prop-2-yne, the ion peak was small. Clearly, this mode of ionization may be of considerable analytical value but must be cautiously interpreted. In the work of Frkdel and Sharkey, the mass 47 ion was reported for the methoxy alkanes, b c t in the present investigation it was absent from the spectra of metho.xyhexoxyethane, methoxyheptoxyethar e, and methoxyoctoxyethane. A corresponding rearrangement ion was not observed for propoxy, butoxoxy, etc., at masses 61, 75, etc. Presumably, this unique species a t mass 47 depends exclusively upon the ethoxy groip. High resolution mass spectral data indicate it to he (CzH,O)+ (1) and the suggestion that it is (CH302)+ [(Z)F. 1171 seems unsupported. Unsaturated and Aromatic Acetals.
Seven of the acetals listed in Table I11 contain unsaturation and two contain phenyl groups. Most of the general breakdown features were observed, but a few exceptions were noted. Most important of these is that if unsaturation occurred in the alcoholic portion then the predominant mode of decomposition in which R1.is lost was essentially absent. The resulting spectrum was characterized primarily by the saturated R1CHOR2]+ ion and the OR2]+ion. The remalnder of the peaks seem to be caused by hydrocarbon ions.
Ident,ification of such compounds as acetals is often difficult. KO similar anomaly occurred if the unsaturation was in the aldehydic portion of the acetal. The normal breakdown modes were observed, but of course the R1CHOR2]+ ion now occurred a t masses isobaric with the saturated hydrocarbon ions, and identification is again somewhat speculative. However, establishment of acetal characteristic is generally certain through the strong CH(OR2)(OR3)+ ion and other acetal peaks. The mass spectra of the two aromatic acetals showed some features characteristic of acetals and some characteristic of aromaticity. Thus, both have a mass 103 ion; however, it is not known whether these ions are CHThe di(OCzHs)+ or +-CH=CH+. ethoxyphenylethane showed no ionization due to loss of . OCZHJbut the other aromatic compound did and, in addition, the ion due to loss of mass 73 (possibly loss of .OCzHs followed by loss of CzHJ was the base peak. Both showed the expected rearrangement ion a t mass 75, but for diethoxyphenylethane the ion was not in the usual range of 2 to 10% of the total ionization but was 47% (the base peak). The unsaturated 3 phenyl - 1,l - diethoxyprop-2-yne was the only acetal studied that gave ionization a t the parent mass,
-
ACKNOWLEDGMENT
Thc authors thank J. W.Ralls and R. RI. Seifert who synthesized some of the acetals used in this work. LITERATURE CITED
(1) Beynon, J. H., Lester, G. R., Williams, A. E., J. Phys. Chem. 63,1861 (1959). (2) Biemann, Klaus, “Mass Spectrometry,” pp. 74, 117, McGraw-Hill, S e w
York, 1962. (3) Friedel, R. A,, Sharkey, A. G., Jr., ANAL.CHEM.28, 940 (1956). (4) McFadden, W. H., Lounsbury, XI., Wahrhaftia. A. L.. Can. J. Chem. 26, 990 (1958):‘ (5) McFadden, W. H., Teranishi, R., Nature 200, 329 (1963). (6) McLafferty, F. W.,ANAL.CHEM.29, 1782 (1957). (7) Ralls, J., McFadden, W., H., Seifert, R., Black, D. R., Kilpatrick, P., unpublished results on pea volatiles. (8) Sharkey, A. G., Jr., Shultz, Janet L., Friedel, R. A., ANAL. CHEM.31, 87 (1959). (9) Teranishi, R., Corse, J. W.,McFadden. W. H.. Black. D. R.. hforcran, A. I., J,’Food Shi. 28,478 (1963). RECEIVED for review November 6, 1963. Accepted January 30, 1964. Western Regional Research Laboratory is a laboratory of the Western Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture. Reference t o a company or product name does not imply approval or recommendation by the U. S. Department of Agriculture t o the exclusion of others that may be suitable.
Acid-Base Method for Determining Mixtures of Either Hydrazine-1,1 -dimethylhydrazine or Monomethy Ihy d ra z ine- 1,I- dimethy Ihy dra z ine HUGH E. MALONE and ROBERT A. BIGGERS Air force Rocket Propulsion laboratory, Edwards, Calif.
B A method is presented for. determining mixtures of hydrazine-1 ,I -dior methylhydrazine (NzH4/UDMH) monomethylhydrazine 1 ,I dimethylhydrazine (MMH/UDh\H). This method i s based on the difference in reaction rates for acetylating hydrazines. Both N2H4 and MMH react iinmediately while the acetylation of UDMH proceeds slowly. The reactions are conducted in acetic acid medium. Two titrations are required: one measure:;the total basicity of the hydrazine mixtures; the other measures UDMH after the NzH4 or MMH has reacted with Ac20.
-
H
-
(NzH~),monomethylhydrazine (MMH), and 1,l-dimethylhydrazine (UIXMH) are important both individually and in mixtures as rocket .‘uels. -4 50-50 YDRAZINE
mixture of NzHdIUDhIH is used as the fuel blend for the Titan I1 ICBM. Though mixtures of MMH/UDMH are discussed herein, they are not being used in any weapon system. Several methods have been developed for analysis of N2H4/UDMH. These methods use gas chromatographic techniques (1, 6), standard iodate titration in an aqueous system (9), or the selective reaction of hydrazine with salicylaldehyde and subsequent titration of basicity with perchloric acid in nonaqueous medium (6). The salicylaldehyde method has the end point disadvantage encountered in most weak base-strong acid titrations. Acetic anhydride used herein for acetylating hydrazines was used primarily as a solvent for titrations of amides (IO), weak bases (S),and nitrogen bases (8),
and for improvement of the end point in nonaqueous titrations (11). Fritz and Schenk (4) used acetic anhydride for acid catalyzed acetylation of hydroxyl compounds in ethyl acetate. Although the reactions for acetylating hydrazines are known (a) and reported ( 7 ) , the authors are unaware of any efforts to determine hydrazines and substituted hydrazines by this method. EXPERIMENTAL
Preparation of Sample. Pipet 0.4 ml. of the N2H4(UDMH or M M H / U D M H mixture into a tared, cooled 50-ml. volumetric flask containing 40 ml. of glacial acetic acid. Weigh to the nearest 0.1 mg., obtaining the sample weight by difference. Dilute t o the 50-ml. mark with acetic acid and mix thoroughly. VOL 36, NO. 6, MAY 1964
1037
I ml oliquol of UOMH (2ml UDMH / 50ml Acelic Acid1 t 2 ml Acetic Anhydride
70
N2b
-
x MMH o
= 60.3 millimoles/l ml aliquol :
UDMH
38.0 millimoles/lml oliquol
: 26.1
millimoles / I ml aliquot
1000 95 4
76 3
c1 W
I-
2
572
W
l Y
f
382
8
10
19 0
0
60
30
90
120
150
180
210
240
270
300
330
20
360
40
80
60
100
120
140
160
MILLIMOLES OF ACETIC ANHYDRIDE
TIME IN MINUTES
Figure 2. Immediate effect of acetic anhydride on hydrazines
Fiaure 1 . Effect of time and temperature on the reaction rate of UDMH with acetic anhydride Determination of Total Basicity of the N2H4/UDMH Mixture. Pipet a 5.0-ml. aliquot from the prepared sample into a 50-ml. beaker containing 20 ml. of spectrograde acetonitrile. Add 5 drops of filtered 0.2% quinaldine red indicator in acetonitrile and titrate with 0.1N perchloric acid in acetic acid standardized against potassium acid phthalate in acetic acid until the red color of the indicator changes to colorless. Indicate this amount for value A in calculations. Titrate a blank of acetonitrile and quinaldine red indicator to the colorless end point. Determination of UDMH. Pipet a 5.0-ml. aliquot of the prepared sample into a 50-ml. beaker containing 20 ml. of acetic acid, 2 ml. of acetic anhydride, and 5 drops of quinaldine red indicator. Stir 1 minute and titrate with 0.1N perchloric acid in acetic acid until the red color of the indicator changes to colorless. Indicate this amount for value B in calculations. Titrate a blank of acetic acid, acetic anhydride, and quinaldine red indicator to the colorless end p k t .
-
UDMH-acetic anhydride mction. The reaction, as indicated by a decrease in milliliters of HC104, is slow until the temperature is increased. Effect of Acetic Anhydride. As the quantity of acetic anhydride is increased in samples of N2H4, UDMH, and M M H , the milliliters of HClO4 titrant required for neutralization decrease much faster with NzH4 and MMH. The U D M H is slow to react
RESULTS A N D DISCUSSION
Reactions of Hydrazine, Monomethylhydrazine, and 1,l-Dimethylhydrazine with Acetic Anhydride. The experimental procedures developed are based on the reactions of NzH4, M M H , and U D M H with acetic anhydride. Reaction products are shown in the following equations: With N2H4-1,Zdiacetylhydrazine:
0
ti
NZH4
+2
Hac-C
N
+ 2 CHsCOOH
’
HsC4 \0
(1)
HP\C-CHs
ll
0
With MMH-l,2-diacetylmethylhydraeine :
CALCULATIONS
% Hydrazine (or MMH)
=
(A-U)- (B-b) X N HC104 X MEW W
% UDMH
With UDMH-2-acetyl-1, l-dimethylhydrazine :
=
(B-b) X NHClOI X MEW W
x
0
10
A Beckman eeromatic p H meter wit,h glass-platinum calomel electrodes was used to determine the stoichiometric end points for both the total alkalinity titration and the acetic anhydride titration. The quinaldine red end point changes from red (actually pink) to colorless approximately 0.01 ml. after the greatest change in potential. The indicator and potentiometric end points can also be improved appreciably by using either dioxane or nitromethane However, each of these solvents must be eepecially purified to remove basic impurities which produce high blanks. 1038 *
ANALYTICAL CHEMISTRY
Hac\
N
/CHs
I
H/N\H
+
II
Hac-C
O \
H3C-C/
il
The rates of the reaction differ greatly as both the NzH4and MMH are rendered neutral to perchloric acid titration almost immediately, while UDMH reacts slowly in acetic acid medium. The product of Equation 3 occurs only after a considerable time lapse a t room temperatures. Figure 1 shows the effect of time and temperature on the
Hac\ +
/CH3
N
+ CHsCOOH
i
(3)
H/’\C-CHa
il
0
even in a n excess of acetic anhydride. This effect is shown in Figure 2. Shown also is the plot of the titration with perchloric acid of individual samples of NzH4 and MMH. acetic anhydride was added in increasing molar concentrations from 20 mmoles to 130 mmoles to these samples. The curves for NzH4 and M M H sub-
Table I.
Effect of Water Content
Sample weight M1. NZH4/ M1. Hclo4 UDMH HClO, after before Totd total‘ acetWater, HzO wt. of alka- yla% addeda sample linity tion 0.99 2.31 4.65 7.84
0.8918 0.8913 0.8903 0.8818
0.9007 0.9124 0.93:37 0.95’70
4.24 4.24 4.24 4.19
1.42 1.42 1.42 1.40
a Used 1-ml. aliquot, I-gram sample/50 ml. acetic acid.
stantiate the molar rztios presented in Equations 1 and 2. Effect of Water. The water content i n N2H4-UDMH samples was increased from 0.99$& t o 7.84%, a n d the samples were malyzed by the procedure presented. Table I shows t h a t increasing the water content does not interfere wif,h the titration. Individual samples of N2H4, MMH, and U D M H were leach assayed by potassium iodate tit *ation. Mixtures of NzH4/UDMH were prepared and analyzed by the scetic anhydride method. Table I1 presents the experimental, theoretical, and variation from the calculated per cent obtained for samples ranging frorr 10% N2H4-90% UDMH to 90% N2H4-10% UDMH. Several samples cf MMH-UDMH mixtures were prepared and analyzed. Table I11 presents bhe experimental, theoretical, and variation from calculated per cents. Effect of Contaminants. The variation in per cent shown in Tables I1 and I11 results from the presence of contaminants in the hydrazines. Of these contaminants, aniline from NzH4, methylhydrazine, mei;hylene dimethylhydrazine, dimethylamine, and nitrosodimethylamine from UDMH ( l a ) will be acetylated at different rates and will titrate similarly to either Nz& or UDMH depending on the time allowed for acetylation. Further work is necessary to establish not only the reaction rates for these contaminants, but also to determine the contaminants in M M H and measure their reaction rates. Titration of Contaminants. Samples of each of the hydrazines were acetylated a n d titrsted with 0.1N HC104. Several of the N2H4 samples were from drums which had been stored over five years, while the U D N H a n d M M H were stored for one year. The N2Hl and ,MMH gave a titration value s fter acetylation ranging from 0.10 to 0.20 ml. The UDMH samples required 0.05 ml. less after acetylation than a total alkalinity
Table II. Analysis of NaH&DMH Mixtures Theoretical Variation in 70 Experimental N ~ H I UDMH‘ N2H4 UDMH N2I4 UDMH 92.2 7.6 92.3 7.3 -0.1 $0.3 86.3 13.0 86.6 13.1 -0.3 -0.1 74.0 25.4 74.3 25.4 -0.3 0.0 65.6 34.4 65.3 $0.3 -0.3 34.7 56.0 44.4 56.0 44.0 0.0 $0.4 57.8 42.0 41.8 -0.4 $0.2 58.2 $0.3 55.1 45.1 44.8 -0.1 55.2 50.4 48.1 50.3 48.3 $0.1 -0.2 20.7 78.4 20.3 78.8 $0.4 -0.4 12.2 87.6 11.7 $0.5 -0.6 88.2
Table 111. Experimental MMH UDMH 41.6 56.5 50.4 49.2 40.1 56.0 47.0 49.8 63.0 34.5 63.6 36.1
Analysis of MMH-UDMH Mixtures Theoretical Variation in % MMH UDMH MMH UDMH 41.7 57.0 -0.1 -0.5 51.1 48.2 -0.7 $1.0 40.5 56.1 -0.4 -0.1 47.6 -0.6 -0.4 50.2 63.1 34.9 -0.1 -0.4 63.9 35.3 -0.3 +0.8
titration. The results after acetylating the hydrazines are shown in Table IV. The first two samples of MMH/ UDMH shown in Table I11 were corrected using the values shown in Table IV. The variation in per cent decreased from 0.5% to 0.1% as shown in Table V. The contaminant titration values used for correction can be used only when the individual hydrazines are available. ACKNOWLEDGMENT
The authors thank Charles K. Arpke and Louis A. Dee for their technical assistance in the preparation of this paper.
Table V. Experimental MMH UDMH 41.8 57.1 50.7 48.0
Table IV.
Sample NO. l b
26 36
Titration of Contaminants in Hydrazines N2H4 GDMH ml. ml. MMHml. HC10, HC10, HClOd after after after AcnO AczOa AczO 0.20 0.04 0.14 0.23 0.03 0.10 0.20 0.06 ... 0.21 0.06 ... 0.20 ... ...
4 55 6 0.17 ... ... 7” 0.05 ... ... M1. HClOd less than total alkalinity value. Sample size 0.025 gram. I, Drum samples stored up to five years. Distilled over 75-plate distillation column.
Contaminant Correction for MMHIUDMH Theoretical Variation in yo _ ~ _ _ _ _ _ _ MMH UDMH MMH UDMH 41.7 57.0 +o. 1 $0.1 51.1 45.2 -0.4 -0.2
LITERATURE CITED
(1) Cain, E. F. C., Stevens, M. R., paper
from 2nd International Biannual Symposium on Gas Chromatography, June, 1959. (2) Clark, C. C., “Hydrazine,” p. 43, Mathieson Chemical Corp., 1953. (3) Fritz, J. S., Fulda, M. O., AXAL. CHEY.25,1837 (1953). (4) Fritz, J. S., Schenk, G. H., Ibid., 31, 1808 (1959). (5) Mackey, M. D., Cnited Technology Corporation, Sunnyvale, Calif., unublished paper, May 28,1962. (6P Malone, H. E., ANAL.CHEM.33, 574 (1961). (7) Sadtler, Samuel P. & Son, Inc.,
Standard Spectra, No. 19955, Aldrich Chemical Co.; KO.11889, Iowa State College. No. 11890, Iowa State College. (8) Streuh, C. A., ANAL. CHEM.30, 997 (1958). (91 Weed, A. F., Analytical Method CA-106, Food Machinery and Chemical Corp., May 1960. (:LO) Wimer, D. C., ANAL.CHEM.30, 77 (1958). (11) Ibicl., p. 2060. (12) Zarembo, J. D., Analytical Method CA-196. Food Machinerv and Chemical Corp., February 1962. ‘ RECEIVEDfor review October 29, 1962. Resubmitted n’ovember 18, 1963. Accepted January 31, 1964. VOL. 36, NO. 6, MAY 1964
e
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