LA 3-FORMYL-3-METHYL-2,6-DIHYDROXYPYRIDINE ET PROCEDE POUR SA PREPARATION

3-FORMYL-4-METHYL-2,6-DIHYDROXYPYRIDINE AND A PROCESS FOR ITS PREPARATION

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
The present invention relates to a new 3-formyl-4-methyl-2,6-
dihydroxypyridine of the formula I
<IMG> I
its alkali metal and alkaline earth metal salts and their preparation by
hydrolysing the 2,6-dihydroxypyridine derivative of the formula II
<IMG> II
or one of its alkali metal or alkaline earth metal salts in a basic medium
with the elimination of chloroform. The compound of formula I above is a
valuable intermediate product especially for the production of dyestuffs.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. 3- Formyl -4-methyl-2,6-dihydroxypyridine of the formula I
<IMG> I
and its alkali metal and alkaline earth metal salts.
2. Process for the preparation of 3-formyl-4-methyl-2,6-dihydroxypyri-
dine of the formula I
<IMG> I
characterized in that 3-(.beta.,.beta.,.beta.-trichloro-.alpha.-hydroxy)ethyl-4-methyl-2,6-dihy-
droxypyridine of the formula II
<IMG> II
or one of its alkali metal or alkaline earth metal salts is hydrolysed in a
basic medium with elimination of chloroform.
3. Process according to Claim 2, characterized in that the hydrolysis
is carried out with an aqueous alcoholic solution of an alkali metal hydroxide
at the boil under reflux.
4. 3-formyl-4-methyl-2,6-dihydroxypyridine as defined in Claim 1.
5. Potassium 3-formyl-4-methyl-2,6-dihydroxypyridine as defined in
Claim 1.

Description

-- 6~,,',2~L
.. . .
The invention concerns the new 3-formyl-~-methyl-2,6-dihydroxypyri-
dine of the formula I -~
~ CHO
H ~ N ~ OH
and its alkali metal and alkaline earth metal salts. As alkali metal or
alkaline earth metal salts, the sodium and potassium salts, especially, are
significant.
The compound according to the present invention can exist in several
tautomeric forms and this description obviously embraces all the possible
tautomeric forms.
The subject of the invention is also a process for the preparation
of 3-formyl-4-methyl-2,6-dihydroxypyridine of the formula I, which is charac-
terized in that a 2,6-dihydroxypyridine derivative of the formula II
H-CC13
ll ¦ OH II
H ~ ~ H
or one of its alkali metal or alkaline earth metal salts is hydrolysed in a
basic medium with the elimination of chloroform.
A process for the introduction of a formyl group into 2,6-dihydroxy-
pyridine compounds, which are substituted in a specific way, is admittedly
already known from the literature (DOS 2,025,427), the reaction being carried
out in the presence of aci.d chlorides. Howeverj this method easily leads to
decomposition reactions and does not produce the desired result. On the other
hand, the hydrolysis in a basic medium, according to the present invention~ of
3-(~ -trichloro-~-hydroxy)ethyl ~-methyl-2,6-dihydroxypyridine of the
formula II, with elimination of chloroform, gives the end product in good
yield and free of substantial impurities. The reaction of the compound of
the formula II with, for example, alkali metal hydroxide as the base is ~ ;

Z91
carried out in an aqueous alcoholic medium, preferably in aqueous-ethanolic
potassium hydroxide solution, at the reflux temperature. The 3-formyl-4-
methyl-2,6-dihydroxypyridine according to the invention is thus obtained in
the form of the alkali metal salt, from which the metal-free compound can be
prepared by acidification.
The conversion of the alkali metal or alkaline earth metal salts of
the compound according to the invention into the metal-free compound is car-
ried out by treatment of the aqueous solutions with an acid and isolation of
the product by concentration. It is particularly advantageous to use acetic
acid as the acid. Since the free compound of the formula ~ tends very easily,
in particular in an acid medium, to undergo condensation or polymerization
reactions with itself, it is especially advantageous that the alkali metal or ;;-
alkaline earth metal salts should be very stable forms.
The 3-formyl-4-methyl-2,6-dihydroxypyridine according to the inven-
tion is a valuable intermediate product, which is suitable for the preparation
of dyestuffs, and plant protection agents. In this, it is of particular
advantage that the compound should be in the form of its stable salt. The
stable aIkali metal salt of 3-formyl-4-methyl-2,6-dihydroxypyridine, for
example, shows all the reactions of a compound with an acidic CH- and can, in ;~
addition, be used for the customary carbonyl reactions at the formyl group.
Example 1
;." : '
272.5 parts of 3-(~ -trichloro-2-hydroxy)ethyl-4 methyl-2,6-
dihydroxypyridine are introduced into 3,000 parts of ethanol and treated with
a solution of 500 parts of potassium hydroxide in 400 parts of water and 1,700
parts of ethanol. The reaction mixture is kept at the boil under reflux for
30 minutes, with stirring, and is then cooled down to 20C. The product
which has separated out in the course of this operation is filtered off, wash-
ed with 200 parts of ethanol and dried. The crude product thus obtained can
be freed from adhering excess potassium hydroxide by washing with dilute
.
. , . . . .: , :.' , , .: . .,. .: : .
' ' " ' .' ' ' ' ' ' . . . , : :: ; i ' ' : ' .

~6162~
acetic acid until a neutral reaction is obtained. 94 parts are thus obtained
of potassium 3-formyl-4-methyl-2,6-dihydroxypyridine (=~9% of the theoretical
- yield) which possesses a melting point of above 350C after recrystallization
from water.
Analysis: calculated: C 44.0% H 3.2% N 7.3%
found: C 44.2% H 3.4% N 7.3%
W and IR spectra confirm ~he assumed structure.
The conversion of the potassium salt into the metal-free compound
is carried out as follows: 191.1 parts of the product obtained are suspended ~ ~
in 200 parts of a mixture of 160 parts of acetic acid and 40 parts of water, ~ -
and the reaction mixture is concentrated to 50 parts under vacuum. On allow- ~ -
ing the concentrated solution to stand, the metal-free compound crystallizes
out. The pure 3-formyl-4-methyl-2,6-dihydroxypyridine, with a melting point
of 180-182C, is obtained by redissolution and recrystallization from a mix-
ture of 160 parts of ethanol and 40 parts of water.
Analysis: calculated: C 54.9% H 4.6% N 9.1%
found: C 55.1% H 4.7% N 9.0%
Example 2
-- .
; The initial compound named 3~ trichloro-~-hydroxy)ethyl ~-
methyl-2,6-dihydroxypyrldine can be prepared as follows:
125 parts of 4-methyl-2,6-dihydroxypyridine dissolved in 400 parts
of ethanol, 80 parts of sodium acetate dissolved in 100 parts of water and
148 parts of chloral dissolved in 400 parts of water are mixed together and
the whole is stirred for eight hours at 20 CO The reaction mixture is allow- ~
ed to stand at room temperature for another 48 hours, the product which has ;
separated out in the course of this operation is filtered with suction,
washed with water and dried _ vacuo at 30 ~
Obtained are 218 parts (= 80% of the theoretical) of 3~ tri-
chloro-~-hydroxy)ethyl-4-methyl-2,6-dihydroxypyridine which, when recrystallized.
_ 3 -
.- -. ~

~0~6'~
from ethyl acetate, has a melting point of 195 C.
Aralysis:calculated: N 5.4% Cl 39.9%
found: N 5.1% Cl 39.1%
.''~'' ~
''; ';''~' ~' . '"
. .~,.
- 4 ~ ..
......................... ............. ............................ .. . .
......................... ............. ............................ : .
,., , ':', '' , . ' . ' , . ,, , '' ~,',