Lippincott and Schroeder.6
..
-
results are shown by circles (for original references see 4). The fully drawn curve shows the plot calculated according to equation 3. For comparison's sake some other curves recently proposed have been included. Lippinmtt and Schroeder6 base their curve on a n expression derived from (8) (4) (6)
W. R. Busing and H. A. Levy, J . Chcrn. Phyr.,
26, 563 (1957).
H. K. Welsh, ibid., 86, 710 (1957). E. R. Lippinoott and R. Scbroeder, ibid., 23, lOQQ (1955).
