DICHLOROTRIFLUOROPROPIONALDEHYDE ET METHODE DE PREPARATION

DICHLOROTRIFLUOROPROPION-ALDEHYDE AND A PROCESS FOR ITS PREPARATION

Abrégé anglais

ABSTRACT
The present invention relates to 2,2-dichloro-3,3,3-trifluoro-
propionaldehyde of the formula III

CF3-CC12-CHO (III)

and to a novel process for its production. 2,2-Dichloro-3,3,3-trifluoro-
propionaldehyde is a valuable intermediate for the synthesis of 2,3-dichloro-
5-trifluoromethylpyridine.

Revendications

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What is claimed is

1. 2,2-dichloro-3,3,3-trifluoropropionaldehyde.

2. A process for the production of 2,2-dichloro-3,3,3-trifluoropropion-
aldehyde, which comprises subjecting a corresponding olefin to
ozonolysis and working up the reaction mass by reduction.

Description

This is a divisional patent application to the Canadian Patent
Application Patent Application No. 384 531.

Case 5-13034/ZF0/1+2/DIV


2,2-Dichloro-3,3,3-trifluoropropionaldehyde and _ process for the
preparation thereof
-

The present invention relates to 2,2-dichloro-3,3,3-trîfluoro-
propionaldehyde of the formula III

CF3-CC12-CH0 (III)

and to a novel process for its production.

2,2-Dichloro-3,3,3-trifluoropropionaldehyde is a valuable intermediate
for the synthesis of 2,3-dichloro-5-triEluoromethylpyridine.

Up to now it was possible to obtain chloropyridines substituted by
~ethyl, trichloromethyl or trifluoromethyl groups only by means of
complicated muLti-step processes. For example, 2,3-dichlorowS-methyl
pyridine can be obtained by diazotising 2-chloro-3-amino-5-methyl-
pyridine and replacing the diazo group with chlorine.

The above aminopyridine can be ob~tained by chlorinating 3-methyl-
pyridine to 2-chloro-5-methylpyridine, nitrating this compound
to 2-chloro-3-methyl-5-nitropyridine and reducing the nitro compounds.
When chlorinating 3-methylpyridine, several isomers are usually
obtained in addition to the desired compound. Chlorination of 2,3-
dichloro 5-methylpyridine gives ~,3-dichloro-5-trichloromethyl-
pyridine, which can be converted into 2,3-dichloro-5-trifluoromethyl-

,

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-- 2 --

pyridine by replacing the chlorine atoms of the trichloromethyl groupby fluorine atoms (q.~. for e~ample European patent publication
004414).

Chloropyridines of the ormula I,

R\ ~-\ /R'
11 (I)
~/ \Cl
wherein either R i8 chlorine and R' is methyl or trifluoromethyl, or
R is methyl, trichloromethyl or trifluoromethyl and R' is chlorine,
or R and R' are me~hyl, can be obtained by the addition of

a) trichloroacetaldehyde to methaçrylonitrile or ~-trifluorometh-
acrylonitrile,

b) 2,2-dichloropropionaldehyde, pentachloropropionaldehyde or 2,2-
dichloro-3,3,3-trifluoropropionaldehyde to acrylonitrile, or

c) 2,2-dichloropropionaldehyde to methacrylonitrile,

in the presence of a catalyst, and cyclising the intermediate of
the formula II

Cl Cl
I
OCH-C-GH -C-CN (II)
: 1 2 1
R R"

:wherein either R is chlorine and R" is methyl or trifluoromethyl,
or R ie methyl, trichloromethyl or trifluoromethyl and R" is hydrogen,
or R and R" are methyl, to give a compound of the formula I.
., : :
,


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; : : .

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According to ~he present invention 2,2-dichloro-3,3,3-trifluoro-
propionaldehyde can be obtained by ~reating corresponding olefins with ozone
and ~orking up the reaction mass by reduction. Suitable solvents which can
be employed are: organic acids such as formic acid~ acetic acid, propionic
acid; the esters of these acids, such as ethyl acetate, methyl ace~ate, ethyl
formate, methyl formate; aliphatic hydrocarbons such as pcntane, hexane,
heptane, octane, cyclopentane, cyclohexane; chlorinated hydrocarbons such as
methylene chloride, chloroform, carbon tetrachloride; or also water. Depending
on the nature of the solvent 0mployed, the reaction temperatures are in the
~ange ~rom -90 to ~70C, preferably from -70 to ~30C.
The reduction oE the products of the ozonolysis can be effectecl
either by direct catalytic hydrogenation w;th hydrogen and a noble metal
catalyst such as platinum, palladium, or rhodium, which catalyst may, if
desired, be applied to a carrier, or by addition of reducing agents such as
zinc or dimethyl sulfide.
A prefe-rred embodiment of this ozonolysis comprises ozonising
4,4-dichloro-5,5,5-trifluoro-2-methyl-2-pentenecarboxylic acid methyl ester
in acetic acid at 20CJ then adding an aqueous suspension of zinc powder to the
reaction mixture, and distilling off 2,2-dichloro-3,3,3-trifl~loropropional-
dehyde direct from the mixture.
The chloropyridines of the formula I can be used in manner known
per se via one or more intermediate steps for the production of different
compounds, especially insecticides and herbicides ~cf. for example S~iss patent
622 170 ~published 3I March 1981), European patent publications 00176 ~published
10 Janu~ry 1979) and 04414 ~published 3 October 1~79); German Offenlengungs-




--3--

.....

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schrift specifications 2 812 649 (published 26 April 1979) and 2 748 636
~published 3 May 1978); South African patent ~published 15 March 1979)
78.02440; Japanese patent publications 5 4115-380 ~published 1979), 5 5038-356
(published 1979), and 5 5079-369 (published 14 June 1980); and Canadian patent
1,120~480).
The process of the present invention is illustrated in more
detail by the following Examples.




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Example 1: Preparation of 2,2-dichloro-3~3,3-trifluoropropion-
aldehyde
19.2 g of ozone (admixed with oxygen) are introduced at 20C into
a solution of 100.4 g o 4,4-dichloro-5,5,5-trifluoro-2-methyl-
2-pentenecarboxylic acid methyl ester in 800 ml of glacial acetic
acid. Then a suspension of 15 g of zinc dust in 15 ml of water
is added and 2,2-dichloro-3,3,3-trifluoropropionaldehyde is
distilled off under normal pressure. Yield: 52.8 g of product
in the form of a colourless li~uid with a pungent odour. Boiling
point: 66-67C.
IR (CC14):~co 1770 cm
H-NMR (CDC13): ~=9.3 (~, J = 2Hz) ppm-
Analysis: C3HC12E'30 tl80.9)
calculated: C 19.92~ H 0.56% F 31.50~ Cl 39.19
found: C 20.2% H 0.8% F 30,9% Cl 38.5
Example 2: Preparation of 4-formyl-2,4-dichloro-5,5,5-trifluoro~
valeronitrile
A mixture of 36 g of 2,2-dichloro-3,3/3-trifluoropropionaldehyde,
80 ml of acetonitrile, 80 ml of acrylonitrile and 0.5 g of copper
(I) chloride is heated in a tantalum autoclave for 12 hours to
; 120C. After the mixture has cooled, the solvent is distilled
ofE, at about 40-50C in water jet vacuum. The residue is taken
up in 50 ml of diethyl ether and the precipitated copper sludge
is removed by filtration. The diethyl ether ls distilled off
and the residue is rectified in a high vacuum. The 4-formyl-~,4-

,
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~,....

~Z'~6~
- 4a -

dichloro-5,5,5-trifluorovaleronitrile is obtained as a colour-
less oil; boiling point: 85-86C/900 Pa.
IR (CC14): ~CN 2550 cm , ~CO 1750 cm
H-NMR (CDC13): ~ = 9.56 (m; lH, CHO); 4.7 (m, lH, C-2-3);
2.7-3.3 (m, 2H, C-3-H) ppm (m.ixture of diasteroisomers).
Analysis: C6H4C12F3NO (234.0)
calculated: C 30.80% H 1.73% N 5.99% ~ 24.36%
found: C 31.5% H 2.0% N 5.9% F 23.8% .




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-- 5 --

Example 3: Preparation of 2 7 3-dichloro-5-trifluoromethylpyridine
_
25 g of the 4-formyl-2~4-dichloro-5,595-trifluorovaleronitrile
obtained in Example 2 and 0.1 g of copper powder are heated in a
tantalum autoclave for 5 hours to 170C. Stea~ distillatiou of the
contents of the autoclave yields 11.9 g of 2,3-dichloro-5-trifluoro-
methylpyridine as a colourless oil with a pepp~rmint odour.
Boiling point: 80C/3325 Pa.
H-NMR SCDC13): ~= 8.63 (d, J = 2Hz, lH); 8.03 (d, J = 2Hz, lH) ppm.
Analysis C6~2C12F3N (216-0)
calculated: C 33.36~ H 0.93% N 6.48% Cl 32.82~ F 26.38%
found: C 33.5% H 1.0% ~ 6.5% Cl 33.4~ F 25~9%o

Example _ Single-step process for the preparation of 2,3-dichloro-
5-trifluoromethylpyrldine
The batch employed in Example 2 is heated in a tantalum autoclave
for 2 hours to 150C and then for a further 2 hours to 180C. The
solvent is then distilled off~ the residue is taken up in 50 ml
of diethyl ether, and the ethereal solution is filtered. The diethyl
ether is distilled off in a water jet vacuum and the residue is
subjected to steam distillation. The product is identical with the
compound of Example 3.




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