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Induced reactions in the peroxy compounds—IV
Talanta,
1963, Vol.
10, pp. 449 to 465. Per&m~on Press Ltd. Printed in Northern Ireland
INDUCED
REACTIONS IN THE PEROXY COMPOUNDS-IV
A STIJDY OF THE HOOK-OsO~-K~nO*
[AND -Ce(SO&
SYSTEM
L. J. CSANYI, S. KASZAI and I. MOLNAR Institute for Inorganic and Analytical Chemistry, University of Szeged, Hungary (Received 14 August 1962) Summary-_lt has been observed that the decomposition of hydrogen peroxide is induced if it is oxidised by l-equivalent reagents (potassium. permanganate or ceriumIv sulphate). The main factors of this induced chain decomposition as well as the effects of foreign substances are described in detail.
It is known that during the oxidimetric determination of hydrogen peroxide in the presence of osmium tetroxide, a considerable negative error occurs. Because at the acid concentration employed osmium tetroxide sparingly catalyses the decomposition of hydrogen peroxide, it is reasonable to suppose that in the H,O,-OsO,KMnO, [or -Ce(SO&] system the induced decomposition of hydrogen peroxide takes place. A study of this induced reaction appears interesting not only because the results obtained may contribute to a more correct knowledge of induced reactions of peroxy compounds, but also because data may be obtained to elucidate the mechanism of osmium tetroxide catalysis. EXPERIMENTAL Reagents O.lN KMnO, usual manner. OaO1M OsO( required. 044N (about To study the
and O.lN As,O, reagents: Prepared from c.p. chemicals and standardised
in the
solution in @lNsulpRuric acid: Prepared and diluted with O*lN sulphuric acid as 2%) nitric acid solution: Prepared by diluting c.p. concentrated effect of foreign substances c-p. chemicals were employed.
acid.
Procedure For the study of the induced decomposition of hydrogen peroxide it was desirable to establish such exper~ental conditions under which, on the one hand, there appears a considerable error and, on the other, which assure the greatest reproducibility. According to the preliminary investigations the acid concentration decreases the induction error. Samples of 150-ml initial volume contained 20 ml of 044N nitric acid. Alteration of the stirring rate similarly exerts a marked influence on the measurements. To avoid a fluctuation in data from changes in the stirring rate, a synchronous motor of high output, fitted with a glass propeller, was employed. It was necessary to keep the rate of the titration constant. A capillary of corresponding diameter was therefore fitted to the burette by means of a rubber tube. The average delivery rate of the reagent was 2.52 f 0.18 ml/min in the 1 to lo-ml range (Table I) and the reproducibility was sufficient. Because hydrogen peroxide reacted too slowly with permanganate at the applied low acid concentration and at great dilution at the beginning of the titration the permanganate colour temporarily remained. The slow initial rate of the reaction does not disturb the dete~nation of the end-point; however, it is not without influence on the results. According to Tables II and HI permanganate, accumulated during slow periods of the reaction but disappearing instantaneously after some time, does not cause an induced error. Therefore the initial period of the reaction cannot be well reproduced in spite of the utmost care and before titration 2 ml of 1% manganese” nitrate solution were added to each sample. This amount of manganeseI ensures the instan~n~us reaction of potassium ~~~~ate from the very ~~n~g. 449
L. J. C&n,
450
S.
KASZAI
TABLRI-DELIVERY PERMANGANATE
O.lN KMnO&, ml
Time, min
1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
0.370 0.762 1.168 1.550 1,990 2.390 2.790 3.242 3.700 4.269
and I. MOLN~R RATE OF THE SOLUTION
Delivery rate, ml/min
Average: TABLE
II-EFFECT OF INITIAL RATE OF THE REACTION ON THE INDUCEDERROR
O.lN HaOar ml Taken Found 8.92 8.92 8.92 8.92 -
2.70 2.62 257 2.58 2.51 2.50 2.50 2.47 244 2.34 2.523
O.lN KMnO,, ml
O.lN As,O,, ml 9.90
7.02 7.10 6.82 6.90 6.92 6.90 6.90 6.85
1.90 2.80 2.10 3.00 2.00 3.00 202 3.05
9.90 9>0 9.90
H,OII-KMnO,
BETWEEN
oso,
AH&,+ ml
+ + + + -
1.82 202 2.02 2.07 -
* 20 ml of 2% KNO, added to a known amount of hydrogen peroxide, diluted to 150 ml with water and stirring started (1260 rpm). Then 2 ml of 6 x lo-‘M 0~0, added to the solution and the titration begun at a constant delivery rate. First the permanganate colour remained. The burette was closed when the solution suddenly lost its colour. This consumption was noted. Then arsenous acid was added and its excess determined permanganometrically. By this method the amount of untitrated hydrogen peroxide in the solution was determined. TABLEIII-EFFECT
OF MANGANESE~~ IONS ON THE INDUCED ERROR
O*lN HBOB, ml Found Taken lO*OO 10.00 10.00 lO*OO lOGO lO@O lO*OO
lO*OO 6.45 6.55 6.37 5.67 5.67 5.67
oso, + + + +
2mlof 1% Mn(NO& + + +
AH& ml 0.00 -3.55 -3.4 -3.63 -4.33 -4.33 -4.33
In view of the above mentioned facts, the following method was developed for the study of the induced reaction: Measure 20 ml of 044N nitric acid, 10 ml of O*lN hydrogen peroxide and 2 ml of 1% mangane~e~~ nitrate solution into a 250-ml beaker and dilute to 150 ml. Then add 2 ml of 6 x 10-W osmium tetroxide solution and start the stirring at 1260 rpm. Begin the titration 1 min after the addition of osmic acid and continue till the permanganate colour remains. Besides the direct method, there was frequently used an indirect one which made it possible to determine the hydrogen peroxide content without induced error. To this end arsenous acid in known quantity was added to the solution at the required phase of the permanganometric titration, and the excess of arsenous acid was back-titrated permanganometrically.
Induced reactions in the peroxy compounds
451
RESULTS
I. Induced decomposition of hydrogen peroxide in absence of foreign substances (1) The rate of the titration markedly influences the induced decomposition (Table IV). On decreasing the delivery rate the error first strongly increases, then after about 5 min it reaches a limiting value. TABLE IV-EFFECT OF TITRATIONRATE ON THE INDUCED REACTION O.lN HBOB, ml Taken Found 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30
9.30 8.69 8.51 7.31 7.03 6.79 5.99 5.33 4.32 3.72 3.66 3.45 3.18
Time, min
oso,*
-
-
0.23 0.26 0.72 0.84 1.22 1.99 2.08 3.26 4.61 4.83 6.95 9.82
1 + + + + + + 1 i-
AI-ML ml 0.00 -0.61 -0.73 -1.99 -2.27 -2.61 -3.31 -3.97 -4,98 -5.58 -564 -5.85 -6.12
* 7.8 x 10-BM 0~0,
(2) With increasing dilution of the titrated solution, keeping the acid concentration constant, the induced error considerably increases (Fig. 1). (3) Increasing the stirring rate markedly increases the induced reaction (Fig. 2).
ml
FIG. 1.
452
L. J. CSANYI, S. KASZAI and I. MOLN~ 5
1000
2000 rpm FIG. 2.
(4) Increase of the acid concentration lowers the induced error (Table V). From Tables V and VI the error-decreasing effect depends on the strength of the acids: HClO, > HNO, > H&30, > H,PO,. TABLE V-EFFECT
O.lN H308, ml Taken Found 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30
9.30 4.11 4.15 5.38 5.38 5.42 5.96 5.95 6.65 6.15 7.39 7.41 7.53 7.81 I.80 8.50 8.67 8.63 8.96 9.00
OF ACID CONCENTRATIONOF THE SOLUTION ON THE INDUCED ERROR
OS04
HN% N
AHa%
ml
090
+ : + + + + : +
1 +
z + + + +
0.0147 0.0147 0.0588 0.0588 0.07 0.1176 0.1176 0.236 O-236 0.354 0.354 0.7000 l@OO l+KKJ 2.65 3.000 3mO 5@00 5.000
-4.53 -4.55 -3.92 -3.92 -3.88 -3.34 -3.35 -2.65 -2.55 -1.91 -1.89 -1.77 -1.49 -1.50 -0.80 -0.63 -0.67 -0.34 -0.30
(5) The induced decomposition is proportional to the hydrogen peroxide concentration (Table VII). (6) With an increase in the osmium tetroxide concentration the induced error strongly increases (Table VIII). At a fairly high osmic acid concentration ( 10m4M)the hydrogen peroxide-permanganate reaction becomes perceptibility slow.
453
Induced reactions in the peroxy compounds TABLE VI-EFFECT O.lN HsOs, ml Found Taken HCl 9.32 9.32 9.32 9.32 9.32 9.32 9.32 HClO, 9.32 9.32 9.32 9.32 9.32 9.32 9.32 HISO* 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 HJ’O, 9.32 9.32 9.32 9.32 9.32 9.32 9.32
OF THE QUALITY OF ACID ON THE INDUCED REACTION oso,
-
9.32 6.85 686 8.66 8.61 8.83 8.81 9.32 553 5.58 7.61 7.63 8.26 8.21
Acid concn., N
0.07 0.07 0.70 0.70 I,15 7.75
+ +
z+ +
0.069 0.069 0.690 0.690 3.780 3.780
-
AHIS,
ml 0.00 -2.47 -2.46 -0.66 -0.71 -0.49 -0.45 0 WI -3.19 -3.74 -1.71 -1.69 -1.06 -1.11
9.32 4.15 4.16 5.68 5.70 6.44 6.41 8.34
0.03 0.09 0.30 0.30 1.10 1.10 3.32
O+O -4.57 -4.56 -3.64 -3.62 -2.88 -2.91 0.98
9.32 4.36 4.12 4.71 5.85 6.15 6.12
0.07 0.70 0.70 3.00 7.25 7.23
0.00 -4.96 -4.60 -4.61 -3.41 -2.57 -2.60
TABLE VII-EFFECT OF CHANGES IN HYDROGEN PEROXIDE CONCENTRATION ON THE INDUCED REACTION O*lN H,O,, ml Taken Found 3.76 7.53 11.30 11.30 15.04 15.04 22.56 22.56 30.08 3760
4
2.71 4.50 6.36 6.38 7.90 7.93 11.31 11.38 14.92 18.61
oso,
Ha%, N x lo* 3.3 6.6 9.9 9.9 13.2 13.2 19.8 19.8 26.4 33.0
AH& ml -1.05 -3.03 -4.94 -4.92 -7.14 -7.11 -11.25 -11.18 -15.16 -18.99
L. J. Cshn,
454
S. KASZPJ and I. MOLX&
(7) With the aid of the indirect method the distribution of the induced error during titration was examined. At a constant delivery rate permanganate was added to the solution in varying quantity, then the hydrogen peroxide remaining was determined. The specific error, H20,* (the error caused by the reaction of 1 ml of permanganate) proved to be practically constant in the different phases of titration (Table IX). (8) Measurements were made at the given delivery rate with 0.5-ml portions of permanganate added to the solution and waiting for 15, 30 and 50 set after the addition of each portion. On comparing the obtained results with the data of continuous titration it appears that the waiting causes a slight increase in the error. The longer the waiting period, the greater is the deviation (Table X). TABLE VIII-EFFECT OF CHANGESIN THE CONCENTR4TION OF OSMIC ACID ON THE INDUCEDREACnON O*lN HpOl, ml Taken Found 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30
9.30 9.15 8.96 8.15 8.15 6.20 6.22 5.06 5.12 3.45 3.41 2.99 2.91 1.83 1.86
TABLE TX-DISTRIBUTION O*lN HnOe, ml Found Taken 14.31 14.31 14.31 14.37 14.37 14.37
HaOa, ml
-
0.00 -0.15 -0.34 -1.15 -1.15 -3 10 -3 08 -4.24 -4.18 -5.85 -5.83 -6.31 -6.39 -1.41 -144
0.01 0.10 1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0 100.0 100.0 500.0 500.0
OF INDUCED ERROR DURING TITRATION
1.00 2.00 3.00 5.00 7.00 I.55
TABLE X-EFFECT 0.1 N HaOa. ml Found Taken 9.58 5.64 5.58 5.35 5.27
AJW,, ml
O*lN KMnO,, ml Formerly added Consumed
1.06 2.02 3.08 4.67 6.63 6.83
12.31 10.35 8.29 4.70 0.74 0.00
oso.,
M x 106
9.58 9.58 9.58 9.58 9.58
12.54 14.50 16.56 20.15 24.11 -
0.1 N As,O,,
ml
24.85 24.85 24.85 24.85 24.85 -
1.06 1.01 1.02 0.93 0.95 0.90
OF FRACTIONAL TITRATION ON THE INDUCED REACI'ION oso, + + + +
Waiting time, see 15 30 50
AH&*
ml
AH&. ml 0.00 -3.94 -4wl -4.25 -4.31
Induced
reactions in the peroxy compounds
455
(9) According to the data of Table XI, under optimal experimental conditions the limiting value of the induction factor is about 7.5. TALWJ? XI O.lN
Ti&ll 1-92 3.84 5.76 768 960 1440 18.14 27.21 48oO
HnOl, ml Found 068
1.16 1.37 1.49 1.62 2.18 254 3.25 5.78
A&O., ml
1.24 2.68 4.39 619 7.98 12.22 15.60 23.96 42.22
a%, M x
10
6.67 6.67 6.67 6-67 667 6.67 667 6.67 6.67
H*O,*
FI
F0
0.65 O-70 0.76 0.81 0.83
1.82 2-31 3.20 4.15 4.93
0.85 0.86 0.88 0.88
E 7.37 7-30
1.93 3.78 6.34 10.55 16.30 25*00 38.70 482.0 310.0
(10) Experiments described under 1-9 were repeated with ceriumrv sulphate instead of permanganate. The results agreed qualitively with those obtained with permanganate but striking quantitative differences appeared. With ceriumrv sulphate the induced error was always smaller than in the case of permanganate. It was observed that the induced error is partly reduced because ceriumIV sulphate reacts more rapidly with hydrogen peroxide and moreover, the ferroin used as indicator exerts an inhibiting effect. The error-decreasing effect of ferrom can be well studied by permanganometric ti~ations. FerroB indicator is irreversibly oxidised during titration : the colour of the indicator completely disappears before the end-point. II. E$ect of foreign substances cm the induced decomposition of hydrogen peroxide A study of the effect of foreign substances was carried out as follows: Acidify 10mt of O*liVhydrogen peroxide with 20 ml of O&N nitric acid and add 2 ml of 1% manganesennitrate solution. Before the titration add osmium tetroxide solution (F8 x lO-+M)and dilute to 150ml. Adjust the stirring rate to 1260rpm (the delivery rate was 2.52 jt 0.18ml/ml). Results are summarised below. (1) Alkali metal and ammonium ions do not influence the induced reaction even in great quantity (Table XII). (2) Alkaline earth metal ions proved to be ineffective (Table XIII). (3) Beryllium, magnesium, zinc and cadmium ions were found to be ineffective (Table XIV). It must be noted, however, that the ions mentioned did not increase the induction error only if the salts employed were entirely pure. To remove the impurities D’Ans and Matter’s method was applied. i We believe, that in the case of beryllium and cadmium ions the moderate increase in the error can be ascribed to impurities remaining in spite of purification, the solubility product of the hydroxide of these ions being smaller than that of ma~esium hydroxide. In contrast to the previous ions mercuryI causes a marked increase in the induced error. (4) In the presence of boric acid the induction error increases. A similar effect was experienced in the case of aluminium ions (Table XV). In the latter case the activity can be ascribed to the iron imp~ties. Metasilicate ions increase the error (iron and copper impurities were found to be present). TinIV ions practically do not influence the induced error.
L. J. CSANYI, S. KASZAI and I.
456 TABLE
XII-EFFKT
OF TfiE
0.1 N HeOar ml Taken Found
ALKALI-METAL INDUCED
8.98 5.50 5.41 5.38 5.35 5.50 5.32 5.38 5.50 5.50 900 4.93 4.93 4.93 483 4.85 4-93 4.93 4.93
SONIC
rONS
ON
REACTIONS
Salt concn., M x 10s
LiNO, &98 8.98 8.98 8.98 8.98 8.98 ,8-98 8-98 8.98 8.98 NaNOs 9.00 9.00 9.00 9.00 9.00 9.00 9.00 9.00 9.00 KNO, 9.58 9.58 9.58 9-58 9.58 9.58 9.58 9.58 9.58 NH,NO, 9.39 9.39 9.39 9.39 9.39 939 9.39 9.39 9.39 9.39
AND
MOLN~
1.0 ::; 1:.: 10.0 50.0 50.0
oso,
+ : + -I+ + : -
1.0 :::: lsopo 50-o 50.0
AHBOa. ml
-3.57 -360 -3.63 -348 -366 -3.60 -3.48 -3.48
:: + -If -I+
0.00 -407 -4.07 -4.07 -4.18 -4.15 -4.07 -4.05 -407
+ + -t + + + + +
-!.Z -3.94 -3.94 -3.96 -3.94 -3.92 -3.94 -3.92
-
@OO -4.65 -4*51 -4.50 -4.65 -4.52 -459 -457 -4.59 -4.51
i-
9.58 ;:z z:z 5.64 5.66 564 5.66 9.39 4.74 482 4.89 4.74 4.87 4.80 4.82 4.80 4.82
1.0 1.0 5-O 1i.i 10.0 50-O 1.0 ::; 5.0 10.0 10.0 50.0 50.0
+ +f + + +
1 +
(5) Halide ions strongly influence the induced decomposition. On adding fluoride ions the error increases, while in the case of chloride, bromide and iodide ions a strong decrease was found in the order given. Further, iodine also decreases the induced decomposition (Table XVI). (6) As can be seen from data of TabIe XVII, IanthanumIII, cerium’I’and uraniumV1 ions markedly decrease the induced decomposition, the effect of uraniumvr being extremely strong. (7) ManganeseIr ions, as has already been seen from Tables II and III, cause an increase in the induced error. On the other hand, chromium”’ ions exert a strong error-decreasing effect (Table XVIII),
Induced reactions in the peroxy compounds TABLE XIII-EFFECT
O.lNHeOB, ml Taken Found CWW
2
9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9,32 WNW, 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 WNQJ, 9.39 9.39 9.39 9.39 9.39 9.39 9.39 9.39 9,39 9.39
457
OF ALKALINE EARTH METAL IONS ON THE INDUCED REACTION
Salt concn., M x 10s
9.32 5.01 5.12 5.10 5.22 5.11 5.11 5.10 5.36 540
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
9.32 4.83 495 4.82 5.01 4.98 5.00 496 5.00 486
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
9.39 4.82 479 4.71 4.75 484 4.92 5.00 4.75 4.70
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
oso, -t 1 + + -t -t -I+ : -I+ -t : + : + : + I+ +
AHA ml
0.00 -4.31 -4.20 -4.22 -4.10 -421 -4.21 -4.22 -3.96 -3.92 OGO -4.57 -4.60 -4.68 -464 -4.55 -4.39 -464 -4.69 OGO -4.57 -4.60 -4.68 -464 -4.55 -4.47 -4.39 -464 -4.69
(8) IronIn ions in small quantity strongly quantity they decrease it. Cobaltrl ions scarcely
increase the error, while in greater influence the induced error. NickelI ions, however, result in an increase of error (Table XIX). (9) CoppeP and silver1 ions are strong catalysts of the induced decomposition (Table XX). DISCUSSION From the data of Table XI it appears that under the most favourable conditions
experimental
the limiting value of function
Fi = f(Ac/I), is 7.3-7.5, which means that reacting 1 equivalent of permanganate induces the decomposition of about 7.5 equivalents of hydrogen peroxide. On the basis of this result the induced decomposition can be written formally by the following overall equation: 20H,02 + 8KMn0,
+ 24HN0,
+ 150H,O, + 8Mn(NO& + + 8KN0, + 950, + 182H,O
which points to this induced reaction belonging to the group of induced chain reactions.
458
L. J. Cohn, TABLE XIV-EFFECT
O*lN H,O,, ml
Taken
~(NO*)*
S. KASZM and I. MOLN.~R
OF IONS OF THE ZINC GROUP ON THE INDUCED RJIACTION
Found
Salt concn., A4 x 10’
-
958 9.58 9.58 9.58 958 9.58
9.58 5.52 5.48 5.34 5.08 465
MgW’3, 9.32 932 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32
9.32 5.58 5.58 5.62 5.63 5.62 5.58 564 5.56 5.58
50.0 50.0
Zn(NW, 9.57 9.57 9.57 9.57 9.57 9.57 9.57 957 9.57 9.57
9.57 5.71 5.66 5.64 5.69 5.67 5.69 5.71 5.69 5.69
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
Cd(NW, 9.70 9.70 9.30 9.70 9.70 9.70
9.70 5.65 5.76 5.70 5.75 5.80
1.0 G.8 50.0
IWW~ 9.57 9.57 9.57 9.57 9.57 957 9.57 9.57
9.57 5.37 5.33 5.11 4.77 4.82 4.23 3.76
1.0 1.0 5.0 5.0 10.0 50.0
oso,
+
1.0
5.0 10.0 50.0 1.0 1.0 5.0 5.0 10.0 lo.0
i
+’ + :+ + + +
z + +
T 1 + + + + + + 1 + + T + + +
AI-Mb, ml
-4.10 -4.24 -4.50 -493 O+O -3.74 -3.74 -3.70 -3.69 -3.70 -3.74 -3.68 -3.76 -3.74 0.00 -3.86 -3.91 -3.93 -3.88 -390 -3.88 -3.86 -3.88 -3.88 003 -4.05 -3.94 -4.0 -3.95 -3.90 om -4.20 -4,24 -4.46 -4.80 -4.75 -5.34 -5.81
To understand the reaction in detail it is necessary to take into consideration following
the
potential equilibria :3
HO,+e+H++H,O, O,+e+H++HO,
1.50 v
-0.13
v
459
Induced reactions in the peroxy compounds TABLE XV
@lN HIlO%,ml Taken Found
H,BO,
9.57 957 957 9.57 9.57 9.57 9.57 9.57 9.57 9.57 AKNW 1 9.57 9.57 9.57 9.57 9.57 9.57 9.57 9.57 9.57 Na,SiO, 9.58 9.58 9.58 9.58 9.58 9.58 Pb(NO& 9.45 9.45 9.45 9.45 9.45 9.45 9.45 9.45 954
Salt concn., M x 10J
9.57 564 5.64 5.58 5.30 5.34 5.07 5.14 4.34 4,32
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
9.51 560 5.63 5.64 5.20 5.18 4.84 4.87 4.22
1.0 1.0 5.0 5.0 10.0 10.0 50.0
9.58 564 5.68 5.53 5.48 5.38
1.0 5.0 10.0 50.0
9.45 5.68 5.68 5.72 5.78 5.79 5.88 5.92 5,72
I.0 I.0 5.0 5.0 IO.0 10.0 50.0
oso,
-
z +
1 + + + + + + + + + + + + + + + 1 :+ + +
z +
AH& ml
0.00
-3.93 -3.93 -3.99 -4.27 -4.23 -4.50 -4.43 -5.23 -5.25 -I: -3.94 -3.93 -4.37 -4.39 -4.73 -4.70 -5.35
0.00 -3.94 -390 -4.05 -4.10 -4.20 0.00 -3.77 -3.77 - 3.73 -3.67 -3.66 -3.57 -3.53 -3.73
From this data it would be expected that the reaction of hydrogen peroxide with l-equivalent oxidants would take place in two steps:
H,O, + Ox + HO, + Red
(1)
H,O +0x-+0,
(2)
+Red
From the estimations of Baxendale5 and Sigler and Masters6 reaction (1) is about eight times slower than reaction (2). Therefore it would be expected that the HO, radical formed in reaction (l), having strong reducing properties, attacks the oxidant present in the solution. Such an oxidising agent in the H,O,-0~0, system may be the osmium tetroxide itself’ and peroxyosmic acid formed by the interaction of the two partners. From the results of a polarographic study of the H,O,-0~0, system it can be concluded that in neutral and weakly acidic solutions (pH 75-6.0) peroxyosmic
L. J. CSANYI, S. KASZAI and I. MOLNAR
460
TABLE XVI-EFFECT O*lN HBOS, ml Taken Found
OF HALIDE IONS ON THE INDUCED REACTION Salt concn., A4 x 108
NaF 9.45 9.45 9.45 9.45 9.45 9.45 9.45 9.45 9.45 9.45
9.45 5.59 5.56 5.53 5.39 5.45 5.27 5.29 4.62 4.57
9.43 9.43 943 943 9.43 9.43 9.43 9.43 9.43 9.43
9.43 5.52 5.58 5.55 6.09 6.12 6.55 647 7.03 6.99
944 9.44 9.44 944 944 944 944 944 944 9.44
9.44 5.63 6.44 6.43 6.93 6.92 7.21 7.18 7.72 7.78
9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46
9.46 5.63 5.87 5.77 6.72 6.72 7.72 7.69 7.85 7.87 8.53 8.53 8.92 8.82 9.05 9.03 9.18
944 944 944
944 9.02 8.97
-
KBr
Kl
1,
-
-Z -3.85 -3.88 -3.34 -3.31 -2.88 -2.96 -240 -244
1.0 ::; 5.0 10.0 10.0 50.0 50.0
-
O+O -3.81 -3m -3.01 -2.51 -2.52 -2.23 -2.26 -1.72 -1.66
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
0.2 0.2 0.66 0.66 2.0 2.0 3.3 3.3 6.6 6.6 33.3 33.3 100~0 100.0 160.0
ml
0.00 -3.86 -3.89 -3.92 -4.06 -4.00 -4.18 -4.16 -4-83 -4.88
1*01.0 5.0 5.0 10.0 10.0 50.0 5@0
KC1
AH& 0504
x x x x x x x x x x x x x x x
108 108 108 10s 10’ 108 108 10s 10s 108 10s 108 10s 10’ 10’
Saturated solution Saturated solution
0.00 -3.83 -3.57 -3.69 -2.74 -2.74 -1.74 -1.77 -1.61 -1.59 -0.93 -0.93 -0.54 -0.64 -0.41 -0.43 -0.26 0.00 -0.42 -0.47
Induced reactions in the peroxy compounds
461
TABLE XVII O.lN HaOe. ml Taken _ -.Found LaWAL 9.40 ;:z 940 940 940 9.40 9.40 9.40 9.40 ceWO3, 9.45 9.45 9.45 9.45 9.45 9.45 UO,(r\ro& 9.58 9.58 9.58 9.58 9.58 9.58
Salt concn., M x 108
940 5.12 5.15 5.16 5.20 5.22 5.34 5.34 5.55 5.54 9.45 5.38 5.48 5.14 6.45 6.86 9.58 5.64 5.84 6.40 6.73 7.81
1.0 5.0 10.0 50.0
oso,
1.0 5.0 10.0 50.0
x x x x
10 10 10 10
ml
+ + + + + + + + +
090 -4.28 -4.25 -4.24 -4.20 -4.18 -4.06 -4.06 -3.85 -3.86
+ + + +
-E -3.91 -3.71 -3.00 -2.59
I
-
AH,O,,
+ + + + +
0.00 -3,94 -3.74 -3.18 -2.85 -1.17
oso,
AHa%, ml
TABLE XVIII O.lN HaOa, ml Taken Found MtWW* 9.40 9.40 9.40 9.40 9.40 9.40 9.40 940 9.40 9.40 9.40 9.40 Cr(NO3, 8.85 8.85 8.85 8.85 8.85 8.85 8.85 8.85 8.85 8.85
9.40 5.13 5.98 5.84 5.66 5.35 5.36 4.48 4.46 4.34 4.31 5.12 8.85 4.85 4.93 4.85 5.08 5.12 5.38 5.38 6.62 6.52
Salt concn., Mx lo8
0.02 0066 0.33 1.0 1.0 5.0 5.0 10.0 10.0 50.0
+ + + + + + + + + + +
0.00 -4.21 -3.42 -3.56 -3.74 -4.05 -4.04 -4.92 -4.94 -5.06 -5.09 -4.28
1.0 1.0 5.0
+ + + 1
040 -4GO -3.92 -4+nI -3.13 -3*17
li.8 10.0 50.0 50.0
+ + + +
-3.47 -3.41 -2.23 -2.33
-
-
L. J. CS~NYI, S. KASZAI and I. MOLNAR
462
O*lN H,O, ml Taken Found
FeWAh
9.46 9.46 9-46 946 9.46 9.46 9.46 9.46 946 9.46 9.46 9.46 9.46 Co(NO& 945 9.45 9.45 9.45 9.45 945 945 9.45 9.45 945
Ni@Qh
9.57 9-57 9.57 9.57 957 9.57 9.57 957 9.57 9.57 957
946 5.65 5.23 4.72 4.50 4.52 4-66 5.08 5.41 5.42 6.03 6.07 5.97 9.45 5.99 5.97 5.94 5-96 5.94 5-91 5.89 5.74 5.72 9-57 5.68 5.03 2.14 1.97 1.93 1.81 1.82 1.96 1.93 3.30
Salt concn., Mx 108
oso,
AH& ml
0.066 0.33 1.00 1.00 250 3.30 5GO 5.00 10.00 1000 SOGO 1.0 1.0 5.0 5-o 10.0 10.0 50.0 50.0
Oi66 0.33 1QO l-0 5.0 Ii.8 10.0 50.0
040 -3.81 -4.23 -414 -4.96 -4.94 -4+?o -4.38 - 3.99 -4.04 -3.43 -3.39 -3.49 WOO -3.46 -3.48 -3.51 -3.49 -3*51 -3.54 -3.56 -3.71 -3.73 0.00 - 3.89 -4.54 -743 -760 -7.64 -7.76 -7.75 -7.61 -7.64 -6.27
acid forms. In more acid solutions (pH 6G3.5) the kinetic current is furnished very probably by the OSvlrl/Osvl electron transfer. Considering all of these results it can be said that in neutral and very weakly acid solution the peroxyosmic acid and in more acid media the Osvllr[Osvl couple play an important role in the induced de~m~sition of hydrogen peroxide. We believe that the HOz radical attacks osmiumvlI1 (and/or peroxyosmic acid). The reduction product of osmium compounds reacts with hydrogen peroxide and an OH radical is formed. In this way, without adding any extra oxidising agent, a considerable amount of hydrogen peroxide is decomposed. In more acid media the decomposition may be represented schematically:
HO, + 0~~” -+ Osvu + 0, + H+
(3)
H,O, + Osvl’ --)rOH + OH- + Osvrl’
(4)
OH + H,O,
--+ HO, + H,O
(5)
Induced reactions in the peroxy compounds
463
TABLEXX O*lNHnOs,ml Taken Found
Salt concn., A4 x 10’
oso,
-
-
AH@,, ml
cuwo3, 9.20 9.20 9.20
9.20
9.20 9.20 9.20 9.20 920 9.20 9.20 9.20 9.20 9.20
1.96 522 1.65 1.62 1.75 1.72 230 227 264 269 4.14 4.12
0.02 0.066 0.33 1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
: z
hN?30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30
9.30 5.08 488 475 4.77 446 4.52 412 408 3.16 3.10
0.33 1.0 1.0 5.0 A8
+ 1
10.0 50.0 50.0
f + + 1 -I-I+
1 + + + z
-E -1.24 -1.55 -1.58 -7.45 -7.48 -690 -693 -6.56 -6.51 -5.06 -5.08 -E -4.42 -4.55 -4.53 -4.84 -4.78 -5.18 -5.22 -6.14 -6.20
and in neutral or very weakly acid media: H,O, + 0~0, -+ [OsO,~H,O,]
(6)
HOs + [OsO,.H,O,] --+ OS + OsO,.HO + Hz0
(7)
OsO,*HO + H,O, --f HO, + 0~0, + H,O
(8)
The experimental results agree completely with the above reaction schemes. (1) It was found that increasing the delivery rate of permanganate considerably decreased the induced decomposition. With rapid titration, because of the relatively high local permanganate concentration, the competing reaction (2) considerably lowers the concentration of the HO, radical together with the extent of the induced decomposition. (2) Increasing the dilution of the titrated solution, other factors remaining constant, results in the increasing of the induced decomposition because of the decrease of the local permanganate concentration, and the concentration of HO, radical increases. The opposite effect can be clearly seen from Table II, according to which the induced error practically ceases when permanganate is present transitorily in excess. (3) The increase of the stirring rate promotes the even distribution of permanganate, thus the local permanganate concentration decreases, and together with it the extent of the induced decomposition increases. With the increasing of the stirring rate, the rate of the diffusion cannot increase without limit, so that the induced error alters according to a curve having a limiting value.
464
L. J. Cshw,
S. KASZAI and I. MOLNAR
(4) The induced error is decreased by increasing the hydrogen ion concentration. This can be interpreted in that the potential of the Osvlll/Osvl couple becomes strongly positive and inhibits the regeneration of osmium tetroxide [reaction (4)]. (5) The kinetic nature of the induced error is supported by the fact that the increase of both hydrogen peroxide and osmium tetroxide concentrations brings about an increase of the induced decomposition. (6) The chain character of the induced decomposition seems to be supported by the observation that on titrating with small portions and waiting a given time after the addition of each portion, the induced error is greater than with continuous titration. In the case of titrations performed fractionally, the chain-carriers can react for a longer time than in continuous titrations because the concentration of permanganate will be lower in the pause of the addition. The chain character of the reaction is further supported by the halide and halogen inhibition. These substances annihilate chain carriers. Halide ions react mainly with OH or 0~0,.HO radicals and the halogen molecules with the HO2 radical. Because the mentioned intermediates are not capable of oxidising fluoride ions, the errordecreasing effect is not experienced in the presence of fluoride. The error increasing in the presence of fluoride ions comes back to the increase of the pH of the titrated solution, when adding alkali fluoride, hydrogen fluoride being a weak acid. (7) Cerimetric titration results in a moderate induced error. This can be partly ascribed to the rate of .reactions (1) and (2) in the case of ceriumIV sulphate being higher than in the case of permanganate. The other reason is that the ferroln used as indicator reacts with the radicals, thus consuming the chain-carriers and exerting an inhibiting effect. In the l,lO-phenanthroline molecule the bond between carbon atoms 5 and 6 can be mostly easily attacked. Therefore it can be assumed that this bond is split by OH radicals (and OsO,*HO) and oxidised to carboxyl groups. In this way 2’2-bipyridyl-3,3’-dicarboxylic acid forms and this is not capable of forming complexes in acid solutions. To prove this assumption the end-product of the oxidation of ferronr was collected and compared chromatographically with 2,2’-bipyridyl-3,3’-dicarboxylic acid. The RF-value of the oxidation product agreed satisfactorily with that of the mentioned dicarboxylic acid, thus the above supposition seems qualitatively to be correct. (8) It was found that alkali and alkaline earth metal, zinc group, tinIV, aluminium and silicate ions do not influence the induced decomposition. The error-increase found in the case of beryllium, aluminium and silicate ions can, according to qualitative tests, be ascribed to impurities. A marked increase in the induced error is generally caused by ions which are good catalysts of the self-decomposition of hydrogen peroxide, e.g., iron”I, copperII, silverI, nickellI, manganeseu’), etc. Besides halide ions, ferricyanide, uranium”, ceriumlI1, chromiumlI1 and lanthanumlI1 ions considerably decrease the induced error. The interaction between ferricyanide and osmium tetroxide can be observed optically and supposedly this is the reason of the decrease of the catalytic activity, for example, in the reaction between ceriumIV and arsenous acid. Chromiumlll, 1anthanum”I and ceriumlI1 and probably uraniumV1 ions interact with osmic acid and decrease the catalytic activity. There is no direct experimental proof of this supposition, but we believe that osmium forming polyacid reacts with chromiumrII and the ions mentioned, and results in stable
Induced reactions in the peroxy compounds complexes as can be found in the case of polymolybdates.s photometric measurements are now in progress.
In this direction
465 spectro-
Zusammenfassung-Weim Wasserstoffperoxyd in Anwesenheit von Osmiumtetroxyd mit 1-8quivalenten Oxydations mittem (zB. Kaliumpermanganat, Cer(IV) sulfate) titriert wird eine induzierte Zersetzung des Wasserstoffperoxyd ist zu beobachten. Die Einzelheiten dieser induzierten Reaktion werden ausfahrlich erortert. R&sum&La decomposition de I’eau oxygen& est induite si elle est oxydee par des rbctifs tels que le permanganate de potassium ou le sulfate de ctrium(IV). Les principaux facteurs de cette decomposition induite en chaine de meme que l’influence de substances &rang&es sont d&rites en detail. REFERENCES 1 J. D’Ans and J. Matter, Angew Chem., 1952, 64,448. 2 A. I. Medalia, Analyt. Chenz., 1955,27, 1678. s W. M. Latimer, The Oxidation States of the Elements and their Potentials in Aqueous Solutions. Prentice-Hall Inc., New York, 1952. 4 Sh. Baer and G. Stein, J. Chem. Sot., 1953, 3176. 6 J. H. Baxendale. J. Chem. Sot. Spec. Publ., 1954, 1, 40. 0 P. B. Sigler and B. J. Masters, J. Amer. Chem. Sot., 1957, 79, 6353. 7 L. Cslnyi and K. Fiiliip, K&m. Folydirat Magyar 1958 64,47. 8 L. Cs&nyi, Acta Chim. Acad. Sci. Hung., 1959, 21, 35. g H. T. Hall and H. Eyring, J. Amer. Chem. Sot., 1950, 72, 782.
1963, Vol.
10, pp. 449 to 465. Per&m~on Press Ltd. Printed in Northern Ireland
INDUCED
REACTIONS IN THE PEROXY COMPOUNDS-IV
A STIJDY OF THE HOOK-OsO~-K~nO*
[AND -Ce(SO&
SYSTEM
L. J. CSANYI, S. KASZAI and I. MOLNAR Institute for Inorganic and Analytical Chemistry, University of Szeged, Hungary (Received 14 August 1962) Summary-_lt has been observed that the decomposition of hydrogen peroxide is induced if it is oxidised by l-equivalent reagents (potassium. permanganate or ceriumIv sulphate). The main factors of this induced chain decomposition as well as the effects of foreign substances are described in detail.
It is known that during the oxidimetric determination of hydrogen peroxide in the presence of osmium tetroxide, a considerable negative error occurs. Because at the acid concentration employed osmium tetroxide sparingly catalyses the decomposition of hydrogen peroxide, it is reasonable to suppose that in the H,O,-OsO,KMnO, [or -Ce(SO&] system the induced decomposition of hydrogen peroxide takes place. A study of this induced reaction appears interesting not only because the results obtained may contribute to a more correct knowledge of induced reactions of peroxy compounds, but also because data may be obtained to elucidate the mechanism of osmium tetroxide catalysis. EXPERIMENTAL Reagents O.lN KMnO, usual manner. OaO1M OsO( required. 044N (about To study the
and O.lN As,O, reagents: Prepared from c.p. chemicals and standardised
in the
solution in @lNsulpRuric acid: Prepared and diluted with O*lN sulphuric acid as 2%) nitric acid solution: Prepared by diluting c.p. concentrated effect of foreign substances c-p. chemicals were employed.
acid.
Procedure For the study of the induced decomposition of hydrogen peroxide it was desirable to establish such exper~ental conditions under which, on the one hand, there appears a considerable error and, on the other, which assure the greatest reproducibility. According to the preliminary investigations the acid concentration decreases the induction error. Samples of 150-ml initial volume contained 20 ml of 044N nitric acid. Alteration of the stirring rate similarly exerts a marked influence on the measurements. To avoid a fluctuation in data from changes in the stirring rate, a synchronous motor of high output, fitted with a glass propeller, was employed. It was necessary to keep the rate of the titration constant. A capillary of corresponding diameter was therefore fitted to the burette by means of a rubber tube. The average delivery rate of the reagent was 2.52 f 0.18 ml/min in the 1 to lo-ml range (Table I) and the reproducibility was sufficient. Because hydrogen peroxide reacted too slowly with permanganate at the applied low acid concentration and at great dilution at the beginning of the titration the permanganate colour temporarily remained. The slow initial rate of the reaction does not disturb the dete~nation of the end-point; however, it is not without influence on the results. According to Tables II and HI permanganate, accumulated during slow periods of the reaction but disappearing instantaneously after some time, does not cause an induced error. Therefore the initial period of the reaction cannot be well reproduced in spite of the utmost care and before titration 2 ml of 1% manganese” nitrate solution were added to each sample. This amount of manganeseI ensures the instan~n~us reaction of potassium ~~~~ate from the very ~~n~g. 449
L. J. C&n,
450
S.
KASZAI
TABLRI-DELIVERY PERMANGANATE
O.lN KMnO&, ml
Time, min
1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
0.370 0.762 1.168 1.550 1,990 2.390 2.790 3.242 3.700 4.269
and I. MOLN~R RATE OF THE SOLUTION
Delivery rate, ml/min
Average: TABLE
II-EFFECT OF INITIAL RATE OF THE REACTION ON THE INDUCEDERROR
O.lN HaOar ml Taken Found 8.92 8.92 8.92 8.92 -
2.70 2.62 257 2.58 2.51 2.50 2.50 2.47 244 2.34 2.523
O.lN KMnO,, ml
O.lN As,O,, ml 9.90
7.02 7.10 6.82 6.90 6.92 6.90 6.90 6.85
1.90 2.80 2.10 3.00 2.00 3.00 202 3.05
9.90 9>0 9.90
H,OII-KMnO,
BETWEEN
oso,
AH&,+ ml
+ + + + -
1.82 202 2.02 2.07 -
* 20 ml of 2% KNO, added to a known amount of hydrogen peroxide, diluted to 150 ml with water and stirring started (1260 rpm). Then 2 ml of 6 x lo-‘M 0~0, added to the solution and the titration begun at a constant delivery rate. First the permanganate colour remained. The burette was closed when the solution suddenly lost its colour. This consumption was noted. Then arsenous acid was added and its excess determined permanganometrically. By this method the amount of untitrated hydrogen peroxide in the solution was determined. TABLEIII-EFFECT
OF MANGANESE~~ IONS ON THE INDUCED ERROR
O*lN HBOB, ml Found Taken lO*OO 10.00 10.00 lO*OO lOGO lO@O lO*OO
lO*OO 6.45 6.55 6.37 5.67 5.67 5.67
oso, + + + +
2mlof 1% Mn(NO& + + +
AH& ml 0.00 -3.55 -3.4 -3.63 -4.33 -4.33 -4.33
In view of the above mentioned facts, the following method was developed for the study of the induced reaction: Measure 20 ml of 044N nitric acid, 10 ml of O*lN hydrogen peroxide and 2 ml of 1% mangane~e~~ nitrate solution into a 250-ml beaker and dilute to 150 ml. Then add 2 ml of 6 x 10-W osmium tetroxide solution and start the stirring at 1260 rpm. Begin the titration 1 min after the addition of osmic acid and continue till the permanganate colour remains. Besides the direct method, there was frequently used an indirect one which made it possible to determine the hydrogen peroxide content without induced error. To this end arsenous acid in known quantity was added to the solution at the required phase of the permanganometric titration, and the excess of arsenous acid was back-titrated permanganometrically.
Induced reactions in the peroxy compounds
451
RESULTS
I. Induced decomposition of hydrogen peroxide in absence of foreign substances (1) The rate of the titration markedly influences the induced decomposition (Table IV). On decreasing the delivery rate the error first strongly increases, then after about 5 min it reaches a limiting value. TABLE IV-EFFECT OF TITRATIONRATE ON THE INDUCED REACTION O.lN HBOB, ml Taken Found 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30
9.30 8.69 8.51 7.31 7.03 6.79 5.99 5.33 4.32 3.72 3.66 3.45 3.18
Time, min
oso,*
-
-
0.23 0.26 0.72 0.84 1.22 1.99 2.08 3.26 4.61 4.83 6.95 9.82
1 + + + + + + 1 i-
AI-ML ml 0.00 -0.61 -0.73 -1.99 -2.27 -2.61 -3.31 -3.97 -4,98 -5.58 -564 -5.85 -6.12
* 7.8 x 10-BM 0~0,
(2) With increasing dilution of the titrated solution, keeping the acid concentration constant, the induced error considerably increases (Fig. 1). (3) Increasing the stirring rate markedly increases the induced reaction (Fig. 2).
ml
FIG. 1.
452
L. J. CSANYI, S. KASZAI and I. MOLN~ 5
1000
2000 rpm FIG. 2.
(4) Increase of the acid concentration lowers the induced error (Table V). From Tables V and VI the error-decreasing effect depends on the strength of the acids: HClO, > HNO, > H&30, > H,PO,. TABLE V-EFFECT
O.lN H308, ml Taken Found 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30
9.30 4.11 4.15 5.38 5.38 5.42 5.96 5.95 6.65 6.15 7.39 7.41 7.53 7.81 I.80 8.50 8.67 8.63 8.96 9.00
OF ACID CONCENTRATIONOF THE SOLUTION ON THE INDUCED ERROR
OS04
HN% N
AHa%
ml
090
+ : + + + + : +
1 +
z + + + +
0.0147 0.0147 0.0588 0.0588 0.07 0.1176 0.1176 0.236 O-236 0.354 0.354 0.7000 l@OO l+KKJ 2.65 3.000 3mO 5@00 5.000
-4.53 -4.55 -3.92 -3.92 -3.88 -3.34 -3.35 -2.65 -2.55 -1.91 -1.89 -1.77 -1.49 -1.50 -0.80 -0.63 -0.67 -0.34 -0.30
(5) The induced decomposition is proportional to the hydrogen peroxide concentration (Table VII). (6) With an increase in the osmium tetroxide concentration the induced error strongly increases (Table VIII). At a fairly high osmic acid concentration ( 10m4M)the hydrogen peroxide-permanganate reaction becomes perceptibility slow.
453
Induced reactions in the peroxy compounds TABLE VI-EFFECT O.lN HsOs, ml Found Taken HCl 9.32 9.32 9.32 9.32 9.32 9.32 9.32 HClO, 9.32 9.32 9.32 9.32 9.32 9.32 9.32 HISO* 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 HJ’O, 9.32 9.32 9.32 9.32 9.32 9.32 9.32
OF THE QUALITY OF ACID ON THE INDUCED REACTION oso,
-
9.32 6.85 686 8.66 8.61 8.83 8.81 9.32 553 5.58 7.61 7.63 8.26 8.21
Acid concn., N
0.07 0.07 0.70 0.70 I,15 7.75
+ +
z+ +
0.069 0.069 0.690 0.690 3.780 3.780
-
AHIS,
ml 0.00 -2.47 -2.46 -0.66 -0.71 -0.49 -0.45 0 WI -3.19 -3.74 -1.71 -1.69 -1.06 -1.11
9.32 4.15 4.16 5.68 5.70 6.44 6.41 8.34
0.03 0.09 0.30 0.30 1.10 1.10 3.32
O+O -4.57 -4.56 -3.64 -3.62 -2.88 -2.91 0.98
9.32 4.36 4.12 4.71 5.85 6.15 6.12
0.07 0.70 0.70 3.00 7.25 7.23
0.00 -4.96 -4.60 -4.61 -3.41 -2.57 -2.60
TABLE VII-EFFECT OF CHANGES IN HYDROGEN PEROXIDE CONCENTRATION ON THE INDUCED REACTION O*lN H,O,, ml Taken Found 3.76 7.53 11.30 11.30 15.04 15.04 22.56 22.56 30.08 3760
4
2.71 4.50 6.36 6.38 7.90 7.93 11.31 11.38 14.92 18.61
oso,
Ha%, N x lo* 3.3 6.6 9.9 9.9 13.2 13.2 19.8 19.8 26.4 33.0
AH& ml -1.05 -3.03 -4.94 -4.92 -7.14 -7.11 -11.25 -11.18 -15.16 -18.99
L. J. Cshn,
454
S. KASZPJ and I. MOLX&
(7) With the aid of the indirect method the distribution of the induced error during titration was examined. At a constant delivery rate permanganate was added to the solution in varying quantity, then the hydrogen peroxide remaining was determined. The specific error, H20,* (the error caused by the reaction of 1 ml of permanganate) proved to be practically constant in the different phases of titration (Table IX). (8) Measurements were made at the given delivery rate with 0.5-ml portions of permanganate added to the solution and waiting for 15, 30 and 50 set after the addition of each portion. On comparing the obtained results with the data of continuous titration it appears that the waiting causes a slight increase in the error. The longer the waiting period, the greater is the deviation (Table X). TABLE VIII-EFFECT OF CHANGESIN THE CONCENTR4TION OF OSMIC ACID ON THE INDUCEDREACnON O*lN HpOl, ml Taken Found 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30
9.30 9.15 8.96 8.15 8.15 6.20 6.22 5.06 5.12 3.45 3.41 2.99 2.91 1.83 1.86
TABLE TX-DISTRIBUTION O*lN HnOe, ml Found Taken 14.31 14.31 14.31 14.37 14.37 14.37
HaOa, ml
-
0.00 -0.15 -0.34 -1.15 -1.15 -3 10 -3 08 -4.24 -4.18 -5.85 -5.83 -6.31 -6.39 -1.41 -144
0.01 0.10 1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0 100.0 100.0 500.0 500.0
OF INDUCED ERROR DURING TITRATION
1.00 2.00 3.00 5.00 7.00 I.55
TABLE X-EFFECT 0.1 N HaOa. ml Found Taken 9.58 5.64 5.58 5.35 5.27
AJW,, ml
O*lN KMnO,, ml Formerly added Consumed
1.06 2.02 3.08 4.67 6.63 6.83
12.31 10.35 8.29 4.70 0.74 0.00
oso.,
M x 106
9.58 9.58 9.58 9.58 9.58
12.54 14.50 16.56 20.15 24.11 -
0.1 N As,O,,
ml
24.85 24.85 24.85 24.85 24.85 -
1.06 1.01 1.02 0.93 0.95 0.90
OF FRACTIONAL TITRATION ON THE INDUCED REACI'ION oso, + + + +
Waiting time, see 15 30 50
AH&*
ml
AH&. ml 0.00 -3.94 -4wl -4.25 -4.31
Induced
reactions in the peroxy compounds
455
(9) According to the data of Table XI, under optimal experimental conditions the limiting value of the induction factor is about 7.5. TALWJ? XI O.lN
Ti&ll 1-92 3.84 5.76 768 960 1440 18.14 27.21 48oO
HnOl, ml Found 068
1.16 1.37 1.49 1.62 2.18 254 3.25 5.78
A&O., ml
1.24 2.68 4.39 619 7.98 12.22 15.60 23.96 42.22
a%, M x
10
6.67 6.67 6.67 6-67 667 6.67 667 6.67 6.67
H*O,*
FI
F0
0.65 O-70 0.76 0.81 0.83
1.82 2-31 3.20 4.15 4.93
0.85 0.86 0.88 0.88
E 7.37 7-30
1.93 3.78 6.34 10.55 16.30 25*00 38.70 482.0 310.0
(10) Experiments described under 1-9 were repeated with ceriumrv sulphate instead of permanganate. The results agreed qualitively with those obtained with permanganate but striking quantitative differences appeared. With ceriumrv sulphate the induced error was always smaller than in the case of permanganate. It was observed that the induced error is partly reduced because ceriumIV sulphate reacts more rapidly with hydrogen peroxide and moreover, the ferroin used as indicator exerts an inhibiting effect. The error-decreasing effect of ferrom can be well studied by permanganometric ti~ations. FerroB indicator is irreversibly oxidised during titration : the colour of the indicator completely disappears before the end-point. II. E$ect of foreign substances cm the induced decomposition of hydrogen peroxide A study of the effect of foreign substances was carried out as follows: Acidify 10mt of O*liVhydrogen peroxide with 20 ml of O&N nitric acid and add 2 ml of 1% manganesennitrate solution. Before the titration add osmium tetroxide solution (F8 x lO-+M)and dilute to 150ml. Adjust the stirring rate to 1260rpm (the delivery rate was 2.52 jt 0.18ml/ml). Results are summarised below. (1) Alkali metal and ammonium ions do not influence the induced reaction even in great quantity (Table XII). (2) Alkaline earth metal ions proved to be ineffective (Table XIII). (3) Beryllium, magnesium, zinc and cadmium ions were found to be ineffective (Table XIV). It must be noted, however, that the ions mentioned did not increase the induction error only if the salts employed were entirely pure. To remove the impurities D’Ans and Matter’s method was applied. i We believe, that in the case of beryllium and cadmium ions the moderate increase in the error can be ascribed to impurities remaining in spite of purification, the solubility product of the hydroxide of these ions being smaller than that of ma~esium hydroxide. In contrast to the previous ions mercuryI causes a marked increase in the induced error. (4) In the presence of boric acid the induction error increases. A similar effect was experienced in the case of aluminium ions (Table XV). In the latter case the activity can be ascribed to the iron imp~ties. Metasilicate ions increase the error (iron and copper impurities were found to be present). TinIV ions practically do not influence the induced error.
L. J. CSANYI, S. KASZAI and I.
456 TABLE
XII-EFFKT
OF TfiE
0.1 N HeOar ml Taken Found
ALKALI-METAL INDUCED
8.98 5.50 5.41 5.38 5.35 5.50 5.32 5.38 5.50 5.50 900 4.93 4.93 4.93 483 4.85 4-93 4.93 4.93
SONIC
rONS
ON
REACTIONS
Salt concn., M x 10s
LiNO, &98 8.98 8.98 8.98 8.98 8.98 ,8-98 8-98 8.98 8.98 NaNOs 9.00 9.00 9.00 9.00 9.00 9.00 9.00 9.00 9.00 KNO, 9.58 9.58 9.58 9-58 9.58 9.58 9.58 9.58 9.58 NH,NO, 9.39 9.39 9.39 9.39 9.39 939 9.39 9.39 9.39 9.39
AND
MOLN~
1.0 ::; 1:.: 10.0 50.0 50.0
oso,
+ : + -I+ + : -
1.0 :::: lsopo 50-o 50.0
AHBOa. ml
-3.57 -360 -3.63 -348 -366 -3.60 -3.48 -3.48
:: + -If -I+
0.00 -407 -4.07 -4.07 -4.18 -4.15 -4.07 -4.05 -407
+ + -t + + + + +
-!.Z -3.94 -3.94 -3.96 -3.94 -3.92 -3.94 -3.92
-
@OO -4.65 -4*51 -4.50 -4.65 -4.52 -459 -457 -4.59 -4.51
i-
9.58 ;:z z:z 5.64 5.66 564 5.66 9.39 4.74 482 4.89 4.74 4.87 4.80 4.82 4.80 4.82
1.0 1.0 5-O 1i.i 10.0 50-O 1.0 ::; 5.0 10.0 10.0 50.0 50.0
+ +f + + +
1 +
(5) Halide ions strongly influence the induced decomposition. On adding fluoride ions the error increases, while in the case of chloride, bromide and iodide ions a strong decrease was found in the order given. Further, iodine also decreases the induced decomposition (Table XVI). (6) As can be seen from data of TabIe XVII, IanthanumIII, cerium’I’and uraniumV1 ions markedly decrease the induced decomposition, the effect of uraniumvr being extremely strong. (7) ManganeseIr ions, as has already been seen from Tables II and III, cause an increase in the induced error. On the other hand, chromium”’ ions exert a strong error-decreasing effect (Table XVIII),
Induced reactions in the peroxy compounds TABLE XIII-EFFECT
O.lNHeOB, ml Taken Found CWW
2
9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9,32 WNW, 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32 WNQJ, 9.39 9.39 9.39 9.39 9.39 9.39 9.39 9.39 9,39 9.39
457
OF ALKALINE EARTH METAL IONS ON THE INDUCED REACTION
Salt concn., M x 10s
9.32 5.01 5.12 5.10 5.22 5.11 5.11 5.10 5.36 540
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
9.32 4.83 495 4.82 5.01 4.98 5.00 496 5.00 486
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
9.39 4.82 479 4.71 4.75 484 4.92 5.00 4.75 4.70
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
oso, -t 1 + + -t -t -I+ : -I+ -t : + : + : + I+ +
AHA ml
0.00 -4.31 -4.20 -4.22 -4.10 -421 -4.21 -4.22 -3.96 -3.92 OGO -4.57 -4.60 -4.68 -464 -4.55 -4.39 -464 -4.69 OGO -4.57 -4.60 -4.68 -464 -4.55 -4.47 -4.39 -464 -4.69
(8) IronIn ions in small quantity strongly quantity they decrease it. Cobaltrl ions scarcely
increase the error, while in greater influence the induced error. NickelI ions, however, result in an increase of error (Table XIX). (9) CoppeP and silver1 ions are strong catalysts of the induced decomposition (Table XX). DISCUSSION From the data of Table XI it appears that under the most favourable conditions
experimental
the limiting value of function
Fi = f(Ac/I), is 7.3-7.5, which means that reacting 1 equivalent of permanganate induces the decomposition of about 7.5 equivalents of hydrogen peroxide. On the basis of this result the induced decomposition can be written formally by the following overall equation: 20H,02 + 8KMn0,
+ 24HN0,
+ 150H,O, + 8Mn(NO& + + 8KN0, + 950, + 182H,O
which points to this induced reaction belonging to the group of induced chain reactions.
458
L. J. Cohn, TABLE XIV-EFFECT
O*lN H,O,, ml
Taken
~(NO*)*
S. KASZM and I. MOLN.~R
OF IONS OF THE ZINC GROUP ON THE INDUCED RJIACTION
Found
Salt concn., A4 x 10’
-
958 9.58 9.58 9.58 958 9.58
9.58 5.52 5.48 5.34 5.08 465
MgW’3, 9.32 932 9.32 9.32 9.32 9.32 9.32 9.32 9.32 9.32
9.32 5.58 5.58 5.62 5.63 5.62 5.58 564 5.56 5.58
50.0 50.0
Zn(NW, 9.57 9.57 9.57 9.57 9.57 9.57 9.57 957 9.57 9.57
9.57 5.71 5.66 5.64 5.69 5.67 5.69 5.71 5.69 5.69
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
Cd(NW, 9.70 9.70 9.30 9.70 9.70 9.70
9.70 5.65 5.76 5.70 5.75 5.80
1.0 G.8 50.0
IWW~ 9.57 9.57 9.57 9.57 9.57 957 9.57 9.57
9.57 5.37 5.33 5.11 4.77 4.82 4.23 3.76
1.0 1.0 5.0 5.0 10.0 50.0
oso,
+
1.0
5.0 10.0 50.0 1.0 1.0 5.0 5.0 10.0 lo.0
i
+’ + :+ + + +
z + +
T 1 + + + + + + 1 + + T + + +
AI-Mb, ml
-4.10 -4.24 -4.50 -493 O+O -3.74 -3.74 -3.70 -3.69 -3.70 -3.74 -3.68 -3.76 -3.74 0.00 -3.86 -3.91 -3.93 -3.88 -390 -3.88 -3.86 -3.88 -3.88 003 -4.05 -3.94 -4.0 -3.95 -3.90 om -4.20 -4,24 -4.46 -4.80 -4.75 -5.34 -5.81
To understand the reaction in detail it is necessary to take into consideration following
the
potential equilibria :3
HO,+e+H++H,O, O,+e+H++HO,
1.50 v
-0.13
v
459
Induced reactions in the peroxy compounds TABLE XV
@lN HIlO%,ml Taken Found
H,BO,
9.57 957 957 9.57 9.57 9.57 9.57 9.57 9.57 9.57 AKNW 1 9.57 9.57 9.57 9.57 9.57 9.57 9.57 9.57 9.57 Na,SiO, 9.58 9.58 9.58 9.58 9.58 9.58 Pb(NO& 9.45 9.45 9.45 9.45 9.45 9.45 9.45 9.45 954
Salt concn., M x 10J
9.57 564 5.64 5.58 5.30 5.34 5.07 5.14 4.34 4,32
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
9.51 560 5.63 5.64 5.20 5.18 4.84 4.87 4.22
1.0 1.0 5.0 5.0 10.0 10.0 50.0
9.58 564 5.68 5.53 5.48 5.38
1.0 5.0 10.0 50.0
9.45 5.68 5.68 5.72 5.78 5.79 5.88 5.92 5,72
I.0 I.0 5.0 5.0 IO.0 10.0 50.0
oso,
-
z +
1 + + + + + + + + + + + + + + + 1 :+ + +
z +
AH& ml
0.00
-3.93 -3.93 -3.99 -4.27 -4.23 -4.50 -4.43 -5.23 -5.25 -I: -3.94 -3.93 -4.37 -4.39 -4.73 -4.70 -5.35
0.00 -3.94 -390 -4.05 -4.10 -4.20 0.00 -3.77 -3.77 - 3.73 -3.67 -3.66 -3.57 -3.53 -3.73
From this data it would be expected that the reaction of hydrogen peroxide with l-equivalent oxidants would take place in two steps:
H,O, + Ox + HO, + Red
(1)
H,O +0x-+0,
(2)
+Red
From the estimations of Baxendale5 and Sigler and Masters6 reaction (1) is about eight times slower than reaction (2). Therefore it would be expected that the HO, radical formed in reaction (l), having strong reducing properties, attacks the oxidant present in the solution. Such an oxidising agent in the H,O,-0~0, system may be the osmium tetroxide itself’ and peroxyosmic acid formed by the interaction of the two partners. From the results of a polarographic study of the H,O,-0~0, system it can be concluded that in neutral and weakly acidic solutions (pH 75-6.0) peroxyosmic
L. J. CSANYI, S. KASZAI and I. MOLNAR
460
TABLE XVI-EFFECT O*lN HBOS, ml Taken Found
OF HALIDE IONS ON THE INDUCED REACTION Salt concn., A4 x 108
NaF 9.45 9.45 9.45 9.45 9.45 9.45 9.45 9.45 9.45 9.45
9.45 5.59 5.56 5.53 5.39 5.45 5.27 5.29 4.62 4.57
9.43 9.43 943 943 9.43 9.43 9.43 9.43 9.43 9.43
9.43 5.52 5.58 5.55 6.09 6.12 6.55 647 7.03 6.99
944 9.44 9.44 944 944 944 944 944 944 9.44
9.44 5.63 6.44 6.43 6.93 6.92 7.21 7.18 7.72 7.78
9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46 9.46
9.46 5.63 5.87 5.77 6.72 6.72 7.72 7.69 7.85 7.87 8.53 8.53 8.92 8.82 9.05 9.03 9.18
944 944 944
944 9.02 8.97
-
KBr
Kl
1,
-
-Z -3.85 -3.88 -3.34 -3.31 -2.88 -2.96 -240 -244
1.0 ::; 5.0 10.0 10.0 50.0 50.0
-
O+O -3.81 -3m -3.01 -2.51 -2.52 -2.23 -2.26 -1.72 -1.66
1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
0.2 0.2 0.66 0.66 2.0 2.0 3.3 3.3 6.6 6.6 33.3 33.3 100~0 100.0 160.0
ml
0.00 -3.86 -3.89 -3.92 -4.06 -4.00 -4.18 -4.16 -4-83 -4.88
1*01.0 5.0 5.0 10.0 10.0 50.0 5@0
KC1
AH& 0504
x x x x x x x x x x x x x x x
108 108 108 10s 10’ 108 108 10s 10s 108 10s 108 10s 10’ 10’
Saturated solution Saturated solution
0.00 -3.83 -3.57 -3.69 -2.74 -2.74 -1.74 -1.77 -1.61 -1.59 -0.93 -0.93 -0.54 -0.64 -0.41 -0.43 -0.26 0.00 -0.42 -0.47
Induced reactions in the peroxy compounds
461
TABLE XVII O.lN HaOe. ml Taken _ -.Found LaWAL 9.40 ;:z 940 940 940 9.40 9.40 9.40 9.40 ceWO3, 9.45 9.45 9.45 9.45 9.45 9.45 UO,(r\ro& 9.58 9.58 9.58 9.58 9.58 9.58
Salt concn., M x 108
940 5.12 5.15 5.16 5.20 5.22 5.34 5.34 5.55 5.54 9.45 5.38 5.48 5.14 6.45 6.86 9.58 5.64 5.84 6.40 6.73 7.81
1.0 5.0 10.0 50.0
oso,
1.0 5.0 10.0 50.0
x x x x
10 10 10 10
ml
+ + + + + + + + +
090 -4.28 -4.25 -4.24 -4.20 -4.18 -4.06 -4.06 -3.85 -3.86
+ + + +
-E -3.91 -3.71 -3.00 -2.59
I
-
AH,O,,
+ + + + +
0.00 -3,94 -3.74 -3.18 -2.85 -1.17
oso,
AHa%, ml
TABLE XVIII O.lN HaOa, ml Taken Found MtWW* 9.40 9.40 9.40 9.40 9.40 9.40 9.40 940 9.40 9.40 9.40 9.40 Cr(NO3, 8.85 8.85 8.85 8.85 8.85 8.85 8.85 8.85 8.85 8.85
9.40 5.13 5.98 5.84 5.66 5.35 5.36 4.48 4.46 4.34 4.31 5.12 8.85 4.85 4.93 4.85 5.08 5.12 5.38 5.38 6.62 6.52
Salt concn., Mx lo8
0.02 0066 0.33 1.0 1.0 5.0 5.0 10.0 10.0 50.0
+ + + + + + + + + + +
0.00 -4.21 -3.42 -3.56 -3.74 -4.05 -4.04 -4.92 -4.94 -5.06 -5.09 -4.28
1.0 1.0 5.0
+ + + 1
040 -4GO -3.92 -4+nI -3.13 -3*17
li.8 10.0 50.0 50.0
+ + + +
-3.47 -3.41 -2.23 -2.33
-
-
L. J. CS~NYI, S. KASZAI and I. MOLNAR
462
O*lN H,O, ml Taken Found
FeWAh
9.46 9.46 9-46 946 9.46 9.46 9.46 9.46 946 9.46 9.46 9.46 9.46 Co(NO& 945 9.45 9.45 9.45 9.45 945 945 9.45 9.45 945
Ni@Qh
9.57 9-57 9.57 9.57 957 9.57 9.57 957 9.57 9.57 957
946 5.65 5.23 4.72 4.50 4.52 4-66 5.08 5.41 5.42 6.03 6.07 5.97 9.45 5.99 5.97 5.94 5-96 5.94 5-91 5.89 5.74 5.72 9-57 5.68 5.03 2.14 1.97 1.93 1.81 1.82 1.96 1.93 3.30
Salt concn., Mx 108
oso,
AH& ml
0.066 0.33 1.00 1.00 250 3.30 5GO 5.00 10.00 1000 SOGO 1.0 1.0 5.0 5-o 10.0 10.0 50.0 50.0
Oi66 0.33 1QO l-0 5.0 Ii.8 10.0 50.0
040 -3.81 -4.23 -414 -4.96 -4.94 -4+?o -4.38 - 3.99 -4.04 -3.43 -3.39 -3.49 WOO -3.46 -3.48 -3.51 -3.49 -3*51 -3.54 -3.56 -3.71 -3.73 0.00 - 3.89 -4.54 -743 -760 -7.64 -7.76 -7.75 -7.61 -7.64 -6.27
acid forms. In more acid solutions (pH 6G3.5) the kinetic current is furnished very probably by the OSvlrl/Osvl electron transfer. Considering all of these results it can be said that in neutral and very weakly acid solution the peroxyosmic acid and in more acid media the Osvllr[Osvl couple play an important role in the induced de~m~sition of hydrogen peroxide. We believe that the HOz radical attacks osmiumvlI1 (and/or peroxyosmic acid). The reduction product of osmium compounds reacts with hydrogen peroxide and an OH radical is formed. In this way, without adding any extra oxidising agent, a considerable amount of hydrogen peroxide is decomposed. In more acid media the decomposition may be represented schematically:
HO, + 0~~” -+ Osvu + 0, + H+
(3)
H,O, + Osvl’ --)rOH + OH- + Osvrl’
(4)
OH + H,O,
--+ HO, + H,O
(5)
Induced reactions in the peroxy compounds
463
TABLEXX O*lNHnOs,ml Taken Found
Salt concn., A4 x 10’
oso,
-
-
AH@,, ml
cuwo3, 9.20 9.20 9.20
9.20
9.20 9.20 9.20 9.20 920 9.20 9.20 9.20 9.20 9.20
1.96 522 1.65 1.62 1.75 1.72 230 227 264 269 4.14 4.12
0.02 0.066 0.33 1.0 1.0 5.0 5.0 10.0 10.0 50.0 50.0
: z
hN?30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30
9.30 5.08 488 475 4.77 446 4.52 412 408 3.16 3.10
0.33 1.0 1.0 5.0 A8
+ 1
10.0 50.0 50.0
f + + 1 -I-I+
1 + + + z
-E -1.24 -1.55 -1.58 -7.45 -7.48 -690 -693 -6.56 -6.51 -5.06 -5.08 -E -4.42 -4.55 -4.53 -4.84 -4.78 -5.18 -5.22 -6.14 -6.20
and in neutral or very weakly acid media: H,O, + 0~0, -+ [OsO,~H,O,]
(6)
HOs + [OsO,.H,O,] --+ OS + OsO,.HO + Hz0
(7)
OsO,*HO + H,O, --f HO, + 0~0, + H,O
(8)
The experimental results agree completely with the above reaction schemes. (1) It was found that increasing the delivery rate of permanganate considerably decreased the induced decomposition. With rapid titration, because of the relatively high local permanganate concentration, the competing reaction (2) considerably lowers the concentration of the HO, radical together with the extent of the induced decomposition. (2) Increasing the dilution of the titrated solution, other factors remaining constant, results in the increasing of the induced decomposition because of the decrease of the local permanganate concentration, and the concentration of HO, radical increases. The opposite effect can be clearly seen from Table II, according to which the induced error practically ceases when permanganate is present transitorily in excess. (3) The increase of the stirring rate promotes the even distribution of permanganate, thus the local permanganate concentration decreases, and together with it the extent of the induced decomposition increases. With the increasing of the stirring rate, the rate of the diffusion cannot increase without limit, so that the induced error alters according to a curve having a limiting value.
464
L. J. Cshw,
S. KASZAI and I. MOLNAR
(4) The induced error is decreased by increasing the hydrogen ion concentration. This can be interpreted in that the potential of the Osvlll/Osvl couple becomes strongly positive and inhibits the regeneration of osmium tetroxide [reaction (4)]. (5) The kinetic nature of the induced error is supported by the fact that the increase of both hydrogen peroxide and osmium tetroxide concentrations brings about an increase of the induced decomposition. (6) The chain character of the induced decomposition seems to be supported by the observation that on titrating with small portions and waiting a given time after the addition of each portion, the induced error is greater than with continuous titration. In the case of titrations performed fractionally, the chain-carriers can react for a longer time than in continuous titrations because the concentration of permanganate will be lower in the pause of the addition. The chain character of the reaction is further supported by the halide and halogen inhibition. These substances annihilate chain carriers. Halide ions react mainly with OH or 0~0,.HO radicals and the halogen molecules with the HO2 radical. Because the mentioned intermediates are not capable of oxidising fluoride ions, the errordecreasing effect is not experienced in the presence of fluoride. The error increasing in the presence of fluoride ions comes back to the increase of the pH of the titrated solution, when adding alkali fluoride, hydrogen fluoride being a weak acid. (7) Cerimetric titration results in a moderate induced error. This can be partly ascribed to the rate of .reactions (1) and (2) in the case of ceriumIV sulphate being higher than in the case of permanganate. The other reason is that the ferroln used as indicator reacts with the radicals, thus consuming the chain-carriers and exerting an inhibiting effect. In the l,lO-phenanthroline molecule the bond between carbon atoms 5 and 6 can be mostly easily attacked. Therefore it can be assumed that this bond is split by OH radicals (and OsO,*HO) and oxidised to carboxyl groups. In this way 2’2-bipyridyl-3,3’-dicarboxylic acid forms and this is not capable of forming complexes in acid solutions. To prove this assumption the end-product of the oxidation of ferronr was collected and compared chromatographically with 2,2’-bipyridyl-3,3’-dicarboxylic acid. The RF-value of the oxidation product agreed satisfactorily with that of the mentioned dicarboxylic acid, thus the above supposition seems qualitatively to be correct. (8) It was found that alkali and alkaline earth metal, zinc group, tinIV, aluminium and silicate ions do not influence the induced decomposition. The error-increase found in the case of beryllium, aluminium and silicate ions can, according to qualitative tests, be ascribed to impurities. A marked increase in the induced error is generally caused by ions which are good catalysts of the self-decomposition of hydrogen peroxide, e.g., iron”I, copperII, silverI, nickellI, manganeseu’), etc. Besides halide ions, ferricyanide, uranium”, ceriumlI1, chromiumlI1 and lanthanumlI1 ions considerably decrease the induced error. The interaction between ferricyanide and osmium tetroxide can be observed optically and supposedly this is the reason of the decrease of the catalytic activity, for example, in the reaction between ceriumIV and arsenous acid. Chromiumlll, 1anthanum”I and ceriumlI1 and probably uraniumV1 ions interact with osmic acid and decrease the catalytic activity. There is no direct experimental proof of this supposition, but we believe that osmium forming polyacid reacts with chromiumrII and the ions mentioned, and results in stable
Induced reactions in the peroxy compounds complexes as can be found in the case of polymolybdates.s photometric measurements are now in progress.
In this direction
465 spectro-
Zusammenfassung-Weim Wasserstoffperoxyd in Anwesenheit von Osmiumtetroxyd mit 1-8quivalenten Oxydations mittem (zB. Kaliumpermanganat, Cer(IV) sulfate) titriert wird eine induzierte Zersetzung des Wasserstoffperoxyd ist zu beobachten. Die Einzelheiten dieser induzierten Reaktion werden ausfahrlich erortert. R&sum&La decomposition de I’eau oxygen& est induite si elle est oxydee par des rbctifs tels que le permanganate de potassium ou le sulfate de ctrium(IV). Les principaux facteurs de cette decomposition induite en chaine de meme que l’influence de substances &rang&es sont d&rites en detail. REFERENCES 1 J. D’Ans and J. Matter, Angew Chem., 1952, 64,448. 2 A. I. Medalia, Analyt. Chenz., 1955,27, 1678. s W. M. Latimer, The Oxidation States of the Elements and their Potentials in Aqueous Solutions. Prentice-Hall Inc., New York, 1952. 4 Sh. Baer and G. Stein, J. Chem. Sot., 1953, 3176. 6 J. H. Baxendale. J. Chem. Sot. Spec. Publ., 1954, 1, 40. 0 P. B. Sigler and B. J. Masters, J. Amer. Chem. Sot., 1957, 79, 6353. 7 L. Cslnyi and K. Fiiliip, K&m. Folydirat Magyar 1958 64,47. 8 L. Cs&nyi, Acta Chim. Acad. Sci. Hung., 1959, 21, 35. g H. T. Hall and H. Eyring, J. Amer. Chem. Sot., 1950, 72, 782.