T H E OXIDATION OF SOLUTIONS O F FERROUS CHLORIDE I N ALCOHOLS JAMES R. POUND The School of Mines, Ballarat, Victoria, Australia Received March 4, 1959 I. EXPERIMENTS ON THE RATE OF OXIDATION O F FERROUS CHLORIDE
Anhydrous ferrous chloride, a light brown substance, was made a t a red heat from iron and hydrogen chloride. Its solutions in the various alcohols were allowed to undergo oxidation either in the air or in a desiccator through which dry air was continuously aspirated. The alcoholic solutions, 5 cc. usually, were in test tubes 1 in. in diameter; after a given time the solutions were diluted with water and sulfuric acid, and then were titrated with ceric sulfate solution. The experiments were carried out a t room temperatures. The results of the chief experiments are in tables 1 and 2. In table 1 the relative ferrous salt concentrations of the solutions are given against the time in hours. The results indicate that the initial oxidation is bimolecular with respect to the ferrous salt, as it is in aqueous solutions. Table 1 gives the value of the mecific speed,
where c = the concentration of the ferrous salt in moles per liter (which also is the normality of the ferrous salt as reducing agent), and t = the time, in minutes, during which the oxidation has proceeded. The time, in hours, over which the constant value of IC is obtained, is given immediately after k. The change in k after that period is indicated in the last column, d meaning that k has decreased, i meaning that k has increased thereaft‘er. The experiments marked “dry” were performed in a stream of dry air; those marked “air” were performed in the open air. Evidently the solutions of ferrous chloride in the alcohols oxidize much more quickly than its solution in water. For the aqueous solution of ferrous sulfate in the presence of 0.1 normal sulfuric acid the value of k , taken over a couple of years a t an average temperature of 15”C.,is 0.000,012 (1). In 87 per cent (weight per cent) ethyl alcohol with 0.01 normal hydrochloric acid the oxidation is thirty-six times faster; in methyl alcohol three hundred and eighty times and in ethyl alcohol four thousand 969
JAMES R. POUND
x
g
sa
v)
m
m
t * M
971
OXIDATlON OF FERROUS CHLORIDE IN ALCOHOLS
times faster; while in the higher alcohols the action is up to one hundred times faster than in ethyl alcohol. The speed of these oxidations varies greatly with the water content of the alcohols used, with the acidity of the solutions, and probably with other factors, as is usual in chemical velocity experiments. The alcohols were dehydrated with potassium carbonate and distilled in dry systems. It was noticed that the oxidations in the open air (moist) proceeded faster than those in the desiccator (dry air),-e.g., experiments No. 5 and 6 with ethyl alcohol; with isopropyl alcohol a similar difference was noticed; with the higher alcohols the difference was similar but smaller. Other experiments indicate that water retards the oxidation, but the evaporation of the alcohols may be greater in the open air. In the experiments with dry air the volume of air in the desiccator itself was more than sufficient to oxidize the samples completely, apart from the slow current of air TABLE 2 Values of k for ozidrrtion of ferrous chloride i n alcoholic solutions
Methyl alcohol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ethyl alcohol (99.5 per cent).. .......................... n-Propyl alcohol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isopropyl alcohol. . . . . . . .... n-Butyl alcohol.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isobutyl alcohol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . tert-Butyl alcoh ................................ n-Amyl alcohol ................................ Isoamyl alcohol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isocaprylic alcohol. ..................................... -
0.049 0.039 0.51
0.0046 0.094 0.28 0.061 0.41 0.62 0.65
0.13 0.13
4
972
JAMES H. POUND
suitable time in the open air, and the residual ferrous salt was then estimated. The results are summarized in tables 3 and 4 and in figure 1. The diminution in the rate of oxidation is most marked with the higher alcohols, and it is least with methyl alcohol. With ethyl alcohol solutions, 1 per cent of dissolved water reduces the oxidation to 80 per cent of that occurring in absolute alcohol; 2 per cent of water reduces the oxidation to 62 per cent, 10 per cent of water reduces it to 9 per cent, and 20 per cent of water reduces it to 3.5 per cent. Also, addition of alcohol, up to 50 per cent by weight, to acid aqueous solutions of ferrous chloride had no effect on the oxidation over I1 days. The solutions of table 4(B) were made by adding small quantities of 85 per cent alcohol to the ferrous chloride solution in 99.4 per cent ethyl alcohol; the aqueous solutions with isocaprylic alcohol were made simi100
40 20
'
0
2
4
6
PER CEN I WATER
FIG.1. Relation between the oxidation of ferrous chloride and the per cent of water in the alcoholic solutions used. Curve 1, methyl alcohol; curve 2, ethyl alcohol; curve 3, n-butyl alcohol; curve 4, isocaprylic alcohol.
larly, for water alone was not readily soluble in that alcohol; also in the isoamyl alcohol the whole of the added water did not perhaps dissolve. In table 4 the second column gives the oxidation relative to that which, from extrapolation, would have occurred in absolute (100 per cent) alcohol; the third or last column gives the oxidation relative to the original amount of ferrous salt present. Table 4(A) indicates that the oxidation in absolute alcohol would exceed the original ferrous salt present ; this perhaps indicates a more complex oxidation, which is confirmed by the gasometric experiments later. To make this presentation clear: 5 cc. of the first solution of table 4(A), ferrous chloride in 98.7 per cent alcohol, which at the start needed 1.73 cc. of 0.1035 N ceric sulfate solution to oxidize the ferrous salt, after 20 hr. needed 0.27 cc. of ceric sulfate solution; thus the ferrous salt oxidized in the 20 hr. was equivalent to 1.46 cc.
973
OXIDATION O F FERROUS CHLORIDE I N ALCOHOLS
of ceric sulfate solution, Le., 84 per cent of the ferrous salt was oxidized; but by extrapolation the oxidation in the 100 per cent alcohol would have TABLE 3 Relative amounts of ferrous chloride oxidized in alcoholic solutions containing water
-
-
0 1 2
Hours Temperature, "C Per - centt
' ~
85 72 56 _
I
73 54 30 1;
30
~
~
1
50 37 _ 2 14
,
1
100 100 100 100 63 46 44 16 37 50 24 2 4 __ _ _~_ _ _ _ ~ 1 31 2 4 18 10 17 18 39 71 66 73
100 100 66 (16) 51 (0) 32
1
~
~
55 -
* Column 2 is extrapolated from table 4(A). t Per cent ferrous chloride oxidized in the 100 per cent alcohol in the same time. TABLE 4 Relative oxidations of. ferrous chloride in ethyl alcohol solutions . ______ WATER
1-
6.2 8.7
0
(B) 0.05 N solution; 6 hr. a t 18°C.
OXIDATION RELATIVE T O BERRODS SALT IN ORIOINAL SOLUTION
(100) 69 46 21.5 11.5 7.5 3.5
121 84
percent
0
(A) 0.036 N solution; 20 hr. a t 19°C.
OXIDATION RELATIVE TO TEAT I N ABSOLUTE ALCOHOL
1.1 1.4 1.6 1.9
2.5
(100) 89 83 79 74 71 65 53
55
26 14 0
4 93 82 77 73 68 66 61 49
been 2.1 cc. of ceric sulfate solution, so that the oxidation in the 98.7 per cent alcohol was 69 per cent of that which would have occurred in the 100 per cent alcohol. The results of tables 4(A) and 4(B)agree reasonably
974
JAMES R. POUND
TABLE 5 Effect of reagents on the ozidatwn of alcoholic solutions of f m o u a chloride
-
YOLDBOX ~
BEAQENT U S I D P I E 6 CC. OB m o a o u c UOLUTION
LIABENT ADDID CBWTIB ~
0 0.05cc. water. . . . . . . . . . . . 0.15 cc. water.. . . . . . . . . . . 0.30 cc. water.. . . . . . . . . . . 0.05 Cc. 96% HzSO4.. . . . . . 0.1 Cc. 96% Ht804., . . . . . . 0.2 CC. 96% HrSO,. . . . . . . . 0.5 CC. 96% HzSO4.. . . 0.05 CC. 10 M "01. . . . . . 0.05 cc. 11 M H C l . . . . . . . . 0.075 cc. 11 M H C l . . . . . . . 0.1 cc. 11 M H C l . , . . . . . . . 0.1 cc. acetic acid. . . . . . . . 0.02 g. boric acid.. . . . . . . . 0.05 g. boric acid.. . . 0.10 g. boric acid.. . . . . . . . 0.02 g. buccinic acid. . . . . . 0.5 CC. 90% H8PO4.. . . 0.1 g. sugar. . . . . . . . . . . . . .
0
0.17 0.36 0.72 1.7 0.1 0.1 0.15 0.2 0.3 0.06 0.16 0.32 0.03 0.17 1.7
99.4 wr cent ethyl alcohol Ttgt - - -Propy 22. wt Xt Yt almhol Tt
-~ 0 0.55 1.65 3.3 0.04 0.09 0.18 0.45 0.35 0.45 0.65 0.9
100 57 21 4 26(")
100 47
100 61
100 41
25 17 14 7
28
31 (b)
32 62 57
61 34 67
gg(d
59 0.09 0.9
88
77 59 100 82
0.1 g. magnesia. . . . . . . . . . Platinum, bright or black. 0.05cc. 1 M NaNOz solutio 0.05cc. 1 M NaNOz solutio 0.05 00. H 8 0 4 . . . . . . 0.10cc. 1 M NaNOz solutio 0.05 cC. HI SO^.. . . . . . 0.05 cc. 0.6 M NaOH ir alcohol, . . . . . . . . . . . . . . 0.2 cc. 0.6 M NaOH ir alcohol . . . . . . . . . . . . . . .
I-Butyl alcohol
95(0) 91 91
96 40
0.01
0.5
+
0.01
0.55
12W)
+
0.02
1.15
zrX)(d
0.006 0.024
* 99.4 per cent ethyl alcohol contains 0.25 mole of water per liter; this is not included in column 3. t Experiment W was for 116 min. a t 12°C.;original ferrous chloride was 0.0874N; blank oxidation = 50 per cent. Experiment X was for 97 min. a t 13°C.; original ferrous chloride was 0.0747N;blank oxidation = 50 per cent. Experiment Y was for 79 min. a t 16°C.;original ferrous chloride was 0.1102 N;blank oxidation = 42 per cent. Experiment T was for 75 min. at 17'C.; original ferrous chloride was 0.0485 N;blank oxidation = 52 per cent. (a) with 0.08 cc. of 96 per cent sulfuric acid; (b) with 100 per cent sulfuric acid; ( 0 ) incomplete solution of reagent; (d) trouble with titration; ( 0 ) trouble with titration and oxicration ia complete.; ('1 precipitate formed.
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OXIDATION OF FERROUS CHLORIDE IN ALCOHOLS
closely; in table 3 columns 3 and 4 indicate the agreement of duplicate experiments. 111. EFFECTS OF REAGENTS ON THE OXIDATION OF FERROUS CHLORIDE SOLUTIONS IN ALCOHOLS
The results are given in table 5. The influence of water has been discussed. The presence of acids decreases the oxidation of the ferrous salt, strong acids having a greater influence than weak acids; the effects of water and acid are roughly additive. In contradistinction to the behavior of aqueous solutions of ferrous salts, in the alcoholic solutions phosphoric acid behaves normally and- does not increase the oxidation. Platinum and basic substances do not increase the oxidation. Oxides of nitrogen, but not nitrites, do catalyze the oxidation, as they do also in aqueous solutions. TABLE
6
Electrical conductivities of alcoholic solutions of ferrous chloride during oxidation nm
1
N
1
~ ~ T z o T .
In 98.2 per cent ethyl alcohol
//
ohma per em.
houra
0.1670 0.1088 0.0375 0.0117
0
20 47 96
0
11
!
0.1053 0.0008
RYE
1
~
1
O.oooO84 1 0.000158
AT 2O'C.
In 99.5 per cent ethyl alcohol ohms per cm.
0.1627 0.1011 0.0156 0.0069
43
1
~
houra
0.000866 0.000936
1
--___
N
0 206.25
1 ~
116
0.0567 0.0519 0.0367 0.0158
j 1
1
1I
0.000674 0 . oO0980 O.oO0919 0.000864
