Table 11. Determination of Polymeric Polyisocyanates
7, NCO Sample A B a
ASTM
DMF4
30.7 f 0.1 31.2 i= 0 . 1 30.8 f 0.0
30.9 i= 0 . 1 31.1 & 0.0 31.1 & 0.1
C Reaction time 5 minutes at room temperature.
solution is titrated to the pink end point with standard 0.1N hydrochloric acid. A blank is determined for the same reaction time used for the sample. DISCUSSION
Dipolar aprotic solvents seemed to be ideal for this reaction because dimethyl sulfoxide (DMSO) accelerates the rate of nucleophilic amine reactions (9). DMSO was tried as a solvent for the determination and was found to give high results, especially with aromatic isocyanates. DMF was found to be comparable to DMSO with respect to the rate of the reaction but failed to give high results, thus making it the solvent of choice. (9) M. Friedman, J. Amer. Chem. Soc., 89,4709 (1967).
Results for the determination of isocyanates and isothiocyanates in D M F are found in Table I. The average standard deviation was.0.3% for the compounds listed. Although a 250% excess of amine was usually used, quantitative results were obtained when a 100% excess of amine was present. The amine solution of D M F was fairly stable; the acid titre decreased slowly because of evaporation and oxidation of the amine. However, reagent stored for a period of one month gave satisfactory results. Polymeric polyisocyanates were determined using both the ASTM and the DMF methods. The results are shown in Table 11. The DMF method appears to give similar accuracy and precision with a significant reduction in reaction time; 5 minutes for DMF us. 1 hour for ASTM. ACKNOWLEDGMENT Samples of polymeric polyisocyanates were kindly supplied by Q. Quick of the Union Carbide Corp. RECEIVED for review October 10, 1968. Accepted May 29 1969. Presented at the Middle Atlantic Regional Meeting, Washington D. C., February 1969.
Electron Acceptor Complexes for Chromogenic Detection and Mass Spectrometric Identification of Phenol and Aniline Derivatives, Related Fungicides, and Metabolites Otto Hutzinger Atlantic Regional Laboratory, National Research Council of Canada, Halifax, Nova Scotia, Canada
ELECTRON ACCEPTORS form molecular complexes with many aromatic and “ T excessive” heterocyclic compounds. These complexes ( T - , donor-acceptor-, charge-transfer-, molecularcomplexes; molecular addition compounds) are usually intensely colored in the solid state and generally less soluble in organic solvents than their parent compounds. For these reasons electron acceptors have been used as spray reagents for the detection of certain compounds on chromatograms and for the isolation of compounds from reaction mixtures and their characterization. [For general references see (I).] Aromatic amino and hydroxy derivatives are particularly suitable for these procedures because electron releasing groups in the donor tend to increase color intensity and stability of the complexes. Some relevant examples with references to earlier work are given in (2-6). In this paper the color reactions of several electron acceptors with systematically substituted aniline and phenol derivatives, as well as some chemically related fungicides and fungicide metabolites, were studied. The properties of the 2,4,7trinitro-Pfluorenone complexes of two representative compounds, 3,5-dichloro-4-aminophenol(I) and 2,ddichloro-p0. Hutzinger, J . Chromatog., 40, 117 (1969). H. T. Gordon and M. J. Huraux, ANAL.CHEM., 31, 302 (1959). L. Fishbein, J. Chromatog., 22,480 (1966). F. Feigl, “Spot Tests in Organic Analysis,” Elsevier Publishing Co., Amsterdam, 1966. (5) G, F. Macke, J. Chromatog., 36, 537 (1968). 40, 2138 (1968). (6) J. H. Ross, ANAL.CHEM., (1) (2) (3) (4)
1662
ANALYTICAL CHEMISTRY
phenylenediamine (11), were more closely examined and the use of mass spectrometry for direct identification of compounds of this type in the complexed form was investigated. EXPERIMENTAL
Chemicals. 3,5-Dichloro-4-aminophenol(7) and 7,7,8,8tetracyanoquinodimethane (8) were prepared by literature methods; all other compounds were commercial samples purchased from the Aldrich, B.D.H., DuPont, Eastman, Fisher, K & K , Matheson Coleman & Bell, Nutritional Biochemical and Toms River Chemical companies. Spectra. The spectra were recorded on a Perkin-Elmer Model 521 spectrophotometer, a Beckman DK-2 spectrophotometer and a Varian A-60-A instrument. The mass spectral data were obtained with a Consolidated Electrodynamics Corp. 21-llOB instrument equipped with a controlled temperature probe for introduction of the sample directly into the source (9). Color Development. Hydroxy- and amino-compounds (20 pg) in methanolic or acetone solution were applied (spot diameter -5 mm) to Eastman Chromagram silica thin-layer sheets (6061) and sprayed with a solution (1 %) or the complexing reagent in chloroform or acetone. (7) H. H. Hodgson and J. S . Wignall, J . Chem. Soc., 131, 2216 (1927). (8) D. S . Acker and W. R. Hertler, J. Amer. Chem. SOC.,84, 3370 (1962). (9) W. D. Jamieson and F. G. Mason, submitted for publication
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VOL. 41, NO. 12, OCTOBER 1969
1663
Preparation of Solid 2,4,7-Trinitro-9-Fluorenone (TNF) Complexes. Equimolar solutions of TNF and the aromatic
amino compound in boiling chloroform were mixed. The crystals were collected after cooling and the complexes were recrystallized from chloroform and chloroform-thy1 acetate. The following compounds were prepared in this manner : the 3,5-dichloro-4-aminophenol(I) T N F complex was obtained as black needles, mp 150 "C. Calculated for Cl&loClzN40s: C, 46.28; H, 2.04; C1, 14.38; N, 11.34; found: C, 46.10; H, 1.91; C1, 14.52; N, 11.32z. The 2,6-dichloro-pphenylenediamine (11) T N F complex was obtained as black needles, mp 159-160 "C. Calculated for C1~HllC12N607: C, 46.36; H, 2.26; C1, 14.41; N, 14.23; found: C , 46.09; H, 2.15; C1, 15.08; N, 14.31z. The melting points for both compounds are given for a heating rate of 10 "C/min. When the complexes were heated slowly on a hot stage, thermal dissociation took place and I or I1 sublimed. The residual light yellow sample gave the mp of TNF, 175 "C. Regeneration of 3,5-Dichloro-4-Aminophenol from Its TNF Complex. (a) BY SUBLIMATION. The TNF-I complex (5 mg) was heated (130 OC bath temp.) in a sublimation apparatus at 2 mm. The black complex gradually became yellow and the solid collected from the cold finger had a mp and mixed mp identical with the authentic material (154 "C). (b) BY SOLVATION OF THE COMPLEX.The TNF-I complex (5 mg) was shaken for 2 min with a mixture of chloroform (50 ml) and aqueous HC1 (10 ml; pH 2). The chloroform layer was discarded and the aqueous phase extracted with chloroform (50 ml) again. The water layer was adjusted to pH 7.5 (sodium bicarbonate) and extracted with ether (2 X 20 ml). Part of the ether layer, after it had been dried (Na2S04)and reduced in volume, was chromatographed on Eastman silica thin-layer sheets. The RF values in two solvent systems (0.48 with hexane-acetone 6 : l ; 0.22 with benzene-chloroform 8:2) were identical to that of pure I. A trace of impurity, fluorescent in UV light, was formed during this procedure. Identical results were obtained with the aforementioned procedure when aqueous NaOH (pH 12) was used in the initial shaking and the adjustment to pH 7.5 was done with the hydrochloric acid. RESULTS AND DISCUSSION Color Reactions. The colors obtained from aromatic amino and hydroxy derivatives including some fungicides (10) and metabolites of the fungicide 2,6-dichloro-4-nitroaniline (11) after spraying with the strongest electron acceptors are shown in Table I. The colors produced with the following weaker electron acceptors are not reported in the table: 1,2,4,5benzenetetracarboxylic anhydride, 2,4-dinitrobenzenesulfonicacid, 2,6dinitro-9-fluorenone, 2,7-dinitro-9-fluorenone, 4-nitrophthalic acid, tetrabrornophthalic anhydride, tetrachlorophthalic anhydride, 1,3,5-trinitrobenzene, 2,4,6-trinitrobenzenesulfonic acid, and a mixture of 1,5- and 1,8-dinitroanthraquinone. These complexing reagents gave good color differentiation for diamino, amino-hydroxy, and dihydroxy derivatives but very weak or no colors with chloro- or nitro-substituted compounds. The expected relationship between the structure of the amino or hydroxy derivative and the chromogenic behavior is observed. With electron-donating substituents, colors closer to the violet part of the spectrum are produced and the colors are generally more intense. The order for disubstituted derivatives is diamino > amino-hydroxy > di(10) E. Y.Spencer, "Guide to the Chemicals Used in Crop Protection," The Queen's Printer, Ottawa, 1968. (11) C. Mate, A. J. Ryan, and S. E. Wright, Fd. Comet. Toxicol., 5, 657 (1967). 1664
ANALYTICAL CHEMISTRY
hydroxy. The positional isomers in these cases can be clearly differentiated with most electron acceptors, the p-isomer often being the most intense. Nitro, and to a lesser extent, chlorine substituents decrease the color intensity with a tendency toward yellow colors. With several electron acceptors, this effect is more pronounced with the substituent in the ortho position. All three mononitrophenols, 2,4-dinitrophenol, and 2,4-dinitroaniline gave little color change over their own yellow shades. These compounds were therefore not included in the table. The limits of detection for diamino and amino-hydroxy derivatives is
