Environ. Sci. Technol. 1987, 21, 500-503
dioxide, ammonia, carbon monoxide, and carbon dioxide at much higher concentrations. The reaction product of 1-methylperimidine with nitrogen dioxide (Scheme 11) most likely is either a nitro or nitroso derivative. When 1-methylperimidine alone was exposed to nitrogen dioxide, an orange compound was obtained, but with water present the product was a more intense red. Calcium chloride as a humectant provides water for the desired reaction of 1-methylperimidine. The orange product of dry 1-methylperimidine with nitrogen dioxide tested positive with Feigl’s test (5) for p-nitro aromatic amines, in which a small amount of sample was mixed with diphenylamine in a casserole and heating to melting. A blue color indicated the orange product to be 6- or 7-nitro-1-methylperimidine. When the red product obtained with moist reagent and nitrogen dioxide was treated with phenol and concentrated sulfuric acid (another test described by Feigl), a blue color confirmed the reaction product to be 6- or 7-nitroso-1-methylperimidine. 1-Methylperimidine, a tertiary aromatic amine, thus forms a nitroso derivative rather than the nitro derivative under the conditions in which very small quantities of nitrogen
dioxide are absorbed in the moisture provided by the humectant to form nitrous and nitric acids. Registry No. NO2, 10102-44-0; CaCl,, 10043-52-4; 1methylperimidine, 19585-93-4;1,8-diaminonaphthalene, 479-27-6; formamidine acetate, 3473-63-0; pyrimidine, 289-95-2.
Literature Cited (1) Lambert, J. L.; Beyad, M. H.; Paukstelis, J. V.; Chiang, Y. C. Anal. Lett. 1981, 14, 663. (2) Lambert, J. L.; Beyad, M. H.; Paukstelis, J. V.; Chejlava, M. J.; Chiang, Y. C. Anal. Chem. 1982,54, 1227. (3) Brown, D. J.; Evans, R. F. J . Chem. SOC.1962, 4093. (4) Lambert, J. L.; Paukstelis, J. V.; Liaw, Y.-L.; Chiang, Y . C . Anal. Lett. 1984, 17, 1987. (5) Feigl, F. Spot Tests in Organic Analysis; Elsevier: London, 1960. (6) Carr, D. S.; Harris, B. L. Znd. Eng. Chem. 1949,41, 2014. Received for review March 10,1986. Revised manuscript received December 19,1986. Accepted January 22, 1987. This research was supported in part by National Science Foundation Grant CHE-8311012.
Palladium( 11)-Acetamide Complex as a Solid Monitoring Reagent for Carbon Monoxidet Jack
L. Lambert,* Yun-Long Liaw, and Joseph V. Paukstelis
Department of Chemistry, Kansas State University, Manhattan, Kansas 66506
Yuan C. Chiang Department of Chemistry, Kansas Wesleyan University, Salina, Kansas 6740 1
A study of solid salts containing cationic complexes of palladium(I1) with neutral, weakly complexing ligands resulted in the discovery of the palladium(I1)-acetamide-tetrafluoroborate reagent, in which acetamide is present in 20-fold molar excess. It was found that a successful reagent of this type must have a ligand that complexes palladium(I1) weakly, but more strongly than does water, with water available for subsequent reaction. Carbon monoxide appears to coordinate with the palladium(I1)-acetamide complex, which then reacts with water to form, simultaneously, palladium(0) metal that is black, carbon dioxide, and hydrogen ion. The reagent is described as a visual warning device for the presence of carbon monoxide. Introduction
Chemical methods for carbon monoxide measurement carried out at room temperature rely on either palladium(11) or silver compounds, with the unique exception of hemoglobin. Silver(1) lightly complexed with p-sulfaminobenzoate anion in strongly alkaline solution (1) is reduced by carbon monoxide to a silver sol, the hue and absorbance of which vary with concentration. Palladium(11) salts in aqueous solution are reduced by carbon monoxide to black metallic palladium. A variant of this type of reaction involves complexing the unreacted palladium(I1) cation with excess iodide to form red tetraiodopalladate(I1) anion, which can be determined spec-
trophotometrically (2). Three colorimetric reactions for carbon monoxide that produce soluble colored compounds without free metallic palladium are the tetrachloropalladate~II)-(ethylenediaminetetraacetato)ferrate(III)1,lO-phenanthroline solution that produces red-orange tris(1,lO-phenanthroline)iron(II) cation ( 3 ) , the tetrachloropalladate(I1)-leucocrystal violet-iodate solution that produces crystal violet (4), and the tetrachloropalladate(11)-cacotheline solution that produces violet dihydrocacotheline (5). Solid reagents for carbon monoxide consist generally of moistened palladium(I1) salts on supports, which carbon monoxide reduces to black palladium metal, and palladium(I1) silicomolybdate or molybdate on silica gel, which carbon monoxide reduces to produce “molybdenum blue” (6-8). Yellow tetrasulfitopalladate(I1) complex anion on silica gel is reduced by carbon monoxide to produce a brown color (9). The purpose of this study (10) was to examine the nature of the palladium(I1)-carbon monoxide reaction and, if successful, to develop a solid reagent that would not require liquid water or a substance providing water, such as silica gel. The study provided some insights into the palladium(I1)-carbon monoxide reaction mechanism and produced a palladium(I1) reagent that may be used on supports such as paper. The reagent is dry to the touch but does contain water in the hygroscopic acetamide for a sequential reaction that produces dispersed black palladium metal. Experimental Section
+Thispaper was presented at the 190th National Meeting of the American Chemical Society,Chicago, IL, Sept. 8-13, 1985, as CHAS 11. 500
Environ. Sci. Technol., Vol. 21, No. 5, 1987
Preparation of Test Reagents. All of the compounds discussed here were prepared by displacement of acetonitrile ligand from tetrakis(acetonitrile)palladium(II)
0013-936X/87/0921-0500$01.50/0
0 1987 American Chemical Society
0.8
tetrafluorobroate [ [Pd(CH3CN)4](BF4)z] by a ligand of choice. Tetrakis(acetonitrile)palladium(II) tetrafluoroborate was prepared by the method of Wayland and Schramm (11), in which 1.062 g of nitrosyl fluoroborate
-
r
+ BNOBF, Pd2++ 2 B F r + 2NOf Pd2+ + 4CH3CN [Pd(CH3CN),I2+
Pd
-
(Pfaltz & Bauer) dissolved in 50 mL of anhydrous acetonitrile was reacted with 0.452 g of 20-mesh palladium sponge (Aldrich), with vacuum immediately applied. After 10-h reaction time, during which time the vacuum was occasionally renewed to remove evolved nitrous oxide, 50 mL of absolute diethyl ether was added under a dry nitrogen atmosphere to precipitate [Pd(CH3CN),](BF,),. The product was washed 6 times with absolute ether and dried under vacuum. The yield is nearly stoichiometric and the purity nearly 100%. For preparing the reagents in addition to tetrakidacetonitrile)palladium(II) tetrafluoroborate to be tested for response to carbon monoxide, a quantity of the [Pd(CH,CN),](BF,), complex salt and a 6-fold molar excess of the ligand to be substituted for acetonitrile were dissolved in anhydrous acetone, applied to the support, and dried. [Pd(CH3CN),I2++ 4ligand
-
[Pd(ligand),],+
-
@
I
01 0
I
I
10
Acetomide/[Pd
20 ( C H 3 C N)4]
I
I
30
'-
40
m o l e rat io
Figure 1. Dependence of reagent response on the mole ratio of acetamide to palladium(1I).
0.6
f
a
E
0.6
0 9
+ 4CH3CNt
The reagents so prepared were tested by exposure to pure carbon monoxide immediately after drying and after 1 week sealed in a clear glass bottle. The pure reagents were generally light yellow in hue, but those that were sensitive to moisture turned a distinctive light brown on standing, even when sealed in a bottle, and exhibited reduced sensitivity to reaction with carbon monoxide. Tetrakis(acetamide)palladium(II) Tetrafluoroborate Reagent. For the quantitative studies, 0.40 g of [Pd(CH,CN),](BF,), and 1.06 g of acetamide were dissolved in 10.0 mL of water. Whatman No. 1 filter paper, cut to 22 mm X 22 mm squares, was soaked in this solution for 2 min, dried under vacuum a t room temperature for 5 h, and stored in clear glass bottles. A square of reagent paper was placed in a flask of accurately measured volume, and the appropriate volume of pure carbon monoxide that would provide the desired concentration of carbon monoxide was added by injection with a microsyringe through a rubber septum. Reflection absorbance measurements were made with the Perkin-Elmer Model 124 visible-ultraviolet spectrophotometer modified for reflection absorbance measurements as described in the studies of the tin(I1)-diphenylcarbazide solid reagent for atmospheric oxidants (12) and the Purpald-acetone aminal solid reagent for formaldehyde (13). Results and Discussion The responses, fresh and after 1 week of storage of the 11reagents prepared, are shown in Table I. Only [Pd(CH3CONH2)4](BF,), exhibited undiminished sensitivity to carbon monoxide after storage or exposure to laboratory air. Its lack of response to moisture was such that it could be dissolved in water for application to the paper support without loss of reactivity toward carbon monoxide. As the sensitivity of the [Pd(CH3CONH2),J2+cation toward carbon monoxide appeared to increase with increasing mole ratio of acetamide to palladium(II), the effect on its reactivity at various mole ratios was investigated with the results shown in Figure 1. Accordingly, a reagent with 20-fold excess of acetamide was used in subsequent tests.
F-"'"-L
0
I
I
I
20
I
40 E x p o s u r e !!me
I
1
I
60
60
I
100
I
I
120
mnuter
Figure 2. Reagent response at 580 nm at various exposure times to several fixed carbon monoxide concentrations. Each point represents the average of five determinations: (0)0.867%, (A)0.347%, (0) 0.196%, and (A) 0.051% carbon monoxide.
Comparison of the infrared absorption spectra of the pa'rent [Pd(CH,CN),J(BF,), and the [Pd(CH3CONH,),] (BF4)zreagent shows the disappearance of the cyanide triple bond peak at 2347 cm-l, the appearance of two amide N-H stretching bands at 3420 and 3340 cm-l, and the appearance of two amide bands a t 1667 and 1585 cm-'. These changes indicate that the volatile acetonitrile is lost as it is replaced as a ligand by acetamide. The reaction thus is stoichiometric, and the product is pure. The excess of acetamide apparently serves as a source of the water necessary for the reaction sequence, as it is deliquescent, and may serve as a solvent for carbon monoxide due to its excellent solvent properties. The reagent response to carbon monoxide measured at 580 nm was plotted (a) against various concentrations of carbon monoxide for fixed exposure times (Figure 2) and (b) against various exposure times for fixed concentrations of carbon monoxide (Figure 3). The range of concentrations was 0.051-0.867%, and the range of exposure times was 5-60 min. The nonlinear response curves shown in Figures 2 and 3 are typical of those observed previously with solid reagents for atmospheric oxidants (12) and formaldehyde (13). In actual practice, the preferred method probably would involve visual comparison of color intensities obtained a t constant time of exposure to prepared color standards. The smooth curves obtained indicate an underlying uniformity of response by the reqgent. When reflection absorbance values were plotted against the product of exposure time and carbon monoxide concentration, a Environ. Sci. Technol., Voi. 21, No. 5, 1987 501
0.8
r
0
I
I
I
I
I
0.2
0A
0.6
0.8
1.0
Carbon
monoxide concentration, %
Flgure 3. Reagent response at 580 nm to various carbon monoxide concentrations at several fixed exposure times. Each point represents 60, (A)30, (0) 10,and (A) the average of five determinations: (0) 5 min.
0
2
4
' E x p o s u r e timq'2
6 x
8
(COconcn\"2,
d
n
10
Flgure 5. Reagent response at 580 nm to the square root of the product of carbon monoxide concentration and exposure time. The sample correlation coefficient r 2 is 93.6%.
r
Table I. Palladium(I1) Complexes Prepared and Tested on Cellulose Filter Paper with Carbon Monoxide
I D
0.6 9 0
ligand
0
0
I
I
I
I
20
40
60
80
E x p o s u r e l i m e x CO c o n c e n t r a t l o n , m i n x
I
100
x
Figure 4. Reagent response at 580 nm to the product of carbon monoxide concentration and exposure time. Each point represents the average of five determinations. The sensitivity of the reagent in the most sensitive region of the response curve is the inverse of the straight line shown, which Is 10.1 min % (absorbance unit)-'.
nonlinear response curve was also observed (Figure 4). However, a nearly straight-line relationship was obtained when the square roots of the products of exposure time and carbon monoxide concentration were plotted against reflection absorbance values (Figure 5). The more general treatment of diffuse reflectance from multiple scattering layers proposed by Kubelka and Munk (14-16), which has several constraints when applied to a colored substance on a support such as filter paper, also yielded a straight line when several simplifying assumptions were made. The responses of the reagents shown in Table I reflect a finely tuned comparison of weakly complexing ligands with palladium(I1) as reagents for carbon monoxide. The tetrakis(acetamide)palladium(II) reagent combines the properties of a ligand sufficiently weak to permit the reduction of palladitlm(I1) to palladium(0) by carbon monoxide but sufficiently strong to resist replacement by water or hydroxide ion. It had been observed in previous studies that ammonia and aliphatic primary, secondary, and tertiary amines produce palladium(I1) complexes that are completely resistant to reaction with carbon monoxide. Tetrachloro- and tetrabromopalladate(I1) complexes react with carbon monoxide if liquid water is present. The tetraiodopalladate(I1) complex is highly colored, and re502
Environ. Sci. Technol., Voi. 21, No. 5, 1987
cyanides (nitriles) methyl (acetonitrile) tert-butyl benzyl benzo sulfoxides dimethyl di-n-butyl di-n-octyl 1-thiacyclohexan-4-one 1-oxide imides acetamide succinimide phthalimide
response" freshly after prepared 1 week
+++ +++ ++ +t
++ ++ + + +++ ++ ++
+ t
nt nt
+ nt nt nt
+++ ++ ++
OResponses: (+++) excellent; (++) good; (+) fair. nt denotes not tested.
action with carbon monoxide is difficult to observe. Water would seem to be the ideal complex-forming ligand, but palladium(I1) does not appear to form well-defined aquo complexes. The presence of water appears to lead to nonreactive hydroxo complexes when the ligands of the palladium(I1) complex have complexing ability weaker than that of water. From the reactions observed it would seem that the square-planar dsp2tetrakis(acetamide)palladium(II) complex cation expands to a square-pyramidal dsp3 complex upon the addition of carbon monoxide, followed by attack by a water molecule:
~
Environ. Sci. Technoi. 1987, 27, 503-505
In the process, the pair of electrons left by the carbon monoxide converts the palladium(I1) to finely divided palladium(O), which is black. The hue of the original light yellow complex becomes darker in proportion to the amount of palladium metal produced, which in turn is proportional to the amount of carbon monoxide that has reacted with the palladium(I1) complex. As in other methods based on palladium(II), interference will be observed from gases that precipitate palladium(II), such as hydrogen sulfide, or reduce palladium(I1) to the metal. Normally such gases are present in the atmosphere in much lower concentrations than carbon monoxide. Registry No. [Pd(CH,CONH,),](BF,),, 630-08-0.
(9) (10) (11) (12)
106905-52-6; CO,
Literature C i t e d (1) Ciuhandu, G. Fresenius' 2. Anal. Chem. 1957,. 155, 321. (2) Christman, A. A.; Block, W. D.; Schultz, J. Ind. Eng. Chem. 1937, 9, 153. (3) Lambert, J. L.; Hamlin, P. A. Anal. Lett. 1971, 4 , 745.
(13)
Lambert, J. L.; Weins, R. E. Anal. Chem. 1974, 46, 929. Lambert, J. L.; Chiang, Y. C. Anal. Chem. 1983,55, 1829. Main-Smith, J. D. Royal Aircraft Establishment Report Ch 324; HMSO: London, August 1941. Shepard, M. Anal. Chem. 1947,19, 77. Shepard, M.; Schuhman, S.; Kilday, M. V. Anal. Chem. 1955, 27, 380. Main-Smith, J. D.; Earwicker, G. A. Br. Patent 582 184, Nov. 7, 1946. Liaw, Y.-L. Ph.D. Dissertation, Kansas State University, 1985. Wayland, B. B.; Schramm, R. F. Inorg. Chem. 1969,8,971. Lambert, J. L.; Beyad, M. H.; Paukstelis, J. V.; Chejlava, M. J.; Chiang, Y. C. Anal. Chem. 1982,54, 1227. Lambert, J. L.; Paukstelis, J. V.; Liaw, Y.-L.; Chaing, Y. C. Anal. Lett. 1984, 17, 1987.
Received for review March 10,1986. Accepted December 19,1986. This research was supported in part by National Science Foundation Grant CHE-8311011 and by NSF Grant SPI8013291 t o Y.C.C.
Phenoxazlne as a Solid Monitoring Reagent for Ozonet Jack L. Lambert,* Yun-Long Llaw, and Joseph V. Paukstells Department of Chemistry, Kansas State University, Manhattan, Kansas 66506
w Phenoxazine exhibits selectivity for reaction with ozone in concentrations normally found in air to produce a brown color of exceptional stability. It reacts with nitrogen dioxide to form a red-orange product that is visually distinct from the dull brown produced by the reagent with ozone. The solid reagent on cellulose paper is intended for visual comparison to prepared color standards in passive monitoring or warning devices. Introduction
Tin(I1)-diphenylcarbazide was reported as a solid reagent responsive to the two common strong atmospheric oxidants of concern-ozone and nitrogen dioxide (1, 2). Our efforts to develop or discover reagents for passive monitoring devices that would be specific either for ozone or for nitrogen dioxide produced 1-methylperimidine as a specific reagent for nitrogen dioxide (3). A fortuitous observation during the course of other research on reagents for monitoring devices led to the development of phenoxazine as a selective reagent for ozone. Phenoxazine forms a dull brown color on reaction with ozone that appears to be stable indefinitely. On reaction with nitrogen dioxide, a red-orange color is formed that is visually quite distinct from the brown color produced by ozone. Experimental Section
Reagent Papers. Phenoxazine (Aldrich, 97% purity) is supplied as a nearly colorless compound that does not develop discoloration on standing in a sealed container. Reagent papers were prepared by wetting Whatman No. 'This paper was presented at the 190th National Meeting of the American Chemical Society, Chicago, IL, Sept. 8-13, 1985, as CHAS 11. 0013-936X/87/0921-0503$01.50/0
2 filter paper (4.25-cm circles) in a solution of 0.10 g of phenoxazine in 5.0 mL of ACS certified grade acetone (Fisher), drying at room temperature under vacuum, and storing in a sealed bottle. A study of available compounds chemically similar to phenoxazine revealed no response to ozone comparable to that of phenoxazine. Ozone Generator. Known concentrations of ozone were produced by an MEC 1000 ozone generator (Columbia Scientific Industries Corp.), which was calibrated by the neutral potassium iodide method ( 4 ) . The reagentimpregnated paper circles were exposed to various concentrations of ozone in the modified inverted Kimble low-form cap-style weighing bottle described by Lambert et al. (2). This 55-mm i.d. bottle has inlet and outlet ports for the airstream. Reflection Absorbance Measurements. A PerkinElmer Model 124 visible-ultraviolet spectrophotometer modified for reflection measurements as described by Lambert et al. (2, 4 ) was used. In this instrument, the incident beam from the light source is deflected onto the reagent paper surface and then back to its original path to the photomultiplier tube. The loss of incident radiant energy is read as absorbance in the usual manner. Reflection absorbance values at 500 nm were plotted against fixed ozone concentrations ranging from 0.083 to 0.55 ppm for various exposure times ranging from 5 to 90 min and against fixed exposure times for various ozone concentrations. Chemical Nature of the Reaction Product. A sample of the reaction product prepared by exposing a thick layer of reagent to approximately 1ppm ozone in an airstream for 3 days was ground to form a nujol mull. The infrared absorption spectra for the unexposed reagent and the reaction product, both in nujol mulls on silver chloride plates, were compared. Also, the reaction product sample prepared by passing approximately 1 ppm ozone in an air-
0 1987 American Chemlcal Society
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