Quantitative Spectrophotometric Analysis of Polyn itroa romatic Compounds by Reaction with Ethylenediamine Donald J. Glover and Eleonore G. Kayser Adcariced Chemistry Division, Chemistry Research Department, U . S. Naval Ordnance Laboratory, Silver Spring, Md. A NUMBER of polynitroaromatic compounds have been prepared and studied at the Naval Ordnance Laboratory. These compounds are usually characterized by elemental analysis, melting point, infrared spectrum, molecular weight, and thin-layer chromatography. Other than the last, there has been n o assay procedure available for these compounds. For some years we have been interested in the reaction of polynitroaromatic compounds with ethylenediamine, because the initial colors formed seemed to be related to their structure. However, these initial reactions are usually followed by further reactions to produce essentially red products in nearly every case. We attempted t o stabilize these colors to see if they could be applied to the assay of these materials. This report describes the successful application of the reaction producing red products. There have been analyses of aromatic nitro compounds using EDA, but not as a general procedure. F o r example, Smith and Swank ( I ) used E D A as well as other diamines for the analysis of 3,5-dinitro-o-toluamide and related dinitro benzamides in dimethylformamide. In addition, the work of Schall ( 2 ) would indicate that nitro aromatic complexes with E D A are relatively stable. H e determined pk’s in waterE D A mixtures. For convenience in discussing the compounds used in this study, the following abbreviations have been adopted: EDA DMSO TNB TNT HNBiB OTP HNB HNS
ethylenediamine dimethylsulfoxide 1,3,5-trinitrobenzene 2,4,6-trinitrotoluene 2,2 ’,4,4 ’,6,6’-hexanitrobibenzyl 2,2”,4,4’,4”,6,6 ’,6”-octanitro-mterphen yl 2,2 ‘,4,4 ‘,6,6 ‘-hexanitrobiphenyl 2,2 ’,4,4’,6,6’-hexanitrostilbene EXPERIMENTAL
Fisher Certified anhydrous E D A was used as received. The D M S O was J. T. Baker Analyzed Reagent. There was n o difference in quality, as determined by gas chromatography, between this material and D M S O which had stood over molecular sieves (Linde 13X) and was then distilled at 50 “C, 0.2 mm. All spectra were determined o n a Beckman spectrophotometer, Model DU, with 1-cm quartz cells. All data were obtained a t 28” 1 “C, which was the temperature in the cell compartment. The compounds studied may be divided into two groups: those that require n o more than 0.1 ml E D A per 10 ml of solution (and may have less), and those that require at least 0.1 ml EDA, but usually more. When the compound is in too high concentration to give a reasonable absorbance and then must be diluted, the second group requires the same concentration of E D A in the final solution as was required for complete color development. Otherwise, the absorbance
decreases in the final solution below the maximum possible. This indicates that there is a n equilibrium for the reaction of E D A with the compound. Generally, E D A was put into a volumetric flask, D M S O added and mixed. Enough DMSO was added so that when a n aliquot of the solution of the compound in D M S O was added, the solution was nearly diluted to volume. Finally, enough D M S O was added to dilute to volume and the solution mixed. The absorbance of this latter solution was determined, or if too concentrated, the solution diluted with DMSO (containing E D A if necessary). The absorbance was read within 10 minutes, although in most cases, the spectrum was stable for a t least one hour. There were two exceptions to this. F o r 2,4,6-trinitrobiphenyl, complete color development required a t least 8 minutes, and then the spectrum was stable. F o r 2,2’,4,4’-tetranitrobiphenylthe absorbance decreased and readings were taken every half minute for six minutes. F r o m a plot of this data, the molar absorptivity was determined a t zero time. RESULTS
One of the initial compounds studied in this report was OTP. Preliminary experiments showed that the spectrum of the product of the reaction with E D A was not stable in methanol, nitromethane, or E D A itself. Neither was the spectrum stable with n-propylamine, or its mixtures with similar solvents. Only when O T P was first dissolved in D M S O and then added t o a mixture of E D A in DMSO, was a stable spectrum obtained. This spectrum was stable for at least one hour. The other compounds were then tried with stability defined as at least ten minutes. In most cases the spectrum was stable for longer periods than this; then the absorbancy decreased, followed by shifts in the original maxima. The variation of the molar absorptivity with concentration is shown in Tables I and I1 for O T P and TNB. Thus, for OTP over a nine-fold range and T N B over a n eight-fold range, the molar absorptivity is constant with the largest standard deviation being 0.04. The data for all the c o m p o m d s studied are summarized in Tables I11 and IV. I n no case were the number
*
(1) G . N. Smith and M. G. Swank, ANAL.CHEM., 32, 978 (1960). ( 2 ) R. Schall, Compt. Rend., 239, 1036 (1954).
a
Table I. Variation of Molar Absorptivity with Concentration (EDA = 0.15) for OTP OTP, M x 105 530 mp X 445 rnfi X 10-4 0.825 3.09 4.30 1.21 3.11 4.35 1.61 3.120 4.37a 1.65 3.13 4.35 2.41 3.03 4.33 3.62 3.04 4.29 4.13 3.09 4.30 6.60 3.00 4.26 7.42 3.09 4.34 Mean 3.08 4.32 0.036 Std dev 0,044 Unchanged when EDA varied from 0.015M to 1.5M.
VO1. 40, NO. 13, NOVEMBER 1968
2055
__
-_
,23
-
~
--
.
I
Table 11. Variation Molar Absorptivity with Concentration (EDA = 0.15M) for TNB TNB M x 105 540 mp X 455 mp X 1 51 1 66 2 92 2 90 2 01 1 67 1.69 2.94 2.52 1.67 2.88 4.20 1.69 2.92 8.39 1.68 2.91 12.6 Mean 1.68 2.91 Std dev 0.013 0.021
c 23
r
24
-
12
of determinations less than five, nor the concentration range studied less than about four-fold. Data for the compounds requiring 0.1 ml or less of E D A are shown in Table 111, while that for those requiring a n amount of E D A greater than 0.1 ml are shown in Table IV. These results show that the compounds in Tables I11 and IV can be analyzed in solutions as low as 10-6MM.Because of the similar spectra of most of the compounds, the identification of a given compound in a mixture can probably only be made after a preliminary separation. This can be done conveniently by thin-layer chromatography. Hoffsommer (3) has used this procedure to separate and quantitatively determine the tetranitrobiphenyls (Table IV) from their decomposition products at elevated temperatures. H e has also shown the feasibility of determining each of several compounds in mixtures. (This will be the subject of a report in the near future.) It is possible that some identification can be achieved without previous separation because of the differences in the ratios of the two peaks as shown by the R values in the Tables. The spectrum of a typical compound is shown by that for T N B ( 4 ) in Figure 1. Although the spectra of a number of the compounds are stabilized by, and indeed require the presence of, DMSO, the formation of the spectra d o not require that DMSO be present for the initial reaction. This is shown by (3) J. C. Hoffsommer, U. s. Naval Ordnance Laboratory, personal communication, 1967. (4) M. R. Crampton and V. Gold, J. Chem. SOC.,B , 1967,23.
t t--
L 309
-
b
A
340
a 330
-
?
-
420
-
i
460
A
i
500
. 540
l
~1 $50
-1
620
A,mv
+
Figure 1. Molar absorptivity 6s. wavelength, mp for TNB EDA - 0.045M EDA in DMSO 0 13.5M EDA in methanol (1 ml methanol to 10 ml with EDA) the data in Figure 1, where the spectrum is the same in methanol-EDA and in DMSO only (containing 0.1 ml E D A per 10 ml solution). The solvent cut off point for EDA is 275 mp and for DMSO is 263 mp. DISCUSSION
The usefulness of the procedure can be seen by the analysis of T N T in mixtures with R D X , as shown in Table V. Three RDX-TNT mixtures were prepared and analyzed. The mole ratios of RDX/TNT were 1.47,2.94, and 14.7. In n o case was there interference by the presence of RDX, nor did R D X react with EDA when T N T was absent. The ratio 14.7 is equivalent to 93.5% (by weight) of RDX. The lesser ratios essentially correspond to cyclotols currently in use. Several other compounds were investigated but are not included in the tables for they could not be determined quantitatively or stable spectra for the molar absorptivity could not
Table 111. Spectral Data at Low Ethylenediamine Concentration
Compound 1,3,5-Trinitrobenzene
Concn range M X 105 1.5-12.6
No. of detns 6
2,4,6-Trinitrobiphenyl
2.4-21 .5
6
2,3 ',4,5',6-PentanitrobiphenyI
2.1-23.9
6
2,2',4,4',6,6'-Hexanitrobibenzyl
0.9-4.3
5
2,2' ',4,4',4' ',6,6',6 ' '-Octanitro-m-terphenyl
0.8-7.4
9
2,2',2",4,4',4",6,6',6"-Nonanitroterphenyl
0.4-2.7
11
',6" '0.9-3.3 5 Dodecanitroquaterphenyl a Ratio of molar absorbancy index at short wavelength to that at
2,2',2",2"',4,4',4",4"',6,6',6'
~~
~
2056
ANALYTICAL CHEMISTRY
Molar absorptivity at A,,
x Std dev 455(2.91) 0.021 540(1.68) 0.013 455(2.97) 0.021 545 (1.49) 0.019 450(3.00) 0.020 555 (1.46) 0.013 465(6.25) 0.088 530 (3.10) 0.016 445 (4.32) 0.036 530 (3.08) 0.044 450 (4.32) 0.040 530 (2.84) 0.033 450(5.52) 0.034 540 (4.45) 0.045 the long wavelength.
Ra 1.73
Concn of EDA, M Reaction Solution for mixture absorbance 0.15 0.015-0.15
1.99
0.15 -1.5
0.015-1.5
2.05
0.15 -1.5
0.015-1.5
2.02
0.15
0.03 -0.15
1.40
0.015-1.5
0.015-1.5
1.52
0.15
0.15
1.24
0.15
0.045-0.15
~~~~~
Table IV.
Spectral Data a t High Ethylenediamine Concentration
Concn range
No. of
Compound 2,4,6-Trinitrotoluene
M X los
2.3-23.0
detns. 4
2,2 ’,4,4’,6,6’-Hexanitrobiphenyl
1 .4-12,5
5
2,2’.4.4’.6.6’-HexanI trostilbene
1 .I-9.9
5
2,2 ’.4,4’-Tetranitrobiphenyl
2.7-21.4
6
3,3 ’,5,5’-Tetranitrobiphenyl
2.2-20.1
8
2,2’,6,6’-Tetranitrobiphenq 1
0.6-3.7
14
4.1-40.8
8
~,4,j,S-Tetranitronapl7thalene’ ‘1 ‘1
c
Ratio of molar absorptivity at short wavelength to that at Value is obtained by extrapolation to zero time. Stock solution must be fresh and used within one hour.
Molar absorptivity at, , , ,A rnp
x
lo-‘
465 (2.34) 540(1.51) 460 (4,06) 550 (3.58) 460 (6.45) 510 (3.39) 355 (1.07) 545 (2.61)h 450 (1.34) 550 (1 .99) 560 ( 2 .OX, 350 (1.08) 320 (1.44) 620 (2.92) the long wavelength.
be found. With 1,3,5-trimethyl-2,4,6-trinitrobenzenen o reaction occurred in the usual time period even with 13.5M EDA. This would eliminate, as the initial step leading to the observed spectra, the direct reaction of a nitro group and confirm that the products formed with the other compounds are Meisenheimer adducts. With E D A from 0.015M to 1.5M, 1,3-dimethyl-2,4,6-trinitrobenzene gave two maxima, 410 m p (1.55 x lo4) and 610 m p (9.3 X lo3). When the E D A concentration was increased t o 13.5M, there were three maxima, 620 mp (8.03 X lo3),560 mp (8.99 X lo3),and 410 m p (1.32 X 10”. Concentrations of EDA from 0.015Mto 0.15Mgave a spectrum o f T N T with three maxima, 380 mp (8 X IO3), 530 mp (1.4 x lo4), and 620 mp (6 X lo3), and a shoulder at 470 mp. When the EDA was increased to 1.5M, the maximum at 380 m p decreased, at 530 increased, and at 620 decreased. In addition, a new peak appeared at 460 mp with a n absorbancy equal to that at 530 mp. Finally, when the concentration of E D A was at least 12M, there were only two maxima (Table IV) at 465 mp and 540 mp. Only the last spectrum was stable for at least 10 minutes. These data would seem to indicate that if the base concentration could be increased, only two maxima in the 400 and 500 mp ranges would be produced with 1,3-dimethyl-2,4,6-trinitrobenzene. Pure E D A has a concentration of 15M. As was shown earlier, the reaction producing the maxima in the 400 mp and 500 mp ranges is apparently a n equilibrium reaction. It was of interest to see if a methyl group was necessary for the production of the 600 mp maximum. TNB, which gave a quantitative reaction with 0 . 1 5 M E D A (455 mp and 540 mp),was allowed to react with 0.0015M E D A whereby a shoulder was obtained at 580 mp, a maximum at 520 mp,and a shoulder at 380 mp. This showed that a methyl group is not necessary for this blue color formation and accounts for the earlier statement that the initial colors were usually followed in all cases by the formation of red solutions. To gain a further insight into the effect of structure on spectra formation, the reaction of E D A with the three dinitrobenzenes was investigated. Only one maximum was found with p-dinitrobenzene (430 mp, 1.24 X lo4) and n-dinitro-
Std dev 0.027 0.012 0.032 0,044 0.058
1.55
Concn of EDA, M Reaction Solution for mixture absorbance 12.0 14.7
1.13
1.5
R a
1.5
1.90
1 . 5 -3.0
1 . 5 -3.0
0.41
3.0 -7.5
3 . 0 -7.5
0.67
1.5
1.5
0.52
9 . 0 -13.5
9.0-1 3 . 5
0.15-1.5
0.15-1.5
0.024
... 0.020 ... 0.017 0.035
... 0.009 0.084
Table V.
Determination of TNT in the Presence of RDX TNT found. Af x 106 RDX, TNT added, by absorbance M x 106 M X 1oj at 465 r n M 0 2.65 2.70 39.0 2.65 2.69 3.90 2.65 2.68 7.80 2.65 2.68 77.7 0 0
benzene (441 mp, 6.38 X IO3). However, with m-dinitrobenzene two maxima were found at 560 mp and 355 mp, Crampton and Gold (9,who investigated the reaction of mdinitrobenzene with sodium methoxide, have shown that the reaction is reversible with attack at the position which is ortho and para to the nitro groups and not in between the nitro groups. In our work, nearly 1 2 M E D A was required for maximum color development and Beer’s law did not hold. For p-dinitrobenzene 1.5M E D A required 1.5 hours for maximum color development and the conformance t o Beer’s law was not investigated. Only with o-dinitrobenzene did Beer’s law hold, with maximum absorbance obtained 8-10 minutes after mixing. It may be that the reaction with both ortho and para dinitrobenzene is not reversible, but occurs by replacement of a nitro group with a -NHCH2CH2NH2 group. Compounds producing such spectra are exemplified by o-nitro-N-ethylaniline, 425 mp (6200) andp-nitro-N-ethylaniline, 390 m p (1.9 X IO4) (6). These data are consistent with the reaction products from ortho and para dinitrobenzene with EDA. The additive nature of reaction with two picryl groups is shown by the data for HNB. That ring interaction interferes with this addition is evident from the fact that both molar (5) M. R. Crampton and V. Gold, J . Cliem. SOC., B, 1966, 498. (6) M. J. Karnlet, “Organic Electronic Spectral Data,” Vol. I, Interscience, New York, N. Y . , 1946-1952, p 207. VOL. 40, NO. 13, NOVEMBER 1968
2057
absorbancies are not twice that for TNB. However, when an ethyl group is inserted between the rings ("BIB), the additive nature is confirmed, for the molar absorbance is twice that of TNB. Likewise, with HNS, reaction with both rings is evident; further, there is probably additional stabilization due to the double bond, with coplanarity likely.
ACKNOWLEDGMENT The polynitropolyaromatic compounds were prepared by members o f t h e Advanced Chemistry ~ i ~ iH, ~G. i~ ~d ~~ l , ~ h , K , G. Shipp, J . c. D ~ and J~, c. ~ ~ ~ ~ f ~ f , ~ RECEIVED for review May 13, 1968. Accepted July 12, 1968,
Determination of Total Hydroxyl on the Surface of Silicas by Lithium Aluminum Di-n-Butyl Amide Titration Gene E. Kellum,' R o b e r t C. S m i t h , and Kenneth L. Uglum2 Dow Corning Corp., Midland,Mich.48640 A RECENT PAPER described the use of lithium aluminum di-nbutyl amide as a direct titrant for quantitative determination of silanol and water ( I ) . The procedure utilized N-phenyl-paminoazobenzene as a visual indicator t o detect the end point. The titration method was employed to determine total hydroxyl (silanol and water) in monomers, low and high molecular weight polymers, and resins. Reaction times from 30 t o 60 seconds were reported. This note describes the application of lithium aluminum din-butyl amide (amide) as a titrant for total hydroxyl o n the surface of various silicas. A differential reaction rate titration method was utilized to obtain total hydroxyl concentration in the presence of a slow residual reaction. The visual end point was maintained over a specified time interval (7 t o 10 minutes) and the result obtained by extrapolation of the titration curve t o zero time.
ML AMIDE REAGENT
IR
EXPERIMENTAL Reagents and Apparatus. The majority of reagents and titration apparatus were the same as previously reported ( I ) . As before, the amide titrant was prepared by reacting lithium aluminum hydride with di-n-butyl amine. Diphenylsilanediol was dried over barium oxide in a desiccator under slight vacuum. Procedure. The titration was carried out similar to that reported earlier (1). Forty milliliters of dry 1:l THFpyridine and 10 drops of the 0.1% N-phenyl-p-aminoazobenzene indicator solution were added to the titration cell and titrated to a purple-red color persisting for about one minute. Sufficient diphenylsilanediol (or some other available silanol-containing material) was added to the titration cell to give about 5 ml titration to a red color, signifying a n excess of amide titrant. This end point was maintained with titrant addition until the color persisted for about two minutes. The titration of the silanol served as a pre-treatment for the solvent and indicator system. Immediately after establishing the end point, a 0.2- to 0.5-gram silica sample was introduced into the cell o n the solvent surface using a small tapered aluminum cylinder. The sample weight was obtained by difference by weighing the cylinder before and after sample addition to the cell. Titration to the end point was performed at several intervals until the reagent consumption rate was constant for 3 to 4 minutes. A plot of milliliters of reagent added c's. time was prepared as in Figure 1, 1 Present address, Gulf Research and Development Company, Kansas City Laboratory, 9009 W. 67th St., Merriam, Kan. 66204. 2 Central Michigan University, Mount Pleasant, Mich. 48858.
(1) G. E. Kellum and K. L. Uglum, ANAL.CHEM., 39, 1623 (1967).
2058
ANALYTICAL CHEMISTRY
4.0
0
2.0
4.0
6.0
8.0
10.0
TI ME( MIN Figure 1. Typical amide titration curves 1. QUSO F-20, 2. Cab-0-Si1 S-17, 3. Water, 4. Treated Dow Corning Silica A, 5. Dow Corning Silica A and the end point determined by extrapolating the curve to zero time. Daily standardization of the amide reagent was carried out as before (1) employing dry reagent grade 3-methyl-1 -butanol as the source of hydroxyl. The normality of the reagent was calculated by :
N =
( Z OH, alcohol standard) (alcohol weight, grams)
-
(ml)(0.017)( 100) (19.3)(grams)
(1) (ml>(l.7) Total per cent hydroxyl in the silica samples was determined by: (ml)(N)(O.O17)(100) % OH (amide) = (2) Sample weight
