Process for the preparation of diacetone acrylamide

A process is disclosed whereby acrylonitrile and diacetone alcohol are reacted in at least 93% sulfuric acid to form a novel intermediate reaction product which is recovered as a crystalline solid, washed with an organic solvent to remove colored oily impurities along with sulfuric acid, and hydrolyzed to produce diacetone acrylamide, a reactive monomer useful for preparing polymeric components of photographic films and adhesives. The intermediate reaction product is identified as 5,6-dihydro-6-hydroxy-4,4,6-trimethyl-2-vinyl-1,3(4H)-oxazine sulfate (1:1).

BACKGROUND OF THE INVENTION 
This invention relates to a new process for the preparation of diacetone 
acrylamide (also referred to hereinafter as DIAC), also known as 
N-(1,1-dimethyl-3-oxobutyl)acrylamide, which is represented by formula 
(I). 
##STR1## 
Applicant is not aware of any prior art reference which, in his judgment as 
one skilled in the art of preparing diacetone acrylamide, would anticipate 
or render obvious the process of the instant invention; however, for the 
purpose of fully developing the background of the invention and 
establishing the state of the requisite art, the following references are 
set forth. 
In U.S. Pat. No. 3,649,688, an improved method is disclosed for preparing 
DIAC by reacting acrylonitrile with diacetone alcohol in the presence of 
sulfuric acid, the improvement comprising preparing a mixture of 
acrylonitrile and sulfuric acid, said sulfuric acid being at least 93% 
concentration, and the molar ratio of sulfuric acid to acrylonitrile being 
at least 1.6 to 1, introducing the diacetone alcohol into said mix at a 
temperature below 30.degree. C. and maintaining said temperature during 
the reaction of the alcohol with the acrylonitrile, and recovering the 
DIAC from the reaction mixture. However, the product obtained is 
yellow-colored and contains about 5-10% by weight of acrylamide 
by-product. 
In U.S. Pat. No. 3,542,867, an improved method is disclosed for preparing 
diacetone acrylamide by reacting diacetone alcohol, or mesityl oxide, or 
at least 2 moles of acetone in the presence of acrylonitrile and sulfuric 
acid, the improvement consisting of diluting the reaction mixture with 
water to a sulfuric acid content of 25-80% by weight, extracting the DIAC 
from the acidic reaction mixture with a water-immiscible organic solvent 
and recovering the DIAC from the extract. 
In U.S. Pat. No. 3,542,875, an improved method is disclosed for preparing 
DIAC by reacting one mole of acrylonitrile with at least one mole of 
diacetone alcohol or mesityl oxide, or with at least two moles of acetone, 
in the presence of at least one mole of sulfuric acid, neutralizing the 
reaction mixture by addition of alkali to a pH at least above 7.5 and 
subsequently extracting with a water-immiscible organic solvent and 
recovering DIAC therefrom, the improvement consisting of heating the 
organic solution of DIAC at 50.degree.-100.degree. C. with aqueous alkali 
and recovering DIAC from the organic solution. 
The DIAC produced by the process of the present invention has advantages 
over that produced by the processes of U.S. Pat. Nos. 3,542,867 and 
3,542,875 in that it requires no further purification after isolation. The 
product obtained is substantially free of colored and polymeric 
by-products. 
In U.S. Pat. No. 3,277,056, a series of equations is disclosed to 
illustrate the preparation of diacetone acrylamide by reacting diacetone 
alcohol and acrylonitrile in the presence of sulfuric acid. A hypothetical 
intermediate in this reaction is assigned formula (II) 
##STR2## 
with the understanding that the formula is only illustrative. However, no 
intermediate such as (II) is actually isolated. 
In general, the prior art teaches the preparation of DIAC by reacting 
acrylonitrile and 4-hydroxy-4-methyl-2-pentanone in the presence of at 
least 93% sulfuric acid, the mole ratios of said sulfuric acid and 
acrylonitrile to said 4-hydroxy-4-methyl-2-pentanone being about 1-2 and 
1-1.5 moles, respectively, at a temperature below 15.degree. C., allowing 
the reaction mixture to warm up to ambient to moderately elevated 
temperatures to complete the reaction, cooling the reaction mixture, 
contacting the reaction mixture with water and a water-immiscible organic 
solvent, neutralizing the aqueous phase with an alkalizing agent, 
separating the organic phase, stripping the organic phase of volatile 
materials, and recovering N-(1,1-dimethyl-3-oxobutyl)acrylamide therefrom. 
DIAC is useful in photographic films, adhesives, as a reactive 
cross-linking monomer in unsaturated polyester resins, as a stabilizer in 
paper and glass reinforced prepregs, and as an additive in hydrocarbon 
oils. For a description of how to use as an oil additive, see for example, 
U.S. Pat. No. 3,227,056, Example 18, which is incorporated herein by 
reference. 
In order to obtain DIAC of acceptable color and purity for use in 
photographic films, it has been generally necessary either to distill or 
recrystallize the crude product. 
There is a need, therefore, for a process that will give high yields of 
essentially colorless DIAC, having a melting point above 54.degree. C., 
which does not have to be purified by subsequent recrystallization or 
distillation. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided a process for 
preparing N-(1,1-dimethyl-3-oxobutyl)acrylamide via a novel crystalline 
intermediate reaction product comprising reacting acrylonitrile and 
4-hydroxy-4-methyl-2-pentanone in the presence of at least 93% sulfuric 
acid, at a temperature below about 20.degree. C., to form a reaction 
mixture; heating the resulting reaction mixture up to a temperature of 
about 55.degree. C. to complete the reaction; cooling the reaction mixture 
to about 15.degree. C. and adding a suitable organic solvent thereto, 
while maintaining the temperature at about 15.degree.-20.degree. C., to 
precipitate a crystalline intermediate reaction product from said reaction 
mixture; washing said intermediate reaction product with a suitable 
organic solvent to remove oily impurities and sulfuric acid therefrom; 
dissolving the crystalline intermediate in water and contacting the 
resulting aqueous solution with a suitable water-immiscible organic 
solvent to form a liquid two-phase mixture consisting of an aqueous phase 
and an organic phase; neutralizing or alkalizing the aqueous phase with an 
alkalizing agent; separating the neutralized or alkalized aqueous phase; 
and recovering N-(1,1-dimethyl-3-oxobutyl)acrylamide from the organic 
phase. 
In a preferred embodiment, after separating the neutralized or alkalized 
aqueous phase, the organic phase is stripped of volatile materials before 
recovering N-(1,1-dimethyl-3-oxobutyl)acrylamide therefrom. 
In a more preferred embodiment, after separating the neutralized or 
alkalized aqueous phase, the organic phase is contacted with a 
decolorizing agent, preferably after stripping volatile materials from the 
organic phase, the decolorizing agent is separated, and the 
N-(1,1-dimethyl-3-oxobutyl)acrylamide is recovered from the organic phase. 
In the preferred embodiments, the crystalline intermediate is precipitated 
from the reaction mixture by adding acetone thereto, and the 
water-immiscible organic solvent of the dissolving step is toluene. Still 
more preferably, the water-immiscible organic solvent of the dissolving 
step is a recycled mother liquor from the liquid organic phase of the 
recovering step. Preferably, the recycled mother liquor from the recovery 
step is toluene. 
There is also provided a process for preparing the above-described 
crystalline intermediate, 
5,6-dihydro-6-hydroxy-4,4,6-trimethyl-2-vinyl-1,3-(4H)-oxazine sulfate 
(1:1) a novel compound represented by formula (III), 
##STR3## 
by reacting acrylonitrile and 4-hydroxy-4-methyl-2-pentanone in the 
presence of at least 93% sulfuric acid, at a temperature below about 
20.degree. C., to form a reaction mixture; heating the resulting reaction 
mixture up to a temperature of about 55.degree. C. to complete the 
reaction; cooling the reaction mixture to about 15.degree. C. and adding a 
suitable organic solvent thereto, while maintaining the temperature at 
about 15.degree.-20.degree. C. to precipitate 
5,6-dihydro-6-hydroxy-4,4,6-trimethyl-2-vinyl-1,3-(4H)-oxazine sulfate 
(1:1), and recovering the same. In this process the suitable organic 
solvent is selected from the group consisting of acetone, methyl isobutyl 
ketone, mesityl oxide, and isopropanol. 
FIG. 1 is an infrared absorption spectrum of the compound 
5,6-dihydro-6-hydroxy-4,4,6-trimethyl-2-vinyl-1,3-(4H)-oxazine sulfate 
(1:1). 
The processes of the present invention offer the following advantages. The 
DIAC obtained is essentially colorless, essentially free of polymeric 
materials and acrylamide, and melts above 54.degree. C. The purity of the 
DIAC obtained is so high that recrystallization or distillation is 
unnecessary. This results in a substantial saving in operating costs. By 
recycling the toluene mother liquors, the yield of DIAC can be increased 
to as high as 45% of theoretical based on diacetone alcohol. Isolation of 
the crystalline intermediate of formula (III) renders the process 
operationally flexible since it can be stored and used at a later time. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
The process of this invention may be divided into the following stages: 
(1) The formation and isolation of the crystalline intermediate reaction 
product, referred to hereinafter as the intermediate. 
(2) The removal of impurities from the intermediate by washing with an 
appropriate solvent. 
(3) The neutralizing or alkalizing of the intermediate to form DIAC. 
(4) The removal of colored impurities from the DIAC by treatment of a 
solution of the DIAC with a decolorizing agent. 
(5) The isolation of the DIAC. 
The various stages of the present invention are described in detail below: 
(1) FORMATION AND ISOLATION OF THE INTERMEDIATE 
At least 93% sulfuric acid, preferably 96-98%, is cooled to about 
-10.degree. C. to 20.degree. C., preferably about 0.degree.-5.degree. C., 
and a mixture of acrylonitrile and diacetone alcohol is added thereto over 
a period of 1-20 hours, preferably 2-4 hours, while maintaining the 
temperature of the reaction mixture at -10.degree. C. to 20.degree. C., 
preferably about 0.degree.-5.degree. C. About 1-2 moles of sulfuric acid 
and about 1-1.5 moles of acrylonitrile are used per mole of 
4-hydroxy-4-methyl-2-pentanone. In the most preferred embodiment, about 2 
moles of sulfuric acid and about 1-1.2 moles of acrylonitrile are used per 
mole of 4-hydroxy-4-methyl-2-pentanone. The reaction mixture is stirred 
about 0-20 hours at -10.degree. C. to 20.degree. C., preferably 1/2-1 
hours at 0.degree.-5.degree. C., allowed to warm up to 
30.degree.-60.degree. C. over a period 1-20 hours, preferably to 
45.degree.-50.degree. C. over a period of 3-6 hours, held at 
30.degree.-60.degree. C. for a period of 1/2-20 hours, preferably at 
45.degree.-50.degree. C. for a period of 1-3 hours, cooled to 
10.degree.-30.degree. C., preferably to 10.degree.-20.degree. C., allowed 
to stand until the crystallization of the intermediate from the reaction 
mixture is complete, and the crystals are then recovered. 
In an alternative preferred embodiment, the procedure of (1) is followed in 
every detail up to and including the cooling step after the warm up step. 
The reaction mixture is then diluted with a suitable organic liquid 
solvent to precipitate the intermediate from the solution. Suitable 
organic solvents include acetone, methyl isobutyl ketone, ethanol, 
isopropanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 
2-methyl-2-propanol, methyl ethyl ketone, diethyl ketone, mesityl oxide, 
and the like. The resulting slurry is stirred at 0.degree.-30.degree. C., 
preferably at 15.degree.-20.degree. C., for a period of about 1/2-20 
hours, preferably about 1-3 hours, and then processed following the 
procedures of (2) to (5) below. 
(2) PURIFICATION OF THE INTERMEDIATE 
The crude crystals from (1) are washed with a suitable organic liquid 
solvent to remove sulfuric acid, oily colored impurities and by-product 
acrylamide therefrom. Suitable solvents include acetone, ethanol, 
isopropanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 
2-methyl-2-propanol, methyl ethyl ketone, methyl isobutyl ketone, diethyl 
ketone, mesityl oxide, and the like. The preferred solvent is acetone. If 
an alcohol is used to wash the crystals, it should be cold, about 
-10.degree. C. to 0.degree. C. 
(3) NEUTRALIZATION OR ALKALIZATION OF THE INTERMEDIATE 
The washed crystals from (2) are dissolved in water at ambient temperature 
using about 0.5 part to about 2 parts of water per part of intermediate 
and the resulting solution is mixed with a suitable water-immiscible 
organic solvent in which DIAC is soluble, using about 1-2 parts by volume 
of said water-immiscible organic solvent per part by weight of 
intermediate. Suitable water-immiscible organic solvents include naphtha, 
chloroform, methyl isobutyl ketone, dibutyl ether, aromatic hydrocarbons 
such as benzene, toluene, xylene, and the like. The preferred 
water-immiscible organic solvent is toluene. 
The stirred two-phase mixture is cooled to about 5.degree.-30.degree. C., 
preferably about 15.degree.-20.degree. C., and an alkalizing agent, 
preferably 50% caustic soda, is added to adjust the pH of the aqueous 
layer to about 7-12, preferably about 9-10, to convert the intermediate to 
DIAC. It is critical that the washed crystals from (2) be dissolved in 
water and mixed with the water-immiscible organic solvent before adding 
the alkali in order to avoid the formation of low-molecular-weight 
polymers. On completion of the addition, the temperature should be between 
32.degree. C. and 40.degree. C. Keeping the temperature above 32.degree. 
C. avoids the precipitation of sodium sulfate, while keeping the 
temperature below 40.degree. C. avoids the formation of polymers. The 
two-phase mixture is stirred for about 1/2-20 hours, preferably about 
1/2-7 hours, to complete the extraction of the DIAC into the 
water-immiscible organic solvent, and the aqueous phase is separated after 
allowing the mixture to settle. 
(4) THE REMOVAL OF COLORED IMPURITIES 
The organic phase from (3) is dried to a water content of about 0.1-1% by 
weight, preferably about 0.1-0.5%, by azeotropic distillation under vacuum 
while keeping the temperature of the solution below 40.degree. C. The 
dried solution is then stirred with finely powdered, heat-activated 
alumina, for example activated Alumina F-1 (Aluminum Company of America), 
using about 0.05-1 part, preferably 0.1-0.2 part of No. 325 mesh activated 
alumina per part by volume of dried organic, for a period of about 1/2 
hour to remove colored impurities and the mixture is clarified by 
filtration. Other decolorizing agents which may be used include carbon 
black, Super-Filtrol.RTM. (Filtrol Corporation) and the like. In a most 
preferred embodiment, the organic phase is stripped of volatile materials 
before being contacted with the decolorizing agent. 
(5) THE ISOLATION OF DIAC 
The clear filtrate from (4) is cooled to about -10.degree. C. to 20.degree. 
C., preferably about -8.degree. C. to 10.degree. C., and stirred thereat 
for about 1-20 hours, preferably about 2-8 hours, to crystallize the DIAC. 
The crude DIAC is then recovered by filtration, washed with a cold 
(-5.degree. to -10.degree. C.) water-immiscible organic solvent, 
preferably toluene at about -8.degree. C., and dried. The overall yield of 
4-hydroxy-4-methyl-2-pentanone is about 30-35% of theoretical, depending 
on the quality of the product desired. Reuse of the recovered mother 
liquor in (3) increases the overall yield to about 40-45% of theoretical. 
The product obtained melts above 54.degree. C. and contains less than 0.1% 
by weight of acrylamide.

The following examples further illustrate the invention. All parts and 
percentages are by weight unless otherwise specified. All ranges expressed 
are inclusive of both numbers. 
EXAMPLE 1 
Preparation of 
5,6-Dihydro-6-Hydroxy-4,4,6-Trimethyl-2-Vinyl-1,3-(4H)-Oxazine Sulfate 
(1:1) 
##STR4## 
Sulfuric acid (392 grams; 98% real; 3.92 moles) is cooled to 0.degree. C. 
and a mixture of acrylonitrile (113.5 grams; 2.14 moles) and diacetone 
alcohol (203.5 grams; 1.75 moles) is added thereto over 1.5 hours while 
maintaining the temperature at 0.degree.-5.degree. C. The resulting 
mixture is stirred at 0.degree.-5.degree. C. for 0.5 hour, allowed to warm 
up slowly to 40.degree.-42.degree. C., held thereat for 3 hours and then 
cooled at 15.degree. C. Acetone (443 grams; 0.625 ml./gram of reaction 
mixture) is added to the reaction mixture while keeping the temperature at 
15.degree.-20.degree. C. Upon completion of the addition, the solution is 
cooled to 0.degree.-5.degree. C. and held thereat for 4 hours. The 
resulting crystals are separated by filtration, washed with acetone and 
dried to obtain 234 grams of product which has the infrared absorption 
spectrum shown in FIG. 1. The yield of product is 50% of theoretical based 
on diacetone alcohol. 
Calculated for C.sub.9 H.sub.17 NO.sub.6 S: C,40.45%; H,6.41%; N,5.24%; 
S,11.97%; Found: C,39.77%; H,6.35%; N,5.10%; S,11.74%; H.sub.2 O, 1.55% 
Corrected for 1.55% H.sub.2 O: C,40.40%; H,6.28%; N,5.18%; S,11.92% 
Calculated for % H.sub.2 SO.sub.4 : 36.7% 
EXAMPLE 2 
Sulfuric acid (392 grams; 98% real; 3.92 moles) is cooled to 0.degree. C. 
and a mixture of acrylonitrile (113.5 grams; 2.14 moles) and diacetone 
alcohol (203.5 grams; 1.75 moles) is added thereto over 1.5 hours while 
maintaining the temperature at 0.degree.-5.degree. C. The resulting 
mixture is stirred at 0.degree.-5.degree. C. for 0.5 hour, allowed to warm 
up slowly to 40.degree.-42.degree. C., held thereat for 3 hours and then 
cooled at 15.degree. C. 
Acetone (500 mls.) is added to the reaction mixture while maintaining the 
temperature between 15.degree.-20.degree. C. After stirring for 1 hour, 
the resulting crystals are filtered, washed with acetone and dried. The 
crystals (283 grams) are dissolved in water (500 mls.) and toluene (500 
mls.) is added thereto to form a two-phase mixture. The mixture is cooled 
to 15.degree. C., and caustic soda (110 mls. of 50% real) is added thereto 
while maintaining the temperature between 15.degree.-20.degree. C. After 
stirring for 0.5 hour, the aqueous layer is separated and the organic 
layer is dried by azeotropic distillation (176 mls. of distillate). The 
residual solution is stirred with heat-activated alumina (10 grams; 325 
mesh) for 0.5 hour and filtered. The filtrate is cooled to 10.degree. C. 
and the resulting crystals are recovered and dried to obtain 93 grams of 
diacetone acrylamide (31% of theoretical; m.p. 55.8.degree.-56.7.degree. 
C.). 
In the manner described above, substituting ethanol, isopropanol, methyl 
ethyl ketone, mesityl oxide or methyl isobutyl ketone for the acetone, 
similar crystals are obtained. 
EXAMPLE 3 
Sulfuric acid (98%; 391.6 grams; 3.91 moles) is charged to a suitable 
reactor vessel and cooled to 0.degree. C. A mixture of acrylonitrile 
(113.5 grams; 2.14 moles) and diacetone alcohol (203.5 grams; 1.75 moles) 
is added thereto over a period of 1.5 hours while maintaining the reaction 
mixture at 0.degree.-5.degree. C. The reaction mixture is then stirred at 
0.degree.-5.degree. C. for an additional 0.5 hour and allowed to slowly 
warm up to 25.degree. C. The reaction mixture is then carefully and slowly 
heated to 40.degree.-42.degree. C., held thereat for 3 hours, and then 
cooled to 10.degree. C. After standing at 10.degree.-20.degree. C. for 96 
hours, the resulting crystals are recovered by filtration. 
The crystals are dissolved in water (500 mls.), toluene (500 mls.) is added 
thereto, the two-phase mixture is cooled to 15.degree. C. and aqueous 
sodium hydroxide (50% real; 110 mls.) is added thereto while keeping the 
temperature at 15.degree.-20.degree. C. After stirring for about 0.5 hour, 
the aqueous layer is separated and the toluene layer is dried by 
azeotroping off the water. The residual toluene solution is stirred with 
activated alumina (10 grams of No. 325 mesh) for 0.5 hour and clarified by 
filtration. The filtrate is then cooled to 10.degree. C., and the 
resulting crystals are recovered by filtration and dried to obtain 
diacetone acylamide (50 grams; 20% of theoretical) which melts at 
55.0.degree.-57.2.degree. C. 
EXAMPLE 4 
The procedure of Example 2 is followed in every detail utilizing 500 mls. 
of toluene mother liquors from a previous preparation of DIAC to extract 
the alkalized product from the aqueous phase. The yield of DIAC is 39% of 
theoretical. The product is of acceptable purity. 
EXAMPLE 5 
The procedure of Example 2 is followed in every detail utilizing the 
toluene mother liquors recovered from Example 4 to extract the hydrolysis 
product from the aqueous phase. The yield of DIAC is 45% of theoretical. 
The product is of acceptable purity.