ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2008, Vol. 82, No. 6, pp. 911–915. © Pleiades Publishing, Ltd., 2008. Original Russian Text © I.A. Rodin, D.N. Moskvin, A.D. Smolenkov, O.A. Shpigun, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 6, pp. 1039–1044.

PRESENTED AT THE CONFERENCE “CHROMATOGRAPHY IN CHEMICAL ANALYSIS AND PHYSICOCHEMICAL INVESTIGATIONS”

Transformations of Asymmetric Dimethylhydrazine in Soils I. A. Rodin, D. N. Moskvin, A. D. Smolenkov, and O. A. Shpigun Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119992 Russia e-mail: [email protected] Abstract—High-performance liquid chromatography and mass spectrometry were used to find that the decomposition of asymmetric dimethylhydrazine (I) in soils occurred with the formation of dimethylamine, formaldehyde dimethylhydrazone, methylhydrazine, trimethylhydrazine, N-nitrosodimethylamine, 1-methyl-1,2,4triazole, formic acid dimethylhydrazide, 1,5,5-trimethylformazane, 1-methyl-1,6-dihydro-1,2,4,5-tetrazine, N,N-dimethylaminoguanidine, and several other products. High-reliability structure identification was achieved using independent methods, including gas chromatography–mass spectrometry, 1H and 13C NMR, and UV spectroscopy, and by measuring retention times and spectral characteristics after the counter-synthesis of the suggested structures. The products of the decomposition of I potentially capable of forming initial I and characterized by high migration mobility in soils were identified. DOI: 10.1134/S003602440806006X

INTRODUCTION Asymmetric dimethylhydrazine (I) is an exceedingly dangerous pollutant of the environment. It is characterized by high toxicity and has pronounced mutagenic properties [1]. The main source of I in the environment is space rocket technology, in which I is extensively used as the main component of effective rocket fuel, and the use of succinic acid 2,2-dimethylhydrazide, which is a plant growth regulator capable of experiencing hydrolysis with the formation of I. A characteristic feature of I is its pronounced liability to oxidation, which considerably decreases the total content of I spilled on earth [2]. Nevertheless, there are data according to which I can exist in soil for several years where carrier rocket stages fall [3]. It follows that studies of the behavior of I in soils is an important problem related to the safety of space rocket work. The authors of [4–9] were unable to give a complete picture of processes that occurred during the chemical oxidation of I and compile a complete list of I decomposition products for several reasons. Usually, compounds were identified by methods (UV and IR spectroscopy) incapable of providing reliable information about the structure of the products formed, or gas chromatography (GC)–mass spectrometry (MS) was used without preliminary derivatization. This method is of limited applicability to the compounds under study, first, because of their volatility and thermal stability characteristics. Secondly, I gives several high-polarity oxidation products. These substances were virtually impossible to extract from water, whereas GC–MS measurements were as a rule performed after extraction with organic solvents. Thirdly, GC–MS peaks were analyzed using commercial libraries of mass spectra, which prevented the authors from identifying

compounds not included in these libraries. In our view, the best variant of studies of I oxidation products is the high performance liquid chromatography (HPLC)–MS method characterized by high detection universality and convenient for analyzing high-polarity compounds. The purpose of this work was to study the chemical transformations of I in soils and identify the transformation products by the HPLC–MS method. EXPERIMENTAL Apparatus. We used an HPLC–MS system (Shimadzu, Japan) equipped with an LC-10 ADvp HPLC pump, SCL-10 Avp controller, DGU-14A mobile phase degasser, injector with a 20 μl loop (Rheodyne, USA), and LCMS-2010A (Shimadzu, Japan) quadrupole mass spectrometric detector with an electrospray ionization source. The parameters of the mass spectrometer were: ionization source voltage 4 kV, ion transport and focusing system temperature 250°C, the rate of nitrogen supply through a nebulizer needle 1.5 l/min, the rate of blowing with a gas-drying agent (nitrogen) 10 l/min, the interval of recordable m/z values 25–150. The electronic spectra of the compounds were studied using an Agilent 1200 (Agilent tech., USA) liquid chromatograph equipped with a diode matrix as a detector. Optical densities were recorded over the wavelength range 200–650 nm. The electrochemical activity of the compounds was studied using the HPLC system with amperometric detection equipped with a pump (Shimadzu, Japan), LC-10 ADvp pump, injector with a 20 μl loop (Rheodyne, USA), and a Tsvet-Yauza detector (Khimavtomatika, Russia). Chromatograms and spectral data were recorded using LCMS Solution

911

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Table 1. Extraction of I (mg/l) from soils using (A) extraction and (B) extraction with alkaline extract distillation Extractant

A

B

HCl

0.96

37

NaOH

0.49

43

KCl

0.15

31

CH3COOK

0.07

33

Note: All the results are reduced to the initial volume of the supernatant liquid (50 ml).

(Shimadzu, Japan), ChemStation (Agilent tech., USA), and Ekokhrom (Russia) packages. Conditions of HPLC measurements. Components were separated on a Nucleosil 5 SA (150 × 2.1 mm) column, sorbent grain diameter was 5 μm (Macherey Nagel, Germany). The mobile phase was ammonium– acetate buffer of concentration 100 mM with 3 vol % acetonitrile. The rate of mobile phase flow was 0.2 ml/min. Conditions of GC–MS measurements. We used an Agilent 6850 gas chromatograph with an Agilent 5973 N mass spectrometric detector (Agilent tech., USA). Measurements were taken under electron impact ionization conditions (70 eV). Chromatographic separation was performed on an HP INNOWAX (30 m × 0.25 mm × 0.25 mm) column, the parameters of measurements were: sample volume 1 μl, vaporizer temperature 150°ë, samples were introduced without flow splitting. Temperature programs were varied. Chromatograms and spectral data were recorded using the ChemStation (Agilent tech., USA) package. Conditions of NMR measurements. The 1H and 13C NMR spectra were recorded in deuterated methylene chloride with the use of a Varian Inova 400 NMR (Varian, the Netherlands) spectrometer operating at 400 MHz. Preparation of water–soil suspensions. Soil (5 g) was placed into a conical flask of capacity 100 ml and poured over with a solution of I (50 ml, 500 mg/l). Extraction of I. A weighed amount of a reagent or concentrated hydrochloric acid was added to a water– soil suspension to make the concentration of the extractant in the aqueous suspension phase (supernatant liquid) equal to 1 mol/l. Extraction was performed for 1 h. Alkaline distillation. A water–soil suspension or an extract (40 ml) was transferred quantitatively into a round-bottom flask of capacity 250 ml. Sodium hydroxide (20 g) and sodium sulfide (2 g) were added, and the mixture was distilled into a receiving vessel containing a 0.1 M solution of sulfuric acid (10 ml) following the procedure described in [2]. The final volume of the solution after distillation taking into account dilution in a measuring flask was 100 ml.

Sample preparation for NMR studies. Eluate portions from the chromatographic column corresponding to pure component zones were evaporated to dryness in a flow of nitrogen at room temperature and dissolved in deuterated methylene chloride. RESULTS AND DISCUSSION Forms of I in soils. The use of extraction for transfer of I from water–soil suspensions into a supernatant liquid changed the content of the component to be determined when various sample preparation schemes were used (Table 1). The use of mild extractants (salts) was characterized by the extraction of smaller amounts of I compared with those extracted by 1 M solutions of alkali and acid. At the same time, the distillation of extracts in an alkaline medium noticeably increased the content of I irrespective of the type of the extractant (Table 1). A study of aqueous extracts from soils acidified after soil separation showed that an increase in the content of I (c, mg/l) occurred not only as a result of distillation but also after the addition of 1 M hydrochloric acid, probably, because of the spontaneous hydrolysis of the products of the transformation of I (τ is the duration of hydrolysis, min): τ

5

60

160

1200

3000

4800

c

5

14

15

21

35

45

Lastly, our third observation was that the results of the determination of I (c, mg/l) in supernatant liquids of suspensions obtained after the transformation of I for different times t and an additional sample preparation stage were substantially different before (A) and after (B) distillation: t

1h

1 month

A B

420 390

25 205

These observations were explained on the assumption of the existence of I in soils in four forms (Table 2). To correctly estimate the toxicity of I in soils, it is very important to determine the composition of the most important form, the water-soluble bound form, because I is regenerated from it fairly easily as medium pH changes. In addition, this form is characterized by high mobility and potentially effects the migration of I. According to the data given above, the major part of I in soils exists just in this form, and it is therefore of key importance for I transformation processes in the environment. To study this form, we used high-performance liquid chromatography with mass spectrometric

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Table 2. Forms of I in soils Form

Properties

Supposed nature

Free

Extracted as aqueous (buffer) extracts at room Dissolved in a soil solution and physically temperature absorbed by the soil phase

Water-soluble mobile, bound

Extracted as aqueous (buffer) extracts at room Products of I decomposition capable of temperature, transforms into initial I after reversible hydrolysis with the formation alkaline distillation of the initial substance

Reversibly bound with the soil absorbing complex

Isolated from soil using alkaline distillation

Reversibly chemisorbed I

Irreversibly bound

Cannot be extracted even when harsh sample preparation conditions are used

Irreversibly chemisorbed I

detection. This method possesses several obvious advantages: (1) it is universal (allows separation and detection of arbitrary compounds, including nonvolatile and lowstability compounds, to be performed irrespective of the special features of their structure); (2) it is highly informative (allows not only information about the number of components in a mixture and their retention times to be obtained but also data to be collected for the determination of the structure of substances through the interpretation of their mass spectra); (3) MS detectors can be used to reconstruct chromatograms according to the identified ions, which allows peaks of all the components to be found in a complex mixture and the highest selectivity to be obtained; (4) the broad spectrum of chromatographic separation variants (ion chromatography, reversed phase high performance chromatography) provides the possibility of separating closely similar compounds and obtaining undistorted mass spectra. The products of the transformation of I were identified as follows. First, solutions containing the products of I decomposition, for instance, soil extracts obtained from a sample contaminated with I and subjected to the action of atmospheric oxygen, were studied by the HPLC–MS method. The most intense peaks of I decomposition products were selected on the chromatogram obtained. For this purpose, contaminated soil samples were compared with soil samples used as control tests (soil of the same type not contaminated with I but stored under the same conditions for the same time). Mass spectra were studied for the peaks selected. Since the structure of the mass spectra of lowmolecular-weight substances obtained using electrospray ionization is fairly simple, peaks corresponding to protonated molecular ions and fragment ions were examined. The data obtained were used to determine the molecular formula of the component RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A

subjected to identification using isotopic splitting, the nitrogen rule, and the formal valence rule. Next, the probable structural formula (formulas) of the component was obtained using the data on its fragmentation on the basis of the rules governing fragmentation under electrospray. In addition, we determined the electrochemical activity of the component. The use of amperometric detection at a 1.3 V electrode potential allows substances with the N–N hydrazine fragment to be identified with high selectivity [10]. A comparison of chromatograms obtained using amperometric and mass spectrometric detectors allowed us to identify electroactive mixture components, that is, components containing hydrazine fragments (Table 3). The use of the diode matrix detector to record absorption spectra of the components of interest in the UV and visible ranges allowed us to determine absorption maxima for the compounds studied and thereby reveal the presence of multiple bonds, conjugated multiple bonds, and aromatic fragments in the structure of the substances. For instance, absorption at 200–220 nm is characteristic of C=O bonds, absorption at 220– 240 nm is characteristic of C=N bonds, and absorption at 300–350 nm can be evidence of the presence of conjugated double bonds. The absence of absorption at 215–400 nm can be considered a sufficient argument for the absence of multiple carbon–element (nitrogen or oxygen) bonds. Table 3 contains data on the UV and visible absorption spectra of the substances studied. The data obtained led us to suggest the structures of oxidation products listed in Table 3. In order to reliably identify structures and obtain additional information when the determination of complex structures caused difficulties, we isolated certain compounds using the semipreparative variant of HPLC. The fractions isolated by HPLC were studied by GC– MS and NMR methods. The data on the spectral properties of the substances are listed in Table 4. The structures listed in Table 3 were substantiated using commercial standards (1, 2, 5, 7, 12) or substances synthesized following the procedures described in [11] for 3

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Table 3. Structure and properties of the identified products of the decomposition of I No.

Substance

M, g/mol

Structure H3C

1 Dimethylamine

3

46 (MH+)

No

–

46

CN2H6

47 (MH+)

Yes

–

N N CH2

72

C3N2H8

73 (MH+)

Yes

238

N NH CH3

74

C3N2H10

75 (MH+)

Yes

–

74

C2N2H6O

75 (MH+), 44 ((CH3)2N+)

No

230

74

C3N2H10

75 (MH+), + 58 ((CH3)2N=CH 2 )

No

–

83

C3N3H5

84 (MH+)

No

240

88

C3N2H8O

89 (MH+), 44 ((CH3)2N+)

Yes

210

104

C3N2H8O2

105 (MH+), 146 ([MH · CH3CN]+)

Yes

–

114

C4N4H10

115 (MH+)

Yes

230, 340

98

C3H6N4

98 (MH+)

Yes

238 330 420

87

C3N3H9

88 (MH+) 71 (MH+/NH3)

No

218

NH NH2 H3C H3C H3C

4 Trimethylhydrazine

H3C H3C

5 N-Nitrosodimethylamine

6

H3C

O N

NH2

CH3 N N N H3C

7 1-Methyl-1,2,4-triazole

8

N N

H3C

N,N-dimethylmethylenediamine

H3C

Formic acid dimethylhydrazide

N NH O

H3C H3C

N,N-Dimethylhydrazine 9 carboxylic acid

χ (Eox = λmax , +1.3 V) nm

C2NH7

H3C

Formaldehyde dimethylhydrazone

ESI(+), m/z

45

NH

H3C 2 Methylhydrazine

Formula

N NH O

H3C HO

10 1,5,5-Trimethylformazane

1-Methyl-1,6-dihydro11 1,2,4,5-tetrazine

12

N,N-Dimethylaminoguanidine

H3C

N N CH3

N N H3C

N

N

CH3 N N

NH N

H3C

CH3

NH2

Note: The structure of compounds 6 and 9 is hypothetical at present (it was not substantiated either by NMR or by counter-synthesis); M is the molecular weight, and χ is the electrical activity. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A

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Table 4. Spectral properties of identified substances 7, 8, 10, and 11 (see Table 3) Substance

1H

δ, ppm

13C

NMR δ, ppm

assignment

NMR

m/z (GC–MS)

assignment

7

3.76 7.75 7.92

3 H, CH3 1 H, CH 1 H, CH

35.9 145.5 151.7

CH3 CH CH

83, 56, 40, 28

8

2.54 2.57 7.78 8.22

3 H, CH3 3 H, CH3 1 H, NH 1 H, COH

47.3 48.8 167.2

CH3 CH3 COH

88, 59, 43, 42, 30, 15

10

3.11 3.81 7.75

6 H, (CH3)2N 3 H, CH3N 1 H, CH

43.1 56.2 143.5

CH3N (CH3)2N CH

11

3.36 4.07 8.44

3 H, CH3N 2 H, CH2 1 H, CH

42.4 70.2 141.9

CH3N CH2 CH

114, 71, 44, 42, 18, 15

–

Note: Compound 11 is thermally unstable and decomposes in the gas chromatograph vaporizer; all the 1H NMR signals specified are singlets.

and 4, [12] for 8, and [13] for 10. The chromatographic and spectral properties of all the substances whose structures were substantiated using synthetic standards were in close agreement with those of the latter. The determination of the nature of the water-soluble bound form of I. A criterion for classifying a product of I transformations as the water-soluble bound form was the presence of a fragment of I in its structure and its ability to transform with the formation of initial I. To finally assign the products of the decomposition of I, the chromatograms of extracts from soils obtained before and after distillation were compared. A comparison of chromatographic peak heights in chromatograms for solution of the model mixture of components before and after distillation is given in Table 5. As a result, among the identified products of I transformations, formic acid dimethylhydrazide [14], 1,5,5-trimTable 5. Chromatographic analysis data on the dissolved model mixture (H1 is the chromatographic peak area before sample distillation and H2 is the peak area after distillation) Substance

H1

H2

1 I 3 7 8 10

600000 350000 1100000 1600000 1200000 250000

600000 800000 0 1500000 0 0

Note: Compounds 3, 8, and 10 contain fragments of I and are components of the mobile bound form of I. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A

ethylformazane, formaldehyde dimethylhydrazone, and a component with m/z = 105 assigned the structure of dimethylhydrazocarboxylic acid were identified as components of the water-soluble bound form of I. REFERENCES 1. G. Ghoudhary and H. Hansen, Chemosphere 37, 801 (1998). 2. A. D. Smolenkov, P. P. Krechetov, A. V. Pirogov, et al., Int. J. Environ. Anal. Chem. 85, 1089 (2005). 3. V. S. Kasimov, V. B. Grebenyuk, T. V. Koroleva, and Yu. V. Proskuryakov, Pochvovedenie, No. 9, 110 (1994). 4. W. Mitch, O. Sharp, R. Trussel, et al., Environ. Eng. Sci. 20, 389 (2003). 5. O. Pestunova, G. Elizarova, Z. Ismagilov, et al., Catal. Today 75, 219 (2002). 6. Z. Ismagilov, M. Kerzhentsev, V. Ismagilov, et al., Catal. Today 75, 277 (2002). 7. M. Mathur and H. Sisler, Inorg. Chem. 20, 426 (1981). 8. A. K. Buryak, O. G. Tataurova, and A. V. Ul’yanov, Mass-Spektrometriya 1 (2), 147 (2004). 9. O. A. Makhotkina, E. V. Kuznetsova, and S. V. Preis, Appl. Catal., B 68, 85 (2006). 10. A. D. Smolenkov, A. V. Pirogov, and O. A. Shpigun, Anal. Sci. 17, 1769 (2001). 11. J. B. Class, J. G. Aston, and T. S. Oakwood, J. Am. Chem. Soc. 75, 2937 (1953). 12. R. Beltrami and E. Bissell, J. Am. Chem. Soc. 78, 2467 (1956). 13. J. R. Boehm, A. L. Balch, K. F. Bizot, and J. H. Enemark, J. Am. Chem. Soc. 97, 501 (1975). 14. A. D. Smolenkov, I. A. Rodin, A. V. Shpak, and O. A. Shpigun, Int. J. Environ. Anal. Chem. 87, 351 (2007).

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