Reaction of Sulfur Dioxide with Olefins R. D.SNOW AND F. E. FREY Phillips Petroleum Company, Bartlesville, Okla.
Many olefins react with sulfur dioxide to yield resinous heteropolymeric products that give coherent moldings comparable in mechanical and electrical properties to some commercial plastics. The reaction exhibits unusual chemical behavior. Light of less than 3000 A. or a catalyst are necessary to effect the reaction. Several new catalysts which have long life and are effective in very low concentrations are described. These include
mild oxidizing agents such as nitrates. Certain olefins, such as isobutene, which will itself react with sulfur dioxide at a suitably low temperature, will inhibit the reaction of n-butenes with sulfur dioxide at room temperature. The reaction exhibits an unusual temperature effect. There exists a rather sharp temperature apparently characteristic of the olefin, above which the reaction does not take place.
I T H I N the past ten years much scientific interest has developed in the reaction of sulfur dioxide with olefins, no doubt because the reaction was accidentally encountered during physical studies of olefin-sulfur dioxide systems (6, 16). This reaction is one of polymerization and produces resinlike polymers of high molecular weight, containing both sulfur dioxide and olefin as constituents of the molecule. Interest in the reaction has been stimulated by the possibility of producing synthetic thermoplastics from enormous quantities of inexpensive raw materials. In addition to the commercial aspects, the reaction itself exhibits unusual chemical behavior which makes it of intense theoretical interest. The first published mention of a reaction between sulfur dioxide and an unsaturated compound was made in 1898 in an article by Solonina (17) describing the reaction of sulfur dioxide with allyl alcohol and allyl ethers. A patent to the Badische Anilin- und Soda-Fabrik (2-4) described the reaction of sulfur dioxide with conjugated diolefins in 1910. I n 1914 a British patent was granted to Mathews and Elder (11) covering the reaction of sulfur dioxide with monoijlefin hydrocarbons such as propylene and butylenes to produce plastic masses. When sulfur dioxide reacts with conjugated diolefins, the formation of polymeric products of high molecular weight has been observed, and in addition simple monomeric sulfones have been identified. With the exception of several publications on the reaction of sulfur dioxide with such diolefins (3, 4, 9, 18), virtually nothing was published in the next fifteen years. During the past eight years, however, the reaction has been studied in several laboratories, with increased attention to the monoolefin reaction, and a number of papers have appeared. Seyer and King (16), Staudinger and Ritzenthaler (19), and Marvel and coworkers (6, 8, 10, 13, 14) have made an extensive study of this reaction. The reaction has been found to be rather general for unsaturated organic compounds. Table I gives the monoolefins, conjugated diolefins, acetylenes, and polyfunctional unsaturated compounds which have been reported to react with sulfur dioxide to form polymeric products. The yields, in per cent of theoretical, and the published melting or decomposition temperature of the polymers are also given. Unsuccessful attempts to react trimethylethylene, tetra176
methylethylene, ethyl crotonate, crotonaldehyde, methyl acrylate, acrolein, vinyl chloride (I?‘, 19), acrylic acid (17, 19), pinene, 1,4-dihydronaphthalene, chloroprene, trichloroethylene, and oleyl alcohol have also been described. The reaction of sulfur dioxide with monoolefins involves substantially equimolecular quantities of sulfur dioxide and olefin. For most olefins the reaction takes place a t ordinary temperatures. Mathews and Elder (11) observed that the reaction of sulfur dioxide with monoolefins could be brought about b y sunlight or other actinic light, but that it would not take place in the absence of light. Fitch (6), Seyer and King (16)) and Staudinger and Ritzenthaler (19) found that the reaction could be brought about in the absence of light by catalysts. Catalysts mentioned in the literature are oxygen, hydrogen peroxide, benzoyl peroxide, perbenzoic acid, peroxidized ether, paraldehyde, hydrogen peroxide and paraldehyde, ozone in chloroform, and ascaridole. As a rule, comparatively large percentages of these catalysts have been used. For example, typical catalytic mixtures used by Marvel (8, 13) are as follows, on the basis of percentage b y weight of the mixture of equal volumes of liquid sylfur dioxide and olefin reactant: A 7.5-8y0 ethyl alcohol
3
rtraldehyde o ofOld” 3% ydrogen peroxide (0.150.3% by weight of pure HzOz)
R
B 8% ethyl alcohol 1-4% ascaridole
Several anticatalysts, or inhibitors, have been reported. Staudinger and Ritzenthaler (18, 19) reported that polyhydric phenols inhibited the reaction of sulfur dioxide with conjugated diolefins; pyrogallic acid had the greatest effect, and pyrocatechol, hydroquinone, phloroglucinol, resorcinol, and phenol exerted a decreasing effect in the order named. Fitch (6) observed that unsymmetrically di- and trisubstituted olefinic hydrocarbons, such as isobutylene and trimethylethylene, inhibited the reaction of sulfur dioxide with other monoolefins. The effect of temperature on the reaction of sulfur dioxide with olefins has received little attention in the published work. Most of the reactions reported have been carried out at, or somewhat below, ordinary room temperature. However, Perkins (12) proposed to control the 1,4-addition of
FEBRUARY, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
sulfur dioxide to conjugated diolefins by carrying out the reaction at 100" C. in order to prevent the formation of the polymeric sulfone, which is rapid a t ordinary temperatures, and thereby favor the slower reaction by which the monomeric sulfone is formed. The reaction products obtained from conjugated diolefins are of two kinds: a crystalline monomeric sulfone with a definite melting point, and an.amorphous heteropolymeric sulfone. Both are formed simultaneously, hut under ordinary conditions the polymer usually predominates (18). Positive catalysts favor the rapid reaction leading to the polymer. Kegative catalysts (18, 19) and elevated temperatures (18) are reported to suppress the formation of the polymeric compound and permit the slow reaction by which the monomer is formed to go to completion. Once formed, the monomer is said to be stable under the conditions which favor the formation of polymer Srom the sulfur dioxide and diolefin and probably is not an intermediate compound in the polymer formation. In the case of mouoolefins, no monomeric sulfone has been reported. These facts would suggest that the mechanism of polysiilfone formation involves the rapid stepwise addition of molecules of sulfur dioxide and olefin alternately to the chain, although the transitory existence of an unstable sulfur dioxideolefin complex is possible. Standinger and Marvel both propose a polysulfone structure consisting OS long chains where tlie olefin molecules are linked through tlie sulfur atoms of the sulfur dioxide vith which thcy alt.er11at.ein the clisin, but thcy represent differently the manner of orientation of successive olefin groups
OF OLEPETSWITH SULFUR DIOXIDE TABLE1. I~EACTION Yield
%
" e.
... ..
...
... 76
Yo
so;'i0 < .1
. .
s;nHll
76-80 ...
small 78
Conjugated diolefins: Biitsdiene llimethylbutvdienr Pentadiene Cyeluhcrsdieiie
Isoprene
'leetylener:
Acetylene Methylaoetyleno Etlrylanetyleoo I-Pentyne
...
...
I b e v e 200 330 185-100 ,380
...
...
...
...
...
00
203:~i08 195--205
50-00 (70:
160-170 180 160 120 140 2,511 275 110- 145
,XI
... ,rnnouedr:
...
CRUDE MATERIAL A N D MOLDEDOB.JECT.3 DIOXIDE RESIN
OF
OI.EFIN-sULYUA
Products ranging from those that are completely iusoluble in all organic solvents to those having quite high solubility in a vide variety of solvents have been reported. Most of the products are resistant to decompositioii by acids, and many will dissolve in concentrated nitric or sulfuric acid from which solution they can be recovered in tlie original cheinical state by dilution witli water. Although some of the products are fairly resistant t.o weak alkalies, all can be decomposed by concentrated alkalies at elevated tempcratures. The purpose of this papcr is to cont,ribute some additional information rcIative to catalysts, inhibitors, temperature effect, and properties of tlie products of t,liis interesting reaction.
,..
... ...
Raw Materials In view of the effects of catalysts and inliibit,ors on the reaction. the more important inaterials iised !Till bo briefly discussed : BPHYLENE. The cylinder product of the Ohio Chemical Oom- . pmy wad used as received. PROPENE.In most of the work the cylinder product of tlie Matheson Company wy&6 wed. However, about 150 pounds of 95 per cent propylene \Tore prepared by refractionating the C3 fraction of liquefied petroleum cracking-still gases. No ohomical treaLment of t h i s product was found necessary. I-HUTENEwaij first synthesized in sniall quantities by the Grimard reaction. 1,arser quantities xere then made by dri;vdn,xide solution for uolvmerizat,ion of tlie small quantities
222
180~~280 150-1 8 0
o-Allylailirolo
ien~iei~ 2.55
...
... ...
. .
.Ab& 350 262-273
In gome casea thir U.RS the temperature at whielr softei>jinp and Row were ohaerred: in others it w w the leiwerature at whicli active decomponoted.
iition wna
in the case of substituted ethylenes. There is evidence that molecular weights as high &s 280,000 are attained (14, 19). The products are thermoplastic. Ilowever, the effect of temperatures a great deal higher than the softening range is to decompose the polymers, largely to sulfur dioxide and the original olefin, rather than to produce further polymerization and hardening.
375-.100
... ... ...
no
"-A!lrlpI,en"i Allyl ether il-nrumosiiyiijeo2ene Methy! undecylenate Dndecylenyl aiaohol Undee~lenicarid
340 200-5011
...
...
CI
...
...
340
...
...
1.iteratura Referenre
...
... ... ...
...
I.IkXY"S
P"1yf"notio"Rl unsatd. Allyl aino1,oi Allyl ethyl ether Allyl methyl ether Allyl eyapide Allyiseotic acid
Meitins Point'
177
octane and solid carbon diuxid;.' Wlw< the same rs,lely& & used for an extendod tine, inoreasing quant,it,iesof %butene are said to bo formed. The butcnc so prepared oont.ained at, least 85 oer cent I-butene and litt,le imourits other than 2-butcnes. ~-ELTENE was prepared by .dcli);drating Eastman's best grade of sec-l,utanol with 03 per cent sulfuric acid at 90-130" C. Tire eas >+-asscrrihhed with cold 63 Der rent sulfuric acid and dilutg sodium hydruxidc solution. dr;rcl over calcium eliloride. and condensed.
INDUSTRIAL AND ENGINEERING CHEMISTRY
178
ISOBUTENE was prepared by dehydrating Eastman's best tert-butanol by heating with oxalic acid, washing the gas with dilute sodium hydroxide solutions, drying over calcium chloride, and condensing. Oxalic acid dehydrates the tertiary alcohol specifically and gives a very pure product. ~-PENTENE was first prepared in small quantities by the Grignard method. Larger quantities were then made by dehydrating n-amyl alcohol obtained from the Sharples Solvents Corporation over activated aluminum oxide at 375400' C. This product was washed with strong caustic, rinsed, dried over calcium chloride, and twice refractionated through efficient columns. About a pound of sodium hydroxide pellets was added to the kettle of the still before beginning the fractionation for the purpose of polymerizing the small quantities of aldehydes formed by dehydrogenation. ~-PENTENE was made by dehydrating Eastman's best secamyl alcohol with 63 per cent sulfuric acid at 90-130' C., washing with cold 63 per cent sulfuric acid followed by a caustic wash, drying with calcium chloride, and refractionating. ISOPROPYLETHYLENE was made by the Grignard method and was carefully fractionated in an analytical column of the Podbielniak type. SULFUR DIOXIDE of refrigerating grade was used without further purification. The following petroleum products were also used as olefin reactants in the experiments: n-butane and n-pentane dehydrogenated over a chromium oxide gel catalyst under conditions giving 20-25 per cent of normal olefins in the product; a propane-pro ylene traction of the gases of a liquid-phase crackfractions of gases from liquid-phase and vaporing still; phase cracking stills after treatment t o eliminate isobutene; and 2-butene made by treating the Cq fraction of gases from liquid-phase cracking stills with strong sulfuric acid, and separating, diluting, and heating the acid extract.
&
Experimental Procedure Most of the small-scale resin-forming reactions were carried out in Pyrex glass tubes sealed at the bottom and bearing a tube with a 3-5 mm. diameter neck a t the top, which could be readily sealed by a flame after filling. The tubes were 15 to 30 cm. long to facilitate cooling in a Dewar flask filed with liquid nitrogen or solid carbon dioxide, and varied from a few millimeters to 5 cm. in diameter, depending upon the quantity of product desired and the vapor pressure to be withstood. When a catalyst was used, it was introduced first. The tube was then connected to a manifold bearing connections to a vacuum pump, closed manometer, and cylinders of olefins and of sulfur dioxide. Usually the tube was cooled in liquid nitrogen while being evacuated. Approximately equal liquid volumes of olefin and sulfur dioxide were then condensed in the tube, which was again evacuated a n d sealed with a torch. Equal volumes of solidified olefin and sulfur dioxide1 correspond to about 2 moles of sulfur dioxide to 1 mole of a simple olefin. This excess of sulfur . dioxide was found desirable because most of the resins which are insoluble in the reaction mixture tend to carry down dissolved sulfur dioxide, thereby depleting the olefin-sulfur dioxide liquid phase in which the reaction takes place. In the case of the more soluble resins, excess of sulfur dioxide maintains a fluid condition throughout the reaction. After being sealed, the tubes were allowed to warm in the dark. As soon as the contents of the tube had melted, they were thoroughly mixed and were then brought to the desired conditions of the experiment. At the end of the reaction the tubes were cooled to about - 10" C., opened, and allowed to warm to room temperature so that the unreacted olefin and sulfur dioxide could escape. Experiments on a larger scale were carried out in cylindrical stainless-steel bombs holding 1 to 4 gallons. To facilitate the removal of solid resin, both ends of the bomb were closed with blind flanges lined with stainless-steel plates 1 When filling at liquid nitrogen temperature, at least 30 per cent of the volume of the tube was left to provide for expansion of the charge in coming to room temperature.
VOL. 30, NO. 2
drawn against lead gaskets. The top flange was fitted with one or two filling tubes closed by Hoke valves. The bomb was evacuated and cooled in a n ice water bath to facilitate filling. The olefins and sulfur dioxide were then passed in as liquids and thoroughly mixed by tumbling the bomb on a shaft in the manner of a n old-fashioned churn. The required amount of catalyst, usually in the form of a n alcoholic solution, was then forced into the bomb, and the contents were again mixed by tumbling. For the rapid propylene reaction which is quite exothermic, it was found advantageous to keep the bomb in the cooling bath for an hour or so after filling. In many cases it was observed that higher conversions could be obtained by adding the catalyst in two or more portions a t intervals than by adding the same total quantity at the start of the reaction. At the end of the experiment the valves were opened, and unreacted olefin and sulfur dioxide were allowed to escape before dissembling the bomb to remove resin.
Scope of the Reaction These experiments have extended our knowledge of the applicability of the reaction to a variety of unsaturated compounds. Sulfur dioxide was successfully reacted with several unsaturated compounds which have not been previously reported to react, and also some which were reported not to react. Some compounds previously reported on have been reacted under new conditions. Isopropylethylene reacted very rapidly with sulfur dioxide in the dark, forming a white, chalky material which softened a t 200" C. It gave unsatisfactory brittle specimens when molded under heat and pressure. Although this reaction proceeded rapidly in the dark without added catalyst, the experiment was performed before the catalytic effect of oxygen and peroxides was discovered, and it is very likely that the mixture contained traces of such catalysts. 2-Pentene and 2-hexene, prepared from the secondary alcohols, were reacted with sulfur dioxide a t 0" C. The resins obtained had noticeably higher softening temperatures and lower solubilities in organic solvents than those of the isomeric 1-olefins, and were more resistant to attack by alkalies. 1-Hexene, 1-heptene, and 1-decene, made by the Grignard reaction, were each reacted with an excess of sulfur dioxide by exposing the mixture to sunlight. The clear solutions gradually increased in viscosity as resin formation proceeded, and finally set to a gel. After removing volatile material the sulfur dioxide-1-hexene resin was found to soften a t 100" C.; the 1-decene resin was soft and rubbery a t room temperature. The sulfur dioxide-1-heptene resin was somewhat softer than the sulfur dioxide-1-hexene resin. An insoluble white resin was obtained from sulfur dioxide and 1,5-hexadiene (diallyl). It could not be molded under pressure a t 185" C. This unconjugated diolefin is interesting because of the possibility of building branched-chain resin molecules. Cyclopentadiene reacted rapidly with sulfur dioxide a t 0" C. in the presence of a catalyst to form an insoluble white polymer. Allyl alcohol and allyl ethyl ether reacted readily in the presence of catalysts; the former gave a resin with favorable molding and mechanical properties. Although Solonina and Staudinger and Ritzenthaler reported that the reaction between sulfur dioxide and unsaturated compounds would not take place in the presence of negative groups such as -COOH, - COOR, and halogens, it was found that allyl acetic acid, undecylenic acid, and methyl undecylenate could be made to react with sulfur dioxide, either photochemically or catalytically. The resin
FEBRUARY, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
products from the last two were soft and rubbery. The sulfur content of the undecylenic acid product was 91.3 per cent of that represented by equimolecular quantities of sulfur dioxide and undecylenic acid. Vinylacetic acid reacted rapidly to form a n insoluble white resin.
The Reaction and Factors Affecting I t
'
The reaction between olefins and sulfur dioxide takes place in the liquid phase. Although in the sunlight-induced reaction one frequently finds a film of resin on the inside of t h e tube above the liquid phase, this resin appears to form from a condensed film of sulfur dioxide and olefin. No formation of resin in the vapor phase proper has been observed. Reaction usually appears to be most rapid in those cases in which a resin is formed which is insoluble in the reaction mixture. For example, a mixture of propylene and sulfur dioxide containing a nitrate catalyst will usually have a n induction period a t 0-10" C. of 5 to 30minutes, during the end of which a uniform turbidity develops throughout the mixture. Thereafter, the reaction proceeds with a rapidly accelerating velocity and may reach 60-70 per cent conversion in 2-3 minutes if temperature is allowed to rise spontaneously. I n the case of higher olefins such as 1-hexene and 1-heptene in which the resin formed remains dissolved in the reaction mixture, the reaction is much slower and may require days for completion. The reaction of olefins with sulfur dioxide is mildly exothermic. The heat developed by the reaction of propylene with sulfur dioxide is noticeably higher than that of the higher olefins. During 60 to 70 per cent conversion of a mixture of equal volumes of liquid sulfur dioxide and propylene, the heat liberated by a rapidly catalyzed reaction raises the temperature of the system to about 88" C. I n the case of 1or 2-butene, the reaction mixture is never self-heated above 40 " C. This is not necessarily an indication of a much smaller heat of reaction but may be due entirely to the slower reaction and lower "ceiling temperature," a peculiarity to be further discussed. For most olefins the reaction is apparently not reversed 100" C. or more above the temperature a t which the heteropolymer forms. The reaction is invariably accompanied by a contraction in volume. A measurement of this property permits a fairly reliable estimate of the state and rate of the reaction, but it may be difficult to measure where a n insoluble resin is formed. I n the case of the normal butenes containing not over 100 per cent excess sulfur dioxide, a heavy clear liquid phase consisting of resin dissolved in sulfur dioxide separates. The extent of conversion can be estimated approximately from the relative volumes of the two liquid phases. The reaction system 1-butene with sufficient excess sulfur dioxide (several hundred per cent) to prevent the separation of a second liquid phase exhibits a n unusual viscosity effect. A Pyrex glass tube with bulbs and a n intervening orifice and containing 1-butene with 800 per cent excess sulfur dioxide was exposed to sunlight. The viscosity, as determined by timing the flow through the orifice, increased rapidly from 3.5 to 70 seconds in a n 80-minute exposure. Then i t began to decrease, a t first rapidly, falling from 70 seconds to 44 se'conds in 80 minutes, then more slowly, reaching 5.6 seconds in 48 hours and 4 seconds in 96 hours. Then more butene was added to reduce the excess sulfur dioxide to 400 per cent. Upon further exposure, the viscosity increased from 3.5 to 100 seconds in the first hour, to 175 seconds in the second hour, and to a maximum of 350 seconds in the fifth hour. Thereafter it fell slowly to 245 seconds in 65 hours.
179
Effect of Catalysts I n every case in which special care was taken to exclude both light and catalysts, no reaction occurred during extended periods of time. Mixtures of sulfur dioxide with propylene and with butenes have stood in the dark a t room temperature for periods of months, in one case for over a year, without a trace of resin forming. It appears, then, that the action of a catalyst in this case is not merely a n acceleration of a sluggish reaction, but that light or a positive catalyst is necessary to initiate the reaction. Many compounds were tested to determine their ability to catalyze the olefin-sulfur dioxide reaction. Most of the catalyst-testing experiments were carried out a t room temperature with equal volumes of sulfur dioxide and 2-butene because of the convenience and ease of preparing and working with that olefin. The solid catalyst was added as a fine powder, or preferably in solution in the alcohol or acetone. As in Seyer and King's work, the first catalyst discovered was oxygen. Following that discovery, great care was taken to exclude oxygen from the reaction mixture when testing other substances as catalysts. Organic peroxides such as benzoyl peroxide, diethyl peroxide, and those occurring in cyclohexene which had been exposed to air for some time were next found to be active. Silver nitrate was a very active catalyst. As little as 0.006 per cent produced a fairly rapid conversion of 2butene, and later experiments proved that i t maintained its activity over much longer periods of time and gave much greater yields of resin than oxygen or the peroxides tested. The effect of the concentration of silver nitrate (per cent by weight of the sulfur dioxide-2-butene mixture) on the rate of conversion is as follows : Concn. of AgNOs by weight 0.006 0.03 0.15
5 hr.
--
Conversion t o Resin16 hr.
%
%
%
66
90 100 100
100
65 65
40 h r .
... ...
In a long series of experiments, catalytic activity for the olefin-sulfur dioxide reaction was shown to be a common property of nitrates which have appreciable solubility in the reaction mixture. The rate of conversion of 2-butene plus sulfur dioxide to resin by equimolecular quantities of four nitrates added as alcoholic solution is shown in Table 11. The effectiveness of the dilute nitric acid catalyst was undoubtedly decreased by reaction with the alcohol used as a solvent in this case. TABLE11. COMPARISON OF EFFECTOF EQUIMOLECULAR PROPORTIONS OF SEVERAL NITRATES
-
Catalyst AgNOa LiNOa NHaNOa HNOa
1.5 hr.
.. .. ..
10
2 hr.
.. 25
..
Per Cent Conversion t o Resin--6 Q 14 18 24 hr. hr. hr. hr. hr. .. 60 100 3
hr.
io
..
3
... ... .. . .. ..
90
100
90
io0
... ... ... ...
96 hr.
120 hr.
:: : : :::
25
ii
io0
A considerable number of nitrates were tested for catalytic activity, as well as a number of other classes of compounds, and the results are listed in Table 111; the more active head the list. Several nitrates which were almost insoluble in the olefinsulfur dioxide mixture initiated a slow conversion to resin after a n extended induction period during which no resin seemed to form. Typical of these are the nitrates of sodium, barium, strontium, lead, cobalt, and titanium. Several organometallic compounds, such as tetraethyllead
INDUSTRIAL AND ENGINEERING CHEMISTRY
180
VOL. 30, NO. 2
TABLE111. PERCENTAGE CONVERSION 4 Hr. Cat alvs t Dilut;! nitric acid Lithium nitrate Ammonium nitrate Ethyl nitrite Beryllium nitrate Potassium nitrate Magnesium perchlorate Perchloric acid Thallium nitrate Calcium nitrate Sodium nitroprusside Phenyl mercuric nitrate Merouric nitrate Triphenyl bismuthine Tetraethyllead Diethvlmercurv Di-n-6utylmeraury Zirconium nitrate Titanium nitrate Sodium nitrite Uranyl acetate Barium nitrate Strontium nitrate Lead nitrate Cobalt nitrate Isoamyl nitrite Sodium chlorate
io6 ... ... ... ... ... ... 0
... ...
...
G Hr.
1 Day
... io0 100 ...
.. .. .. ..
, . .
"i
...
... ...
...
... ...
... ...
... ,.. ... ... ...
... ... ... ...
.. .. .. ... , . .
...
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...
..
,..
...
... ... ... ... ... ,..
...
...
2 Days
t .
io
10
'0
... ... ... ioi) 60 20
...
..
5.
10 12
, . .
, .
50 ... 50
2
30
.. .. ..
5
.. .. .. .. .. .. .. '6
...
,.. ,
3 Days
4 Days
.. ..
..... .. .. ...
..
.. .. ..
.. ..
..
..
10 20
..
15 75 50
..
.
10
...
,.. 5
... ... ,.. ...
, .
0
.. .. .. .. .. .. .. 25
tetraphenyllead, triphenyl bismuthine, di-n-butylmercury, and diethyllead, effected a slow conversion of the sulfur dioxide-2-butene mixture. Ozonized olefins, concentrGted nitric acid, oxygen, hydrogen peroxide, and several other strongly oxidizing materials started the reaction a t low temperatures but rapidly lost their effectiveness a t room temperature. I n most cases the reaction came to a halt when less than 50 per cent of the mixture was converted. The mechanism of the deactivation of these catalysts is probably the oxidation of sulfur dioxide to sulfur trioxide and consequent reduction of the active agent. Traces of sulfuric acid and hydrocarbon polymers have been found in resins formed by such catalysts. The resins usually have more or less color and darken on heating. The presence of alcohol has a beneficial effect in preventing the darkening of the resin, and this may be due to its ability to combine with the sulfur trioxide and sulfuric acid present. The experiments with light and catalysts appear to justify the following conclusions : 1. Light of less than about 3800 A. or a catalyst is necessary t o effect the heteropolymerization of sulfur dioxide and olefins. 2. The catalyst should be soluble in the reaction mixture or react with it to produce a soluble catalyst. The use of solvents such as alcohols, for the catalyst affords a convenient method
for introducing the catalyst. 3. The most effective catalysts are oxidizing or oxygencontaining substances. Whereas strongly oxidizing agents appear to lose their reactivity rapidly by side reactions, mild oxidizing agents, such as nitrates, retain their catalytic activity over an extended reaction time.
Photochemical Reaction The wave length range of light necessary to bring about reaction of 2-butene with sulfur dioxide was roughly ascertained by exposing to outdoor noon sunlight a series of long thin tubes containing a mixture of 2-butene with sulfur dioxide in liquid volume ratio of 1 to 8 The extent of reaction was estimated by measuring the fall in the meniscus of the clear liquid as volume shrinkage took place with polymer formation. The rate of reaction was nearly equal in clear silica and Pyrex glass tubes, indicating little contribution from the shortest wave lengths; it was reduced to onetenth in the presence of a n Aesculine filter which stops wave lengths shorter than approximately 3800 A. About 3000 to 3800 d. embraces the effective range transmitted by the Pyrex glass, and the activation may perhaps be related to the strong absorption of sulfur dioxide in the 3100 8. region.
io6 80 95 75 45
... ... ... ... ... ... ... ... .. 0
... 20
... ... ... ... ...
O F %BUTENE TO RESIN 5 Days 7 Days 9 Days 15 Days 21 Days 26 Days 35 Days45 Days
...
...
... ... I
.
.
...
100 100 90
... ... ...
...
...
'70 20 25
..
6 ... 30 0 0 0 0
.3i) .
..
..
.. .. .. .. .. .. .. 65 ..
.. .. .. .. ..
..
90 90
..
75 30 30
..
..
..
.. .. .. .. ..
20
, .
..
, .
.. G5 .. .. ..
95 80 40 40 17 10
..
..
0 0 0 0
..
35
... ...
... ... I
.
.
...
...
...
io0
100 100 100
95 99
80 70 GO 75 50 10 GO 3 15 0 15 40
...
... ... ...
...
... ... ... ... ... ... ... ... ... ... ...
...
...
... ... ...
'SO
... ..
... .
I
.
...
... ... I
.
.
...
... ... ...
... ... ...
...
...
100
100 90
...
95
100 100 80
... ...
...
12 25 10
...
... 65
...
65 20 40 20 20 85 65
... t . .
...
... ... ...
... , . .
.. .. .. ... ...
100 70 40 40 40
..
..
.. .. .. .. ..
.. .. .. .. .. ..
..
..
.. .. ..
..
.. .. 75 50 45
40
...
...
Effect of Inhibitors I n early attempts to react sulfur dioxide directly with the Cd fraction of gases from liquid-phase cracking stills, which fraction contains all the isomeric butenes and butanes, it was found that the isobutene present inhibited the reaction with the n-butenes. Subsequent experiments with mixtures of synthetic olefins confirmed this observation and shpwed that some other unsymmetrically disubstituted ethylenes were inhibitors as well. The addition of 10 per cent of isobutene to 1-butene slowed down the room temperature reaction with sulfur dioxide to about one-tenth of the normal rate. The isobutene apparently did not enter into the reaction but concentrated in the liquid phase and finally brought the reaction to a stop. This is the more interesting in view of the fact that isobutene was found to react readily itself with sulfur dioxide a t lower temperatures. Isobutene was found to be about equally effective in inhibiting the photochemical and the catalyzed reactions. During 20-day exposure to summer sunlight, mixtures of 75 parts of 2-butene with 25 parts isobutene gave only 15 per cent conversion, and with 25 parts trimethylethylene gave 30 per cent conversion. Mixtures of 2-butene and similar quantities of 2-pentene and 2-hexene gave complete conversion in less than 20 days. Pure 2-butene, under the same conditions, reacted completely in one day or less. A series of experiments was then conducted in which various molar proportions of 2-butene and a branched olefin, mixed with a volume of liquid sulfur dioxide equal to the total volume of liquid hydrocarbon, were used. A quantity of silver nitrate (in saturated alcoholic solution) equal to 0.03 per cent by weight of the olefin-sulfur dioxide mixture was added as catalyst. The conversion to resin was determined by the volume contraction and the relative volumes of the two condensed phases. The results obtained are shown graphically in Figure 1. It is evident that quantities of isobutene in excess of 2 per cent exert a pronounced inhibiting effect. unsym-Methylethylethylene inhibits reaction somewhat less than isobutene. Trimethylethylene is still less effective in low concentrations, and 2-pentene has very little inhibiting effect. I n order to obtain a satisfactory reaction of sulfur dioxide with the n-butenes in the CJ fraction of cracking-still gases, i t was necessary to eliminate 70 per cent or more of the isobutene. Olefm polymers separated from the sulfuric acid used to prepare 2-butene were moderate inhibitors. Some of the experiments indicated also that olefin polymers and oxida-
FEBRUARY, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
181
100
90
80
70
en Ya I-
s
60
50
u
40
30 A-0 5%
ISOBUTYLENE
20 A- IO % 2-PENTENE
IO
TIME OF REACTION IN DAYS
EFFECT OF VARIOUS OLEFINS FIGURE 1. INHIBITORY
tion products generated in a n olefin-sulfur dioxide mixture by a strong oxidizing catalyst such as hydrogen peroxide and strong nitric acid are likewise inhibitors, but this has not been definitely proved. Hydrogen sulfide and methyl mercaptan were found to inhibit the sunlight reaction. Hydrogen sulfide gives free sulfur by reaction with the sulfur dioxide. None of the lower alcohols which might be present in the olefins or formed by hydration inhibited the reaction. Paraffins acted mainly as diluents, reducing the effective concentration of olefins and slowing down the reaction.
Effect of Proportions of Sulfur Dioxide and Olefins It was thought that the character of the product with regard to degree of polymerization, toughness, etc., could be controlled over a considerable range by varying the proportions of the reactants. Since the resin is soluble in sulfur dioxide and not in butene, the resin molecules should be retained in the liquid phase longer, the greater the sulfur dioxide concentration. A series of mixtures was reacted in which the ratio of sulfur dioxide to 2-butene ranged from 0.5 to 7.5 moles, both in the sunlight and in the presence of catalysts. No marked or consistent differences were found in the appearance, molding properties, or mechanical strength of the resins produced. In the case of propylene, however, somewhat better results were obtained by using a larger than fheoretical ratio of sulfur dioxide to olefin u p to 3 moles sulfur dioxide to 1 mole propylene.
Effect of Temperature These reactions exhibit a very unusual temperature behavior. As stated previously, the only mention in the literature regarding the effect of temperature is that contained in the Mathews a n d Elder patent ( 1 1 ) where it is stated: "Amylene (trimethylethylene or any of the isomeric amylenes) and liquid sulfur dioxide which may conveniently be
taken in equal molecular proportions are mixed together in a closed glass vessel and the combination accelerated either by warming in a water bath at a suitable temperature, say at 50" C., but preferably by exposing to bright sunlight as in the previous examples." This implies that the effect of sunlight is simply to accelerate a slow reaction and that the same effect can be accomplished by heating. The acceleration of a chemical reaction by rise in temperature is of course required by the conventional rules of physical chemistry and is found in the majority of chemical reactions, except the few cases of authentic negative temperature coefficients. The reaction shows abnormal behavior, a t least with regard to a rather sharp upper limit above which reaction does not take place, which the authors have chosen to call the "ceiling temperature." I n order to check the above statement of Mathews and Elder, mixtures of equal volumes of sulfur dioxide a n d 1pentene, 2-pentene1 trimethylethylene, and unsym-methylethylethylene were sealed in Pyrex glass tubes without catalyst and were heated a t 50-60" C. in diffused light. No resin formed in any of the tubes during 3 weeks. I n order to react 2-pentene with sulfur dioxide catalytically, it was necessary to keep the temperature well below that of the room. Isobutene was likewise found to require a subatmospherio temperature to react. Isobutene and sulfur dioxide were sealed in a glass tube containing a little alcoholic lithium nitrate. The behavior of isobutene was fairly typical, and the reaction was easily followed by inspection, since the resin is insoluble and separates from solution as reaction takes place. At room temperature no reaction was apparent. On cooling to 4" C., reaction took place steadily; on warming to room temperature, reaction stopped; and on cooling again ' C., reaction began again. The tube containing the to 4 material, still mostly unreacted, was maintained a t 8.5" to 9.5" C. for 36 hours, and very little, if any, further reaction took place. On cooling to 2-3" C. and maintaining a t this level, reaction set in at once and went to virtual completion in several hours. This anomalous temperature effect will be dealt with in a future paper.
INDUSTRIAL AND ENGINEERING CHEMISTRY
182
TABLEIV.
%e:$ Propylene Propylene Propylene Propylene 2 parts SOz to 1 propylene 5 parts SO2 to 1 propylene 10 parts 8 0 %t o 1 propylene 92 propylene, 8% 1-butene 84 propylene 16 1-butene 7 5 g propylene: 25% 1-butene 50% propylene, 50% 1-butene
1.49-1.51
.......
.......
....... ....... ....... ,
., ., ,.
....... ..,,. ..... . . .
..... . . . . .. . . . . .. . . . . .. .... 2-Butene %Butene 2-Butene 50% 2-butene, 50% 1-butene 1-Butene 1-Butene 1-Butene from n-butyl chloride Allyl alcohol Allvl alcohol 1-Pentene 1-Pentene 1-Pentene Treated refinery butene Acid-regenerated refinery butene 1-Pentene (with paper pulp filler) Mixed butene (with paper pulp filler) ~
1.30- . 3 6
.. .. . . . . .. 1,35- .40 . . . . .. .... ,. .... ....
1.31
...... ....... ....... . . . . . ....... . . . .
VOL. 30, NO. 2
PROPERTIES OF MOLDED RESINS
Tensile Strength
Lb./sq. in. 2000-3200 3200-3685 1800-3950 1800-2575
Compressive Strength
Lb./sq. in. 20,400-23,650
..........
.......... .......... .......... ..........
34813 3733
3343 3780-4300 3820-4260 5615 5929 4330-4415 3820-4080 4070-4200 3360-4370 2792-3715 2800-3820 2465 2800-4200 3100-4000 2300-4460 3820 3200-4100 3113 4298 2400-4100 2355 2100-2350 2100-3190
.......
3200-3450 3330-3955 6408 5500
;‘,“;,”
16,35040,560
..........
..........
15,600 12,050-16,350
.......... .......... ..........
Transverse Strength
Dielectrio Strength Impact (InstantaneStrength ous) per Mi1 Energy Thickness Hardness Ft. Ib. f o r an in. SQ. Volts Brinell N o .
Lb./sq. in. 2000-t i_O_O_O 1.43-1.72 4 1 0 _ 0 1 6 i ~ ~ 1.84-1.96 OZ89
5380 5330-54+4 4080-6195 6000-7150 7100-7980 6570-8450 7210-8050 5910-7000 4900-5290 4800-6900 6530-6720 3650-4960 4235-5700 5135-5520 4730-6025 4845-5150 4730 4800-6000 4100-4250
....... .......
.......
....... ....... ....... 1.42-1.76 .......
1.50-1.92 1.42-1.83 1.68-1.79 1.74-1.98 1.77-1.82 1.73-1.77 1.49-1.81 1.37-1.54 1.78-1.88
.....
...
,..
389-393 3.47-381
...
.....
...
...
372-417 36 1-40 1
...
.....
.........
.........
0.279-0.297 0.347-0.378
........
0.357-0.372 0.477-0.490
0.695-0.748
1.85 1.14-1.18
.....
...
...
.........
329-360
20-23
..... ..... 355-369 ..... .....
35-40 18-19
0,315-0.345
.....
...
.........
.......
.......
3600-4300 3190-4295
12,350-15,100
4600-5280 3550-4375
0,665-1.26 0.95-1.32 1.12-1.20 1.08-1.11
....... .......
......... ......... ......... .........
... ... ... ... ... ...
25-30
12,350-13,350 12,350-15,350
..........
...
.....
1.16-1.26
.......... ..........
0,262-0.285
346-358
.......
3745-7050
.......
..... ..... ..... ..... .....
%
40
1.47-1.73 1.69-1.83
..........
..........
338-381
Moie t u p
Absorption in 48 Hr.
.......
....... 3.94 4.57
.....
..... .....
...
... ...
.........
......... 0.371-0.398
.........
.........
...
... ... ... ... ...
..... ..... .....
......... ......... .........
......... .........
The Products
Literature Cited
Many of the polymers produced by the olefin-sulfur dioxide reaction were found to be thermoplastic resins, and coherent moldings were obtained, in some instances quite colorless and transparent. The resins produced from the 1-olefins vary in steady steps as the molecular weight of the olefin increases from that of ethylene, which has a n extremely high softening temperature and is insoluble in practically all organic solvents, to that of 1-decene which is soft and rubbery a t ordinary temperatures and is soluble in many organic solvents. The resins of 2-olefins have higher softening points, are less soluble in solvents, and are more resistant to alkalies than are those of the isomeric 1-olefins. Although the resins are decomposed by heating well above the softening points, there are fairly wide ranges of temperature within which they can be satisfactorily molded under pressure. Propylene resin can be molded in the range 180-200’ C., and n-butene resins in the range 125-180” C. Table IV shows the values obtained by standard A. S. T. M. tests of the mplded resins derived from various olefins. Under proper conditions a rather high degree of toughness and of hardness is obtained, and with variation in the olefin species reacted, widely varying mechanical properties are produced.
(1) Backer and Botema, Rec. trav. chim., 51, 294 (1932). (2) Backer and Strateng, Ibid., 53, 525 (1934). (2A) Badische Anilin- und Soda-Fabrik, German Patent 236,386 (1910). (3) Bruin. G. de. 1. erslao. A k a d . Wetenschazmen. 23. 445 (1914). (4) Eigenberger, J . p r a k i Chem., 127, 307 (1930); 129, 312’(1931). (5) Fitch, U. S. Patent 2,045,592 (1936). (6) Frederick, Cogan, and Marvel, J . Am. Chem. Soc., 56, 1816. (1934). (7) Friedl, German Patent 236,386; Fortschr. Teerfarb-Fabrik, 10, 1908 (1910). (8) Glavis, Rydan, and Marvel, S. Am. Chem. SOC.,59, 707 (1937). (9) Hoffman and Damm, Chem. Zentr., 97, I, 2342 (1926). (10) Hunt and Marvel, J. Am. Chem. SOC.,57, 1691 (1935). (11) Mathews and Elder, British Patent 11,635 (1914). (12) Perkins, Canadian Patent 329,043 (1933). 59, 1014 (1937). (13) Ryden, Glavis, and Marvel, S.Am. Chem. SOC., (14) Ryden and Marvel, Ibid., 57, 2311 (1935). (15) Ibid., 58, 2047 (1936). (16) Sever and Kine. Ibid.. 55. 3140 (1933). i17j Soionins, J . Russ. Phys.’ Chem.’ Soc., 30, 826 (1898); Chem. Zentr., (I) 249 (1899). (18) Staudinger, German Patent 606,839 (1929) ; French Patent 698,857 (1930). (19) Staudingy and Ritzenthaler, Ber., 68B, 455 (1935). RglCEIVED November 9, 1937.
Acknowledgment The authors wish to express their sincere thanks to G. G. OberfelI, vice president, and R. C. Alden, director of research, Phillips Petroleum Company, for permission to publish the information contained in this paper; to the late L. H. Fitch, Jr., for rediscovering the reaction and conducting many of the early experiments; to Harold Hepp and L. V. Chaney for their studies of the chemical reaction; to Paul A. Bury for preparing resins on a large scale and molding and testing; and to W. A. Schulze, A. E. Buell, and W. H. Wood for synthesizing several of the hydrocarbons used.
Acid Pulping of Southern PineCorrection In Table I11 of the article on the above subject, which appeared on pages 15 to 20 of the January, 1938, issue, an error occurred in footnotea. The footnote should read: “Grams ovendry pulp per 100 grams liquor.” CHARLESCARPENTER FRANKMCCALL
