ELECTRICAL CONDTCTIF'ITY STUDIES OF THE IKTERACTIOK OF SULPHUROUS ACID AND CERTAIN ALDEHYDES* BY G. I. HOOVER, K. w. HUSTEN, A N D
c. A .
SANKEY'
PART I G . I. HOOTER AND K. W. HUNTEN
A thorough knowledge of the nature and reactions of the sulphonic acids is of great importance to the theoretical consideration of the chemistry of the sulphite process for the manufacture of paper pulp, since by this process the lignin is removed from the wood as ligno-sulphonic acids. While the chemistry of lignin has not as yet been elucidated there is a certain amount of evidence to indicate that the ethylene linkage,* the keto group,3 and possibly the aldehyde group4 are present in the lignin molecule, all of which may react with sulphurous acid. I t is to a study of the reactions between sulphurous acid and pure organic substances containing one or more of these groups that this investigation has been directed. There has been considerable discussion in the literature about whether the products of reaction between sulphurous acid and the simple aldehydes are sulphite esters -R - CHOH or true sulphonic acids R-CHOH. The
\
0 - SO.OH
1
SO20H
former with C - 0 - S linkage would be primary esters possessing weak acid properties and could readily be decomposed whereas compounds of the latter type should be strong acids. h thorough review of this field has recently been made by Stellingj so mention need be made here to only one additional paper. Kerp,6 by means of electrical conductivity measurements obtained the following data for the electrolytic dissociation of formaldehyde and acetaldehyde sulphonic acids. Formaldehyde rulphonic acid: W I O ,85yc; * Contribution from the Ikpartment of Industrial and Crllulose Chemistry. Mc(;ill University. This work has been carried out as part of a co-operative scheme of research under the auspices of the Canadian Pulp and Paper Division of the Forest Products Lahoiatories of Canada and the Department of Industrial and Cellrilose Chemistry, RIc~Gill University. It represents the first of a series of communications relating to t!ie fundsmental principles of sulphite pulp manufacture being carried out tinder the general direction of Dr. Harold Hibbert, Professor of Industrial and Cellulose Chemistry. AIeGill University, to whom the investigators wish t o espress their thanks for his kind interest and advice. Holder of Bursary, Kational Research Council of Canada. Klason: Ber.. 53, 706. 1663 (1920);55,448,.+jj(19221;56,300 (1923'1; 58, 1761 (192jj; 61, 1 7 1 (19281;TTilliams and James: J. Cliem. Soc., 50, 343 (1928,; Fbchs: Ber.. 60, 776 fI9271;61, 2197 (1926 Researches on Cellulose" (19oj-191oi p. 104; Schrauth: Z. angen. Friedrich: Z.physiol. Chem., 168. 50 (1927). Chem., 36, 149 (1923'; Cf. Klason's papers: lor. cit. Stelling: Cellulosechemie. 9, 100 (1928). Kerp: Schn-rflige Saure iind ihre Verhindungen mit Aldehyden und Icetonen. Arbeiten aus der Kaiserlicher Gesundhritsamte, Band S X I , Heft 2 , 1904, Part 11.
1362
(;.
I . H O O V E R A S D K. TT, H U S T E S
?\Ilzo, 9 1 5 ; j ; 96':; : 11 '300, 99';;. Acetaldehyde sulphonic acid: 1I,'js, 8 8 . 1 9 thereby placing these substances in the class of the strong mintral acids like hydrochloric. From this standpoint therefore they may be considered to be true sulphonic acicls. This viewpoint is strongly supported by the results of t'he X-ray analyses of Stelling, the pattern so obtained fitting almost pcrfectly with the idea of a carbon-sulphur linkage. The presence of an hydrosy group on the same carbon atom would esplain the fact that the hydrolytic dissociation of these acids and their salts is somewhat greater than might be expected from the carbon-sulphur linkage. However, since Iierp's esperimental data in the case of acetaldehyde sulphonic acid are somewhat meagre, further work along these lines seemed desirable, especially since too definite conclusions may not usually be drawn from a consideration of only the first member of an homologous series. The reaction between sulphurous acid and both saturated and unsaturatrd aldehydes is considered in the present, paper; that with ketones and similar substances is now under investigation, the results of which will, it is hoped, be incorporated in a subsequent communication. The following aldehydes w r e chosen for study: I. 2.
CH3 - C"?- C'H? - CHO CH3 - C'H = ('H - C R O 8Hj - C " = ('H - ('HO SHj - ('I12 - CH, - CHO
Butyric Crotonic Cinnamic Hydrocinnamic
on account of the fact that the corresponding sulphonic acids arc supposed to be simple relatives of the sulphonic acids formed during the sulphite cooking of wood. Electrical conductivity measurements were obtained for aqueous solutions of these acids at various dilutions and for the temperature range 18-1j j"C, the full range of the sulphite pulping process. Experimental Procedure Coitductiztity Cell. The electrical conductivity cell (Fig. I ) used throughout this investigation is a modified form of the pyres pressure cell designed by Campbell7 in the Department of Chemistry of IIcCill University. The essentia! modifications are these: In order t o obtain a cell of lorn constant (approximately 0.3) the electrodes of . O O I in. platinum foil 6 nim. wide and 4 cin. long, cut to shape S (Fig. I ) are sealed longitudinally and opposite one another t o the inside malls of a piece of I Z mm. (i.d.) pyres tubing by the following method. The narrow end of the electrode foil is drawn from the inside through a hole blown in the wall of the cell. The hole is filled with a molten blob of glass and the protruding tip of foil is folded over it. The glass is thoroughly worked a t this point in a small gas-oxygen flame till a perfectly air-tight seal results. During this operation the tip of foil becomes fused to the outside wall of the cell. Then working from the fixed end of the foil, the electrode is sealed to the inside wall of the cell by applying gentle 7
J. Am. Chem. Soc., 51, 2419 (1929).
1363
ELECTRICAL CONDUCTIVITY STUDIES
heat to the outside while pressing the foil to the glass with a suitable shaped fold of nichrome wire. After inserting the opposite electrode in a similar manner, the electrode contact tubes H are sealed to the outside wall of the cell around the platinum contacts thereby producing a cell of sturdier construction than when the electrodes are sealed directly through side-arms as in the original design. Pressure up to I I O lbs, per sq. in. may be maintained on the cell by means of a high pressure water line applied to the apparatus at A and regulated and controlled by the needle valves BCD and the gauge E. An expansion chamber F is also provided. M
FIG.I
The cell and capillary sidearm are filled through the tubes ?\I which are immediately sealed off in a small flame. Repeated and careful tests showed conclusively that the long fine capillary leading to the cell was successful in preventing the diffusion of t a p water into the body of the cell for a period of at least several days.
Thermostat. The thermostat, a 4-litre pyrex beaker containing alba oil, is heated by means of t w o separate internal electrical resistance coils, one of which is controlled by a deKhotinsky (Cenco) regulator fitted with a tapping device. By this means regulation to less than O.IT from 18-1 j j " C with rapid setting at any temperature is obtained. Without the tapping device variations of z degrees or more occurred. The auxiliary heater is capable of raising the bath temperature 8" per minute. Conductivity M e a s u r e m e n t s . Resistances were measured on a Kheatstone bridge using a slide wire in conjunction with a standard resistance box, telephones and a Leeds 6: Korthrup 1000 frequency oscillator. The degree of accuracy obtainable is 0 . j - 15of the resistance reading.
G , I . HOOVER A S D K. W. H U S T E S
1364
Cell Constant After platinizing the electrodes in the usual way, the cell constant n a b determined at z j3, j", roo', r 2 g c and 1 5 6 T by means of N,'roo potassium chloride qolution which had been very carefully made up from the recrystalhAed salt and conductivity n ater Conductivity data of S o p s a was used for purpo-e- of calculation, the values given being corrected to the actual concentration at any particular temperature by means of the expression 1
A
=
I
A,
+ K(cLi)'-l
FIG.2
The cell constant so obtained, 0.316, remained fixed in value throughout the temperature range. P ~ p t i r ~ tofi ~t h,e ~SirIphonic Acid Solutions. Solutions of the sulphonic acids were prepared by two methods: (a) By the very careful and accurate neutralization with sulphuric acid of an aqueous solution of the pure crystallized barium salt of the acid. The solution of sulphonic acid so obtained is decanted, filtered and analyzed. This method is especially applicable t o the preparation of the mono acid of crotonic and cinnamic aldehydr. However so much difficulty was encountered in the r:urification of these salt; that before this x a s finally accomplishrd a second inethod ib) was deveIoped. (b) By the direct intrraction of aldehyde and sulphurous acid in aqueous solution. -
Cariiegie Institution of Kashington Pul~lications,S o . 63 (190;).
ELECTRICAL COSDCCTIVITY STUDIES
1365
Due to the readily oxidizable nature of sulphurous acid, aldehydes and the sulphonic acids, it was found necessary to carry out the reactions and to keep and handle all the solutions in an atmosphere of nitrogen. The apparatus for doing this is shown in Fig. 2 . Cylinder nitrogen, after passing through a purification train, enters the apparatus, oxygen-free at A, and against a slight back-pressure of water, bubbles continuously out to the air at C. A gas reservoir D serves to prevent sudden changes in pressure in the system. Boiled-out distilled water for the preparation of solutions is stored under nitrogen in the 5-litre pyrex flask B. Before beginning operations the entire apparatus with the exception of the flask B is cleaned and dried and by a suitable manipulation of stop-cocks completely flushed out with nitrogen. A sulphurous acid solution of about the desired strength (usually 1/10 molar) is prepared in the nitrogen filled bottle W. Samples for rough analysis are removed through a syphon not shown in the diagram. By means of gentle suction applied at 2 the measuring bulb T is filled ISith the solution. The stop-cock J7 is closed and P turned to connect the bulb T to the nitrogen line. The liquid level in the bulb T is broughc to the mark by manipulating V,which is then turned so as t,o allow the solution in the bulb T to flow into the reaction vessel R-consisting of a I-litre 3-neck pyrex flask fitted wit>ha mercury-sealed stirrer S as shown in Fig. 2 . The nitrogen displaced by the liquid returns t o the system through the stop-cock 0 which remains open. After draining for exactly five minutes, the bulb T is again filled and allowed to drain into the reaction vessel as before. Careful calibration has shown that solutions may be accurately measured in this way, the two aliquots equalling 983.2 .os cc. of solution. Samples of solution for analysis are obtained by applying gentle suction through G to the top of the burette F with E closed. With E open nitrogen enters the burette as the sample is withdrawn. I t is found that if the solution is drawn into the burette sufficiently slowly, no appreciable loss of sulphur dioxide occurs. An accurate analysis of the solution is now made and the volume used for analysis noted. The volume and strength of the solution in the reaction vessel are therefore known. The volume of aldehyde (the density of which has been accurately determined) necessary to react with this quantity of sulphurous acid may therefore be calculated. The aldehyde is slowly added t o the solution with stirring from a graduated pipette with a long capillary tip which passes through one hole of the stopper at N. A-ifterthe addition of aldehyde the glass plug N is replaced and the reaction allowed to proceed with stirring. Samples of the reaction mixture may be removed from time to time for analysis. By the above method sulphonic acids have been kept for a period of ten days without appreciable change in the analysis or conductivity of the solution. Analytical Procedure. In order to obtain accurate results the analytical methods applicable to sulphurous and sulphonic acids described in the litera-
1366
G . I. HOOVER AND K. W. HUXTEN
ture had in most cases to be somewhat modified. After exhaustive study the following methods were found to be satisfactory when employed under the conditions specified. Sulphurous acid may be determined either alone, or in the presence of aldehydes, and their sulphonic acids, by means of standard iodine solution. h definite volume of the acid solution is run as rapidly as accuracy permits from nitrogen-filled burette (cf. F, Fig. 2 ) into an excess of standard iodine solution contained preferably in a nitrogen-filled Erlenmyer flask. The excess iodine is determined immediately by means of standard thiosulphate solution. Sulphurous acid may also be determined by the use of standard sodium hydroxide solution. For one half of the SO2, Brom Cresol Green is a more satisfactory indicator than Methyl Orange. X definite volume of the acid is run from the burette as described above, into approximately 0.5 cc. less of the sodium hydroxide solution than is required for the titration. After adding the indicator the titration is then completed. Accurate results were obtained in this way which was not the case when excess sodium hydroxide was used followed by back-titration with acid. The above method is also applicable to total SO2 using Cresolphthalein as the indicator. The results so obtained were less accurate than those by the former method. Sulphonic acids may be estimated by means of standard sodium hydroxide solution by the method outlined for sulphurousacid (one-half of the SO?)using Brom Cresol Green as the indicator, In the case of monosulphonic acids one mole of sodium hydroxide corresponds to one mole of sulphonic acid and the total titration represents sulphonic acid plus I / Z of the free SO?
R-CHOH.S02.0 Na
+ iYaH407
The free SOz is determined by means of iodine by the method already described. When a sulphonic acid is formed by the addition of an aldehyde to a sulphurous acid solution the sodium hydroxide titration of the solution with Rrom Cresol Green is therefore the same before and after the addition of aldehyde. The total SO? content of butyraldehyde sulphonic acid solutions were also measured by hydrolizing off the sulphurous acid followed by determination of the resultant free SO2 by means of iodine. The following procedure proved to be satisfactory. 2 j cc. of the solution are run into an excess of saturated baryta solution contained in a nitrogen-filled 1 2 5 cc. Erlenmyer flask which is then stoppered and allowed to stand for 30 minutes. A slight excess of standard iodine is placed in another flask and acidified with hydrochloric. The contents of the previous flask are now quickly poured into the acidified iodine solution, some of the mixture is poured back and forth a few times and finally the contents of one flask is washed into the other by means of dilute hydrochloric followed by water. The excess iodine is then titrated with thiosulphate. Accurate results may be obtained in this way, This is not the case when
1367
ELECTRICAL CONDUCT1VITY STUDIES
sodium hydroxide is used as a hydrolizing agent since an equilibrium is set up for each concentration of soda used. With baryta, a n insoluble precipitate is formed and hydrolysis of the sulphonic acid may therefore proceed t o completion. Experimental Results
Preparation o j the B a r i u m Salts of Crotonaldehyde and Cinnamicaldehyde Sulphonzc A c i d s . Haubnerg describes a method for the preparation of the barium salts of both the mono- and di-sulphonic acids of crotonaldehyde. CH3-CH-CH2-CH0 MonoI
SOsba CH3-CH-CH2-CHOH DiI S03ba S03ba The aldehyde is disRolved in ten times its volume of water, the mixture cooled with ice and saturated with SO,, then exactly neutralized n l t h baryta solution and the solution filtered from the precipitakd barium sulphite. When the mono-salt is desired, the acid solution is boiled with steam before neutralization in order to remove the sulphurous acid from the -CHO group. After concentration in a water bath at about 60°, a syrup is obtained which on drying over sulphuric acid gives in one case a white amorphous mass corresponding on analysis to CH, - C H - C H 2 - CHOH and in
I
1
j
SO?Oba S0,Oba the other case a yellow amorphous mass corresponding to C H - CH - CHB - CHO SO,.Oba In the present investigation it has been shown that while addition of sulphurous acid to the -CHO group will readily take place in the cold, no appreciable addition to the - C H = C H - group takes place under these conditione. This fact would explain the difficulty Haubner encountered in the purification of these salts since barium disulphonate could only be formed during the water bath treatment and at the expense of the -CHOH group
SO.O. ba so the resultant product would most likely be a mixture of the disulphonate, the yellow coloration being due to the polymerization of the free unsaturated aldehyde which would undoubtedly be present. Haubner’s procedure therefore requires modification. The method finally adopted for the preparation of these salts is as follows. SO,gas is run into the aldehyde solution maintained a t approximately room temperature till the odour of SOB is appreciable. The solution is then heated to about 9
Monatsheft, 12, 541 (1891).
1368
G . I. HOOVER A S D K . W. H U S T E S
90°C on the water bath for a short time to allow the addition of SO,to the -CH=CH- group to take place. In concentrated solution, this reaction apparently proceeds with appreciable velocity at this temperature. At this stage SO, is maintained in the solution. \Then the reaction has gone t o completion most of the frce SO? is removed by exhausting the solution on the water bath. The warm solution is then neutralized with barium carbonate in fine suspension. After decanting and filtering, the solution is concentrated to a thick syrup under r c d u c d pressure on the water bath at 60". Crystallization was finally obtained after prolongrd effort by accidentally stirring the syrup on a scratched watch-glass. The crystals so obtained were effective in seeding other solutions for crystallization thereby permitting of the purification of the salts by recrystallization. The barium monosulphonate is prepared from the barium disulphonate in solution by the very careful addition of baryta with rapid stirring thus precipitating the sulphite from the -C'HO group. If excws is used the second sulphonate group will also be hydrolyzed off. The resultant solution is concentrated and after seeding is set aside to crystallize as before. By the above method the crystallized barium salts of the moco- and the di-sulphonic acids of croton and cinnamic aldehyde \wre prepared. Careful analyses of these salts gave results which correspond very closely t o the theoretical values. The disulphonates decompose on standing even when kept in the dark in stoppered bottles. The only solvent? other than water, found for any of these salts was methyl alcohol in which the crotonaldehyde nionosulphonate (CH, -C'H-CWr-CHO) is slightly soluble.
SC)?ba Butyraldehyde A d d i t i o n P ~ o d u c t . The reaction betwen molar proportions of butyraldehyde and sulphurous acid mas carried out in the reaction apparatus already described (Fig. 2 ) . The usual tests showed that an equilihriurn is set up between addition product, aldehyde and sulphurous acid which can be represented as follows:-
C~H,-CHOH.SO?OH$CBH,.CHO
+ H?SOB
The position of the equilibriuni in equimolar solution was not determined accurately since the information was not essential to this investigation. It is represented in molar-tenth solution at z j" by approximately 9 7 5 combination. X few conductivity measurements were made O R these equimolar solutions, which will be referred t o as such. Generally, however, the solutions used for conductivity work contained enough excess aldehyde to reduce the free SO2 concentration nearly to zero at room temperature, as first suggested by ICerp6. An excess of three times was found sufficient for this purpose, whereas an excess of ten times used in a few experiments gave trouble a b o x roo°C due to polynierization of the aldehyde. When a solution was vvantpd for conductivity measurements a sample from the reaction vessel was diluted to the required volume with boiled-out
ELECTRICAL C O S D U C T I V I T Y STVDIES
1369
distilled water in a nitrogen-filled volumetric flask. The determinations were carried out in the pressure cell over the temperature range 1 8 ' - r ~ j ~ C . The complete specific conductivity data obtained are shown in Table I and Fig. 3 , Ildehyde correction determinations were carried out under similar conditions and immediately following the original experiment. The conductivity of the aldehyde solution is apparently due both to traces of impurities and to the interaction of the aldehyk and small quantities of oxygen in the water. Since this reaction goes quickly t o completion only at the higher temperatures, reproducible rcsults were obtained with both sulphonic acid and aldehyde solutions only after the solution in the cell has been heated for ten minutes to the maxinium experimental temperature. This
FIG.3 Butyraldehyde Sillphonic Acid I. 26.4 L dilution V , 466.2 11. jo.2 VI. 1602.6 111. 1 0 8 . 1 VII. 26.4 equimolat IV. 401 1-111. 1 0 8 . 1
procedure was therefore followed for all solutions containing excess aldehyde. The reproducibility of the result? is shown in Table I (26.4 L dilution) where XI and K 2 are duplicate determinations on the same solution and also in Table I (108.r L dilution) where K, and K, are values for solutions of the same concentration prepared at different times. Conductivity values for each of the solutions increase at first with rising temperature, reach a maximum, then decrease again due to the hydrolysis of the sulphonic acid to aldehyde and SO,. The maximum represents the point where the effect of hydrolysis on the conductivity of the solution just overcomes the effect due to the increase in temperature. As might be expected on this basis, the effect of increasing dilution is to shift the maxima t o slightly higher temperatures. The presence of excess aldehyde decreases
I370
G. I. HOOVER A S D K. W. HUSTEN
the extent of hydrolysir at any temperature as is shown by Curves I 8: J'II, and I11 8. TIII, Fig 3 representing solutions containing three times excess aldehyde and no excess aldehyde respectively That these curves represent equilibrium conditions is shown by the fact that they may be repeated-a solution may be heated and cooled several tiiiieq and will continue t o give points on the same curve
FIG.4 Hydrolysis of Butyraldehyde Snlplionic Acid A. 26.4 I, dilution c. 401 L B 108 I L D 1602.6L.
.A knowledge of the extent of the hydrolysis is essential if any inforiiiation is to be obtained concerning the strength of the sulphonic acid a t higher temperatures. Hydrolysis data have bern determined up to 85' nith a fair degree cf accuracy by the follolving method. z j cc. of the sulphonic acid solution is placed in a 1 2 j cc. nitrogen filled stoppered Erlenmeyer flask and heated in a thermostat for 2 0 minutes. iodine over that required for reaction is RIeanwhile a slight excess of S,!IOO made up t o I O O cc. with water in another flask and cooled in a freezing mix-
ELECTRICAL CONDUCTIVITY STUDIES
I3iI
ture till some ice forms in the solution. This solution is poured quickly into the flask in the thermostat which is immediately removed. Excess iodine is then determined with N/IOOthuosulphate. The cold iodine solution reacts with the free SO2 and also cools the solution before the equilibrium has had time to readjust itself. Reproduceable results were obtained with the solutions containing excess aldehyde. Analyses carried out on the equilibrium solutions Fere less accurate due both to the higher hydrolysis value and the less stable character of these solutions The experimental data obtained are shown in Table I1 and Fig. 4. Since the 401 L solution shows nearly 4oCc hydrolysis at 85OC, butyraldehyde sulphonic acid must, be almost completely hydrohzed at the higher temperatures. Knowing the extent of hydrolysis, the true dilution of the sulphonic acid may be calculated. However, before the equivalent conductivity may be calculated, a correction due to the free sulphurous acid formed by hydrolysis must be applied to the specific conductivity. Conductihlty measurements Rere therefore made on solutions of sulphurous acid over the required range of concentrations and, for the sake of completeness up t o 14j"C. Specific conductivities plotted against concentration, Fig. 6, give approximately straight lines. The SO? correction values were read from these curves. The specific conductivity temperature data for sulphurous acid, Fig. 5 , FIG.5 and Table 111, is interesting. The SulDhuroua Acid Solutions curves indicate that almost complete 4. .003j1 Molar C. ,00143 M. hydrolysis of the sulphurous acid D. .000672 11. : ; . 00276 11, E. .ooor85 M. takes place at the higher temperatures, probably as follows :
1
+
H2SOaFtSOz H?O thus agreeing with the results of Carol E. lIaasslo and of W, B. Campbell" on much more concentrated solutions. The conductivities of the sulphurous acid solutions at higher temperatures have a tendency to increase slowly with l o Carol E. Maass: Ph.D. Thesis, McGill University (1928). l1 W. B. Campbell: Ph.D. Thesis, McGill University (1929); Campbell and 0. Maass: Can. J. Res., 2, 42, (1930).
1372
G . I. HOOVER A S D K. W. HUSTEX
time as is shown by curve B' Fig. 5 , which represents the curve for solution B after it has been heated to I A j ' . Campbell noted this change and explained it on the basis of the formation of sulphuric acid through the intermediate stages of polythionic acids. I t is of especial interest to note that the sulphonic acid solutions containing excess aldehyde do not show this change t o any marked degree although at the higher temperatures there must be a large percentage of free SO2 in solution. In this case, however, on cooling the solution, the conductivity returns to its former value. Sulphonic acid
solutions containing no excess aldehyde are somewhat less stable, indicating that the aldehyde in some way protects the SO2 from these changes. Complete data are now available for the calculation of the equivalent conductivity A (Table IV). Some earlier values obtained by Hunten, using a Washburn cell (Table V ) , and solutions containing I O times excess aldehyde, agree well with the later results using the pressure cell. Complete results are shown graphically in Fig. along with those of Kerp for formaldehyde sulphonic acid.6 The equivalent conductivities at infinite dilution were estimated from the maxima of the curves and by graphical extrapolation using the empirical expression
I,'A
= I,IA=
=
Iil(CA)~"
of Soyes.8 Since either method is subject to slight error, the average of the two values of Am was used for purposes of calculation. On this basis, the percentage ionization of butyraldehyde sulphonic acid as calculated from the ratio h : ' . A m ~ o ois given below.
ELECTRICAL COXDUCTIVITY STCDIES Temp
. I m
'C.
from curves
I8
341
25
average
)
94 5'< 93 7
3 13
3 51 385
45
3i.5 47 I
488
380 480
95
2
6;
jj0
j8r
566
95
I
/ 3
592
633
613
91 3
--
S
I .\= 11 j o
Aw
cc
kale
IOO
HC'l 1'Az = 97.4cc at
2j0.
I I
I
I
I
-v-
LOG,0 D ~ - ~ T o N
FIG.7 Butyraldehyde Sulphonic Acid A-Washburn Cell-Hunten 0-Pressure Cell-Hooier and Hunten t-Formaldehyde Sulphonic Acid. z,j0-Kerp
These acids are therefore comparable in strength to hydrochloric and so must be considered as true eulphonic acids. This is in agrremrnt with Kerp's results with formaldehyde sulphonic acid. The presence of the hydroxyl group on the same carbon atom would account for the unstable natureof these acids. Crotonnldehyde Sulphonic A c i d s .
Hunten prepared the free mono-acid
CHs - CH - CH, I
- CHO
8020H from the barium salt by the method already described. Conductivity data for this acid at zsoC is given below.
G. I. HOOVER AND K . W. HUNTES
1374
Electrical Conductivity of Crotonaldehyde Llonosulphonic Acid Temp.
K corr.
x
C
2 j"
105
3000
j
60
162
33
1
I1
c
j 28
Dil L.
Ionization
.I
IC
42
313
52
I
3 96
260
j
122
1300 3 900
429
j800
412
A,
=
431
11
50
A A,
=
91 tic;
11
100
A Am
=
95 6';
430
FIG.8 Crotonaldc3liyde Sulplionic .Acid A . j o L dilution ald./S02-I:r B. jo L dilution ald./SO9-I : z
The ionization values place the -CH-(.'H?-
acid which is known to be a
I
I
AO2OH true sulphonic acid in the same strength class as the -CHOH acids thus
1
SO2OH furnishing further evidence for considering the latter to be true sulphonic acids. The interaction of crotonaldehyde and sulphurous acid was also investigated by the method used for butyraldehyde. With crotonaldehyde, addition of sulphurous acid may take place to the - C H = C H - group and to the -CHO group. Solutions were prepared therefore in which the molar ratio of aldehyde and sulphurous acid were I : I and also I : 2 . Within the range of concentration investigated (up to &%/IC), and for a time period of .several days, direct analyses showed that a t room temperature addition takes place to the -CHO group only, even in the presence of excess sulphurous acid. ,is with butyraldehyde sulphonic acid, an equilibrium solution results which at concentration molar/Io consists of approximately 9 ~ sulphonic 7 ~ acid at z j o .
I375
ELECTRICAL COSDL*CTIVITY STUDIES
C'onductivity data for solutions of this acid are shown in Table VI and graphically in Fig. 8. Up to approximately I 10' curves similar to those obtained for butyraldehyde sulphonic acid are obtained. However, above I 10' the specific conductivity increases rapidly and the curve breaks upward as shown. It should be noted that the form of the curve above 110' corresponding to this change depends upon the time interval between readings until the reaction is complete. With falling temperature conductivity values for the colution follow a new curve which thereafter may be repeated. The dotted linc represents a typical curve for a -CHO group sulphonic acid. That this curve is followed slightly past the maximum is due to the fact that the addition of sulphurous acid to the double bond happens not to take place till a rcmperature above that corresponding to the maximum is reached. Otherwise curves of quite different form might have been obtained. Analyses of the resulting solution show that the break in the first curve represents in A (ratio aldehyde: to SO2 - I : I ) the formation of the -CH = C H - addition product at the expense of the -CHOH group and in I
S020H
B (ratio aldehyde to SO2 - 1 : 2 ) the formation of the more or less hydrolyzed disulphonic acid. The curves indicate that the formation of the -('H = C" - addition product does not take place at appreciable velocity much below I IO' (conductivity readings represent constant value for approximately one-half hour) even in the presence of excess sulphurous acid and that this product when formed is not hydrolyzed a t the higher temperatures as in the CHOH compound. The fact that no break occurs in the curve upon
I SOzOH again heating the solution shows that the - C H = C H addition product when formed does not change back into the -CHO acid on cooling to room temperature again even after standing for several days. Analyses carried out on these solutions indicate that the change over to the - C H = C H group goes very nearly if not entirely to completion. l h e fact that in A (Fig. 8) the lower part of the two curves approach each other is therefore an indication that the two acids are of approximately the same strength, as might be expected from the results already obtained concerning the strength of butyraldehyde sulphonic acid and of crotonaldehyde monosulphonic acid. At higher temperatures the -CHOH acid decomposes
I
SOzOH whereas the -CH.CH, acid is stable throughout the range.
I
SOzOH
1376
G . I. H O O T E R A S D B. W. HUNTEX
It is interesting to note that the actual value of the specific conductivity of the -CHO acid at IS' and j o L dilution - 666 X IO-5 is approximately the same as that for butyraldehyde sulphonic acid at 18' and j 0 . z L namely 649 X IO-j. The agreenient is even closer than is indicated by these figures since the crotonaldehyde acid is in equilibriurn solution and therefore the specific conductivity value obtained is slightly high due to the conductivity of the S O z present, in the solution.
Cinviu~iialdehyrle Szrlphoilic Acid.$. The reaction bet ween this aldehyde and sulphurous acid was studied by the niethod previously outlined. -1s with crotonaldehyde, addition of sulphurous acid at rooni temperature takes place to the -CHO group only. The results of specific conductivity measurements made on solutions of this acid are given in Table VI1 and Fig. 9. Due to the greater tendency of
FIG.9 Cinnamic .-ildc~h?-deSulphonic Arid 4.. zoo 1, dilution slcI:SO2-~ : I B. zoo L " ald. SO?-i:z
cinnamaldehyde to polynirrize at the higher temperatures, it was found desirable to work with niore dilute solution than with the other aldehydcs investigated. Howevrr, the one value obtsincd of the qxcific conductivity at j o L dilution is of the ~ a n i cmagnitude as that ohtainrd for the -CHO group acid of both butyric and crotonic aldehydes. Conductivity curves (Fig. 9) are of the sanic form as t h o x obtained for crotonaldehyde sulphonic acid and the sanie general conclusions may be drawn. hbove I '01 tlie - c " O group sulphonic acid change? to the -C" = CH group acid and thereafter remains a.; sucli.
Discussion The gr ncral cl~rcu~-ion of Part I of thiz paper ha- been incorporated 171th that of Pait I1 and may he found along nit11 a complete .uiiiii-~aryat the end of the vconcl papcr.
ELECTRICAL CONDUCTIVITY STUDIES
I377
TABLE I Specific Conductivity of Aqueous Solutions of Butyraldehyde Sulphonic Acid I1 I11 I Dil. 5 0 . 2 L Dil. 108.1 L Dil. 26 4 L KI cow. K? corr. Ald. corr. K c o r . Ald. corr. K1 corr. K2 corr. Ald. corr. Temp. C
X
I8
1208
--
2080
I 3
85
J.
105
x
105
x
~ 1 0 5
x
105
x105
4
649
3
2
303
306
2 0
IO
1095 1143 1084
j . 2
536 546
5.9 6.0 6.0
533 547 519 357 289 236 '97
3.2 3.3 3,4 3.5 3.5 3.5 4.0
1203
-
105
IO I i O J ,
21:
IO
I2j
I250
I2jO
IO
'35
951
IO
145
722
968 733
7'7 jj8
IO
427
572
I1
IO0
-
155
Temp. "C
IV Dil. 401.0 L K. corr. Ald. corr. X 105 X 105
-
-
18' I8 65
85.0
-
1.2
-
75
150,o
2.0
8;
Ij5.0
2.0
IO0
150.0
2.0
I2j
115.0
2 . 0
I35
100.0
2 . 0
145
86.1
2.2
_
155
_
5.4
5.7
-
-
v
x
~ 1 0 5
105
524
368 291 234 -
VI1
VI
VI11 Dil. 466.2 L Dil. 1602.6 L Dil. 26.4 L Dil. 108.1 L K. corr. Ald. corr. K corr. Ald. corr. equimolar equimolar x IO^ X1os X IO^ x105 K x IO^ K x 105
-
75.7
-
648 2.3
-
129.0 2 . 3 135.0 2 . 3 129.0 4 . 0 102.0 4.1 89.9 4.1 78.6 4.1
_
_
-
j . 2 21.0
_
39.9 41.6 42.1
38.3 3j.9 33.5
-
.i8
_
1.j8 1.65 1.73 1.80 1.80 1.80
-
-
1230 1850 1840
309 476 487 465
1jj0
1490 913 7'3
4Oj
554
198
438
-
278
-
18'
TABLE I1 Hydrolysis of Butyraldehyde Sulphonic Acid in Aqueous Solution Tzmp. C.
Titration Hydrolysis
N/IOO
%
SO M/L ~
1 0 5
Iodine
I.
L
Dil. (corr.) at T o
hl/L.
45
0.67
0.3;
excess aldehyde 3 X . 2 5 cc solution = 189.4 cc h T ; / ~ o Iodine o
65 75 85
2 .12
1.12
6.02 17.50
3.18 9,25
45
0.29
65 75
0,7I
14.2
I12
46.0 90.6
117
26.4
= .03788
11. 108.1 L = . 0 0 9 2 j o M / L . excess aldehyde 3 X . 2 5 cc solution = 46.25 c c X / ~ o oIodine
+
111. 401 L ,002494 l I / L . excess aldehyde 3 X . 2 5 cc solution = 1 2 . 4 7 cc S;IOO Iodine
13.4 42.4 120.4 3jo.o
5.8
85
4.53
0.63 1.54 4.97 9.80
4j 6j
0.12
0.96
2.4
0.93 1.29 2.36
i.40
10.30 19.70
18.6 zj.8 49.2
I 3
*I
85
2.30
26.j 27.2 28.0
30.0 I10
124
408 442
458 j16
G . I. HOOVER A?iD K . Fv. H U S T E S
I378
T ~ U LI1L (Continued) Hydrolysis of Butyraldehyde Sulphonic Acid in Aqueou~Solution Tgmp. C
L
IT-. 1602.6L
= 006240 M excess aldehyde 3 X . 2 5 cc solution = 3 1 2 cc N I O O Iodine
T-.
108 I
L
=
.009250;\I
L.
equimolar
VI. 401 L
= 002494
JI’L.
cT
o ~j
6;
_-
o
13
0 71
22
8j
I 42
45 5
32
IO
13 i
j
14
2
2124
28
4
3032
73 9
4 03 5 ii
85
1697 1818
3 0 6 4
IO 2
6
;j
8;
SO L1I \I’L X I O ~ c o n ) at T’
4 9
4j
jj
equimolar
Hydrolysis
Titration Y’xoo Iodine
29
i
32
3
38
2
T ~ B LI11 E Specific Conductivity of .Iqueous Solutions of Sulphur Dioxide I
Temp “C
ooijr hl I, SO K X ioa Conc T‘C JI 1, x I O >
IT oo2;h 11 I,
I
281.2
2 j j . 2
--
2 3 3 .o 4268 o 260 2
85 IO0
I IO
-
1 15. I20
263 3
I2j
270 0
135
282 0
'45
309
0
TABLE IS C'rotonaldehyde Sulphomc .Icid-lii~ie l'actor for l
I
322.8
6
5
325.5
h
58
8
3
331.9 336 . o
>
I
298.9 306. j
9
312.0
I IO0
105
I384
C . I. HOOVER .4KD C. A . SAXKEY
TABLE N specific ('onductivity of Hydrocinnamic Aldehyde Sulphonic dcids in Aqueous Solution Tzmp.
C.
18 45 65 85 IC0
IIC IZj
'35 14: 18'
Dil. zoo L K x 105
Dil. 400 L K x 105
168.9
84 3
232.5
I23 j
266.5 267. j 239.5 216.1 174.2 'jI.3
13; . 8 139.9 I34 8 12j c io8 6 IC0 0
132.9 175.4
87
0
90
8
General Discussion Parts I and I1 By means of electrical conductivity measurements, butyraldehyde sulphonic acid has been shown to be a strong acid of approximately hydrochloric acid strength thus agreeing with the results obtained by Kerp6 for formaldehyde sulphonic acid.%Butyraldehyde sulphonic acid has also been shown to be of the same order of strength as the monosulphonic acid of crotonaldehyde C'H, - CH - CH? - CHO
9020H which is known to be a true sulphonic acid. On the above basis therefore the aldehyde sulphonic acids of the type 1L - CHOH may be considered to
\
SOyOH be true sulphonic acids with carbon-sulphur linkage. The presence of the hydroxyl group on the same carbon atom would account for the fact that these acids are very readily hydrolyzed in aqueous solution. The unsaturated rnonowlphonic acids of crotonic and einnamaldehyde change over fairly rapidly above I IC' t o the corresponding saturated nionosulphonic acids as is evidenced by the breaks occurring in the specific conductivity curves obtained for these acid.. This probably represents the addition t o the double bond of the free sulphurous acid formed by hydrolysis and not an interniolecular rrarrangenient. The reaction is apparently autocatalytic in nature. In dilute solution it proceeds very s l o ~ l ybelow 1 10°C and even when in concentrated solution there is no appreciable addition t o the double bond at room temperature. The saturated rnonosulphonic acid when formed is not hydrolyzed at higher temperatures as is the unsaturated mono acid.
ELECTRICAL C O S D U CTI VITY STUDIES
1385
Since the specific conductivity curves obtained for solutions of hydrocinnamic aldehyde are identical in form to those for butyraldehyde sulphonic acid, no addition of sulphurous acid takes place to the double bonds within the benzene nucleus. The specific conductivity curves obtained for very dilute solutions of sulphurous acid are similar in form to those obtained by Campbell" at higher concentrations and indicate almost' complete hydrolysis of the acid at the higher temperatures. After heating, the conductivities of these solutions increase even when no free oxygen is present in solution, which has been explained by Campbell as being due to the formation of sulphuric acid through the intermediate stages of polythionic acids. I t has been shown that this reaction is very much slowed up if not entirely prevented by the presence of aldehydes in the solution. Due to the possible structural similarity between the aldehydes studied and lignin, the results obtained may shed some light on the chemistry of the sulphite process for the manufacture of wood pulp.'* It has been found in mill practice that a digester temperature of approximately I I O O C should not be exceedcd until a certain time interval has elapsed. Xlthough this fact has usually been regarded as dependent upon the rate of penetration of the cooking liquor into the wood: it may also be connected Tvith the fact observed in this investigation that the addition of sulphurous acid to the ethylene linkage does not take place n-ith appreciable velocity in dilute Although at the concentrations found solution at temperatures below I IO'. in digester liquor, this reaction could take place at temperatures below 110') the effect of the rate of penetration may be sueh as to bring the concentration within the wood to low values corresponding to the dilute solutions investigated. Even above 110' the reaction does not go instantaneously but requires considerable time. When the sulphite addition product of an unsaturated aldehyde is heated too rapidly to temperatures considerably above I IO', decomposition and polymerization take place with the formation of resins which are frequently coloured. Lignin rnight conceivably behave in similar fashion unless sufficient time is given for the saturation of an ethylene linkage. Therefore some of the ill effects of the too rapid heating may be due to polymerization. The sulphonic acids formed by the addition of sulphurous acid to the ethylene linkages of unsaturated aldehydes are strong acids even at the higher temperature. Thus strong acids other than sulphuric may be formed during the sulphite process, a fact not usually recognized in this connection. Some interesting speculation concerning the nature of the sulphite reactions is therefore possible. Assuming that the SO, penetrates into the wood in adrance of the base, the first reaction at about, 110°C. would be the formation of a sulphonic acid bv the saturation of the ethylene-tvDe " . double bonds l* This point has been previouslv emphasised bv Hibbert (Internat. No. Pulp and Paper Mag. of Canada,,f928,p. 126). 1t"was predicted 1Tech. Section C. P. P. A. 1926 Meeting -Discussion on Mechanism of Sulfite Pulp Manufacture") t h i t the reaction-products of sulfurous acid with unsaturated aldehydes and with lignin would prove t o be very strong sulfonic acids.
1386
G . I . HOOTER AND C. .%, S A N K E T
of lignin. This acid would then be neutralized by the penctration of the base. It may be possible that both these reactions must be allowed to proceed to completion before proceeding to higher temperatures;. Otherwise, on the onc hand, polymerization of the lignin may result and on the other decomposition of the cellulose by the strong acids present. L-nfortunately the relationship between the factors mentioned abovr has not been determined but might well form the basis for the further consideration of the subject of wood penetration by sulphite 1iqu0r.l~ The fact that the addition of sulphurous acid to the ethylene linkage of unsaturated aldehydes is apparently autocatalytic in nature may be of some importance since in certain caws wood apparently cooks more readily in thc presence of some of the liquor from a previous cook. As noted by Campbell, sulphurous acid at the higher temperatures may change over, even in the absence of free oxygen to sulphuric acid. The fact brought out in this investigation that aldehydrs tend to prevent thi5 change may be of interest since lignin, sugars, etc., produced during the digestion of wood may exert a similar action.
General Summary Parts I and I1 I. Electrical conductivities of aqueous solutions of butyraldehyde zulphonic acid at various dilutions have been drtermined in the teniperaturc range 18-155°C. Percentage ionization values have been calculated arid place this acid in the class of the strong mineral acids. 2. The hydrolysis of butyraldehyde sulphonic acid in aqueous solution has been measured at 45', 6 5 " , ;jo, and 8j'. 3 . Conductivity data have been obtained for very dilute solution of sulphurous acid in the temperature range 18"-14j0. 3 . The crystallized barium salts of the mono- and di-sulphonic acids of both crotonic and cinnamic aldehydes have been prepared. 5 . Crotonaldehyde monosulphonic acid has been shown by means of conductivity measurement,sto be a strong acid. 6. Specific conductivity data for solutions of crotonaldehyde acid and cinnamaldehyde sulphonic acids have been determined in the temperature range 18"-145'. sulphonic acid of croton7. The rate of formation of the - C H = C H aldehyde in a solution of the -THO acid has been determined at 100' and I IO' 8 Specific conductivity curves for solutions of hydrocinnaniic aldehyde sulphonic acid have been obtained and are compared with those for cinnamic aldehyde and butyraldehyde sulphonic acids. 9. Possible applications of the results of this investigation to the cheniistry of the sulphite process for the manufacture of wood pulp are discuwd. '3
These problems are being investigated by Hihbert and eo-workers.
