100-
-+-
O A M B E R L Y S T - 1 5 RESIN
z
A A C T I V A T E D CHARCOAL
W
3 -I LL
-z
84-
0 LL
z
u
+
60
W z
-
a -I U. W. U
5
40-
v I
I
I
5
20
-
0 0
2
4
6
I 8
1
I
10
12
T I M E (HOURS)
Figure 1. Comparative removal of DMMP from a humidifled air stream by resin and by charcoal Bed volume 25 ml.; bed t e m p e r a t u r e 70“ C.; 4.8 liters air/min.; 1.7 mg. DMMPlliter air; 6.2 mg. HzO/liter air
carried out with the same volume (10.7 grams) of activated charcoal. Under similar conditions no D M M P was observed in the effluent from the charcoal bed for about 6 hours, as shown in Figure 1. However, in both cases after 10 hours the effluent D M M P concentration was approximately 98$, of the inlet value. No D M M P was desorbed from either a n Amberlyst-15 resin bed or a n equal volume of activated charcoal, each of which initially contained an amount of D M M P approximately equivalent to one-half its capacity, by a 507, R H fresh air stream flowing a t a rate of 4.5 liters per minute for 26 hours. Some additional studies were made in a n attempt to determine the process by which the resin removed D M M P from the air stream. At the conclusion of a run, such as that shown in Figure 1, the “spent” resin bed was extracted with acetone. Infrared analysis of the acetone extract showed that 5.43 grams of D M M P had been recovered. A graphical integration of a plot of effluent D M M P us. time indicated that 5.32
grams of D M M P should have been retained on the resin bed. There appeared to be complete recovery, within experimental error, and hence no chemical change in the sorbed DMAMP. Direct titration of the unused, washed resin with standard base showed that the capacity of the Amberlyst-15 resin was 3.91 meq. of acid per gram. After the run shown in Figure 1 the spent resin bed was extracted with water. T h e capacity of the used resin bed was redetermined and found to be 3.83 meq. of acid per gram of resin. Such close agreement with the result obtained with the unused resin suggested that no permanent change in the resin had occurred. As a further check on this point the used resin was recharged with acid, washed, and subjected to a repetition of the test with a 507, R H air stream containing 1.7 mg. of D M M P per liter at a flow rate of 4.8 liters per minute. T h e original ability of the resin to remove D M M P had returned, since no D M M P appeared in the effluent from the bed until after 5 hours on stream Although no hydrolysis of the ester appeared to have occurred, as indicated by the complete recovery of the D M M P from the resin by acetone extraction, an approximate correlation existed between the amount of D M M P retained by the resin (5.4 grams or 44 mmoles) and that which would be expected on the basis of the resin capacity (14 x 3.9 or 55 meq.) if one D M M P molecule were absorbed by each exchange site of the resin. Some of the D M M P molecules may have occupied more than one exchange site, or the entire resin bed may not have been completely utilized because of the relatively high rate of “throughput” of the air stream. It is less likely that a purely physical adsorption on the surface of the Amberlyst-15 resin accounts for its behavior toward D M M P , since the resin shows approximatelv the same capacity for D M M P as does an equal volume of activated charcoal, although the surface area of the charcoal is more than 20-fold greater than that of the resin (40 to 50 sq. meters per gram for Amberlyst-15 us. 1200 to 1400 for activated charcoal). literature Cited
( 1 ) Kunin, R., Meitzner, E., Bortnick: N., J . .4m. Chem. SOC.84 305 (1962). (2) Kunin, R.,Meitzner, E. F.: Oline, J. A , , Fisher, S..4., Frisch, N., IND.ENG. CHEM.PROD.RES.DEVELOP. 1, 140 (1962).
RECEIVED for review August 9, 1965 ACCEPTED December 22, 1965
ISOCYANURATE S Y N T H E S E S VIA T R I ET HY LEN ED I A M I N E - C O C A T A L Y S T CO M BI N A T I O N S .
B E I T C H M A N , Houdry Process and Chemical Co., .Marcus Hook, Pa.
are a class of compounds which have high
catalysts. A number of references on isocyanate trimerization have been cited in review articles on isocyanate chemistry (7, 9 ) . In an attempt to prepare copolymers of isocyanates and olefin oxides by the action of triethylenediamine (sold commercially under the name DABCO by the Houdry Process and Chemical Co., a Division of Air Products and Chemicals,
6U R T 0 N D SOCYANGRATES
I thermal stability and, as such, have potential applications in the development of high temperature polymers (70) or in the modification of better known polymers, such as polyurethanes (2-7. 72). Many procedures have been described for preparing isocyanurates. the most common being the trimerization of isocyanates by the action of various
VOL. 5
NO. 1
MARCH 1966
35
Combinations of triethylenediamine and various cocatalysts (olefin oxides, aldehydes and alkylenimines) are extremely active catalysts for trimerization of isocyanates. Olefin oxides and aldehydes of lower molecular weight were significantly more active as cocatalysts than the higher homologs. The combination of triethylenediarnine and N-methylethylenimine was the most active catalyst observed. Adducts of ethylenimine (ureides or phosphine oxides), which are less volatile and easier to handle than ethylenimine, also proved to be active cocatalysts. The triethylenediamine-olefin oxide-catalyzed reaction i s characterized b y an induction period, followed b y a rapid consumption of isocyanate. Kinetic studies indicated that the reaction was approximately first-order in isocyanate. The observed autocatalysis may be a result of the establishment of a steady-state concentration of a transitory intermediate, involving the catalyst and one or two isocyanate molecules. Several possible mechanisms to account for the catalytic nature of triethylenediamine-cocatalyst combinations are considered.
Inc.), it was found that the isocyanate underwent an extremely rapid trimerization to triphenyl isocyanurate. A search of the literature indicated that Jones and Savi11 ( 7 7 ) had described the effect of alkylene oxides and catalytic amounts of pyridine on this trimerization reaction. These authors postulated a zwitterion structure (I) to be the active
I catalytic species. It was of interest to us to determine the relative catalytic efficiency of triethylenediamine-olefin oxide combinations us. combinations with other amines and to determine whether cocatalysts other than olefin oxides could be effectively employed. This report describes our studies of the trimerization of isocyanates using catalysts comprised of amines (primarily triethylenediamine) and cocatalysts (principally olefin oxides, aldehydes, or alkylenimines) . Experimental Procedures
Determination of Relative Effectiveness of CatalystCocatalyst Combinations. To determine the relative effectiveness of various amine-cocatalyst combinations, a fixed quantity of TDI-80 (an 80-20 mixture of 2>4-and 2,6-tolylene diisocyanate) was stirred with the catalyst mixture and the temperature recorded with a manual potentiometer. T h e time required to reach the maximum exotherm temperature or to produce complete solidification of the mixture into a solid plastic mass was noted. With active catalyst combinations, TDI-80 solidified at the peak of the exotherm or shortly afterwards. Effect of Triethylenediamine Alone on Isocyanates. Phenyl isocyanate (3.0 grams) and triethylenediamine (0.3 gram) were placed in a capped vial and allowed to stand overnight. A crystalline product formed, which was filtered off and washed with toluene. T h e crude product (1.0 gram) was recrystallized once from toluene. The product was identified as the dimer of phenyl isocyanate by its melting point (173’ C., reported value 175’ C.) ( 7 ) and by the characteristic infrared absorption bands for the dimer a t 5.54 and near 7.2 microns. Trimerization of Phenyl Isocyanate with a Triethylenediamine-Propylene Oxide Catalyst Combination. Phenyl isocyanate (9.8 grams) and propylene oxide (10.0 grams) were placed in an Erlenmeyer flask. Triethylenediamine (0.1 gram) was added and the mixture shaken. Within several minutes. an exothermic reaction occurred, and the reaction mixture solidified. An infrared spectrum of the product indicated the formation of phenyl isocyanate trimer with the characteristic absorption bands at 5.8 and 7.06 microns. The excessive temperature rise of this trimerization could be avoided by conducting the reaction in benzene solution and by adding phenyl isocyanate slowly to a solution of the catalysts. 36
I B E C PRODUCT RESEARCH A N D DEVELOPMENT
Trimerization of Phenyl Isocyanate via a Triethylenediamine-Trioxymethylene Catalyst Combination. To a mixture of triethylenediamine (0.25 gram, 0.0022 mole) and trioxymethylene (1.0 gram, 0.012 mole) in a flask was added 26.7 grams (0.224 mole) of phenyl isocyanate. After about 10 minutes, an exothermic reaction occurred, resulting in almost complete solidification of the reaction mixture. The mixture was diluted with benzene and filtered. T h e product weighed 22 grams and was identified as triphenyl isocyanurate by its infrared spectrum and melting point (284-84.9’ C., reported value 282’ C.) (70). Rate Studies of Phenyl Isocyanate Polymerization. An aliquot of a stock solution of phenyl isocyanate in benzene (dried over sodium and distilled) was added by syringe to a 100-cc. volumetric flask. Propylene oxide (dried over calcium hydride and distilled) was added and the solution diluted further with benzene. An aliquot of a stock solution of triethylenediamine in benzene was added to the flask and the solution diluted to volume. The flask was shaken and placed in an 80’ F. constant temperature bath. Aliquots (0.5 cc.) were withdrawn periodically and diluted to 10 cc. with benzene, and spectra of the NCO band were taken. Results
Effect of Amine. In comparative studies of the trimerization of phenyl isocyanate with various amines and propylene oxide, triethylenediamine in combination with an olefin oxide was found to be Significantly more active than any other amine-olefin oxide combination examined (Table I). In other studies it was found that a triethylamine-propylene oxide mixture was also much less active than a triethylenediamine-propylene oxide combination. With effective catalyst combinations, the isocyanate generally solidified i n nearly quantitative yield to the isocyanurate product on reaching the peak temperatures or very shortly afterwards. The rate of polymerization can be more accurately measured by determining the amount of residual isocyanate after various
Table 1. Relative Effectiveness of Amines in Amine-Olefin Oxide-Catalyzed Polymerization of isocyanates [In all runs shown, 61 g. (0.35 mole) of TDI-80 and 1.66 g. (0.030 mole) of propylene oxide employed] Time ( M i n . ) to M a x . T f m p . or Solidification OJ Reactant Mass Amine, C. ( M o l e )
Triethylenediamine, 0 . 2 5 (0.0022)
6.0
30,8 butanediamine, 0 . 5 (0.0035) Pyridine, 0 . 2 (0.0025) >75 After 2 hours reactant mass was N-Methylmorpholine, 0 . 2 3 paste-like in consistency (0.0023) 2-Methylimidazole, 1 , O (0.012) After 3 hours reactant mass was a milk-colored liquid N,N,h”,,2:’-Tetramethyl-l,3-
i
26
I
s
\
24
(3
8. z
'
22
6
3
12
9
1 18
15
HOURS
Figure 1 .
Rate of polymerization of isocyanate a t 25.7" C.
Initial concentration.
2,4-Tolylene diirocyanate, 3.51 M Triethylene diamine, 0 . 0 2 2 3 M Propylene oxide A None 0 0.0287M
time intervals. Figure 1 shows two such experiments comparing the relative catalytic efficiency of triethylenediamine us. triethylenediamine plus propylene oxide in the polymerization of phenyl isocyanate. T h e triethylenediamine-propylene oxide-catalyzed reaction exhibited a definite induction period before the reaction appeared. T h e polymerization catalyzed by triethylenediamine alone proceeds a t a much slower rate. Additional rate studies of isocyanate polymerization were conducted a t fixed concentrations of triethylenediamine and propylene oxide and a t several different concentrations of phenyl isocyanate. Each reaction mixture exhibited an initially slow reaction rate, followed by a rapid isocyanate consumption. Results a t four isocyanate concentrations are shown in Figure 2. The half lives-i.e., the times required for 50% conversion-determined from these results are summarized in Table I1 and indicate that the reaction is close to firstorder in isocyanate. Other workers have recently reported that the trimerization reaction is first-order in isocyanate (70). When the propylene oxide concentration was reduced to one tenth, the reaction slowed down to a third (see Figure 3), but the reaction order for the isocyanate concentration remained unity (Table 11). T h e shape of the rate curves sugg a t e d autocatalysis by one of the products or by a transitory complex. Therefore, the effect of the addition of triphenyl isocyanurate or the dimer of phenyl isocyanate on the reaction was determined. However, neither of these compounds had any catalytic effects, as the curves in Figure 4 show when compared with the corresponding rate curves in Figure 2 obtained in the absence of the dimer or trimer. Therefore, one can assume that the observed autocatalysis of the trimerization is a consequence of the establishment of a steadystate concentration of a transitory intermediate which could
INITIAL CONCENTRATIONS OF PHENYL ISOCYANATE
-
0.584 M 0.292 M 0.146M0.0304M-
*3
0
A 0 0
t
/
I
J
0
20
40
60
80
0.0286
0.292 0.146 0.0304 0.293 0.0308
114
0.89
163
0.62
157 345 424
0.64 0.29 0.24
100 120
140
160
180 2 0 0 220
.O
MINUTES
Figure 2 . Polymerization of phenyl isocyanate with 0.0032M triethylenediamine and 0.0286M propylene oxide in benzene solution a t 26-27" C.
be the catalyst-isocyanate complex containing one or two isocyanate molecules. Accordingly, one can visualize the sequence of reactions as follows (C = triethylenediamine-cocatalyst combination, I = isocyanate, T = isocyanurate) :
c + I $c.1 c.1
Table II. Polymerization of Phenyl Isocyanate in Presence of Triethylenediamine and Propylene Oxide in Benzene Solution at 26-27' C. (Triethylenediamine concentration, 0.0032 mole/liter) Phenyl Propylene, Isocyanate, Half Life, Relative Oxide, MolelLiter MolelLiter Min. Rate 0.286 0.584 102 1.oo
/
'2.12
+ISC.I* +I
+
C
+T
Triethylenediamine without olefin oxide was found to be a catalyst for dimerization of phenyl isocyanate The dimer was identified by its infrared spectrum and melting point. Whereas pyridine and triethylenediamine produced dimerization of 2,4-tolylene diisocyanate, triethylamine catalyzed trimerization a t a slow rate. The dimeric product was identified by both its melting point, 157-59" C. (reported value is 156" C.) ( 7 ) and its infrared spectrum. Infrared alone was used to identify the isocyanurate product formed from diisocyanates. VOL. 5
NO. 1
MARCH 1966
37
TY
I
200
100
300
I
I
400
so0
MINUTES
Figure 3. Polymerization of phenyl isocyanate with 0.0032M triethylenediamine and 0.0286M propylene oxide in benzene solution a t
26-27" C. Initial concentrotion of phenyl isocyonote
0
0.293M 0.0308M
0 .5 W K
c-I \
2
PHENYL ISOCYANATE TRIETHYLENEDIAMINE PROPYLENE OXIDE
4
0 W
z 2 a
, ,
--.--
TRIMER
.3
& W 0
z
8
.2
0 z 0
a
L
.I
w 0 L
a 0 I
0
0
IO
20
30
40
50
60
70
80
90
100 110
120
I30
140
150
160
170
IO
MINUTES
figure 4. Polymerization of phenyl isocyanate in presence of phenyl isocyanate dimer and trimer in benzene solution at 26-27' C.
Table 111.
Effectiveness of Various Alkylene Oxides as Isocyanate Polymerization Catalysts [61 g. (0.35 mole) of 2,4-tolylene diisocyanate and 0.25 g. (0.0022
mole) of triethylenediamine employed in all experiments] Alkylene Oxide,
Time to M a x .
Temp., M i n . G. (More) 3.0 Ethylene oxide, 0 . 9 ( 0 . 0 2 ) 6.3 Propylene oxide, 1 .66 8.5 (0.03) 7.7 Butylene 1&oxide, 2.16 (0.03) 16.0 Epichlorohydrin, 2 , 9 6 (0.032) 49.0 Styrene oxide, 3 . 6 0 ( 0 . 0 3 ) Hard brittle resin in 3 Nexohexene oxide, 3 . 0 hours (0.03) Crystalline product on Octylene 1&oxide, 3 , 8 4 standing overnight (0.03)
Max. Temp. Observed, O
c.
207 202
[In all experiments, 0.25 g. (0.0022 mole) of triethylenediamine and 61 g. (0.35 mole) of TDI-80 employed along with karying concentrations of propylene oxide] Propylene Oxzde, G. (Mole)
0.00( 0 0 0 )
164
T h e triethylenediamine-epoxide-catalyzed polymerization of isocyanates could be controlled so as to avoid the violent exothermic reaction by use of a solvent and gradual addition of isocyanate to the reaction mixture. 38
Table IV. Effect of Concentration of Propylene Oxide as a Cocatalyst in Polymerization of Isocyanates
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
0.17 (0.0029) 0.42(0.0072) 0 . 8 3 (0.014) 1.66(0.030) 3.32(0.060) 7.47 (0.129)
Tzme to M a x . Temp. or Exotherm, Mzn. No significant reaction
aft& 6 . 3 hours 30 12.9 8.5 6.3 4.6 3.9
Effect of Various Cocatalysts. OLEFIN OXIDES.Combinations of triethylenediamine with various alkylene oxides were studied for their effectiveness in polymerizing TDI T h e results of this study, shown in Table 111, indicate that the
Table V.
TDI Polymerization with Triethylenediamine (0.25 G., 0.0022 Mole) and Aldehydes
[TDI Aldehyde or Polymeric Aldehyde
Acetaldehyde Butyraldehyde Trioxymethylene Heptaldehyde Benzaldehyde Isodecaldehyde a- Anisaldehyde Paraldehyde 1-Naphthaldehyde
G. (Mole) 2.44(0.055) 4.55 (0.063) 1 . 7 (0.056) 6.33(0.056) 5.88(0.055) 8.74(0.056) 7.55 (0.063) 2.49(0.057) 8.74(0.056)
=
61 g. (0.35 mole)]
Max. Temp., a C.
M i n . to M a x . Temp.
72.8 16 110 45 128 67 53 93 82 69 87 128 70 242 28 , . . (None in first 76 min.)
lower alkylene oxides are much more effective as cocatalysts than the higher homologs. From the results shown in Table 111, it is concluded that the order of cocatalyst efficiency is: butylene oxide-1,2 > Ethylene oxide > propylene oxide epichlorohydrin > styrene oxide > neohexene oxide > octylene 1,%-oxide. T h e effect of alkylene oxide concentration on catalytic activity is shown in Table IV. There appeared to be a leveling off in effectiveness a t a concentration somewhat greater than 2 equivalents of alkylene oxide per nitrogen equivalent of triethylenediamine. This may be d u e to loss of the volatile epoxide during the exotherm or possibly to the interaction of the triethylenediamine with more than 2 equivalents of epoxide, forming a polyether adduct of low molecular weight prior to catalyzing the reaction. Triethylenediamine has been observed to promote formation of l o w molecular weight polyethers when admixed with propylene oxide. ALDEHYDES.Other compounds in combination with amines were thought to be capable of forming catalyst species structurally related to I a n d thus were investigated for their effect on trimerization of isocyanates. T h e structural simi: larity of these catalyst species is discussed below. As shown in Table V, aldehydes c a n also serve as cocatalysts with amines. Again, lower homologs were more efficient as cocatalysts. T h e results of a comparison of various amines with benzaldehyde as a cocatalyst are shown in Table V I . Of the various amines examined, only triethylenediamine in combination with the benzaldehyde gave a polymeric product in a reasonably short time (69 minutes); polymeric products were obtained with two other amines only after standing for a n extended period (overnight). ALKYLENIMINES. Some of the most active catalyst combinations observed for trimerization of isocyanates were those involving combinations of triethylenediamine with alkylenimines (see Table V I I ) . lV-Methylethylenimine alone is a n active polymerization catalyst but in combination with triethylenediamine gave the most active catalyst observed for trimerization of isocyanates. Y-Methylethylenimine is activated to some extent by a n alkylene oxide. T h e lower alkylenimines are volatile a n d toxic. There are adducts of ethylenimine which are commercially available a n d easier to handle. These alkylenimine derivatives could serve as useful cocatalysts with triethylenediamine. T h e effectiveness of several catalyst combinations is demonstrated in Table V I I . None of these imine adducts had appreciable activity when employed alone as catalysts. OTHERCOCATALYSTS. Propylene carbonate (2.93 grams, 0.033 mole) in combination with triethylenediamine (0.25 gram, 0.0022 mole) was considerably less active than other catalyst combinations when mixed with TDI-80 (61 grams, 0.35 mole), but did promote a reaction within a n 1 8 1 / 2 - h o ~ r period. Tsuzuki et al. (73'1 have reported that trimerization
Table VI.
Product Description
Hard yellow solid Pale yellow solid Yellow solid Yellow solid Hard yellow solid Yellow solid Pale yellow solid Copious precipitate overnight Yellow solution on standing overnight
Isocyanate Polymerization with Benzaldehyde and Tertiary Aminesamb
Triethylenediamine Triethylamine
Hard yellow solid Yellow transparent solid overnight 59 26 Yellow transparent solid overnight 33 2 Milkv solution some precipitation No apprecia- Yellow solution some able ternprecipitation perature change 82
44
N,N,X',.V'-Tetramethyl butane 1,3-diarnine N-Meth ylmorpholine Pyridine
69 31
a Corresponding reactions with tertiary amine but with no aldehyde present did not produce hard resins on standing overnight. * In each experiment, 0.0022 mole of amine, 0.055 mole of benzaldehyde, and 0.35 mole of tolylene diisocyanate ( TDI-80) employed.
Table VII. TDI Polymerization with Triethylenediamine and Alkylenimines or Alkylenimine Adducts"sb Alkylenimine or Alkylenimine Adduct
N-Methylethylenimine N-Methylethylenimine N-Methylethylenimine 2-Methylethylenimine 2-Methylethylenimine Ethylenimine Tris-aziridiny phosphine oxidec 1,6-Bis(N,N-ethylenecarbamido )-hexaned 2,4-Bis(N,.V-ethylenecarbamido )-toluene*
G. (Mole) 0 . 3 7 (0.0065) 0.37 (0.0065) 0 . 1 0 (0.0018) 0 , l (0.0018) 0 , 2 (0.0035) 0 . 1 ( 0 0023) 0 , 5 (0.0029)
Time to .Max. M a x . Temp., Temp., (Min.) C.
117 133 141 129
5 4.5
290° C.; product of Chemirad Carp.
of phenyl isocyanate occurs when ethylene carbonate a n d a n amine are employed as catalysts. T h e use of catalytic quantities of P-propiolactone (0.23 gram, 0.0023 mole) with triethylenediamine (0.25 gram, 0.0022 mole) in TDI-80 (61 grams, 0.35 mole) produced a very exothermic reaction with gas evolution a n d resultant polymerization of the isocyanate. I n contrast, trizthylamine (0.25 gram, 0.0022 mole) a n d the same quantity of 8-propiolactone produced a sluggish reaction. T h e reaction mass did not gel even on standing overnight but produced a n amber viscous mass. Tsuzuki et al. (74) have reported that equivalent quantities of isocyanate a n d P-propiolactone react exothermically with each other in the presence of tertiary amines affording CO2, :V>.;?A."-diphenylurea,acrylic anhydride, and acrylVOL. 5
NO. 1
MARCH 1966
39
~~
IO
0
20
2U- 40
50
60
70
80
SO
100
110
120
I30
140
150
160
I70
MINUTES
Figure 5. Polymerization of 0.588M phenyl isocyanate with 0.0032M triethylenediamine and 0.286M propylene oxide in benzene solution a t 26-27' C.
A
No H 2 0 added
0 0.096M
anilide and that trimerization of the isocyanate occurs under some conditions. T h e experiments performed in our work were conducted with catalytic quantities of the P-propiolactone and trimerization (especially with triethylenediamine) may have been the predominant reaction. Ketones (such as acetone a n d methyl isobutyl ketone), ethers! such as Ansul 141 (diethylene glycol dimethyl ether), tetrahydrofuran and dioxane, an ester (ethyl acetate), a n d a nitrile (acetonitrile) did not produce significant activating effects. T h e Ansul 141, however, caused ultimate formation of a hard yellow plastic-like material on standing overnight. An orthoester, triethyl orthoformate, had a slight activating effect on triethylenediamine. 2-Methylimidazole appears to act synergistically with triethylenediamine in isocyanate polymerization. Triphenyl isocyanurate, melting a t 284-87' C . , was obtained from phenyl isocyanate by employing this catalyst combination. Studies of Mechanism of Catalysis. Jones and Savill ( 1 7 ) have postulated that amines a n d olefin oxides form zwitterions ()Ne--CH2CH20") which are the active catalyst species for trimerization of isocyanates. By analogy the active catalyst species for the amine-imine combinations should have the structure :
S-cH?-cH?-&R / I
R = H, alkyl or other groups, -PO,,
/
or ureido groups T h e active species formed with aldehydes would then presumably be :
R
\
-N-
I
- -CH-0
/a -
6-
I n reactions of propiolactone with isocyanates in the presence of amine catalysts, Tsuzuki et al. (74) have proposed formation of the betaine: e
@
R ,N--CH 2-CH
z-CO--O
Isocvanate trirnerization was observed to occur when pyridine 40
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
H20
was employed as a catalyst or when acetonitrile was employed as a solvent with ,l'-methylmorpholine as the catalyst. Another possibility for the active species in amine-olefin oxide combinations is the formation of a quaternary hydroxide. Triethylenediamine reacts with 2 equivalents each of propylene oxide and water to form a diquaternary hydroxide ( 8 ):
CHS
CH3 HO-HC-CHg-N
OH -
A I /T N-CH2-CH-OH
-uOH -
This base, although not easily soluble in TDI-80, readily polymerizes this diisocyanate. T h e TDI-80 was polymerized in 41/'2 to 5 minutes by 1% of the diquaternary hydroxide (based on the weight of the isocyanate). I n view of the catalytic effect of this diquaternary hydroxide on polyrnerization, the effect of water on the reaction was examined further. Sublimed triethylenediamine and dry, distilled propylene oxide were prepared in reaction tubes under vacuum. Phenyl isocyanate was added to the reaction tubes with a syringe. I n one case, the rapid exothermic reaction generally produced by this cataly-st combination did not occur for more than 4l/2 hours. Repetition of this experiment, however, resulted in a n almost instantaneous reaction. A third trial resulted in the exothermic reaction occurring in 1 hour and 1 3 minutes. These experiments suggest that trace amounts of water may be necessary for an active catalyst combination. Triethylenediamine is known to be hygroscopic and some of the diquaternary hydroxide may be present in the catalyst mixture. Addition of water in more than trace amounts, however, did not shorten the induction period for the reaction (see Figure 5). Comparison of the same quantities of a catalyst solution of triethylenediamine and propylene oxide in dioxane, one freshly prepared and the other aged for 21 minutes, showed no significant difference in catalytic activity. Thus the induction period observed in these exothermic reactions was not attributed to a buildup of a catalyst complex of triethylenediamine and epoxide. I n another series of experiments, a study was made of the catalytic activity of the products of a triethylenediamine-
butylene oxide niix as a function of the time during which these components are in contact. These components on standing formed a bro\vn gummy sirup. 7’he supernatant liquid retained its catalytic activity. perhaps even having slightly greater activity, on standing for a day. ‘ I h e brown gummy 5irup which had formed during this same period of one day was not nearly as active as the supernatant solution; however. ‘lDI-80 did form a product in its presence on standing overnight. O n the basis of our results, it appears that these gummy products d o not contain the active catalyst species. Earlier Xvork in our 1aboraror)- has shown. as indicated earlier, that these gummy products contained low molecular \veight polye thers. If, in fact, a zwitterion species is formed from a n amine and olefin oxide, it would appear that this intermediate has a n extremely loose association brt\veen the tkvo components, as \vas demonstrated by the following experiment. Triethylenediamine (6.6 grams) and propylene oxide (29.9 grams) Lvere mixed and allowed to stand in a closed vessel for 14 minutes. An aliquot of this solution (1.7 cc.) was pipetted into a flask, containing ‘TDI-80 (61 grams). Another aliquot (1.9 cc.) \vas placed in a flask, connected to a rotary evaporator, and pumped off a t room temperature bvith water aspirator vacuum. T h e solution added to the TDI-80 produced reaction in 14 minutes. T h e evacuated aliquot on treatment with TDI-80 gave no indication of reaction in 2 hours, but when this mixture was treated with additional propylene oxide (2.0 ml.), a n exothermic reaction occurred in less than 5 minutes. If the zwitterion ( I ) is the active species, the association between amine and olefin oxide must be a weak one. Other possible explanations for the catalytic nature of this reaction which may be considered are : Formation of an unstable complex of olefin oxide and isocyanate due to the catalytic effect of triethylenediamine. Formation of an unstable molecular complex of triethylenediamine, olefin oxide, and isocyanate.
Miscellaneous Polymerizations and Copolymerizations. Attempts to extend the olefin oxide-triethylenediaminecatalyzed trimerization to aliphatic isocyanates (n-propyl isocyanate) or to phenyl isothiocyanate failed to give trimeric products. Similarly, attempted copolymerizations of these Compounds with phenyl isocyanate resulted in the isolation of triphenyl isocyanurate as the only product. Acknowledgment
T h e author thanks the Houdry Process and Chemical Co., Division of .4ir Products and Chemicals, Inc., for permission to publish this paper. He also acknowledges with gratitude the suggestions received from A. Farkas during the course of this work. literature Cited ( 1 ) .\mold, K. G , , Nelson, J. A , , Verbanc, J. J., Chem. Revs. 57, 47 (1957). ( 2 ) I3eitchnian. B. D. (to Air Products and Chemicals, Inc.), U. S. Patent 3,146,219 (hug. 25. 1964). 13) Ibzd.. 3.154.522 fOct. 27. 1964) ( 4 ) Ibzd., 311791626 (April 20, 1965). ( 5 ) Heitchman, H. D., Erner. \V. E. (to Air Products and Chemicals. Inc.), Ibzd.,3,168,483 iFeb. 2, 1965). ( 6 ) Heitchman, B. D., Krause, J. H. (to .4ir Products and Chemicals. Inc.). Ihid..3.179.628 (Aoril 20. 1965). ( 7 ) Rurkus.”J. ( c o knifed St& Rubber ’Co.), Ibid., 2,979,485 (April 11, 1961). ( 8 ) I h e r , W. I:. ( t o Houdry Process Corp.), Ibid., 3,010,963 (Kov. 28, 1961). ( 9 ) Farkas. X.. Mills. G. A , . Advan. Catalvsis 13. 393 11962). ( 1 0 ) Gilman, ‘L.. O’Connell, J. J., Hathaway, C. E., (Vurster, C. F., Technical Documentary Rept. No. ASD-TDR-63-396 (April 1963). ( 1 1 ) Jones, J. I., Savill, N. G., J . Chem. Soc. 1957, 4392. (12) Xicholas, L., Gmitter, G. T., J . Cellular Plastics 1, No. 1, 85 (1965). (13) Tsuzuki, K., Ichikawa, K., Kase, M., J . Org. Chem. 25, 1009 ( 1 960). ( 1 4 ) Ibid., 26, 1808 (1961).
RECEIVED for review October 26; 1965 ACCEPTED December 29, 1965
COLLOIDAL OXYCELLULOSE BY NITROGEN DIOXIDE TREATMENT OF LEVEL-OFF DEGREE OF POLYMERIZATION CELLULOSE A L A N
M . BELFORT A N D
R O B E R T B . W O R T 2
Avzcel Laboratory, Amprzcan Viscose Dtuiszon, F M C Gorp., M a r c u s Hook, Pa.
microcrystalline cellulose (FMC Corp., Marcus Hook, Pa.) is level-off degree of polymerization cellulose obtained from acid hydrolysis of high purity a-cellulose pulp. T h e term “level-off degree of polymerization” refers to the relatively constant value of degree of polymerization which results when cellulose is subjected to severe acid hydrolysise.g., 2 . 5 s hydrochloric acid solution at the boil for 15 minutes. Aqueous gels can be prepared from this product by mechanical attrition of high solids wet cakes. Centrifugation of gels yields a minor fraction consisting of cellulose microcrystals which measure approximately 0.1 micron in length and 0.01 micron in thickness. vrEL
A
T h e flow properties of fractionated microcrystalline cellulose gels were studied by Hermans (5). Shear stress was measured as a function of the shear rate with a Couette viscometer. T h e rheology of the fractionated gels is similar to the rheology of certain clay systems ( 3 ) :wherein each elongated particle is in contact cvith a few others. ’The greater stiffness and viscosity of these gels depend on the increased content of colloidal rigid particles. A continuing objective of this laboratory is to increase the colloidal nature of gels from microcrystalline cellulose. Mechanical attrition is one approach to produce colloidal gels, but it is inefficient. Chemical means Lvere sought to reduce VOL.
5
NO. 1
MARCH 1966
41
