Note: Descriptions are shown in the official language in which they were submitted.
2151323
- HULS A~TID G~RT~T-~C~A~T 0.Z. 4849
- Patent Department -
Process for the prearation of 2,2-dlchloromalonic
diesters
The present invention relates to a process for the
preparation of 2,2-dichloromalonic diesters by reacting
malonic diesters with aqueous alkali metal hypochlorite
solutions or alk~ine earth metal hypochlorite suspen-
sions in the pH range > 8 at low reaction temperatures.
Dialkyl dichloromalonates are used as activators in EPM/
EPDM copolymerization (German Offenlegungsschrift
23 44 267 and Canadian Patent 1 014 299) or aæ fireproof-
ing agents in polycarbonates (German Offenlegungsschrift
24 60 946). They are also uæed aæ photographic developers
(German Offenlegungsschrift 21 46 430) or as additives to
chromium plating baths (Trans. Int. Met. Finish 1985,
34).
Examples of synthesis of 2,2-dichloromalonic diesters
starting from the corresponding malonic diester are
described in the literature:
Forster et al. tJ~ Chem. Soc. 97 (1910), 130] and Amriev
et al. tZh. Prikl. Rhim. (Leningrad) 1985, 2504] report
the chlorination of diethyl malonate with elemental
chlorine at elevated temperature to give a mixture of
monochloro- and, predomin~ntly, dichloromalonic ester.
Conrad et al. [Chem. Ber. 35 (1902), 1815] carried out
the chlorination of malonic acid using sulphuryl chloride
in addition to subsequent esterification of the dichloro-
malonic acid formed. Swiss Patent 599 092 reports an
analogous reaction although using thionyl chloride in
acetic acid as solvent.
Other authors, æuch as Just et al., [Tetrahedron Lett.
1979, 3643], carry out the chlorination of diethyl
malonate with trifluoromethanesulphonic acid chloride,
Hori et al. [Chem. Abstr. 93, 95 231 h (1988)] with
' '
215~323
- 2 - O.Z. 48~g
carbon tetrachloride in the presence of tertiary organic
N base~, Terpighorev et al. tZh. Org. ~hlm. 1980, 2545]
of mono-Na salts of malonic diesters with carbon
tetrachloride, Yonemura et al. tBull. Chem. 80C. Jap.
1987, 809] with the Mn(III) acetate/chloride redo~
system.
Chlorinations of monochloromalonic diester are al~o
reported:
Thus, monochloromalonic diester ha6 been chlorinated to
the desired product by Conrad et al. tChem. Ber. 24
(1981), 2993] using elemental chlorine, by Macbeth et al.
[J. Chem. Soc. 121 (1922), 1120 and 2177] using sulphuryl
chloride, and by Shevchenko et al. tZhur. Obshch. Rhim.
32 (1962), 2994] using phosphorus pentachloride.
It is common to all the processes described in the
literature that the yields of the required products are
usually only unsatisfactory, the dichloro derivatives
being cont~min~ted with varying amounts of monochloro
compounds, and that the chlorinating agents used to
prepare the required products are, because of their
nature or their reaction products resulting in the
desired reaction, of low suitability for industrial
manufacture of the desired products from the viewpoints
of process technology, economics and ecology.
The object therefore was to find a process which is
simple in terms of process technology, is economic and
gives good yields, for the preparation of 2 r 2-dichloro-
malonic diesters from the underlying malonic diesters
which can be obtained conveniently.
Surprisingly, this object has been achieved by the
process according to the invention in which malonic
diesters of the general formula I
- 2151323
- 3 - O.Z. 4849
H\ ~ CO2_ R1
H \ C02- R2
in which Rl and Rz have the meaning of straight-chain or
branched Cl- to C6-alkyl, cycloalkyl and aralkyl, and the
radicals Rl and R2 can be identical or different, are
reacted with aqueous alkali metal hypochlorite 801ut~0n8
S or alkaline earth metal hypochlorite suspensions at pH
values 2 8 at low temperatures to give the desired
products of the general formula II
a C2 - R
/C /
a co2--R2
in which Rl and R2 have the abovementioned meAnin~.
The reaction which has been found can be described, for
example when sodium hypochlorite solution is used, by the
following formal reaction equation:
H~ ~CC~--R
~C~ ~ 2 I`bOCI --~ 2 NqOH + ~C~
H C~--R2 a o~-- ~
It was also surprising that buffering of the sodium
hydroxide solution which is liberated in the reaction by
dilute mineral acids such as hydrochloric, sulphuric or
phosphoric acid, or else by suitable organic acids such
as formic acid, or substituted acetic and propionic
acids, such as, for example, monochloro-, dichloro- or
trichloroacetic acid, or aromatic carboxylic acids which
can be diluted with water and optionally carry one or
more inert substituents, and maintAinin~ the pH of the
reaction mixture constant in the pH range 8 to 14,
preferably in the pH range 8.5 to 14, and particularly
2 i S 1 3 2 3
- 4 - O.g. 4849
preferably in the range 9 to 14, leads to extremely high
yields of dichloromalonic esters co~bined with estremely
high product purities.
The pH range in which the desired reaction is carried out
lies in a wide range. Thus, on the one hand, account
should be taken of the stability of the hypochlorites
used by a pH ~ 8 and, on the other hand, the pH should be
re~tricted in the alkalinity of the reaction mixture to
achieve optimal yields, that is to say to avoid losses of
precursor and desired product as a consequence of hydro-
lysis reactions; for this reason it i8 expedient for the
upper limit of the reaction pH to be limited to ~ 14. The
preferred pH range is 8.5 to 14.
It has furthermore been found that low reaction tempera-
tures are beneficial for the yields and product puritywhich can be achieved. The temperature range is therefore
expediently from 0 to 50C, and the preferred temperature
range is from 2 to 25C. This temperature range ensures
fast and mild reaction of the precursors used; however,
it is also possible to use lower temperatures.
The described reaction can be carried out, for example,
by initially introducing the hypochlorite in the form of
an aqueous solution or suspension, and metering in the
precursor while maintaining the pH range constant, as
described above, by metering of one of the acids
described above, which takes place in parallel, it also
being possible to continue the acid metering in the
after-reaction phase to maintain the chosen pH range.
However, a reverse procedure may also be chosen, that is
to say initial introduction of the precursor and metering
of the hypochlorite solution in addition to the acid
metering.
It is possible and expedient in the malonic ester chlori-
nation to be carried out using hypochlorites for a slight
21S1323 ~ `
_ 5 _ O.Z. 48~49
excess of hypochlorite to be used, based on the mnlonic
esters used; the eXCQ88 to be U8Qd i8 not critical. In
general, 2 to 20%, preferably 5 to 10%, excess of hypo-
halite are used. The malonic ester/hypochlorite ratios
are from 1 : 1 to 1 : 2, preferably from 1 : 1.05 to 1 :
1.2. After the end of the reaction, this hypochlorite
content which is still present is decomposed in a known
manner, for example by A~ g a~ueous ~odiu~ ~ulphite
where appropriate.
These reactions generally result in a two-phase reaction
mixture from which it is easy to remove the organic
phase. In this connection, it is expedient to remove
desired product which is still dissolved in the resulting
aqueous phase using a suitable extractant.
Extractants which are suitably used are preferably
solvents which are immiscible with water, such as
halogenated hydrocarbons, aliphatic, cycloaliphatic and
aromatic hydrocarbons, esters and ethers, which can
easily be removed after the extraction from the desired
product, for example by normal or fractional vacuum
distillation.
The following examples demonstrate the range of applica-
tion of the process which has been devised.
Example 1
217.8 g of aqueous sodium hypochlorite solution (content:
8.55% NaOCl equivalent to 250 mmol of NaOCl) are cooled
to 5C, and the pH of the solution is adjusted to about
9.1 by adding aqueous 20% strength hydrochloric acid.
36.0 g of diethyl malonate (225 mmol) are added dropwise
over the course of about 30 minutes to this cooled
initial solution, maint~i n; ng the pH of the solution in
the range 9.0 to 9.2 by the simultaneous metering of an
aqueous 20% strength hydrochloric acid, and maint~ining
the internal temperature at about 5~C by cooling.
~ 2 1 5 1 3 2 3
- - 6 - O.Z. 4849
After the metering of malonic ester is complete, reaction
is allowed to continue for 10 minute~ while ~ainta~ning
the pH range constant. Then excess sodium hypochlorite
which is still present is decomposed by adding sodium
sulphite, the organic phase is removed from the 2-phase
mixture, the aqueous phase is exhaustively extracted with
tert-butyl methyl ether, and the organic phase and
extracts are combined.
After evaporation of this solution, the resulting residue
is sub~ected to vacuum di~tillation. 50.8 g of diethyl
2,2-dichloromalonate of boiling point 95 to 96C (S hPa)
are obtained, which is equivalent to a yield of 98.6% of
theory; the purity of the product determined by gas
chromatography is ~ 99.5%, the content of monochloro
compound is ' 0.2%.
ExamPle 2
In analogy to Example 1 but using 48.6 g of diisobutyl
malonate (225 mmol). The initial and reaction pH range is
12.0 to 12.2.
After analogous ~ Jl~U~ 58.0 g of diisobutyl 2,2-di-
chloromalonate of boiling point 114 to 117C (5 hPa) are
obtained (purity of the desired product: > 99.3%), which
is equivalent to a yield of 90.4% of theory.
Example 3
In analogy to Example 1 but using 29.7 g of dimethyl
malonate (225 mmol).
Analogous workup results in 39.9 g of dimethyl 2,2-di-
chloromalonate of boiling point 72 to 73C (5 hPa)
(purity: > 99.5~), which is equivalent to a yield of
88.2~ of theory.
- ~ = 2 1 ~ 1 3 ~ J
~- 7 - O.Z. 48~9
Exam~le 4
In analogy to Example 1 but using 42.3 g of diisG~o~yl
malonate (225 mmol). The reaction i8 started at pH 13 and
carried out in the range 13.0 to 13.5, with the after-
reaction time being about 60 minutes.
Analogous workup results in 52.5 g of diisopropyl 2,2-di-
chloromalonate of boiling point 92 to 93C (5 hPa)
(purity: 2 99.5%), which is equivalent to a yield of
90.8% of theory.
ExamPle 5
In analogy to Example 4 but using 42.3 g of tert-butyl
ethyl malonate (225 mmol). The reaction and after-reac-
tion is carried out in the temperature range 20 to 22C.
Analogous workup results in 48.8 g of tert-butyl ethyl
2,2-dichloromalonate of boiling point 95 to 96C (5 hPa)
(purity: > 98%), which is equivalent to a yield of 84.4
of theory.
Example 6
Analogous to Example 4 but using 39.2 g of tert-butyl
methyl malonate (225 mmol).
Analogous workup results in 46.8 g of tert-butyl methyl
2,2-dichloromalonate of boiling point 86 to 88C (5 hPa)
(purity: > 99%), which is equivalent to a yield of 85.2
of theory.
.
