The Coulometric Determination of Hydrazine and Substituted Hydrazines EDWARD C. OLSON The Upjohn Co., Kalamazoo, Mich.
b A rapid, accurate, and automatic coulometric titration procedure far the determination of hydrazine and monosubstituted hydrazines with electrolytically generated bromine has been developed. The method has a standard deviation of approximately & 1 %, and is based upon the use of the faraday as a standard. Samples in the 3- to 5-mg. range may be handled readily, and in most cases the procedure can b e applied without prior separation of the hydrazine. The use of chlorine as an oxidizing agent offers no advantage over bromine. Unsymmetrically disubstituted hydrazines react stoichiometrically, but consume six equivalents of bromine rather than four as does hydrazine. Symmetrically disubstituted compounds do not give stoichiometric results.
I
h ~ d r a z i n canti ~ hj-tlr:izinc, tlcrivativcs haw rwc4vctl c ~ t ~ n s i d ~ ~ rattrrition al~lt~ :is propc’llants ant1 :IS ~~l~:irmac~ologicaI agcnts, and scvc w l Imwtlurcs for thtsir rlctrrmiiiation Iiav(3 h ~ , ~)ublislic~l. n Th(, majority are .~:l)c’c’troi)liotometrieantl are b a s d upon thv rvart,ion of hydrazine in acidic- solution \\-it11 p-dinic~thylaminobcnzaldeliyrlc,, Rtwtion 1. This reaction is N WX~I,:ST \-i:.ms
u
H
R;-N=C0N(CH312
+
H20
(21
to p t ~ i n i tthr drterniination of micronirth!-ihydrazin(,. .Ill c-olorimrtriv methods suffer from
g ~ i n qunntitics i of
O H
u
c ~ s t r c ~ r i ircmitiw i ~ l ~ ~ and is best uscd for thc tl(~torniination of trac’cs of hydrazinc. ( 7 ) . T h e s:inie rcwtion has also I)wn a p p l i d to thc dctc~niination of iric~tli~lli~tlrazinc ( 6 ) . In this casr the sc’nsitivity of thc rcac*tion is drcrmsed wnsidorably, sinw rcaction can occur with only one mole of p-dimethylaminobc~nz:ildrh~-dc,Reaction 2. The reaction is, ho\vcvc,r, still sufficirntlysc’nsitive
H
the disadvantage of requiring a primary standard of th(, inatcrial to be determined. If this is not available, the results must hc given in tcrms of some spec-ificdstantlard samplc. In addition, the wartions cmploywl are not generally fast rnough to pcrmit automatic titrations. Sinrc niany hydrazines :ire not readily obtainablc in a high state of purity, the usdiffri,rnt s o l \ ~ n t sy st (Tins \ v c ~ i c~niployt~ti ~ tl u rip g this s t u d y . ’l’hv choict~of solvrnt systcm I Y R B , LIS \ \ i l l hv tliscausseti I:itc>i,, dictatcitl 11). thv particular h\,tli,:izine bring titr:itrtl. ‘I‘hc solvents \vi,r(\: that ( iiililoyc,tl by IA ( 2 ) for tht’ tlctc~rniii~ation of 1ins:tturation \vhic.li t~)niistaof 30 nil. of : t c d c arid, 13 1111. of inc~th:iriol,7 nil. of 1.11 aquc’ous potassiuni hroniitl(~. and 0.1 gram of nit,r(,uric, a(~i~t:itv pvr 50 ml. : aquoous 0.3.11 h)-tlroc.lilorir acaiti c~ontaining0.1.If potussiuni 1)roinidr; a n d 80yc arctic. a(.icl-20% a.atc,r c+ontuining1.0.1/ h ~ d r o vhlorir a d .
Procedure. ‘Ti~aiisfrr a \vc~ighd sampli~containing from 3 t o ti nig. of the hydrnzinr t o bc drtcrniincd t o a 100-nil. hvak(,r ctontaining a magnc~tic?stii,ring h i r . Add 50 nil. of solvrnt, inscirt the c~lwtrodcassembly, :md titratc, a t a t~onstantcwrrcnt chosen to givr :I 200- t o 300-~eroiidtitration. Dt~tc~riiiint~ thc ])lank time on the solvent and c a l d a t c thP amount of hydrazine prcwiit. The rncl point, is taken as that tinit, : i t ivliirh thr. meter remains a t the cutoff crvrcmt (10 pa.) for not Icss than 30 w c ~ ~ i d s . RESULTS AND DISCUSSION
Thc rwults in Table I shon. thr c>ffccts of substitution upon thc consumption of broniinr. by hydrazines. For hydrazine itsrlf arid for monosubstituted hydrazinrs, thc r c ~ t i o nproceeds according to Rtwtion 4 if the substituent is not a tleac~tivatt~l aryl substituent. For ex-
+ + + 4HRr
R S H S H , t- 2Br H?O ROH X2 -+
(4)
anipl(,, 2,~-tlinitrophrnylhydraziiic rcarts v c ~ ys h l y nit11 the consumption of only t n o equivalents of bromine. VOL. 32, NO. 12, NOVEMBER 1960
1545
Effect of Substitution on the Titration of Hydrazines with Electrolytically Generated Brz
Table 1.
[In acetic acid-water-methanol containing Hg(OAc)n] Mol.
E#?'
Wt.
Compound
Equiv. of Bromine Consumed
obtained in acetic acid-water-methanol and in aqueous systems for hydraziIie and monosubstituted hydrazines. The notable exceptions are o-methoxy-amethylphenethylhydraeine and a-methylphenethylhydraiine The consumption of the third mole of bromine in these cases is due to the spontaneous dehydration of the primary reaction product in aqueous acid followed by addition of bromine to the double bond, as in Reactions 5 to 7. This was proved by large
.
Remarks
130.1
32.83
3.96
100% by titration with NaOH
144.2
35.96
4.01
100% by titration with NaOH
144.6
37.01
3.91
CH3 I QCR2-;-NHNH2+ OCH3
186.7
45.62
4.10
216.7
54.31
3.99
99.6% by titration with NaOH
198.2
96.48
2.05
Very slow reaction
229.2
61.67
3.72
About 94.9% pure by solubility analysis
18.72
3.96
\
'
OCH~
\
O C H ~ H
0
//"
74.08
CH3C - N H N H 2
118.1
14.84
7.96
t BrZ
60.1
10.22
5.88
Technical grade
220.7
36.23
6.09
Slow reaction
133.0
...
3.6-4.9
OCH3
Table II.
Variable from day to day and with solvent
Effect of Solvent on the Oxidation of Hydrazines by Br?
HOAc-MeOH-HtO-Hg(OAc)2 B. Aqueous 0.3M HCl-O.1M KBr
A.
Compound
Solvent
Hz SO4
CH3NHNH2.H2S04
ru.
A B A B A B
Unsymmetrically disubstituted hydrazines react stoichiometrically, but apparently by a completely different mechanism, since they consume six equivalents of bromine per mole. The results ANALYTICAL CHEMISTRY
Equiv. of Br2 Consumed/Mole of Hydrazine
B
4 4 4 4 4 Variable, always greater than 4 4 6
A B
4
A
1546
H
?L=;-CH3
OJ -"NH2
NH2 NH2
H
OCH) H
-NHNH2
H 2 0 t 2 B r 2 -+
4
obtained with symmetrically disubstituted compounds are highly variable. Table I1 shows the effect of solvent upon the titration results. I n general, there is no difference between the results
Br
Br
OCH3
scale electrolysis and isolation of a 90% yield of the dibromo compound which was identified by its infrared and ultraviolet spectra and by elemental analysis. The presence of mercuric acetate in the acetic acid-water-methanol system greatly increases the rate of oxidation of hydrazines and, in addition, causes the oxidation to take place a t a lower concentration of bromine. For example, the oxidation of methylhydraeine takes place at less than mole per liter of bromine in the presence of mercury as compared with about 5 X 10" mole per liter in the absence of catalyst. I n systems containing a high concentration of chloride ion, mercury is without catalytic effect, presumably because of the formation of undissociated mercuric chloride. The data in Table I11 indicate that for hydrazine there is no advantage in the use of chlorine as a n oxidant, but rather that the efficiency of the electrode reaction in this medium may not be 100%. The use of chlorine as a n oxidizing agent was expected t o give more rapid reaction with the more stable hydrazines since chlorine is a considerably more powerful oxidizing agent than bromine. However, in most cases the reaction was too slow to permit a direct titration with chlorine as the oxidant.
Table 111.
Comparison of Brz and Clz as Oxidizing Agents for Hydrazine
Oxidizing Agent Mole Consumed/Mole
Compound
IV. Analysis
of Hydrazine
Monoalkyl
Remarks
3.96 4.15
Very rapid Proceeds a t higher concentration of C12 than with Brz
Brz c12
4.01 4.21
Very rapid Too slow for good titration
Br? Clr
3.91 4.19
Rapid Slow
NH2NHz.HZS04
Table
(20-ma. generation current, solvent A )
All other compounds reacted too slowly with C12to give reliable results. Per Cent RNHNHz of 25 Random Samples of a Single Lot
Table V.
(High results from presence of small amount of hydrazine in o-methoxy-a-methylphenethylhydrazine) Sample 3
Day
1
2
1
101.85 104.46
100.82 101.22
102.54 101.75
101.21 101.91
102.75 102.19
2
102.87 102.09
101.50 102,22
102.85 102.53
102.35 102.28
102.56 102.41
3
103.36 101.43
100.30 101.00
100.18 97.21
107.67 99.77
97.84 99,79
4
100.28 103.78
5
100.58 102.32
100.66 101.23 101.75 103.44
98.95 101.79 105.58 103.31 .4v.
Reaction Mechanisms. 2,4-Dinitrophenylhydrazine reacts very slowly and consumes two equivalents of bromine. The product of the osidation was isolated and identified by elemental analysis and by its infrared and ultraviolet absorption spectra as the disubstituted tetrazene. The reaction may be postulated as the sum of Reactions 8 and 9.
+ PHBr
i
L
-
4
5
100.25 100.88 103.15 102.48 101.518% u f. 1.87%
97.88 101.46 103.69 103.53
Unsymmetrically disubstituted hydrazines react with the consumption of six equivalents of bromine and give, as one of the reaction products, the corresponding tetrasubstituted hydrazine. With certain oxidizing agents compoiiuLh of this type are osidized to the wiresponding tetrasubstituted tetrazenes. Formation of the tetrasubstituted tetrazene would require only two equivalents of bromine per mole of hydrazine, so that additional steps requiring four equivalents of bromine must be involved in the osidation of the tetrazene or the radical from which the tetrazene is formed. iiudrieth (I) also points out that tetrazenes lose nitrogen on heating in a n inert solvent to yield the corresponding tetraalkyl hydrazine. Simple loss of nitrogen cannot account for the consumption of bromine. The mechanism of reaction of the symmetrically disubstituted compounds is not understood at this time,
------+
RESULTS
(01
The data in Table IV mere obtained from a single lot of a highly purified sample of o-methoxy-a-methylphenethylhydrazine hydrochloride and indi-
Taken, Found, Mg. Mg. 4.440 4.641 3.581 4.368 3.500 3.300 4.851 3.582 4.842 5.087 5.066
4.469 4.587 3.600 4.343 3.515 3.277 4.938 3.575 4.794 5.091 5.057
A, Mg.
A,
+O. 029
%
+0.65 -0.95 +0.53 -0.57 +0.43 -0.70 +1.79 -0.19 $0.99
-0.044 +0.019 -0.025 4-0.015 -0.023 +O. 087 -0.007 +0.048 +O. 004 -0.009
+0.08
-0.18 u =
*0.83
cate the precision obtainable by the method under optimum conditions. Table V shows data gathered on a less pure sample of the same material by nontechnical personnel. These d a t a give a standard deviation of 1.87%. The high value of the mean was traced to the presence of a small amount of hydrazine hydrochloride remaining in the sample. By a thorough study of the reaction variables and the effects of structure upon the stoichiometry of the reon, ion i t should be possible to extend this procedure to more highly substituted compounds. Smaller samples can be analyzed with approximately the same accuracy by using a smaller generation current. Compounds which consume bromine rapidly under these conditions must be excluded from the reaction mixture. However, many unsaturated compounds, phenol, and aniline, react slowly and do not muse serious interference. LITERATURE CITED
(1) Audrieth, L. F., Ogg, B. A,, “The Chemistry of Hydrazine,” p. 128, Wiley, New York. 1961. (2) Leisey, E. A.; Grutsch, J. F., ANAL. CHEM.28, 1553 (1956). (3) Kawamura, F., Mombki, K., Suzuki, S., Bull. Fac. Eng., Yokohama, Null. Uniu. 4, 12’: (1955). (4) Kolthoff; I. M., J . Am. Chem. SOC. 46,2009 (1924). (5) McKennis, H., Yard, A, S., ANAL. CHEM.25, 1360 (1954). (6) Szebelledy, L., Somogyi, Z., Z. anal Chem. 112 (1938). (7),Watt, G. W., Ctrisp, J. D.? As. C,HEM. 24,2006 (1952). RECEIVED for review Ikcembar 28, 1959. Accepted X: 16, 1960. VOL. 32, NO. ?.- NGVEMBER ! 9 M
e
1547
