ride is not present, 60 mg. of silver can be tolerated. Iodide is destroyed by boiling the solution with concentrated HSOa before the extraction of palladium. The interference of SzH4 is eliminated by extracting it with salicylaldehyde from acid solution. Nature of the Extracted Species. The extraction of yellow color into nonpolar organic solvents suggests t h a t palladium(I1) is probably extracted as a neutral species into the organic phase. T h e composition of the extracted species has been determined by Job’s continuous variation method (2, 3 ) . The curve (Figure 2) obtained by plotting absorbance against R (1-01. of Pd soln./vol. of Pd soln. vol. of H I S A S soln.) shows two maxima at the points corresponding to H1NAA:Pd equal to 1:l and 2 : 1, which are independent of concentrations of reactants and the wavelength of the light employed. The reaction of HINAX with palladium may therefore be represented as follows:
+
+ HINAA f Pd(ISA.4) + H + Pd(I?;-&A) + HIXAA + Pd(1Srlh)z + H + Pd-2
+
+
The yellow color extracted into CCll from solutions containing palladium
and excess of HINXA is due to a neutral chelate, Pd(IKAA)?. Precision, Accuracy, and Sensitivity. The precision and accuracy of the proposed method were tested by analyzing solutions containing known amounts of palladium according to the recommended procedure. The average of 10 determinations with 5.00 pg. of P d per ml. is 5.01 pg. and it varies between 5.07 pg. and 4.96 pg. at 95% confidence limit. The practical sensitivity of the method is 1.5 pg. of Pd per ml. of solution. However, the sensitivity can be increased by volume concentration techniques. ACKNOWLEDGMENT
Our grateful thanks to A. B. Kulkarni, Institute of Science, for providing facilities to use the Hilger and Watts ultraviolet spectrophotometer. The authors also express thanks to James R. DeVoe, U. S. National Bureau of Standards, for his constructive comments on the original manuscript. LITERATURE CITED
(1) Feigl, F., “Chemistry of
Specific, Selective and Sensitive Reaction,” R. E. Oesper, transl., p. 209, Bcademic Press, New York, 1949. (2) Irving, H., Pierce, T. B., J. Chem. SOC. 1959, 2965. (3) Job, P., Ann. Chim. 9, 113, 1928.
Table II. Masking Agents Required to Suppress the Interference by Other ions
Interfering ions
Masking agents added Mercuric nitrate Ammonium molybdate Tartaric acid Sodium fluoride Potassium sulfate Ferric chloride Sodium molybdate hydrogen peroxide f sulfuric acid
+
N.J., h1.S~.thesis, University of Bombay, India, 1965. (5) Sandel!, E. B., “Colorimetric Determination of Al‘etals,” Interscience, Kew York, 1959. (6) Taylor, T., EqFbank, E., J . Chem. Xoc, 1926, 2819. (7) T’ogel, 8. I,, “Textbook of Quantitative Inorganic Analysis,” Longman’s Green Pvt. Ltd., London, 1962. (8) Welcher, F. J., “Organic Analytical Reagents,” Vol. 111, p.2 80, Van Nostrand, Kew York, 1955. (4) Patel,
U. B. TALWAR B. C. HALDAE
Inorganic and Nuclear Chemistry Laboratory Institute of Science Bombay, India WORKsupported by Grant PL 480, U. S. National Bureau of Standards, and a research scholarship (E. B. T.), University Grants Commission, India.
Analysis of Diaminotoluene Isomer Mixtures by Nuclear crg netis Resonance Spectrometry SIR: The diaminotoluenes (D.A.T.’s) are important commercial compounds. They are intermediates in several largescale manufacturing processes-e.g., in the production of polyurethane foams where large quantities of toluene diisocyanates are prepared from the diamines. The diamines themselves are normally obtained by reduction of the dinitrotoluenes (D.N.T.’s) produced by direct nitration of toluene under allpropriate conditions. The nitration gives a mixture of isomers, mainly 2,4and 2,6-D.N.T. with smaller amounts of 2,3- and 3,4-D.N.T. and possible traces of the 2,5-isoniera When the D.K.T.’s and D.A.T.’s are process intermediates, it is often important t o know the isomer proportions, but hitherto no satisfactory single method has been available for a full quantitative analysis. For the D.A.T.’s, isomer content information can be obtained by a coinbination of several methods. Reaction with acidified SaNOz followed by ultraviolet examination of the resulting bisdiazonium derivatives can give the ratio
of 2 4 - to 2,6-isomers. The standard colorimetric test, using a diketone to give the o-diamine content, determines the sum of the 2,3- and 3,4-isomers. The colorimetric test with iron(II1) chloride gives the p-diamine content arising from any 2,6-isomer. However, it has been shown (2) that D.K.T. isomer mixtures can be analyzed by nuclear magnetic resonance ( N X R ) using the fact that the methyl proton resonances of all the isomers are slightly separated in CDCls solution. This same approach has now been tried for the diaminotoluenes. Each of the three chemical methods mentioned above is able to give results for part of the isomer analysis more accurately than NILIR. However NMR gains by giving a quick and convenient method of analysis of all four main components with an accuracy sufficient for most; purposes. EXPERIMENTAL
Apparatus. A Varian A.60 spectrometer was used with tetramethylsilane as an internal reference. Chemical
shifts are quoted in 6 units-Le., p.p.m. downfield from T.M.S. Chemicals, 99.5% CDCh was obtained from Ciba (A.R.L.) Ltd. Samples of the diaminotoluene isomers were available elsewhere in this Department and the N M R spectra themselves were used as a check for impurities. RESULTS AND DISCUSSION
Reference spectra in CDC13 were obtained for all the D.A.T.’s with the exception of the 3,5-isomer, which is not found in the systems under discussion. The results are given in Table I for 20% w./v. solutions. I t can be seen that a full analysis using the aromatic proton signals is not possible. The ratio of the 2,4- and 2,6-isomers can be obtained, but the substituent chemical shift parameters (1) predict little difference in the shift positions of all the aromatic protons in the 2,3-, 2,5-, and 3,4-isomers, and one overlapping set of signals is found experimentally for these minor components. For the 2,4- and 2,6-isomers where the aromatic proton signals are more widely VOL. 38, NO. 13, DECEMBER 1966
e
1931
scpratcd, J vnlucs (r.)s,) obttiinrd from the spertra art1 alri) rworded. For the methyl protons, small dnrvrifield chemical shift changes of about 0.02 p.p.in. were apparent for all five *iwniers on tlilution from ZO(g w./v. to 5%, w./v. The ~ireviouswork on the D.N.T.’s (P) showed, however, that the methyl group proton chemical shift,s in mistures of the isomers can be different from those in snlutioir3 of the pure components. The last rnlunin in Table I, therefore, shows the chemical shift positious 6C&’ of the I?..l.‘l’. i:lumt.rs in a misture of th- five components (total concn. 2570 w.;v. in CDCIl3). The L‘k& resonances cf the four irnportqnt isomers, the 2,4-, 2,6-, 2,3-, and 3,1-D.A.T.’s are now separated and can be used to give a method of analysis of the isomer misture. Variations in the CH3’ positions of about 0.02 p.p.m. ran be found as the relative propfiiiiuus of the isomers change, even though the tots1 isnmpr ccxcntratioii is kept constant at 25% v;.,;v, These small shifts are not enough to cause any confusion in identifying the methyl group signsls of the four isomers, however. The 2,5-i.onzer peak is close to that of the 2,4-isonier, but this is not a serious hindrance, because the 2,sisomer is normally present only in trace amounts. T h k point is discussed more fully later.
NMR
Table 1.
Data for Diaminotolucncs in CDCh Solution 6 Aromatic
BCH,‘
6 45-6 65 (close multiplet)
2.13 2.12 2.04 2.00
Isomer 2.19 2 19 ‘2.10 2.05
6 64 (single peak) 6 5‘3 c-ingle peak) €16. 6 81 Hs,6 07 J S S= 7 5 H a , 6 IK)Jae = 2 4 HI, 6 81 Ha, 6 14 J ~ = c 7 8
I .h9
Table 11.
42.951 i.25 4 $3
1 ,70 2.04 2 69 0 90 2.82 6.92 2.04 1.94 1.00
1932
1.85
Analysis of Diaminotolucnc Isomer Mixtures Using Methyl Proton Peak Heights
Mole 2 3,4
To asses3 the accuracy with which nnalyscs can be made using the mcthyl proton peaks, weighed mixtures of tlir D,A,‘l’, isomers were prepared. The mixtures were examined in CDClS solution on an A.60 spectrometer undw the following conditions; concentration N 25% w./v. (0.12 gram of isomer mixture in 0.5 cc. of CDCIa is sufficient): Rf 0.2 mg.; filter band-width 4.0 c./s.; sweep width 250 c./s.; sweep time 250 seconds. Becaue of the similarity of the compounds, direct measurenicnt of the me?hy! proton peek heights of the D.A.T. isomers gave results which were as accurate (and indeed, for components below the 10% level more accurate) than the conventional peak area measurements performed by the electronic integrator of the A.60. The average peak heights of two upfield and two downfield scans of the methyl proton region werr taken. Table I1 compares the mole percentages of the mixtures caicuiard f i ~ the i i~eigbts~ i t those h derived from the rnethq-1 proton peak heights. The results show that the estimation of the four main components is straightforward. The following conclusions can be drawn from Tab16 11. For a component present below the 10% level, XJIR ovcrestimates by about 0.5% ai,solute. At the 10 to 50% level, S M R gives results accurate to within 2 1.5%. Above the 50% ievel,
2,s-
2 Wt.
2,,>
2,416.16
ii !>7
4.hl 3.M 3 01 3 I9 0 90 0 55 7.08 1.92 2.x 1 20
6.W 2.08 1.02 0.64
62.71 64 53 74.47 -. 12.74 GO 89 75.22 76.96 64.84 60.04 74 72.20
ANALYTICAL CHEMISTRY
Mole yr by NMR 2,&
21
o7 25.73 20 19 22.21 24 23 22 9s 19.65 15.16 33.92 20 02 24,M
3,448 3 7 8 5 3 2 0 2 8 2.8 0.9 3.6 7 1 2 0
2.0 1.1
2,s
2,s
9 8 5 8 4.2 3.2 3.5 J .O
...
8.2 2.3 3.7 1.4
7.4 4.2
24-
2,z-
15.7 60.3 61.6 71.8 69.5 67.7 72.9 74.9 60.8 57.4 72.7 70.7
36.0 21.1 27.4 22.0 24.5 26.0 25.0 21.5 16.5 34.1 21.6 26.8
NMIi unclrrebtiiiiuteb a coinporwnt by about 2.5‘% ahillrte. ‘I%> Jciw(int detertahlc ainourt L of i r i i n o i i w n i e r (3,4and ‘2,3-I),A.T.) is ahout U.H‘&. Vuriations in R , power or c’wq)C(JIldltI(l1lS from those giver1 &b(JVt. were not foiind to give bctter rwiults. The last four samples in Teble 11 nhow the eifrcl of small amountn fJf the 2,5isonier. A t the normul levrli.e., below l%,--this iwinrr is not, tietectcd arid does not interfcir with the analysis of thc other comlionrnts. Above the 1.5Yl level, a separate r)cak is observed for this isomer a t the babe of thP large peak due to the 2,4-immer which ia normally the major component of the mixture. When this peak is used, the 2,5-isonier omtent is overestimated somewhat, while the 2,4-isoiner content is underestimated, but the method enables the presence of abnormally large amounts of the 2,5-isomer to be detected qiialitRtively. I s miytw-es of i)..4.T.’s obtnined by the reduction of D.N.T.’s, the most probable impurities are unreacted dinitrotoluenes and also the half reduced products, the mised monoaminoIiitrotoluenes. Both these classes of compounds can be recognized readily since they have specific methyl proton peak ranges sepnrated from that of the cliaminotoluenes Thus the methyl proton peaks of the various D.S.T. !scn~e:’srani;; f r m 2.4 tu 2.Sb 111 CIiC i3, while those of the mixed aminonitrotoluenes are fourid apprournately midway between the D.A.T.’s and tile Il.N.T.’s-i.e., centered around 2.36. I t is perhaps worth noting that if, as is usually the case, the small samples of D.X.T.’s or DA.T.’s required for XMR snalysis have been taken from the molten main product, then these samples must be remelted and homogenized prior to being used to make up the SJIR solutions, in order that any errors due to preferential solidification of the isomers may be avoided. Also for a routine series of samples, because the S M R method of analysis involves only the alkyl proton region of the spectrum, CHCI, can be used as solvent rather than the more expensive C‘DCl~. LITERATURE CITED
(1) Jackman, I,. \I., “Applicittioiis of
NMR Spectroscopy in Organic Chemistry,” Chap. 4, p. 63, I’ergarnon Press, London, lY5!). (2) Mathias, A., .4nal. Chitn. Acla 35, 376 (1966).
ALAN3IamirAs Imperial Chemical Industries Ltd. Dywtiiffs 1)ivisioii Rlaekley, hlaiichebter England
