Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for producing diols and N,N-
dialkyl carboxylic acid amides which comprises reacting carboxylic acid
esters with dialkyl amines in the presence of a lower alkanol and a trans-
esterification-aminolysis catalyst.
BACKGROUND OF THE INVENTION
The reaction of amines and esters to produce amides and alcohols
has long been known. The practical applicability of this kind of process
is somewhat restricted in scope, however. In particular, the reaction of
secondary amines with esters derived from higher alcohols to produce the
corresponding amides and the alcohols is not a facile process under ordinary
conditions, and other methods are generally practiced. In production of
N,N-dimethylacetamide, for example, dimethylamine and acetic acid are
combined under conditions of elevated temperature and pressure as disclosed
in U.S. Patents 2,667,511 and 3,006,956. Acetic anhydride may also be
employed as the acylating agent as shown in U.S. Patent 3,006,956. In more
recently described methods, N,N-dimethylacetamide is prepared from trimethyl- ~ -
amine and carbon monoxide in the presence of a cobalt carbonyl catalyst as
described in U.S. Patent 3,407,231, or by reaction of dimethylamine and
ketene as disclosed in U.S.S.R. Patent 183,731.
N,N-dimethylacetamide has been produced in relatively low yield
by reaction of dimethylamine and polyvinyl acetate in methanol solvent in
absence of added catalyst as shown in U.S. Patent 3,197,450. N,N-dimethyl- -
acetamide has also been produced by reaction of aqueous dimethylamine with
allyl acetate or vinyl acetate as described in Netherlands Application
6,602,128. In the latter process, a substantial amount of acetic acid by-
product is also formed.
N,N-dialkyl carboxylic acid amides have found important utility.
N,N-dimethylacetamide and N,N-dimethylformamide in particular are widely
used in spinning of fibers and in other solvent applications.
-1- ~ -
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.
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Diols also constitute a class of valuable compounds. They have
wide utility in manufacture of polyesters and polyurethanes and as solvents
and synthetic intermediates. There are a number of methods known in the
art by which diol esters may be converted to these more useful diols.
Aqueous base hydrolysis is unacceptable in that it involves the formation
of salts which must be treated for recovery of their valuable components.
With esters of 1,4-butanediol especially, acidic conditions can be employed ;only with severe restrictionsj so as to avoid the cyclization reaction
producing tetrahydrofuran.
In Canadian applications of Will Dockery Merritt, Jr., Ser.
No. 196,825, dated April 4, 1974, and John E. Corn et al, Ser.
No. 209,309 dated September 16, 1974, both assigned to the
same assignee as this invention, processes involving alcoholysis
of diol esters promoted by alkali metal hydroxides and acidic
ion exchange resins, respectively, are disclosed. In a
Canadian application of William Edward Smith, Serial No.
217,507 dated Jan/7/1975, and assigned to the same assignee -~
as this invention, the vapor phase alcoholysis of diol esters
over magnesia catalysts is described.
DESCRIPTION OF THE INVENTION -~
It has been discovered that diols and N,N-dialkyl carboxylic ~ ~ -
acid amides can be obtained from the corresponding carboxylic acid esters -~ -
and dialkyl amines by a highly efficient method which involves the use of
a lower alkanol mediating agent and a transesterification-aminolysis catalyst.
This invention has been found particularly useful for simultaneously producing
diols and N,N-dimethyl carboxylic acid amides from the corresponding diol
esters. In this case especially methanol solvent and a basic catalyst (such
as sodium hydroxide) serve to bring about rapid reaction under mild conditions, -
affording the desired products in excellent yield and to the virtually com-
plete exclusion of any by-products. mè term "diol esters" refers to
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particular diol esters and mixtures of diol esters as well. The term is
also meant to include both mono- and di-ester derivatives of diols.
The process is illustrated for the case of production of 1,4-
butanediol and N,N-dimethylacetamide from 4-acetoxybutanol and dimethylamine
in equation (1): -
(1) ,
,~ base catalyst ,.
HO(CH2)4 C CH3 + (CH3) NH ~ HO(CH2)4 OH ~ Me2 N C CH3
The process may be employed for conversion of a wide variety of
diol carboxylic acid esters including aliphatic, cycloaliphatic and aromatic
diol esters. Preferrably these are aliphatic diol esters. Most preferred ~
diol esters include acetates and formates of 1,4-butanediol, 2-methyl-1,3- -
propanediol, 1,2-butanediol, 1,3-propanediol, 1,2-propanediol, ethylene gly-
col, 1,6-hexanediol, 1,5-pentanediol, 2-methyl-1,4-butanediol and 1,4-di(hydro-
xymethyl) cyclohexane. The method is particularly applicable to production
of a mixture of 1,4-butanediol, 2-methyl-1,3-propanediol and 1,2-butanediol
from a mixture of the corresponding acetate esters.
The dialkyl amines included within the scope of this invention are
those wherein each alkyl group contains from 1 to 4 carbon atoms.
The lower alkanols that may be employed in this invention are those
which contain one to six carbon atoms. The preferred alkanol is methanol. ~~
Since the lower alkanol is not consumed in the reaction, it may be used in
amounts that vary widely. It may be used as the solvent or, alternatively,
in amounts as small as one equivalent or less.
The transesterification-aminolysis catalysts that may be used
within the scope of this invention are bases that are known in the art to
promote transesterification reactions. These include alkali metal and
.. , ~
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alkaline earth metal hydroxides, alkoxides and carboxylates, examples of
which are sodium hydroxide, potassium hydroxide, magnesium hydroxide, sodium
methoxide and lithium acetate. Strongly basic ion exchange resins may also
be employed as catalyst; resins bearing the quaternary ammonium hydroxide
function are very effective.
The temperature at which the process can be carried out varies widely
and is not critical. Temperatures from room temperature to about 225C are
found suitable. A preferred temperature range is from about 60C to about
180C.
A wide range of pressure may be used within the scope of this in-
vention since pressure is not critical. Preferred pressure ranges are
those that are required to contain the dialkyl amine at the operating tempera-
ture.
The actual course by which this transformation proceeds is illustrated
in equations 2 and 3 for the case of production of 1,4-butanediol and N,N-
dimethylacetamide from 4-acetoxybutanol and dimethylamine in the presence
of methanol and a basic catalyst. me net conversion is shown in equation 4. -
(2)
" OH O .
HO(CH2)4 0 C CH3 + CH30H - ~ Ho(cH2)4oH + CH3 0 C CH3
(3) 0
.. -OH ..
CH3 0 C CH3 + (CH3)2NH > CH30H + (CH3)2 N C 3
(4) ~; -
O O
20HO(CH2)4 0 C CH3 + (CH3)2 NH HO(CH2)4 OH + (CH3)2 N C C 3
As indicated, the methanol participates in the process by entering
into a transesterification reaction with the ester starting material. me
methyl acetate produced is a more efficient acylating agent than the diol
esteri under the process conditions, it readily combines with dimethylamine
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to form N,N-dimethylacetamide with regeneration of the methanol. (This
reaction course was observed experimentally using gas-liquid partition
chromotography (glpc) analysis.) Both the transesterification and aminolysis
reactions are accelerated by the catalyst.
An important feature of this method is the facility with which
the complete conversion of the diol ester to the diol is accomplished. The
purification of that product is accordingly made considerably easier. Any
incompletely converted lower alkanol carboxylate intermediate (for example,
methyl acetate as in equations 1 and 2) can be recycled with the excess ,~
amine and lower alkanol, and can in that way be ultimately used in the amide
formation.
The process can be efficiently carried out by heating the combined
ester, amine, alkanol and catalyst in an autoclave until a satisfactory
conversion to the diol and amide is attained. me products can be isolated
by distillation, with recycle of the alkanol (and unconverted lower alkanol
carboxylate as mentioned supra) to the reaction vessel. The catalyst can
be recycled in the distillation residue.
PREFERRED EMBODIMENT OF THE INVENTION
The following examples are set forth to illustrate more clearly
the principle and practice of this invention to those skilled in the art. -
Unless otherwise specified, where parts or percents are mentioned, they are
parts or percents by weight.
EXAMPLE I -
Dimethylamine gas was bubbled into a solution of 25.0 grams of 1,4-
butanediol diacetate in 100 ml of methanol. When about 15 grams had been
absorbed, 0.5 grams of sodium hydroxide was added. The mixture warmed
spontaneously; analysis by glpc within three minutes showed that the diace-
tate had already reacted with the solvent to produce an equilibrium mixture
of methyl acetate, butanediol and the monoacetate, with but a small amount
,: . ,
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of residual diacetate. A small amount of N,N-dimethylacetamide had also
appeared.
The mixture was heated at reflux (50C) for one hour while more
of the amine was bubbled in (total of about 50 grams). During this time,
the acetates were consumed and the diol and amide were produced as the
exclusive products. Direct quantitative glpc analysis of the mixture
(chlorobenzene as added internal standard) at that point revealed the
presence of 12.9 grams of 1,4-butanediol (100% yield) and 25.1 grams of
N,N-dimethylacetamide (100% yield). -
EXAMPLE II
A solution of 25.0 grams of 1,4-butanediol diacetate and 100 ml :
of methanol was saturated with dimethylamine gas, then treated with 0.5
grams of sodium methoxide. The mixture was examined by glpc within a minute
of the catalyst addition and was found to be more than halfway converted r
` 15 to the equilibrated methyl acetate-diol monoacetate-diol diacetate mixture.
It was heated at reflux while dimethylamine was slowly added. After three - -
hours at 60C, the solution was cooled and subjected to quantitative glpc
- analysis, which revealed the presence of 12.2 grams of 1,4-butanediol (95%
yield) and 19.6 grams of N,N-dimethylacetamide (78% yield). Distillation -~ -
afforded the isolated products for spectral comparison with authentic ~ -
samples.
EXAMPLE III
A solution of 9.0 grams of dimethylamine in 43.0 grams of methanol -~
was combined in a "Vitro 400" pressure bot.le with 0.3 grams of potassium
hydroxide and 10.0 grams of crude butanediol acetate obtained from allyl
acetate via the oxo process (containing, as determined by glpc analysis of
a completely acetylated sample, 60 m mols of 1,4-butanediol derivatives, c
3.9 m ls of 2-methyl-1,3-propanediol derivatives and 9.6 m mols of 1,2-
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butanediol derivatives). The mixture was heated at 85C for 30 minutes,
then cooled and subjected to glpc analysis. me essentially complete con-
version to N,N-dimethylacetamide and the diols (1,4-butanediol, 2-methyl-1,3-
propanediol and 1,2-butanediol are indicated.
S EXAMPLE IV
A mixture of 7.3 grams of ethylene glycol diacetate, 9.0 grams of
dimethylamine, 44.7 grams of methanol and 0.2 grams of sodium hydroxide
was heated in a pressure bottle at 110-130C for one hour. me product
mixture was cooled and subjected to quantitative glpc analysis, which
indicated the presence of 2.8 grams of ethylene glycol (90% yield), 6.6 -~
grams of N,N-dimethylacetamide (76% yield) and 1.8 grams of methyl acetate
(24% yield). On the basis of 76% conversion of the methyl acetate inter- - -mediate, the yield of N,N-dimethylacetamide was 100~.
EXAMPLE V
A mixture of 7.4 grams of 1,4-butenediol diacetate, 9.0 grams of
dimethylamine, 44.7 grams of methanol and 0.2 grams of sodium hydroxide
was heated in a pressure bottle at 150C for two hours. The product
solution was cooled and subjected to quantitative glpc analysis, which
indicated the presence of 7.1 grams of N,N-dimethylacetamide (96% yield)
and 1.7 grams of 1,4-butenediol (45% yield).
EXAMPLE VI
A mixture of 8.7 grams of 1,4-butanediol diacetate, 9.0 grams of
dimethylamine, 43.0 grams of methanol and 0.5 grams of lithium acetate
dihydrate was heated at 140C for 20 minutes in a pressure bottle, then cooled `
and subjected to glpc analysis. The substantial conversion to 1,4-butanediol
and N,N-dimethylacetamide was indicated.
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~. .
EXAMPLE VII
A mixture of 11.8 grams of ethylene glycol diformate, 13.0 grams
of dimethylamine, 23.4 grams of methanol and 5.0 grams of Rexyn~ 201 basic
+ --
ion exchange resin (R4N OH form) was stirred at 25C for 30 minutes.
5 Analysis of the supernatant liquid showed that complete conversion to
ethylene glycol and N,N-dimethylformamide had been effected in that time.
A quantitative analysis showed the presence of 5.7 grams of ethylene glycol
(92% yield) and 13.9 grams of N,N-dimethylformamide (95% yield). A trace
of methyl formate was also detected. -~ -
EXAMPLE VIII
This example is included to show that the base catalyst promotes - :~
the aminolysis as well as the transesterification reaction in this process.
A mixture of 7.4 grams of methyl acetate, 9.0 grams of dimethylamine ;;
and 43.0 grams of methanol was stirred at 25C. After one hour, no N,N-
dimethylacetamide could be detected. At that point, 0.3 grams of sodium
hydroxide was added. Within minutes the presence of the amide was evident
(glpc analysis). After two hours, the reaction was about 80% complete.
After 16 hours, no residual methyl acetate was detected; the conversion to
N,N-dimethylacetamide was complete. -
It will thus be seen that the objects set forth above among those
~- ~ made apparent from the preceding description are efficiently attained and
since certain changes may be made in carrying out the above process and in
the composition set forth without departing from the scope of this invention,
it is intended that all matters contained in the above description shall
be interpreted as illustrative and not in a limiting sense.
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