THE REACTION B E T W E E N CHLOROFORM A N D POTASSIUM HYDROXIDE
BY A. P. SAUNDERS
This reaction is generally represented in the textbooks by the equation : CHC1,
+ 4KOH = 3KCl+
zH,O
+ CH0,K.
According to this the reaction might involve primarily three molecules of potassium hydroxide and one of chloroform, to give potassium chloride and formic acid, the last being then at once neutralized by another niolecule of potash ; or it might be pentamolecular from the start, one molecule of chloroform reacting at once with four molecules of potash ; or, finally, it inight go in stages, each one of which is bimolecular, consisting of successive replacements of chlorine in the chloroform molecule. T h e object of the present investigation was to determine, if possible, the order of this reaction. T h e case is coinplicated by the fact that potassium formate is unstable and breaks down partiallv to carbon monoxide and potash;' thus the concentration changes are here subject to varying influences, the exact nature of which is not as yet understood. T h e experiments recorded below were carried out in the following manner : From ordinary 95 percent alcohol, a solution of alcoholic potash was prepared, of known strength. T h e alcohol, when tested as to its neutrality, was found to be faintly acid ; the error introduced in this way in those cases where alcohol was used as a diluent was not large enough to affect the results in any sensible degree. A solution of chloroform of equivalent concentration was also made in alcohol, reckoning three Geuther.
Liebig's Ann. 123,
1 2 1 (1862)
Reactioiz between Chlorofo~nzaizd Potassium Nydrcxide 66 I molecules of potash to one of chloroform ; i. e., the chloroform solution was one-third as concentrated as the potash solution when calculated in gram-equivalents per liter. Owing to the partial and variable decomposition of the formate it is impossible to prepare solutions which shall remain equivalent after the reaction has begun, because there is no constant ratio between the change of concentration of potash and that of chloroform. T h e solutions so prepared were placed in an Ostwald thermostat and, after a sufficient time had elapsed, were mixed in the desired proportions in separate small flasks, standing in the same bath ; these were then removed at stated intervals, immediately cooled under a tap, made up with water to a certain volume, and analyzed. T h e alkalinity was determined by titrating against a hydrochloric acid solution, using phenol phthalein, and chlorine was determined by silver nitrate against ammonium sulphocyanate. All the messuring vessels employed were previously calibrated. T h e series are as follows : SERIESI
Temperature Alcoholic potash Chloroform
, I
44.5' corr. 0.482 N. 0.1625 gr. equiv. per liter.
T h e separate reaction solutions were made by mixing 2 5 cc of alcoholic potash with an equal volume of chloroform solution ; their initial concentrations were therefore one-half of the above. T h e values recorded in the table below are as follows : I. Arbitrary numbers of the experiments. 2 . Interval of time in minutes between each experiment and the succeeding one (At). 3. Concentration of potassium chloride in the mixture (initial conc. 0.0). 4. Concentration of potassium hydroxide in the mixture (initial conc. 0.241). 5. Total change in conc. of potash from the initial conc.
A.P.Suunders
66 2
6. Actual concentration of potassium as formate ; i. e., the difference between the values of 5 and 3. 7. Calculated concentration of potassium as formate ; i. e., one-third of the values in 3. 8. Percent of undecomposed formate ; i. e., 6 divided by 7. 9. Change of conc. of potassium chloride (by intervals) (Ax). IO.
Change per minute
(a.
Mean concentrations of potash (c,) calculated from 4, by taking the mean of each value and the preceding one. I 2. Concentration of chloroform, calculated by deducting the values of 7 from the initial concentration of chloroform 11.
0.0812.
13. Mean concentration of chloroform (c,)
by taking the
mean of each value and the preceding one.
14. K
=
Ax At
-.
104.
(Assuming the reaction to be bi-
C,CZ
molecular.) Ax At
L_
15. K = molecular.)
c, c,
. IO*. (Assuming
the reaction to be tetra-
Reaction bedween Chlorofornz and Potassium Hydvoxide 663
-
(n
ci
Ln
0
0
w
0 P -
N 0 1
m
G,
V
u3
U
P
- . I C -
w N -
H
0
QOvmCnPwNu
A.P. Sauizders
664
SERIES I1 T h e results of this series and of those which follow are recorded in the same way as the above. Temperature Alcoholic potash Chloroform
1 I
44.50 corr. o 482 N. 0. I 6 2 j gr. equiv. per liter.
T h e separate reaction solutions were made up by adding 2 5 cc of alcoholic potash to 2 5 cc of chloroform solution, and then diluting with 50 cc of alcohol. T h e solutions therefore contained 0.1205 gr. equiv. KOH, and 0.0406 gr. equiv. CHCI, per liter, ' If the reaction proceeds as a bimolecular one, then by halving the concentration of both the reacting substances, we should find that the decomposition goes on one-fourth as fast in the more dilute solution as in the more concentrated one ; whereas if the reaction is tetramolecular, i t should go on one-sixteenth as fast. Plainly the former is much nearer the truth than the latter ; and the first values are fairly correct for the former assumption. But the solutions which begin with the concentrations in the proportion of two to one, soon depart from this ratio. We can calculate from the velocity in Series I. what the velocity in SeriesII. should be a t any time, by taking, not one-fourth of
Ax
in Series
I, but that fraction which corresponds to the concentrations themselves. T h u s if we call cI(')the concentration of potash in the first series, c2(I) that of chloroform ; and for the second series, and ~ ~ ( we ~ 1 can , calculate at each point, from the value of
AX at
Ax in Series I., and the values of c1('),cz('), ~ ~ ( c~(~), ~ 1 , what value At
should have in Series II., by using the formula Ad2) -AAx (t.1 ) ~cl(r)cz(l) - - ____ At -
These calculations yield the results :
'
Reaction between ChZov0)'bvm nnd Potassium Hydroxide 665
H
P
cc
? ? ?
?
?
P O ? ? ?
U N
CO U
0
A.P.Sauizdevs '
666
I
I
I
I
I
-_ Temperature
21.5"
corr.
Reaction between Chlovofovm and Potassium Hydroxide 667
n
D
%
u
A. E Saunders
668 I,
Reactioit between Chlo~ofoovmand Potassium Hydvoxide 669 Making the same calculation that was made for the other series, i. e., from the relative concentration of potash at each point, calculating the reaction velocity for Series IV. from Series 111. allowing for the fact that the chloroform was uniformly oneAx
half as concentrated, we find for a f in Series IV : '
1
::;ahd
I ,I1
I11 IV
2
IO
i
1
I
4~
1
I5
0.000850 o.oo0500 0.000443 0.000260 0.000184 0.000860 0.000648 0.000417 0.000422 0.000316 ~
I cc KOH in alcohol cc CHC1,+in alcohol , 116.5 75.3 68.4 65.I j O . 0 2j cc KOH in alcohol ) 2 j cc CHCI, in alcohol 326 I 60 737 I20 I O 0 50 cc alcohol 25 cc KOH in alcohol 0.0 0.0 3.9 11.8 12.2 25 cc pure CHCI, 25 cc KOH in alcohol 22.4 13.0 28.4 34.6 26.2 25 cc pure CHCI, j o cc alcohol 25
2j
1
i
I
I t will be understood that these percentages are not .quantitatively accurate ; it did not lie within the scope of this investigation to obtain results of extreme accuracy ; rather to find in general the nature of the changes which go on. Comparisons can only be made independently between Series
670
A. R Saundevs
I. and II., and Series 111. and IV., because the temperature was lower for the latter pair ; but it is plain that dilution with alcohol tends to prevent the decomposition of the formate. . Furthermore, Series 11. shows that there is in that case a formation of some other substance than formic acid, probably some of the intermediate compounds between chloroforni and orthoformic acid, or even, in the earlier stages of the reaction, potassium orthoformate itself. In this connection it is worth while to call attention to the experiments of Williamson and Kay,' who found that sodium etliylate and chloroform yielded ethyl orthoformate. T h e results of Series 11. indicate that, if such a formation of potassium orthoformate actually takes place, it does not remain in the solution, but is decomposed as the reaction proceeds. A reaction velocity constant can hardly be deduced from these results. In view of the wide variation in each series, it was not considered worth while to attempt to apply a complex and tedious integration. T h e Series I. and 11. indicate a value lying perhaps between 600 hnd 700, and they show at least, clearly, that the tetramolecular formula gives values which vary much more widely than those obtained with the bimolecular formula. Among the disturbingfactbrs, we have to consider, besides the irregularities, arising from the formation of potassium formate, the separation of potassium chloride in crystalline form, which begins very early in the history of the change ; there may in some cases be a separation of potassium formate as well, out of the solution. T h e formation of water produced by the reaction would also affect the reaction velocity in one way or the other ; Dumas2 states that an aqueous solution of caustic potash has no action on chloroform, even when boiled with it ; from this it would seem probable that the presence of water in an alcoholic solution would retard the reaction ; and we might therefore expect that the constantly increasing amount of water in the experiments here described would lead to a corresponding decrease in the reMem. Chem. SOC.7, 224. l A n n . Phys. Chim. ( 2 ) 56, 115 (1834).
Reaction Jetween Chlovofonlz aizd Potassium Hydvoxia’e 67 I
A.P.Sauna’evs
M
/I
II
w
II
w
Reaction between ChZo?Fofilvmand Potassium Hydvon-ide 673 action-velocity constant ; on the other hand, the amount of water present in the alcohol to begin with was so large that the changes produced in this way would be relatively trifling.
*
SERIESV Temperature Alcoholic potash Chloroform
I
I I
43 50 corr. 0 . 5 7 7 N. o I o j gr. equiv. per liter.
T h e separate reaction solutions were made u p by adding 2 j cc of alcoholic potash to 2 j cc of chloroform solution ; they therefore had a concentration of 0.2885 gr. equiv. of potash and 0.0525 gr. equiv. of chloroform per liter. One analysis was made immediately, to ascertain the initial concentration. SERIESVI ~
Temperature Alcoholic potash Chlorof orin
1 ~
_
43. j ocorr. 0.577 N. 0.170 gr. equiv per liter.
T h e separate reaction solutions were made up by adding 2 5 cc of alcoholic potash to 2 j cc of chloroform solution ; they had a concentration of 0.2885 gr. equiv. of potash and 0.0850 gr. equiv. of chloroform per liter. While the variations in the reaction-velocity constant calculated from the bimolecular formula are a good deal larger than one would wish, it is plain that they are quite irregular, at least in most of the series ; and the results obtained from this formula are in all cases much better than those which come out for the tetramolecular formula ; probably a more exact study of the reaction under better conditions would yield a satisfactory constant. CONCLUSIOP\'
T h e present investigation shows that i n all probability the reaction between chloroform and potassium hydroxide proceeds in stages, in each of which only two molecules react together.
_
674 Reaction between C/zZoroform and Potassium Hydroxide T h e experinlental part of the investigation was carried on at Cornel1 University, in the laboratory of Professor Bancroft, to whom I am indebted for his friendly interest and useful s'iggestions. Hamilton College, Cliaton, Sept., 1900.
