WO2010028844A1 - Light curing compositions - Google Patents

Abstract

The present invention relates to light curing compositions, comprising radically polymerizable vinyl compounds and daylight sensitive radical initiators of the formula (I) and/or (II), and optionally containing further additives, such as fillers, pigments, solvents, and to the use thereof as a coating material for technical, optical, and medical applications.

Description

 Light-curing compositions

The present invention relates to light-curable or photocurable compositions comprising radically polymerizable compounds, in particular vinyl compounds and daylight-sensitive radical initiators and optionally further additives such as fillers, pigments, solvents, and their use as coating material for technical, optical and medical applications. Moreover, the invention relates to cured products prepared from the compositions, including their methods of preparation. Finally, the invention also relates to the novel compounds used as radical initiators as such and to a process for their preparation.

Photoinitiators absorb radiation in the UV or in the visual range, thus providing polymerization-initiating species. In the case of radical polymerization, these are free radicals. Generally, radical photoinitiators (radical initiators) are classified into two classes based on the chemical mechanism of radical formation. Norrish Type I photoinitiators form free radicals due to unimolecular bond breaking radiation. Opposite, Norrish Type II photoinitiators undergo a bimolecular reaction upon exposure to radiation, with the photoinitiator reacting with a second molecule (the coinitiator) and forming the polymerization initiating species by electron and proton transfer or directly by hydrogen abstraction. Norrish type I and II photoinitiators are used in curing with UV light. Currently, almost exclusively Norrish type II photoinitiators are used for polymerization by irradiation with visual light.

Characteristic of the curing by radiation in the UV range is the high reaction rate. This type of curing is used for example for coatings of various substrates such as wood. Such an example of UV-curable coatings of materials with Norrish Type I photoinitiators, such as diethoxyphenylacetophenone or acrylic phosphine oxides, is disclosed in U.S. Pat EP 1247843. Further, WO 01/51533 describes a UV-curable wood-plating material using acrylphosphine oxides, α-hydroxyalkylphenones or α-dialkoxyacetophenones as photoinitiators.

UV curing can be used for all transparent coatings with low layer thicknesses. However, it reaches its limits with an admixture of pigments and at higher layer thicknesses. Such photopoly-reactive compounds therefore cure only incompletely by UV radiation. If a deeper through cure is desired, such as in the photohardening of dental materials to be used as a dental filling, visible light may be used for irradiation which has a higher penetrating power. A photoinitiator that can be used for such purposes is a combination of α-diketones and amino coinitiators. Such a system is described in GB 1, 408,265. Examples in which dental materials and photoinitiators are used are described in US 4,457,818, or in US 4,525,256, in which camphor quinone is preferably used. Camphorquinone has an absorption maximum of 468 nm, which explains the intense yellow color. This may be to the disadvantage that the materials cured by camphorquinone-amine systems as photoinitiators have an undesirable visible yellow tinge. Another system which induces radical polymerization of dental materials by radiation in the visual field is based on acylgermanium compounds and is described in US 2008/0076847.

It thus turns out that the initiator systems known in the prior art are not capable of ensuring sufficiently rapid and complete curing of the desired materials in each case. Rather, the known compounds which provide by means of short-wave light (UV range) polymerization initializing species available, the disadvantage that the short-wave radiation achieves only a small penetration depth. This is particularly problematic when used in systems with fillers. Moreover, no systems were available that readily provide polymerization initiating species by means of visible light (daylight) and without coinitiators. Thus, there was still an urgent need to divide up new ones simple yet powerful initiators that can be efficiently activated by visible light.

It is an object of the present invention to provide a novel radical polymerization initiator which, upon irradiation with visible light (ie, long wavelength daylight), provides sufficiently fast and complete cure of the desired materials, even without a coinitiator and negative side effects ,

This object has surprisingly been achieved by the present invention according to the appended claims.

The novel photoinitiators for radical polymerization according to the invention are represented by formulas (I) and (II) wherein the compounds of formula (I) are the monomers and those of formula (II) are the dimeric structures , The dimeric structures have approximately the same efficiency in the initiator effect, but also have a lower diffusibility, which may be of practical relevance.

Formulas (I) and (II):

wherein in the formulas (I) and (II) each independently

X = S, CHR ⁴ , O, or NR ⁴ ;

R ¹ and R ^{2 are} each independently H, linear or branched C 1 -C 20

alkyl; thioalkyl; aryl; or heteroaryl, wherein R ¹ and R ^{2 may} also be linked together to form saturated or unsaturated cyclics or heterocycles; R ³ = H, linear or branched C ¹ -C 20 -alkyl; thioalkyl; aryl; Heteroaryl is; R ⁴ = H, linear or branched C 1 -C 20 -alkyl, where the alkyl substituent may have cyclic substructures; acyloxy; aryl; or heteroaryl; A is an aliphatic, aromatic or heteroaromatic compound group.

The polymerization initiators according to formula (I) or (II) according to the invention are used in light-curing or photocurable composition. These compositions comprise: a. at least one radically polymerizable compound, in particular vinyl compound; and b. at least one compound of formula (I) and / or formula (II) as a radical initiator.

The invention further relates to the cured product obtainable by photohardening this composition with visible light, and to the photohardening process for producing such a cured product as such.

In addition, the invention relates in particular to the use of the compounds of the formula (I) and / or of the formula (II) as radical initiator for free-radical polymerization.

Finally, the invention also relates to a novel preparation process for the compounds of the formula (I) and / or of the formula (II).

The substituent R ¹ in formulas (I) and (II) may preferably be varied as follows: R ¹ = H, C ¹ -C 20 alkyl; Aryl, wherein aryl may be a mono- to tri-substituted phenyl substituent, a monosubstituted to trisubstituted naphthalene substituent; Substituents may be halogen, preferably chloro, alkoxy, C 1 -C 20 alkyl, aminoalkyl, diaminoalkyl, acylamino, nitro, cyano, alkoxycarbonyl, wherein alkoxy = C 1 -C 10 alkyl is attached to a monovalent oxygen substituent; acyloxy; Dialkylamino = one or two C1-C10 alkyl bonded to a divalent nitrogen atom; Acylamino = C1-C10 alkanoyl or substituted benzoyl or naphthoyl bonded to an amino nitrogen. The substituent R ² in the formulas (I) and (II) may preferably be varied as follows: R ² = H, C ¹ -C 20 -alkyl; Aryl, wherein aryl may be a mono- to tri-substituted phenyl substituent, a monosubstituted to trisubstituted naphthalene substituent; Substituents may be halogen, preferably chloro, alkoxy, dialkylamino, acylamino, methyl, nitro, cyano, alkoxycarbonyl, wherein alkoxy = C1-C10 alkyl is attached to a monovalent oxygen substituent; acyloxy; Dialkylamino = one or two C1-C10 alkyl bonded to a divalent nitrogen atom, acylamino = C1-C10 alkanoyl or substituted benzoyl or naphthoyl bonded to an amino nitrogen; Heteroaryl, wherein preferably a mono- to tetra-substituted pyridine substituent, substituted thiazole, oxazole and imidazyl substituents are used.

The substituent R ³ in the formula (I) may preferably be varied as follows: R ³ = H, C ¹ -C 20 -alkyl, preferably a mono- to quintuply-substituted phenyl radical, a monosubstituted to trisubstituted naphthalene substituent; Substituents are selected from halogen, preferably chloro, methoxy, methyl, nitro, cyano, alkoxycarbonyl, where alkoxy = C 1 -C 10 alkyl bonded to a monovalent oxygen substituent gene; acyloxy; Dialkylamino = one or two C1-C10 alkyl bonded to a divalent nitrogen atom, acylamino = C1-C10 alkanoyl or substituted benzoyl or naphthoyl bonded to an amino nitrogen. Also, single and multiple condensation products between a cyclic thiohydroxamic acid and a substituted benzene-1, 2-, -1, 3- or -1, 4-dicarboxylic acid or a naphthalene di-, tri-, tetracarboxylic can be mentioned as R ³ . Furthermore, R ³ may be a heteroaromatic radical, wherein the term heteroaroamtisch preferably refers to pyridine, pyrrole, thiophene and furan and derivatives thereof.

The substituent R ⁴ in the formulas (I) and (II) can preferably be varied as follows: R ⁴ = H, C 1 -C 10 -alkyl, where from C ³ the alkyl chain can be linear or branched or the alkyl substituent can have cyclic substructures, Phenyl, one to five times substituted phenyl groups.

The ring-shaped group X in the formulas (I) and (II) may preferably be varied as follows, but more preferably X = S. Formula (I) is exemplified below. CHR ⁴ , O, NR ⁴ preferably S

In the compounds of the formula (II), A is preferably a pyridine, pyrrole, thiophene, furan, thiazole, oxazole or imidazole group or a derivative thereof or a monosubstituted to tetra-substituted or unsubstituted phenylene group.

Preferred embodiments of the invention have compounds of the formula (I) or (II) in which X = S. In addition, R ¹ , R ² , R ³ and R ⁴ are preferably independently of one another H, C ¹ -C 20 -alkyl, aryl or heteroaryl; where aryl is a monosubstituted to trisubstituted phenyl substituent or a monosubstituted to trisubstituted naphthalene substituent, the substituents being selected from halogen, in particular chlorine, C 1 -C 10 -alkoxy, C 1 -C 20 -alkyl, aminoalkyl, C 1 -C 10 -alkyl, Mono- or dialkylamino, acylamino, nitro, cyano, alkoxycarbonyl; and heteroaryl is substituted or unsubstituted pyridine, pyrrole, thiophene or furan. Further, A is preferably a pyridine, pyrrole, thiophene, furan, thiazole, oxazole or imidazole group or a derivative thereof, or a mono- to tetra-substituted or unsubstituted phenylene group. The definition of the substituents on the phenylene group corresponds to the definition given above. R ² in formula (I) or (II) is particularly preferably not H ₁ because in these compounds (ie in which R ^{2 is} C ₁ -C 20 -alkyl, aryl or heteroaryl as defined above) a surprisingly higher sensitivity in the visible range of Light occurs. The reason for this is assumed to be a bathochromic shift of the longest-wavelength absorption maximum of the chromophore (eg of the thiazole-2 (3H) chromophore) in the case of alkyl and in particular aryl substituents R ² and an associated higher sensitivity in the visible range.

Further preferred are compounds of formula (I) wherein X is S, R ¹ is C 1 -C 4 alkyl, R ^{2 is} phenyl or a phenyl radical having another ortho, meta or para substituent, said Substituent is selected from methoxy, C1- C4 alkyl, amino, dialkylamino, acylamino and chloro; or R ¹ and R ^{2 form} an unsaturated cycle; R ³ = phenyl or a phenyl radical having another ortho, meta or para substituent selected from methoxy, C 1 -C 4 alkyl, amino, dialkylamino, acylamino and chloro. Unsaturated cyclics formed by R ¹ and R ² are especially phenyl, indene, coumarone (benzofuran), indole, thionaphthene (benzothiophene), naphthalene which may be substituted. Particularly suitable substituents are halogen, preferably chlorine, C 1 -C 10 -alkoxy, C 1 -C 20 -alkyl, aminoalkyl, C 1 -C 10 -mono- or -dialkylamino, acylamino, nitro, cyano, alkoxycarbonyl.

Very particularly preferred compounds according to the invention are represented by the following formulas (IN) - (V). In this case, the compounds (III) and (IV) are particularly suitable for the photopolymerization with pure blue light of the wavelength of about 380-500 nm.

(III) (IV) (V)

In the formulas (III) to (V), R ^{5 represents} chlorine, alkoxy, C 1 -C 20 -alkyl, aminoalkyl, diaminoalkyl, acylamino, nitro, cyano, alkoxycarbonyl, wherein: alkoxy = C 1 -C 10 -alkyl to a monovalent oxygen -Substituenten bound; acyloxy; Dialkylamino = one or two C1-C10 alkyl bonded to a divalent nitrogen atom; Acylamino = C1-C10 alkanoyl or substituted benzoyl or naphthoyl bonded to an amino nitrogen. Further, X = O, S, CHR ⁴ , NR ⁴ , preferably S, and n ranges from 1 to 4. R 4 is as defined above for the formulas (I) and (II). Examples of the invention in which X is NR ⁴ are as follows (formulas (VI) and (VII)):

(VI) (VII)

The polymerization initiators according to formula (I) or (II) according to the invention, which can be activated by the irradiation with visible light, are prepared according to the methods of Acta Cryst. (2005). E61, O1738-01741; Eur. J. Org. Chem. (1999). 1275-1290; or Synlett 2000, 371-373.

In addition, the polymerization initiators of the formula (I) or (II) according to the invention can be prepared by a novel process which comprises reacting the free N-hydroxy compound of the following formula

wherein X, R ¹ and R ^{2 are} as defined above, with a carboxylic acid chloride or bis (carboxylic acid chloride) of one of the following two formulas

wherein R ^{3 is} as defined above and is also part of the invention. In the following the synthesis becomes exemplary for the preferred embodiment with X = S, ie using N-Hydroxythiazolthionen as starting material described. The same applies to the other definitions of X above.

The formation of the compound of the formula (I) or the formula (II) depends on the molar ratios of the starting materials used. At an approximately 1: 1 molar ratio of N-hydroxythiazolethione to carboxylic acid chloride, the compounds of formula (I) result in an approximately 2: 1 molar ratio of N-hydroxythiazolethione to bis (carboxylic acid chloride) resulting in the compounds of formula (II). The reaction takes place in an alkaline aqueous / organic medium (preferably an alkali metal carbonate in acetone) in a temperature range of 10 ° to 5O ⁰ C, preferably at ambient temperature (about 20 ⁰ C). The starting materials are either commercially available or can be prepared by methods known to those skilled in the art.

Advantage over the known methods is the use of the free N-Hydroxythiazolthione instead of their salts, since the free acids generally incurred as a product of Thizaolthion synthesis and in contrast to most hygroscopic alkali metal salts are neither hygroscopic nor react basic. Consequently, the new process is characterized in particular by a higher efficiency and easier handling of the educts.

The polymerization initiators of the formula (I) or (II) according to the invention have a through hardening with a high degree of through-cure or a high penetration depth and can be used in a wide technical field. In addition, they have some significant advantages compared to already known UV and VIS photoinitiators. These include that the new initiators metal-free, easy to synthesize and can be used with, but in particular without amine co-initiators. The photoinitiators are weighed for the stated fields of application in amounts of 0.001 to 20 wt .-%, preferably 0.01 to 1 wt .-% and particularly preferably from 0.01 to 0.1 wt .-%, based on the monomer system. Thanks to their good solubility, the photoinitiators can simply be stirred into the system used, which ensures a uniform distribution of the initiators and the transparency of the polymer. The photopolymerization can take place by means of solar radiation or by known methods of photopolymerization, that is to say by irradiation by means of light sources which emit the required wavelengths to a sufficient extent. Suitable wavelengths are 300 <λ <780 nm, preferably 350 <λ <600.

The new compound can be used as a photoinitiator for photopolymerizable unsaturated compounds. Such compounds are, for example, unsaturated monomers such as esters of (meth) acrylic acid, e.g. Methyl, ethyl, n- or tert-butyl, isooctyl, hydroxyethyl, glycidyl or tetrahydrofufuryl (meth) acrylate, ethylene glycol di (meth) acrylate, neopentyl di (meth) acrylate, trimethylolpropane tri (meth) acrylate; Pentaerythritol tetra (meth) acrylate or pentaerythritol (meth) acrylate; Acrylonitrile, (meth) acrylonitrile, (meth) acrylamide, N-substituted (meth) acrylamides; Vinyl esters such as e.g. Styrene, alkylstyrenes, halostyrenes, divinylbenzene, vinylnaphthalene, N-vinylpyrrolidone, vinyl chloride; Allyl compounds such as diallyl phthalate, diallyl maleate, triallyl isocyanurate, triallyl phosphate, or ethylene glycol diallyl ether, and the mixture of such unsaturated monomers.

Photopolymerizable compounds are also unsaturated oligomers or polymers and mixtures thereof with unsaturated monomers. These include thermoplastic resins containing unsaturated groups such as maleic acid esters, fumaric acid, allyl groups or acrylic or methacrylic groups. Examples of such oligomers are unsaturated polyesters, unsaturated acrylic resins and Polyetheracrylatoligomere. Examples of polyunsaturated compounds are especially the acrylates or methacrylates of diols and polyols, e.g. Hexamethylene di (meth) acrylate, trimethylene propane tri (meth) acrylate, or pentaerythritol tetra (meth) acrylate.

Furthermore, polymerization may be carried out in the usual manner in emulsion, in reverse emulsion, in bulk or in solution. As solvents, water, aqueous organic solvents, purely organic solvents, solvent mixtures or ionic liquids can be used. When using a transparent apparatus or a high-pressure-stable light source, the polymerization can also be carried out in supercritical carbon dioxide. The polymerization may in particular under for the radical polymerization typical conditions are carried out. The exact conditions are not critical and can be adjusted by the skilled person in the usual way.

The invention further relates to the use of the above-described composition which comprises at least one free-radically polymerizable compound, in particular vinyl compound; and at least one compound of formula (I) and / or formula (II) as a radical initiator, as a coating material for technical, optical, medical applications and in photolithography. Photohardening is of particular importance for printing inks since the drying time of the binder decisively influences the production speed of the product. Likewise, the photocuring of surface coatings, as obtained in the coating of sheets, or plastic parts of any kind, another field of application. Again, there is the advantage that by the irradiation with visible light (blue light) initializes the hardening and thus can be dispensed with the irradiation of harmful to humans UV rays. Also, a photoinitiator according to the present invention which provides by visible light the polymerization-initializing species is suitable for use in photolithography. Here, a substrate is coated with photopolymerizable monomers and irradiated certain areas of the substrate with visible light. Subsequently, the uncured fractions are rinsed out by means of solvents. In this way, with the help of the new photoinitiator three-dimensional structures can be constructed, as used for example in printing plates, or in a partial coating of silicon wafers. The light-curing compositions used for various purposes may contain fillers such as silica, gypsum, pigments, dyes, fibers, flow control agents or blowing agents, or other conventional additives, other than the photopolymerizable compounds and the corresponding photoinitiator.

The invention is further illustrated by the following examples: Application examples:

1. Synthesis of Compounds of Formula (I) and (II):

The preparation of the compounds of formula (I) and (II) according to the invention according to the following general schemes:

(I)

For the preferred embodiment, X = S (i.e., using an N-hydroxythiazole thione as a starting material), the synthesis proceeds as follows:

Eine Lösung aus N-Hydroxythiazolthion (1.00 mmol) in einem adäquaten Volumen Aceton wird mit K₂CO₃ (3 mmol) versetzt und 10 min bei 20 ⁰C gerührt. Zu der Reaktionsmischung tropfenweise ein Carbonsäurechlorid (1.1 mmol) gegeben. Die Reaktionsmischung wird bei 20 ⁰C nachgerührt. Die erhaltene Suspension wird mit Wasser versetzt, die Phasen getrennt und die wässrige Phase sukzessiv mit Diethylether und mit Ethylacetat extrahiert. Die organischen Phase wird mit den organischen Extrakten vereinigt und mit 2 M NaOH, sowie mit gesättigter wässriger NaCI-Lösung gewaschen. Die organische Phase wird abgetrennt, mit MgSO₄ getrocknet und bei vermindertem Druck eingeengt. Der erhaltene Rückstand wird aus CH₂CI₂/Et₂O/Pentan umkristallisiert.(I)

A solution of N-hydroxythiazolethione (1.00 mmol) in an adequate volume of acetone is treated with K ₂ CO ₃ (3 mmol) and stirred at 20 ⁰ C for 10 min. To the reaction mixture was added dropwise a carboxylic acid chloride (1.1 mmol). The reaction mixture is stirred at 20 ⁰ C. Water is added to the resulting suspension, the phases are separated and the aqueous phase is extracted successively with diethyl ether and with ethyl acetate. The organic phase is combined with the organic extracts and washed with 2 M NaOH and with saturated aqueous NaCl solution. The organic phase is separated, dried with MgSO ₄ and concentrated under reduced pressure. The residue obtained is recrystallized from CH ₂ Cl ₂ / Et ₂ O / pentane.

2. Use of the compounds of the formula (I) and (II) as photoinitiator:

2 g of monomer and 0.5% by weight of ethylene glycol dimethacrylate (EGDMA) are initially charged as cross-linking agent in a Schlenk flask and the mixture is stirred until a homogeneous solution has formed. To start the polymerization, to the monomer solution with 0.07 wt.% (1, 4 mg / 0, 0039 mmol) of 5- (4-methoxyphenyl) -4-methyl-2-thioxo-2,3-dihydro-1 , 3-thiazol-3-yl-benzoate stirred and the polymer exposed to direct sunlight. After just a few minutes curing has progressed so far that a solid polymer has been formed.

The results are shown in the following Table 1.

Tab 1 Application examples

Monomer EGDMA initiator cure

(100 wt.%) (Wt.%) (Wt.%) (Min.)

Hydroxyethyl methacrylate 0.5 0.07

Vinyl acetate 0.5 0.07 15 «

1-vinyl-2-pyroMdon 0.5 0.07 5-10 °

Styrene 0.5 0.07 8-10 °

Methacrylic acid 0.5 0.07 5 *

Acrylonitrile 0.5 0.07 20-30 ⁿ⁾

Styrene + maleic anhydride ^a) 0.5 0.07 30 ⁿ⁾

^a) Polymerization in solution with toluene as LM ^ solid polymer n ⁾ polymer precipitate

^*} Curing after exposure to sunlight in direct sunlight in the month of May

Claims

claims A light-curing composition comprising a. at least one radically polymerizable compound; and b. at least one compound of the formula (I) and / or of the formula (II) as free-radical initiator,

wherein in the formulas (I) and (II) each independently X = S, CHR ⁴ , O, or NR ⁴ ; R ¹ and R ^{2 are} each independently H, linear or branched C 1 -C 20 alkyl; thioalkyl; aryl; or heteroaryl, wherein R ¹ and R ^{2 may} also be linked together to form saturated or unsaturated cyclics or heterocycles; R ³ = H, linear or branched C ¹ -C 20 -alkyl; thioalkyl; aryl; Heteroaryl is; R ⁴ = H, linear or branched C 1 -C 20 -alkyl, where the alkyl substituent may have cyclic substructures; acyloxy; aryl; or heteroaryl; A is an aliphatic, aromatic or heteroaromatic compound group. 2. A composition according to claim 1, wherein X = S is and / or R ¹ , R ² , R ³ and R ^{4 are} independently H, C ¹ -C 20 alkyl, aryl, or heteroaryl; where aryl is a monosubstituted to trisubstituted phenyl substituent or a monosubstituted to trisubstituted naphthalene substituent, where the Substituents selected from chlorine, C 1 -C 10 alkoxy, C 1 -C 20 alkyl, aminoalkyl, C 1 -C 10 mono- or dialkylamino, acylamino, nitro, cyano, alkoxycarbonyl; and Heteroaryl is substituted or unsubstituted pyridine, pyrrole, thiophene or furan; and A is a pyridine, pyrrole, thiophene, furan, thiazole, oxazole or imidazole group or a derivative thereof or a substituted or unsubstituted phenylene group. 3. Composition according to claim 1 and / or 2, wherein in the formula (I) X is S, R ¹ is C ¹ -C ⁴ -alkyl, R ^{2 is} phenyl or a phenyl radical with a further ortho, meta or para-substituent, wherein the substituent is selected from methoxy, C 1 -C 4 alkyl, amino, dialkylamino, acylamino and chloro; or R ¹ and R ^{2 form} an unsaturated cycle; R ³ = phenyl or a phenyl radical having another ortho, meta or para substituent selected from methoxy, C 1 -C 4 alkyl, amino, dialkylamino, acylamino and chloro. 4. Use of the composition according to any one of claims 1 to 3 as a coating material for technical, optical, medical applications and in photolithography. 5. A cured product obtainable by photocuring the composition of any of claims 1 to 3 with visible light. 6. A process for producing a cured product, which comprises curing the composition according to any one of claims 1 to 3 by exposure to daylight. 7. Use of the product according to claim 5 as a dental material, printing ink, lacquer, or surface coating. 8. Use of the compound of formula (I) and / or of formula (II) as defined in any one of claims 1 to 3, as radical initiator for the radical polymerization. 9. compound of the formula (I)

wherein X = S, CHR ⁴ , O, or NR ⁴ ; R ¹ and R ^{2 are} each independently H, linear or branched C 1 -C 20 alkyl; thioalkyl; aryl; or heteroaryl, wherein R ¹ and R ^{2 may} also be linked together to form saturated or unsaturated cyclics or heterocycles; R ³ = linear or branched C ¹ -C 20 -alkyl; thioalkyl; aryl; Heteroaryl is; R ⁴ = H, linear or branched C 1 -C 20 -alkyl, where the alkyl substituent may have cyclic substructures; acyloxy; aryl; or heteroaryl; with the proviso that (a) R ^{2 is} not H when X = S; and (b) not simultaneously X = S, R ¹ = methyl, R ² = p-methoxyphenyl and R ³ = phenyl. 10. compound of the formula (II)

wherein X = S, CHR ⁴ , O, or NR ⁴ ; R ¹ and R ^{2 are} each independently H, linear or branched C 1 -C 20 alkyl; thioalkyl; aryl; or heteroaryl, wherein R ¹ and R ^{2 may} also be linked together to form saturated or unsaturated cyclics or heterocycles; R ⁴ = H, linear or branched C 1 -C 20 -alkyl, where the alkyl substituent may have cyclic substructures; acyloxy; aryl; or heteroary! is; A is an aliphatic, aromatic or heteroaromatic compound group, with the proviso that R ^{2 is} not H when X = S. 11. Process for the preparation of the compound of formula (I) or (II)

wherein R ¹ , R ² , R ³ and A are as defined in any one of claims 1 to 3, which is the reaction of a free N-hydroxy compound of the following formula

with a carboxylic acid chloride or a bis (carboxylic acid chloride) according to one of the following two formulas

includes. 12. The method of claim 11, wherein X = S.