T H E CHEMISTRY O F BERYLLIUM. VI
REACTIONS OF SULFUR DIOXIDE WITH ORGANIC BERYLLIUM COMPOUNDS HAROLD SIMMONS BOOTH
AND
VIRGIL D. SMILEY
Morley Chemical Laboratory, Western Reserve University, Cleveland, Ohio Received October 31, 1931 PURPOSES O F THE INVESTIGATION
During.studies of electrolysis of beryllium salts in non-aqueous solvents, Booth and Torrey (1) discovered that cold beryllium acetylacetonate rapidly absorbed sulfur dioxide to form a liquid. The sulfur dioxide could be boiled off by gentle warming and recondensed, dissolving the beryllium compound as frequently as desired without any apparent change in the beryllium acetylacetonate. A sample of the sulfur dioxide-beryllium acetylacetonate solution containing some crystals was sealed off in a test tube and has remained unchanged for the last eight years. The remarkable absorbing power of this beryllium compound immediately suggested to the discoverers that, in the first place, the study of this reaction might yield information of interest, since it apparently represented a novel type of reaction, possibly a general one, with metallic compounds containing a C:O grouping. The second point is of course the possible application of this reaction to the development of an absorption type refrigerator. HISTORICAL DISCUSSION
If, as Booth and Torrey thought, the reaction of sulfur dioxide on beryllium acetylacetonate was completely reversible, it would seem probable that the compound formed was of the so-called molecular compound type analogous to hydrates. In other words,' the sulfur dioxide was absorbed as sulfur dioxide of crystallization. The question may be raised at once as t o whether the absorption of sulfur dioxide is a function of the beryllium or of the organic part of the compound. A search of the literature reveals no study of the action of sulfur dioxide on beryllium compounds, but certain reactions of sulfur dioxide on organic compounds have been studied. H. 0. Schulze (2) found that acetone absorbed a litt,le less than two moles of sulfur dioxide per mole of acetone a t 0°C. Boessneck (3) passed 171
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HAROLD SIMMONS BOOTH AND VIRGIL D. SMILEY
sulfur dioxide into acetone and found the gas to be absorbed with the evolution of considerable heat. He proposed the formula
CHs
0-0
for this liquid compound. On heating it he found that it decomposed into its constituents. Apparently no one has studied this system precisely. Bellucci and Grassi (4) found that sulfur dioxide forms two compounds with camphor (a ketone of higher molecular weight), namely, (1)so~c~~Hl m.p. -45"C., and (2) 2s0z.c~oH1~0, m.p. -24OC. Very little else has been done with the reactions of sulfur dioxide and ketones. PLAN OF INVESTIGATION
It was thought that a study of the pressure-concentration relations in this system, a t constant temperature, would best establish the nature of the reaction. This study would show : first, the solubility of the compound formed in liquid sulfur dioxide; second, the number of moles of sulfur dioxide reacting with one mole of the compound; third, the vapor pressure of the compound formed; fourth, the vapor pressure of the mixed salt and compound formed. In order to determine whether it was a function of the beryllium or of other groups in the compound, other beryllium compounds were prepared and tested-such as beryllium basic acetate, beryllium ethyl acetoacetate, etc. Acetylacetone exists as an equilibrium mixture of the enol form and of the keto form, and the beryllium compound is probably H
O
0
I
Be
or
I
/I
0
I
I
\L
0 CH3-C
I
/ O
Be : C-C-CHI
I II
H
/7
O
\
CH3 (Sidgwick)
CH3
CHEMISTRY OF BERYLLIUM
173
There are two carbonyl groups still free through which the sulfur dioxide may react, or the sulfur dioxide may combine owing to the double bonds. To see whether other similar enol-keto compounds were reactive with sulfur dioxide, beryllium ethyl acetoacetate and beryllium benzoylacetonate were tried. To check up on the importance of carbonyl groups in the reaction, such a compound as beryllium basic acetate, which contains both beryllium and carbonyl groups, was studied and also certain organic compounds such as benzophenone, urea, acetamide, etc., containing carbonyl groups but no beryllium. The effect of replacing beryllium by sodium, magnesium, and aluminum, etc., was then tried, as well as a number of other salts of organic acids. PREPARATION OF COMPOUNDS
The beryllium acetylacetonate, beryllium ethyl acetoacetate, beryllium basic acetate, beryllium benzoylacetonate and sodium acetylacetonate, were prepared in the course of study of the organic salts of beryllium (5). Compounds prepared in a similar manner were magnesium ethyl acetoacetate, magnesium acetylacetonate, and aluminum et.hyl acetoacetate. Other compounds were from chemically pure material. APPARATUS
The apparatus consists of three essential parts: the gas purification system (6), the constant temperature bath, and the baro-buret for measuring gas volumes and pressures (see figure 1). The entire apparatus was constructed of soda-lime glass fused together at all connections. The constant temperature bath consisted of a gallon capacity Dewar flask, in which was mounted a thermostat (T), lamp for heating, stirrer (S), thermometer, and reaction tube (V). The lamp was controlled by means of a mercury-xylene expansion thermostat through a suitable relay and maintained a constant bath temperature within f.001"C. The baro-buret was used because it measures accurately and simultaneously pressure and volume in one instrument and thus cuts down the "dead space" from the buret to the reaction bulb to a minimum (7). EXPERIMENTAL PROCEDURE
Preliminary tests Before a system was studied a preliminary test was made in a sample bulb adjacent to the gas supply tank. Here the sample was placed in a suitable reaction bulb of about 5 cc. capacity and sulfur dioxide was condensed on it to see if the sample would dissolve. Slight solubility was checked by evaporating separately the supernatant sulfur dioxide. The preliminary tests showed that a t the boiling point of sulfur dioxide, the
174
HAROLD SIMMONS BOOTH AND VIRGIL D. SMILEY
following compounds were insoluble in sulfur dioxide and apparently did not react with it: barium acetate, copper acetate, lead acetate, sodium acetate, sodium formate, ammonium oxalate, ammonium tartrate, alumi-
R
FIQ. 1. APPARATUSFOR STUDYING ABSORPTIONOF SULFURDIOXIDE BY ORQANIC BERYLLIUM COMPOUNDS
num ethyl acetoacetate, magnesium ethyl acetoacetate, sodium acetylacetonate. The following substances seemed to show slight solubility or slight reaction with liquid sulfur dioxide at its boiling point : beryllium benzoyl-
CHEMISTRY OF BERYLLIUM
175
acetonate, magnesium acetylacetonate, benzophenone, urea. The urea seemed to swell in the liquid sulfur dioxide though it did not seem to dissolve. The following were quite soluble in boiling liquid sulfur dioxide: beryllium acetylacetonate, beryllium basic acetate, beryllium ethyl acetoacetate, acetamide.
Course of a determination Sulfur dioxide was purified by fractional distillation a sufficient number of times to eliminate all impurities, usually by from eight to twelve distillations. The chief impurities were sulfur trioxide and air. Finally, the remaining gas was solidified with liquid air and the system was evacuated to insure the removal of any residual gas other than sulfur dioxide, and the sulfur dioxide was then boiled into the storage reservoir. The sample of the compound to be tested was then weighed into the reaction tube (V) (figure l), which was then sealed into position. The volume of the reaction bulb (V) connected to the baro-buret was next determined. The system was washed several times with dry, carbon dioxide-free air and the mercury reservoir (R) was lowered, bringing into the buret a sample of the dry carbon dioxide-free air. The stopcock (F) was then turned 180" connecting the baro-buret to the reaction bulb and a number of readings of volume a t different pressures were made. From these readings the volume of the reaction tube (V) was calculated by means of the following formula:
The apparatus was evacuated and all but the reaction tube was flushed out with sulfur dioxide several times. A sample of pure sulfur dioxide was then drawn into the baro-buret (K) and its volume and pressure observed and calculated to standard conditions. Connection was then made with the reaction bulb (V) by turning the stopcock BO", and the pressure was increased by raising the mercury reservoir (R), compelling absorption of the sulfur dioxide. This was continued at increasing pressures until the compound had turned to a liquid or until all the sulfur dioxide was absorbed that would be absorbed a t the highest pressure attainable. If more than one buret full of gas was required the stopcock (F) was turned 180' to draw in a fresh supply of gas from the gas reservoir, the volume and pressure being observed before and after the addition of the fresh quantity. The bath was maintained a t 25°C. =t ,001"C. When the reaction had come to equilibrium the pressure, temperature, and volume were read and the total amount of the sulfur dioxide absorbed by the sample was calculated. The mercury reservoir was lowered suffi-
176
HAROLD SIMMONS BOOTH AND VIRGIL D. SMILEY
ciently to diminish the pressure in the system about 2 cm.; after standing twenty-four hours to attain equilibrium, the pressure, volume, and temperatures were again observed. The amount of gas still combined with the sample was calculated by subtracting the total volume passed from the buret from the volume of the gas present in the buret and reaction bulb. This gave the amount of TABLE 1 T h e system sulfur dioxide-beryllium acetylacetonate PREEIEIURE
103.80 85.75 75.90 69.35 59.35 53.75 57.10 67.70 70.40 72.25 72.65 72.85 73.05 73.40 73.65 73.65 74.40 78.50 56.40 54.95 53.55 51.20 50.45 73.70 62.55 53.40 41.40 16.30 7.40
MOLES OF
'
80%PER
MOLE OF BERYLL.IUM ACETYLACETONATE
1.6600 1.3680 1.2090 1.0990 0.9620 0.8650 0.9110 0.1310 crystallized 0.1840 0.3660 0.4560 0.5120 0.5680 0.6500 0.7670 1.0270 1.1550 1.2490 0.9190 0.8940 0.8773 0.8355 0.8255 0.6015 crystallized 0.0980 0.0638 0.0568 0.0438 0.0378
gas freed at each equilibrium, and from this the amount still held was
readily calculated. This procedure was continued until the pressure reached zero. If the volume of the gas reached the capacity of the buret before the pressure reached zero, the stopcock (F) was turned 180°, exhausting most of the gas in the buret, and then the observations were continued as before.
177
CHEMISTRY OF BERYLLIUM RESULTS
The data obtained are given in tables 1,2, and 3, and plotted in figure 2. As the sulfur dioxide was forced into the reaction tube, there was a wetting of the compound on its surface; this became more pronounced as the pressure increased. Finally the entire compound assumed the liquid state, except in the case of beryllium ethyl acetoacetate, which changed first to a gel. As the pressure was reduced the compound remained in liquid state until the solution was considerably supersaturated when suddenly the liquid turned almost explosively to a white solid. This solid TABLE 2 T h e system sulfur dioxide-beryllium ethyl acetoacetate PR ES8 U R E
1
MOLES OF 802 PER MOLE OB BERYL.LlUM ETHYL ACETOACETATE
132.15 99.80 97.15 94.40 89.05 83.00 79.22 70.80 67.80 64.83 60.50 59.00 52.65 44.90
1.7820 1,8000 1.5300 1.5580 1.5570 1.7260 1.6020 1.5470 1.4290 1.4630 1.2990 0.5676 0.3590 0.3100
TABLE 3 T h e system sulfur dioxide-phenyl benzoate Pmaaum
112.85 93.40
I
MOLES OF
so2 PER
MOLE OF PHENYL BENZOATE
0.0689 0.0397
was the molecular compound with sulfur dioxide. The compounds could change to liquid under pressure, give up sulfur dioxide, and change to a solid state as many times as desired. I n fact they seemed to take up sulfur dioxide more freely after the first pumping. Beryllium acetylacetonate combined with one mole of sulfur dioxide and this compound then dissolved in the sulfur dioxide gas forming a liquid. The portion of the curve (see figure 2) from pressures of 75 cm. to 104 em. is merely the vapor pressure curve for increasing dilution of this
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HAROLD SIMMONS BOOTH AND VIRGIL D. SMILEY
compound dissolved in sulfur dioxide. On cooling, supersaturation is shown in the curve of beryllium acetylacetonate as a dotted line. The beryllium acetylacetonate solution could be supersaturated to the point where approximately only one-half mole of sulfur dioxide per mole of beryllium acetylacetonate was left in the cell. The vapor pressure of the compound Be(CH3COCHCOCH& .SOz varies between 72 and 76 cm. and averages 73 cm. On carrying the pressure to zero, all the sulfur dioxide was removed and the beryllium acetylacetonate was found to be unchanged.
10
-
In the case of beryllium ethyl acetoacetate quite a different condition was found. Instead of combining and forming a true solution, apparently a colloidal solution was formed, since on pumping off the sulfur dioxide during the determination, the liquid first became vjscous and then set to a gel. This gel remained quite stable a t pressures from 132 cm. down to 60 cm. Finally after pumping off sulfur dioxide a t a pressure of 59 cm., the gel suddenly decrepitated leaving a fine powder. The gel formation hindered the free loss of sulfur dioxide and so gave a rather irregular set of points on the upper slope of the curve; although the points are uniformly placed on the horizontal part. The authors restudied this system three
CHEMISTRY OF BERYLLIUM
179
times over a period of eight months, without being able to improve the irregularity of these points. This is probably a hysteresis phenomenon (8, 9) due to variation of the capillary pore size as the sulfur dioxide of the gel leaves the solid Be(CH3COCHC0-OCzH&.SO2 structure. This is also suggested by the sudden collapse of the gel on further removal of the sulfur dioxide. The phenomenon may be further complicated by solubility of the compound in the sulfur dioxide. However, the curve shows a general shape similar to the other and the gel reverted to the solid state, showing an approximate composition of 1.0 mole of sulfur dioxide per mole of compound. The vapor pressure of this compound, .SO2, averages 80 cm. Be(CH3COCHC0,0CzH5)z The phenyl benzoate absorbed so little sulfur dioxide that the curve showed plainly that it was merely an adsorption curve; since its further study would contribute nothing it was discontinued. CONCLUSION
It has been established that sulfur dioxide forms addition compounds with beryllium acetylacetonate and beryllium ethyl acetoacetate. In attempting to explain the addition of sulfur dioxide to these compounds several possibilities may be considered. Any rearrangement that is involved must be an easily reversible one; this seems to preclude the possibility of oxidation or reduction. These compounds are apparently of the so-called molecular compound type analogous to the hydrates. Both beryllium acetylacetonate and ethyl acetoacetate formed additive compounds containing one mole of sulfur dioxide to one of the compound. That the addition of sulfur dioxide is not a function of the beryllium alone is suggested by the fact that both Schulze and Boessneck (2,3) showed that acetone formed an additive compound with sulfur dioxide. However, the organic compounds formed in which sodium and aluminum replace the beryllium apparently do not react with sulfur dioxide-at least below two atmospheres pressure, though the magnesium acetylacetonate shows slight solubility or reaction. These latter compounds are probably more polar than the corresponding beryllium compounds, while the beryllium atom does not change the essentially non-polar character of the original organic compound. The react'ion may be analogous to hydration where one of the bonds of the oxygen is opened, permitting the addition of (OH) and (H) thus:
R1'
\\
+HOH= R 0
/ \
OH
OH
180
HAROLD SIMMONS BOOTH AND VIRGIL D. SMILEY
which by analogy in the case of sulfur dioxide would be: H I
0
/ \ R s=o \ /
-S=O
Be
I
0
O
H
0
I I II
CHa-C=C-C-CHs
On t.his basis, however, one wonders why another sulfur dioxide molecule is not taken up by the other =CO group. An arrangement such as the following in which both =CO groups are involved is unorthodox, since it produces a twelve-membered ring of which other examples are practically unknown; furthermore the sulfur dioxide compound should be more stable if this were its structure: H
I CH~-C=C-C-CH~
I I Be I 0 I
/ \ 0 \ / S / \ 0 0 \ / CH,--C=C-C-CH, I 0 0
H
The fact that only beryllium chelate compounds, beryllium acetylacetonate, beryllium ethyl acetoacetate, and beryllium basic acetate react with sulfur dioxide readily would suggest that the reaction took place via the atom of beryllium were it not for the fact that magnesium acetylacetonate also reacts to a certain extent, and that acetone itself reacts readily. I t will be remembered that liquid sulfur dioxide is an excellent solvent for non-polar compounds in general, particularly esters and fats, in which of course there is a =CO group. It may be that the character of the beryllium in these chelate compounds is sufficiently negative so that they behave towards sulfur dioxide exactly like such non-polar compounds as the fats, which contain no metals. In a former paper (10) it was reported that the hydrolysis of beryllium basic acetate was very slow and difficult, in-
CHEMISTRY OF BERYLLIUM
181
dicating extremely slight ionization to yield Be++ ions and that the beryllium was acting in a r81e not unlike that of carbon itself. The evidence seems to point to the formation here of molecular compounds as a function of the carbonyl group of compounds in which the metal present does not diminish the non-polar character of the organic compound. It would be interesting to test boron chelate compounds with sulfur dioxide if they could be prepared. They should react in a similar fashion, though this would be complicated by the known characteristic of boron compounds to form molecular compounds. SUMMARY
1. The systems sulfur dioxide-beryllium acetylacetonate and sulfur dioxide-beryllium ethyl acetoacetate have been studied a t 25°C. It is found that these beryllium compounds combine in the ratio of one mole of compound to one mole of sulfur dioxide. 2. The vapor pressure of the compound Be(CH3COCHCOCH3)2. SO2 averages 73 em. and that of the compound Be(CH3COCHCO-OC2H&. SO2 averages 60 em. 3. The nature of these compounds and their possible structure is discussed. 4. The baro-buret is found to be a valuable tool in studying gas-solid equilibria. REFERENCES BOOTH, H. S.,AND TORREY, G. G.: J. Phys. Chem. 36,2476 (1931). H. 0.: J. prakt. Chem. [2] 24, 168 (1881). SCHULZE, BOESSNECK: Ber. 21, 1906 (1888). BELLKJCCI AND GRASSI: Atti accad. Lincei 22, 11, 675-80 (1913). BOOTH, H. S., AND PIERCE, D. G.: J. Phys. Chem. 37, 59-78 (1933). For description of operation see J. Chem. Education 7, 1249 (1930). BOOTH, H. S.:Ind. Eng. Chem., Anal. Ed. 2, 182-6 (1930). BOOTHAND JONES:Ibid. 2, 237 (1930). BOOTHAND WILLSON:Ibid. 4, 427 (1932). (8) VANBEMMELN: Die Absorption, pp. 196, 214, 232 (1910). AND ANDERSON: Z. physik. Chem. 88, 191 (1914). (9) VAN BEMMELN (10) BOOTH, H. S., AND TORREY, G. G.: J. Phys. Chem. 36, 2468 (1931). (1) (2) (3) (4) (5) (6) (7)
