[CONTRIBUTION FROM
NOYES
CHEMICAL LABORATORY, UNIVERSITY
O F ILLINOIS]
REACTIOXS AKD ANALYSIS OF P-CHLOROETHYL SULFIDE IN WATER1 CHARLES C. PRICE2
AXD
LYNN B. WAKEFIELD
Received August 19, 1946
The observations of Peters and Walker (1) and Mohler and Hartnagel (2) that the rate of hydrolysis of 6-chloroethyl sulfide (I) in water was first order, independent of the pH and a number of added anions and cations, led the latter authors to point out that this behavior resembled that of an S N process ~ proceeding by a solvolytic mechanism in which the rate controlling step was an ionization of the carbon-chlorine bond.
,
ClCKzCHzSCHzCHzCl I
+
ClCHzCHzSCHzCHz IIa
C1-
i H ~ 0
(HOCH2CHz)zS IV
HzO
+
ClCHzCHzSCHzCHzOH I11
Hf
The solvolytic nature of the reaction is substantiated by the observations (1, 2) that alcohol as a solvent markedly decreases the rate, propanol being more effective than ethanol which in turn is more effective than methanol (2), as expected for a solvolytic reaction. In unpublished work, Peters and Ogston have made the significant discovery that, in the presence of a number of compounds, especially thiol and sulfide derivatives, the rate of the reaction remains essentially unchanged, although the course of the reaction becomes metathesis rather than hydrolysis. These observations were interpreted on the basis of the ionic intermediate IIa above, RSCHzCHzOH
II& IV
\’L
+
H+
(a)
+ RSCHzCH2S(CHz C H Z O H ) ~
(c)
The work described in this paper was carried out under a contract, recommended by the Kational Defense Research Committee, between the Office of Scientific Research and Development and the University of Illinois. 2 Present address: University of Notre Dame, h’otre Dame, Indiana. 232
REACTIOXS OF P-CHLOROETHYL SULFIDE IN WATER
233
Since the common behavior of reactions proceeding through a cation of the type IIa is that the ion reacts immediately with the solvent, regardless of other reagents present, it seems necessary to postulate some other type of intermediate. The most likely form would be a cyclic sulfonium salt (IIb).
/\+
..
CH2
RSCH~CH, -+
RS+’
\ I \
I
’
CH2 IIb
IIa
Such an intermediate, although considerably more reactive than I, would be stable enough to discriminate between the molecular species with which it might react. A very much higher value for kl than for k, would therefore change the course of reaction from hydrolysis (a) to metathesis (b, c) in the presence of even relatively small concentrations of thiosulfate. The ratio of these rate constants has been termed the “competition factor” by Peters and Ogston, who found the competition factor for thiosulfate (kl/k,) to be 2.7 X lo4. This has suggested that a convenient procedure for analysis of /3-chloroethyl sulfide in the presence of hydrolysis products might be devised making use of its “thiosulfate-demand”. Since both hydrolysis and metathesis involved the same rate-controlling step the rates of both processes would be the same. In water a t 25”, the value for this constant is about 0.10 min.-l (1, 2), which corresponds to a half-life of about seven or eight minutes. Either reaction would thus be about 96% complete in forty minutes. These expectations have been verified experimentally and the method utilized to confirm the rate of hydrolysis of I in water. In addition, some observations are recorded on the stability of vapor of I in moist air. As would be expected from the mechanism of hydrolysis outlined above, hydrolysis in the “nonpolar solvent” air did not proceed measurably over :L two-week period. Exposure of the vapor of I to liquid water (or synthetic seawater) did lead to absorption and hydrolysis, to some extent favored by an oil film on the water. EXPERIMENTAL
Analysis of aqueous 8-chloroethyl sul$de solutions. Approximately 1%solutions of pure redistilled p-chloroethyl sulfide (prepared by the action of thionyl chloride on thiodiglycol) were made up by dissolving weighed quantities in 100 cc. of anhydrous Cellosolve, Methyl Cellosolve, or dioxane. One-cc. portions of these solutions were pipetted into 25-cc. portions of 0.01 N sodium thiosulfate, and, after periods of 5,10,15,25,40, and 80 minutes at room temperature (ca. 27”), a 25-cc. portion of 0.01 N iodine in potassium iodide was added t o each mixture. The excess of iodine was then back-titrated with thiosulfate. The results of the measurements of the rate are summarized in Table I. The first order rate constants included were estimated graphically. For the first three experiments, the I was added in dioxane solution, for the fourth, in Methyl Cellosolve, and for the last two, in Cellosolve. Since the reactions were essentially complete aft,er forty minutes, this time was chosen in carrying out analysis for I by this procedure. The average of the forty-minute values from Table I, 95.97% with a mean deviation of 2.4%, compares favorably with the theoretical
234
CHARLES C. PRICE AND LYNN B. WAKEFIELD
value of 96.9% oalculated on the basis of a half-life for the reaction of eight minutes. Some hydrolyeis (rather than metathesis) may take place in dilute thiosulfate solution but, in 0.01 N thiosulfate,it should amount to less than 1% of the over-all reaction, based on Peters and Ogstons’ value of 2.7 X lO4for the “competition factor” of thiosulfate ion. As a further check on the analytical procedure, the rate of hydrolysis of I in aqueous solution was measured and found to be the same as the rate of reaction with thiosulfate ion. One-cc. portions of solutions of I were added to 25-cc. portions of distilled water at room temperature (ca. 27”). After periods of 5, 10, 15, 25, 40, and 80 minutes, 25 cc. of 0.01 N thiosulfate was added to each mixture and, forty minutes later, the unreacted thiosufate was titrated with 0.01 N iodine solution. On the basis of 96% reaction with thiosulfate after
TABLE I RATE OF REACTIONOF 6-CHLOROETKYL SULFIDEWITH AQUEOUSSODIUMTHIOSULFATE ( C A . 27”)
I
I
% HYDROLYSIS (Methyl Cellosolve)
AVERAGE
(Cellosolve)
~~
5 10 15 25 40 80 Rate Constant (min.-l)
41.1 63.8 78.0 90.8 96.3 97.3 0.098
45.7 66.2 79.3 93.0 96.0 97.3 0.097
38.5 63.7 79.6 89.5 93.5 94.9 0.101
44.1 66.1 82.4 93.2 97.8 99.4 0.097
48.2 72.8 87.2 96.4 100.5
34.5 55.3 66.1 84.2 91.0 95.9 2.4 92.4 0.083 0.101 z k .009
-
0.127
1
I
TABLE I1
RATEOF HYDROLYSIS OF 8-CHLOROETHYL SULFIDEIN WATER( C A . 27’) % HYDROLYSIS
5 10 15 25 40 80 Rate Constant (min.-l)
40.4 65.9 80.8 92.5 95.7 97.3 0.108
41.3 69.3 83.8 97.5 100. 0.118
forty minutes, the total amount of I in the solution at the time of addition of thiosulfate was readily estimated. The data for the rate of hydrolysis as measured in this manner are summarized in Table 11. Stability of p-chloroethyl sulfide vapor in moist air. A one-liter flask, fitted with a 24/40 standard-taper ground joint, was equipped with an inner joint carrying a short glass tube and a stopcock. This flask was evacuated to a pressure of 4 to 5 mm. Moisture was removed either by heating with a free flame during evacuation or by alternately refilling with air dried by passage through calcium chloride and reevacuating several times. Finally the evacuated, dried flask was connected to a Geissler potash-bulb apparatus, the three bulbs of which were filled with I, and slowly allowed to refill by passage of dry air through the bubbler (15 t o ’20 minutes). I n this way a definite volume of air, essentially saturated with mustard vapor, was obtained. If the presence of moisture was desired, one cc. of
REACTIONS OF
P-CHLOROETHYLSULFIDE
235
IN WATER
water was added to the flask before evacuating, and the process of evacuation continued until the last of the liquid water evaporated. This gave a saturated vapor at the pressure finally prevailing in the flask, amounting to about 40 to 50 mg. of water per liter of vapor. T o effect the absorption of the vapors, a small volume of Cellosolve,* usually 5 cc., was added to the flask and spread out over the walls by rotating the flask periodically. A period of one hour was allowed for absorption: the liquid contents of the flask were then washed out into a measured amount of standard thiosulfate and after forty minutes, the excess thiosulfate was titrated with iodine. For the very small amounts of I encountered (about TABLE I11 1)ETERMINATION OF 8-CHLOROETAYL SULFIDE VAPOR P R E S E N T IN A
LITEROF
RATTJRATED
DRYAIR
I
GLASS PLASX
Absorbed at once
1
COPPEX FLASK
Absorbed after 15 hours
Absorbed at once
Absorbed after 15 hours
0.52 mg. .51 .56
0.72 mg. .59
0.54 mg. .55
0.68 mg. .73
--
0.63 f .IO I
I
I
I
TABLE IV DETERMINATION OF ,~-CHLOROETHYL SULFIDEVAPORPRESENT IN MOISTAIR
I
GLASS P W S K
Absorbed at once
0.65 mg. .59 .61 .63
1
Absorbed after 15 hours
0.47 mg. .68 .51 0.55 f .08
0.62 f .02 after 142 hrs.
0.57 mg.
0.65 f .08
~
A
LITEROF SATURATED
COP€%P m s x
Abmrbed at once
0.51 mg. .48 .55 -52 .72 .67 .67 .53 .58 f .08
Absorbed after 15 hours
0.60 mg. .50 .59 .56 0.56 f .03 after 120 hrs.
0.52 mg.
0.5 mg.) 0.001N solutions were used. These dilute solutions were made up and standardized frequently. A summary of the results is given below in Tables I11 and IV. Each value is the result of a separate determination. Although there is a faint indication of hydrolysis of the moist vapor, the deviations in this direction are probably within the limits of experimental error. The value of 0.64f.09mg. of I per 1025 cc. of air saturated by bubbling through the liquid checks well with measurements by Yabliok, Perrott, and Furman (3),who found 0.00623 When dioxane was used, the results were erratic, apparently due t o the tendency for peroxide formation in the dioxane.
236
CHARLES C. PRICE AND LYNN B. WAKEFIELD
.ooo4mg.of I per 11 cc. of vapor similarly prepared. This is about half the concentration t o be expected for saturated vapor on the basis of the vapor pressure as measured by Mumford, Phillips, and Ball (4). However, these authors mentioned that most of the previous estimates of the vapor pressure of I at 20' were just about half the value they found. TABLE V DETERMINATION DF &CHLOROETHYL SULFIDE IN ABSOBEED BY 6 CC. OF CELLOSOLVE
0.65 mg. .51 .76 .63 .53
A
LITEROF VAPOR
ABSORBED BY 6 CC. OF ~ L L O S O L V E82 1 CC. OF
HIO
-
0.53 mg. .57 .68 .58 .54 .54 .52 .50 .55 .56 .62
I
.60 .68
.54 0.61 i .07 mg.
0.56 f .04 mg.
I
DISTILLED WATEP
f hr.
2 hrs.
0.06 mg. .09 -09 .06 .10
15 hrs.
0.13 mg. .17 .22 .01 .16 .24 0.01 f .01 .14 0.08 f .02 .21 .14 0 . 2 7 3 ~.02 .14
0.28mg. .26 .23 .31 .32 .27
0.03 mg.
f hr. (with oil)
.oo .oo
"SEA" WATER
4 hr. 0.41 mg. .45 .44 .53
2 hrs.
1.28 mg.
.08 .08 .28 .14 1.17 f .OE
15 hrs.
.05 mg. .07 .05 .01 .02 .05
.oo
hr. (withoil)
.41 mg. .54 .37 .50 .54 .41 .47
.02 .09
.oo
.45 f .05
.03 f .03
Reaction of 8-chloroethyl sulfide vapor with liquid water. The reactions of mustard vapor with water were carried on in the same apparatus described above. Since experiments with one cc. of liquid water in the flask would give absorbent contaminated with water, the effect of water in the Cellosolve used as absorbent has been investigated. It has been found that absorption of mustard vapor in 6 cc. of Cellosolve and one cc. of water gives values about 10% lower than witshout water. The results are summarized in Table V. T o measure the rate of hydrolysis of mustard vapor in the presence of liquid water, 1.0 cc. of water was added through the stopcock to the flask containing the saturated vapor.
REACTIONS OF
P-CHLOROETHYLSULFIDE
IN WATER
237
The flask was then rotated periodically to spread the water over the walls of the flask in order to offer a large surface for absorption of the I. At the end of a specified interval, half an hour, two hours or fifteen hours, 6 cc. of Cellosolve was added. Absorption and analysis for unreacted I were carried out as described above. The results are summarized in Table VI. The values have been corrected for the 10% hydrolysis which may occur during absorption. Some of the reactions were carried out with distilled water, some with a synthetic “sea” water, prepared by dissolving 28 g. of sodium chloride, 8.5 g. of magnesium chloride hexahydrate, 2 g. of potassium sulfate, and 2 g. of calcium chloride in one liter of distilled water. To ascertain whether a film of oil on the water might interfere with the ease of absorption and hydrolysis of mustard vapor, several experiments were carried out with distilled water and Kith “sea” water, each contaminated with five drops of light lubricating oil per 100 cc. The suspensions were agitated thoroughly before withdrawing a 1.O-cc. sample t o add to the mustard vapor. The results, also summarized in Table VI, indicate that the oil film considerably increased the rate of disappearance of I in contact with distilled water but had only a slight effect with “sea” water. The increased rate of disappearance is undoubtedly due to the much greater solubility and hence much greater rate of absorption of I in oil than in water. SUMMARY
The “thiosulfate demand” of 0-chloroethyl sulfide offers a convenient method for analysis in dilute aqueous solution. There is no measurable hydrolysis of /3-chloroethyl sulfide vapor in moist air but it is absorbed and hydrolyzed by liquid water. URBANA, ILL.
REFEREXCES (1) PETERSAND WALKER, Biochem. J . , 17, 260 (1923). (2) MOHLERAND HARTNAGEL, Helv. Chim. Acta, 24, 564 (1941). (3) YABLICK, PERROTT, AND FURMAN, J . A m . Chem. SOC.,42, 266 (1920) (4) MUMFORD, PHILLIPS, AND BALL, J . Chem. Soc., 589 (1932).
