without great modification of the existing equipment. Analysis of Blood Plasma Samples. Several dozen blood plasma samples were analyzed directly by the continuous enzyme procedure by diluting 0.2 ml. of plasma to 10 ml. 1%-ithbuffer solution, and the values were compared with those obtained by a n automated ferricyanide procedure. Agreement was roughly in accord with previous comparisons ( 9 ) . No mechanical or chemical difficulties were observed with the plasma samples. The continuous enzyme procedure was also tested on standard commercial blood samples. Results on a standard blood plasma sample (Dade Reagents, Inc., Miami, Fla.) were 17% lower than the value of 118 mg. yo given on the label for the method of Folin and Wu. Three consecutive re-
coveries of 100 mg. % of glucose added to the same standard sample gave an average of 94.6% with a range of 92.6 to 97.2%. Unequivocal evaluation of the accuracy of the continuous enzyme procedure by comparison with other accepted methods of glucose analysis is difficult, because of considerable differences among the methods ( 9 ) . Investigation of these differences is under way in this laboratory.
REFERENCES
(1 ) Devlin, T. M., -4h.a~.CHEV. 31,
977 (1959).
( 2 ) Furness, F. K.,Easton, C.. eds., X. Y . Acad. Sci. 87 (Art. 2 ) , 609-951 (1960). (3) Hill, J. B., Kessler, G., J . Lab. Clzn. M e d . 57 (6), 970 (1961). ( 4 ) Malmstadt, H. V., Hicks, G. P., h A L . CHEhZ. 32, 394 (1960). (5) Malmstadt, H. V., Pardue, H. L., Ibzd., 33, 1040 (1961). (6) Middleton, J. E., Brit. X e d . J . 1, 824 (1959). (7) Noller, C. R., “Chemistrj- of Organic Compounds,” p. 553, R. B. Saunders,
Philadelphia, 1951.
(8) Salomon, L. L., Johnson, J. J., .$VAL. ACKNOWLEDGMENT
The authors thank Frank C. Larson, of the University Hospitals, Madison, Wis., for supplying blood plasma samples that had been analyzed by the automated Technicon ferricyanide method.
Titrimetric Determination of p-Phenylenediamines
CHEM.31. 453 (1959).
(9) SunderiAan, F. W., Jr., Sunderman, F. R., Tech. Bull. Registry X e d . Technologists 31 (B), 93 (1961). RECEIVED for review September 15, 1961. Accepted December 18, 1961. \Tork sup-
ported in part by a grant from the \Tisconsin Alumni Research Foundation, and in part by a grant from the C . S. Atomic Energy Commission.
N, ”-Disubstituted
OTTO LORENZ and C. R. PARKS Research Division, The Goodyear Tire & Rubber Co., Akron, Ohio
b A spot test is described for the detection of N,N’-di-sec-alkyl-, N-secalkyl-”-aryl-, and N,N’-diaryl-pphenylenediamines in rubber compounds. The test is based on the deep coloration of the corresponding Wurster’s salts. Titrimetric methods for the quantitative determination of these diamines are discussed, including N,N’diaryl-p-quinonediimines as well as mixtures of N,N’-diaryl-p-phenylenediamines and their corresponding diimines. The determinations are based on a neutralization with perchloric acid in nonaqueous solution. The N,N’diary1 derivatives were converted to the Wurster’s salts by the addition of chloranil or hydroquinone prior to the neutralization.
compounds. This test permits one to differentiate the three types of p phenylenediamines An investigation of the neutralization of p-phenylenediamines in nonaqueous solvents showed that N,N’-disec-alkyl- and N-sec-alkyl-N‘-aryl-pphenylenediamines could be determined readily in this way. The N,N’-diary1 derivatives did not give satisfactory titration curves because of their low basicity. By the addition of chloranil, however, diaryl-p-phenylenediamines were oxidized to the Wurster’s salts with the formation of one equivalent of base which could be neutralized by acid. A similar procedure was applicable to the determination of N,N‘diaryl-p-quinonediimines, or mixtures of these diamines and diimines. I
20 ml. of acetone for about 10 minutes at room temperature. After the addition of each drop of the diamine solution, the solvent was allowed to evaporate before the addition of the next drop. The amount of diamine placed on the filter paper in this way should be 10 to 100 fig. One drop of chloranil solution and, after drying, 1 drop of the acid mere added to develop the color which appeared at once. With dialkyl-p-phenylenediamines a reddish color was formed which deepened after the addition of acid but faded after several minutes. Alkyl-aryl-p-phenylenediamines developed a violet or blueviolet color which also usually faded after several minutes. The coloration formed by diaryl-p-phenylenediamines was blue or blue-green and was usually stable. Titration with Perchloric Acid.
T
of p-phenylenediamine derivatives used extensively as antioxidants and antiozonants in rubber compounds are N,N’-di-sec-alkyl-, N sec-alkyl-”-aryl-, and N,N‘-diaryl-pphenylenediamines. Available methods for these compounds are based mainly on a colorimetric determination of their colored oxidation products, the Wurster’s salts (2) or the p-quinonediimiines (1, 7). The deep coloration of the Wurster’s salts was used as the basis of a spot test for the rapid detection of these diamines in rubber HREE TYPES
394
ANALYTICAL CHEMISTRY
EXPERIMENTAL
Spot Test for p-Phenylenediamines.
REAGENTS. Hydrochloric acid, approximately 0.1N in isopropyl alcohol or perchloric acid in glacial acetic acid. Chloranil, 0.2y0solution in acetone. PROCEDURE. A solution containing 5 to 10 mg. of the diamine in 10 ml. of acetone was added dropwise onto filter paper with an eyedropper or small pipet. The acetone extract of a rubber compound can also be used, in which case about 1 gram of rubber was cut in small pieces and extracted with 10 to
AP-
p H Meter, Beckman Model 9600 Zeromatic with glass indicator and sleeve-type silver-silver chloride reference electrodes. Microburet, 2 ml. REAGENTS.0.1N Perchloric acid in glacial acetic acid, chloranil, hydroquinone. SOLVENTS.Acetone, glacial acetic acid, acetonitrile, isopropyl alcohol, ethylene glycol. All solvents m-ere purified by distillation except acetic acid which was reagent grade. All the p-phenylenediamine derivatives were purified materials and are listed in Table I. Most of the pphenylenediamines were prepared by R. B. Spacht and his associates. PARATUS.
Table 1.
Titration of N,N’-Disubstituted p-Phenylenediamines with Perchloric Acid in Nonaqueous Solvents
ALP., O
c.
uncorr.
Weight Taken, MilliMg. mole
0.1005
Solvent
HC10,. 311.
Recovery,
70
Dialkyl-p-phenylenediamines
S,N’-Bis( 1-methylhepty1)- 36,5-38 41.65 0.1252 41.65 0.1252
Acetone 1.255 Acetonitrile 1 , 2 6 5 2.515 (2nd
0
1.0
2.0
3.0
break)
40
106-107
ML. OF 0.100 N HCLOI
Figure 1 . Titration with 0.1N perchloric acid: 41.65 mg. (0.12 5 2 mmole) of N,N’-bis(l -methylhepty1)-p-phenylenediamine
Solvents: A. HAC 8. Acetonitrile C. Acetone
PROCEDURE. Titration of A7,A7’di-sec-alkyl- or N-sec-alkyl-N’-aryl-pphenylenediamines. A 20- to 100nig. sample was dissolved in 50 ml. of the chosen solvent. Standard perchloric acid solution was added with stirring in 0.1-ml. increments, 0.05-ml. additions being made in the neighborhood of the inflection point. Care was taken to keep the tip of the buret beneath the surface of the liquid. Titration of IL’,N’-diaryl-p-phenylenediamines. A 20- to 100-mg. sample was dissolved in 50 ml. of glacial acetic acid. A pinch of solid chloranil was added lvhich colored the solution a deep blue-green. The amount of chloranil added must be a t least equal to or greater than one half of the molar concentration of the diamine. Standard perchloric acid solution was added in increments with stirring. A break in the titration curve was observed after an equimolar amount of perchloric acid had been consumed, the solution turning deep blue a t the end of the titration. Titration of S,S‘-diaryl-p-quinonediimines. The procedure is the same as described above for diaryl-p-phenylenediamines except that hydroquinone was added to thp acetic acid solution of the diimine before the titration (instead of chloranil) . Titration of mixtures of N.N’-diarvlp-phenylenediamines and N,N’-diar$lp-quinonediimines. A mixture of the tn.0 compounds dissolved in glacial acetic acid formed a dark green solution. Standard perchloric acid was added with stirring. If the diamine was in excess, a first inflection point appeared corresponding to twice the molar amount of diimine present. Chloranil was then added and after further addition of perchloric acid solution, a second break n-as observed corresponding to the sum of diamine and diimine. If the diimine was in excess, the first break corresponded to twice the molar amount of diamine. Hydroquinone was then added. The second break again correspondcd to the sum of diamine and diimine.
100.2 101,o 100.4
41.65 0.1252 Acetic acid 2 , 5 0 26.85 0.0985 Acetone 0.97 26.85 0.0985 Acetonitrile 1.00 1.99 (2nd 26.85 0.0985
break) Acetic acid 1 . 9 5
99.8 98.5 101.5 101.0 99.0
Alkyl-ayyl-p-phenylenedi-
amines
S-Isopropyl-.\-’-phenyl-
N-Cyclohexyl-A: ’-phenylDiaryl-p-phenylenediamines
N,iV’-DiphenylK-Phenyl-S ‘-o-tolyl
81
76.9 93.8 89.2 85.2
0.3398 Acetone 3.34 0.4145 Acetonitrile 4.07 0.3942 Acetic acid 3 . 9 0 0.3765 Isopropyl 3 . 7 2
98.3 98.2 98.8 98.8
alcohol Glycol (1: 1) 119-120 47.8 0.1794 Acetone 1.795 23.9 0,0897 Acetonitrile 0.905 23.9 0,0897 Acetic acid 0.895
100.1 100,9 99.8
Acetic acida 1.435 Acetic acida 2 125 Acetic acid“ 2 95 ilcetic acida 4 885 iicetic acida 1 085 Acetic acid“ 1.965 .4c~t,icacid0 3 18 acetic acida 4 128 Acetic acida 3.595 Acet,ic acida 3.305 Acetic acida 3.675 Acetic acida 3.24 Acetic acid” 5.09
97.8 98.6 97.2 97.1 98.0 97.0 96.7 96.8 99.6 98 .? 97.4 98.7 96.2
154
3 8 . 2 0.1467 56.1 0 2155 79 0 0 3035 130 9 0 5029 130 30 35 0 1107 55 55 0 2025 90 2 0 3288 121.3 0,4422 121 99.0 0.3610 151 91.9 0.3350 135-136 108.8 0.3773 183 9 4 . 8 0.3288 98.5 167.4 0.5292
K-Phenyl-N’-m-tolylN-Phenyl-N’-p-tolylA’,”-Di-o-tolylN,S’-Di-p-tolyl.V,N’-Di-o-ethylphenylDiaryl-p-phen ylenediimines N,N’-Diphenyl180 86.0 0,3330 Acetic acidb 3.245 X ,N’-Di-p-tolyl124-125 35.05 0,1224 Acetic acidb 1,185 Chloranil added. b Hydroquinone added.
97.5 96.8
Q
RESULTS A N D DISCUSSION
The deep coloration of the univalent oxidation products of p-phenylenediamines, the Wurster’s salts, can be used for the qualitative detection of this class of antioxidants and antiozonants in elastomers. Results showed that i t was possible to distinguish by the color developed between N,N’-disec - alkyl - (red), N - sec - alkyl - N’aryl- (violet or blue-violet), and N,N’diaryl-p-phenylenediamines (deep blue or blue-green). If mixtures were present, a blue or blue-violet color predominated. The limit detectable by this method was about 5 pg. for N , N ’ diphenyl - p - phenylenediamine, somewhat larger amounts being necessary for N , N ’ - dialkyl - p - phenylenediamines. Tetraalkyl substituted p phenylenediamines gave intense violet colorations under the same conditions and, if present, would interfere with the test. These substances, however, are not commonly used in rubber compounds. p,p’-Diaminodiphenylmethane
and 6 -substituted 1,2 - dihydro - 2,2,4trimethylquinolines produced slight colorations, although their presence generally did not interfere. The structure of the deeply colored Wurster’s salts is that of a paramagnetic diaminium cation which is in equilibrium with a diamagnetic dimer (6). The paramagnetic monomer is stabilized by resonance between the two equivalent structures and B taking place through structures such as C and D (6):
B
C
D
Neutralization with perchloric acid in nonaqueous solution was suitable for the quantitative determination of VOL. 34, NO. 3, MARCH 1962
395
A‘,iV’-di-sec-alkyl- and S-sec-alky1-N’aryl-p-phenylenediamines, the end point being detected potentiometrically. The results (Table I) show that both amino groups of N,iV’-dialkyl-~-phenylenediamines could be neutralized. The shape of the titration curve, however, d(Jpended somewhat on the solvent that was used. I n acetonitrile two inflection points were observed, one after the neutralization of each amino group. Using acetone, only the first break was sharp. I n glacial acetic acid only one break was observed corresponding to the neutralization of the tn-o amino groups. Figure 1 shows the titration for Ar,A;’-bis( l-methylheptyl)p-phenylenediamine using different solvents. The titration of Y--sec-alkyl-Ar’aryl p - phenylenediamines with perchloric acid gave only a single break corresponding to the neutralization of one amino group independent of the solvent that TVaSused. Evidently the amino group containing the aromatic substituent is not basic enough under these conditions to give a sharp end point, This ’ L ~ a s by the fact that N,N’-diaryl-p-phenylenediamines could not be titrated satisfactorily evcn in glacial acetic acid. iV,.V’ - Diary1 - p - phenylenediamines could be determined quanbitatively in acetic acid solution by titration with perchloric acid provided chloranil had been added previously. The addition of chloranil oxidized the diamine to the corresponding Wurster’s salt and raised the apparent pH value from about 0.5 to 1.0 indicating that a stronger base than the diaryl-p-phenylenediamine itself had been liberated. This base is either the acetate anion, the anion of tetrachlorohydroquinone, or that of its semiquinone. A sharp break in the titration curve was observed after one equivalent of perchloric acid had been added. Chloranil must be present in a molar ratio of diamine to chloranil 7 2. An excess of chloranil did not influence the titration results. The stoichiometry of the reaction can be described by
-
chloranil or hydroquinone had been added) a break in the titration curve was observed corresponding to twice the concentration of that compound present in the lower concentration. The break, however, was not very pronounced. This reaction can be described as follows :
2 5
100 YV.
u‘
ADDED
H
R’ 0
0.5
1.5
1.0
ML. OF 0.100N HCLO,
Figure 2.
R
2.0
+ 2H + -,
HAC
R-fi=a= fi-R -
(4)
Titration of a mixture:
H
30.67 mg. (0.1 178 mmole) of N,N’-diphenyl-pphenylenediamine and 9.62 mg. (0.0372mmole) of N,N ~-diphenyl.p-quinonediimine
After this titration chloranil (or hydroquinone) was added and the sum of The results of the determination of diamine and diimine was determined on different N , N ’ - diaryl - - phenylenethe Same sample. A typical titration curve obtained with a mixture of :ITIN’diamines by this method are listed in diphen3‘l-p-Pheny1enediamine and ~v11v’Table 1. Ar-Alkyl-N’-aryl-p-phenylenediamines could also be determined by diphenyl-p-quinonediimine is shon-n in Figure 2 , this method. Glacial acetic acid, howThe described methods have been ever, was the only suitable solvent as in to inrestigate the kinetics of all other solvents investigated, results theconsumption Of p-phen!.Ienediamines [yere as low as 90% of the theoretical l.nlue, Dialkgl-p-phenylenediamines during t.he oxidation of vulcanized prepared samples rubbers. behaved differently as no sharp end were used for this investigation to I,oint ITas observed when the eliminate the effect of natural or added ~ y a s carried out in the presence of antioxidants as well as vulcaiiizat,ion chloranil. l~7,i$rt - Diaryl - phellylenediimines residues. These ingredients were resuitable could also be titrated TVithperchloric moved by extraction solvents such as acetone or chloroform. acid in acetic acid solution but only after the diimine had been reduced to The p-phenylenediamines were then the jyurSter’s bJT, e.g., hydroadded to the extracted vukanizates by in a benzenethe quinone, Table 1. 24nalogous to Equaacetone solution containing a known tion one can formulate the following concentration of the diamine. Results stoichiometry of these investigations have been reported elsewhere (4). For the de2 n-N===y-~ __ + termination of p-phenylenediamines in factory stocks by the described titraKBc tion method, interferences can be 2 H+ (3) HOO -H anticipated from the presence of oils and certain other amines such as H diphenylguanidine. Compounding oils 2 R) $ e f i < z f can be readily separated, however, using chromatographic techniques ( 3 ) .
’
+
-
( R = aryl) LITERATURE CITED
R
c1 c1
c1
c1 (2)
2
H
R
+
R
c1
c1 396
0
c1
C1
(R =aryl)
ANALYTICAL CHEMISTRY
Equations 2 and 3 indicate that in the presence of mixtures of diaryl-pphenylenediamines and their corresponding diimines the sum of the two compounds can be determined if care has been taken to convert both compounds to the Wurster’s Thir was done adding c h l o r a d to the acetic acid solution if the diamine was present in a larger concentration, or by adding hydroquinone if the diimine was in excess. It was also possible to determine the concentration of that component of the mixture present in the lower concentration. When perchloric acid was added to a mixture of diamine and diimine (whereby no
(1) Burchfield, H. P., Judy, J. N.,ANAL. CHEM.19, 786 (1947). (2) Hilton, C. L., Ibid., 321 1554 (1960). (3) Hively, R. A., Cole, J. O., Parks,
c. R,, Field,
E., Fink, Raymond,
J.
Zbid., 27, 100 (1955). (4) Lorenz, 0.) Parks, c. R., Rubber Chem. and Technol. 34, 816 (1961). (5) Michaelis, L., Schubert, M. P., Granick, S., J. Am. Chem. SOC.61, 1981 (1939). ( 6 ) Pading, L., “The Nature of The Chemical Bond,” 3rd ed.7 P. 360, Cornel1 Univ. Press, Ithaca, N. Y., 1960. (7) zijv J. W. H., Kautschuk u. Gummi 10. 1 T 14 (1957).
.
,
RECEIVED for review August 22, 1961. Accepted December 21, 1961. Contribu. from The Goodyear ~i~~ & tion N ~ 273 Rubber Co., Research Division.
