Process for preparation of 2-vinylimidazolines

2-vinyl-2-imidazolines are prepared by cleaving 2-acylamidoethyl-2-imidazolines at suitable temperature, distilling the cleavage products, and recovering the desired product from the distillate.

CROSS-REFERENCE TO RELATED APPLICATIONS 
This application is related to applications Ser. Nos. 867,252 and 867,251, 
filed on even date herewith. The instant application relates to the 
preparation of 2-vinyl-2-imidazolines. Ser. No. 867,252 relates to 
2-acylamido-ethyl-2-imidazoles which are cleaved in the present 
application and Ser. No. 867,351 relates to a process for preparing 
2-acylamidoethyl-2-imidazolines. 
This invention relates to a process for preparing 2-vinyl-2-imidazolines. 
More particularly, this invention relates to such a process wherein a 
2-acylamidoethyl-2-imidazoline is cleaved to provide the desired 
2-vinyl-2-imidazoline. 
The need for high efficiency products for use in the treatment of aqueous 
suspensions of solids has continued to grow in recent years because of the 
increasing awareness of the environment pollution caused by such 
substances and other considerations. Accordingly, there have been 
increased efforts expended in attempts to provide such products which can 
be used to facilitate the dewatering of aqueous suspensions of organic, or 
mixtures of organic and inorganic materials, such as distillery wastes, 
fermentation wastes, wastes from paper manufacturing plants, dye plant 
wastes, and sewage suspension such as digested sludges, activated sludges, 
or raw and primary sludges from sewage treatment plants as well as a host 
of other suspension types. 
The more recent and more successful materials used in the treatment of such 
suspensions have been amidine or imidazoline polymers, see U.S. Pat. Nos. 
3,406,139; 3,450,646; 3,576,740 and 3,666,705. Such polymers are very 
effective materials for use in the treatment of industrial wastes. The 
polymers are produced, however, by the treatment of corresponding nitrile 
polymers and are therefore governed by the structure of the nitrile 
polymers. Furthermore, conversion of the nitrile polymers to the 
imidazoline or amidine form does not reach 100% and therefore a portion of 
the resultant polymer is in improper form to function in water treating 
capacity. 
Prior attempts to obviate these difficulties have included rearrangement of 
the groups present in the nitrile charge polymer and the attempted 
production of unsaturated imidazolines and amides which may be 
homopolymerized or copolymerized into more active imidazoline and amidine 
polymers. However, attempts to produce intermediates, from which the 
unsaturated imidazolines and amidines may be prepared have proven 
unsuccessful. Furthermore, attempts to follow the teachings of U.S. Pat. 
No. 3,210,371 resulted only in the production of undesired polymeric 
material and the teachings of Oxley et al., J. Chem. Soc. 1947, page 
497-505, also resulted in the recovery of undesired polymeric products. 
Recent developments are typified by U.S. Pat. Nos. 4,006,247 and 
4,007,200. In U.S. Pat. No. 4,007,200, there are disclosed intermediates 
which require numerous preparative steps which are difficult to perform, 
thus complicating processing and reducing yields of the intermediate. In 
U.S. Pat. No. 4,006,247, it is disclosed that the intermediates of U.S. 
Pat. No. 4,007,200 can be cracked to provide unsaturated imidazolines and 
amidines. However, the intermediate is unstable in cracking, thus reducing 
yields of unsaturated compounds. The cracking process is difficult to 
perform and undesirable. 
There continues to exist the need for a process for unsaturated 
imidazolines which is free of deficiencies of former processes and 
provides such compounds by simple processing. Such a provision would 
fulfill a long-felt need and constitute a notable advance in the art. 
In accordance with the present invention, there is provided a process for 
preparing compounds of the structure: 
##STR1## 
wherein R.sub.1 is hydrogen or an alkyl group of about 1 to 5 carbon 
atoms, said process comprising heating to cracking temperature a compound 
of the structure: 
##STR2## 
wherein R is an alkyl group of about 1 to 5 carbon atoms and R.sub.1 is 
hydrogen or an alkyl group of about 1 to 5 carbon atoms, distilling the 
cleavage products, and recovering the desired compound from the 
distillate. 
The process of the present invention provides 2-vinyl-2-imidazolines in 
monomer form which can be readily processed to the desired polymers for 
the various uses previously mentioned. The present process employs stable 
intermediates which enable the desired vinylimidazoline monomers to be 
distilled from the reaction vessel under vacuum. 
In carrying out the process of the present invention, the starting 
intermediate is a 2-acylamidoethyl-2-imidazoline of the structure: 
##STR3## 
wherein R is an alkyl group of about 1 to 5 carbon atoms and R.sub.1 is 
hydrogen or an alkyl group of about 1 to 5 carbon atoms. The 
2-acylamidoethyl-2-imidazolines are readily prepared by reacting a 
2-cyanoethylacylamide with a suitable ethylenediamine in equal molar 
proportions under conditions such that one molar equivalent of NH.sub.3 is 
evolved and ring closure results. The 2-cyanoethylacylamides are 
well-known in the art and are obtained by reacting an acylamide with 
acrylonitrile in the presence of a strong alkali. The reaction is 
described in the Chemistry of Acrylonitrile, IV Cyanoethylation of Active 
Hydrogen Groups, Bruson and Riener, J. Am. Chem. Soc., 65, page 23 (1943). 
This reaction is given by the equation RCONH.sub.2 + CH.sub.2 = CHCN 
.sup.alkali RCONHCH.sub.2 CH.sub.2 CN. For purposes of the present 
invention, R is an alkyl group of about 1 to 5 carbon atoms. 
Using a selected 2-cyanoethylacylamide as described, the desired 
2-acylamidoethyl-2-imidazoline is prepared by reaction with an 
ethylenediamine of the structure R.sub.1 HNCH.sub.2 CH.sub.2 NH.sub.2 
wherein R.sub.1 is hydrogen or an alkyl group of about 1 to 5 carbon 
atoms, preferably in the presence of a suitable catalyst. A preferred 
catalyst is sulfur. The reaction is carried out at an elevated temperature 
to minimize reaction time but at a temperature safely below that at which 
decomposition occurs. Reaction is quite rapid, generally 90 minutes or 
less at 115.degree. C. A solvent may be used if desired but reaction can 
be effected in the absence of solvent. The crude product obtained is 
readily purified by recrystallization, for example, and yields of pure 
product are 70% or higher. The reaction follows the equation 
##STR4## 
The reactants are generally employed in equal molar amounts. If a catalyst 
is employed it is used in effective amount. Preferably, sulfur is used at 
a concentration of about 0.5 to 1.0 weight percent based on the weight of 
reactants. As indicated, a solvent may be used if desired and, if used, 
should generally be in an amount providing suitable fluidity to the 
reaction mixture. A preferred solvent is toluene. 
2-acylamidoethyl-2-imidazolines are readily cleaved according to the 
process of the present invention to 2-vinyl-2-imidazolines. In carrying 
out the process of the present invention, the 
2-acylamidoethyl-2-imidazoline is one having the general structure: 
##STR5## 
wherein R is an alkyl group of about 1 to 5 carbon atoms and R.sub.1 is 
hydrogen or an alkyl group of about 1 to 5 carbon atoms. 
The selected 2-acylamidoethyl-2-imidazoline is heated to cracking 
temperature, to provide a 2-vinyl-2-imidazoline and an acylamide according 
to the reaction 
##STR6## 
The cleavage products are distilled and since the 2-vinyl-2-imidazoline 
has a lower boiling temperature than the acylamide, it constitutes a major 
fraction of the distillate. The distillate is collected and the desired 
2-vinyl-2-imidazoline is recovered from the distillate, generally as a 
suitable salt.

The invention is more fully illustrated by the examples which follow 
wherein all parts and percentages are by weight unless otherwise 
specified. 
INTERMEDIATE PREATION 
Preparation of 2-acetamidoethyl-2-imidazoline 
To a 500 ml. round-bottomed flask equipped with a thermometer and reflux 
condenser were added 129.00 grams (1.15 mol) of 2-cyanoethylacetamide, 
67.7 grams (1.13 mol) of ethylenediamine and 1.5 grams of sulfur. The 
reaction mixture was heated to 115.degree. C. and held at that temperature 
for 90 minutes. Solidification of the reaction mixture occurred on 
cooling. The crude product weight 158 grams. It was recrystallized from 80 
mol. of 2 -propanol. 142 grams of pure product were obtained representing 
a yield of 81.2%. The product had a melting point of 
137.degree.-139.degree. C. 
EXAMPLE 1 
Cleavage Of 2-Acetamidoethyl-2-Imidazoline 
To a 250 ml. round-bottomed flask equipped with a distillation head, vacuum 
take-off adapter, and a receiver were added 22.2 grams (0.144 mol) of 
2-acetamidoethyl-2-imidazoline prepared as described above, 70 grams of 
Carbowax 700, 4 grams of potassium hydroxide, 4.8 milligrams of Cupferon 
and 0.5 gram of phenothazine. The mixture was thoroughly mixed and heated 
to 200.degree. C. at a pressure equivalent to 0.5 millimeters of mercury. 
At 80.degree.-125.degree. C. 2-vinyl-2-imidazoline codistilled with 
acetamide. 15.4 grams of product was isolated. NMR analysis of the 
bisulfate salt of 2-vinyl-2-imidazoline indicated a yield of 60%. 
The recovered 2-vinyl-2-imidazoline was readily polymerized in aqueous 
solution to provide a high molecular weight polymer which showed excellent 
properties as a flocculant and dewatering agent. 
EXAMPLE 2 
In 4 milliliters of methanol was dissolved 1.5 grams of 
2-acetamidoethyl-2-imidazoline and the resulting solution was passed 
through a 16 centimeter column of barium oxide impregnated on silica gel 
at 390.degree. C. and a pressure equivalent to 23 millimeters of mercury. 
The 2-vinyl-2-imidazoline was collected as a light yellow solid in a 50 
milliliter round-bottomed flask. The yield of 2-vinyl-2-imidazoline was 
35% by nuclear magnetic resonance measured on the bisulfate salt. 
EXAMPLE 3 
The procedure of Example 1 was repeated in all essential details that 
hydrocarbon wax (M and M7334) was used instead of Celite. 
2-vinyl-2-imidazoline was obtained in 50% yield (NMR). 
EXAMPLE 4 
The procedure of Example 1 was again followed except that Carbowax 600, 45 
grams, was also employed. The yield of 2-vinyl-2-imidazoline was 68%. 
EXAMPLE 5 
The procedure of Example 1 was again repeated except that Carbowax 400, 70 
grams, was also employed. The yield of 2-vinyl-2-imidazoline was 80%. 
EXAMPLE 6 
The procedure of Example 5 was followed reusing the Carbowax used in 
Example 5. The yield of 2-vinyl-2-imidazoline was 64%. 
EXAMPLE 7 
The procedure of Example 1 was again followed except Carbowax 400, 70 grams 
was used in place of Celite and sodium methoxide was used to replace the 
potassium hydroxide employed. The yield of 2-vinyl-2-imidazoline was 75%. 
EXAMPLES 8 - 11 
The following 2-acylamidoethyl-2-imidazolines were satisfactorily cracked 
followed the procedure of Example 1. The compounds and example number are 
listed below. 
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Example 2-acylamidoethyl-2-imidazoline 
No. R-group R.sub.1 -group 
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8 C.sub.2 H.sub.5 -- 
H-- 
9 C.sub.3 H.sub.7 -- 
CH.sub.3 -- 
10 C.sub.2 H.sub.5 -- 
C.sub.2 H.sub.5 -- 
11 CH.sub.3 -- C.sub.3 H.sub.7 -- 
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