Detection and identification of oxocarboxylic and dicarboxylic acids in


480. Benzenesulfonic acid. 550 sodium salt. 2-Naphthalenesulfonic acid. 510 sodium salt m-Benzenedisulfonic acid. 530. 575 sodium salt p-Sulfobenzoic ...
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Table 111. Decomposition Temperature of Some Sulfonic Acid Salts and Phenol Salts in Air and Helium Decomposition temperature, "C Air Helium Compound Potassium phenolate 215 420 Potassium 2-naphtholate 250 480 Benzenesulfonic acid 550 ... sodium salt 2-Naphthalenesulfonic acid ... 510 sodium salt m-Benzenedisulfonic acid 530 575 sodium salt 390 405 p-Sulfobenzoic acid monopotassium salt p-Diphenylaminesulfonic acid ... 400 sodium salt

benzenesulfonate. Thermal analysis showed that the compound decomposes near this temperature. When the fusion temperature was lowered to 360 "C, the fusions were quantitative. The analysis of sulfonic acids containing substituents which react with alkali, as, for example, free halogen, can be analyzed by the sulfite method without interference. However, the phenol method would not necessarily yield unambiguous results, because each halogen group would be replaced by a hydroxyl substituent. Analysis of Mixtures. To illustrate the versatility and selectivity of the phenol method using gas chromatography, several test mixtures were devised. Mixtures of the sodium salts of benzenesulfonic acid, p-toluenesulfonic acid, and 2,5-dimethylbenzenesulfonicacid were prepared, fused, and analyzed by programmed temperature gas chromatography. A typical chromatogram of the phenol

Table IV. Analysis of Sulfonic Acid Sodium Salt Mixtures by the Phenol Method Benzenesulfonic p-Toluenesul2,5-Dimethylacid sodium fonic acid benzenesulfonic salt, sodium salt, acid sodium wt K O , Wt 72 salt, wt Blend Actual Found Actual Found Actual Found

z

A B C

28.6 69.0 25.7

x

27.8 67.8 26.3

20.4 10.8 35.2

20.5 10.5 34.0

51.0

20.2 39.1

48.7 19.3 38.0

derivatives is shown in Figure 5. The small unidentified peaks on the chromatogram are from impurities in the aqueous maleic acid solution used for acidification of the fusion mixture. The concentrations of the three components were determined from peak area comparisons to phenol standards run separately. The results of the study are given in Table IV. In addition to the capability for analyzing mixtures, another advantage of the phenol method over the sulfite method, and in general over most sulfonate analysis techniques, is its great sensitivity for the analysis of small samples. Using gas chromatography, a complete analysis can be made using only a few milligrams of sample. ACKNOWLEDGMENT Acknowledgment is made t o the early efforts of J. Gordon Hanna who studied the caustic fusion. Those efforts led to the current study. RECEIVED for review May 5 , 1969. Accepted June 16, 1969. The authors also acknowledge the support of the National Science Foundation under grant GP-7360.

Detection and Identification of Oxocarboxylic and Dicarboxylic Acids in Complex Mixtures by Reductive Silylation and ComputerAided Analysis of High Resolution Mass Spectral Data W. J. Richter, B. R. Simoneit, D. H. Smith, and A. L. Burlingame Space Sciences Laboratory, Uniaersity of California, Berkeley, Calg. 94720 The complex nature of the acidic fractions of Green River Formation oil shale solvent extracts makes it necessary to carry out chemical transformations to study the various classes of compounds. One such class, the oxoacids, was substantiated by borohydride reduction, followed by silylation of the hydroxy derivatives thus formed. This procedure allows a differentiation by means of mass spectrometry between the oxoacids and other oxygen containing components present in the fractions, ;.e., dicarboxylic and aromatic acids. High resolution mass spectra of the treated mixtures, followed by computer sorting and heteroatomic plotting of the silicon containing peaks, separates the derivatized oxoacids from other classes of compounds. It also allows assignment of the location of the keto functionality along the hydrocarbon chains of the oxoacid homologs in the extract. This method i s applicable to mixture samples ranging from 0.5 to 3 mg. As an example, a sample obtained from oxidation of Green River Formation kerogen was analyzed and a homologous series of (w-1)-oxoacids ranging from C4to Clzwas thus established. 1392

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SUCCESSIVE SOLVENT extractions of a n oil shale from the Green River Formation yield complex mixtures of similar classes of compounds (a) prior to chemical, (b) after demineralization with HF/HCl, and (c) after chromic acid oxidations of varying duration. The sample of oil shale was collected by one of us (BRS)from a cliff outcrop at Parachute Creek, 8 miles NW of Grand Valley, Colo. (lat. N 39" 37'; long. W 108" 7'; elev. 7300 ft.) The acidic fractions of these mixtures were found to consist mainly of aliphatic monocarboxylic and dicarboxylic acids, with aliphatic oxoacids and aromatic carboxylic acids being present in lesser amounts (1-4). ~~

~

(1) P. Haug, H. K. Schnoes, and A. L. Burlingame, Chem. Commun., 1967, 1130. (2) A. L. Burlingame and B. R. Sirnoneit, Nature, 218, 252 (1968). (3) A. L. Burlingame and B. R. Simoneit, Nature, 222, 741 (1969). (4) A. L. Burlingame, P. Haug, H. K. Schnoes, and B. R. Simoneit,

in "Advances in Organic Geochemistry 1968," I. Havenaar and P. A. Schenck, Eds., Vieweg, Braunschweig, Germany, 1969.

I 1;3

2;s

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Figure 1. Partial high resolution mass spectral data of the ether extract acids from 24-hour oxidation of Green River Formation kerogen Scale factors X 3 with respect to the base peak, CaH~Oz The presence of the oxoacids was deduced from high resolution mass spectral data determined on the total acid fractions after conversion to methyl esters, in particular by inspection of the pertinent C/H Oaand C/H O4heteroatomic plots (5), thus avoiding interference of fragments of lower oxygen content formed, e.g., from monocarboxylic esters. T o confirm the presence of oxoacids independently and, more importantly, to furnish conclusive information regarding the position of the oxofunction within the aliphatic chain, chemical transformation specifically affecting this group was carried out, Reduction of the ester mixture with sodium borohydride (use of sodium borodeuteride would eliminate ambiguities in the case of hydroxy acids originally present in the mixture) was expected to result in the quantitative conversion of the oxoesters to hydroxy analogs, leaving any diester components unaffected. Thus, ambiguity with regard to the origin of the majority of prominent fragment ions is eliminated. Although in the absence of chemical modification only little uncertainty exists in the detection of the molecular ions, an assignment of important fragments to their parent species is largely impeded by their concomitant formation from either source due to closely analogous secondary fragmentation :

Although reductive treatment already provides per se for sufficient mass spectrometric differentiation of both ester types by altering hydrogen content and thus fragment ion composition, additional silylation of the hydroxy constituents seemed desirable from several other points of view. In particular, the increased volatility of the trimethylsilyl derivatives and, to a certain extent, their simplified fragmentation patterns are attractive features, which include the enhanced production of “ester-” as well as “alcohol-fragments” as possible a-cleavage products (a2 and a).(In contrast to this, the free hydroxy esters tend to produce only “ester fragments”.) These fragments are highly characteristic of the original position of the functional group, since they represent overlapping portions in the respective molecule :

0

II

CHSO,C-(CHJ~C-OCH~

II

C%O.&-(CHkC-R O

I-

(5) A. L. Burlingame and D. H. Smith, Tetrahedron, 24, 5749 (1968).

OH

OTMS a1

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J

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Figure 2. Computer sorted high resolution mass spectral data of the oxoacid holologs Scale factor for the C/H Si0 plot is X5 and for the C/H SiOa plot X 3 with respect to the base peak, C 3 H 0 2

In addition, silylation of the hydroxy function introduces a new heteroatom into structurally significant fragment ions which are unambiguously detected in the high resolution mass spectra and ideally suited for computer search and preinterpretation. EXPERIMENTAL

Because of the abundance of highly oxygenated constituents, the ether soluble acid fraction obtained from a 24-hour oxidation experiment (3, 4) was selected to test the procedure of analysis. Figure 1 provides mass spectrometric evidence for the presence of both types of esters in this fraction. A series of molecular ions (6) of dicarboxylic esters is readily recognized by their composition CnHzn--204, ranging from n = 5-14. CnH2n-303 ions, corresponding to M-OCH3 fragments (6') and arising from diester precursors, are recorded in the C/HOa plot together with a series of peaks a (CnH2n--203), which correspond to molecular ions of oxoacids. Although an overlap of the I3C isotope peaks of the 6' fragments with the a ions has to be taken into account, it is in most cases small enough to allow recognition of the latter. In a typical experiment, a mixture (2 mg) of free acids was dissolved in 10 ml of methanol and a total of 100 mg of sodium borohydride added over a period of one hour to the 1394

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stirred, heated solution. Methanol was removed in vacuo after excess hydride was decomposed by addition of dilute hydrochloric acid. The acidic aqueous solution (pH 4-5) was extracted several times with chloroform and the residue of the combined organic extracts treated with diazomethane in ether to effect conversion to the methyl esters. Removal of the solvent was followed by silylation of the residue with a few microliters of silylating agent (Tri-Si1 "Z," Pierce Chemical Company, Rockford, Ill.). Mass spectra were obtained from a 1-pl portion of the crude reaction mixture by direct sample introduction after evaporation of excess reagent. Complete high resolution mass spectra were determined in real time, employing an on-line digital computer for data acquisition and reduction as has been described previously (6-8). A resolution of 10,000 was attained under the following conditions: ionizing current 500 PA; ionizing voltage 50 eV; source temperature 220 "C; scan rate 16 sec./decade in mass. ( 6 ) A. L. Burlingame in "Advances in Mass Spectrometry," Vol. 4, E. Kendrick, Ed., The Institute of Petroleum, London, 1968,

p 15. (7) D. H. Smith, R. W. Olsen, and A. L. Burlingame, Proc. 16th Ann. Conf. Mass Spectrometry Allied Topics, Pittsburgh, Pa., May 13-17, 1968, p 101. (8) A. L.Burlingame, D. H. Smith, T. 0. Merren, and R. W. Olsen, ibid., p 109.

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Figure 3. Partial high resolution mass spectral data of the reduced and silylated mixture of ether acids from 24-hour oxidation Scale factor for the C/H O3plot is X5 and for the C/H O4plot X20 with respect to the base peak, C3H602 RESULTS

The computer sorted data obtained from this mixture and presented as heteroatomic plots are illustrated in Figures 2 and 3. The C/H Si O3plot of Figure 2 displays a series of CnHznflSi03 ions which represent the “ester-fragments” of the silylated hydroxyesters (az), thus incorporating both original carbonyl functions. The supplementing C/H S i 0 plot is comprised of fragments representing the original ketoalkyl portions of the molecules (“alcohol-fragments” al>:

The distinct dominance Of a ul ion (C6H13SiOI = CH3) in the latter plot in conjunction with an extended succession of a2 ions, which range from n = 1-9 and maximize around n = 7-8, suggest a homologous series Of (w-l)-oxocarboxylic acids as main constituents of the original mixture. The C/HO3 and C/HOI plots of the reduced, silylated mixand M-OCH3 ions (b and b’) ture (Figure 3) exhibit of the unchanged dicarboxylic esters, but are void of ketoester

molecular ions a. This complementary finding represents evidence not only for the presence of dicarboxylic esters but also for complete conversion of the oxoesters to silyloxy derivatives. The most abundant ion of the C/H Si O3 plot, C6H13Si03 (a3 at m/e 149, Figure 2), (All peaks in Figures 1-3 are expanded relative to the base peak, C3H601, by the scale factors indicated in the legends.) deserves special comment. This species does not belong to the series of uq ions, as is apparent from its increased hydrogen content. The retention of all

three oxygen atoms together with only five carbon atoms indicates a fusion of both functional groups with expulsion of the total intermediate aliphatic moiety. The net result would thus amount to a migration of a trimethylsilyloxy substituent toward the ester function. Migration has so far been mainly observed for trimethylsilyl groups (9), although at least one (9) W. J. Richter and A. L. Burlingame, Chem. Commun., 1968, 1158, and references cited therein. VOL. 41,NO. 11, SEPTEMBER 1969

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case reported can be viewed as a trimethylsilyloxy transfer (IO). The following pathway might be proposed for the genesis of this structurally insignificant but mechanistically interesting fragment, although such a rationale is likely to be an oversimplification of a more complex process :

TMS-0

x

OR

(a3, mle 149)

While such fragments are of little importance in the spectra of single trimethylsilyloxy esters (see e.g., reference 9), they are likely to be produced in the present case by the majority of the members of the homologous ester series. This accounts for the unexpected excessive abundance of the a3 ion with respect to the a2 ions by simple accumulation of a3 ions from each homolog. (10) W. J. Richter, M. Vecchi, W. Vetter, and W. Walther, Helv. Chim. Acfa, 50, 364 (1967).

CONCLUSIONS

A homologous series of (w-1)-oxoacids, ranging from C4to CIZ,was found present in an acid mixture obtained by oxidation of Green River Formation kerogen. The method chosen for analysis of this mixture consists of borohydride reduction of the keto functionality, treatment of the hydroxy derivative with silylating reagent and computerized search for characteristic mass spectrometric fragments. This procedure is well suited for application on a microscale and serves specifically for the detection of oxoacids in the presence of other carboxylic acid constituents. In addition, it yields conclusive structural information regarding the position of the oxofunction. In particular, the suitability of the technique to computeraided data analysis and interpretation should also permit its useful application to biochemical areas, e.g., lipid analysis of similar complexity (11).

RECEIVEDfor review February 17, 1969. Resubmitted: April 2, 1969. Accepted June 10, 1969. This work was supported by the National Aeronautics and Space Administration (Grants NGR 05-003-134 and NAS 9-7889). This paper represents part XXV in the series High Resolution Mass Spectrometry in Molecular Structure Studies. For part XXIV, see P. Schulze, B. R. Simoneit, and A. L. Burlingame, J. Mass Spec. ion Physics, 2, 183 (1969). (11) E. G. Perkins, J. Amer. Oil Chem. SOC.,44, 197 (1967), and

other papers by the same author.

Determination of Aluminum and Chlorine in Composite Propellants by Nondestructive Activation Analysis Using a Mixture of 14.5 MeV and Slow Neutrons A. E. Richardson' and Alex Harrison Biological-Chemical-Metallurgical Branch, Department of the Army, White Sands Missile Range, N . M . 88002

Use of a mixture of 14.5-MeV and slow neutrons has made possible the simultaneous determination of aluminum and chlorine in solid composite propellants by nondestructive activation analysis with a precision of better than =t1%. The method was developed and evaluated by carrying out a series of determinations on samples of known composition and comparing the results with those obtained by X-ray fluorescence. The overall agreement between the results of the two methods is quite good, and both appear to be sufficiently accurate for quality control purposes.

ALTHOUGH X-ray fluorescence methods had been developed for the nondestructive analysis of composite propellants by Alley and Higgins (I, 2), it was felt that other methods might be developed which were not as sensitive to matrix effects and Currently on leave at the Chemistry Department, University of Colorado, Boulder, Colo. 80302 from the Chemistry Department, New Mexico State University, Las Cruces, N. M. 88001. (1) B. J. Alley and J. H. Higgins, Bulletin of 18th JANAF Panel Meeting, Thiokol Chemical Corp., Elkton, Md., Aug 1962, SPIA/ AC-18, Johns Hopkins University, Silver Spring, Md., Oct. 1962, pp 123-40. (2) B. J. Alley, Bulletin of the 20th Meeting ICRPG Working Group on Analytical Chemistry, United Technology Corp., Sunnyvale Calif. June 1964, CPIA Publication No. 52, Johns Hopkins University, Silver Spring, Md., July 1964, pp 279-88. 1396

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particle size as the X-ray fluorescence method. The primary purpose of the analysis would be for quality control of composite propellants with a composition of approximately 70 % ammonium perchlorate, 15 % aluminum, and 15 % binder and other minor additives. Neutron activation analysis appeared to be one approach to the problem. Several nuclear reactions were studied, but the 27Al(n,p)27Mg reaction with 14.5MeVneutrons and the 37Cl(n,y)3sC1 reaction with slow neutrons gave the best results. It was found possible to produce a useful mixture of 14.5-MeV and slow neutrons, so that both aluminum and chlorine could be determined simultaneously from a single irradiation. It was necessary to make a Compton correction for Z4Na produced from 27Al(n,a)by 14.5-MeV neutrons in order to obtain reproducible results for W1. The method was developed and evaluated by comparing a series of batches of known composition with a given batch whose composition was also known. As this work was being completed, Rison and co-workers reported the application of activation analysis to the determination of nitrogen in propellants and explosives (3) and to the determination of phosphorus in composite propellants (4). (3) M. H. Rison, W. H. Barber, and P. E. Wilkniss, Radiochim. Acta, 7 (4), 196 (1967). (4) M. H. Rison, W. H. Barber, and Peter Wilkniss, ANAL.CHEM., 39, 1028 (1967).