(26) J. Maire and J. Mering, Graphitization of Soft Carbons, from "Chemistry and Physics of Carbon", Vol. 6, P. L. Walker, Ed., Marcel Dekker, New York, 1970. 127), E. Grushka. Ed.. "Bonded Stationaw Phases in ChromatmraDhv". Ann Arbor Science Pub.,'Ann Arbor, Mich., i974. (28) P. R. Moses, University of North Carolina, 1975, unwblished results. (29) K. Siegbahn et al., "ESCA, Atomic, Molecular, and Solid State Structure Studied by Means of Electron Spectroscopy", Almquist and Wiksells, Uppsala, 1967. (30) L. E. Cox, J. J. Jack, and D. M. Hercules, J. Am. Cbem. Soc., 94, 6575 (1972).
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(31) K. F. Sugawara, H. H.Weetall, and G. D. Schucker, Anal. Cbem., 46,489 (1974). (32) P. E. Larson, J. Electron Spectrosc. Relat. Pbenom. 4, 213 (1974).
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RECEIVEDfor review February 17, 1976. Accepted April 5, l976. This mN?arch has been facilitated by National S c i ~ n c e Foundation Grant GP-38633X and bv U.N.C. Materials Re. . . . ~ search Center under Defense Advanced Research Projects Agency Grant DAHC-15-73-G-0009.
CORRESPONDENCE I
Deuterium Magnetic Resonance Spectrometry as a Tracer Tool in Coal Liquefaction Processes Sir: The purpose of this communication is to show the potential of deuterium magnetic resonance (2H NMR) as a means for determining the distribution of incorporated hydrogen among various organic structures in coal liquids. Although the use of deuterium tracer techniques in studies of coal reactions is not new (1,2), prior work generally involved determination of the composition of product gases. To the best of our knowledge, the use of 2HNMR to identify the labeled sites in coal liquids has heretofore not been reported. The experimental conditions for the initial deuteration were chosen to closely simulate those within the preheater section of the U.S. Energy Research and Development Administration's 1/2-tonper day coal liquefaction pilot plant ( 3 ) and to produce a labeled material suitable for use in future investigations of the hydrogen-donor properties of vehicle oils. The deuteration was performed in a stirred autoclave, in which the centrifuged liquid product (CLP) from a previous SYNTHOIL run and deuterium gas were heated to a maximum of 450 "C a t 1600 psig Dz; the temperature was held above 400 O C for 15 min. No catalyst was added to the reaction mixture; the possibility of catalysis by minerals and trace elements originating from the coal in the original pilot plant run, however, cannot be ruled out. Mass spectrometric analysis of the product gases showed the presence of H2, HD, and Dz and indicated that approximately 4.5% of the hydrogen originally present in the CLP had been replaced by deuterium. NMR spectra were obtained a t nominal operating frequencies of 38.6 MHz and 250 MHz for deuterons and protons, respectively. The required magnetic field of 59 kG was produced within a superconducting solenoid. A more detailed description of the spectrometer has been reported elsewhere ( 4 ) . The relatively new technique of correlation spectrometry ( 5 )was employed to obtain all spectra. It should be noted that although NMR correlation spectra resemble slow passage spectra, they are in fact, obtained by cross-correlation of fast passage, continuous wave spectra with a calculated reference line. Acetone-de was used as the internal chemical shift standard for the deuteron measurements; chemical shifts were then converted to ppm from tetramethylsilane using the published proton chemical shift value of 2.17 ppm (6) for acetone. Assignments of resonances to specific types of deuterons 1254
ANALYTICAL CHEMISTRY, VOL. 48, NO. 8, JULY 1976
or protons were made on the basis of previous proton NMR studies (7-9) of materials derived from coal. Others (10-12) have shown that proton and deuteron chemical shifts measured in the same sample (natural abundance) are identical. A representative 2H NMR spectrum of a distillation fraction from the deuterated CLP is reproduced in Figure 1.The resonances of the aromatic deuterons appear as a broad band a t 6, 7-8 ppm. The band centered near 6, 3 ppm, assigned to deuterons in nonaromatic positions, is partially resolved. The more intense component is due to benzylic deuterons, whereas the smaller, high field components are assigned to deuterons bonded to nonaromatic carbons other than benzylic carbons. A sample of unlabeled CLP examined under identical instrumental conditions revealed no detectable deuteron NMR signals, showing that only resonances of deuterium present in excess of natural abundance were observed. The hydrogen and deuterium distributions as determined by integration of the NMR spectra are summarized in Table I for the deuterated CLP and several fractions thereof. These included 1)distillation cuts covering a wide range of boiling points, 2) the asphaltene components, and 3) hydrocarbon and
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CHEMICAL SHlFT,ppm from TMS
Flgure 1. Deuterium magnetic resonance spectrum of 140-190 OC boiling material (0.1 Torr) from a SYNTHOIL centrifuged liquid product
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Table I. Deuterium and Hydrogen Distribution in Isotopically-Labeled SYNTHOILa Product Material
Nucleus
Deuterated centrifuged liquid product (CLP)
D H
CLP asphaltenesd
D H
Aromatic b total 0.35 0.24 1.5 0.48 0.45 1.1
CLP heavy oild Hydrocarbon fractione Phenol-rich fractionejf
D H
D H
0.20 0.13 1.5 0.41 0.30
1.4 CLP distillation fractions,g boiling range, OC 49-100
Benzvlic total
Other nonaromaticc total
0.49 0.30 1.6 0.40 0.33 1.2
0.16 0.46 0.35 0.12 0.22 0.55
0.66 0.35 1.9 0.46 0.35 1.3
0.14 0.52 0.27 0.13 0.35
0.37
D H
0.42 0.10 0.48 0.49 0.29 0.22 0.20 2.2 1.5 0.13 D 0.55 0.32 100-138 H 0.46 0.17 0.37 0.28 1.5 1.9 D 0.26 0.58 0.16 140-190 H 0.21 0.48 0.31 0.33 1.9 1.2 0.17 D 0.46 0.37 190-220 0.40 H 0.31 0.29 0.43 1.2 1.6 D 0.47 0.09 0.44 Residue (bp > 258) H 0.37 0.28 0.35 0.32 1.3 1.3 See Reference 3. Also includes phenolic protons or deuterons. Refers to hydrogen or deuterium in aliphatic structures or those bonded to carbon atoms p or further removed from aromatic rings. Asphaltenes are operationally defined as benzene-soluble, pentane-insoluble material; the deasphaltenated liquids are called heavy oils. e Fractions separated chromatographically; F. K. Schweighardt, H. L. Retcofsky, and R. A. Friedel, Fuel, in press. f Phenols detected by thin-layer chromatography; fraction also contains other polar compounds. g Distillation carried out at 0.1 Torr. Distillate accounted for 59.7% of the total CLP.
phenol-rich fractions of the heavy oil. Labeled material was found in all fractions examined and, for each fraction, deuterium was found a t both aromatic and nonaromatic sites. This broad distribution of the label can be best rationalized on the basis of a combination of rapid incorporation and scrambling reactions. Closer scrutiny of the data in Table I shows that a degree of specificity for incorporation at benzylic and aromatic positions prevails. Hydrogens bonded to carbons p or further removed from aromatic rings appear to be the least susceptible to deuterium labeling under the experimental conditions employed. This specificity becomes even more apparent when the deuteron and proton data for the various materials are compared using (D,/D)/(H,/H) ratios (x = aromatic, benzylic, or other nonaromatic carbons). In all cases, this ratio lies within the approximate range 1-2 for the aromatic and benzylic sites, whereas the ratio is much smaller, 0.2-0.6, for hydrogens bonded t o carbons p or further removed from aromatic rings. The fact that the distribution of deuterium among these three sites is not the same as the corresponding hydrogen distribution for any individual fraction or for the total CLP indicates that thermal isotopic equilibrium has not been achieved.
ACKNOWLEDGMENT The authors gratefully acknowledge the cooperation of Josef Dadok for use of the Mellon Institute NMR spectrometer. The spectrometer facility is supported by PHS grant RR 00292.
LITERATURE CITED (1) Y. C. Fu and B. D. Blaustein, Chem. hd., 1257 (1967). (2) T. Kessler and A. G. Sharkey, Jr., Spectrosc. Lett., 1, 177 (1968). (3) P. M. Yavorsky, S. Akhtar. J. J. Lacey, M. Weintraub, and A. A. Reznik, Chem. Eng. Frog., 71, 79 (1975). (4) J. Dadok, R. F. Sprecher, A. A. Bothner-by, and T. Link, Paper presented at the 1lth Experimental NMR Conference, Pittsburgh, Pa. 1970. (5) J. Dadok and R. F. Sprecher, J. Magn. Reson., 13, 243 (1974). (6) N. S. Bhacca, L. F. Johnson, and J. N. Shoolery, “NMR Spectra Catalog”, Varian Associates, 1962, p 7. (7) J. K. Brown and W. R. Ladner, Fuel, 39, 67 (1960). (8) H. L. Retcofsky and R. A. Friedel in “Spectrometry of Fuels”, R. A. Friedel, Ed., Plenum Press, New York, 1970, pp 70-89. (9) G. Takeya, M.Itoh. A. Suzuki, and J. Yokoyama, J. FuelSoc. Jpn, 43, 837 (1964). (IO) P. Diehl and T. Leipert, Helv. Chim. Acta, 47, 545 (1964). (11) H. Jensen and K. Schaumburg, Acta Chem. Scand., 25,663 (1971). (12) P. Diehl in “Nuclear Magnetic Resonance Spectroscopy of Nuclai Other Than Protons”, T. Axenrod and G. A. Webb, Ed.. John Wiley & Sons, New York, 1974, pp 275 -285.
F. K. Schweighardt B. C. Bockrath R. A. Friedel H. L. Retcofsky* Energy Research and Development Administration Pittsburgh Energy Research Center 4800 Forbes Avenue Pittsburgh, Pa. 15213
RECEIVEDfor review December 24,1975. Accepted April 27, 1976. Presented in part a t the 1976 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio. ANALYTICAL CHEMISTRY, VOL. 48, NO. 8 , JULY 1976
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