DE2214608C3 - Process for the preparation of J-hydroxy-2-pyridones - Google Patents

Description

R ₂ denotes a hydrogen atom, a low molecular weight alkyl, alkenyl or alkynyl radical or a benzyl radical, where R ₂ can also form a five- or six-membered carbocyclic ring together with R ₁ or R _3,
R _{3 is} a hydrogen atom, a low molecular weight alkyl radical or a phenyl radical and R _{4 is} a hydrogen atom, a low molecular weight alkyl or alkenyl radical, a methoxymethyl, a benzyl radical, a chlorine or bromine atom, by reaction of a 2-pyron of the general formula II

R ₃

(II)

in which R ₁ , R ₂ , R ₃ , R _{1 have} the abovementioned meanings, with hydroxylamine or one of its salts in the presence of an amine, characterized in that the amine is an aminopyridine or optionally substituted in the ring or in the amino group by low molecular weight alkyl radicals Imidazole used.

in which R _{1 is} an optionally branched alkyl radical

ti to 17 carbon atoms, an aikenyl radical with

This 17 carbon atoms, having a cycloalkyl radical

3 to 8 carbon atoms, a cyclohexylalkyl radical,

, an optionally in the aromatic nucleus by a

or more alkyl, alkoxy, amino, nitro, alk-

_knnv l Cvan groups or halogen atoms sub-

Ä & SÄ, Phenylalkenyl- Ben *

hydryl phenoxymethyl-, phenylmercapiornethy - Phe-

nylsulfonylmethylrest, a furyl- or furylalkenyl-R ^St 'means a hydrogen atom, a low molecular weight alkvl alkenyl or alkynyl radical or a benzyl radical, where also R ₂ together with R ₁ or

R _{3 can form} a five- or six-membered carbocyclic ring,

R represents a hydrogen atom, a low molecular weight alkyl radical or a phenyl radical and R is a hydrogen atom, a low molecular one

* o Alkvl- or alkenyl-, a methoxymethyl-, a Benzyl radical, a chlorine or bromine atom, by reaction of a 2-pyron of the general formula II

.R ₁

The invention relates to a process for the preparation of l-hydroxy-2-pyridones in general Shape! I.

Rr

OH

"O R ₃

"O'

in which R _1, R ₂ , R ₃ , R4 have the abovementioned meanings with hydroxylamine or one of its salts in the presence of an amine, characterized in that

the amine is one which is optionally substituted in the ring or in the amino group by low molecular weight alkyl radicals Aminopyridine or imidazole used.

Preferred among the alkylene radicals mentioned above for R ₂ to R ₄ are generally the low molecular weight ones

Alkyl radicals having 1 to 4 carbon atoms, in particular having 1 or 2 carbon atoms, among the alkenyl radicals those with 2, 3 or 4 carbon atoms. Among the radicals containing the phenyl nucleus are those preferably in which this phenyl nucleus is not or only

is substituted once or twice, among the phenalkyl radicals the benzyl radical.

From representatives of this general type is a good one known antibacterial and antifungal activity (See. US-PS 25 40 218 and 32 69 904, BE-PS

It is in some cases the conversion of 2-pyrones to l-hydroxy-2-pyridone by treatment with Hydroxylamine hydrochloride has been described in the presence of pyridine (cf. J. Am. Chem. Soc. 78, [1956],

P. 2393 98 and J. Chem. Soc. [London] 1961,

S 4490-98). However, this procedure is specific Substituents on the 2-pyrone ring are limited and cannot be generalized. If you try it to differently substituted 2-pyrones

wear, it is found that the yields of 1-hydroxy-2-pyridones low and their production is practically not feasible in this way.

It has now surprisingly been found that according to the invention 2-pyron in a generalizing

capable process in good yields and under mild conditions in l-hydroxy-2-pyridone higher Purity can be converted if the 2-pyrone is mixed with hydroxylamine or one of its salts in the presence

3 4

of 2-, 3- or 4-aminopyridine or imidazo! or The amine to be used according to the invention is used in the ring or on the amino group by amino pyridine which is substituted on the hydroxylamine salt, advantageously in at least an equimolar amount, in an at least equimolar amount. Part of 4-Me- can be replaced by other acid acceptors thyI-6-cyclohexyl-2-pyrone by heating for 5 hours, of an organic or inorganic nature, but with hydroxylamine hydrochloride in pyridine at C this sometimes leads to a noticeable slowdown in the corresponding oil -Hydroxy-2-pyridone in a mis- reaction, also the recovery of the amine, loot of 2.6% of theory, with \ -Picolin instead of pyri- which is generally, for example, by distillation or Exdin the yield 3.0%. If, however, traction is replaced, it is very easy to make the pyrio more difficult by such additives under otherwise identical reaction conditions If a large excess of the aminopyridine or amine is to be used according to the invention, the yields of the desired imidazole, e.g. U. 20 times the molar amount, based on reaction product about twenty times, z. B. with on the hydroxylamine salt, no disadvantageous one-2-aminopyridine 49%, with 2-amino-6-methylpyridine flows on the reaction process.

47%, with 2-amino-4-methylpyridine 53%, with imide 15 The hydroxylamine or its salt must naturally

azole 47% d. Th. In addition, this is characterized in equimolar amounts, based on the converted

according to the method of the invention shown pro-setting 2-pyrone, are used to accelerate

is characterized by a particularly high degree of purity. the reaction and to increase the yields

The situation is similar with others, but it can also be in excess, e.g. B. up to 5 or

2-pyrones. 20 10 moles, based on one mole of the 2-pyron, used

As amines in the context of the invention are two. It can also be useful to use the hydroxyl

for example: 2-aminopyridine, 3-aminopyridine, amine salt in several portions in the course of the reaction

Add 4-aminopyridine, 2-methylaminopyridine, 2-ethyiamination.

nopyridine, 2-amino-4-methyl-pyridine, 2-amino-6-me compounds, which according to the invention

thyl-pyridine, 2-amino-4-ethyl-pyridine, 2-amino-4,6-di- 25 process can be obtained, are, for. B .: methyl-pyridine, 3-amino-6-methylpyridine. Imidazole,

1-methyl-imidazole, 2-methyl-imidazole, 4-methyl-imide- melting point (C)

azole and 2-ethyl imidazole. In the eye, l-hydroxy-6-methyl-2-pyridone 141 ° is preferred

mean the parent body or by a methyl-l-hydroxy-4,6-dimethyl-2-pyridone ... 135 °

group substituted representatives, especially because of 30 l-hydroxy-3,4,6-trimethyl-2-pyridone .. 130 ^:

their easy technical accessibility, their lower l-hydroxy-4-methyl-6-ethyl-2-pyridone 110 °

rigen molecular weight and their high solubility- l-Hydroxy ^ -methyl-o-isopropyl-

like for the reactants, and not just 2-pyridone 110 ^J

for the organic components but also the l-hydroxy-4-methyl-6-heptyl-2-pyridone 48 °

Hydroxy! Amine salts. Since most of these 35 l-Hydroxy ^ methyl-o-undecyl-

bonds are solid at room temperature, it can be pre- 2-pyridon 63 '

be part of liquid mixtures of these compounds l-hydroxy-S ^ -dimethyl-G-heptadecyl-

to be used if the implementation of low-2-pyridone 60 '

rigen temperatures, e.g. B. 200 ⁰ C want to perform. l-hydroxy- ^ äthyl-S.ö-dimethyl-

The reaction can be carried out within a further temperature 40 2-pyridone 139 °

temperature limits, e.g. B. between room temperature and l-hydroxy ^ S-trimethylene-o-methyl-

150 ⁰ C or even above can be carried out. In the 2-pyridon 177 "

In most cases , satisfactory reaction gel-hydroxy- ^ methyl-o-cyclohexyl-

speeds between approx. 50 and 120 ⁰ C reached, 2-pyridone 143 °

this is therefore a preferred temperature range. 45 l-hydroxy ^ -methyl-o-cyclohexyl-

The addition of methyl-2-pyridone 131 under the reaction conditions

inert solvents or diluents is possible, l-Hydroxy ^ -methyl-ö-cycIohexyl-

but generally not required. In special ethyl-2-pyridone 90 ^J.

In some cases, however, it can be beneficial. Such l-hydroxy ^ -methyl-o-isobutenyl-

Solvents or diluents can be polar or 50 2-pyridon 116 °

non-polar, miscible or immiscible with water l-hydroxy ^ o-dimethyl-S-benzyl-

being. For example, the following substances can be found in 2-pyridon 165 °

in this sense the following are used: water, low molar- l-hydroxy-3-benzyl-4,6-dimethyl-

kular alcohols such as methanol, ethanol, isopropanol, 2-pyridone 148 °

Ethylene glycol, ethylene glycol monomethyl ether and 55 l-hydroxy ^ -methyl-o-benzyl-

Propylene glycol, amines such as triethylamine, morpholine, 2-pyridone 135 °

Pyrrolidine, piperidine, pyridine and picolines, acid- l-hydroxy-4-methyl-6- (4-chlorobenzyl) -

amides, such as formamide, dimethylformamide, diethyl 2-pyridone 142 °

formamide, monomethylacetamide, N-methylpyrrolidine l-hydroxy-6-phenylsulfonylmetliyl-

and hexamethyl-phosphoric acid triamide, esters such as 60 2-pyridone 260 °

Ethyl acetate, methyl propionate and ethylene carbonate, l-hydroxy-S-broirHt.o-dimethyl-

Ethers such as diethyl ether, diisopropyl ether, dioxane and 2-pyridone 220 °

Tetrahydrofuran, chlorinated hydrocarbons, such as l-hydroxy-3,4-dimethyl-6- (2,4-dim-

Methylene chloride and chlorobenzene, nitro compounds, ethylbenzyl) -2-pyridone 141 °

such as nitromethane, 2-nilropropane and nitrobenzene, ni-

trile, such as acetonitrile, propionitrile and benzonitrile, 2-pyridone 191 °

furthermore compounds such as dimethyl sulfoxide and l-hydroxy-4-methyl-6- (4-chlorophene

Tetramethylene sulfone. oxymethyl) -2-pyridone 16Γ

22nd

Melting point (Ό l-hydroxy-4-methyl-6- (2,4,6-trichloro-

phenoxyniethyI) -2-pyridone 216 °

1-Hydroxy-4-methy! 6- (3-nitrophene

oxymethyl) -2-pyridone 216 °

l-hydroxy-4-methyl-6- (phenylmer-

captomcthyl) -2-pyr: don 126 '

l-hydroxy ^ -methyl-o-phenyl-

2-pyridon 135 "

l-Hydroxy-4-methyl-6- (4-toyl) -

2-pyridone 125 °

1 Hyiiroxy-3,4-dimet hyI-6- (4-tolyI) -

2-pyridone 125 °

1 - Hydroxy-4-methyl-6- (2,4-dimethyl-

pheny]) - 2-pyridone 109 °

l-Hydroxy-4-methyl-6- (4-chloro-

phenyl) -2-pyridone 123 °

l-hydroxy-4-methy] -5-ethyI-

6- (4-tolyl) -2-pyridone 180 °

l-Hydroxy-4,6-diphenyl-2-pyridon .... 160 ° 1 -Hydroxy ^ -phenyl-ö-methyl-

2-pyridone 185 °

l-hydroxy-S-ethyM-methyl-

6- (4-tolyl) -2-pyridone 100 °

l-Hydroxy-4-methyl-6- (4-nitro-

phenyl) -2-pyridone 190 °

l-hydroxy-4-methyl-6- (4-methoxy-

phenyl) -2-pyridone 174 °

l-hydroxy ^ -methyl-o-phenyl-

5.2 '- (2-methyl-ethylene) -2-pyridone 174 °

1-Hydroxy-4-methyl-6-furyl-2-pyridone 147 ° l-Hydroxy-4-methyl-6- (2-furyl-vinyl) -

2-pyridone 166 °

1-Hydroxy ^ -methyl-o-styryl ^ -pyridone 176 ° i-Hydroxy-S-methoxymethyl ^ methyl-

6- (4-toyl) -2-pyridone 130 °

l-Hydroxy-S-allyM-methyl-o-phenyl-

2-pyridone 115 °

l-Hydroxy ^ -methyl-i-allyl-o-phenyl-

2-pyridone 176 °

1-Hydroxy-1-methyl-S-propargyl-6-phenyl-2-pyridone 200 °

The above list of hydroxypyridones which can be prepared according to the invention is intended to reflect the wide range of applications demonstrate the procedure. Of course it is not on the named representatives limited.

The 2-pyrones to be used as starting materials are easily accessible by various processes (cf. R. C. EIderfield, Heterocyclic Compounds, 2nd ed., Vol. 1, p. 354 ff., J. Wiley and Sons, Inc., New York 1959; Chem. Ber. 100, P. 658 ff. [1967]).

55 examples

example 1

g of 4-methyl-6-cyclohexyl-2-pyrone are mixed with 1 g of hydroxylamine hydrochloride and 5 g of 2-aminopyridine Heated to 80 ° C. for hours. The mixture is then taken up in methylene chloride and the amine is removed by shuffling with dilute hydrochloric acid, the reaction product is extracted from the organic phase with a diluent Sodium hydroxide solution and acidify the alkaline solution with acetic acid to a pH value of 6. 1-Hydroxy-4-methyl-6-cyclohexyl-2-pyridone. falls crystalline

608

If

out. It is suctioned off, washed with water and

'The yield is 1.05 g (49% of theory), the Melting point 14J ° C (calc .: 6.8% N, found: 6.8% N). Under the otherwise identical reaction conditions obtained when using 2-amino-4-methylpyridine 1.15 g (53%) with 2-amino-6-methyl-pyridine 1 01 g (47%), with 3-aminopyridine 0.52 g (24%). With imidazole 1.01g (47%), on the other hand with pyridine 0.056 g (2.6%) and with α-picoline 0.065 g (3.0%) of the l-hydroxy-2-pyridone.

Example 2

2 g 3-benzyl-4,6-dimethyl-2-pyrone, 6 g 2-amino pyridine and 1 g of hydroxylamine hydrochloride are heated to 70 ° C. for 8 hours. According to the example 1 The work-up described gives 0.65 g (30%) of 1-hydroxy-3-benzyl-4,6-dimethyl-2-pyridone with a melting point of 148 ° C (calc .: 6.1% N, found:

6.1% N).

If, under otherwise identical conditions, pyridine is used instead of aminopyridine, then none is obtained Obtained l-hydroxy-2-pyridone.

Example 3

2 g of 4-methyl-6-benzyl-2-pyrone, 6 g of 2-aminopyridine and 1 g of hydroxylamine hydrochloride are used for 5 hours heated to 80 ° C. After the usual work-up, 1.41 g (66%) of 1-hydroxy-4-methyl-6-benzyI-2-pyridone are isolated of melting point 135 ° C (Ben: 6.5% N, found: 6.6% N).

If the aminopyridine is replaced by imidazole under otherwise identical conditions, the yield is 1.33 g (62%), with pyridine on the other hand only 0.26 g (12%). There are also those with aminopyridine and imidazole products obtained pure white, while the product obtained with pyridine is yellowish in color.

Example 4

a) 2 g of 4,6-dimethyl-5-benzyl-2-pyrone, 4 g of 2-aminopyridine and 0.9 g of hydroxylamine hydrochloride are used Heated to 80 ° C for 5 hours. After the usual work-up, 0.89 g (42%) of 1-hydroxy-4,6-dimethyl-5-benzyl-2-pyridone are obtained with a melting point of 165 ° C (calc .: 6.1% N, found: 6.1% N).

Under comparable conditions one obtains

b) from the 4-methyl-6-phenylsulfonylmethyl-2-pyrone, the l-hydroxy ^ -methyl-o-phenylsulfonylmethyl-2-pyridone with a melting point of approx. 260 ° C (36%; calc .: 5.0% N, found: 5.1% N) ₁

c)-ethyl-5,6-dimethyl-2-pyrone 4 from which the 1-hydroxy-4-ethyl-5,6-dimethyl-2-pyridone of melting point 139 ⁰ C (33%; Calc .: 8.4 % N, found: 8.2% N),

d) from 3-bromo-4,6-dimethyl-2-pyrone, 1-hydroxy-3-bromo-4,6-dimethyl-2-pyridone of melting point 220 ° C (37%; calc .: 6.4% N, found: 6.3% N),

e) from 4-methyl-6-isobutenyl-2-pyrone, 1-hydroxy-4-methyl-6-isobutenyl-2-pyridone with a melting point of 116 ° C (24%; calc .: 7.8% N, found: 7.7% N),

f) from the 3,4-dimethyl-6- (4-tolyl) -2-pyrone the 1 - hydroxy - 3,4 - dimethyl - 6 - (4 - tolyl) - 2 - pyridone with a melting point of 125 ° C (41%; calc .: 6.1% N, found: 5.8% N),

g) from 4-methyl-5-ethyl-6- (4-tolyl) -2-pyrone the l-hydroxy-4-methyl-5-ethyl-6- (4-tolvn-2-dvridone from

7 ⁸

««, " , Aco- _{R r} . SR ° / N eef ■ Yield of 17.2%, with pyridine on the other hand only with

Melting point 180 ° C. (49%; calc. 5.8 / ₀ N, _{obtained. Q yield of} 1.3% obtained.

5 8 V N)

'h) from 4-methyl-6- (4-chlorophenoxyrnethyl) - B e i s ρ i e 1 6

2-pyrone the l-hydroxy-4-methyl-6- (4-chlorophenoxy- ^^ ^. _{N fe} , _{4 process> but} instead

methyl) -2-pyridone of melting point 161 μ c // _ο, ^ 2-Aminop _y ridin 2-Amino-6-meth _y l-pyridin comparable

Calc .: 5.3% N, found: 5.6% N), turns. The following are obtained:

i) from 4-methyl-6-phenylmercaptomethyW-py ^ ₄ . _Methyl . _{6th cyc} i _oh ex _y lmethyl-2-pyrone

rondasl-hydroxy ^ methyl-ophenylrnercaptome ^ yl-; ^., nethyl-e-cyclohexylmethyW-pyndon

2-pyridone of melting point 126 C _(43/0, Ber .. ^ J J _{om Sc} i _{melzpunkt 13 "C} (44%; Calc .: 6.3% N, Found .:

⁵¹ X) L · the ^ SthyW-pyrone the 1-hydroxy- 6.5% ^ ₄ . _Methyl . _{6th isop} ro _Py l-2-p _y ron das 1-Hy-

_{4,6-dimethyl-2-Py} Ridon of melting point IJD _dro ^ x _{y. 4th me} th _y l-6-isopro _Py l-2-pyridon from the enamel

(46%; calc .: 10.0% N, found: 10.1% N) J _unk ^y _{t 110} ° C (47%; calc .: 8.4% N found: 8.2% N) ,

1) from the 3,4,6-trimethyl-2-pyrone the 1-hydroxy pu 4.Methyl-6- (4-methoxyphenyl) -2-pyrone

; ^ 5 _{Ä 4} . _Me , _hyl . _{6th phEny} , ₅ , ₂ , _{(2. raetl} , _{> lätl} , _y .

d 1 hydroxy 4 - methyl - 6 - phe-

ι $ ^ ΧΖ8 £ 2 ££ * ®ο & b „^ _{Ä 4} . _Me , _hyl . _{6th phEny} , ₅ , ₂ , _{(2. raetl} , _{> lätl} , _y

11.2% N, found: 11.0% N), _{ao len)} . ₂ - pyrone the 1 - hydroxy - 4 - methyl - 6 - phe-

n) from the ^ methyl-o-heptyW-pyrone the 1-Hy- ^le 7. ₅ j ,. _(P. ^y _{methyläthyle} n) -2- _py Ridon nyi a melting point of from Schmelzdroxy-4-methyl-6-heptyl-2-pyridone, K ^. ^ _{%% N gef 56} o _{/ o N)}

48 ⁰ C (38%; calc .: 6.3% N, found: 6.0% N), P ^and _de ^v _{m 4} . _M ethyl-6- (3-nitrophenoxymethyl) -

O) from the 4-methyl-6- _U ndecyl-2-pyrone the 1-Hy- e ^ a ^ !. Hydro ^ y ^ methyl ^ -mijophMO ^

droxy-4-methyl-6-undecyl-2-pyridone / ^{om 1} ^ "^ _{a5 m} ethyl) -2-pyridone of melting point 216 C _(34/0> punkt63 ^o C (33%; Calculated: 5.0%. N, ger: 5 4 ^ N) »5 me y ^ ν _m%

ρ) from 4,5-trimethylene-6-methyl-2-pyrone that. /. ^ ₄ _ _methyl _ _6. Ethyl-2-pyrone the 1-hy-

l-Hyd _r oxy-4,5-trim _e th _y len-6-meth _y l-2- _P yndon vom ^ _{fc äthy,. 2} . _ldon from the melting point

Melting point 177 ° C (44%;. Ber .: 8.5 / ₀ N, _n0 GEF _c ^y ₍₄₁ o _{/ o; B} he .: 9.2% N Found .: 9.4% N) 8- 4 / N) α \ i \ from the 3-ethyl-4-methyi-o- ^ ioiyu-4-pyruii

'f "d 4Mthl6 (4chlor _P hen _y l) -2-pyron da» 3o g) ^^! h ^ tll ^ pyridon

· 8-4 / N) α \ i \ of the 3-ethyl-4-methyl-o- ^ ioiyu-4-pyruii among others _S 'qfau "4-Meth _y l-6- (4-chloro _P hen _y l) -2-pyron da "3o g) ^^, !!" ethy ^ tolyl ^ pyridon vom

. lH _y droxy-4-methyl-6- (4-chlorophenyl) -2- _Py ndon from _hmelzpunkt ^ _m ° C (29%; Calc .: 5.8 / N, obs ..

Melting point 123 ° C (26%; calc .: 6.0 / ₀ in, ge .. _{55% N)}

6l ° / N) j μ from 3-methoxymethyl-4-methyl-6- (4-tolyl -

'Λη' the 4,6-di _P -phenyl-2-pyrone, the 1-HydW J ^ co »d ^ .Hydroxy-3-methoxymethyl ^ methyl,! -

_{4,6-diphenyl-2-P} yridon of melting point 160 C _g P £ _{tolyl). 2} _p _yri do vo mSchimelzpunkt 130 C _(51/0,

^%% Ί ^^ δί ^ Α ^ 1-hybrid Bee · M% N. J *: ^^

IÄ! ^; droxy-4-methyl-bH «-iuryi; - ^ - ^"'"" - · ■ - ■ "", _{N1 d} as l-nyaroAy-t - «» - »- ^'" ^ ^ ₄₁₀ /. npr-'fiO ⁰ / N

; - | l: Point147 ° C (26%; Calc.: 7.3% Njef.: ^ 6 ^ N), _ron ^ _{don of} melting point 90 C (41 /, Calc. 6.0 /. N,

H ,, IHv- Melting point 191'C (JJ "/ .; ^ r P 'u)"au;' the 4-phenyl-6-methyl-2-pyrone i-My
te: droxy-4-phenyl-6-methyl-2-pyridone of melting point Example?

¹ ^ *. _L η Minounsen is nus the 65 _Mclliy 1.6- (4-chlorobenzyl) -2-pyrone, 2.5 g hy-

Under the same ^Bcdl "ß ^um3 ?? X _x y-4-methyl-, ⁵ ^ ⁴ _m ^, _vdr ochloride and 10 g of 2-aminopyridine

4-M _e thyl-6-phenyl-2- yron _P ^ ^s _e. ¹ ^ _n ^y _k ^d ₁ ^r0 ₁ ^X 35 ^o C (Ber .: ^ J ₅ J Jf 60 "C. Heated according to the usual

TÄTST ge ^P f ^yri 7roV "mU ^h Ä, n ^{n n} opyridin in one be 16

Work-up gives 3.3 g (62%) of l-hydroxy-4-methyl-6- (4-chlorobenzyl) -2-pyridone of melting point 142 ⁰ C (Ber .: 5.6% N, Found .: 5, 9% N).

Example 9

10 g of 4-methyl-6- (2,4,4-trimethylpentyl) -2-pyrone, 5 g hydroxylamine hydrochloride and 20 g of 2-aminopyridine are heated 26 hours at 7O ⁰ C, wherein further after 17 hours 2 g of hydroxylamine hydrochloride can be added. It is worked up as usual, and 7.1 g (67%) of l-hydroxy-4-methyl-6- (2,4,4-trimethylpentyl) -2-pyridone with a melting point of 108 ° C. are obtained (calc .: 5 , 9% N, found: 5.9% N).

15 Example 10

2 g of 4-methyl-6-cyclohexyl-2-pyrone and 1 g of hydroxylamine are dissolved in a mixture of 1.5 g of 2-aminopyridine and 4.5 g of 2-amino-6-methylpyridine and stored at room temperature for 9 days. After the usual work-up, 0.79 g (37%) 1 is - hydroxy - 4 - methyl - 6 - cyclohexyl - 2 - pyridone a melting point of 143 ⁰ C.

Example 11

1 g of 3,4-dimethyl-6- (2,4-dimethylbenzyl) -2-pyrone, 0.5 g of hydroxylamine hydrochloride and 3 g of imidazole are heated to 75 ° C. for 8 hours and then worked up in the usual way. This gives 0.63 g (59%) of l-hydroxy-3,4-dimethyl-6- (2,4-dimethylbenzyl) -2-pyridone of melting point 141 ⁰ C (Ber .: 5.4% N, Found .: 5 , 6% N). If pyridine is used instead of imidazole under otherwise identical conditions, the yield is 0.003 g (0.3%).

Example 12

20 g of 4-methyl-6-cyclohexyl-2-pyrone, 8 g of hydroxylamine sulfate and 50 g of imidazole are heated to 90 ⁰ C. A further 10 g of hydroxylamine sulfate are added in portions over the course of 3 hours. After a total of 5 hours of reaction time, work-up is carried out. 11.8 g of l-hydroxy ^ -methyl-o-cyclohexyl-2-pyridone with a melting point of 143 ° C. are obtained.

Example 13

2 g of 4-methyl-6-cyclohexyl-2-pyrone, 1.2 g of hydroxylamine sulfate and 5 g of imidazole are heated ^{to 110 ° C. for 1 hour.} The yield of l-hydroxy ^ -methyl-o-cyclohexyl ^ -pyridone, which melts at up to 143 ° C., is 1.01 g.

If the reaction by 15 minutes heating at 15O ⁰ C, the yield is 0.94 g.

Example 14

1 g of 4-methyl-6-cyclohexyI-2-pyrone, 0.5 g of hydroxylamine hydrochloride, 2 g of 2-aminopyridine and 1 g of toluene are heated for 5 hours at 8O ⁰ C. After about 1 hour, the initially two-phase system becomes homogeneous. The yield of 1-hydroxy-2-pyridone is 0.44 g.

If 1 g of glycol monomethyl ether is added instead of the toluene, the yield is 0.47 g.

Claims (1)

Patenlan ^ p: loaned: Process for the preparation of 1-hydroxy-2-pyridones of the general formula I. (i) Oll in which R _{1 is} an optionally branched alkyl radical with 1 to 17 carbon atoms, an alkenyl radical with 2 to 17 carbon atoms, a cycloalkyl radical with 3 to 8 carbon atoms, a cyclohexylalkyl radical, an optionally in the aromatic nucleus by one or more alkyl, alkoxy, amino , Nitro, alkoxycarbonyl, cyano groups or halogen atoms substituted phenyl, phenylalkyl, phenylalkenyl, benzhydryl, phenoxymethyl, phenylmercaptomethyl, phenylsulfonylmethyl radical, a furyl or furylalkenyl radical