DE19956509A1 - Inhibitor composition for (meth)acrylic acid stabilization comprises nitroxyl radical(s) (derivative) and a phenothiazine(s) and/or phenothiazine derivative(s) - Google Patents

Abstract

Inhibitor composition comprises a nitroxyl radical(s) (derivative) and a phenothiazine(s) and/or phenothiazine derivative(s). Inhibitor composition comprises a nitroxyl radical(s) (derivative) (N) and a phenothiazine(s) and/or phenothiazine derivative(s) (P) in a N/P weight ratio of at least 1. An Independent claim is included for a mixture comprising the above inhibitor composition and an ethylenically unsaturated compound(s).

Description

The invention relates to an inhibitor composition, its use and a mixture containing the inhibitor composition.

Many compounds that have one or more vinyl unsaturated groups sen, have a pronounced tendency to radical polymerization. Such Compounds are also used as monomers for radical polymerization purposefully used. At the same time there is a pronounced tendency towards radical buttocks lymerisation is disadvantageous insofar as it applies to both storage and in chemical and / or physical processing (e.g. distillation or Rectification), especially under the influence of heat and / or light undesired radical polymerization of the vinylically unsaturated verb can come. An undesired radical polymerization can, ins especially if polymer is deposited, ne in different ways have a negative impact. For example, in the distillation of vinylic saturated compounds formed by radical polymerization polymer knock down the surface of the evaporator used - that's where the Nei is radical polymerization due to the high temperatures very pronounced. Polymerization in the area of the surface of an evaporator Fers usually means that a polymer layer forms on the surface det. Due to the insulating effect of the polymer layer, the heat transition undesirably reduced. By radical polymerization undesirably formed polymer can also be used for rectification  on columns clog, which causes undesirable pressure losses. The Ab Separation of polymer can ultimately interrupt rectification make the process necessary, because the continued rectification different polymer must be removed.

It is therefore common practice to have vinylically unsaturated compounds called radicals are chemically polymerizable, and mixtures containing such compounds, Add compounds that act as inhibitors or retarders of the radical Polymerization act. While inhibitors radical polymerization - until they are fully implemented with free radicals - prevent, ver slow retarders the radical polymerization. Inhibitors and retarders are generally summarized under the generic term stabilizers. In the following, however, both inhibitors and retarders are said to be inhibitors be understood. Both in storage and in chemical and / or physical treatment (e.g. distillation) of vinylically unsaturated Compounds that can be polymerized by free radicals is the use of inhibito important or retarders.

Acrylic acid shows a particularly high Re due to the influence of the carboxyl group activity. It therefore tends to premature polymerization. this leads to Difficulty in storing the pure acrylic acid, since after a short time Polymerization with gel formation begins. Another difficulty with The processing and cleaning of acrylic acid consists in the great warmth amount released during the polymerization. This can, especially with heating the acrylic acid leads to an explosive course of the reaction ren. Especially in the purification of acrylic acid by distillation and in the case of reak tions under heat, z. B. the esterification, is therefore sufficient Stabilize the acrylic acid.

When developing new stabilizer systems, especially for processing of acrylic acid, there is another difficulty that the reaction procedures  in rectification columns or reactors with dimensions for an indu strial application insufficiently by mathematical models or praxis Have it reproduced on a laboratory scale. The industrial one The usual stabilizer systems are based on empirical values that exceed longer periods have been obtained. Especially in the case of acrylic acid who can get the reaction out of control due to incorrect reaction management, what leads to disastrous effects, the composition of the Stabili sator systems only developed in very small steps. The specialist stands hence further developments in the field of stabilizer systems, in particular for acrylic acid, extremely skeptical of. This is especially true when systems with low radical scavenger concentrations are proposed the.

To stabilize radical polymerizable substances that are ethylenically Containing unsaturated groups, a number of stabilizer systems are featured which contain stable N-oxyl radicals. It is common, ne ben these compounds add other substances as costabilizers ben, which synergistically ver the stabilizing effect of the N-oxyl radicals strengthen. In the technical application there are mainly phenothiazine as well Hydroquinone or the hydroquinone monomethyl ether in use. This Costa Bilisators are used in excess based on the stable N-oxyl radical puts.

EP-A-0 178 168 describes a process for inhibiting the polymerization of α, β-ethylenically unsaturated monocarboxylic acids during distillative processes described. For this purpose, it is proposed that the starting material be a free N-oxyl To admit radical. A number of connections are proposed for this purpose, which are derived from secondary amines.

The object of the invention is therefore the stabilizers known per se systems consisting of an N-oxyl radical and phenothiazine or a Phe develop nothiazine derivative in such a way that better stabilization  effect is achieved, or with the same stabilizing effect low stabilizer concentration is sufficient.

This object is achieved with an inhibitor composition containing a compo at least one nitroxyl radical (derivative) and at least one phenothia tin and / or a phenothiazine derivative, the at least one nitroxyl Radical (derivative) (N) and the at least one phenothiazine (derivative) (P) related to the weight in a ratio N / P of ≧ 1 in the inhibitor composition are holding. It has been shown that the stabilizing effect of an Inhi bitor composition, which is a stable N-oxyl radical and phenothiazine and / or a phenothiazine derivative contains disproportionately improved when the phenothia tin or the phenothiazine derivative in deficit in the inhibitor composition hold is.

Suitable N-oxyl radicals (also referred to as nitroxyl radicals (derivatives)) In principle, according to the invention, all compounds are considered that have little have at least one <N-O • group. The nitroxyl radical (derivatives) can also be generated in situ from other compounds, such as. B. by H- Abstraction from hydroxylamines or by adding C radicals to nitro no But you can also from aromatic amines, which are derived from aniline or Derive phenylenediamine, generated in situ. As suitable according to the invention Nitroxyl radical (derivatives) come into consideration especially those who are from derive a secondary amine which does not contain any hydrogen atoms on the α-C- Atoms (i.e., the N-oxyl groups derive from corresponding secondary ren amino groups).

Such suitable, derived from a secondary amine, stable Nitroxyl radical (derivatives) are, for. B. those of the general formula I.

With
R ¹ , R ² , R ⁵ and R ⁶ = the same or different straight or branched chain, optionally substituted alkyl groups and
R ³ and R ⁴ = the same or different straight or branched chain, optionally substituted alkyl groups or
R ³ CNCR ⁴ = an optionally substituted, cyclic structure.

Examples of suitable compounds are those stable nitroxyl radical (derivatives) of the general formula I in which R ¹ , R ² , R ⁵ and R ^{6 are} for (identical or different) C ₁ to C ₄ alkyl groups such as methyl, Ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl or tert-butyl, linear or branched pentyl, phenyl or substituted groups thereof and R3 and R4 for (same or different various) C ₁ - to C ₄ -alkyl groups such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl or tert-butyl, linear or branched pentyl, substituted groups of them or together with CNC the cyclical structure

where n is an integer from 1 to 10 (often 1 to 6), including sub of such cyclical structures. As an exemplary representative en 2,2,6,6-tetramethyl-1-oxyl-piperidine, 2,2,5,5-tetramethyl-1-oxyl-pyrrolidine and 4-oxo-2,2,6,6-tetramethyl-1-oxyl-piperidine.

The N-oxyl radical (derivatives) I can be derived from the corresponding secondary Amines by oxidation, e.g. B. with hydrogen peroxide. Usually they can be represented as pure substance.  

The nitroxyl radicals (derivatives) I which are suitable according to the invention include in particular piperidine or pyrrolidine N-oxyls and di-N-oxyls of the following general formulas II to IX:

With
m = 2 to 10.

R ⁷ , R ⁸ , R ⁹ = independently of one another

M ^⊕ = a hydrogen or an alkali metal ion,
q = an integer from 1 to 10,
R ^{1 '} , R ^2' , R ^{5 '} , R ^6' = independently of one another and independently of R ¹ , R ² , R ⁵ , R ^{6 the} same groups as R ¹ ,
R ^{7 '} = straight or branched chain alkyl group with 1 to 8 carbon atoms, SiR ^8' R ^{9 '} R ^10' , where R ^{8 '} , R ^9' and R ^{10 'the} same or different straight or branched chain alkyl groups with 1 to 8 carbon atoms are.

R ¹⁰ = C ₁ to C ₄ alkyl, -CH = CH ₂ , -C ,CH, -CN,

R ¹¹ = an organic radical which has at least one primary, secondary (e.g. -NHR ¹ ) or tertiary amino group (e.g. -NR ¹ R ² ) or at least one ammonium group -N ^⊕ ®R ¹⁴ R15R ¹⁶ X ^⊖ with X ^⊖ = F ^⊖ , Cl ^⊖ , Br ^⊖ , HSO ₄ ^⊖ , SO ₄ ^{2 ⊖} H ₂ PO ₄ ^⊖ HPO ₄ ^{2 ⊖} or PO ₄ ^{3 ⊖} and R ¹⁴ , R ¹⁵ , R ¹⁶ mutually independent organic radicals (e.g. independently of one another and independently of R ^{1, the} same groups as R ¹ ),
R ¹² = independently of R ^{11 the} same groups as R1 l or -H, -OH, C ₁ - to C ₄ ^-alkyl , -COO ^⊖ M ^⊕ , -C∼CH,

or hydroxy-substituted C ₁ - to C ₄ -alkyl (e.g. hydroxyethyl or hydroxypropyl) or R ¹¹ , R ¹² = together the oxygen of a carbonyl group and

Preferably R ¹ = R ² = R ⁵ = R ⁶ = R ^{1 '} = R ^2' = R ^{5 '} = R ^6' -CH ₃ .

N-oxyl radicals (derivatives) suitable as exemplary representatives according to the invention be 1-oxyl-2,2,6,6-tetramethylpiperidine, 1-oxyl-2,2,6,6-tetramethylpiperidine-4-  ol, 1-oxyl-2,2,6,6-tetramethyl-4-methoxypiperidine, 1-oxyl-2,2,6,6-tetramethyl-4- ethoxypiperidine, 1-oxyl-2,2,6,6-tetramethyl-4-trimethylsiloxypiperidine, 1-oxyl 2,2,6,6-tetramethylpiperidin-4-one, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl acetate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl-2-ethylhexanoate, 1-oxyl-2,2,6,6- tetramethylpiperidin-4-yl stearate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl benzoate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl- (4-tert-butyl) benzoate, bis (1- oxyl-2,2,6,6-tetramethylpiperidin-4-yl) succinate, bis (1-oxyl-2,2,6,6-tetramethyl piperidin-4-yl) adipate, bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate, Bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) -n-butylmalonate, bis (1-oxyl-2,2, - 6,6-tetramethylpiperidin-4-yl) phthalate, bis (1-oxyl-2,2,6,6-tetramethylpiperidine- 4-yl) isophthalate, bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) terephthalate, Bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) hexahydroterephthalate, N, N'-bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipinamide, N- (1-oxyl-2,2,6,6-tetra methylpiperidin-4-yl) caprolactam, N- (1-oxyl-2,2,6,6-tetramethylpiperidin-4- yl) -dodecylsuccinimide, 2,4,6-tris- [N-butyl-N- (1-oxyl-2,2,6,6-tetramethylpiperi din-4-yl] -s-triazine, N, N'-bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) -N, N'-bis formyl-1, 6-diaminohexane, 4,4'-ethylene-bis (1-oxyl-2,2,6,6-tetramethyl-piperazine- 3-one) and tris (2,2,6,6-tetramethyl-1-oxyl-piperidin-4-yl) phosphite and additional Lich called 1-oxyl-2,2,6,6-tetramethyl-1,2,3,6-tetrahydropyridine.

Other suitable exemplary representatives are (for reasons of clarity are the hydrogen atoms in the formula pictures, which represent the free valences of Saturate nitrogen and oxygen, not shown):

Sunamoto, Junzo; Akiyoshi, Kuzunari, Kihara, Tetsuji; Endo, Masayuki, BCS JA 8, Bull. Chem. Soc. Jpn., EN, 65, 4, 1992, pp. 1041-1046;

Beilstein Registry Number 6926369 (C ₁₁ H ₂₂ N ₃ O ₂ );

Beilstein Registry Number 6498805 (4-Amino-2,2,6,6-tetramethyl-1-oxylpiperidine);

Beilstein Registry Number 6800244 (C ₁₁ H ₂₃ N2O ₂ O

Beilstein Registry Number 5730772 (N-methyl-4-amino) -2,2,6,6-tetramethyl-1-oxyl piperidine;

Beilstein Registry Number 5507538 (2,2,6,6-tetramethyl-4- (2-aminoethylamino) -1-oxyl piperidine);

Beilstein Registry Number 4417950 (4 <bis (2-hydroxyethyl) <- amino-2,2,6,6-tetramethyl-1-oxyl-piperidine);

Beilstein Registry Number 4396625 (C ₁₂ H ₂₃ N ₂ O ₂ );

Beilstein Registry Number 4139900 (4-Amino-2,2,6,6-tetramethyl-4-carboxy-1-oxyl-piperidine);

Beilstein Registry Number 4137088 (4-Amino-4-cyano-2,2,6,6-tetramethyl-1-oxyl piperidine);

Beilstein Registry Number 3942714 (C ₁₂ H ₂₅ N ₂ O ₂ O);

Beilstein Registry Number 1468515 (2,2,6,6-tetramethyl-4-hydroxy-4-acetyl-1-oxyl piperidine);

Beilstein Registry Number 1423410 (2, 2,4,6,6-pentamethyl-4-hydroxy-1-oxyl piperidine);

Beilstein Registry Number 6205316 (4-carboxymethylene-2,2,6,6-tetramethyl-1-oxyl-piperidine);

Beilstein Registry Number 1395538 (4- <2-carboxyl-benzoyloxy <-2,2,6,6-tetramethyl-1-oxyl-piperidine);

Beilstein Registry Number 3546230 (4-carboxymethyl-2,2,6,6-tetramethyl-1-oxyl piperidine);

Beilstein Registry Number 3949026 (4-acetyl-2,2,6,6-tetramethyl-1-oxyl-piperidine);

Beilstein Registry Number 4611003 ethylenediamine, triacetic acid mono (1-oxy-2,2,6,6-tetramethylpiperidinyl-4-amide);

Beilstein Registry Number 5961636 (C ₁₃ H ₂₁ N ₂ O ₄ )

Beilstein Registry Number 5592232 (C3H ₂₇ N ₂ O ₄ );

Beilstein Registry Number 5080576 (Bernstoneic acid N- (2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl) monoamide);

Beilstein Registry Number 5051814 (4- (4-hydroxybutanoxylamino) -2,2,6,6-tetramethyl-1-oxyl-piperidine);

Beilstein Registry Number 4677496 (2,2,6,6-tetramethyl-4-oximino-1-oxyl-piperidine);

Beilstein Registry Number 1451068 (C ₁₁ H ₁₈ NO ₂ );

Beilstein Registry Number 1451075 (C ₁₁ H ₂₀ NO ₂ );

Beilstein Registry Number 1423698 (4-ethyl-4-hydroxy-2,2,6,6-tetramethyl-1-oxyl piperidine);

Beilstein Registry Number 5509793 (4-ethoxymethyl-4-hydroxy-2,2,6,6-tetramethyl-1-oxyl-piperidine);

Beilstein Registry Number 3960373 (C ₁₀ H ₁₉ N ₂ O ₃ );

Beilstein Registry Number (C ₁₀ H ₁₇ N ₂ O ₂ );

Beilstein Registry Number 3985130 (2,2,6,6-tetramethyl-1-oxyl-4-piperidylidene) succinic acid);

Of course, according to the invention, mixtures of N-oxyl Radical (derivatives) can be used.

Phenothia is preferably a further component in the inhibitor composition contain zin. However, derivatives of phenothiazine can also be used the.

Residues can be bound both to the sulfur atom and / or to the nitrogen atom and / or to one or more of the carbon atoms of the phenothiazine as the base body. In principle, any residues are possible, but alkyl and aryl residues are preferred. Particularly preferred phenothiazine derivatives are represented by the structural formulas below:

-oligomeric phenothiazines such as:

In the above structural formulas, R ₁ and R _{2 may be the} same or different, H, halogen, C ₁ to C ₂₀ alkyl or aryl, SO ₃ H or SO ₃ ^- M ⁺ - with m = 1 to 4, n = 1 to 4 and k = 1 to 8.

Particularly preferred in the inhibitor composition as N-oxyl radical 4- Hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine and / or N, N'-bis (1-oxyl-2,2,6,6- tetramethylpiperidin-4-yl) -N, N'-bis-formyl-1,6-diaminohexane.

In addition to a stable N-oxyl radical and phenothiazine or a phenothia zinderivat can ent other costabilizers in the inhibitor composition to be hold. Hydroquinone and in particular the Hydroquinone monomethyl ether shown.

According to the invention, the inhibitor compositions are used to stabilize Pure substances that have at least one ethylenically unsaturated group or of mixtures which contain at least one substance which at least has an ethylenically unsaturated group. The inhibitor compositions tion also works in the presence of oxygen.

According to the invention, a mixture comprising at least one is also provided a compound which has at least one ethylenically unsaturated group, and an inhibitor composition according to the invention.

Suitable compounds which have at least one ethylenically unsaturated group are, in particular, those which can be radically homo- and / or copolymerized. These are, for example, olefins such as isobutene, ethylene or propylene, vinyl aromatic monomers such as styrene, α-methylstyrene, o-chlorostyrene or vinyltoluenes, C ₄ -C ₈ -conjugated dienes such as butadiene or isoprene, esters from vinyl alcohol and 1 to 18 C. -Atomic monocarboxylic acids such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate or vinyl stearate. In particular, α, β monoethylenically unsaturated mono- and dicarboxylic acids having 3 to 6 carbon atoms, such as in particular acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid, are the esters of the aforementioned carboxylic acids and 1 to 12, preferably 1 to 4, carbon atoms containing alkanols, such as, in particular, acrylic acid and methacrylic acid methyl, ethyl, n-butyl, isobutyl, tert-butyl and 2-ethylhexyl esters, and dimethyl maleate and di-n-butyl maleate, suitable.

However, precursor aldehydes, nitriles and amides are also suitable named 3 to 6 carbon atoms containing α, βmonoethylenically unsaturated Mo no- and dicarboxylic acids, for example acrolein, methacrolein, acrylonitrile, Methacrylonitrile, acrylamide and methacrylamide. Monomers such as vinyl sulfonic acid, Vinylphosphonic acid, N-vinylimidazole and N-vinylpyrrolidone also come in Question.

The inhibitor composition according to the invention is an addition to both the storage stabilizer lization as well as for process stabilization (manufacture, cleaning and chemi reaction) of at least one ethylenically unsaturated group send connections suitable. The latter also applies in particular to distillation Processes that are usually carried out at temperatures of 50 to 300 ° C, preferably at 50 to 200 ° C, particularly preferably at 50 to 150 ° C, run off.

The stabilization with the inhibitor composition according to the invention is particularly suitable for the distillative (rectificative) treatment of (meth) acrylic acid esters (in particular the exemplary representatives mentioned above), for their distillative or rectificative separation from product mixtures, as is the result of an acid-catalyzed esterification of (meth) acrylic acid with alcohols, in particular alkanols (in particular C ₁ - to C12- or C ₁ - to C ₈ -alkanols) are present before and / or after removal of the acid catalyst.

However, it is also suitable for stabilizing the aforementioned (meth) mixtures containing acrylic esters, neither the esterification catalyst nor Acrylic or methacrylic acid itself included. Such (meth) acrylic acid esters holding mixtures form, for example, the aforementioned esterification product mixtures after, for example, extractive and / or rectificative separation of the acid catalyst and after appropriate removal of the excess (Meth) acrylic acid.

The stabilization of one subjected to distillation or rectification Mixture containing (meth) acrylic acid esters can be such that the Inhibitors are added to the mixture before distillation.

In addition, an inhibitor can be added to the top of the column for stabilization respectively. Of course, the entire stabilization can also be done exclusively by adding an inhibitor to the top of the column.

The various components of the inhibitor composition according to the invention can be added sequentially, simultaneously or even premixed become. The above also applies to the other inhibitors if the inhibitor composition includes such.

The addition of the components of the inhibitor composition to below different addition locations can be made. For example, com components of the inhibitor system at the top of the rectification column and others Components of the inhibitor system in the sump and / or the inlet of the recti fiction column are given. This applies both to such rectifications in In the context of which the (meth) acrylic acid ester via overhead, via sump and / or via Side deduction is separated. It may also be appropriate that the fiction moderate procedure in the case of a continuous distillative (rectificative) Ab separation of (meth) acrylic acid esters so that at least one too supplying inhibitor component not continuously, but only of time  at the time, d. H. periodically recurring, is added (e.g. at the top of the column, in the swamp and / or in the inlet).

In the following, the invention will be described with reference to a drawing of an embodiment will be explained in more detail. It shows:

Fig. 1 is a graphical representation of the stabilizing effect of a Sta bilisergemisches from phenothiazine and HO-TEMPO.

General test conditions:

Acrylic acid was in each case with the amounts of pheno given in Table I. thiazine and 4-hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine (HO-TEMPO) ver puts. The quantities given relate to the weight and the menus of acrylic acid used. 1.2 ml of the stabilized acrylic acid and 0.5 ml Glass balls (diameter 2 mm) were placed in a glass ampoule with an inside volume of 1.9 ml and an outer diameter of 8 ml under oxygenate enclosed gas-tight atmosphere. The glass ampoule was completely opened Oil bath heated to 113 ° C. and immersed in the dark. It was determines the time required for the contents of the glass ampoule to fill constantly solidified. The determined times are in the last column of Ta belle 1 stated.  

Table 1

Inhibitory effects of phenothiazine / 4-hydroxy-1-oxyl-2,2,6,6-tetramethyl piperidine (HO-TEMPO)

If the proportion of 4-hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine (HO-TEMPO) is plotted against the storage stability determined in the experiments, as has been done in FIG. 1, it is evident that at a proportion of the HO-TEMPO in the stabilizer mixture of less than 50%, a change in the weight ratio of phenothiazine / HO-TEMPO causes only slight changes in the storage stability. If the nitroxyl radical is used in excess, ie the proportion of HO- TEMPO in the stabilizer mixture is greater than 50%, there is a sharp increase in storage stability. The best storage stability is obtained according to FIG. 1 if the use of phenothiazine is completely dispensed with. However, this case is not practical for industrial applications. 4-Hydroxy-1-oxyl-2,2,6,6-tetramthylpiperidine (HT) is stable up to a temperature of 140 ° C, at higher temperatures it begins to decompose. The behavior of other nitroxyl radicals is comparable. For example, N, N'-bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) -N, N '-bis-formyl-1,6-diaminohexane (TEMPO-BFDH) decomposes Temperatures above 150 ° C.

Phenothiazine (PTZ) melts at 182-185 ° C, boils at 235 ° C and decomposes only at temperatures above 250 ° C.

In the production of acrylic acid, for example, when quenching the Gas flow temperatures of over 150 ° C occur. Since also under these Be conditions a stabilization of acrylic acid is required, a stabilizer be used, which is stable at these temperatures. These requirements are met by PTZ while nitroxyl radicals do not have sufficient stability exhibit.

Since the gaseous stream of acrylic acid with stabilized acrylic acid or with reverse quenched high-boiling solvent, at least one stabilizer lizer, which is stable under these conditions, to ensure adequate security. A Ni Troxyl radical alone is not satisfied.

Claims (6)

1. inhibitor composition containing as components at least one nitroxyl Radical (derivative) and at least one phenothiazine and / or one phenothia zinderivat, wherein the at least one nitroxyl radical (derivative) (N) and the at least one phenothiazine (derivative) (P) by weight in one Ratio N / P of ≧ 1 are contained in the inhibitor composition. 2. inhibitor composition according to claim 1, wherein as a nitroxyl radical (derivative) 4- Hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine and / or N, N'-bis (1-oxyl- 2,2,6,6-tetramethylpiperidin-4-4-yl) -N, N'-bis-formyl-1,6-diaminohexane ent hold is. 3. inhibitor composition according to claim 1 or 2, wherein as a further component a hydroquinone, especially hydroquinone monomethyl ether is contained. 4. Mixture containing at least one compound which is at least one ethyle nisch unsaturated group, and an inhibitor composition according to ei nem of claims 1 to 3. 5. Mixture according to claim 4, wherein the at least one ethylenically unsaturated Group containing compounds is acrylic acid and / or methacrylic acid.   6. Use of an inhibitor composition according to one of claims 1 to 4 for the stabilization of radically polymerizable, ethylenically unsaturated ten compounds, these compounds individually or in a mixture can lie.