Phosphorus-containing s-heptazine compounds as flame retardants

Abstract

In a first aspect, the invention relates to heptazine derivatives of the formula (I) wherein X, Y, Z is each an oxygen or a sulfur atom; R1, R2 are identical and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radicals have at least one substituent selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radicals have at least one substituent selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals;R7, R8 are identical and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals.A second aspect of the invention relates to the use of a heptazine derivative of the general formula (I) according to the first aspect of the invention as a flame retardant for a plastic. In a third aspect, the invention relates to a flame-retardant plastic comprising at least one heptazine derivative of the general formula (I) according to the first aspect of the invention and a plastic. A fourth aspect of the invention relates to a process for producing a heptazine derivative of the general formula (I).;

Description

[0001] In a first aspect, the invention relates to a heptazine derivative of the formula (I). A second aspect of the invention relates to the use of a heptazine derivative of the general formula (I) according to the first aspect of the invention as a flame retardant for a plastic. In a third aspect, the invention relates to a flame-retardant plastic comprising at least one heptazine derivative of the general formula (I) according to the first aspect of the invention and a plastic. A fourth aspect of the invention relates to a process for producing a heptazine derivative of the general formula (I).

[0002] Plastics are widely used as materials today, and their fire behavior is of crucial importance. For example, the European standard DIN EN 13501-1:2010-01 classifies building materials according to their fire behavior and thus also according to their compliance with corresponding building regulations. For plastics, the burning behavior is often characterized by the oxygen index (LOI = Limiting Oxygen Index) according to DIN EN ISO 4589. Standard plastics are highly flammable, which is why flame retardants often have to be added to meet fire protection requirements in the construction and transport industries, as well as in the electrical / electronics sector. However, flame retardants can pose health and / or environmental risks or have other disadvantages, for example, with regard to their processability.

[0003] To date, solid substances that are solid at room temperature have predominantly been used as flame retardants. However, liquid flame retardants would be suitable for many applications. Liquid flame retardants of industrial importance are currently generally based on low-molecular-weight halogenated phosphorus-containing compounds and polymeric phosphorus-containing compounds. However, due to environmental concerns, halogenated flame retardants are becoming increasingly less important. It is expected that the widely used liquid halogenated flame retardant TCPP (tris(2-chloroisopropyl) phosphate) will have its use restricted or even banned entirely.

[0004] Halogen-free flame retardants based on nitrogen-carbon cycles are known. s-triazine derivatives and isolated s-heptazine derivatives are described in the literature as potential flame retardants, for example melem (C6N7(NH2)3, which is free of phosphorus). Höhne et. a / (C.-C. Höhne, C. Posern, U. Böhme, F. Eichler, E. Kroke, Polym. Degrad. Stab. 2019, 166, 17-30.) describe thiocyanurates and thiocyamelurates as potential flame retardants for polypropylene. Saplinova et. a / (T. Saplinova, V. Bakumov, T. Gmeiner, J. Wagler, M. Schwarz, E. Kroke, Z. anorg. allg. Chem. 2009, 2480-2487.) describe iminophosphorane derivatives of s-Triazine and s-heptazine are potential flame retardants and have demonstrated this with UL94 flame retardancy tests. Halogen-free, phosphorus-containing triazine compounds are known, for example, from DE 10 2022 205 709 A1 and can be produced by reacting cyanuric chloride with trialkyl phosphites.However, liquid flame retardants containing both phosphorus and nitrogen as elements with flame retardant effects have not yet been established.

[0005] The object of the invention was therefore to provide a flame retardant which does not have the above-mentioned disadvantages or at least partially overcomes them.

[0006] In a first aspect, the invention therefore relates to a heptazine derivative of the formula (I)wherein each X, Y, Z each represents an oxygen or a sulfur atom; R 1 , R 2 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radical and C6 to C12 aryl radical, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radical; R 4 , R 5are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radical and C6 to C12 aryl radical, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radical; R 7 , R 8 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals.

[0007] Surprisingly, it was found that the use of a heptazine of formula (I) makes it possible to achieve a flame-retardant effect when incorporated into plastics, which was evident, for example, from an increase in the LOI value of the flame-retardant-containing plastic compared to the flame-retardant-free plastic. Symmetric heptazines

[0008] In a preferred embodiment of the heptazine derivative of the general formula (I), R 1 , R 2 and R 4 , R 5 and R 7 , R 8 equal (R 1 = R 2 = R 4 = R 5 = R 7 = R 8 ). - Liquid symmetrical heptazines

[0009] In a preferred embodiment of the heptazine derivative of the general formula (I), R 1 , R 2 and R 4 , R 5 and R 7 , R 8selected from the group consisting of branched and unbranched C4 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C18 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C17 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C16 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C15 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C14 alkyl radicals,more preferably from the group consisting of branched and unbranched C4 to C13 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C12 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C11 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C10 alkyl radicals.

[0010] In particular, symmetrically substituted heptazines with the above-mentioned radical combinations exhibit a liquid state at a temperature in the range of 15 to 30 °C and at a pressure of 800 to 1200 mbar, especially at 25 °C and 1013 mbar, and can therefore be used in liquid form as flame retardants. Liquid flame retardants offer significant advantages over conventional solid flame retardants, as they can prevent both settling in / segregation of a composition and abrasive effects on device components. Unsymmetrical heptazines

[0011] In a preferred alternative embodiment of the heptazine derivative of the general formula (I), R 1 , R 2 not equal to R 4 , R 5 and to R 7 , R 8 (R 1 , R 2 ≠ R 4 , R 5 and R 1 , R 2 ≠ R7 , R 8 ). - Liquid asymmetric heptazines

[0012] In the alternative embodiment of the heptazine derivative of the general formula (I) R 4 , R 5 equal to R 7 , R 8 (R 4 , R 5 = R 7 , R 8 ), where R 1 , R 2 are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals and R 4 , R 5 and R 7 , R 8are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals.

[0013] In the alternative embodiment of the heptazine derivative of the general formula (I) R 1 , R 2are selected from the group consisting of branched and unbranched C1 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C1 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C4 alkyl radicals; and / or R 4 , R 5 , R 7 , R 8are selected from the group consisting of branched and unbranched C1 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C1 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C4 alkyl radicals. - Completely asymmetrically substituted heptazines

[0014] In a preferred alternative embodiment of the heptazine derivative of the general formula (I), R 1 , R 2are not equal to R 4 , R 5 and to R 7 , R 8 (R 1 , R 2 ≠ R 4 , R 5 and R 1 , R 2 ≠ R 7 , R 8 ) and R 4 , R 5 are not equal to R 7 , R 8 (R 4 , R 5 ≠ R 7 , R 8 ), where R 1 , R 2 are selected from the group consisting of branched and unbranched C1 to C20 alkyl radical and C6 to C12 aryl radical, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radical; R 4 , R 5are selected from the group consisting of branched and unbranched C2 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals; and R 7 , R 8 are selected from the group consisting of branched and unbranched C3 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals.

[0015] In the alternative embodiment of the heptazine derivative of the general formula (I) R 1 , R 2selected from the group consisting of branched and unbranched C1 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C1 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C4 alkyl radicals; and / or R 4 , R 5selected from the group consisting of branched and unbranched C2 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C2 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C4 alkyl radicals; and / or R 7 , R 8selected from the group consisting of branched and unbranched C3 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C3 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C4 alkyl radicals. 2. Aspect - Use as a flame retardant

[0016] A second aspect of the invention relates to the use of a heptazine derivative of the general formula (I) according to the first aspect as a flame retardant for a plastic.

[0017] All details, embodiments, alternative embodiments and preferred (alternative) embodiments described above for the first aspect of the invention also apply to the second aspect of the invention.

[0018] In a preferred embodiment of the use as a flame retardant, the plastic is selected from the group of thermoplastics and mixtures thereof, preferably from the group consisting of polyurethane (PU), polyisocyanurate (PIR), polyester and mixtures of two or more of these plastics.

[0019] In a preferred embodiment of the use as flame retardant, a heptazine derivative of the general formula (I) or mixtures of two or more heptazine derivatives of the general formula (I) is / are used.

[0020] In a preferred embodiment of the use as a flame retardant, the plastic comprises at least one PU, preferably a thermoplastic PU (TPU).

[0021] In a preferred embodiment of the use as a flame retardant, the plastic comprises at least one polylactide (PLA). 3. Aspect - Flame-retardant plastic

[0022] A third aspect of the invention relates to a flame-retardant plastic comprising at least - a heptazine derivative of general formula (I) according to the first aspect; - a plastic.

[0023] All details, embodiments, alternative embodiments and preferred (alternative) embodiments described above for the first aspect of the invention and the second aspect of the invention also apply to the third aspect of the invention.

[0024] In a preferred embodiment of the flame-retardant plastic, the plastic is selected from the group of thermoplastics and mixtures thereof, more preferably selected from the group consisting of polyurethane (PU), polyisocyanurate (PIR), polyester and mixtures of two or more of these plastics.

[0025] In a preferred embodiment of the flame-retardant plastic, the heptazine derivative is contained in an amount of 0.1 to 30% by weight, preferably 0.5 to 10% by weight, based on the total weight of 100% by weight of the flame-retardant plastic.

[0026] In a preferred embodiment of the flame-retardant plastic, it further comprises one or more additional flame retardants, with suitable additional flame retardants being known to those skilled in the art. For example, the one or more additional flame retardants are selected from the groups of phosphorus-, inorganic-, and nitrogen-based flame retardants. 4th aspect - Process for the preparation of a heptazine derivative

[0027] A fourth aspect of the invention relates to a process for preparing a heptazine derivative of the general formula (I) comprising (i) providing a phosphite mixture comprising (i.1) a first trialkyl or triarylphosphite of the general formula (A)wherein X is a heteroatom, in particular an oxygen or a sulfur atom; R 1 , R 2 , R 3are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals; and (i.2) optionally a second trialkyl or triarylphosphite of the general formula (B)wherein Y is a heteroatom, in particular an oxygen or a sulfur atom; R 4 , R 5 , R 6 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and C1 to C10 alkyl radicals; where R 1 , R 2 , R 3 of the first trialkyl phosphite according to (i.1) are not equal to R 4 , R 5 , R 6the second trialkyl phosphite according to (i.2); and (i.3) optionally a third trialkyl or triarylphosphite of the general formula (C) where Z is a heteroatom, in particular an oxygen or a sulfur atom; R 7 , R 8 , R 9 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and C1 to C10 alkyl radicals; where R 7 , R 8 , R 9 are not equal to R 1 , R 2 , R 3 of the first trialkyl phosphite according to (i.1) and are not equal to R 4 , R 5 , R 6 the second trialkyl phosphite according to (i.2); (ii) providing heptazine chloride; (iii) reacting the phosphite mixture according to (i) with the heptazine chloride according to (ii), to obtain at least one heptazine derivative of the general formula (I) , where the residues R 1 -R 9 and X, Y, Z have the meaning given in any of embodiments 1 to 6.

[0028] Heptazine chloride is 2,5,8-trichloro-s-heptazine (C6N7Cl3). The preparation of heptazine chloride is known to the person skilled in the art and is carried out, for example, as described in Kroke et al. (E. Kroke, M. Schwarz, P. Kroll, E. Bordon, B. Noll, A. Norman, New J. Chem., 26 (2002), 508-512).

[0029] If primarily fully symmetrically substituted heptazine derivatives of the general formula (I) in which R 1 , R 2 and R 4 , R 5 and R 7 , R 8 are equal (R 1 = R 2 = R 4 = R 5 = R 7 = R 8), the optional second trialkyl or triarylphosphite of the general formula (B) and the optional third trialkyl or triarylphosphite of the general formula (C) are preferably omitted, and accordingly only the first trialkyl or triarylphosphite of the general formula (A) is used. If at least partially asymmetrically substituted heptazine derivatives of the general formula (I) in which R 1 , R 2 not equal to R 4 , R 5 and to R 7 , R 8 are (R 1 , R 2 ≠ R 4 , R 5 and R 1 , R 2 ≠ R 7 , R 8), the optional second trialkyl or triarylphosphite of the general formula (B) and optionally the optional third trialkyl or triarylphosphite of the general formula (C) are preferably used in addition to the first trialkyl or triarylphosphite of the general formula (A). If priority is given to completely asymmetrically substituted heptazine derivatives of the general formula (I), in which R 1 , R 2 are not equal to R 4 , R 5 and to R 7 , R 8 (R 1 , R 2 ≠ R 4 , R 5 and R 1 , R 2 ≠ R 7 , R 8 ) and R 4 , R 5 are not equal to R 7 , R 8 (R 4 , R 5 ≠ R 7 , R 8), the optional second trialkyl or triarylphosphite of the general formula (B) and the optional third trialkyl or triarylphosphite of the general formula (C) are preferably used in addition to the first trialkyl or triarylphosphite of the general formula (A). "Primarily produced" means that although a mixture of heptazines is optionally obtained, the respective heptazine is obtained in this mixture to an extent of more than 50 mol%, preferably more than 55 mol%, preferably more than 60 mol%, preferably more than 65 mol%, based on 100 mol% of the heptazines present in the mixture.

[0030] In a preferred embodiment of the process for preparing a heptazine derivative of the general formula (I), no solvent is present in at least (i), (ii) or (iii), preferably no solvent is present in either (i) or (ii) or (iii) (solvent-free synthesis).

[0031] In a preferred embodiment of the process for preparing a heptazine derivative of the general formula (I), the reaction according to (iii) is carried out at a temperature in the range from 5 to 120 °C, preferably in the range from 10 to 90 °C, more preferably in the range from 20 to 80 °C.

[0032] The reaction is optionally carried out with cooling, which is achieved by means known to those skilled in the art. The reaction is preferably carried out at a pressure in the range from 800 to 1300 mbar, more preferably in the range from 900 to 1200 mbar, more preferably in the range from 950 to 1050 mbar. These temperatures and pressures are particularly preferred when the synthesis is carried out solvent-free. If a solvent is present, it is preferably carried out at a temperature in the range of the boiling point of the solvent (±10°C) at the stated pressures. The solvent used is preferably one or more solvents from the group of organic solvents, preferably benzene and / or toluene, more preferably toluene.

[0033] In a preferred embodiment of the process for preparing a heptazine derivative of the general formula (I), at least one of the trialkyl or triarylphosphites of the general formula (A), optionally (B) or optionally (C) is liquid at 25 °C and 1013 mbar.

[0034] In a preferred embodiment of the process for preparing a heptazine derivative of the general formula (I), if at least one further of the trialkyl or triarylphosphites of the general formula (A), optionally (B) or optionally (C) is solid at 25 °C and 1013 mbar, at least one further solid trialkyl or triarylphosphite is dissolved in the at least one liquid trialkyl or triarylphosphite, so that the phosphite mixture according to (i) is liquid at 25 °C and 1013 mbar.

[0035] In a preferred embodiment of the process for preparing a heptazine derivative of the general formula (I), the molar ratio of the sum of all trialkyl or triarylphosphite [(A) or (A) + (B) or (A) + (C) or (A) + (B) + (C)] contained in the phosphite mixture according to (i) to the heptazine chloride in the reaction according to (iii) is > 1:1, preferably in the range from 5:1 to 3:1, more preferably in the range from 4:1 to 3:1, more preferably 3.5:1 to 3:1.

[0036] In a preferred embodiment of the process for preparing a heptazine derivative of the general formula (I), the molar ratio of the first trialkyl or triarylphosphite of the general formula (A) to the second trialkyl or triarylphosphite of the general formula (B) is in the range from 1:0.5 to 1:1.5, preferably in the range from 1:0.8 to 1:1.2, more preferably 1:1; or the molar ratio of the first trialkyl or triarylphosphite of the general formula (A) to the second trialkyl or triarylphosphite of the general formula (B) is in the range from 1:1.5 to 1:2.5, preferably in the range from 1:1.8 to 1:2.2, more preferably 1:2.

[0037] In a preferred embodiment of the process for preparing a heptazine derivative of the general formula (I), the molar ratio of second trialkyl or triarylphosphite of the general formula (B) to third trialkyl or triarylphosphite of the general formula (C) is in the range from 1:0.5 to 1:1.5, preferably in the range from 1:0.8 to 1:1.2, more preferably 1:1.

[0038] In a preferred embodiment of the process for preparing a heptazine derivative of general formula (I), step (iii) comprises (iii.1a) introducing the first trialkyl or triarylphosphite of general formula (A) provided according to (i), optionally the second trialkyl or triarylphosphite (B) and optionally the third trialkyl or triarylphosphite (C) into a reaction vessel, (iii.2a) adding the heptazine chloride provided in (ii) to the reaction vessel; or (iii.1b) placing heptazine chloride provided in accordance with (ii) in a reaction vessel; (iii.2b) Addition of the first trialkyl or triarylphosphite of general formula (A) provided according to (i), optionally the second trialkyl or triarylphosphite (A), (B) and optionally the third trialkyl or triarylphosphite (C) into the reaction vessel.

[0039] The present invention is explained in more detail by the following embodiments and combinations of embodiments which result from the specified dependencies and references. In particular, it is pointed out that in each case in which a range of embodiments is mentioned, for example in connection with a term such as “The heptazine derivative according to any one of embodiments 1 to 4”, each embodiment in this range is explicitly disclosed to the person skilled in the art, i.e. the wording of this term is to be understood by the person skilled in the art as a synonym for “The heptazine derivative according to any one of embodiments 1, 2, 3 and 4”. Furthermore, it is expressly pointed out that the following embodiments represent a suitably structured part of the general description directed to preferred aspects of the present invention and thus suitably support the claims of the present invention, but do not represent them. 1. Heptazine derivative of formula (I)wherein each X, Y, Z each represents an oxygen or a sulfur atom; R 1 , R 2 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radical and C6 to C12 aryl radical, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radical; R 4 , R 5 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radical and C6 to C12 aryl radical, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radical; R 7 , R 8are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals. 2. Heptazine derivative of the general formula (I) according to embodiment 1, wherein R 1 , R 2 and R 4 , R 5 and R 7 , R 8 are equal (R 1 = R 2 = R 4 = R 5 = R 7 = R 8 ). 3. Heptazine derivative of general formula (I) according to embodiment 2, wherein R 1 , R 2 and R 4 , R 5 and R 7 , R 8are selected from the group consisting of branched and unbranched C4 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C18 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C17 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C16 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C15 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C14 alkyl radicals,more preferably from the group consisting of branched and unbranched C4 to C13 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C12 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C11 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C10 alkyl radicals. 4. Heptazine derivative of general formula (I) according to embodiment 1, wherein R 1 , R 2 are not equal to R 4 , R 5 and to R 7 , R 8 (R 1 , R 2 ≠ R 4 , R 5 and R 1 , R 2 ≠ R 7 , R 8 ). 5. Heptazine derivative of general formula (I) according to embodiment 4, wherein R 4 , R 5 are equal to R 7 , R 8 (R 4 , R 5 = R 7 , R 8 ) and where R1 , R 2 are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals and R 4 , R 5 and R 7 , R 8 are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals. 6. Heptazine derivative of general formula (I) according to embodiment 4 or 5, wherein R 1 , R 2are selected from the group consisting of branched and unbranched C1 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C1 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C4 alkyl radicals; and / or R 4 , R 5 , R 7 , R 8are selected from the group consisting of branched and unbranched C1 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C1 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C4 alkyl radicals. 7. Heptazine derivative of general formula (I) according to embodiment 4, wherein R 1 , R 2 are not equal to R 4 , R 5 and to R 7 , R 8 (R 1 , R2 ≠ R 4 , R 5 and R 1 , R 2 ≠ R 7 , R 8 ) and R 4 , R 5 are not equal to R 7 , R 8 (R 4 , R 5 ≠ R 7 , R 8 ), where R 1 , R 2 are selected from the group consisting of branched and unbranched C1 to C20 alkyl radical and C6 to C12 aryl radical, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radical; R 4 , R 5 are selected from the group consisting of branched and unbranched C2 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals; and R 7 , R 8are selected from the group consisting of branched and unbranched C3 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals. 8. Heptazine derivative of general formula (I) according to embodiment 4 or 7, wherein R 1 , R 2are selected from the group consisting of branched and unbranched C1 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C1 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C4 alkyl radicals; and / or R 4 , R 5are selected from the group consisting of branched and unbranched C2 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C2 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C4 alkyl radicals; and / or R 7 , R 8are selected from the group consisting of branched and unbranched C3 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C3 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C4 alkyl radicals. 9. Use of a heptazine derivative of the general formula (I) according to any one of embodiments 1 to 8 as a flame retardant for a plastic. 10. Use according to embodiment 9, wherein the plastic is selected from the group of thermoplastics and mixtures thereof, preferably from the group consisting of polyurethane (PU), polyisocyanurate (PIR), polyester and mixtures of two or more of these plastics. 11. Use according to embodiment 9 or 10, wherein a heptazine derivative of the general formula (I) or mixtures of two or more heptazine derivatives of the general formula (I) are used. 12. Use according to any one of embodiments 9 to 11, wherein the plastic comprises at least one PU, preferably a thermoplastic PU (TPU). 13. Use according to any one of embodiments 9 to 11, wherein the plastic comprises at least one polylactide (PLA). 14. Flame-retardant plastic comprising at least - a heptazine derivative of the general formula (I) according to any one of embodiments 1 to 8; - a plastic. 15. Flame-retardant plastic according to embodiment 14, wherein the plastic is selected from the group of thermoplastics and mixtures thereof, more preferably selected from the group consisting of polyurethane (PU), polyisocyanurate (PIR), polyester and mixtures of two or more of these plastics. 16. Flame-retardant plastic according to embodiment 14 or 15, wherein the heptazine derivative is contained in an amount of 0.1 to 30% by weight, preferably 0.5 to 10% by weight, based on the total weight of 100% by weight of the flame-retardant plastic. 17. Flame-retardant plastic according to any one of embodiments 12 to 16, comprising one or more further flame retardants selected from the groups of phosphorus-, inorganic- and nitrogen-based flame retardants. 18. A process for the preparation of a heptazine derivative of the general formula (I) comprising (i) providing a phosphite mixture comprising (i.1) a first trialkyl or triarylphosphite of the general formula (A)wherein X is a heteroatom, in particular an oxygen or a sulfur atom; R 1 , R 2 , R 3 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals; and (i.2) optionally a second trialkyl or triarylphosphite of the general formula (B)wherein Y is a heteroatom, in particular an oxygen or a sulfur atom; R 4 , R 5 , R 6are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and C1 to C10 alkyl radicals;wherein R 1 , R 2 , R 3 of the first trialkyl phosphite according to (i.1) are not equal to R 4 , R 5 , R 6 the second trialkyl phosphite according to (i.2); and (i.3) optionally a third trialkyl or triarylphosphite of the general formula (C)wherein Z is a heteroatom, in particular an oxygen or a sulfur atom; R 7 , R 8 , R 9 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and C1 to C10 alkyl radicals; where R7 , R 8 , R 9 are not equal to R 1 , R 2 , R 3 of the first trialkyl phosphite according to (i.1) and are not equal to R 4 , R 5 , R 6 of the second trialkyl phosphite according to (i.2). and (ii) providing heptazine chloride; (iii) reacting the phosphite mixture according to (i) with the heptazine chloride according to (ii), to obtain at least one heptazine derivative of the general formula (I), wherein the radicals R 1 -R 9 and X, Y, Z have the meaning given in any of embodiments 1 to 6. 19. A process for preparing a heptazine derivative of the general formula (I) according to embodiment 18, wherein at least in (i), (ii) or (iii) no solvent is present, preferably no solvent is present in either (i) or (ii) or (iii) (solvent-free synthesis). 20. A process for preparing a heptazine derivative of the general formula (I) according to embodiment 18 or 19, wherein the reaction according to (iii) is carried out at a temperature in the range from 5 to 120 °C, preferably in the range from 10 to 90 °C, more preferably in the range from 20 to 80 °C. 21. A process for preparing a heptazine derivative of the general formula (I) according to any one of embodiments 18 to 20, wherein at least one of the trialkyl or triarylphosphites of the general formula (A), optionally (B) or optionally (C) is liquid at 25 °C and 1013 mbar. 22. A process for preparing a heptazine derivative of the general formula (I) according to embodiment 21, wherein, if at least one further of the trialkyl or triarylphosphites of the general formula (A), optionally (B) or optionally (C) is solid at 25 °C and 1013 mbar, at least one further solid trialkyl or triarylphosphite is dissolved in the at least one liquid trialkyl or triarylphosphite, so that the phosphite mixture according to (i) is liquid at 25 °C and 1013 mbar. 23. A process for preparing a heptazine derivative of the general formula (I) according to any one of embodiments 18 to 22, wherein the molar ratio of the sum of all trialkyl or triarylphosphite [(A) or (A) + (B) or (A) + (C) or (A) + (B) + (C)] present in the phosphite mixture according to (i) to the heptazine chloride in the reaction according to (iii) is > 1:1, preferably in the range from 5:1 to 3:1, more preferably in the range from 4:1 to 3:1, more preferably 3.5:1 to 3:1. 24. A process for preparing a heptazine derivative of the general formula (I) according to any one of embodiments 18 to 23, wherein the molar ratio of the first trialkyl or triarylphosphite of the general formula (A) to the second trialkyl or triarylphosphite of the general formula (B) is in the range from 1:0.5 to 1:1.5, preferably in the range from 1:0.8 to 1:1.2, more preferably 1:1; or wherein the molar ratio of first trialkyl or triarylphosphite of the general formula (A) to second trialkyl or triarylphosphite of the general formula (B) is in the range from 1:1.5 to 1:2.5, preferably in the range from 1:1.8 to 1:2.2, more preferably 1:2. 25. A process for preparing a heptazine derivative of the general formula (I) according to any one of embodiments 18 to 24, wherein the molar ratio of second trialkyl or triarylphosphite of the general formula (B) to third trialkyl or triarylphosphite of the general formula (C) is in the range from 1:0.5 to 1:1.5, preferably in the range from 1:0.8 to 1:1.2, more preferably 1:1. 26. A process for preparing a heptazine derivative of general formula (I) according to any one of embodiments 18 to 25, wherein step (iii) comprises: (iii.1a) introducing the first trialkyl or triarylphosphite of general formula (A) provided according to (i), optionally the second trialkyl or triarylphosphite (B) and optionally the third trialkyl or triarylphosphite (C) into a reaction vessel, (iii.2a) adding the heptazine chloride provided in (ii) to the reaction vessel; or (iii.1b) placing heptazine chloride provided in accordance with (ii) in a reaction vessel; (iii.2b) Addition of the first trialkyl or triarylphosphite of general formula (A) provided according to (i), optionally the second trialkyl or triarylphosphite (A), (B) and optionally the third trialkyl or triarylphosphite (C) into the reaction vessel.

[0040] The present invention is further explained by the following reference examples, comparative examples and examples. Examples Methods Nuclear magnetic resonance (NMR) spectroscopy: All solution NMR spectra were recorded either with a Bruker Nanobay 400 at 400.13 MHz ( 1 H-NMR), 100.61 MHz ( 13 C-NMR) and 161.98 MHz ( 31 P-NMR) or with a Bruker Avance 500 at 500.13 MHz ( 1 H-NMR), 125.76 MHz ( 13 C-NMR) and 202.46 MHz ( 31 P-NMR). The samples were measured in the deuterated solvent chloroform (CDCl3) or deuterated dimethyl sulfoxide (DMSO). ATR spectroscopy: The ATR infrared spectra were recorded on a Nicolet 380 IR spectrometer. The measurement was carried out in a range of 4000 cm -1 up to 600 cm -1 at a resolution of 4 cm -1 and 132 scans. The data were recorded in cm -1 In the range of 2300 cm -1 a device-related CO2 band (ambient air) was observed. Thermogravimetric Analysis (TGA): Thermogravimetric analyses were performed using a Netzsch TG 209 F1 under a nitrogen atmosphere and a heating rate of 10 K / min. Limiting Oxygen Index (LOI) test: The LOI was determined using an Oxygen Index Module from FIRE according to DIN EN ISO 4589-2. Fourier transform infrared spectroscopy (FTIR): FTIR spectra were recorded using a Nicolet 380 FT-IR spectrometer with an ATR unit. The measurements were performed with 128 scans at a resolution of 4 cm -1 . Ultraviolet-visual (UV / VIS) spectrophotometry: The UV / Vis spectra were recorded with a JASCO V-650 using 10 mm quartz glass cuvettes or an integrating sphere. X-ray structure analysis: The data sets were acquired using a STOE IPDS-2T X-ray machine or IPDS II with Mo-K α -radiation (λ = 0.71073 Å). The single crystals were measured while cooling in a nitrogen stream. The software X-AREA, X-RED, XShape, SHELXS, and SHELXL were used to acquire and refine the data. Melting point determination: The melting point determinations were carried out using a Polytherm A hot-stage microscope from Wagner & Munz. Reference Example 1: Heptazine Synthesis

[0041] The heptazines were prepared analogously to the phosphite using liquid trialkyl and / or triaryl phosphites, without the addition of a solvent. Solid trialkyl or triaryl phosphites were used in dissolved form, for example, dissolved in an organic solvent or, when used simultaneously, dissolved in a liquid phosphite.

[0042] 5.4 mmol of a phosphite in the case of symmetrical compounds or a mixture of phosphites in the case of asymmetrical compounds were slowly added, with stirring and ice cooling, to 1.8 mmol of heptazine chloride, optionally suspended in toluene, via a dropping funnel. Stoichiometries were adjusted according to the purity of the reactants. After the addition was complete, the suspension was heated, if necessary under reflux, for a specified period of time. Any chloromethane formed during the reaction was frozen out using a cold trap with an isopropanol / dry ice mixture. After cooling to room temperature, the product was obtained, which was filtered and dried under vacuum. Examples 1 to 22: Heptazine syntheses

[0043] Heptazines were prepared according to Reference Example 1. The phosphites used and their amounts, if different from those specified in Reference Example 1, the amounts of toluene used, if any, and further reaction details are shown in Table 1: Table 1 Compounds prepared, starting materials and reaction conditions Example# Phosphite(s) (and possibly different amounts) Reaction temperature, duration Amount of toluene [ml] Heptazine (target product) Stoichiometric (molar) ratio of P(OR) 3 R 1,2 : R 4,5 : R 7,8 symmetry (1) State of matter (2) 1 Trimethyl phosphite Reflux, 5 h 50 2,5,8-Tris(dimethyl2phosphonate)-s-heptazine Methyl (Me) sym firmly 2 Triethyl phosphite Reflux, 5 h 50 2,5,8-Tris(diethylphosphonate)-s-heptazine Ethyl (Et) sym firmly 3 Tri-iso-propyl phosphite Reflux, 5 h 50 2,5,8-Tris(di-isopropylphosphonate)-s-heptazine isopropyl (iPr) sym firmly 4 Tri-n-butyl phosphite 75 °C, 4 hours - 2,5,8-Tris(di-n-butylphosphonate)-s-heptazine n-Butyl (nBu) sym fluid* 5 Tri-iso-decyl phosphite (16.3 mmol tri-isodecyl phosphite + 5.4 mmol heptazine chloride) 75 °C, 2 hours - 2,5,8-Tris(di-isodecylphosphonate)-s-heptazine iso-Decyl (iDec) sym fluid* 6 Tri-2-ethylhexyl phosphite Reflux, 3 h 50 2,5,8-Tris(di-2-ethylhexylphosphonate)-s-heptazine Ethylhexyl (EtHex) sym fluid* (10.8 mmol tris(2-ethylhexyl) phosphite + 3.6 mmol heptazine chloride) 7 Tri-para-tolyl phosphite (10.8 mmol tri-p-tolyl phosphite + 3.6 mmol heptazine chloride) Reflux, 3 h 50 2,5,8-Tris(di-paratolylphosphonate)-s-heptazine para-Tolyl sym fluid* 8 Tri-oleyl phosphite (10.8 mmol tri-oleyl phosphite + 3.6 mmol heptazine chloride) Reflux, 3 h 50 2,5,8-Tris(di-oleylphosphonate)-s-heptazine Oleyl sym fluid* 9 Tri-lauryl trithiophosphite (10.8 mmol trilauryl trithiophosphite + 3.6 mmol heptazine chloride) Reflux, 3 h 50 2,5,8-Tris(dilauryl trithiophosphonate)-s-heptazine Lauryl sym solid / liquid * 10 Trimethyl phosphite and triethyl phosphite (5.4 mmol trimethyl phosphite, 5.4 mmol triethyl phosphite + 3.6 mmol heptazine chloride) Reflux, 3 h 50 2,5,8-Tris(dimethyl / ethylphosphonato)-s-heptazine Me : Et 1:1 unsym fluid* 11 Trimethyl phosphite and triethyl phosphite (7.2 mmol trimethyl phosphite and 3.6 mmol triethyl phosphite + 3.6 mmol heptazine chloride) Reflux, 3 h 50 2,5-Bis(dimethyl)-8-diethylphosphonato-s-heptazine Me : Et 2: 1 unsym fluid* 12 Trimethyl phosphite and triethyl phosphite (3.6 mmol trimethyl phosphite and 7.2 mmol triethyl phosphite + 3.6 mmol heptazine chloride) Reflux, 3 h 50 2-Dimethyl-5,8-bis-(diethyl)phosphonatos-heptazine Me:Et 1:2 unsym fluid* 13 Tri-isopropyl phosphite and tri-n-butyl phosphite (5.4 mmol tri-isopropyl phosphite and 5.4 mmol tri-n-butyl phosphite + 3.6 mmol heptazine chloride) Reflux, 3 h 50 2,5,8-Tris(di-iso-propyl / n-butylphosphonato)-s-heptazine iPr: nBu 1 : 1 unsym fluid* 14 Tri-iso-propyl phosphite and tri-n-butyl phosphite (7.2 mmol tri-isopropyl phosphite and 3.6 mmol tri-n- Reflux, 3 h 50 2,5-Bis(di-isopropylphosphonato)-8-(di-n-butylphosphonato)-s-heptazine iPr : nBu 2 : 1 unsym fluid* butyl phosphite + 3.6 mmol heptazine chloride) 15 Tri-isopropyl phosphite and tri-n-butyl phosphite (3.6 mmol and 7.2 mmol tri-n-butyl phosphite + 3.6 mmol heptazine chloride) Reflux, 3 h 50 2-(Di-isopropylphosphonato)-5,8-bis(di-n-butylphosphonato)-s-heptazine iPr: nBu 1 : 2 unsym fluid* 16 Trimethyl phosphite and tri-n-butyl phosphite (5.4 mmol trimethyl phosphite and 5.4 mmol tri-n-butyl phosphite + 3.6 mmol heptazine chloride) Reflux, 3 h 50 2,5,8-Tris(di-methyl / din-butylphosphonato)-s-heptazine Me: nBu 1:1 unsym fluid* 17 Trimethyl phosphite and tri-n-butyl phosphite (3.6 mmol trimethyl phosphite and 7.2 mmol tri-n-butyl phosphite + 3.6 mmol heptazine chloride) Backflow, 3 50 2-(Dimethylphosphonato)-5,8-bis(di-n-butylphosphonato)-s-heptazine Me: nBu 1:2 unsym fluid* 18 Trimethyl phosphite and tri-n-butyl phosphite (7.2 mmol trimethyl phosphite and 3.6 mmol tri-n-butyl phosphite + 3.6 mmol heptazine chloride) Backflow, 3 50 2,5-Bis(dimethylphosphonato)-8-(di-n-butylphosphonato)-s-heptazine Me: nBu 2:1 unsym fluid* 19 Trimethyl phosphite and tri-isopropyl phosphite (5.4 mmol trimethyl phosphite, 5.4 mmol tri-isopropyl phosphite and 5.4 mmol tri-n-butyl phosphite + 5.4 mmol heptazine chloride) Backflow, 3 50 2-(Dimethylphosphonato)-5-(di-iso-propylphosphonato)-8-(di-n-butylphosphonato)-s-heptazine Et : iPr : nBu 1 : 1 : 1 unsym fluid* 20 Triethyl phosphite and tri-isopropyl phosphite and tri-n-butyl phosphite (5.4 mmol triethyl phosphite and 5.4 mmol tri-isopropyl phosphite and 5.4 mmol tri-n-butyl phosphite + 5.4 mmol heptazine chloride) Backflow, 3 50 2-(Diethylphosphonato)-5-(di-iso-propylphosphonato)-8-(di-n-butylphosphonato)-s-heptazine Me : Et : iPr 1 : 1 : 1 unsym fluid* 21 Trimethyl phosphite and triethyl phosphite and tri-iso-propyl phosphite (5.4 mmol trimethyl phosphite and 5.4 mmol triethyl phosphite and 5.4 mmol tri-iso- Backflow, 3 50 2-(Dimethylphosphonato)-5-(diethylphosphonato)-8-(di-iso-propylphosphonato)-s-heptazine Me : iPr: nBu 1 : 1 : 1 unsym fluid* propyl phosphite + 5.4 mmol heptazine chloride) 22 Trimethyl phosphite and triethyl phosphite and tri-n-butyl phosphite (5.4 mmol trimethyl phosphite and 5.4 mmol triethyl phosphite and 5.4 mmol tri-n-butyl phosphite + 5.4 mmol heptazine chloride) Backflow, 3 50 2-(Dimethylphosphonato)-5-(diethylphosphonato)-8-(di-n-butylphosphonato)-s-heptazine Me : Et: nBu 1 : 1 : 1 unsym fluid* (1) Symmetrical (sym), asymmetrical (unsym) (2) "Liquid" and "solid" respectively referred to the aggregate state of heptazine at 25 °C and 1013 mbar * Compound contains traces of reactants and solvent Characterization of the compoundsNuclear magnetic resonance (NMR) spectroscopy

[0044] The products obtained in Examples 1, 4 and 17 were characterized as follows: - Example 1: 2,5,8-Tris(dimethylphosphonate)-s-heptazine (solid symmetrical compound) 13 C NMR (100.61 MHz, DMSO, δ [ppm]): 177.6, 175.0, 158.7 (t), 54.3 (d), 38.9 (m, DMSO) 1 H NMR (400.13 MHz), DMSO, δ [ppm]): 3.89 (d), 3.42, 2.50 (m, DMSO) 31 P NMR (161.98 MHz), DMSO, δ [ppm]): 11.98, 4.00, 3.82, 3.69, 2.94 (product), 0.84, - 0.20 - Example 4: 2,5,8-Tris(di-n-butylphosphonate)-s-heptazine (liquid symmetrical compound) 13 C NMR (100.61 MHz, CDCl3, δ [ppm]): 173.7, 172.2, 171.1, 169.6, 153.8 (t), 150.9 (d), 142.1, 69.5, 68.7-67.1, 65.3 (d), 65.0 (d), 62.1, 61.8 (d), 49.5, 48.2-46.7, 43.4, 34.8, 34.0, 33.1 (d), 32.7-32.0, 29.8, 29.1, 28.7 (d), 28.3, 25.8, 24.4 (d), 23.6 (d), 22.2, 20.1 (t), 18.9, 18.6-18.5, 13.9-13.4, 1 H NMR (400.13 MHz), CDCl3, δ [ppm]): 7.67, 7.41, 5.95, 4.23, 4.05 (d), 3.79 (q), 3.79 (q), 3.60, 1.76-1.60, 1.49-1.30, 0.97-0.88, 31 P NMR (161.98 MHz), CDCl3, δ [ppm]): 138.96 (reactant, tri-n-butyl phosphite), 32.26, 30.19, 12.50, 12.16-11.55, 10.33, 7.49, 2.62, 1.29 (product), -0.78, -12.92 - Example 17: 2-Dimethyl-5,8-bis(di-n-butylphosphonato)-s-heptazine (liquid unsymmetrical compound) 13C NMR (100.61 MHz, CDCl3, δ [ppm]): 180.3, 177.8, 172.2, 171.0, 159.4 (t), 151.1 (t), 142.3, 137.8 (toluene), 132.5 (toluene), 130.5 (toluene), 129.0 (Toluene), 128.2 (Toluene), 127.7 (Toluene), 125.2 (Toluene), 68.8 (d), 32.4, 21.4 (Toluene), 18.6, 13.5 1 H NMR (400.13 MHz), CDCl3, δ [ppm]): 7.44-7.41, 7.25-7.11, 4.35-4.24, 4.05-3.91, 3.76 (d), 2.34, 1.75-1.62, 1.48-1.36, 0.98-0.91, 31 P NMR (161.98 MHz), CDCl3, δ [ppm]): 30.41, 12.76-11.31, 10.63, 10.46-9.91, 7.81, 3.05, 2.90, 2.72, 2.51, 2.30, 1.69, 1.42, 0.93, 0.40 FTIR spectroscopy

[0045] The products obtained in Examples 1 and 17 were characterized as follows: - Example 1: 2,5,8-Tris(di-methylphosphonate)-s-heptazine (solid symmetric compound) FTIR (ATR, v [cm -1 ]): 2960, 1582, 1497, 1445, 1377, 1358, 1255, 1179, 1087, 1022, 940, 841, 767, 669, 658, 625 - Example 17: 2-Dimethoxyphosphonato-5,8-bis(di-n-butoxyphosphonato)-s-heptazine (liquid unsymmetrical compound) FTIR (ATR, v [cm -1 ]): 3851, 3646, 2959, 2873, 1683, 1596, 1554, 1457, 1387, 1349, 1262, 1027, 632 Thermal decomposition

[0046] The products obtained from Examples 1, 4, 5, 13, and 14 were characterized as examples. In thermogravimetric analysis (TGA), the compounds investigated showed a decomposition temperature in the range between 180 °C and 240 °C, see Table 2. Table 2 Results of thermogravimetric analysis. Example# Heptazine 5% weight loss / °C T / onset °C Residual mass at 995 °C / % 4 2,5,8-Tris(di-n-butylphosphonate)-s-heptazine (147) Toluene (121) 218 3,6 5 2,5,8-Tris(di-isodecylphosphonate)-s-heptazine 221 240 8,9 1 2,5,8-Tris(di-n-methylphosphonate)-s-heptazine 184 287 13,6 13 2,5,8-Tris(di-iso-propyl / n-butylphosphonate)-s-heptazine 159 182 6,8 14 2,5-Bis(di-iso-propyl)-8-di-n-butylphosphonate-s-heptazine 169 182 4,7 Further analyses

[0047] As an example, the product from Example 1 was analyzed by FTIR, UV / VIS and the melting point and yield were determined, as well as crystallographic data recorded: - FTIR (ATR, v [cm -1]): 2960, 1582, 1497, 1445, 1377, 1358, 1255, 1179, 1087, 1022, 940, 841, 767, 669, 658, 625 - UV / VIS ([nm], 10 mm cuvette, CHCl3): 302, 362 - Yield: 58% - Melting point: 205 °C - Crystallographic data for the product of Example 1, determined by single-crystal X-ray diffraction analysis, are listed below in Table 3 and the molecular structure of 2,5,8-tris(dimethylphosphonate)-s-heptazine is shown in Fig. shown: Table 3 Crystallographic data for product from Example 1. The compound crystallizes with one molecule of acetonitrile per formula unit. Connection 2,5,8-Tris(dimethylphosphonate)-s-heptazine molecular formula C 12 H 18 N7O9P3, C2H3N mass 538.30 Crystal system monoclinic Space group P21 / n Cell constants a [Å] 17.0267(9) b [Å] and β [°] 7.5318(2) and 91.511(4) c [Å] 18.2753(9) V[Å 3 ] 2342.84(18) Z 4 F (000) 1112 D ber. [g·cm -3 ] 1.526 µ(MoK α ) [mm -1 ] 0.316 Measuring temperature [K] 203 Θ range [°] 2.393 - 27.500 h, k, l range -22 ≤ h ≤ 22, -9 ≤ k ≤ 9, -23 ≤ l ≤ 23 Measured / independent reflexes 22317 / 5354 R int 0.0479 refinement least squares Data / Restraints / Parameters 5354 / 27 / 400 R1 / wR2 [l ≥ 2σ(l)] 0.0446 / 0.1089 R1(F) / wR2(F 2 ) (all data) 0.0571 / 0.1209 Goof* 1.113 Residual electron density Δρ max / min [e · Å -3 ] 0.576 / -0.398 *Goodness of fit Example 23: Flame retardant properties

[0048] To evaluate the flame retardancy, the liquid symmetrical flame retardant (FR) 2,5,8-tris(di-n-butylphosphonate)-s-heptazine from Example 4 was compounded into polylactide (PLA), see Table , or into thermoplastic polyurethane (TPU), see Table , and processed into test specimens by injection molding:

[0049] Regarding PLA: Powdered PLA (Luminy L130, TotalEnergies Corbion) was manually mixed with the FR and then compounded using a Thermo-Haake MiniLab mini-extruder at 100 rpm at 190 °C. LOI test specimens were fabricated from the resulting compound at 200 °C using a Thermo Scientific, Haake, MiniJet II injection molding machine.

[0050] Regarding TPU: Powdered TPU (Elastollan 1180A, BASF) was manually mixed with the FR and then compounded using a Thermo-Haake MiniLab mini-extruder at 100 rpm at 190 °C. LOI test specimens were produced from the resulting compound at 210 °C using a Thermo Scientific, Haake, MiniJet II injection molding machine.

[0051] The resulting compounds containing PLA and TPU were evaluated using the Limiting Oxygen Index (LOI) test. Flame-retardant properties were demonstrated. This was evident by the increased LOI value of the flame-retardant-containing material compared to the flame-retardant-free material. Table 4 Flame retardancy results of 2,5,8-tris(di-n-butylphosphonate)-s-heptazine in PLA. LOI / O 2 % FR / wt.% PLA (without FSM) 24,6 ± 0,38 - PLA with 2,5,8-tris(di-n-butylphosphonate)-s-heptazine 29,6 ± 0,38 5 Table 5 Flame retardancy results of 2,5,8-tris(di-n-butylphosphonate)-s-heptazine in TPU. LOI / O 2 % FR / wt.% TPU (without FR) 23,8 ± 0,48 - TPU with 2,5,8-tris(di-n-butylphosphonate)-s-heptazine 24,4 ± 0,38* 5 * Visual observation: TPU + flame retardant showed higher flame resistance. The lateral runoff of a weakly burning melt droplet on the test specimen over the 50 mm mark (LOI test criterion) resulted in the reported slight increase in the LOI value. Short description of the figure Fig. shows the molecular structure of 2,5,8-tris(dimethylphosphonate)-s-heptazine (product from Example 1). References C.-C. Höhne, C. Posern, U. Böhme, F. Eichler, E. Kroke, Polym. Degrad. Stab. 2019, 166, 17-30 T. Saplinova, V. Bakumov, T. Gmeiner, J. Wagler, M. Schwarz, E. Kroke, Z. anorg. general Chem. 2009, 2480-2487 DE 10 2022 205 709 A1 E. Kroke, M. Schwarz, P. Kroll, E. Bordon, B. Noll, A. Norman, New J. Chem., 26 (2002), 508-512 QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2022 205 709 A1 [0004, 0051] Cited non-patent literature

[0000] DIN EN 13501-1:2010-01

[0002] C.-C. Höhne, C. Posern, U. Böhme, F. Eichler, E. Kroke, Polym. Degrad. Stab. 2019, 166, 17-30 [0004, 0051] T. Saplinova, V. Bakumov, T. Gmeiner, J. Wagler, M. Schwarz, E. Kroke, Z. anorg. general Chem. 2009, 2480-2487 [0004, 0051] E. Kroke, M. Schwarz, P. Kroll, E. Bordon, B. Noll, A. Norman, New J. Chem., 26 (2002), 508-512 [0028, 0051]

Claims

[1] Heptazine derivative of formula (I)wherein each X, Y, Z each represents an oxygen or a sulfur atom; R 1 , R 2 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radical and C6 to C12 aryl radical, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radical; R 4 , R 5 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radical and C6 to C12 aryl radical, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radical; R 7 , R 8are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals. [2] Heptazine derivative of the general formula (I) according to claim 1, wherein R 1 , R 2 and R 4 , R 5 and R 7 , R 8 are equal; where R 1 , R 2 and R 4 , R 5 and R 7 , R 8are preferably selected from the group consisting of branched and unbranched C4 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C18 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C17 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C16 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C15 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C14 alkyl radicals,more preferably from the group consisting of branched and unbranched C4 to C13 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C12 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C11 alkyl radicals, more preferably from the group consisting of branched and unbranched C4 to C10 alkyl radicals. [3] Heptazine derivative of the general formula (I) according to claim 1, wherein R 1 , R 2 are not equal to R 4 , R 5 and to R 7 , R 8 . [4] Heptazine derivative of the general formula (I) according to claim 3, wherein R 4 , R 5 are equal to 7 , R 8 (R 4 , R 5 = R 7 , R 8 ) and where R 1 , R 2are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals and R 4 , R 5 R 7 , R 8 and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals; wherein R 1 , R 2are preferably selected from the group consisting of branched and unbranched C1 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C1 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C4 alkyl radicals; and / or R 4 , R 5 , R 7 , R 8are preferably selected from the group consisting of branched and unbranched C1 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C1 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C4 alkyl radicals. [5] Heptazine derivative of the general formula (I) according to claim 3, wherein R 1 , R 2 are not equal to R 4 , R 5 and to R 7 , R 8 and R 4, R 5 are not equal to R 7 , R 8 , where R 1 , R 2 are selected from the group consisting of branched and unbranched C1 to C20 alkyl radical and C6 to C12 aryl radical, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radical; R 4 , R 5 are selected from the group consisting of branched and unbranched C2 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals; and R 7 , R 8are selected from the group consisting of branched and unbranched C3 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals; wherein R 1 , R 2are preferably selected from the group consisting of branched and unbranched C1 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C1 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C1 to C4 alkyl radicals; and / or R 4 , R 5are preferably selected from the group consisting of branched and unbranched C2 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C2 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C2 to C4 alkyl radicals; and / or R 7 , R 8are preferably selected from the group consisting of branched and unbranched C3 to C18 alkyl radicals, preferably from the group consisting of branched and unbranched C3 to C16 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C14 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C12 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C10 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C8 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C6 alkyl radicals, further preferably from the group consisting of branched and unbranched C3 to C4 alkyl radicals. [6] Use of a heptazine derivative of the general formula (I) according to one of claims 1 to 5 as a flame retardant for a plastic; wherein the plastic is preferably selected from the group of thermoplastics and mixtures thereof, more preferably from the group consisting of polyurethane (PU), polyisocyanurate (PIR), polyester and mixtures of two or more of these plastics. [7] Flame-retardant plastic comprising at least - a heptazine derivative of the general formula (I) according to any one of claims 1 to 5; - a plastic; wherein the plastic is preferably selected from the group of thermoplastics and mixtures thereof, more preferably selected from the group consisting of polyurethane (PU), polyisocyanurate (PIR), polyester and mixtures of two or more of these plastics. [8] A process for preparing a heptazine derivative of the general formula (I) comprising (i) providing a phosphite mixture comprising (i.1) a first trialkyl or triarylphosphite of the general formula (A)wherein X is a heteroatom, in particular an oxygen or a sulfur atom; R 1 , R 2 , R 3 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and branched and unbranched C1 to C10 alkyl radicals; and (i.2) optionally a second trialkyl or triarylphosphite of the general formula (B) where Y is a heteroatom, in particular an oxygen or a sulfur atom; R 4 , R 5 , R 6are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and C1 to C10 alkyl radicals; wherein R 1 , R 2 , R 3 of the first trialkyl phosphite according to (i.1) are not equal to R 4 , R 5 , R 6 the second trialkyl phosphite according to (i.2); and (i.3) optionally a third trialkyl or triarylphosphite of the general formula (C)wherein Z is a heteroatom, in particular an oxygen or a sulfur atom; R 7 , R 8 , R 9 are the same and are selected from the group consisting of branched and unbranched C1 to C20 alkyl radicals and C6 to C12 aryl radicals, wherein the C6 to C12 aryl radical has at least one substituent selected from hydrogen atom and C1 to C10 alkyl radicals; where R7 , R 8 , R 9 are not equal to R 1 , R 2 , R 3 of the first trialkyl phosphite according to (i.1) and are not equal to R 4 , R 5 , R 6 of the second trialkyl phosphite according to (i.2). and (ii) providing heptazine chloride; (iii) reacting the phosphite mixture according to (i) with the heptazine chloride according to (ii), to obtain at least one heptazine derivative of the general formula (I), wherein the radicals R 1 -R 9 and X, Y, Z have the meaning given in any of claims 1 to 5. [9] A process for preparing a heptazine derivative of the general formula (I) according to claim 8, wherein no solvent is present in at least (i), (ii) or (iii), preferably no solvent is present in either (i) or (ii) or (iii). [10] A process for preparing a heptazine derivative of the general formula (I) according to claim 8 or 9, wherein the reaction according to (iii) is carried out at a temperature in the range of 5 to 120 °C, preferably in the range of 10 to 90 °C, more preferably in the range of 20 to 80 °C. [11] Process for the preparation of a heptazine derivative of the general formula (I) according to any one of claims 8 to 10, wherein at least one of the trialkyl or triarylphosphites of the general formula (A), optionally (B) or optionally (C) is liquid at 25 °C and 1013 mbar. [12] A process for preparing a heptazine derivative of the general formula (I) according to any one of claims 8 to 11, wherein step (iii) comprises: (iii.1a) introducing the first trialkyl or triarylphosphite of general formula (A) provided according to (i), optionally the second trialkyl or triarylphosphite (B) and optionally the third trialkyl or triarylphosphite (C) into a reaction vessel, (iii.2a) adding the heptazine chloride provided in (ii) to the reaction vessel; or (iii.1b) placing heptazine chloride provided in accordance with (ii) in a reaction vessel; (iii.2b) Addition of the first trialkyl or triarylphosphite of general formula (A) provided according to (i), optionally the second trialkyl or triarylphosphite (A), (B) and optionally the third trialkyl or triarylphosphite (C) into the reaction vessel.

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