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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is in the field of preparing ethylidene bisformamide from
acetaldehyde and formamide, and, optionally thereafter, cracking
(thermally decomposing) the ethylidene bisformamide to N-vinylformamide.
This invention also relates to a chemical process for forming
poly(vinylamine) salts of mineral acids, especially poly(vinylamine
hydrochloride) from the resulting N-vinylformamide.
2. Description of the Prior Art
Poly(vinylamine), its salts, and products based thereon are desirable
chemicals. Efficient and effective integrated overall processes for the
production of poly(vinylamine) salts and poly(vinylamine) itself, of
course, would encourage and promote the widespread commercial use of said
chemicals. U.S. Pat. No. 4,018,826, issued on Apr. 19, 1977, to Richard
Gless, Daniel J. Dawson, and Robert E. Wingard, discloses a process for
preparing poly(vinylamine) wherein acetaldehyde and acetamide are formed
into ethylidene-bisacetamide which is then cracked to yield vinylacetamide
which is polymerized and hydrolyzed to poly(vinylamine). In said patent,
acetaldehyde and acetamide are reacted in a liquid phase in the presence
of an aqueous strong liquid mineral acid.
In U.S. Pat. No. 4,176,136, issued on Nov. 27, 1979 to Daniel J. Brenzel,
an improved method for carrying out this reaction is disclosed wherein
ethylidene-bisacetamide is prepared by the process of contacting a liquid
mixture of acetaldehyde and acetamide with a solid cation exchange resin
at a temperature of from about 10.degree. C. to about 110.degree. C.
Other references to the condensation reaction of acetaldehyde and acetamide
in the prior art include V. V. Richter, Ber. 5,477(1877); W. Noyes et al,
J. Am. Chem. Soc., 55,3493 (1933) and Ben Ishai et al, Tetrahedron
Letters, 50,4523 (1965). Also, a general review article on the
condensation of aldehydes and amines may be found in Organic Reactions,
14,52 (1965).
An effective and efficient process for producing poly(vinylamine) salts in
good yields beginning with formamide, however, has heretofore not been
known. Indeed, the sole references known to us regarding even the
preparation ethylidene bisformamide, Keimmel, et al; J. Org. Chem., 36,
350 (1971), and Takase, et al, Sci.Rep. (Osaka), 16(1), 7 (1967) shows
very mediocre yields. Similarly, when acetamide is merely replaced by
formamide in the Gless et al or Brenzel processes, a usable product is not
obtained. Rather, a low yield dark-colored degraded product is generally
the result.
It is an object of the instant invention to provide an effective process
for producing ethylidene bisformamide from formamide and acetaldehyde.
SUMMARY OF THE INVENTION
We have now found that ethylidene bisformamide can be formed in high yields
from formamide and acetaldehyde provided that the following precautions,
to our knowledge previously neither known nor disclosed to be important,
are observed. First, the reaction must be carried out at an elevated
temperature that is generally above the temperature achieved by the
reaction's exotherm on a laboratory scale. Second, the reaction must be
scrupulously freed of ammonia which is present as a contaminant in the
formamide feed and tends to be generated during the condensation reaction
as well. Two other factors which enhance yield are minimizing water in the
reaction zone and employing a low residence time means such as a film
evaporator to isolate the ethylidene bisformamide as a bottoms. It is an
aspect of this invention to prepare and recover ethylidene bisformamide by
a process incorporating these precautions.
Further aspects of this invention involve the use of this improved process
in combination with further steps to provide intermediate polymers and
ultimately poly(vinylamine) and polymer products based thereon.
BRIEF DESCRIPTION OF THE DRAWINGS
In the DETAILED DESCRIPTION OF THE INVENTION, reference will be made to the
drawings in which
FIG. 1 illustrates a continuous embodiment of the instant invention wherein
ethylidene bisformamide is produced in the presence of an ion exchange
resin catalyst, recovered using a wiped film evaporator and pyrolyzed to
give N-vinylformamide;
FIG. 2 illustrates a semi-batch embodiment of the invention as it relates
to the preparation of ethylidene bisformamide; and
FIG. 3 illustrates a device for pyrolyzing (cracking) ethylidene
bisformamide.
DETAILED DESCRIPTION OF THE INVENTION
Fundamentally, this process for preparing ethylidene bisformamide proceeds
via the condensation reaction of formamide and acetaldehyde shown in
General Formula I.
##STR1##
This reaction is carried out in the presence of an acid catalyst.
The invention concerns factors that must be controlled to achieve
acceptable yields of ethylidene bisformamide from this reaction. Two major
factors that must be controlled are:
Scrupulous minimization of free ammonia in the reaction feeds, reaction
zone, and reaction products and
Use of elevated reaction temperatures.
Two other factors that advantageously are controlled are:
Minimization of water in the reaction zone and
Use of a low resistance time distillation means, such as a film evaporator
to remove light impurities, unreacted feedstocks and the like to give the
"bis" product as bottoms.
AMMONIA CONTROL
Formamide is an inherent source of ammonia contamination. It almost always
contains ammonia or degrades to give minor amounts of ammonia. In the
present reaction, ammonia can be generated as a side product. We have
found that this ammonia leads to side reactions, major yield losses and
gross product discoloration. Accordingly, it is necessary to minimize
ammonia build-up. This is done by adding an ammonia scavenger, a compound
that will consume a base like ammonia. Such scavengers include acetic
anhydride, acetic-formic anhydride or an acidic ion exchange resin or the
like that will absorb any ammonia that may be present. Acetic anhydride is
quite effective, while solid ion exchange resins offer the advantage of
being easily separated from the reaction mixture. The ion exchange resin
employed in general is the same type of acidic resin that can be employed
as catalyst for the desired condensation reaction and that will be
discussed in more detail in that context. Combinations of acetic anhydride
and resin can be employed, as well.
The amount of acetic anhydride is generally from about 0.003 to 0.500
equivalents (based on the formamide present) with amounts from 0.005 to
0.100 equivalents being preferred. Larger amounts may be employed but are
seen to possibly offer cost and purification disadvantages not clearly
offset by superior yields, etc.
TEMPERATURE CONTROL
The reaction must be carried out at moderately elevated temperatures. The
reaction is exothermic so that, on a laboratory scale, room temperature
feedstocks can result in a reaction zone temperature of from about
25.degree. to about 50.degree. C. This temperature is too low. Higher
temperatures, such as from 50.degree. to 100.degree. C. or higher, must be
employed. Preferred temperatures are from 50.degree. C. to 90.degree. C.
with 50.degree. C. to 80.degree. C. being the most preferred temperature
range.
WATER CONTROL
It is advantageous to minimize water in the reaction zone. This can be
accomplished by drying feedstocks and the catalyst employed. Water is
generated in the desired reaction and can in part be trapped by acetic
anhydride if present. Other steps to minimize water include blanketing the
reaction zone with a dry gas and the like.
HIGH SPEED DISTILLATION
Following the reaction, the acidic catalyst for the condensation is removed
from the ethylidene bisformamide reaction product. If the catalyst
employed is a liquid acid, it can be eliminated either by physical removal
or by reaction with a neutralizing amount of an acid acceptor. Suitable
acid acceptors include alkali metal and alkaline earth metal hydroxides,
carbonates, bicarbonates and oxides. Satisfactory results can be obtained
with any of these materials, so cost factors dictate a preferance for
sodium, potassium and calcium hydroxides, carbonates, bicarbonates and
oxides. The carbonates are most preferred if the reaction product is to be
thermally decomposed (cracked) to N-vinylformamide since that reaction
should be carried out under nonacidic conditions and carbonates provide a
buffering action at or about the desired neutral pH's. If the condensation
catalyst was an ion exchange resin, as is preferred, the catalyst removal
is simply effected since the resin is solid and the reaction product is
liquid. For example, in a continuous reaction mode, the reaction product
can be drawn off through a filter, settling basin or a like solid-liquid
separation means. When employing a batch mode, a similar solid-liquid
separation step can be employed to effect isolation of the crude reaction
product from the solid resin.
The catalyst-free crude reaction product generally contains ethylidene
bisformamide, water, acetic acid and unreacted formamide and acetaldehyde
as its principal components. It also likely contains minor amounts of
byproducts.
In recovering the ethylidene bisformamide from this reaction product, it is
preferred that the recovery be conducted under high speed-low residence
time conditions in order to obtain a usable product. It has been found
that conventional column vacuum distillation techniques wherein the
impurities, i.e., formamide, acetaldehyde, acetic acid and water, all
being more volatile than ethylidene bisformamide, are distilled overhead
result in poor product quality and large yield losses. Thus, for
acceptable results this recovery comprises treating the crude reaction
product in a "thin film" configuration rather than in a "bulk" form, with
exposure to a relatively high temperature being maintained for a
relatively brief time.
The exposure to heat takes place under volatilizing conditions and high
surface area conditions, which allows for the high speed-low residence
time of the recovery process. The exposure temperature is suitably in the
range of from about 150.degree. C. to about 350.degree. C., with
temperatures in the range of from about 160.degree. C. to about
300.degree. C. being preferred. These temperatures are wall temperatures,
with the actual temperature of the ethylidene bisformamide being somewhat
lower as a result of cooling caused by the evaporation of the water and
unreacted reagents.
A vacuum is employed and will generally fall in the range of from about 1.0
mm Hg absolute to about 100 mm Hg absolute. Absolute pressures below 1.0
mm are very satisfactory as well but are difficult to achieve in
commercial scale equipment with substantial reactant and water partial
pressures being exhibited. Pressures above 100 mm Hg should generally be
avoided as it is difficult to obtain desired removal of contaminants at
higher pressures without resorting to detrimentally high temperatures or
detrimentally long residence times. Preferred absolute pressures are in
the range of from about 1.0 mm Hg to about 35 mm Hg with 2.0 mm Hg to 30
mm Hg being a most preferred range.
The time during which the ethylidene bisformamide is exposed to high
temperature should be limited as much as possible. Generally, times at
temperature of from about a second or so to a minute or two are
acceptable, with times from 1 second to 30 seconds and especially 1.0 to
20 seconds being preferred. It is to be understood, of course, that in the
case of continuous processing these times would be mean times.
The bisformamide is treated in a "thin film" form and during treatment
should have a surface area of at least 4 cm.sup.2 /gram, and preferably of
at least 6 cm.sup.2 /gram and more preferably of at least 8 cm.sup.2
/gram. To obtain reasonable processing rates, it is generally desirable to
limit surface area to a maximum of about 50 cm.sup.2 /gram. These
conditions can be attained in "thin film" evaporators such as horizontal
or vertical wiped film evaporators, multiple screw extruder evaporators,
or the like. Falling film evaporators can also be employed but care must
be taken to avoid scorching which can develop if the resulting film is not
sufficiently uniform.
Of these types of evaporating apparatus, those such as wiped film
evaporators which cause the bisformamide to be agitated during recovery
are preferred.
The product of this distillation generally is relatively pure ethylidene
bisformamide.
OTHER CONDENSATION REACTION CONDITIONS
As can be seen in General Formula I, above, stoichiometrically,
acetaldehyde and formamide react in a molar ratio of 1:2. Generally,
however, it is preferred to use somewhat of an excess of formamide. Major
excesses do not appear to offer any benefit, so suitably the ratio is
controlled from 1:2 to about 1:6 inclusive, with ratios of from about 1:2
to 1:3 being most preferred. Reaction will occur at ratios outside these
ranges, such as below 1:2 or above 1:6, but such conditions are not seen
to offer any advantage and present the obvious disadvantage of involving a
large excess of one reactant or the other which must be recovered and
recycled.
The condensation reaction is conducted in the presence of a catalytic
amount of an acidic catalyst, selected from among lower alkanoic acids
(formic or acetic), mineral acids, or acidic ion exchange resins. Good
results are obtained when a mineral acid, such as sulfuric or hydrochloric
acid, or formic or acetic acid is added in a catalytically effective
amount such as from about 0.001 to 1 mole of acid per mole of formamide.
More preferred is from 0.002 to 0.1 mole of acid per mole of formamide. As
previously noted, water addition with such catalysts should be minimized.
When an ion exchange resin is employed in the present process it is
preferably solid and insoluble in the reaction medium, the reactants and
the products. It is a cation exchange resin.
Cation exchange resins contain acidic groups such as carboxylic acid and
sulfonic acid groups or radicals. They are not, however, necessarily
acidic in the sense of giving a pH value of less than 7 to water in
contact therewith. Examples of suitable resins include resins derived from
monohydric and polyhydric phenols and aldehydes which are further modified
by reaction with sulfurous acid, sulfites and sulfur dioxide and
sulfonated polystyrene which is crosslinked such as with divinylbenzene.
Examples of such materials are those which are available commercially from
Dow Chemical Company under trademarks such as Dowex 50W-X8, 10, 12 and 16
and Dowex MSC-1; from Rohm and Hass Company under the trademarks Amberlite
200, Amberlite 1R 118, 120, 122 and Amberlite IRC 50; from Diamond
Shamrock as Duolite C-3, C-20, C-20X10, CC-33 and C-25D; from Permutit
Company (England) as Zeocarb 225, 215 and 266; from Permutit Company (USA)
as Permutit Q, Q 110, and Q 210; and from Bio-Rad Laboratories as BioRex
40 and 70 and as AG-50-X8 and AG-MP-50. Other comparable commercial or
prepared ion exchange resins can be used, as well as can mixtures of two
or more resins.
Preferred because of ready availability, are the sulfonated
divinylbenzene-crosslinked polystyrenes such as Amberlite IR-120 and
AG-MP-50. The resins should be employed in a protonated state, that is in
their H.sup.+ forms. This form is obtained by contacting the resin with
aqueous mineral acid, such as aqueous H.sub.2 SO.sub.4, HCl, HBr,
HNO.sub.3 or the like, prior to use. This acid treatment can also serve to
regenerate an ion exchange resin which has become deactivated. This
deactivation can occur when ammonia and ammonium ions present in the
formamide-acetaldehyde feed displace the hydrogen ions on the resin. The
acid treatment may be carried out at a temperature of 10.degree. to about
100.degree. C. and, preferably from 20.degree. C. to about 50.degree. C.,
and for a time of about 10 minutes to about 24 hours, and preferably 1
hour to about 4 hours. The acid is generally dilute, with concentrations
of from 0.1 to 6 molar in water being preferred, with at least one mole of
acid per mole of protonated sites desired being employed. Following the
acid treatment, the resin may suitably be rinsed with water to remove
residual acid and dried.
An additional resin treatment also is advantageous. Immediately prior to
use, the resin is washed with a mixture of acetic anhydride and formamide
and dried. When this is done, the necessity of adding acetic anhydride to
the reaction mixture lessens. A suitable catalyst rinse for a kg of resin
would be a kg or two of formamide containing 5 to 20% acetic anhydride.
The contacting of the reactants with the catalyst, e.g., ion exchange
resin, or acid catalyst, with or without acetic anhydride may be carried
out in a continuous or a batch mode. In the continuous mode, the reactants
are generally fed in the desired ratio to a reaction zone containing the
catalyst, preferably an ion exchange resin. The resin may be in a fixed
bed, stirred or fluidized bed configuration. The reaction products are
continuously withdrawn from the reaction zone. The rate at which the
reactants are fed to the reaction zone is expressed in terms of the weight
hourly space velocity (WHSV) of acetaldehyde passed over or contacted with
the ion exchange resin in
##EQU1##
WHSVs of from 0.01 to 2 kg/kg.times.hour are usefully employed with WHSVs
of from 0.05 to 1 kg/kg.times.hour being preferred.
In a batch mode, it is suitable to react from about 0.01 to about 10 kg of
acetaldehyde per kg of resin and to employ reaction times of from about
0.25 hour to about 24 hours. Preferably about 0.05 to about 1 kg of
acetaldehyde are used per kg of resin with times of from about 0.5 hours
to about 24 hours. Most preferred batch conditions include 0.1 to 1.0 kg
of acetaldehyde per kg of resin and a time of 1 hour to 6 hours. In either
the batch or the continuous mode, the catalyst resin is usually employed
in particulate form.
CRACKING OF THE ETHYLIDENE BISFORMAMIDE
Ethylidene bisformamide product of the aforediscussed process, can be
thermally decomposed (cracked) to N-vinylformamide in accord with General
Formula II
##STR2##
This cracking is carried out by heating the ethylidene bisformamide to a
temperature in the range of from about 150.degree. C. to 750.degree. C.
preferably 300.degree. C.-625.degree. C. for from about 0.1 seconds to
about 1 hour, more preferably for from 0.2 seconds to 2 minutes in the
presence of a solid surface catalyst. Suitable catalysts include solid
inorganic materials, preferably of a siliceous, carbonate or oxidic
nature. As a general rule, catalysts that are not strongly acidic give
best results. (A useful catalyst is one which by art-known tests, such as
Hammett indicators, does not give a strongly acidic reading.) Typical
useful catalysts include siliceous catalysts such as diatomaceous earth,
fumed silica, chopped glass fiber, powdered or formed glass, silica gel,
and fine sand; and inorganic carbonate minerals such as marble or other
forms of calcium carbonate. Inert solid metals such as steel and stainless
steel may be used as well. Strongly acidic materials to be avoided include
silica-alumina hydrocarbon cracking catalysts and the like. With carbonate
catalysts, such as marble, somewhat lower temperatures, say
300.degree.-425.degree., are effective. With other of these nonacidic
materials that exact nature and form of the catalyst is not critical as
these other materials may largely serve as heat transfer media.
These catalysts can be employed in low surface area forms such as in the
form of glass chips, marble chips, and the like. They may also be in high
surface area forms having areas of at least about 1 m.sup.2 /g, such as
with surface areas of from about 10 m.sup.2 /g to about 400 m.sup.2 /g.
They may be added to the reaction mixture as powders, pellets or the like
or can be employed as a bed through which the reaction mixture is passed.
The area or form of the catalysts is not seen to be critical to their use
in this reaction. Preferred catalysts include glass chips or the like and
marble chips having a 0.01 to 1.0 m.sup.2 /g surface area and diatomaceous
earth "Celite" having a 0.1 to 5 m.sup.2 /g area. Suitable reaction times
for the catalytic cracking step are from 0.01 minute to about 1 hour,
preferably 0.03 minutes to 0.25 hours.
The N-vinylformamide which is formed in this reaction step is more volatile
than the ethylidene bisformamide feed material. It is desirable to remove
it by volatilization from the pyrolysis reaction zone as it is formed.
This may be done by pulling a vacuum on the reaction zone during reaction.
Vacuums of from about 10 mm Hg to about 100 mm Hg are suitable to effect
volatilization of the N-vinylformamide at the cracking reaction
temperatures. Residual formamide volatilized along with the
N-vinylformamide may be removed, if desired from the N-vinylformamide.
This treatment may take the form of fractional crystallization,
distillation, or the like.
POLYMERIZATION OF N-VINYLFORMAMIDE
The N-vinylformamide monomer, with or without purification treatment, can
be polymerized or copolymerized. This polymerization can be carried out in
a liquid reaction medium using a free-radical initiator catalyst. There
are two classes of suitable liquid media. Polar hydrogen-bonding liquids,
like water and lower alkanols, are suitable and function as solvents for
the monomer and the polymer product. Nonpolar liquids, such as
hydrocarbons, ethers, and ketones, are also suitable, functioning as
monomer solvents but not as solvents for the polymer, the polymer thereby
forming a second phase. Lower alkanols of from one to five carbons such as
methanol, isopropanol, n-butanol and the like, are preferred media, with
isopropanol being most preferred.
The amount of reaction media is generally selected to provide a
concentration of monomer of from about 10% to 50% by weight. Lower
concentrations could be employed, but are not seen to offer any
significant advantage.
N-vinylformamide can be formed into homopolymers or it can be formed into
copolymers with other free-radical polymerizable monomers. These other
monomers can be selected from among other vinyl group containing compounds
such as vinyl chloride, vinyl acetate, vinyl sulfonate, acrylic acid,
acrylic acid esters, styrene, divinylbenzene, and the like. Other
comonomers such as ethylene, propylene, butadiene, vinyl ethers, maleic
anhydride, acrylamide, and N-vinylacetamide can be added as well. The
comonomers may be added eight to "dilute" the N-vinylformamide
functionality and likely give a lower priced product or to impart a new or
different functionality. Certainly, the above list of possible monomers is
not to be construed as limiting and other compounds known to the art as
comonomers in "vinyl"-type polymers may be employed.
A free-radical initiator is required to catalyze the polymerization.
Suitable catalysts include the organic peroxides such as dicumylperoxide
and other materials known in the art for this purpose. A commonly
available catalyst is AIBN, 2,2,-azobis-(2-methylpropionitrile). The
amount of catalyst is not critical. Generally, amounts of from about 0.1
gram to about 20 grams of catalyst per 100 grams of vinyl monomer are
employed with additions of from 0.1 to 2 grams of catalyst per 100 grams
of vinyl monomer being preferred.
The polymerization is generally carried out at a moderately elevated
temperature such as from about 25.degree. C. to about 125.degree. C., with
temperatures of from about 50.degree. C. to about 110.degree. C. being
preferred. The polymerization requires from about 1 to 8 hours for
completion, depending upon the exact temperature, catalyst, and monomer
concentration employed. Generally, the reaction will be monitored by NMR
or gas chromatography for unreacted monomer and continued until no
significant monomer remains, for example, less than 5%, preferably less
than 1%. The reaction medium is then removed and the polymer is recovered
by precipitation in a nonsolvent. Typical nonsolvents include nonpolar
organic liquids such as ketones, ethers and hydrocarbons, for example
acetone, methyl ethyl ketone, methyl isobutyl ketone, diethyl ether,
diisopropyl ether, hexane, cyclohexanol, n-pentane, benzene, and the like.
Following precipitation, the polymer product which is represented by
general Formula III is recovered and optionally washed and/or dried.
##STR3##
wherein CU is the optional copolymeric unit, n is a positive integer and m
is 0 or a positive integer.
HYDROLYSIS
The N-vinylformamide polymers or copolymers so formed are often hydrolyzed
to polymeric amines.
This hydrolysis is suitably carried out in water in the presence of a
strong acid. At least one equivalent of acid per equivalent of
poly(vinylformamide) should be used, such as from 1.05 to 3 equivalents of
acid per equivalent of polymer. Too great an excess of acid can cause the
hydrolysis product to precipitate prematurely. Suitable acids include, for
example, hydrochloric, sulfuric, p-toluene sulfonic, trifluoroacetic,
perchloric and hydrobromic acids, with hydrochloric acid being preferred.
This hydrolysis is carried out at elevated temperatures such as at the
reflux temperature of the solution (about 110.degree. C.) or temperatures
in the range of from about 60.degree. C. to 175.degree. C. and, depending
upon the temperature, requires from about 1 hour to about 36 hours,
preferably 3 hours to 12 hours, to complete.
Following hydrolysis, the polymer salt can be recovered by further
acidifying to cause it to precipitate. This may be carried out by adding
additional acid to a concentration of 1 to 3N, cooling, and isolating the
precipitating polymer. The precipitated polymer initially is a gum, but,
upon drying, forms a granular solid of poly(vinylamine) salt, such as the
hydrochloride or the like. This product is a linear repeating polymer of
the formula
##STR4##
wherein CU is the optional copolymeric unit(s), n is 25 to 10,000 and m is
0 to 10,000 so as to provide a molecular weight of from about 4,000 to
800,000 and X.sup.- is the anion corresponding to the acid employed in the
hydrolysis.
The process may be halted at this point, yielding as its product a
poly(vinylamine) salt. It also may be carried further, such as to form the
free amine. This conversion may be effected by contacting the salt with an
aqueous base such as an alkali metal or alkaline earth metal oxide or
hydroxide, at a pH of 10 or greater. Typical useful bases include sodium
hydroxide and potassium hydroxide. Other basic materials may be used as
well, but are not as advantageous costwise. This neutralization may be
carried out at temperatures in the range of 15.degree.-50.degree. C., such
as at room temperature. This yields the polymeric free amine which may be
isolated and dried, if desired. The polyvinyl amine product is a linear
polymer. It is water-soluble and has a formula
##STR5##
wherein n and m have values as above described such that the polymer has a
molecular weight of from about 2,000 to about 450,000.
One excellent use of the polymeric amine is in the manufacture of polymeric
azo and non-azo colorants with the amine functionalities being useful for
attaching the chromophoric groups to the polymer backbone. This use is
fully described in U.S. Pat. Nos. 4,018,826 and Re. 30,362 of Gless et al;
4,051,138 of Wingard et al, 4,107,336 of Otteson et al or 4,182,885 of
Bunes. It may also be used as a water clarification aid as shown in U.S
Pat. No. 4,217,214 of Dubin or as a polymeric drug backbone as shown in
U.S. Pat. No. 4,190,716 of Parkinson et al. All these patents are herein
expressly incorporated by reference.
The invention will be further described with reference to the accompanying
drawings.
Referring to FIG. 1, ethylidene bisformamide is produced in the presence of
an ion exchange resin catalyst and acetic anhydride. Elongated cylindrical
reactor 10 is charged with a bed 11 of particulate sulfonated
divinylbenzene-cross-linked polystyrene ion exchange resin previously
rinsed with formamide containing 10% acetic anhydride and thereafter
together with the reaction zone, dried. This resin is in the protonated
(H.sup.+) form. Dried formamide, acetaldehyde and acetic anhydride, in a
3:1:0.2 mole ratio, are continuously fed to the top of the resin bed via
valved conduits 12, 14 and 15, respectively. The rate of reactant feed is
regulated to provide a WHSV of from 0.01 to 2 kg of acetaldehyde/kg of
resin/hour. Heat can be added to or removed from reactor 10 by means not
shown as needed to control the reaction temperature above 50.degree. C. A
crude reaction product composed principally of water, unreacted,
acetaldehyde and formamide, acetic acid and ethylidene bisformamide is
continuously removed via valved conduit 16 to metering pump 17 by which it
is fed via conduit 18 to wiped film evaporator 19. Optionally, the crude
reaction product drawn off can be first passed through a filter or the
like.
The evaporator 19, which can be any suitable high speed-low residence time
(high surface area) film evaporator, in the Fig. comprises an outer
housing 20, internal rotating wiper blade 21 driven by shaft 22 and motor
23, and a base 24. Outer housing 20 is maintained at a temperature of
180.degree.-270.degree. C. A vacuum of less than 50 mm Hg absolute is
pulled on evaporator 19 via conduit 25. As the reaction product mixture is
fed into the evaporator it is spread on the inside of heated housing 20 by
rotating wiper blade 21. The feed rate is controlled to give a mean
residence time in the evaporator of about only 2-30 seconds. The clearance
between blade 21 and housing 20 is such that the surface area of the
liquid is about 10-15 cm.sup.2 /gm.
As liquid is fed, it moves from the feed end of evaporator 19 to the
product end. The ethylidene bisformamide product is withdrawn from the
evaporator as a liquid via conduit 27. The water, unreacted reactants,
by-products and acetic acid are taken off as vapors via conduit 25 to a
trap 26 where condensation takes place. The condensed materials are
removed via conduit 28 and the remaining volatiles are removed via conduit
29. The formamide and other unreacted feeds are preferably recovered and
recycled to the feed conduits following condensation by means not shown.
The ethylidene bisformamide, in order to form N-vinylformamide, can then be
passed via line 27 to cracker 32. Cracker 32 is made up of feed vessel 34
equipped with agitator 35 and heating means (not shown) to prevent
solidification of the bisformamide feed. The bisformamide is passed
through line 36 at a rate controlled by valve 37 to pyrolysis column 39
which is heated by means not shown to 200.degree.-250.degree. C. in a top
evaporator stage followed by 550.degree. C. in a lower pyrolysis section
that contains a bed of pyrolysis catalyst. Pyrolysis column 39 is at an
absolute pressure of from 10 to 100 mmHg with a stream of nitrogen
provided via lines 40 and 41 carrying the volatile pyrolysis products down
from column 39 to condenser 42 where the N-vinylformamide liquifies and is
collected in chilled receiver 44. A vacuum is pulled on receiver 44 to
remove volatile contaminants. The N-vinylformamide product is removed via
line 45.
As the continuous process shown in FIG. 1 is run, the resin bed 11
gradually becomes contaminated and deactivated by ammonia and ammonium
salts which are normally present in the formamide feed. Periodically, feed
conduits 12, 14 and 15 are blocked off. The valve on product conduit 16 is
closed and an aqueous mixture of acid and water, such as sulfuric acid, is
charged to the reactor via lines 46 and 47, respectively. This removes the
deactivating salts and returns the resin bed to activity. The acid-water
mixture is removed via conduit 48 and the bed is rinsed with water via
conduit 47 which rinse is also removed via conduit 48. Thereafter, the bed
is optionally rinsed with formamide and acetic anhydride and dried.
In FIG. 2, a schematic flow diagram of a semibatch embodiment of the
process of this invention is there depicted. Formamide and acetic
anhydride are charged to reactor 51 via conduits 52, and 53 respectively.
Particulate ion exchange resin, e.g., sulfonated
divinylbenzene-crosslinked polystyrene, is charged to reactor 51 through
conduit 54 in an amount of 0.2 kg per 1.0 kg of formamide. Acetaldehyde
(1/2 to 1/3 moles per mole of formamide) is then added via conduit 55. The
mixture is heated to about 60.degree. C. by means not shown while stirring
with agitator 56 driven by electric motor 57. After about 30 minutes,
there has been substantial reaction to form ethylidene bisformamide. A
crude reaction product comprising water, unreacted acetaldehyde and
formamide, acetic acid and ethylidene bisformamide is removed via conduit
58 to metering pump 59 by which it is fed to catalyst filter 60 to form a
catalyst phase that is removed via conduit 61 and a catalyst-free stream
that is fed to wiped film evaporator 62 by conduit 64. The clearance
between the blade 65 and housing 66 of evaporator 62 is such that the
surface area of the liquid is about 8-15 cm.sup.2 /gm. The exposure
temperature is about 200.degree. C. and a vacuum in the range of about
25-50 mm Hg absolute is pulled in the evaporator. The ethylidene
bisformamide product is withdrawn from the evaporator 62 via conduit 67 to
cracking as described in FIG. 1 while the remaining constituents are
removed via conduit 69.
The invention will be further described by the following examples. These
are provided to illustrate the invention and are not to be construed as
limiting in scope.
EXAMPLE I
Condensation
Into a 500 ml round-bottomed flank equipped with overhead stirrer,
condenser, pressure regulator, thermowell and oil bath was added 260 g
(5.7 moles) of formamide and 10 g of acetic anhydride. These materials
were stirred for ten minutes to permit the anhydride to react with any
water and ammonia present in the reaction zone. An acidic solid
particulate ion exchange catalyst (Bio-Rad AG-MP-50), 70 g, that had been
previously washed with a dry solution of acetic anhydride in formamide and
then dried, was added. One mole (44 g) of acetaldehyde was then slowly
added with stirring. The reaction warmed itself to about
35.degree.-40.degree. C. during 10 minutes. External heat was added until
the internal temperature reached 50.degree.-54.degree. C. Seventy minutes
after reaction initiation, the reaction mixture was still virtually
colorless. An additional ten g of acetic anhydride was then added and the
reaction was continued for a total of 21/2 hours. The catalyst was then
removed by filtration.
DISTILLATION
A laboratory scale (315 sq cm surface area) wiped film evaporator (WFE) was
preheated and turned on. It had a wall temperature profile of from
160.degree. to 210.degree. C. A vacuum was pulled. The
bisformamide-containing reaction product was then fed to the WFE at a rate
of between 7.75 and 10.6 ml/minute. The WFE vacuum fluctuated as the
liquid was fed and averaged about 20-25 mm Hg. absolute. The ethylidene
bisformamide was taken off as a pale-yellow clear WFE bottoms in an amount
equal to 72% of theoretical. Unreacted formamide and light byproducts were
taken off as a vapor phase.
PYROLYSIS
The above preparation of this example was repeated several times varying
feed concentrations and proportions. The products were the same. One such
repeat was pyrolyzed to form N-vinylformamide as follows: An apparatus as
shown in FIG. 3 was set up. A 30 g ethylidene bisformamide wiped film
evaporator bottoms product was charged to feed pot 65 via line 66. Motor
driven agitator 67 and heating bath 69 at 91.degree.-119.degree. C. melted
the feed. The melted feed was then poured into evaporator 70 along with a
stream of dry nitrogen supplied via line 72. Evaporator 70 was at
252.degree. C. and vaporized the feed. The vaporized feed then passed into
pyrolysis tube 74 containing glass helix bed A. The temperature of the bed
was monitored at five points, T.sub.1, T.sub.2, T.sub.3, T.sub.4, and
T.sub.5. T.sub.1 ranged from 365.degree.-371.degree. C.; T.sub.2 254-266;
T.sub.3 369.degree.-454.degree. C.; T.sub.4 543.degree.-541.degree. C. and
T.sub.5 577.degree.-607.degree. C. The gaseous pyrolysis product was then
condensed in condenser 75 and collected in flask 76 in chiller bath 77. A
vacuum of 14-24 mmHg was maintained during the pyrolysis. The liquid
product contained formamide, side products, small amounts of unpyrolyzed
bisformamide, and N-vinylformamide. While it was not possible to
accurately determine a mass balance yield due to losses to equipment,
etc., anaylsis indicated a bisformamide conversion of about 95%.
The product was distilled using a lab scale (Bantamware) Vigreaux
distillation column. Three cuts were taken with the first being 86-87%
N-vinylformamide, the second being 76% N-vinylformamide and the third
being 47% N-vinylformamide.
EXAMPLE II
The condensation of Example I was repeated with the following changes:
The reactants were
______________________________________
Formamide 270 g 6 moles
Acetaldehyde 88 g 2 moles
Acetic Anhydride 4.3 g
0.04 moles
AG-MP-50 Resin 50 g 0.11 moles
______________________________________
The resin had been previously rinsed with formamide/acetic anhydride
mixture. The condensation was carried out at 51.degree.-67.degree. C. The
acetaldehyde was added over a 47 minute period. The total reaction time
was 85 minutes. The product was filtered to remove the catalyst. A good
quality product, based on its light color, was formed and isolated by WFE.
A twenty gram portion of the product was then pyrolyzed generally following
the method of Example I. Two changes were made, however. First, 4 inches
of the glass helixes of bed A were replaced with marble chips
(CaCO.sub.3). Second, the pyrolysis temperature was lowered to
405.degree.-443.degree. C. in the CaCO.sub.3 area. Again, 90+% conversions
of ethylidene bisformamide to N-vinylformamide were observed.
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