ALCOHOL AKD SODA-LIME BY BURT H. CARROLL
Introduction I n 1840, Dumas and Stasl showed that sodium acetate and hydrogen are formed when alcohol and potash-lime are heated, the apparent reaction being CH3CH20H KOH = CH3C02K 2H2. In four runs the following percentages of hydrogen and hydrocarbons were found in the gases given
+
+
Off:
Hydrogen Hydrocarbons
I
94.1 4.4
I
93.3 4.4
I
89.2 7.2
I
86.3 6.3
If the experiment is not stopped when the alcohol is converted completely into acetic acid, the acetate will, of course, decompose to methane and potassium carbonate. No book on organic chemistry explains why hydrogen should be evolved under these circumstances ; but the superficial analogy with Sabatier’s work on the contact catalysis of alcohol is so striking that it was suggested by Professor Bancroft that I study this reaction in some detail as part of my senior research work. It seemed possible that soda-lime might cause the catalytic decomposition of alcohol into aldehyde and hydrogen, after which the aldehyde would react with the soda-lime, the reaction taking place in at least two stages, according to the reactions CH3CHzOH CH3CH0
+ NaOH = CH3CH0 + NaOH + Hs + NaOH = CH3C02Na + Hz.
Sabatier had already shown that some decomposition of alcohol into aldehyde and hydrogen is caused by lime, though this substance is a poor catalytic agent. The plan of attack was to study the reaction a t varying temperatures as a reaction between alcohol vapor and sodalime. After this a test was to be made to see what parts were 1
Liebig’s Ann., 35, 129 (1840).
Alcohol and Soda-Lime
129
played by the caustic soda and the lime, respectively. Finally, aldehyde vapor was to be passed over the heated soda-lime to see whether it reacted according to the hypothetical equation as written. I n case lime alone split alcohol into aldehyde and hydrogen and if pure NaOH did not bring about this reaction, it could be assumed that the whole reaction depended on the catalytic action of the lime. If any aldehyde were found in the products of the alcohol reaction and if aldehyde reacted with soda-lime as hoped, this would be fairly conclusive that the reaction passed through the aldehyde stage. On the other hand a negative result with aldehyde and soda-lime would not necessarily justify the conclusion that aldehyde was not an intermediate step. It is possible that aldehyde vapor might react more readily as it was forming from alcohol than at other times. Fortunately, this particular hypothesis proved not to be needed. Apparatus The apparatus, shown in the following diagrams, Fig. 1-2, was largely designed by Mr. Engelder in a previous investigation. It was altered somewhat during the course of the term, and a large amount of time spent in its construction, in developing the manipulation, and in adapting it to the varied conditions. The modifications of apparatus and procedure necessary with the use of alcohol and aldehyde, and of the three solids, will be given in more detail under the account of the experimental work. The liquid used was contained in the vertical tube at the left of the diagram, Fig. I . When using aldehyde, after the first experiment, this was kept in ice. To the vertical tube, which was 14 X 1.5 cm, was sealed a capillary tube leading through a glass stopcock, t o the vaporizer. The vaporizer A was a box of asbestos board, 2 0 X 8 X I 2 cm, through which the tube from liquid container t o furnace, passed. It was heated by an 80-watt electric bulb, which, in the closed box, gave a temperature of over 150'. This temperature was more than sufficient for complete vaporization of the liquid slowly through to the furnace, the highest
Burt H . Carroll
130
rate of feed for alcohol being nine grams per hour, and ten for aldehyde; the use of the light avoided an open flame. To aid in rapid vaporization, a length of ordinary glass tubing about I O cm long was sealed in between the capillary tube used elsewhere on the liquid side of the furnace. The tube furnace, Fig. 2 , used was also heated by electricity, nichrome wire of a total resistance of 14.3ohms being wound upon an alundum tube 40 cm long and 2.6 cm inside bore, and held in place by alundum cement. This was then
srt dundurn reman /OOXQ asb~-stos r r i m n
D€TA fL O f FURNAC&
Fig 2
put into a section of ordinary drain tile about 3" in diameter, and loosely packed with asbestos cement as a heat insulator. The temperature was controlled by a lamp bank, by which the temperatures of 2 50' to 450' were easily obtained. The higher temperatures were measured by a Hoskins pyrometer and thermoelement, which checked with a good mercury thermometer up to 350'. Inside the alundum tube was placed a porcelain tube, closely fitting it; this is the tube in which the reaction took place. From the furnace the gases and vapors passed into the
Alcohol and Soda-Lime
131
collecting and condensing apparatus shown. The two or three test-tubes were kept immersed in ice water; the first and second were empty, and served to condense vapors of alcohol, aldehyde, etc., the second also acting as a guard tube to protect the greater part of the liquid products from a NaOH solution sucked back from the third tube. This KaOH solution, through which the gases bubbled, prevented aldehyde vapor from passing on with the permanent gases. The gases were collected over water in a ten-liter bottle, the water being siphoned out and providing the suction for operation of the apparatus. For sampling the gas for analysis, a threeway stopcock was provided between the purifying chain and the collecting bottle. I n this way a burette could be attached and draw a direct sample, uncontaminated by standing over water. In the latter part of the term, a sample of 200-300 cc was collected by means of a sample tube, with glass stopcocks a t each end, and level bottle; I : I glycerine and water, in which the gases obtained are practically insoluble, being used as the confining liquid. The solid material used in the reaction was contained in boats, in the porcelain tube of the furnace. For soda-lime and lime, porcelain boats were used; for NaOH, which fused at most of the temperatures employed, boats were made up of sheet copper or nickel, as it attacks porcelain when fused.
Methods of Analysis Gas Analysis.-The Hempel apparatus was employed, using water-jacketed burettes, with mercury as the confining liquid. The methods given in Dennis’ “Gas Analysis” were followed. The determinations made were 02,CO, unsaturated hydrocarbons, H2, CH4 and other paraffins, and Nz by difference. COz was removed by the NaOH used to take out aldehyde vapor. In experiments with Mr. Engelder, it was found that the aldehyde vapor was partially or wholly condensed by almost all the reagents used for the gas analysis, and, therefore, must first be removed before any accurate analysis was possi-
132
Burt H.Carroll
ble. All analyses, when sufficient gas was available, were made in duplicate; by checking analyses taken a t all parts of the run with the average analysis of the gas obtained from that in the collecting bottle, it seems that the composition varied very little during the course of the reaction, and that representative samples were secured. COz was determined by one-minute standing over I : I KOH s o h O2 was determined by three minutes’ shaking with alkaline pyrogallol, made up as given in Dennis. CO was determined by three minutes’ shaking with ammoniacal cuprous chloride, and removal of NH3 by 5 percent HzS04. CzH4and other unsaturated hydrocarbons were determined by fuming sulphuric acid. Hz was most commonly determined by fractional combustion over CuO heated to 2 5 0 ° , as given in Dennis, flushing out the tube with nitrogen before and after the combustion. CH4 and any other paraffins were determined by combustion in the Dennis combustion pipette. Liquid A?zalysis.-Test for aldehyde in the liquid products was made with an ammoniacal solution of silver oxide, in the usual way. Tests for unsaturated compounds, in the absence of aldehyde were made with I percent KMn04 solution. Solid A?zaZysis.--The solids after a run were analyzed for acetate (plus formate) by the method used in the course in organic analysis. Briefly, a two-gram sample is distilled with 1 5 cc syrupy phosphoric acid and 50 cc water, the water level being kept constant by means of a separatory funnel, until 2 5 0 cc have been distilled over. Further distillation was always carried out, but no measurable amount of acid found. 50 cc samples of the distillate were titrated with standard NaOH, giving acetate direct.
Materials AZcohol.-Absolute alcohol, obtained from the department of organic chemistry, was used. AZdehyde.-Aldehyde was made by the distillation of
Alcohol and Soda-Lime
I33
pure paraldehyde with small amounts of sulphuric or phosphoric acid, a Hempel fractionating column being employed. The boiling point varied from 2 I O to 29 O, impurities being probably paraldehyde, certainly not alcohol. Soda-Lime.-A finely divided granulated soda-lime, specially prepared for organic analysis, was used. The composition given was 33 percent NazO, 67 percent CaO. NaOH.-After the first few runs, the YaOH was prepared by fusing the “C. p . ” sticks in a nickel crucible, until the water was driven off, and pouring while molten into the metal boats used. Considerable difficulty was found in expelling all the water, and there was considerable loss in all but the last case by sputtering as the soda heated up; even with all water removed, it seemed to creep around the edges of the boats in spite of all precautions. NaCzH30z.--Fused sodium acetate, C. P., was fused again and poured molten into the boats. NaOH Solution Jor Purifying.-About a I : I solution of the C. P. sticks was used.
Experimental Procedure SuppZy of AZcohoZ.-The container A’ in the diagram was filled with alcohol to a mark. After the run it was refilled to the same point with alcohol from a burette, the amount used up thus being obtained directly. Supply OJ Aldehyde.-Aldehyde was weighed up in a glassstoppered weighing bottle, and poured into the container, which was kept in ice water. It was either entirely used, or the remainder after the run poured back into the bottle, and weighed. The Vaporizer.-The vaporizer was always given at least ten minutes to heat up before starting generation of vapor. The Jurnace was brought to constant temperature before starting the reaction. After a calibration in which temperatures with a given resistance had been determined, the furnace was frequently brought up to temperature by throwing on the line without resistance in series, until the pyrometer indicated the desired temperature ; the appropriate resistance was
I34
B u r t H . Carroll
then cut in. The boats with material were generally heated up with the furnace, and were never given less than twenty minutes to attain its temperature. The condensing tGbes and solution were thoroughly cooled before starting, and kept in ice water throughout the experiment ; liquid products were measured by emptying the first tube, taken directly out of the bath, into a glass stoppered weighing bottle. The collecting bottle contained water which was saturated by shaking with the gases of the first few runs, and gave little change in the composition of gas standing over it, as checked by comparison of direct samples. The furnace and vaporizer was first started up with a weighed amount of material in the boats. The liquid container was put in ice, if aldehyde was to be used, and the tubes in all cases. All connections were made, and the apparatus tested for leaks by opening the siphon tube on the collecting bottle, and thus applying suction to the apparatus as far as the stopcock which controlled liquid flow. The apparatus being found air-tight, fully heated, etc., and slight vacuum in the vaporizer, furnace and tubes, the first stopcock was cautiously opened so as to allow a slow flow of liquid (about I cm per second in t h e capillary tube) into the vaporizer. Increase of pressure and evolution of gas generally began almost immediately. The pinchcock on the siphon tube was now adjusted so as to allow a slight flow of the water with constant pressure indicated by the manometer. With active reaction such as the alcohol over NaOH it was possible to maintain a pressure of 1-2 inches of mercury in the apparatus; with others, especially a t lower temperatures, a corresponding suction was used to keep up the feed of liquid. The liquid generally did not feed into the vaporizer continuously, but in small quantities, intermittently, giving a fairly constant supply of vapor. The end of the reaction was almost invariably marked by a rapid decrease in pressure and evolution of gas, a run of an hour’s length frequently ending in a few minutes. When this stage was reached, the stopcocks at each end of the furnace were closed, the flow of liquid from the siphon shut off, power
Alcohol and Soda-Liwe
I35
cut off from the furnace, and liquid products, gas volume and liquid used were measured. In the latter part of the term, after measuring the gas volume, vapors were swept out of the furnace and condensing tubes by passing one-half to one liter of air through them, either through the entire apparatus, all liquid being used up, or through a supplementary stopcock (not shown) inserted in the stopper in the “vaporizer end” of the furnace tube. The gas sample was collected during the run, generally at about the most active part, always late enough to allow all air to be removed from the furnace.
Reaction of Absolute Alcohol Vapor with Soda-Lime Four preliminary runs were made, without complete analysis of gas or solid, which served to prove that the reaction went on very much as described by Dumas and Stas, except for some formation of tar; a comparatively large quantity of permanent combustible gas was liberated ; temperatures of 2 8 0 ~ - - 4 0 0 were ~ used. As this work was chiefly to develop the methods of procedure, no further results will be given; no quantitative data were obtained, and the qualitative results were more fully confirmed later. Three fairly quantitative experiments were made between Nov. 3 and Nov. 1 7 , 1916. A tabulation of results is shown in Table I. The lower temperature limit for the reaction seems to be about 250’ C. Some tar was always found, especially in the first part of the first boat, the entire half becoming semi-liquid in the lower temperature runs. The liquid products were largely unchanged alcohol, but always had a sharp acrid odor, and by I percent KMn04 solution indicated the presence of some unsaturated compound. KO aldehyde test was obtained in any case; but the unsaturation test, and the fact that some tar always formed in the NaOH in the last test tube, similar to that formed later when aldehyde was known to be present, indicates that there was some present in the exit gases from the furnace.
Burt H.Carroll TABLEI ~
Temperature Alcohol fed in Liquid products Alcohol apparently reacting Gas produced, on air-free basis Time Weight soda-lime a t start Gain in weight during run Percent acetate (as NaC~H302) Weight acetate over weight NaOH a t start Gas analysis on air-free basis : C2H4
co
C 6.8 gm 5.92 0.88 550 cc 2.75 hr 5.00 gn (approx.) 290'
-
c
365O 5.52 gn 3.95 1.57 750 cc 1.75 hr 6.00 gn
420' C
1.94 gm I .oo
0.94 I O 0 cc 0.7 j hr. 3.47 gm
0.63 5-15
0.16 4.92
-
0.45
0.11
0.0%
0.3% 0.8
7.65
-
94.0 6.0 CH4 510 cc Total volume Hz Calculated volume Hf 950 Percent yield on Hz 54% Volume methane 33 cc 0.11 gn NaC2H302 corresponding to CH4 abt. 25 Percent acetate decomposed Calculated gain in weight from total amount acetate formed Actual gain in weight Actual yield acetate Yield on total acetate (calculated from CH4) 35% 16.6 : I Ratio Hs : CHd Indicating percent decomposition of acetate 12.5% Alcohol fed per hour 2.45 gn 0.31 Alcohol apparently reacting per hr 2 0 0 cc Gas formed per hour Hz per hour (primary reaction) 185 CHI per hour (secondary reaction) I 2 Percent alcohol apparently react ing of that fed in 13%
82.1 15.9 420 cc 700 83.5% 292 cc 0.99 gn 75% 0.76 gn 0.63 11.5%
1.7% 0.5 70.3 27.5 770 cc 000
77% cc 1.03 gm 85%
302
0.44 gm 0.16 8.0%
46% 4.86 :
82.5% 2.54 :
41% '3.15 gn
90%
0.90
000
cc
810 167 29%
I
2.48 gm
1.25 460 cc 020
400 48.5%
As the furnace tube, with a capacity of nearly 2 0 0 cc remained full of the gaseous products at the end of the experiment, it seems probable that much of the low yield of hydrogen on the basis of alcohol apparently reacting (alcohol fed in liquid products) is due to unchanged alcohol vapor in the
Alcohol a.izd Soda-Lime
I37
furnace. The yield of hydrogen and weight of acetate is calculated from the equation CSHSOH NaOH = NaCzH3O2 z Hz and the amount of acetate formed and decomposed, and the gain in weight thereby, from the equation NaC2H302 NaOH = Na2C03 CHI. N o determination of COz in the soda-lime after the run was made, but from the violent effervescence, i t seemed probable that the largest past of the soda was converted into acetate and carbonate. Judging by later results, the lime would be little affected. Conclusions Regarding the Reaction The reaction does not begin below about 2 5 0 ' . It was investigated up to about 450', which is nearly the upper limit for the existence of alcohol vapor, some slight spontaneous decomposition beginning around the upper limit used. Beginning around 300°, such alcohol as reacts does so almost quantitatively, as shown by the yield of hydrogen, and the analysis of the gas. Such discrepancy as is shown in the first case is, as already explained, readily accounted for by unchanged alcohol vapor left in the furnace. The gas analysis, showing only traces of olefines and of CO, indicates that practically no secondary decompositions of the vapor take place. The formation of tar, however, proves that some other reaction takes place, and i t would seem probable, in view of later work, that this is due to condensation of aldehyde, after this substance is formed with liberation of hydrogen. As would be expected, the velocity of the reaction increases greatly between the temperature limits used; the amount of alcohol apparently reacting per hour becomes four times as great at 420' as a t 290°, and over five tixnes as shown by hydrogen production; as more alcohol apparently reacting at the higher temperature is actually reacting, than at the lower, due to lower vapor density, these figures check very closely. The alcohol cannot be fed slowly enough to give complete reaction-some excess of vapor must be present; but much of the liquid products in these runs were formed by continuing feed of alcohol after the reaction had almost entirely stopped.
+
+
+ +
Burt H . Carroll
The secondary reaction, of sodium acetate with excess of alkali, while not bearing directly on. the problem, is of interest. It begins at almost as low a temperature as tbe principal reaction, but its velocity increases much more rapidly with rise of temperature. Even at 300° some 25 percent of the acetate formed decomposes, while by 42c0 at least 85 percent breaks up. The decomposition takes place largely along with and not after the main reaction, as shown by the fact that the methane is given off a t the same time as hydrogen. Gas analyses of direct samples taken during the run, and of the entire gaseous products from the collecting bottle, check within limits of error, provided the gas does not stand over the water for more than a few hours. The most favorable temperature for formation o€ acetate is about 3 0 0 ~ below ; this, the amount of tar, and above this the decomposition of acetate, rise. A slight formation of ethylene is noticed; alcoh.ol vapor begins to break up with heat alone at about 400°, and the decomposition goes either to ethylene and water, or to aldehyde and hydrogen; the aldehyde would also decompose somewhat t o CH4 and CO, thus accounting for the CO found. Reaction of Absolute Aleohol Vapor with Lime According to Sabatjer “The pure CaO does not give any It is only perceptible action on primary alcohols at 350’. towards 400° that one begins to observe a little decomposition into aldehyde and hydrogen.” This statement was checked to determine the part played by the CaO in sodalime in causing the reaction. Four experiments were made, three of which were carried to completion; t h e gas sample from the third was lost in moving the apparatus t o a new laboratory. T h e appearance of the CaO was not changed in any case. On adding acid for analysis, a considerable effervescence indicated that some carbonate had been formed. There was no production of tar in any case. The liquid products gave unsaturation, but not aldeh.yde test in the first two runs; in the last two, a marked aldehyde test was obtained. With
Alcohol and Soda-Lime
I39
TABLEI1 Temperature Alcoh.01 fed in Liquid products Alcohol apparently reacting Time Gaseous products on airfree basis Increase weight lime Percent acetate in lime Gas analysis on air-free basis :
co
GH4 Hz CH4 Hz per gram alcohol apparently reacting Percent of calculated, assuming simply splitting to aldehyde Alcohol fed in per hour Alcohol apparently reacting per hour Hydrogen per hour
c
90' C 160' C 190' 2.53 g n 2.37 g n 2.45 gn I .86 I .98 1.74 0.6 j 0 .j o
hr.
65 cc 0.18 gm
0.62 0.50 hr.
-
80 cc
20
1.33 cc
-
0.8%
0.0% 0.0
91.8 8.2
00
00
0.08 gn
3.4 79.9 16.j
15% 5.06 gm
cc 0.24 gn
I j CC
0.0
0.0%
0.47 0.50 hr.
2
-
-
cc
-
4% 4.74 P I .24 30 cc
4.9c gn
1
0.94 -
the exception of the last run, almost all evolution of gar was over in about ten minutes; after this the action was simply distillation of alcohol through the furnace. In the last experiment evolution of gas continued for about forty-five minutes after the feed of alcohol was stopped, about 2 0 0 cc being liberated. Conclusions These results check with those of Sabatier, in that CaO is found to be a poor catalyst for alcohol, and gives largely aldehyde and hydrogen. The action does not begin until about 450') and were it not for t h e fact that hydrogen so predominates over ethylene, might seem to be due to thermal decomposition alone. The small amount of CH, compared with H2, and the almost total absence of any acetate from the lime after the run,show that it i s a case of contact catalysis, largely without other reaction; the formation of CH, may be
1 40
Burt H.Carroll
partly due to decomposition of aldehyde a t above 400'. Increase in weight by the lime must be ascribed to adsorbed alcohol, or to moisture in the alcohol, as no compound is formed in sufficient quantity. Combined with the following results on use of NaOH alone, it seems that the CaO plays no important part in the soda-lime reaction. Even with immediate reaction of the aldehyde formed, its catalytic effect is so small that it could not account for the main reaction; and as the reaction with NaOH was later proved to be more energetic than with sodalime itself, i t seems probable that the use of soda-lime instead of the pure NaOH, by Dumas and Stas, was due to the greater ease of handling; soda-lime is infusible a t the temperatures used, while employment of fused NaOH would have given them great experimental difficulty. Reaction of Absolute Alcohol Vapor with Caustic Soda The next step was the use of the other constituent of the soda-lime-pure caustic soda. Four runs were made a t different temperatures. The results are summarized in Table 111. The lowest temperature used (200') gave no reaction, evidently. Liquid products were spoiled in the second run, but in the other very strong aldehyde tests were obtaiped, indicating that a large percentage was aldehyde rather than alcohol. There was no formation of tar in the solid products; the NaOH darkened somewhat, but only to a gray. There was no free NaOH evident a t the end of the reaction; the material was no longer hygroscopic. I n all these runs, except a t 2 0 0 ° , there was a considerable loss of NaOH by spattering as i t heated up, even though heated slowly with the furnace; the liquid also crept around the edges of the boats in which it was contained, and, of course, attacked the porcelain tube of the furnace, so that altogether no quantitative determination of acetate formation could be made. The rest of the NaOH, beside acetate, is accounted for as carbonate and silicate. The alkali being contained in copper or nickel boats, i t was feared that these might have some catalytic effect, so that
Alcohol a%d Soda-Lzvne
TABLEI11 Temperature Alcohol fed in Alcohol apparently react. ing Gaseous products on air. free basis Time Wt. NaOH a t start Percent NaC2H302 aftei reaction Gas analysis on air-frec basis :
co
4.82 gn
;oso c 2.84 gn
1.74
:.5 abt.
'OOO
c
0
cc 0.75 hr. 2.63 gn
1.4 1 0.67 hr. 1.82 gn
0.0
53%
-
GH, Hz CHI Hz per gram alcohol reacting 0 cc Percent yield 0% Ratio Hz : CH4 Indicating by percent d e composition of acetate formed Alcohol apparently react. ing per hour 0.0 gm H2 per hour 0 cc Percent alcohol fed in ap. parently reacting 36%
-
0.43
2.82
0.4 1 I .o hr. 2.39 gn
3.5 1 0.25 hr. 7.46 gm Trace 1.9%
2.6 85.1 13.2
2.1
65.9 30.2 '50 cc 69.5%
50 cc 51% I
2.3 gm 1.65 1
50' C
6.79 gm
0.1%
48 %
52%
c
2.13 gn
-
0.6% 1.4 79.0 19.0 '50 cc 69.5% 4.1 :
.IO0
6.4 :
I
31% 0.43 gn 0.34 1 20%
2.2
: I
92% 11.3 gm 7.9 1 41%
alcohol was run through the hot furnace containing the empty boats. At 500' a slight aldehyde test was obtained. At 3 0 5 O , out of 8.49 grams of alcohol passed through, 8.41 were recovered as liquid, and there was practically no gas production, the gas collected (not analyzed) being only 50 cc. There was a faint aldehyde test from the liquid products, but altogether the effect of the boats on the alcohol may be taken as negligible, as the alcohol always breaks up slightly at these temperatures. The reaction was a most active one, pressures of 3.4 inches of mercury being readily obtained at 300' and above; the gas production in the run last recorded was a t the rate of 1 2 liters per hour under a pressure of one to two inches of mercury,
142
Burt
H.Carroll
The velocity increases rapidly with the temperature, as would be expected; the secondary reaction attains a high velocity at lower temperatures than with soda-lime. The apparently slow reaction in the third experiment was due to a deliberately very slow feed of alcohol, conditions in the other three runs being closely comparable.
Conelasions Alcohol reacts very readily with caustic alkalis at temperatures of 300' up. The reaction is very like the reaction with soda-lime, and it may be concluded that in the sodalime reaction the NaOH alone really takes part. A considerable quantity of aldehyde is found in the vapors from the furnace ; aldehyde apparently is not condensed by the NaOH at this temperature, which is further evidenced by the nonformation of tar. This points to the formation of aldehyde during the progress of the main reaction. As might be expected from the great activity of fused NaOH, the secondary reaction of the acetate with excess alkali begins with the main reaction and always results in the decomposition of the largest part of the acetate. The side reaction of the alcohol, forming CzH4and water, is slightly higher than with the soda-lime. Aldehyde formed and not immediately reacting seems to escape, rather than be condensed, as by soda-lime. The percentage of alcohol reacting of that passed through the furnace is again low. An experiment in feeding very slowly did not apparently raise the percentage at all, in fact, seemed to lower it; but as the liquid products were probably 1/3 aldehyde, while assumed to be all alcohol in calculation, it was probably a t least as high as before. However, the reaction reaches a state of equilibrium between alcohol vapor, NaOH and products of the reaction, which depends on temperature ; so that if sufficient time is given for equilibrium to be reached, the rate of feed of the alcohol is not the factor which determines the percentage of alcohol converted, although if too fast, it may readily have its effect. It is interesting and rather puzzling to note the high production of aldehyde with slow feed of alcohol, as
Alcohol and Soda-Lime
I43
evidenced by aldehyde in the liquid products in the third run, and by low Hz yield (formation of aldehyde gives only half the hydrogen of the complete reaction). Altogether, from the last two sets of experiments, i t seems thoroughly established that the sodium hydroxide in soda-lime is the substance which really reacts with the alcohol, and that the chemical effect of the lime may be neglected. Reaction of Aldehyde Vapor with Alkali The next step in the proof of the theory is to show that aldehyde, once formed, would react with the alkali with formation of acetate and Hz, a point of considerable interest, since alkali condenses aldehyde a t ordinary temperatures. According to Sabatier, “Aldehyde is slowly condensed by soda-lime-sodium acetate-etc.,” but it is not clear to what conditions he is referring. Three experinents were made passing aldehyde vapor over NaOH, and two using sodalime. The results are tabulated for NaOH in Table IV. TABLE IV Temperature Weight aldehyde fed in Liquid products Aldehyde apparently reacting Gaseous products on air-free basil Time Weight NaOH used Percent acetate after reaction Acetate formed Gas analysis on air-free basis: CO CnH4 Hz CH, Hz : CH4 = Hz per gram aldehyde Percent yield bases on hydrogen Percent yield bases on acetate Percent aldehyde fed in apparent11 reacting Aldehyde apparently reacting per hour Hydrogen per hour
350°
4.82 gm I .o
3.8 700 cc 0 .j o hr. 10.8 gm 11.1%
1.21
gm
-
0.6 70.0 29.4
4.2 : I
450°
5.13 gm 2.58 2.jj
2 0 0 cc I .3 hr.
8.0 gm 6.0% 0.48 gm 0.0% 0 .j
96.8 2.7
26 :
315 cc 56% I770
440 cc 78%
80%
50%
7.6 gm 2.4 1
I
10%
1.96 gm 0.90 1
Burt H.Carroll
I44
The reaction assumed to take place in all cases is CHBCHO NaOH = NaC2H3OZ Hz, and the secondary reaction NaC2H302 NaOH = NazC03 CH4. The free NaOH, as before, was all gone at the end of the reaction. It was, prepared by fusing and pouring into the boats, for the last two runs, but loss could not be entirely prevented. Except a t the lowest temperature, there was no formation of tar a t all in the boats; in this it was slight. There was some carbonate, but not much, formed, as would be expected, from the small amounts of CH,. The furnace and tubes were flushed out by passing air through them after the reaction, so that no aldehyde vapor was left here, 6 u t owing to the great volatility of the substance, it could not all be condensed, and a large amount “apparently reacting” is accounted for by the strong formation of aldehyde tar in the NaOH solution used for purifieation of the gases. Soda-lime was alsp employed, to make certain that the use of this substance instead of aldehyde would not prevent the reaction by condensing effect. One experiment was also made with pure fused sodium acetate, to determine its condensing power, and probable effect on equilibrium. The results of this are given with the soda-lime in Table v. Gas samples from these experiments were collected over glycerine and water, and duplicate analyses made, the results being averaged. On the first runs with both NaOH and soda-lime (the first two made), there was difficulty in securing an even feed of the aldehyde, resulting in a sucking back of NaOH solution into the liquid products. In both soda-lime runs, there was considerable blackening of the lime in the part first passed over by the vapor, and formation of more or less charred tarry products. As before, the presence of tar in the purifying tube accounted for a large proportion of aldehyde apparently reacting. With the exception of the formation of tar in the furnace,, the reaction seemed very similar to that with NaOH.
+
+
+
+
Al~oholand Soda-Liwe
I45
TABLEV With ‘aC2H302 400 O 00 O Temperature 150° 2.40 gm IO gm(?) Weight aldehyde fed in 4.50 gm I -60 I .82 -spoiled Liquid products 0.80 2.68 ? Aldehyde apparently reacting 0 cc Gaseous products on air-free basis 60 cc 525 cc 0.33 hr. 0.25 hr. 0 . 2 5 hr. Time 2.35 gn: ‘used soWeight soda-lime used 3.05 gn: ium aceate used 0.32 Gain in weight 0.57 lnalysis Percent acetate after reaction 6.1% spoiled 0 . 2 2 grr 0.2(?) gn Weight acetate after reaction Gas analysis on air-free basis :
co
-
CzH4 H2
1.4% 97.0% 1.4%
CH4 H2 : CH4 = 70 : Hz per gram aldehyde Percent yield based on hydrogen Percent yield based on acetate Percent aldehyde fed in apparent11 reacting Aldehyde apparently reacting pel hour HZper hour
I
1.1% 1.2%
89.1% 6.5%+ 13.5 : I 180 cc 32% 4% 60% 10.7 gm
1.80 1
-
33% 2.40 gm 1
0.0
Using sodium acetate, there was no reaction, but a blackening of the solid, which was not produced when the salt was heated alone. It seemed to have a slight effect on the aldehyde, in condensing it, but not by any means a powerful one.
Conclusions
Aldehyde reacts with sodium hydroxide or so da-lime with the formation of sodium acetate, the reaction being represented by the equation CHBCHO NaOH = CH3C02Na Hz. Using NaOH, the reaction is nearly quantitative a t around 450’ ; the yield falls off a t lower temperatures, and
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Bwrt H . Carroll
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the reaction does not begin until about 300'. The rate of the reaction is as high as that of alcohol with the same substances, as far as can be judged. With aldehyde a liberation of z . 4 liters of hydrogen per hour could be obtained at 350'; a higher production with alcohol was reached only at 450' (7 9 liters per hour), and the alcohol reaction liberates twice the volume of hydrogen. The rate of feed, amount of alkali, temperature, and other t uncertain factors come into the reaction velocity; but, as far as can be determined, the two are almost the same. Using soda-lime, the reaction of both is slower; but I .8 liters of hydrogen per hour were obtained with aldehyde and soda-lime at 400°, while at 410' the alcohol reaction, yielding nearly twice the volume of hydrogen for a given weight of liquid, gave I .oz liters. As has already been said, aldehyde reacts nearly quantitatively with NaOH ; the yield with soda-lime is much poorer owing to the formation of condensation products. The yield of acetate is much better with NaOH, which is surprising. In both cases the yield of acetate was lower than when alcohol was used. The secondary reaction of acetate with alkali is much smaller when alcohol is present, the percentage of acetate decomposed to form methane being much smaller.
Dissociation of Aldehyde Vapor Now that it has been shown that aldehyde is an intermediate product in the conversion of alcohol into acetate by means of soda-lime, it is necessary to consider what intermediate products there are in the reaction between aldehyde vapor and caustic soda. CH3CH0 NaOH = CH3COzNa Hz. There are at least two possible reactions, though they are not equally probable. The aldehyde may split off one hydrogen, forming temporarily the free acetyl radical, which may react with caustic soda, setting free hydrogen and forming sodium acetate. Acetyl chloride reacts with caustic soda, forming acetate and chloride; and it is conceivable that the
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Alcohol avld Soda-Lime
I47
acetyl radical might set free hydrogen from caustic soda. There is no evidence, however, either that one hydrogen splits off from acetaldehyde or that the acetyl radical will react as suggested. It is therefore more probable to consider the second alternative, namely that the aldehyde dissociates t o keten and that keten reacts with caustic soda, the two reactions being CH3CHO = CHZCO Hz, CH2C0 NaOH = CH3C02Na. Wilsmore prepared keten by the action of a hot platinum wire on acetic anhydride1 or on acetone2 while Schmidlin and Bergmann3 obtained it by passing acetone vapor through a glass tube filled with pieces of earthenware and heated to 500°-6000. It is considered probable that acetone is an intermediate product in the formation of keten from acetic anhydride, in which case the reactions would be, (CH3CO)zO = CHsCOCH, COZ, CHsCOCHs = CHzCO CH4. I have not been able to find any evidence that keten is actually a decomposition product of aldehyde; but it is the normal product in case of a dehydrogenation, which is what we have; and keten reacts readily with water to form acetic acid. While it is not proved that keten is an intermediate product in the conversion of alcohol into acetate by means of sodalime, this seems more probable than to assume that the intermediate product is the free acetyl group. While it might be difficult experimentally to show that aldehyde may yield keten and hydrogen, it ought not to be especially difficult to show the formation of the decomposition product ethylene, according to the equation ’ 2CH3CHO = 2CHzCO ZHZ CzH4 zCO ZHZ.
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Summary The following general conclusions may be drawn from this paper:
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Jour. Chem. SOC., 91, 1938 (1907). Proc. Chem. SOC., 24, 77 (1908). Ber. deutsch. chem. Ges., 43, 2821 (1910).
Burt H.Carroll
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I . The reaction between alcohol vapor and soda-lime begins at about 250°, the primary reaction being represented by the equation CH3CH20H NaOH = CH3C02Na 2H2. The secondary reaction CH3C02Na NaOH = Na2C03 CH, begins a t about the same temperature ; its reaction velocity increases so rapidly with the temperature that at 450' practically all of the acetate decomposes as fast as it is formed. The primary reaction is nearly quantitative, not over ten percent a t the outside estimate of the alcohol taking part in the side reactions which give aldehyde tars, ethylene and water, and methane and carbon monoxide from the high temperature decomposition of acetaldehyde. Under the experimental conditions the reaction does not run to an end, there being always a relatively large amount of unchanged alcohol. Increasing the rate of feed cuts down the percentage of alcohol decomposed; decreasing the rate of feed too much seems to make the secondary reactions relatively more important. 2 . The caustic soda is the active constituent in the sodalime. Lime itself has only a very slight effect on alcohol a t the temperature used, whereas caustic soda reacts with alcohol a t these temperatures with the primary formation of sodium acetate and hydrogen, and the secondary formation of sodium carbonate and methane, just exactly as sodalime does. The only difference is that the reactions take place much more rapidly with caustic soda than with sodalime, and that there is less tar formed. The reason for using soda-lime instead of caustic soda is that the latter is a liquid a t the temperatures involved and is hard to handle. 3. The conversion of alcohol to acetate in presence of soda-lime takes place in a t least three stages. The first stage is the dissociation of alcohol to aldehyde and hydrogen in presence of caustic soda as catalytic agent, CH3H20H NaOH = CH3CH0 NaOH Hs.
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Aldehyde is found in the liquid products when caustic soda is used; when soda-lime is used, some aldehyde tar is formed in the furnace and some in the NaOH washing bulb. At the temperature in question aldehyde reacts with caustic soda or soda-lime at least as rapidly as does alcohol. The second stage of the reaction is the dissociation of aldehyde presumably to keten and hydrogen in presence of caustic soda as catalytic agent, according to the equation CH3CH0 KaOH = CHzCO KaOH H,. The intermediate formation of keten has not been shown; but it is the most probable reaction and it does not seem probable that acetaldehyde splits off one of hydrogen, forming temporarily the free acetyl group. The third stage in the reaction is the combination of keten with caustic soda to form sodium acetate acccording to the equation CHzCO NaOH = CH3CO2Na.
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Cnrnell I;nzoersity
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