The present invention belongs to the technical field of synthesis of amidines, and more particularly to one pot manufacturing of amidines. The present invention relates to a solvent free manufacturing of amidines in a one-pot procedure. The products are formed in high yield and can be used in application areas such as components in paints and lacquers or as flame retardants without further purification.

Background

Amidines are among others useful components in coating formulations, as additives in thermoplastics and as components in flame retardants. Solvents and/or metal complex catalysts are frequently used in order to ensure safe and reliable manufacturing processes.

CN 110078642 A discloses an application of chlorodifluoromethane as a Cl source for synthesis of amidine compounds. Chlorodifluoromethane can be subjected to quadrupole bond cracking under a mild condition, and valuable amidine compounds can be obtained. Water and a solvent are added in the presence of chlorodifluoromethane. The amidine compounds can be obtained by one-step.

WO 17105449 Al describes methods of synthesis of amidines, amidine-metal complexes, thin metal films formed using amidine-metal complexes on semiconductor devices, and semiconductor devices and systems with thin metal films formed using amidine-metal complexes. The synthesis comprises solvents.

US 9988482 BB and EP 3131992 Bl disclose a catalyst containing at least one amidine or guanidine group, which is bound to a siloxane residue. At room temperature, the catalyst is liquid, odourless and suitable as a cross-linking catalyst for curable compositions, in particular for silane group-containing compositions. It is particularly good at accelerating the hardening of such compositions without impairing stability in storage, and displays little volatility but good compatibility. Lanthanum(lll)-trifiuoromethanesulfonate is used as metal complex catalyst in the synthesis of the catalyst containing an amidine group.

KR 790000508 Bl discloses a process for the manufacture of N, N'-disubstituted amidines with anti-inflammatory activity. An imino-compound is reacted with amines in organic solvent. WO 2004/087124 discloses amidine compounds for treating schizophrenia. Manufacturing of such amidine compounds is feasible by condensation of amine with substituted formamide in a solvent.

EP 2264012 Al discloses heteroarylamidines and their use in microorganisms control. A process for the preparation of the heteroarylamidines comprises the conversion of a heteroarylamine with either aminoacetal, amide or amine/orthoformate in solvent.

DE 1267467 discloses the preparation of cyclic amidines by a condensation reaction of dicarboxylic acid semi-amide with diamine in hydrocarbon solvent. The cyclic amidines are useful as fuel additives and biocides.

DE 2036181 discloses a method for the preparation of benzamidines wherein benziminochlorides are reacted with aromatic amines in an inert solvent.

DE 2256755 Al discloses a method for preparation of amidines by reacting silylated amides or lactams with ammonia or amines. Mercury, tin, zinc and titanium chloride are used as catalyst and toluene, xylene, chlorobenzene and anisole as solvent.

EP 0617054 Bl discloses amine functional polymers which are vinyl based terpolymers made up of randomly linked units with formamidine or formamidinium formate, formamide and either amine or ammonium formate as functional groups. The polymers are prepared by aqueous hydrolysis of poly(N-vinylformamide) at a temperature in the range of 90 °C to 175 °C, preferably in the presence of a minor amount of ammonia or volatile amine.

EP0919555A1 a process for preparing a bicyclic amidine by reacting a lactone and a diamine. Water formed during the elimination reaction is distilled from the reaction mixture together with a considerable excess of diamine, which acts as non-reacting solvent.

US 7247749 discloses the synthesis of an amidine catalyst by conversion of fluorinated nitrile with ammonia at high pressure.

W00078725 Al provides a process for preparing amidines starting from carboxylic acid derivatives, in which the carboxylic acid containing moiety is attached to a sp ³ -, or sp ² - or sp- hybridized carbon atom. The sp ² -hybridized carbon atom, to which the carboxylic acid containing moiety is attached to may be part of an aromatic or heteroaromatic or olefinic system. The process comprises use of solvent and purification of intermediates.

EP2260078 Bl, WO 2006045713, EP 1740643 Bl, EP 1756202 Bl, EP 1943293 Bl and EP 3341339 Bl disclose methods for preparing polymers comprising siloxane. The methods comprise conversion of amine bound to hydrolysed siloxane with carboxylic acid derivates. Considerable amounts of solvent are used for lowering viscosity and removal of water or alcohol from elimination reactions. EP 1943293 Bl claims a hybrid polymer which is suitable as UV absorber. The disclosed data for the preparation of the UV-absorber shows that the product is a mixture of solvent, hybrid polymer with claimed amide structure and hybrid polymer with claimed amidine structure.

None of the prior art discloses methods for the preparation of amidines without using solvents and/or metal complex catalysts. Amidine products manufactured by these methods require frequently purification from solvents and catalyst residue. Stripping and recrystallization may be applied. Apart from its negative environmental impact such purification is time consuming and costly. Hence, the useful industrial application of such amidine products is frequently impaired. There is a need for methods for manufacturing of amidines without using solvents and/or metal complex catalysts.

Objects

It is therefore an object of the present invention to provide a method for preparation of amidines, in which neither the use of solvent nor the use of metal complex catalyst is mandatory. It is a further object to provide amidines, which essentially are free of solvent residues and metal complex catalyst residues without a need of post-reactor purification.

The present invention

The above mentioned objects are achieved by a method as defined in claim 1.

According to another aspect, the present invention concerns an amidine or amide as defined by claim 11. Yet another aspect the present invention concerns use of the products as defined by claim 16. Preferred embodiments of the different aspects of the invention are disclosed by the dependent claims.

The preparation of amidines by conversion of two moles of amine and one mole carboxylic acid derivative is known. Since a C=N double bond and a C-N single bond have to be formed, at least one of the moles of amine has to be primary. The other may be either primary or secondary. Suitable amines, which later on may be called first reacting components, may be selected among the group of amines in formula (1).

RI, R2 and R4 are selected independently from each other from C1-C30 alkyl, C5-C30 aryl, Cg-Cso alkylated aryl. Branched, linear, saturated and unsaturated hydrocarbon chains C _n may be applied since these differences do not influence the preparation of amidines in a significant way. C-C and C-H bonds may optionally be interrupted by one or more heteroatoms selected from the group consisting of 0, S and NH.

Ri, R2 and R4 may optionally be bound to one or more silicon based substituent of formula (2).

R5-R7 are chosen among Ci-Cg alkoxy, C1-C30 alkyl, C5-C30 aryl and Cg-Cso alkylated aryl, Xi is 0,

R3 is H, C1-C30 alkyl, C5-C30 aryl, Cg-Cso alkylated aryl and two of Ri, R2 and R4 may be covalently be bound to each other and form ring structures.

Suitable carboxylic acid derivatives, which later on may be called second reacting components, may be selected among the group in formula (3). Xi, X2 and X3 are independently from one another selected from a group consisting of 0, S and NH. Ri is chosen from C1-C30 alkyl, C5-C30 aryl, Cg-Cso alkylated aryl, wherein branched, linear, saturated and unsaturated hydrocarbon chains C _n may be applied. C-C and C-H bonds may optionally be interrupted by one or more heteroatoms chosen among the group of 0, S and NH. R ₅ is chosen among Ci-Cg alkoxy, C1-C30 alkyl, C5-C30 aryl and Cg-Cso alkylated aryl.

The prepared amidines are shown in formula 4 (a) and (b).

RI, R2 and R4 are independently from each other C1-C30 alkyl, C5-C30 aryl, Cg-Cso alkylated aryl wherein branched, linear, saturated and unsaturated hydrocarbon chains C _n may be applied. C-C and C-H bonds may optionally be interrupted by one or more heteroatoms chosen among the group of 0, S and NH.

At least one carboxylic acid derivative has to be soluble in at least one of the amines or vice versa and together with all optionally remaining amines and carboxylic acid derivatives form a solution at a temperature where the amount of formed amidines is negligible. The preparation is a fast and convenient a one-pot reaction process. Studies in a stainless steel vessel equipped with stirrer, distillation cooler and warmed by inductive heating showed that the elimination reaction progress measured by received distillate can be easily controlled by tuning the power transfer into the inductive heating unit. Neither the use of solvent nor the use of metal complex catalyst is necessary.

It is well known that carboxylic acid derivatives which are C3 and higher esters can be prepared by conversion of carboxylic acids with C3 and higher alcohols and azeotropic distillation of formed water. Carboxylic acid derivatives, which are C3 and higher esters, have usually lower melting points than the corresponding carboxylic acids. Carboxylic acid derivatives which are C3 and higher esters may therefore be more suitable for the amidine synthesis according to the present invention than the corresponding carboxylic acids. In a first embodiment at least one of the first reacting components or at least one of the second reacting components preferably has a dynamic viscosity of less than 20 mPa*s at 150 °C, more preferred of less than 20 mPa*s at 100 °C and most preferred of less than 20 mPa*s at 50 °C.

Lower viscosity at a given temperature facilitates the homogenisation of the reaction mixture and thus increases the progress of the reaction and shortens the batch time of the one pot reaction process.

In a second embodiment the temperature at which the solution of all reaction components is formed is preferably less than 180 °C, more preferred less than 120 °C and most preferred of less than 60 °C. Similar to the first embodiment a lower temperature at which the solution of all reaction components is formed increases the progress of the reaction and shortens the batch time of the one pot reaction process.

In a third embodiment clay is added to the reacting components at an amount of up to 70% w/w, more preferred up to 10% w/w and most preferred about 1% w/w of the total mass of starting material. The addition of clay to the first and second reacting components provided surprisingly transparent products, especially when 2- or 4-hydroxybenzoic esters have been used as second reacting component. The surprisingly high transparency of the obtained amidines indicates an excellent dispersion of the clay in the amidine matrix and possibly exfoliation of the layered structure in the clay. An involvement of the clay in the formation process of the amidine may happen. However the amidine is formed in a fast process with about quantitative yield in the absence of clay, too. Excellent dispersed clay in an organic matrix is demanded in many commercial applications and the solvent free process of the present invention may provide a path to satisfy this demand in an economic and ecologic sound manner.

In a forth embodiment at least one of the amines which serve as first reacting components is covalently bound to an at least partially hydrolysable silane. At least one R2 and R4 are bound to one or more silicon based substituent of formula (2). R5-R7 are chosen among Ci-Cg alkoxy, C1-C30 alkyl, C5-C30 aryl and Cg-Cso alkylated aryl, Xi is 0.

Silicon based substituents introduced by amines as first reacting compounds provide the possibility to crosslink the obtained amidine by state-of-the-art hydrolysis Si-OR groups and condensation of the formed Si-OH groups. Silicon based substituents facilitate the chemical bond to inorganic minerals such as fillers, pigments and other HO-functionalized materials, too.

In a fifth embodiment, at least one of the first reacting components comprises at least two amine groups, which are covalently bound to each other. The respective diamine, triamine, oligoamine or polyamine may arise from covalent bonding of at least two of Ri, R2 or R4 and are at least partly described by formula (6).

L is a linkage group selected among the group of C2-C30 alkylene, C2-C30 alkylene comprising one or more double bonds or one or more triple bonds, C7-C30 arylsubstituted alkylene, C5-C30 arylene, Cg-Cso alkylated arylene and optionally interrupted by heteroatoms chosen among the group of 0, S and NH and optionally substituted by halogen.

L may also be the linkage group of formula (7).

R ¹ -R ⁴ are independently from each other selected among the group of H, C1-C4 alkyl, SiO(OH) and AI(OH)2. C1-C4 alkyl refers to non-hydrolysed siloxane, H refers to hydrolysed but not condensed siloxane, , SiO(OH) refers to hydrolysed and condensed siloxane, AI(OH)2 refers to hydrolysed and condensed siloxane in the presence of aluminium oxide or hydroxide matter.

In a sixth embodiment the second reacting component is provided by partial oxidative degradation or hydrolytic degradation of a polymer selected from the group consisting of polyethylene, polypropylene, polyamide, polyester, cellulose and lignin. Oxidative degradation frequently leads to chain scission in polyolefins such as polyethylene and polypropylene. Oxidized carbon end-groups of cleaved polymer chains may comprise -COOH groups, which are suitable as second reaction component in the formation of amidines according to the present invention. Similar is true for other polymers such as polyamides, polyesters, cellulose and lignin. Lignin is a naturally occurring polymer made by crosslinking of phenolic precursors. Oxidation, optionally combined with hydrolysis yields polymer material with -COOH groups, which are suitable as second reaction component in the formation of amidines according to the present invention. Polyamides and polyesters are able to form -COOH groups when submitted to hydrolytic degradation conditions.

In a seventh embodiment the carboxylic acid derivatives selected as second reacting components are selected from a group consisting of 2-hydroxybenzoic acid, 3-hydroxybenzoic acid, 4- hydroxybenzoic acid, 2-hydroxynaphtoic acid, 3-hydroxynaphtoic acid, 4-hydroxynaphtoic acid, 6- hydroxynaphtoic acid and esters or amides thereof, 2-hydroxybenzonitrile, 3- hydroxybenzonitrile, 4-hydroxybenzonitrile, 2-hydroxynaphtonitrile, 3- hydroxynaphtonitrile, 4-hydroxynaphtonitrile and 6-hydroxynaphtonitrile. All of these may additionally comprise one or more functional groups selected from the group consisting of -OH, ORg, -CHO and C=C double bonds, wherein Rs is selected from C1-C30 alkyl. Second reacting compounds derived from natural resources such as lignin may comprise 4-hydroxycinnamic acid, which comprises a C=C double bond linked to a 4-hydroxyphenyl group and a carboxylic acid group. Similar unsaturated acids may be obtained from lignin by known processes. Oxidized vanillin is another suitable second reacting compound which can be obtained from vanillin by known processes.

Hydroxysubstituted aromatic acids as second reacting components provide a number of interesting properties of the prepared amidines: low oxygen diffusion materials, fire retardant materials, materials comprising clay with excellent dispersion and possibly exfoliation, water soluble or dispersible materials by using at least partial deprotonation of the hydroxyl aromatic group. Several of these properties are connected to the formation of intermolecular hydrogen bonds beyond the formation of hydrogen bonds between amidine groups.

In an eighth embodiment the conversion of first reacting components and second reacting components is about quantitative without addition of facilitating components selected from the group of solvents and metal complex catalysts. First reacting components comprising at least two amine groups have shown to provide a fast and about quantitative reaction with second reacting components, especially with hydroxysubstituted aromatic acids. Siloxane moieties are also instrumental in providing fast and about quantitative reaction. Similar the addition of clay provides a fast and about quantitative reaction. In contrast to metal complex catalysts clay is frequently accepted and sometimes appreciated if its dispersion in the amidine product is excellent.

Amidine as manufactured according to the present invention may in bulk form intermolecular hydrogen bonds. The influence of hydrogen bonds on crystallisation behaviour is known from block copolymers such as polyurethaneurea (PUU) block copolymers. PUU block copolymers are made up of soft segments based on polyether or polyester and hard segments based on the reaction of diisocyanate and diamine extender. They can be divided into polyether- and polyester-based PUU depending on the soft segments used. Polyester-based PUU have stronger hydrogen bonds between hard and soft segments for phase mixing than polyether-based PUU. The hydrogen bonds cause an increased cohesion between the hard and soft segments with increasing hard segment contents, and higher hard-soft segment mixing present in these systems may also prevent the crystallization of the soft segments (Hydrogen bonding and crystallization behaviour: Xiu Yuying et al. POLYMER, 1992, Volume 33, Number 6).

Intermolecular hydrogen bonds between amidines may have a major influence on the crystallisation behaviour of these amidines. The amorphous parts in amidines will increase. Amorphous domains in the solidified amidines are likely to withhold solvent residues and metal complex catalysts. As a result, a post-reactor purification by recrystallization or stripping might be impaired. It is therefore a considerable advantage of the present invention to provide a safe and convenient high yield method for the preparation of solvent free and metal complex catalyst free amidines.

It is expected that the influence of hydrogen bonds increases with increasing molecular weight of the amidine. It is well known, that the crystallization and purification of peptides and proteins becomes more and more challenging, when the number of hydrogen bonds between the peptide or protein molecules increases. In a ninth embodiment the molecular weight of the amidine is preferably at least 1000 g/mole, more preferred at least 1500 g/mole and most preferred at least 2000 g/mole.

Most application areas of polymeric amidines require processing as neat materials or in mixtures. Useful molecular weight for such processing is frequently below 500000 g/mole. In a tenth embodiment the molecular weight of the amidine is preferably less than 200000 g/mole, more preferred less than 100000 g/mole and most preferred less than 50000 g/mole. An eleventh embodiment are amidines represented by the dimer in formula 8a or the polymer in formula 8b.

Formula 8: Amidines according to the present invention

The number n is an integer of 8-200 and f -R ⁵ is H or OH. The amidines are made from substituted or non-substituted benzoic acid derivatives as second reacting components and tetraethylenetetramine and polyvinylamine as first reacting components.

Yet another embodiment is the use of amidines according to the present invention as flame retardants. The amidines have a considerable content of nitrogen and a low content of oxygen, which both are important properties of flame retardants. Even more important is the low content of combustible solvent in the amidines. For many applications of flame retardant materials, a single burning item test (SBI) according to EN 13823 is mandatory. Fire retardant wooden building products are not allowed to be sold without a passed SBI with fire class B. A critical parameter of the SBI is the initial fire growth rate (FIGRA) which must not exceed 120 W/s after 0.2 MJ and after 0.4 MJ of total heat release (THR) for fire class B. Typical solvents used in binder manufacturing give an energy release of 27-43 MJ/kg. A hydrocarbon with a boiling point of 170 °C at 1013 mbar can frequently only with considerable efforts be removed from a binder, which is used in a flame retardant coating. Amounts of 5% w/w in the binder are not rare. In the SBI of for example a wallboard about 1 m ² of the board is exposed to a butane flame of 40 kW. A frequently used amount of binder in this type of SBI is 300 g/m ² . This means 15 g of solvent or 0.6 MJ of total heat release. The butane flame is about 1000 °C and an evaporation and combustion of the solvent within a few tenths of seconds is very likely. This would easily lead to a FIGRA > 120 W/s between 0.2 MJ and 0.6 MJ heat release. As a consequence, the SBI test would be failed, even if all other parameters such as THR after 600 seconds and smoke generation are well within the limit for fire class B.

It is a significant advantage of the present invention that solvent free flame retardant binders can be obtained.

Examples to support the patent claims

Example 1:

Preparation of salicylamidine from methyl salicylate and ethylene diamine. Water and methanol are distilled off Salicylamidine has strong intramolecular hydrogen bonds between the phenolic HO-group and the amidine group. The molecular structure is about plane and easily crystallizing due to the intramolecular hydrogen bonds.

2 moles of diethylene amine (is introduced in a 1000 ml 3-necked reaction flask and mixed with 2 moles of methyl salicylate. A clear solution is obtained at room temperature. The mixture is heated to 180 °C under stirring and about 100 g of distillate is collected. A clear slightly yellow and product is obtained. Melting range is 200 °C - 205 °C.

Example 2:

The reactions in example 1 have been characterized by measurement of pH values. 0.1 moles of each mixture of starting materials and each product have been dispersed or dissolved in 100 ml of water by high shear mixing. The obtained dispersions or solutions have been directly measured with a calibrated pH electrode. Table 1 shows the measured pH values and an explanation for the measured pH values on the base of the expected chemical structures of starting materials and products. Table 1: pH values and explanation pH measurement clearly indicates an about quantitative conversion from amine to amidine and finally to amide.

1H-NMR, 13C-NMR and FT-IR data have been evaluated as a support for the obtained amidines. However hydrogen bonds and along with them sample concentration, pH-value, necessary solvents for sample preparation and temperature have a considerable influence on peak shape and position. Data from routine measurements are therefore no reliable proof or dis-proof of the formation of amidines. Reliable 1H-NMR, 13C-NMR and FT-IR data have to be based on a comprehensive scientific work on sample preparation, sample measuring and interpretation of spectra. This would exceed the scope of examples in a patent application. However such work is very welcome and will surely give valuable insights and probably contribute to new inventions.

Example 3:

Preparation amidines from an amine, which is covalently bound to hydrolysable silane and 4- hydroxybenzoic acid methyl ester

2 moles of 3-aminopropyltriethoxysilane are introduced in a 1000 ml 3-necked reaction flask and heated to 80 °C under stirring. 1 mole of 4-hydroxymethyl benzoate is added as powder within 5- 10 minutes. Heating is increased and the reaction mixture becomes clear at 120 °C. The reaction mixture is slowly heated to 180 °C and about 50 g of distillate is collected. A clear colourless and slightly viscous amidine is obtained.

After cooling to 60 °C 3 moles of H2O are added under vigorous stirring within 10-20 minutes. A clear product with reduced viscosity is obtained. Example 4:

Preparation amidines from an amine, which is covalently bound to hydrolysable silane and methyl salicylate

1 mole of N-(2-Aminoethyl)-3-aminopropyl-trimethoxysilane is introduced in a 1000 ml 3-necked reaction flask and heated to 80 °C under stirring. 1 mole of methyl salicylate is added within 5-10 minutes. Heating is increased and the reaction mixture becomes clear at 120 °C. The reaction mixture is slowly heated to 180 °C and about 50 g of distillate is collected. A clear colourless and slightly viscous amidine is obtained.

After cooling to 60 °C 3 moles of H2O are added under vigorous stirring within 10-20 minutes. A clear product with reduced viscosity is obtained.

Example 5:

Preparation amidines from an amine, which is covalently bound to hydrolysable silane and methyl salicylate and addition of clay

1 mole of N-(2-Aminoethyl)-3-aminopropyl-triethoxysilane is introduced in a 1000 ml 3-necked reaction flask and heated to 80 °C under stirring. 1 mole of methyl salicylate is added within 5-10 minutes. About 1% w/w of clay (montmorillonite K-10, Aldrich) is added. Heating is increased and the reaction mixture becomes clear at 120 °C. The reaction mixture is slowly heated to 180 °C and about 55 g of distillate is collected. A clear reddish and slightly viscous amidine is obtained. The obtained yield of amidine is divided into three portions, which were cooled to 80 °C under stirring. No clay is added to the first portion, 9% w/w of clay is added to the second portion, and 69% w/w of clay is added to the third portion. The three portions are stirred at 80 °C and 3 moles of H2O are added under vigorous stirring within 10-20 minutes.

The three obtained portions and the product of example 4 are solidified to 1 mm films by cooling in a 1 mm deep template mounted on glass of 1 mm thickness. The film from example 4 and the portion with 1% w/w clay of example 5 were completely transparent for the naken eye. The film from the portion with about 10% w/w clay of example 5 was slightly hazy but still transparent for the naken eye. The film from the portion with about 70% w/w clay of example 5 was hazy for the naken eye, but it was still transparent enough to clearly read a printed text in Arial type 12 attached to the non-coated side of the glass plate.

It is concluded, that the clay in the film samples was very well spread in the amidine matrix. Example 6

Burning test of cardboard

Packaging type cardboard (ca. 300 g/m ² ) has been coated with amidines obtained in Example 4 and Example 5 with 1% w/w clay (Amidine Ex4, Ex5) and subjected to flame testing. The cardboard samples are about 8 cm in width and 20 cm in length. They are coated by brushing two times on the front side, which is exposed to the flame and one time on the backside. Drying has been performed for 10 min in an air stream at 80 °C.

Flame: butane lighter with about 20 mm flame, top of flame in contact with cardboard sample for 60 seconds.

Table 2: Weight of burning test samples before and after fire test

A clear difference between the uncoated reference and the amidine coated samples has been found. The amidine-coated samples were self-extinguishing within 5 seconds after removal of the butane flame and showed a maximum flame height of 5 cm. The amidine-coated samples are suitable as flame retardant coatings.

Example 7

Preparation of amidines with methyl 4-hydroxybenzoate as carboxylic acid derivative

Two amidines and two amides thereof have been prepared similar to the procedures in example

1. Starting materials, melting range and observations are shown in table 3.

Table 3:

The use of methyl 4-hydroxybenzoate provides products in which intramolecular hydrogen bonds are not possible. This is in contrast to the use of methyl 2-hydroxybenzoate (methyl salicylate) in example 1 where intramolecular hydrogen bonds dominate in the product. The absence of intramolecular hydrogen bonds leads in this case to the stronger presence of intermolecular hydrogen bonds. The melting behaviour and feasibility of drawing wires from molten product can be explained by the presence of intermolecular hydrogen bonds.

The extreme temperature stability of example 8c in combination with a melting range comparable to thermoplastic resins reflects the presence of strong intramolecular hydrogen bonds, too.