T H E ISFLL-EKCE O F S T R O S G SALT SOLLTIONS O S T H E SPOSTAXEOL-S O X I D A T I O S O F PYROGALLIC ACID. FERROUS SULFATE A S D FRUCTOSE BY C . G . MachRTHUR
I n one of M r A. P. Xathews’ papers’ on the oxidation of cystein, he states that upon the addition of salts t o the solutions the rate of oxidation was decreased. He was uncertain whether this effect was caused by the salts decreasing the solubility of the oxygen or by a specific action of the salts on the oxidizing substance. 9 t his suggestion this work was started t o see which of these two theories was correct. Method The quantity of salt that would make a certain molecular concentration was dissolved in j o cc. of -1-I O sodium hydroxide. This was placed in a 400 cc flask? that was provided with a ground glass stopper carrying a mercury thermometer and a glass cock. To this solution was added a definite amount of the substance to be oxidized. The contents were shaken rapidly in a mechanical shaker The amount of oxygen absorbed was determined by the negative pressure in the flask as measured by the manometer. The barometer and thermometer were read a t the same time as the manometer The \-ariations in temperature during any one experiment were not greater than one degree As a rule the difference in temperature between any two experiments mas not greater than three degrees. The results are not materially affected by these irregularities in temperature During any experiment the barometric pressure did not L-ary more than two millimeters
’ Jour
BIOI Chem , 6, j r r 11909). -A P l f a t h t v i I h i d , 6, I (1909).
In this work no attempt was made to work in concentrations of alkali t h a t give maximum speeds. The amount of alkali that would give a desirable reading on the manometer in a reasonable period of time was chosen. This amount was kept constant during the experiments on any one oxidizable substance. For the calculations of the velocity constant ( k ) it was assumed that one-fifth of the initial atmospheric pressure was due to oxygen The oxygen pressure would therefore be about 1 5 0 mm mercury. The negative readings on the manometer subtracted from I j o indicate the millimeters of oxygen pressure remaining. Though it is approximately true, as a rule, that the amount of oxygen dissolved in a solution is directly proportional to the oxygen pressure above the solution, it was noticed in these experiments that slight l-ariations resulted from irregularities in shaking caused by changes in speed of the electric motor. This probably accounts for some of the irregularities in the data. It is believed, however, that the speed of shaking was great enough to keep the solution so nearly saturated a t the then existing oxygen pressure that no serious errors were introduced. The velocity constant was calculated from the monomolecular equation :
I n this expression t is the time in minutes, A the initial oxygen pressure ithe barometric pressure divided by five), and x equals the manometer reading. The values for the solubility of oxygen are to be found in a recent article on the solubility of oxygen in various concentrations of several of the ordinary salts.' The figures in the table are the number of cc of oxygen per liter of salt solution.
*
hlacArthur
Jour. Phys. Chem.,
20,
4 9 j (1916)
I I 1-Rzi e7 I I cc
qt 5t r o I I g
Sa1t S o l zi t io 11s , Et c .
547
Pyrogallic Acid j
+
grams pyrogallic acid the amount of salts given below, dissolved in j 0 cc *Y I O S a O H Barometric pressure = 748. Temperature = 2 0 6' C ~
~~ ~
I
Sol. of 0 k at
Conc of salt
20
llanometer readings
rnin.
to min. jo min.
min.
[IO
~
X o salt
j.78
0.0Ijj
SaCl M SaCl 2 M SaCl 3M Sac1 3M S a C l
4.92 4.20 3.05
0.0146
2.24
0.00j3
T3 70 50 44 28
.62
0.0032
22
M
j
2
I
0,0099
0,0087
95 92 70 60
._
I21
I20
I00
92 68 58
40 32
+
grams pyrogallic acid the amount of salts given below, dissoh-ed in j o cc -Y I O S a O H Temperature = 20' C Barometric pressure = 750 7 . ~
I
I
llanometer readings
Sol of 0 k a t
Conc. of salt
20
min ---- I
I S o salt ' 2111 AlgC12 I M AlgC12 2 M MgC12 311f lfgC12
j
20min iqomin 60min
min.
I IO
I
--I
~
I
78 4 37 3 IS
I
2
22
1
I
j0
j
0 0 0 0
0168 0079 004j 0013
43
73
22
4j
13 4 3
28 6 4
I
0 0010
I20 IOj
92 6j 40 9
82
26 13
5
+
grams pyrogallic acid the amount of salts given below, dissolved in j0 cc IO SaOH Barometric pressure = j j I 8. Iemperature = 20' C A\-
P -
11anometer readings Conc of ,alt
Sol of 0 k at
20
rnin
~ ~
20
~~
~
min. 40 min. 60 min.
~
120
min.
0.0192
I22
0.0164
I22
0.0141
"5
0.0099
IO0
j
G.,IIuc,4 r t h r
C'.
548
+
grams pyrogallic acid the amount of salts given below, dissolved in 50 cc AY I O S a O H Barometric pressure = 751 8. lemperature = 2 0 ' C
.,
~
cotlc. of salt
Sol. of 0
k a t z o miii.
S o salt I&! KaBr 2 M SaBr $kf S a B r 4iW S a B r
o.or92 0.007j 0.0060 O.OO;Li
0. (1020
+
5 grams pyrogallic acid the amount of salt5 given below, dissolved in jo cc .\- I O S a O H Barometric pressure = 748 2 . ieniperature = 20' C J .
11anometer reading. Con?. of salt
sol. of 0 k a t
20
mill. 90 min.
S o salt ' ?;VI KC1 I M KCl 2 M KC1 3-51 KC1 j
I I 0 I02 a2
72
70
+
grams p>-rogallic acid the amount of salts gi\-en helon. dis>ol\-ed in 50 cc *\- I O S a O H Barometric pressure = 748 2 . Temperature = 20' C 5Iaiionieter readings
Cotic. of salt 20
40 rnin 160 rnin
rnin
I
~
90 min
~
The effect that the ,\- I O alkali would haL-e on the solubility of oxygen has been neglected. In the smaller concen-
Iizjlueuce o j Ytroiig S a l t Yolutioiis. Etc.
549
trations of salt t o neglect the effect of the alkali introduces an appreciable error, for alkali influences the solubility of oxygen to about the same extent as sodium chloride. This error decreases, however, with an increase in salt concentration. These experiments show greater manometer readings with an increase in time, for all concentrations of salt. This is to be expected if the salts do not have a direct influence on the substance oxidizing At the end of an?- given period of time, the readings decrease from the solutions containing no salt to those of the highest concentrations This decrease is largest between the more dilute solutions and becomes less and less with an increase in amount of salt, showing t h a t the addition of a given amount of salt has more influence on the decrease in oxygen pressure than an?- subsequent like amounts. The 1-elocity constants decrease with an increase in salt concentration a t about the same rate as the oxygen solubility. Some irregularities are to be noticed among them, but probably no more than is to be expected from the conditions under which these experiments were carried out. If one constructs a curve for k , and another for oxygen solubility against salt concentration, it xi11 be seen that the two curves have a similar form It may be concluded t h a t the principal factor influencing the rate of oxidation of pyrogallic acid in salt solutions is the decrease in solubility of oxygen caused by these salts. That k is a fairly good constant for the oxidation of pyrogallol for any particular concentration of salt is evident from the following table. The data were chosen largely a t random : Time in min.
S o salt
3JI S a C l
o 016s o 0166
0 00jj
30
60
o 01j9
20
o 0052 o 0052
M lIgC11 0045 o 0051 o 0052 0
Jf KCl
o 0141
o 0142 o 0134
3-11 KCI
o 0067 o 0070 0.0069
Ferrous Sulfate 5 grams ferrous sulfate
+ the amount of salts given below, dissolved
I SaOH in j o cc Barometric pressure = 753 4. Temperature ~~~
_
=
20.4' C
_~~
Manometer readings Sol. of 0 k at
Cone. of salt
20
min.
_-
IO
I M XaC1 2M XaC1 3 M NaCl 4 M XaCl
~
5.78
0.018j
4.92 4.20 3.05
0.0163 0 . 0 128
I
Barometric pressure
j0
cc
= j j j~.
- __
~~
KOsalt
l!/Jd NaBr IM XaBr 2M SaBr 3 M KaBr 41V NaBr
I
2
21
18 9
ISaOH Temperature I
'
Sol. of 0 k a t
104 103 93 69 63 45
89 88 78 54 48 31
20
= 2 0 j' _ _ _~_
C ~ ~
Manometer readings
min.
-.
, I
9 7
47 44 34
+ t h e amount of salts gil-en below, dissolved in
Conc. of salt
22
0.0063 0.0031
62
5 grams ferrous sulfate
27 2 j
0 , 0 0 7j
2.24
I
~
60 min.
_ _ ~~_
_
No salt I ' & NaCl I
-
min zomin 40min.
j.78 j.15
4.47
o 0228 0.0192 0.0173 0
2 . ji 2.02
0107
0.0067 0 0031
In ferrous sulfate also the manometer readings decrease with an increase in salt. The velocity constant decreases with an increase in concentrations of salt a t about the same rate as the solubility of oxygen does. The most marked influence is in the smaller concentrations. It would seem t h a t the decrease in oxygen solubility produced by the salt is the most important factor in decreasing the rate of oxidation of ferrous sulfate.
Iizj4ueizce o j Stroiig Salt Solutiom, Etc.
2 ,o
grams fructose
Fructose
+ the
amount of salts given below, dissolved in jo cc -I7I S a O H Barometric pressure = 740.4. Temperature = 20.2' C
__
-
1
Conc of salt
Sol of 0
1k
~_
i
at
20
min.
_
~
Manometer readings
i
I
rnin
120
S o salt & NaCl l I A S~ a c 1 2 M SaCl 3Af S a C l q M NaC1 2
551
-1.0min
6 0 mixi
130 min.
0 . 0059
o.ooj6 0.OOjZ 0 . 0 0 4j 0,0029 0.001;
o grams fructose
+ the
amount of salts given below, dissolved in jo cc I SaOH Barometric pressure = 752 8. Iemperature = 2 1 C A\-
?,
-~
_
_
I
,\Ianometer readings
~
k at
Sol. of 0
Cone. of salt
20
rnin 20
No salt 2f44'SaBr IM XaBr 2 M SaBr 3M S a B r 4 M NaBr 2.0
.o min.
5.78
o.ooj9 0,0079
22 22
43
j.Ij
4.47 3.3;
0.006;
I9
37
0.0031 0.0024.
9
21
0.ooog
3
2 .jj 2.02
grams fructose
-1
42
17
s
+ the amount
of salts given below, dissolved KaOH 736.3. Temperature = 20.4' C
in 50 cc S Barometric pressure
=
I
~.
~
Conc of salt
min
1
~
Manometer readings
Sol. of 0
~
k at
20
min
~
i o min. 60 min. 1
No salt j 78 ?..Ti' S a 2 S 0 4 3.97 I&! Sa2S04 I 3.00 1
~-
.
0.0073 0 0054 0 0032
1
20
40
Ij
32 21
9
I 90 min.
2 .o
grams fructose
+ the
amount of salts given below, dissolved in j o cc -1-I SaOH Barometric pressure = j 3 6 3 . I emperature = 20.4' C ,1
I
llanometer readings
1 sol. of o
Conc of salt
k at
o grams fructose __ __
min
o 0073
20
0
0073
20
0
0053 0036
0
2
20
1 ~
1
60
$0
~
30 26
I j 13
1
$c
~
82 79 63
jj
ii
!
jj
+ the amount of
salts given below, dissolved in j o cc S I NaOH Barometric pressure = 744 j . Temperature = 20.6' C -
-
-
~
I
I
Conc. of salt
k at
Sol of 0
20
20min l $ o m i n 60min __ ~-
~
Sosalt IM KS03 2-44 KNO?
SIanometer readings
min
j 78 4 61 3 65
~
I
o 0076
21
o 0076
21
o 0060
I;
'
~
40
;;
1
j9
IOO
~
min.
91
86 ~
j50 6
82
I n fructose i t was noted that small concentrations of salt had little effect on the manometer readings,' compared with the differences observed for p>-rogallol and ferrous sulfate. ITith the exception of sodium sulfate molecular concentrations caused practically the same decrease in oxygen pressure in the flasks as when no salts were present I n fact in a few instances i t was obsen-ed that a slightly larger negative reading was obtained for molecular salt solutions than for the no salt controls. The differences, however, were so small that they were attributed t o irregularity in the conditions present in each of the flasks. It is certain that the amount of dissolved oxygen is markedlj- decreased in 2 molecular salt solutions It is difficult then to see why small amounts of salt have no effect on the rate of oxidation of fructose If small amounts of salts catalyzed the reaction 1
LIathews Jour. Biol. Chem , 6 ,
310 (1909)
one would not expect the close approach to the controls. If the salt influenced the fructose in any way larger differences from the control would be expected In higher concentrations of salt marked effects on the rate of oxidation are seen. From the following data another difference from pyrogallic acid and ferrous sulfate will be observed Instead of k being a constant it gradually increases ~ ~
~~
~~
minutes
~
I
20
4O 60
I I
No salt
1
I
z J f XaBr
~
-
~
o 0079 0 0084 0.0088
_ _ -~-~ -_ _ __ -
I
0031 o 0037 0 0040
0
zlcf KC1
+1fxaC1
_ _ _ ~
I ~
0°17 0 0021
0
0 OOj3,
0024
It is very probable that the alkali present increases the number of active reducing particles as the reaction progresses. This would cause a gradual increase in the velocity constant.'
Conclusion The tables bring out the fact that sodium chloride, potassium chloride, potassium nitrate have about the same effects on the rate of oxidation of pyrogallol, ferrous sulfate and fructose. Sodium bromide decreases the solubility of oxygen more than the above salts and consequently decreases the rate of oxidation more. Sodium sulfate and magnesium chloride affect both the oxygen solubility and the rate of oxidation more than sodium bromide, even when normal concentrations instead of molecular are compared. In all experiments with increase of salt there is a decrease in the rate of oxidation. The rate of oxidation parallels the solubility of oxygen in all cases except those on fructose in dilute salt solutions. Bzochenizcai Laboratovy of the 17nzzerszty oj' Clizcago
-
_ _ _ _ -______13Iathews Jour. Biol. C h e m , 6 ,
IO
(1909).
