the alcohol that was vinylated had a pronounced effect on reaction rate and also on catalyst life. As shown in Table 111, the general trend of vapor phase vinylation with the most active catalysts goes best with primary alcohols, such as methyl. ethyl, n-octyl, n-dodecyl. and 2-aminoethyl. Poorer results were obtained with secondary alcohols. Vinylation of tertiary alcohols, as typified by 2-methyl-2-propanol. proceeded at a much lower rate than secondary alcohols. .411 results reported are based on acetylene. M’hen Iields of methyl, ethyl. and isopropyl vinyl ethers are calculated on the alcohol. they are higher than the yields shown in Table 111. In these experiments, the alkyl vinyl ether plus alcohol totaled 95 to 98y0 of the reaction product, which indicated very little by-product formation. The material balance based upon weight in and out was usually 95 to 10070. Catalyst life with the most active catalysts (Table 111) was found to be much longer during the vinylation of methanol than ethanol or 2-propanol. Vinylation of 2-methyl-2-
propanol was difficult to achieve and catalysts were prone to rapid and often immediate deactivation. Similarly, phenol which contains an acidic hydroxyl group, was found to vinylate poorly in the presence of basic catalysts. literature Cited
(1) Copenhaver, J. W., Bigelow, M. H., “Acetylene and Carbon Monoxide Chemistry,” p. 32, Reinhold, New York, 1949. (2) Ghosh, J. C., Bhattacharyya, S. K., Chaudhuri, D. K. R.: Petroleum (London) 19, 358 (1956). (3) Hanford, W.E., Fuller, D. L., Ind. Eng. Chem. 40, 1171 (1948). (4) Harshman, R. C., Dtssertation Abrtr. 18, 538 (1958). (5) Reppe, W.,Ann. 601, 81 (1956). (6) Reppe, W. (to I. G. Farbenindustrie), L.S. Patent 1,959,927 (May 22, 1934). (7) Reppe, W., Wolff, W. (to I. G. Farbenindustrie), Ibzd., 2,066,076 (Dec. 29, 1936). (8) Schildknecht, C. E., “Vinyl and Related Polymers,” p. 593, Wiley, New York, 1952. RECEIVED for review May 23, 1963 ACCEPTED August 19, 1963
VINYL ETHERS OF DIETHYLENE GLYCOL R . L. Z I M M E R M A N , G. D. JONES, A N D W. R. NUM-MY The Dow Chemical Co., Midland, Mich.
Diethylene glycol was made to react with acetylene in the presence of a basic catalyst; by operating a t low conversion and separating the mixture by distillation and extraction with water, both the monovinyl ether and the divinyl ether of diethylene glycol were obtained in good purity and characterized. Additives for inhibition or stabilization were investigated. Reactions of the vinyl ether group were investigated, including the free radical-catalyzed addition of hydrogen sulfide, which in the case of the divinyl ether of diethylene glycol yields a tetraethylene glycol dithiol. Homopolymers and copolymers of the monovinyl ether of diethylene glycol were produced by free radical initiation and a series of rubbery copolymers was cured with a rubber vulcanization recipe. Copolymers of the divinyl ether of diethylene glycol were prepared wherein the second vinyl ether group was available for secondary reaction.
synthesis of vinyl ethers of glycols by the reaction of Tacetylene with glycol (Equation 1) HE
HC=CH
+ HOROH
KOH
+
CHe=CHOROH CH2=CHOROCH=CH?
(1 )
in the presence of a basic catalyst is a n attractive reaction from the standpoint of utilization of glycols and acetylene and the production of potentially cheap and unique monomers. Interest by the authors in the possibility of large scale commercialization resulted in the present review and investigation of the synthesis, reactions, and polymerization of diethylene glycol vinyl ethers. Divinyl ether of diethylene glycol is now being sold as a chemical specialty, whereas the monovinyl ether is not known to be available commercially. Monovinyl ether of ethylene glycol was first reported by Hill and Pidgeon ( 6 ) , and using the vinylation reaction, later by Reppe (72-74), who also reported the divinyl ether and synthesized the vinyl ethers of 1,4-butanediol and diethylene glycol. Isomerization of vinyloxyethanol to methyldioxolane (Equation 2) 296
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
CHFCHOCHZCHZOH
-
/O-CH?
CHICH \O--bHt
(2)
was found by these authors to occur in the presence of acidic substances with explosive violence and also occurred during vinylation and distillation. Walling and Faerber (78) employed a process which removed the glycol monovinyl ether of ethylene glycol, 1,3-methylene glycol, or diethylene glycol from the reaction zone with excess acetylene or an inert gas to avoid cyclization. \$‘hen four or more atoms separate the hydroxyl groups, the cyclization tendency is greatly reduced, so that diethylene glycol (DEG) was selected in the present work for the development of a process to produce both the monovinyl ether (MVE) and the divinyl ether (DVE). Preparation
The vinylation of diethylene glycol proceeds smoothly a t temperatures in the range of 160’ to 200’ C. a t acetylene partial pressures of 25 to 200 p.s i. (72, 73, 78). Since acetylene can
decompose violently a t these pressures. adequate precautions are required to preverlt decomposition. The main requirement is that free space in the pressure reactor be avoided by packing with Raschig I ings or other similar distillation-type packing. Purified diethylene glycol free of ethylene glycol is preferred in order to simplify the separation of the final products. Added catalytic reagents, in order of reactivity, are potassium. potassium hydroxide, sodium, and sodium hydroxide. The equivalent of the first of these catalysts can be obtained by dissolving potassium hydroxide in diethylene glycol and distilling off water (Equation 3) :
-
+ HOCH2CH20CH&HzOH H20 + KL-OCH2CH20CH?CH20H
KOH
is z
0 I-
U
a I-
z W
0
z
0 0
(3)
The reaction of acetylene with diethylene glycol is a two-step reaction of the type 0
2
I
3
4
5
6
CY
Since A in this case has two hydroxyl groups and B one, kl = 2k2. The kinetics for this type of reaction can be calculated for both a plug flow pipe reactor (essentially the same as a batch reaction) and a stirred, completely homogeneous reactor ( 5 ) with continuous feed. The relationship of composition to residence time for these cases is illustrated in Figures 1 and 2. In practice, a continuously fed pipe reactor will give results lying between these extremes due to end-to-end mixing. Figure 3 is a plot of actual compositions obtained by varying the inventory time in a continuous system. The specific gravity of the product is a measure of conversion and is related to the total vinyl unsaturation as shown in Figure 4. Composition in the product was determined with fair accuracy by mass spectrometry. Total vinyl unsaturation can be measured by direct iodine titration in the presence of methanol (76). Side reactions of polymerization and dehydrogenation of the potassium glycolate: occur: but are not very significant. Considerable coloring of the product results from reaction of the glycolate with oxygen. The catalyst and unreacted diethylene glycol were recycled many times without appreciable loss in reactivity.
Figure 2. Calculated product composition as function of conversion for homogeneous reaction mixture with continuous feed a = k 2 7 where 7 = mean residence time W T. 'Ye
100
c
C O M P O S I T I O N OF PRODUCT DEG - M V E - D V E C PA R TEAc LI P Y ISTAT T ESI
+ CAT.
.2
I - 8
z
I
0
0
I
2
3
4
5
6
W 0
a w a
4
a Figure 1 . Calculated product composition as function of conversion for batch ( f = time) or plug flow ( f = residence time) reactor O( = kOt
0
Figure 4.
Iodine titration of vinylation product VOL.
2
NO. 4
DECEMBER 1963
297
DRYING
HSTRIPPINGHAZEOTROPEH bMvE
PACKED REACTOR
FINISH
DEG
Figure
COLUMN
COLUMN
MVE FINISH
I -
I
5.
Flowsheet for monomer purification
The reaction product was separated into the pure components as outlined in Figure 5 . The divinyl ether of diethylene glycol is the lowest boiling product. It azeotropes with 15 to 25% of the monovinyl ether. Purification of the divinyl ether by extraction with water, drying, and finishing gave a product of good purity. Figure 6 is the phase diagram of the water-monovinyl ether of diethylene glycol-divinyl ether of diethylene glycol. The monovinyl ether does not form an azeotrope with diethylene glycol, and was purified directly by fractional distillation. If only the divinyl ether of a glycol is desired as a product, the monovinyl ether can be recycled. However, a German process for the production of the divinyl ether of butanediol (73) was run a t about 90% conversion of the butanediol followed by extraction with water saturated with carbon dioxide. This step extracted the catalyst from the organic phase without much loss of the organic materials, and offered the advantage that the residue in the subsequent distillation did not become a viscous slurry due to insolubility of the catalyst. Physical Properties and Purity
Purified samples of the monovinyl ether of diethylene glycol were prepared by fractional distillation and found to have the following properties : Purity, 99+% Boiling point 110' C. at 25 mm. 144' C. at 100 mm. 209' C. at 760 mm. Freezing point, -49.9' C. Density, g./ml. 1.0276 at 20' C. 1.0229 at 25' C. Viscosity 4.739 cps. at 25" C. 1.418 cps. at 75' C. Solubility, g./100 g. solvent at 25" C. Acetone W Benzene W Carbon tetrachloride w Ethyl ether m n-Heptane 4.31 Methanol m Water W Small scale continuous production yielded monomer having the following properties: 298
I&EC PRODUCT RESEARCH A N D DEVELOPMENT
Figure
6.
Phase
diagram
for
system
MVE-DVE-H,O
Purity, 98.0y0 Boiling range ( 5 to 95%), 207.2' to 212.2' C. Specific gravity, 1.022 at 25/4' C. Refractive index, 1.4423 at 35" C. Viscosity, 4.73 cps. at 25" C. Flash point, 230' F. Fire point, 230' F. Color (APHA), 55 Water, 0.27, 2-Methyl-1,3,6-trioxocane.l.OyO Divinyl ether of DEG, 0.8% Diethylene glycol, 0.2% Divinyl ether of diethylene glycol purified by sodium treatment followed by filtration and fractional distillation had the following physical properties: Purity. 99.57c (freezing point curve) Boiling ooint 100%'C. at 25 mm. 135" C. at 100 mm. 196' C. at 760 mm. Freezinq point, -24.3' C. Density, g./ml. 0.9698 at 20" C. 0.9646 at 25" C. Refractive index, n~ 1.4463 at 20' C. 1.4444 at 25' C. Viscosity 1.75 cps. at 25' C. 0.74 cps. at 75' C. Solubility, g./lOO g. solvent at 25' C. Acetone m Benzene m Carbon tetrachloride m Ethyl ether m n-Heptane m Methanol m IVater 0.77
A representative sample from small scale continuous extraction followed by continuous distillation is characterized as follows: Purity, 98Y0 Boiling range ( 5 to 95Yc), 194.7' to 196.7' C. SDecific Fravitv. 0.964 at 2514' C. gefractiFe indkx, n ~ 1.4402 . at 35" C. Viscosity, 1.72 cps. at 25' C. Flash point, 190" F. Fire point, 190" F. Color (APHA). 57 Monovinyl ether of DEG. 1.8r0 Diethylenr glycol, 0.1 %
I .o
I. SAMPLE OF MVE
2. 3. 4. 5.
CENTER CUT FROM I CENTER CUT FROM 2 C E N T E R CUT FROM 3 C E N T E R CUT F R O M 4
d
I
1
I
1
I
I
240
250
260
270
280
WAVEL E N G T H
Figure 7.
I 290
I 300
- M I L L I M ICRONS
Ultraviolet absorption spectra of redistilled
MVE
I .o
Inhibition and Stabilization
( I ) No T R E A T E D D V E ( 2 ) C E N T E R C U T FROM I ( 3 ) 2 A G E D ONE M O N T H (4) 3 T H R O U G H S I L I C A GEL (513 T H R O U G H A L U M I N A
u
z
2r 0.5 -
E d
230
240
250
260
270
280
290
WAVELENGTH- MILLIMICRONS
Figure 8. Ultraviolet absorption purified and treated DVE
Table 1.
spectra
A high boiling amine such as triethylenetetramine, or solid potassium hydroxide, was used as an inhibitor. Figure 7 shows the increasing purity by ultraviolet absorption spectra of a sample of monovinyl ether of diethylene glycol on successive fractionation of center cuts. Ultraviolet absorption spectra of the divinyl ether of diethylene glycol after sodium treatment and fractionation are given in Figure 8 along with the effect of 3 months' aging and attempts to purify with alumina and silica gel. Mass spectrometer analysis can be used to estimate known impurities and was employed for analyzing monomer mixtures, although difficulty was encountered in the gas-handling system because of the polarity of the compounds This was partially overcome by careful programming to make the results more reproducible, but errors of the order shown in Table I were experienced. Gas chromatography provides a promising method for monomer analysis and purity determination. Using a 10foot column packed with 5% Carbowax 20M on Fluoropak maintained a t 138' C., injecting a t 117' C., and sweeping with nitrogen a t 2 5 p.s.i.g., adequate separation of divinyl ether of diethylene glycol. the monovinyl ether, and diethylene glycol. in that order, was obtained. O n a purity analysis of monovinyl ether of diethylene glycol, the impurities separated Ivere 2-methyl-l.3,6-trioxocane (2-methyl-l,3,6-trioxacyclooctane). divinyl ether of diethylene glycol, and diethylene glycol.
of
Mass Spectrometer Analysis of Mixtures Synthetic Component B h d , yc Found. ';c MVE 90.1 90.6 DVE 9.9 9.4 32.7 MVE 34.2 DVE 33.8 33.2 DEG 33.4 32.6 MVE 34.7 36.5 DVE 34.8 36.8 DEG 30.5 26.7
Vinyl ethers are notably reactive in acid-catalyzed hydrolysis, alcoholysis, and polymerization. They are not polymerized readily by heating or by the use of free radical catalysts. The inhibition problem for vinyl ethers therefore primarily involves precautions against the introduction or development of acid catalysts. Autoxidation is also important, particularly at elevated temperatures. Potassium hydroxide in l o ~ rconcentration was used for storage of the monovinyl ether of diethylene glycol to neutralize small amounts of acidic contaminants. This precaution did not prevent formation of small amounts of 2-methyl-1,3,6trioxocane in the finished monomer, however. Some aging experiments with the monovinyl ether a t elevated temperatures were made using a simple flask fitted with a reflux condenser. The per cent vinyl ether was determined by iodine titration. The data of Table I1 at 100' C., 150' C., and the boiling point (205' C.) indicate a slow decrease in vinyl unsaturation in the presence of either potassium hydroxide or diethylenetriamine, with higher temperatures yielding a faster rate of decomposition. Addition of a number of antioxidants failed to stop the decomposition a t the reflux trmperature. Of the compounds tried. 2,4-dinitrophenylhydrazine was best. The compounds tried in the presence of potassium hydroxide were phenylhydrazine, phenanthraquinone. 1,4-naphthoquinone. copper naphthenate, 2,4-dinitrophenylhydrazine, copper sulfate. AgeRite Resin D, ionol, quinone. and ferric 2-ethyl hexoate. Finally, exclusion of oxygen \vith prepurified nitrogen was only partially effective in stopping degradation, and it was concluded that the degree of degradation which could not be suppressed was simply a thermal, uncatalyzed ionic reaction. This applies to the monovinyl and not to the divinyl ether of diethylene glycol. Exclusion of oxygen cut down the development of color, which indicates that autoxidation does occur to some extent in the basic solution. Trace amounts of acid in uninhibited monovinyl ether of diethylene glycol at elevated temperatures led to rapid deVOL. 2
NO. 4 D E C E M B E R 1 9 6 3
299
Table II.
nitrogen checked this degradation and indicated that it was due to autoxidation. The small loss in the assay after 25 hours a t 190" C. in nitrogen was probably due to polymer formation (indicated by turbidity on addition of the solution to 50% methanol in water).
Aging of 100-Gram Samples of Monovinyl Ether of Diethylene Glycol
70 M V D Inhibitor
Weight, G.
Temp.,
c.
25 hr.
50 hr.
100
0.2 0.14 0.1 0.14
100
98
97
96
205
98
96
200 150 205 205
96 93 92 84
94 86
205 190d
81 78
71
DETAb KOH DNPHc KOH DETA DETA DETA None KOH CuSO4.5HzO DETA None (acid contaminant)
0.1
0.2 0.1 0 0.15 0.1 0.1
Reactions
Vinyl ethers of glycols undergo the typical reactions of alkyl vinyl ethers. Hill and Pidgeon (6) characterized vinyloxyethanol by hydrolysis, bromine addition, evolution of hydrogen by reaction with sodium, and esterification to a rnonobenzoate. In the case of monovinyl ether of diethylene glycol, acid catalysis produces a polymeric acetal or the cyclic acetal: 2-methyl-1,3,6-trioxocane,reported by Hurd and Botteron (7) which itself on standing about 2 months polymerized to the polyacetal. Divinyl ether of diethylene glycol was made to react with excess hydrogen sulfide using free radical catalysis to form the dithiol of tetraethylene glycol ( 7 7) (Equation 4) :
90
69
< 10
205
0
Iodine titration. Nitrogen atmosphere.
Diethylenetriamine.
a
hr.
Dinitrophenylhydrazine.
Table 111.
a
Aging of 100-Gram Samples of Divinyl Ether of Diethylene Glycol Temp., 70D V E a Inhibitor Weight, G. O C. after 25 Hr. None 0 190 82 DETAb 0.1 190 87 0.1 150 95 0.1 100 96 0.1 19OC 98 Iodine titration. Diethylenetriamine. E Nitrogen atmosphere.
2H2S
(HSCH~CH?OCH&HZ)?O(4) Polymerization
Polymerization of the monovinyl ether of diethylene glycol with acidic catalysts such as boron fluoride, aluminum chloride, and mineral acids does not follow the usual course of vinyl polymerization of alkyl vinyl ethers. Instead, a polyacetal is formed, as mentioned above. Related polyacetals are described by Neher and Bauer (70). The polyacetals are generally of low molecular weight. Divinyl ethers when polymerized with acidic catalysts form cross-linked gels. By combination with glycols, divinyl ethers can be made to form polyacetals ( 7 ) (Equation 5) :
composition (Table 11). Diethylene glycol, water, and 2-methyl-l,3-dioxolane were isolated from the mixture by distillation. Divinyl ether of diethylene glycol can be inhibited with diethylenetriamine during drying and finishing distillations. The stored monomer retains traces of the inhibitor, which prevents ionic polymerization. Table 111 shows the effect of temperature on the rate of degradation (loss of vinyl unsaturation) of the divinyl ether in contact with air. Elimination of oxygen with prepurified
Table IV. Initator Concn., % 1 .o 1 .o
Initiator AZO
CHP AZO Gamma
C.
75 90 150 80 40 60 120
O.ld
Time, Hr.
40 24 20 5 8
A Z O = azobisisobutyronitrile. C H P = cumene hydroperoxide. a Theoretical OH = 12.85%. 10% solution in water at 25' C.
Table V.
Temp.,
10 20
130 160 150 170
300
+ ~CH?=CHOCH~CH~OCH=CHZ
Yield, yo 50.1
Hydroxyl,a
45 56 38 35 65 42.8
4 4
C
By ebulloscopy.
%
12.55 12.24 7.13 11.37 12 87 12.52 12.35
Visc., Cfs. *
M o l . Wt.O
2.78 4.07 1.42 9.2 4.20 3.80 2.26
751 1302 445
Megarep. per hour.
Continuous Recycle Copolymerization of Styrene and Monovinyl Ether of Diethylene Glycol
Feed, 76 M V E
a
H+
n-HOCH&H?OH
Homopolymers of Monovinyl Ether of Diethylene Glycol Temp.,
1.1 0.3 0 . 3Gd 0 . 36d
+ CH~=CHOCH~CH~OCH~CHZOCH=CH?
c.
20 30 1070 solution in toluene at 25" C.
Rate,
WHr.
Yo Polymer Solids
Recycle, Yo M V E
21 22.5 52 13 29.3 62 5 35.2 73 34.4 Caplastometer at 7 dynes/sq. cm. shear stress. 12
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
Polymer, 70M V E
% Volatile
4.9 8.5 16.3 23.9
3.6 4.6 6.0 7.2
Visc.,Cps." 27.3 6.7 6.8 3.3
Melt Visc., Poisesb
1865 94 176
Table VI.
% Vinyl chloride Acrylonitrile Vinyl acetate
Acrylamide
Copolymerization of Monovinyl Ether of Diethylene Glycol (M2) Polymar MVE Solvent Temp., "C. % ' Conu. 70 M V E
8 10 GOa 98'3 19 40 59 80 27 53 A7 _
I
Acrolein 70 Butadiene 90 Ethyl acrylate 80 Ethyl vinyl ether 50 Diethyl fumarate 45 N-Vinylpyrrolidone 80 Ar-Vinyl-5-methyl-2-oxazolidinone 80 :\ZO = azobisisobutyronitrile. KPS = potassium persulfate. .Ilonotner j p d mixture ftd rontrnuourl~ rc 1 1 i r 1 ~rzortcr 4
None Water MeOH None
Polymer
25 VCN 30 VA 63 BD 40 EA 60 EVE 52 DEF 37 VP
70
None None None None
70 70 80-90 80-90 60
Water Water Water None None None None None None None
50 50 44 60 60 60 60 60 60
50 ..
Catalyst
2
8 12 71 76 21 32 44 50 26
AZO KPS/SBS AZO AZO AZO AZO AZO AZO/LP AZO
3 6 48 9 42 17 67 90 51
76 . _
AZO -
46 76 37 60 40 48 63 71
AZO AZO AZO/LP AZO/LP AZO~LP AZO/LP AZO~LP AZO/LP
40 16 10-22 8 50 30 19 53 ~
SBS = sodium bisulfite. LP = lauroyl peroxide. 11
rrh cierflOw.
Viscous. water-soluble oils or gums of the vinyl homopolymer of monovinyl ether of diethylene glycol have been prepared by free radical catalysis. 'Table IV summarizes data on polymers made in bulk using several initiators, including gamma irradiation. The polymers were isolated by low temperature vacuum devolatilization and could be purified by dissolving in water and precipitating in acetone. At elevated temperatures these products would decrease in hydroxyl content and eventually form a friable gel. A benzoate ester derivative of a homopolymer was stable to prolonged heating, indicating that the hydroxyl group is involved in thermal cross linking. An aqueous solution of such a monovinyl ether homopolymer was found to have utility as a soil antiredeposition agent in conjunction with a n organic detergent or as an additive to carboxymethylcellulose to improve its efficiency as a n antiredeposition agent (77).
Table VII.
65 Room
Vulcanized MVE Copolymer Elastomers Tensile Str., Elong., Shore Recipe P.S.I. % A % Set B 380 400 40 1.5 370 A 50 65 0 A 80 20 35 0 A 290 40 51 0 A 30 15 10 0 A 720 220 50 12.0 B 2160 790 49 15.0 A 260 140 47 0
B 210 470 40 12.0 29 VOM A 700 100 57 0 A. 100 g. crude rubber B. 100 g. crude rubber 40 g. Pelletex carbon 40 g. Pelletex carbon black black 5 g. zinc oxide 5 g. litharge 5 g. sulfur 1 g. stearic acid 3 g. Altax accelerator 2 g. aniline butyroaldehyde VCN = acrylonitrile EVE = ethyl vinyl ether VA = vinyl acetate DEF = diethyl fumarate BD = butadiene VP = A'-vinylpyrrolidone EA = ethyl acrylate VOM = N-vinyl-5-methyl-2-oxizolidinone
Copolymerization
Vinyl ether, have been copolymerized with the well known vinyl monomers and since the reactivity of the vinyl ether is usually low. copolymerization generally favors the other monomer. Lower polymerization rates and lower molecular height usually result. A few monomers-notably maleic anhydride. maleates. fumarates, and acrylonitrile-shoMa tendency to alternate in copolymerization with vinyl ethers. The vinyl ethers of glycols fit into the general class of vinyl ethers, as regards copolymerization, but they have some unique characteristics. For example, the monovinyl ether of diethylene glycol is a water-soluble monomer and in copolymers can impart hydrophilicity by reason of the free hydroxyl group Thus it has the character of hydrolyzed vinyl acetate or the hypothetical vinyl alcohol. The hydroxyl and ether groups are polar. and in copolymer., they tend to improve adhesion to substrates. Styrene copolymerization illustrates the low reactivity of monovinyl ether of diethylene glycol. Table V gives data from continuous recycle copolymerization (I). Assuming the recycle monomer recovered from the reactor product stream by devolatilization represents the average concentration of mono-
Table VIII. Copolymerization with Ethylene BenSol. Vise. rene, Yield, 0.5y0 in Mz, G. G. G. Polymer, yo Tol., Cps. 60 MVE 60 30 14 MVE 0.42 (90') 250 MVE 0 80 21 MVE 0.31 (90') 0 800 MVE 42 MVE 320 0.39 (90') 13 DVE 63 253 7 DVE 0 . 5 0 (75') 30 DVE 90 5 17 DVE 0.42 (90')
320 DVE 320 DVE 150 DVE 60 DVE 90 DVE 120 DVE 50 DVE/ 100 v.4
400 400 210 60 30 0 275
VOL. 2
130 210 120 66 67 54
NO. 4
20 DVE 23 DVE 27 DVE 33 DVE 41 DVE 56 DVE 10 DVE/ 25 VA
0.66 (25') 0.67 (25') 0.72 (25') Insol. Insol.
Insol. 0.76 (25')
DECEMBER 1 9 6 3
301
Table IX.
Curing of Ethylene Copolymers Cure Temp., Time, Addzhe O c. min. ~~
VOEa 3 6 6 2
Polymer D VE
.. . .
-
VA
44 50 50 40
7
BF,d
27 ,..
27 27
...
10
2 DMD 5 DMDb 5 DMD5 6 DMD Nonec
.. 25
2 5 PE 6 5 PE 10 PE 10 PE
107 124 24 140
20 4 da
Room
10
130
40 40 40 40
130
130 130
Tensile Strength, P. S.I.
2050
Elong., % 1060 225 260 490
540
360
1420 2950 2650
yo Set 9.5
5.3 4.6 6.9
VOE = vinyloxyethanol VA vinyl acetate PE = unsaturated polyester resin DMD = p-diphenylmethylene diisocyanate d
a Data from r p f u e n c e ( 3 ) . 5 Plus 50parts Phtblack 0 carbon black per 100parts crude. Sample 42% soluble aftei treatment.
mer in the reactor and that r2 for the monovinyl ether is zero, 71 = 9 i 4 as an average of 12 experiments. The copolymers obtained were low molecular weight. resinous polyols, but they were not readily esterifiable with unsaturated fatty acids by a high temperature esterification cook procedure. Table V I summarizes copolymerization data for the monovinyl ether of diethylene glycol with a variety of other vinyl monomers. The vinyl chloride copolymer had poorer heat stability than straight PVC. The acrylonitrile copolyn~erwith 76% M V E was water-soluble, as were the vinyl acetate copolymers with 44 and 507, M V E and all of the acrylamide copolymers. In the case of acrolein, a friable gel was obtained that could be dissolved in methanol by addition of dilute HCI and then isolated as a white powder by precipitation in ether. An acidic methanol solution of the polymer was infinitely dilutable with water A copolymer of 2-methoxyethyl vinyl ether and acrolein behaved in much the same way, and resins of this type have been described by Miller and Rothrock (9). McWherter ( 8 ) has disclosed a number of M V E copolymers containing less than 30% M V E that are useful as leather finishing coatings with improved adhesion. An example describes a 307, aqueous dispersion of a terpolymer of 50% n-butyl acrylate, 40% acrylonitrile, and 10% MVE. Copolymers containing more than about 407, M V E were found in general to be elastomeric and could be vulcanized with sulfur or aniline butyroaldehyde in rubber recipes (Table VII). These samples were cured at 144' C. for 50 minutes. Both monovinyl and divinyl ethers of diethylene glycol can be copolymerized with ethylene at high pressure. The glycol vinyl ethers exhibit relatively good reactivity with ethylene, producing apparently homogeneous copolymers in spite of the necessity of adding ethylene during the course of the reaction. Table VI11 gives data on the preparation of these copolymers a t about 120' C. using ethylene pressures of 15,000 p.s.i. and repressurizing as the ethylene reacted. Copolymer composition was determined by C, H analysis. The products with high ethylene content were semicrystalline and at high DVE content they were cross-linked. When vinyl acetate was used in a terpolymer, the material was a noncrystalline rubber. Similar glycol monovinyl ether copolymers and terpolymers have been disclosed ( 2 , 3 ) and shown to 302
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
e
Sample 9J% solubls in Decalzn at 720' C. (znhtbzted).
be curable with diisocyanates and other curing agents reactive with hydroxyl groups such as amino aldehyde or phenol aldehyde resins and epoxy resins. Table I X includes patent data ( 3 ) on cure of vinyloxyethanol terpolymers. Alro shown are data on the cure of DVE copolymers by secondary reaction of the free vinyl ether group, in one case by using BF3 to catalyze ionic polymerization, and in the other case using an unsaturated polyester resin to coreact by free radical copolymerization of maleic and vinyl ether groups. -4patent issued to Richards, Myles, and Whittaker (75) indicates that divinyl ether can be copolymerized with ethylene and the resulting rubbery copolymer cured by means of heat or the usual rubber curing conditions.
Conclusions
Current prices of diethylene glycol and acetylene and the relative simplicity of processing to the vinyl ethers are favorable for low cost of the monomers, assuming large scale manufacture. As a higher cost reactive monomer, the monovinyl ether of diethylene glycol should be competitive with hydroxyethyl acrylate or methacrylate and perhaps with allyl alcohol as a source of primary hydroxyl groups in vinyl copolymers. The divinyl ether of diethylene glycol is not an efficient cross-linking monomer except in cationic polymerization or in cases of alternation. Possibly the unique feature of this monomer is the reaction with hydrogen sulfide to form a dithiol which is related to the liquid Thiokols.
Acknowledgment
The authors are indebted to numerous coworkers who participated in the work reported here, particularly T. W. Mulcihy, D. 0. Kluck, A. T. Tweedie, E. Holly, and G. B. Sterling. Analytical data were obtained by the Analytical Laboratories and the Chemical Physics Research Laboratory of The Dow Chemical Co.
literature Cited (1) Aldeman, R. L., U. S. Patent 2,682,532 (1954). (2) Calfee, J. D., Ibid., 3,025,267,3,025,269 (1962). (3) Deex, 0. D., Calfee, .J. D., Ibid., 3,025,268 (1962).
(15) Richards, R. B., Myles, 3. R., Whittaker, D., Zbid., 2,526,773 (19501. ( l i ) Siigia, S., Edsberg, R. L., Anal. Chem. 20, 762 (1948). (17) Stillo, H. S., Kolat, R. S., Nummy, IV. R., U. S. Patent 2,981,692 (1961). (18) IVaIling. E.. Faerber., G.,, Brit. Patent 773.331 (1957); ' German Fatent'958,383. RECEIVED for review May 20, 1963 ACCEPTED October 7, 1963
(4) Hanson, A. \V., Zimmerman, R. L., Znd. Eng. Chem. 49, 1803 (1 057) \ * - /.
(5) Hill, H., Alfrey, T.. private communication. (6) Hill, H. S.. Pidgeon, L. M., J . A m . Chem. SOC.50, 2718 (1928). ( 7 ) Hurd. C. D.. Botteron. D. G.. Zbid.. 68. 1200 (1946). (8j Mc\Vherter,'D. W., U. S. Patent 2;828,220 (i958): (9) Miller, H. C., Rothrock, H. S., Zbzd., 2,657,192 (1953). (10) Neher, H. T., Bauer, L. V. N., Zbzd., 2,633,460 (19.53). (11) Nummy. W.R., Jones. G. D.. Zbzd., 2,873,239 (1959). (12) Reppe,'\V.. Ann. 601, 81-138 (19.56). (13) Reppe, IV., C . S. Dept. Commerce, PB 95217 (1943). (14) Reppe, W., I--. S. Patent 1,959,927 (1934).
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Division of Organic Coatings and Plastics Chemistry, 144th Meeting, ACS, Los Angeles, Calif., April 1963.
A MELAMINE PROCESS BASED ON HYDROGEN
CYANIDE AND AMMONIA INVOLVING ELECTROLYTIC CONVERSION OF HYDROGEN CYANIDE R. W . F0 R EMA N A N D J
,
W
.
SP
R A G U E, The Standard Oil Co. ( O h i o ) , Cleveland, Ohio
A high yield synthesis of cyanogen bromide has been discovered based on a novel electrolytic conversion of hydrogen cyanide in aqueous ammonium bromide. Subsequent ammonolysis of cyanogen bromide in a selected solvent yields a solution of cyanamide plus solid ammonium bromide which is recycled to the electrolysis step. Satisfactory conditions for trimerization of cyanamide in the solvent to melamine have been demonstrated. Over-all yields of high purity melamine exceeding 90% are achieved in the outlined process. Dilute solutions of hydrogen cyanide in aqueous ammonium bromide are electrolyzed a t 100" F. The hydrogen cyanide can be absorbed into the aqueous ammonium bromide from the effluent of a generator using ammonia and a hydrocarbon as feed. The specially designed cell and its operation are described. The selection and optimization of a suitable solvent which serves for both the ammonolyses and trimerization reactions are discussed. Solvents such as dioxane and tetrahydrofuran were particularly useful. The trimerization of cyanamide is shown to b e unexpectedly easy and direct compared with other procedures for producing melamine. for melamine are generally based on dicyandiamide (cyanoguanidine) derived from calcium cyanamide (9). O t h r r starting materials which have been reported useful for synthesis of melamine include cyanamide ( 3 ) , guanidine (73), urea ( 7 ) , cyanuric halides (7, 8 ) , and hydrogen cyanide plus ammonia ( 7 7). In contrast to previously reported hydrogen cyanide-ammonia processes, the melamine process reported here is very efficient. I t also offers an economic advantage over the calcium cyanamidebased route where low cost hydrogen cyanide and electrical power are available. The process involves a novel electrolytic conversion of hydrogen cyanide to cyanogen bromide in aqueous ammonium bromide amination of cyanogen bromide in a selected solvent to cyanamide and recycle ammonium bromide, and trimerization of the cyanamide in the solvent to melamine. A simplified process diagram is presented in Figure 1. The hydrogen cyanide feed for this process can be the pure liquid, or it can be absorbed into the aqueous ammonium bromide from the effluent of a hydrogen cyanide generator operating on an ammonia-hydrocarbon feed. None of the by-products in hydrogen cyanide so produced poses any serious difficulties in the hydrogen cyanide conversion to cyanogen bromide. Over-all yields of melamine from hydrogen cyanide above 90% are achieved by this process. The bromide losses are OMMERCIAL PROCESSES
negligible and the only significant by-product is hydrogen A more detailed description of the process follows. Hydrogen Cyanide-Ammonium Bromide Electrolysis
Cyanogen bromide is produced efficiently in the anode chamber when dilute solutions of hydrogen cyanide in aqueous ammonium bromide are electrolyzed a t about 100' F. in a specially designed cell. Aqueous ammonium bromide is used in the cathode chamber. The cell is described in detail below, but the key feature is the use of an ion selective membrane. T h e membrane prevents mixing of the ammoniacal catholyte with the anolyte and resultant destruction of hydrogen cyanide and cyanogen bromide. At the same time, current densities [lo0 amp. per sq. ft. (a.s.f.)] a t relatively low voltage (3.0) can be maintained by ionic transport through the membrane. The hydrogen cyanide is essentially completely converted to cyanogen bromide. Since the latter is volatile (b.p. = 61.6' C.), it is easily stripped from the anolyte for the subsequent conversion to cyanamide and melamine. The cell design permits ready recovery of the hydrogen formed a t the cathode. .4mmonia escapes with the hydrogen thus maintaining a n equilibrium concentration in the catholyte recycle. The cell operates continuously with the anolyte recycled after cyanogen bromide removal and replenishment of ammonium bromide from the amination step. VOL. 2
NO. 4
DECEMBER 1963
303
