1070
S . L-RI
THE C2IT~\LI7TIC' DEC'OMPOSITIOS OF HI-DROGES PEROXIDE BY 1IISEIl CATLILYSTS K.ERI1, 2 Chemical Laboratories, T h e Hcbreiis 1 7 n i i , c r s i t y ,J e r u s a l e m , Israel Received Scptenihcr IO, 1948 ISTRODL-CTIOf
The catalytic decomposition of hydrogen peroxide by a misture of homogeneous catalysts constitutes a prohlem JF-hich has not yet been finally solved. *I, C. Rohertson (10) has esplained the promoter effect of cations on the catalytic decomposition 1 . y assuming that the valence of'the cation is increased in an intermediary product. Hon-ever, Haber and Keiss (G) considered this assumption t o be insufficiently established. Recent n-ork in this field has failed t o provide an unequivocal esplanation of' the reaction mechanism involved. I n the present investigation the catalytic decomposition of hydrogen peroxide hy sodium tungstate and sodium molybdate in the presence of cations and of their complexes has been studied. Cupric ion \vas found t o be the most active cation, 1r.hether present as such or in a comples. The aim of this study Tvas t o provide a general picture of the reaction mechanism of t.he catalytic decomposition of hydrogen peroxide and t o esplain phenomena n-hich are characteristic of this process. T H E C.iT.1LI-TIC DECOMPOSITIOS O F H T D R O G E S P E R O X I D E BY S O D I L X TCSGSTATF, . I S D SODIUM JSOLTBD.ITE
IS THE P R E S E S C E O F SIMPLE C L T I O S S
Sodium tungstate (or sodium molybdate) by itself exerts only a very feeble effect on hydrogen peroxide. A-ldditionof acetic acid in equivalent amounts depresses the decomposition of hydrogen peroside almost completely. Decomposition nevertheless occurs in equal conditions of pH in the additional presence of certain cations and their compleses. The influence of the folloiving cations was investigated : CUT+, eo++,Si++, 1In++, Cd", Znff. The gasometric measurements w r e carried out n-ith the aid of an apparatus constructed in this laboratory ( 5 ) . Most of the experiments were done in paraffined reaction vessels. The reaction vessels were kept in a thermostat a t a temperature of 15OC. (f0.1'). The volume of the solutions was 20 cc. Hydrogen peroxide n a s added t o the reaction mistures as the last component. The gas volumes measured in microburets w r e cnlculated t o standard conditions of temperature and pressure (S.T.P.). Table 1 summarizes the rcsults of experiments with the cations which h a r e been mentioned. The influence of ferric ions \\-as not further investigated, since precipitates or suspensions are formed in the presence of ferric ion I\-hich fail t o dissolve in ivealdy acid solutions, and it would be incorrect t o class these cases under true homogeneous catalysis. 1 Present :itldrpes : 1'hysie:tl Chemistry I>cp:irtment. The Pniversity, AIanchester, Englar1d. *The :iuthrir is indcl,tetl l o Professor I,. F:irk:is for m a n y helpful suggestions. -1grant from the l'alest,ine 1'ot:ish L t t l . is grntcfully acknowledged.
1071
CATALTTIC DECOMPOSITIOS OF HTDROGES PEROXIDE
The composition of the last mixtures is shown in table 1. T1p represents the time in nhich half of the amount of hydrogen peroxide initially added is decompo~ed,and T1j4 the time in which the first quarter of the initially added hydrogen peroside is decomposed. The difference T I ? - TI14 = :* shon-s the time ot decomposition of the second quarter of the amount of hydrogen peroxide initiai!y added. The last value is independent of the duration of the induction period and is therefore suitable for the determination of the reaction order. The monomolecular velocity constants calculated according to the formula 1; = In 1.3 :* conform to the reaction curves. The data shon-n in table 1 make TABLE 1 Efcct of carious cations on t h e rate of decomposition o j hydrogen peroxide Paraffined vessels; t = 15'C.; volumet = 20 cc.
cc
I
CC
1
2 2 2 2 2 2 2 2 2
1 cc. 5 cc. 1 cc. 1 cc. 1 cc. 1 cc. 1 CC. 1 cc. 1 CC.
31/10 Cu(SO3)r 31/100 CU(SO3), ~1 .11/100 Cu(S03)n X / l O Co(?;O3)2 31/10 Si(S03)2 I 31/10 hInSO: .11/10 C d ( S 0 j ) . 31/10 Zn(XOs). -11/10 cU(i\;o3)? ~1
2 2 2 2 2
1 CC. 1 cc. 1 cc. 1 cc. 1 CC. 1 cc.
.11/10 M/lO 31/10 31/10 M/10 .11/10
cc.
CU(103)2
Co(SO3)? I Si(S03)2 ' lInS04 Cd(SO3): Zn(SOs)?
t T h e amount of n-ater added is not quoted
20 32 54 48 56 72
1 1 1 1
min.
miii
38 60 105
IS 28 51
27
14
1 1
cc
1 1 1 1 1 1
' min.
1
1 1 1
1 1 1
,
13 46
51
' 1
I
i3
i n the table.
$ S o decomposition. 5 Deconiposition very slow.
it evident that the differences betn-een the influence of sodium tungstate and that of sodium molybdate are small and only quantitative in nature. Cupric ion was hy far the most active cation. All the other cations tested shon-ed only small activity, and since experiments n-ith them must be prolonged for many hours, accurate investigation of reaction mechanism in the presence of such cations i E difficult. The influence of cupric ion, the most active of the cations, was investigated in greater detail. Figure 1 presents the course of the reaction curves obtained in the presence 3f different concentrations of copper. It may be mentioned in this connection that sulfate, nitrate, or acetate ions exert no measurable influence on the reaction
1072
S . URI
velocity. The reaction curves follow a monomolecular course. The implication of the data will be discussed later.
MINUTES FIG, 1. Deconiposition of hydrogen peroxide in the presence of different concentrations of cupric ion. ITo1unie = 20 cc.; 1 = 15°C.; pnrtiffined vessels. so.
1.., . . , . . . ,
COMPOSITIOX
, ,
.I
+
or
R E ~ C T I O XMIXTURES
+ 1 c r . 11/10 C u ( N 0 8 ) ? '10 CTT,COOR + 1 c r . :!I'O CLI(SO~)~
. . . . . ' 1 c c . .11/10 S : r ~ l I o O i 2 cc. X j l 0 CHaCOOH 1 c c . 2 .if € l J l L 15 cc. €320
-
+
1 c c . 11.'10 S:i2W04 12 c c . .lI 1 c c . 2 11 11>02- 15 c c . H y O .lI/ 10 c'1I,C001I 5 (>(:. 3... , , . . . . . , . . 1 c c . .lI '10 s:l?\Yo;+ 2 1 C C . 2 .If HZ0, I1 C C . H,O 4 . . , , , , , , . , , , . , 1 cc. J1,lO s:12\vo4 2 c c . 11.10 CII,COOII 1 cc. 1 C C . 2 .I[ FIJOz f 15 C C . HA0 100; f 2 c c . .lf:lO ('H,COOH 1 c c . ?i '10 (2u(SOz)? 5 , . . . , , . . . , , , , . . , . 1 c r . .l1,10 s 1 cc. 0.531 IrJol is c c . H,O
2 . ..
, ,
,
.,. ,
, ,
,
,
,
, ,
,
,
,
,
,
+
+ +
+ +
+
+
~
..
~.~ ~~.~
+
+
.~
T H E ACTIOK OF CHLOHO-COJIPLEXLS I S THE; PItESCXCE O F SODIUM TLI-GSTATC A S D >ODIU.\I \IOLYBDATC
Chloro-compleses of the folio\\ ing cations formed in concentiated ( hloride solutions were examined: Cu*+, Golf, Si++, 31n++, Cd++, Zn+&. -4s in the case of the simple cations the cupric chloro-comples showed the highest activity and was therefore investigated in greater detail. Cupric chloro-complex i)p itself is a pon-erful catalyst of hydrogen peroxide decomposition (2). The catalytic influence of cupric chloro-complex is almost completely destroyed, llon-ever, in weakly acid solutions at a p H of 4.5-5. I n the presence of sodium tungstate or sodium molybdate, the cupric chloro-complex exerts a strong caInlytic effect even at a p H of 4.5-5. Chloride ions by themselves have only a very small in-
1073
C-ITALTTIC DECOMPOSITIOS O F H T D R O G E S P E R O X I D E
fluence even at high concentration of alkali chloride. The results of the experiments are summarized in table 2 . Figure 2 presents the course of several of the reactic )n r u r \ - e ~ . The experinients were carried out in the presence of a large excess of buffer solution ipII = 4.63) in order to ensure maintenance of a constant pH. The concentration of *odium chloride was 3 -)-. I t is seen that T* = Tli2 - Tl)4is independcnr ot tlir initial concentration of hydrogen peroxide. This proves that the hydrogcn pel oxide decomposition follow a monomolecular course. The constant 1: = In 1.3 7 1 ;oi the reaction curves is approximately proportional t o the square root of tlie concentration of the tungstate or molybdate. Also, the relationship betneen 1; arid the cupric-ion concentration is not a linear one. Sodium tungstate AJir ct
(1."
TABLE 2 c h l o m c o n z p l e x e s u n the rate of decomposition o j hydrogen peroxide Glass vessels; t = 15OC.; volume = 20 cc. (HICOO\-a (2
.v
Cu(SOa): (.t1/100)
\-aCl (4 M
cc.
-
H20:
(2 d f ) cc.
1 1 1 1 1 1 0.25 1
1 1 1 1 0.1 1 1
.-~
1
i 1 1
t
T
1
lo
$ 2'. ? 3
1 1 1
1 1
1 1 1
15
1 1
1.5
0 25
3 0 12s 3 7
= 7 5 min. =
90 min.
and sodium molybdate again shon-ed only small quantitative differences. Experiments in glass vessels and in paraffined vessels gave identical results. The comparison oi the catalytic effect of simple cupric ion and of cupric chlorocomplex in the presence of sodium tungstate or sodium molybdate in the same conditions of pH shows that the velocity constants are about forty times as great in mixtures containing an end concentration of sodium chloridc of 3 -1-as in mixtures containing no sodium chloride n-hatsoever. T H E C.1TrlLYTIC
.1CTION
O F COMPLEX CITRATES I S T H E P R E S E S C E O F SODIUbI
TUSGSTATE O R SODIUM MOLYBDATE
Table 3 presents the results of experiments with citrate complexes of the cations Cu++, Co++, Si*?, A h + + , Cd++, Zn++. All experiments were carried out
1074
K. URI
in the presence of acetic acid at a concentration equivalent t o that of the tungstate and molybdate.3 As there n-ere only small quantitative differences hetn-een the results obtained n-ith sodium tungstate and sodium molybdate, rebpectively, only the data of the tungstate experiments are presented in table 3. In this
MINUTES FIG.2 . Effect of chloro-conipleses on the decomposition of hydrogen perosii!e. I-oiume = 20 C C . ; t = 15'C.; glass vessels. __________~~~_~ ~
NO. ~
1 . .. . . . . . . . 2 . .. . . . . .
~
C O U P O S I T I O S O F R E . I C T I O S UIXTURES ~~~
. . . .., . .
3 . ., . . , . . . . . . . . . .
4 . .. . . . . . , . . . . . . . . 5 . . . . . ..., . . . .... 6... .. . . . . . . . . . , . . ,
~
___~
~~
+ + + +
.
~~
1 cc. X i 1 0 Sa.1100~ 1 cc. 2 -11 CHaCOOH f 1 cc. 2 J1 CII:,c'OOSa 1 cc. 31;100 CU(SO3). 15 cc. 4 JI s a c 1 1 cc. 9 11 11.0. 1 C C . Jf/lO SnzJTOI 1 C C . 2 JI CHaCOOH 1 C C . 2 .lI C€I C'0OS:t 1 C C . 3f/100 Cu(SO3). 15 C C . 4 -11 S a C l 1 C C . 2 Jf H,O: 1 cc. 31/10 SaJIoO, 1 cc. 2 11 CH,COOH 1 cc. 9 31 CH3COOS:t f 1 C C .JIi100 C u ( S 0 a ) : 1 C C . 2 31 H202 15 C C . 1320 1 cc. 3fl'10 S n 2 \ V 0 4 1 cc. 2 JI CHICOOK 1 cc. 2 Jf CH:C'OOSa 1 cc. 1f/100 Cu(SOa)p T 1 cc. 2 -11 H?O? 15 cc. E20 1 cc. 2 Jf CH,COOII 1 cc. 2 JI CH3COOSa 1 cc. J f / 100 C:utS03). 15 CC.4 1 I S a C 1 1 C C . 2 JI H302 1 C C . H2O 1 C C . J f j l 0 Sn?\\'Od 1 CC.2 31 CHaCOOH 1 CC.2 Jf CHnCOOSa 15 C C . 4 31 Sac1 1 C C .2 Jf H202 1 C C . HzO
+ +
1 + + , +
+
+
+ +
+ + +
+ + + + + + + + + +
+
series of experiments, as in the previous cases, the cupric complex proved t o he by far the most active, and n as therefore investigated in greater detail. Comparison of the results of tables 3 and 1 s h o n that the activity of the cupric citrate 3hcetate ion in this concentration does not exert any influence on the catalytic deconiposition.
1075
DECOhIPOSITIOS O F HTDROGES PEROXIDE
C.IT.1LITIC
complex in relation to that of the simple cupric ion is approximately as 1 O : l . It is of interest that the cupric citrate complex itself does not decompose hydroT.1BLE 3 Eflect of citrate complexes on the rate of deconiposition of hydrogen peroxide Paraffined vessels; t = 15°C.; volume = 20 cc. Xa?U'O, (-11 10)
CHKOOH
XaaCi ( J I , 101
(MIl0)
________ cc
cc
CC.
1 1 1 1 1 1 1 1
Hz0;
12 M,
_
2 2 2 2 2 2 2 2
1 31/10 31/10 M/l0 31/10 31/10 31/10
Cu(YO3)2 Co(S0a)a Si(SOa)? MnS04 Cd(S0a)L Zn(SOa)l
~
1 1 1 1 1 1 1 1
_
~
~~
mrn.
cc
1 1 cc. 1 cc. 1 cc. 1 cc. 1 CC. 1 cc.
Tl/4
_
miii
miii.
i 2.1 12.5 40
'
t 4.5 23 Si
2.4 10.5 47
1 t t
1
t X o decomposition. $ Decomposition very slo~v-. ThBLE 4 Catalytic effect of the c u p r i c citrate complex on the decomposition of hydrogen p e r o x i d e Paraffined vessels; t = 15°C.; volume = 20 cc. CHaCOOH
SasWOa
____ cc.
1 cc. M/10 1 c c . 31/10 1 cc. J1/10 0.5 cc. 31/10 1 cc. .11;100 1 cc. 31/1000 1 cc. .11/10 1 cc. 31/10 1 cc. 31/10 1 cc. M/10 1 cc. 31/10
SazlIoOi
1 cc. M/10
2 cc. 2 cc. 2 cc. 1 cc. 2 cc. 2 cc. 2 cc. 2 cc. 2 cc. 2 cc. 2 cc.
31/10 M/l0 M/10 x/10 31/100 31/1000 v/10 31/10 M/lO M/l0 31/10
1 cc. M/10 1 cc. M/10 1 cc. 31/10 1 cc. 31/10 1 cc. 31/10 1 cc. 31/10 0.5 cc. 31/10 1 cc. .If 1100 1 cc. 31/10 1 cc. 31/10 1 cc. 31/10 1 cc. 31/10
1 cc. v / 1 0 1 cc. 11/10 1 cc. M/lO 1 cc. M / l 0 1 cc. 31/10 1 cc. 31/10 0.5 cc. .11/10 1 cc. 31,100 0.5 cc. 31/10 1 cc. 31/100 1 cc. 31'1000 1 cc. 31/10
1 0.5 2.0 1 1 1 1 1 1 1 1 1
1 cc. v / 1 0
1 cc. 31/10
1
1
~
miu.
min.
2.1 4.5 2.2 -1.7 1.9 4.3 3.8 7.2 10.3 17.5 4s 73 4.0 7.5 18.4 27 2.4 5.4 3.6 7.S 9 . 5 19.0
min,
2.4 2.5 2.4 3.4 7.5 25 3.8 8.6 3.0 4.2 9.5 t
I
I I 2 cc. 31/10
1.9
4.1
2.2
t X o decomposition. gen peroxide, contrasting in this respect with ferric citrate and cobaltous citrate complexes.
10TO
S . GRI
Table 4 presents data concerning the catalytic effect of the cupric citrate complex at different concentrations of hydrogen peroxide, sodium tungstate, cupric ion, and trisodium citrate (SaaCi). Figure 3 presents several reaction curves with cupric citrate and sodium tungstate at different concentrations. It may he seen from the values presented in table 4 that the catalytic decomposition conf'orms to a reaction of the first order with respect to the hydrogen perox-
MINUTES FIG.3. 1:tirSct of cupric citrate and sodium tungstate at different concentrations on the deconi1)osition of hydrogen peroxide. Volume = 20 cc.; t = 15°C.; parafined vessels. xn,
COUPOSITIOS
OF X E 4 C T I O S HIXTLXES
+ + + + + + + + + +
1 c c 11/10 Sa?WO, + 2 c c J1/10 CHSCOOH Icc .11/10 C U ( S O ~ ) ? 1 C C . 2 11 H?Or 14 cc H?O 1 cc 11/10 Sa3C1 0 5 cc 11 10 h\:i2W04 1 cc 11/10 CH3COOH 1 cc 1 cc 2 If H20? 15 5 cc H20 1 cc 11/10 S s 3 C i 1 cc 11 100 Sn,WO, + 2 cc 11 '100 CI-13COOII 1 cc If/ 10 Cu(S03)2 1 cc 11/10 Sa3Ci 1 cc 2 11 H20i 14 cc H?O 1 cc 11 10 S a ? K 0 4 2 cc 11'10 CH3COOH 1 cc 1f/100 C u ( S 0 a ) ~ - I cc 11 io0 sa3c1 1 cc 2 11 H202 14 cc H?O 1 c c 1111000 Sa?JVOl+ 2 c c 11/1000 CHaCOOH 1 cc .11/10 C ~ ( S 0 3 ) 2 + 1 cc 11/10 SalCi 1 cc 2 31 H?Oi 14 cc HzO
+ + +
+ + + + + + +
ide concentlalion, the value of r* being a constant. With Cu++:SaaCi as 1:l the velocity constant 1: = In 1.5 T* corresponding t o the reaction curves is approsiimtely proportional to the square root of the concentration of sodium tungstate and of cupric citrate. Yery small amounts of citrate suffice to activate the cupric ion. At a citrate concentration of X 20,000 and with C u t + : S a a C ias 100: 1, the reaction velocity is roughly tivice as high as in the absence of citrate (compare table 1).
10T7
CATALYTIC DECOMPOSITIOB O F HYDROGES P E R O X I D E T H E INDUCTION PERIOD
A special phenomenon is observed when the relationship SasCi: Cu++ exceeds 1:1. I n the presence of an excess of trisodium citrate an induction period4 n-hich may last for several minutes t o several hours is observed. During the induction TABLE 5 S t u d y of the i n d u c t i o n period observed in the catalytic decomposition of hydrogctt peroxide b y f e r r i c citrate Unless defined otherwise t = 15OC. and volume = 20 cc.
OIL):
1 cc. 3f/10
1
l1cc. 3f/10 1 cc 1f/10 1 cc. 31/10
1 cc. X / l O 1 cc. M/10 1 5 cc. M / l O
1 2 1120 2 5 75
1
1.3
