Note: Descriptions are shown in the official language in which they were submitted.
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-- 2 --
The industrial preparation of acetoacetic acid
alkyl esters is carried out today, in general, by reaction
of diketene with the corresponding anhydrous aliphatic
alcohol. In this reaction, a crude product is ob-
tained which contains several low-boiling, middle-boiling
and high-boiling compounds, apart from the des1red aceto-
ac_tic acid alkyl ester. Above all, excess alcohol, ace-
~one and alkyl acetate are contained in the crude ester
as low-boiling compounds. In general, dehydroacetic acid
and a thermally little stable residue, which is formed
from diketene, are present as high-boiling compounds.
Mainly 3-acetoxy-crotonic acid alkyl or alkenyl esters, that is, ir.-
the Ci9 form and the trans form, and 3-acetoxyvinylacetic
acid alkyl or alkenyl esters occur as middle-boiling c ~ ounds which
boil in the range of the corresponding acetoacetic acid
alkyl ester. ~he pure acetoacetic acid alkyl ester is
obtained from th s complex mixture by fractional distil-
lation.
Whilst the low-boiling compounds and the high-
boiling compounds may be separa~ed off without difficulty,
this operation in the case of the middle-boiling compounds
3-acetoxycrotonic acid alkyl or alkenyl ester and 3-acetoxyvinyl-
a^etic acid alkyl or alkenyl ester - mostly referred to as AC-ester
or AV-ester in the following text - is not straight-
forward. A separation of these components by fractionaldistillation is troublesome and is successful only with
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~5~528
a high re ~u~ ratio,
In ~heory, a simpler possibility would be a
specific chemical conversion o~ these interfering sub-
stances into o~her compounds more easily separable by
distillation. Ho~ever, it had to be taken into con-
sideration, in this case, that the-acetoacetic acid
alkyl ester present as the main component o~ the mixture
contains three reactive groups - a carbonyl group, a
carbalkoxy group and an active methylene grcup - ard is
there~ore very reactive. A chemical conversio~ of the
interfering components AC-esier and AV-ester without
simultaneous undesired reaction of the acetoacetic acid
alkyl ester did not therefore appear possible.
Surprisingly, it has now been found that, by
action of an alcohol on AC- and/or AV-ester, a smooth
conversion o~ these com~ounds to acetoacetic acid alkyl
ester takes place, without this compound itself reac~ing
with the alcohol.
The pLocess according to the invention Ior the
preparation of acetoacetic acid alkyl ester comprises
the reactior. in the liouid phase at a tem~eratu~e of
50 to 250C o 3-aceiox~rcrotonic acid alkyl or alkenyl ester or
3-acetoxyvinylacetic acid alkyl or alkenyl ester or a mixture
thereof ~rith an aliphatic alcohol w~ich cor.tains 1 to 5
carbon atoms, the alcohol being employed in at least
eauimolar auartity.
The alkyl groups n the 3-acetoxycrotonic acid alkyl or
alkenyl ester and in the 3-acetoxyvinylacetic acid aIkyl.or alkenyl
ester preferably have 1 to 5 C atoms ar.d can be saturated
1~ ..
25;~8
-- 4 --
or unsaturated, straight-chain or branched
In the ~eaction of the AC-ester or of the AV-
ester with the alcohol, ~he acetic acid ester of the
alcohol e~ployed, that is the alkyl aceta~e already men-
.. .. . . . . . . . . .. .. . . . . . . . . .
tioned above as the low-boiling compound, is formed in
... . . . .
addition to the acetoacetic acid alkyl ester.
AC-ester or AV-ester can be employed individually
or mixed.
The two esters can be obtained individually or
as a mixture lrom the crude product ~ihich is formed in
the preparation of acetoacetic acid alkyl esters from
diketene and an alcohol by ~irs~ separating off ~e low-
boiling compounds and the high-boiling compounds and then
.. . . . . ....... . .
isolating AC-ester, AV-ester and acetoacetic acid alkyl
ester by fractional disi-llation. In this manner, AC-
ester and AV-ester or a mixture thereof are obtained,
free from acetoacetic acid alkyl ester.
Preferably, however, this relatively troublesome
complete separation of the acetoacetic acid alkyl ester
is not carried out, but the follo~ring procQdure is
folloThTed: firstly, the 1ow-boi1ing compounds and the high-
boiling compo~nds ar~ again separated olf by distillation
f~om the crude product mentioned and the ~ain fraction
containing the acetoacetic acid alkyl ester, the AC-es-ter
~5 an~ the AV-ester is then separated in a second distilla-
tion into pure acetoacetic acid alkyl ester as the top
product and into a mixture Gf acetoacetic acid alkyl
ester/AC-ester/AV-ester as the ~ottom product This
mixture is then reacted according to ihe invention with
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- 5 -
an aliphatic alcohol at $0 to 250C, preferably at 140
to 180C, and under a pressure corresponding to the
vapor pressure of the mixture. The resulting reaction
mixture is worked up to acetoacetic acid alkyl ester by
distillation.
It is, however, alsopossible- although this is, as a
- rule, less favora~le - to react the main ~raction me~tioned,
.. . ... . . . . . . ... ..
and obtained after separating off the low-boiling compounds
.... . . . . ... . ..
and high-boiling compounds, directly according to the
invention with an aliphatic alcohol, ænd only then is
.. . .. . . .
:pure acetoacetic acid alkyl ester distilled off as the top
.. . . . . . . . .. ...
- product and a bottom produci which contains the remaining
acetoacetic acid alkyl ester and the unreacted AC- and
AV-ester is obtained.
A corresponding procedure is of co~lrse foll~red
with pure (that is,not containing acetoacetic acid alkyl
ester) AC-ester or AV-ester or a mixture thereo~.
Appropriately, the alcohol which was employed in
the preparation of the acetoacetic acid alkyl ester from
diketene is used in the reaction of an AC-ester/AV-ester/
acetoacetic acid alkyl ester mixture obtained as men-
tioned. In the preparation ol methyl acetoacetate
this alcohol is methanol, for ethyl acetoacetate ethanol etc
The AC-ester ~nd AV-ester components to be reacted have
an alkoxy group which corresponds to the alcohol employed
in the diketene reac~ion. Methyl acetoacetate there-
fore contains acetoxycrotonic acid methyl ester and
acetox-yvinylacetic acid methyl ester as acco~panying
components; the homologous compounds behave correspondingl~.
2 52 8
- 6 -
Basic21ly, ho~rever~ an alcohol which does not
correspond to the carbalkoxy group of these esters may also
be used for the reaction of the AC-ester and the AV-ester.
Thus, for example, acetoxycrotonic acid methyl ester and
-acetoxyvinylacetic acid methyl ~ester may be directly
reacted ~ th butanol.
A reaction time of fro~ 4 to 6 hours has proved
to be the most favorable. In this time, an extensive
conversion takes place. This amounts to 65 to 95%
under the c~nditions i~dicated. After reaction has
taken place, the reaction mixture is worked up, prefer-
ably together wi~h the crude product formed in the reac-
tion of diketene with an alcohol, and a complete conver-
sion of the AC-ester and the AV-ester is therefore not
required in the process according to the invention and
is even inexpedient for reasons o~ cost efficiency.
The ~lorkirg-up of the crude product mantionedg
resulting from the reaction of diketene with an alcohol,
is thus simplified b~j coupling with the process according
to the inven~ion: after the separation o~ the high-
.. . . . . . .. . . .. ..
boiling compounds and low-boiling compounds from th~ crude
_ . . . . . .. . . . . ........................ .. ..
product, onl~ the main portion of ~he acetoace~ic acid
alkyl ester is distilled off (instead of distilling it
off as far a~ possible, as hitherto~ and the remaining
portion, togelher with AC- and A~-esters, is employed
in the process according to the invention
For the process a~ccording to the invention, a
mixture which contains as high a portion as possible of
AC- and AV-esters is preferably employed Such a
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mix~ure is obtained from ihe bottom of the column in
which the distillation for the purification of the aceto-
acetic acid alkyl ester, after separation of the high_
..
boiling compounds and low-boilin~ compcunds, is carried
out. The concentration o~ acetoacetic acid alkyl
ester is, in this case, between 20 and 80% by weight,
preferably 40 to 50% by weight. However, even in the
case of substantially higher va~ues, the reaction pro-
ceeds without difficulties
Basically, all aliphatic alcohols ~'nich co-ntain
1 to 5 carbon atoms a~e suitable as t'he alcohol component
in ~he process according io t~e invention. The carbon
chain can be straight-chain or branched and the alconol
can be a primary, secordary or tertiary alcohol; further,
1~ unsaturated alcohols can also be used Thus, for
example, the follo~ing alcohols may be used as reaction
partners: methanol, ethanol, propan-1-ol, propan-2-ol,
butan-1-ol, butan-2-ol, 2-methyl-propan-1-ol, 2-me~hyl~
propan-2-ol, pentan-l-ol, pentan-2-ol, pen-tan-~-ol, 2-
methyl-butan-4-ol, 2-methyl-butan-3-ol, 2-methylbu~an-2-
ol, 2-methylbutan-1-ol, 2,2-dimethyl-propan-1-ol and
prop-l-en-3-ol. Primary alcohols are preferred~ in
particular me~hanol and ethanol.
The two follcwing embodiments ol -the prccess
according to the i~vention are particularly favorable:
.. . ... . . . . . . . . . . .. . ..
- 'a) High-boiling compounds and low-boiling compcunds
_ . . . ~ ...... . . ....... .. . .. . . ... . .
and subseauently the main portion of the methyl aceto-
acetate are separated off from the crude product ~Jhich
has formed in the contin~ous preparation of methyl
~ 2 52 8
- 8 -
acetoacetate fro~ diketene and methanol 3-Acetoxy-
crotonic acid methyl ester, 3-acetox~-vinylacetic acid
methyl ester and the remainder of the methyl acetoacetate
is obtained as the botiom product. This bottom pro-
duct is reacted with methanol according to the inventionto give methyl acetoacetate-. The product obtained in
this reaction is co~bined with the crude product men-
tioned above (from the con~inuous reaction of diketene
and methanol to give methyl acetoacetate) and is w~orked
up ~rith this crude product to give pure methyl aceto-
acetate.
b) Hlgh-bolling compounds and low-bolllng compounds
_ . _ . _ . .. . . ..... . ... .. . . _ . _ ... . .. . .. . . .. _ . .
- ænd subsequently the ~in portion of the ethyl aceto-
acetate are separaied off from the cLude produc~ w~ich
15 has formed in ~he con~inuous preparation of ethyl ;
acetoacetate ~rom diketene and ethanol. 3-Acetoxy-
crotonic acid e~hyl ester, 3-acetoxyvinylacetic acid
ethyl ester and the remairLder of the ethyl acetoacetate
areobiained as the bo~tom product. This bottom pro-
duct is reacted ~i'h ethanol according to the invention
to give ethyl acetoacetate. The product obtained in
this reaction is combined ~.ith the crude ~roduct ~en-
tioned above (from the continuous reac~ion of diketene
and ethanol to give ethyl acetoacetate) and is worked
u~ with this crude product to give pure ethyl aceto-
- - acetate.
The followin~ examples illustrate the process
according to the inNen~ion:
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_ 9 _ .
- Exam~le 1
50 g of a mLxture of the fol'owing composition
were employed: 53.07' by ~igh~ of methanol, 45 ~ by
weight of 3-acetoxycrotonic acid methyl ester (cis- and
- 5 trans-forms) and 3-acetoxyviny:Lacetic acid methyl ester,
0.60~' by weight of methyl acetoaceiate and 0.5% by ~reight
of other middle- and high-boiling compounds. ~his mix-
_ . . _ . . . . . . . . ........... . . . .. . .. . ture was heated in an autoclave to 170C for 6 hours~
-a pressure of 11.3 oars being established at the end
of the reaction. The reaction mixture ~as again
- analy7ed a er it had cooled do~m, g~ving the following
composition: 67.2 ~ by weight of low-boiling compounds
. _ . _ . . . .. . . .. ... . . . . .. . . _ . . . ...
(for the most par~ methyl acet~te and m~thanol), 31.4%
by weight of methyl acetoacetate, 1 4% by ~eight of
ace~ox-ycrotQnic acid meth-yl ester and acetoxyvinylacetic
acid methyl ester and 0.29S by ~reight of other middle-
... . ... . . _ .. . .. ..
and high-boiling compo~ds.
... . . . . .. . .. . . . ~
Example 2
50 g of a mixture of the follo~g composition
~Jere employed: 53.6~/c by ~eight of methanol, 25.0% by
weight of methyl acetoacetate and 2l.4ob by ~Jeight of 3-
- acetoxycrotonic acid methyl ester ~cis and trans) and
~acetoxyvinylacetic acid methyl ester. This mixture
~las heated in an autoclave to 170C for 6 hours, a pres-
2~ sure of 10.8 bars being established at the end of the
reaction. A sample of ~he reaction mixtl~re ~ad ~he
- followi~ composition aft~er it had cooled down: 57.~b
_ . , . . . ... .. . . , . .. . . . . . . . _ _ ..... . . . . ... _ .
by weight of low-boiling com~ounds (for the most part
.... . .
methyl acetate and methanol), 35.7% by w~ight o~ methyl
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- -- 10 --
acetoacetate, 6.1% by weight of 3-acetoxycrotonic acid
methyl ester and 3-acetoxyvinylacetic acid methyl ester
and 0.3% by ~reight of other middle-and high-boiling
. .
- compounds.
.. . . . ... _ .~
~ _xGm~le 3
50 g of a mixture of the ~ollowdng composition
- were employed: 51.3% by weight of ethanol, o.goh by ~leight
of ethyl acetoaceta~e, 47 5% by weight of 3-acetoxycroton-
- ic acid ethyl ester (cis and trans) and 3-acetoxyvinyl-
acetic acid ethyl ester, and 0.3% by weight of other
middle- and high-boiling compounds. This mixture was
.. .. . . . ..
heated in an autoclave to 170C for 6 hours, a pressure
of 10.1 bars being esta~lished at the end of the reac- .
tion. The reaction mixture had the follo~ing compo-
sition after it h~d cooled down: 67 0% by ~reight of lo~r-
.. . . .. . . . . .. . . .. ...
boiling compo~mds (for the most part ethyl acetate and
ethanol), 30.5% by ~reight of ethyl acetoacetate, 1~9% by
~;eight of 3-acetoxycrotonic acid ethyl ester and 3-
ace~oxyvinylacetic acid ethyl ester9 and 0.6q~ by ~rei~ht
of other middle- and high-boiling compounds.
_, _ . . .. . . . _
Exæm~le 4
10~ g of a mixture of the follo~ing composition
ere employed: 44.~ by weight of ethanol, 25.7% by
weight o~ ethyl acetoacetate, 30.1% by weight of 3-
acetoxycrotonic acid ethyl ester (cis and trans) and 3-
acetoxyvinylacetic acid ethyl ester, and O.~,S by ~Jeight
. . .
o~ other middle- and high~boiling co pounds. ~his mi~-
- ture ~ias heated in an autocl~ve to 170C lor 6 hours, a
pressure of 9.7 bars being established at the end
~1 . .
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of the reaction. A sample of reaction mlxture had
the following compos~tion after it ha~ cooled do~Jn
53.1 % by weight of low-boiling compounds (for the most part
ethyl acetate and ethanol), ~5.4% by weight o~ ethyl
acetoacetate, 10.6~' by weight of 3-acetoxycrotonic acid
ethyl ester and 3-acetox~rvinylacetic acid ethyl ester,
and 0.9% by ~Jeight of other middle- and high~boiling
compounds.
... . . . .
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