DE102014212170A1 - Amino-containing organosilicon compounds and process for their preparation - Google Patents

Abstract

The invention relates to aminoalkyl-functional organosilicon compounds in which the aminoalkyl groups are connected via an oxygen atom with the silicon of the organosilicon compounds, wherein the carbon atom adjacent to the oxygen atom of the aminoalkyl carries one or two further hydrocarbon radicals, wherein the number of carbon atoms of the two further hydrocarbon radicals together at least is two and a method for their preparation.

Description

The invention relates to amino-containing organosilicon compounds and a process for their preparation.

Amine-functional organosilicon compounds play an important role in many areas of technology. For example, amino groups significantly affect the adhesiveness and hydrophilicity of a polysiloxane. For example, amine-functionalized polysiloxanes find multiple uses in, for example, the textile industry or personal care. The chemical reactivity of the amine functionality also makes it possible to prepare block copolymers, for example by polyaddition using isocyanates. By combining different polymer blocks, a large number of products with tailor-made property profiles are accessible.

The amine functionalities are usually connected via carbon atoms with the silicon atoms of the siloxane skeleton. The attachment takes place via a noble metal-catalyzed hydrosilylation reaction using H-silanes or H-siloxanes and a functionalized olefin, which then leads to aminopropyl-functionalized siloxanes. However, hydrosilylation reactions are expensive. An expensive precious metal catalyst is needed, which usually needs to be recycled. The reaction is also susceptible to interference, as regards impurities in the starting materials and difficult to control due to the high exothermicity. H-functional silanes and siloxanes are relatively expensive starting materials. Amine-functional olefins, such as. As allylamine can be used only after introduction of an amine protecting group, since they otherwise deactivate the catalyst. After the hydrosilylation, therefore, a further reaction step, the removal of the protective group, is necessary. In addition, the hydrosilylation of allylamine derivatives leads to mixtures of isomers. It will therefore i. A. synthetic strategies used in which the amino group is introduced only in a subsequent hydrosilylation reaction step. This detour makes the manufacturing process even more complicated and expensive.

There is therefore a need for amine-functional organosilicon compounds which can be prepared in a simpler and less expensive way. In particular, compounds of interest which can be prepared via a hydrosilylierungsfreien way. Another important requirement for industrial use is that the amine-functional organosilicon compounds are stable upon storage.

Polysiloxanes having aminoalkyl groups which are linked to the silicon via an oxygen atom are disclosed in US Pat US 6482912 and in the US 3338859 described. The compounds described there are, as in Macromol. Rapid Commun. 2001, 22, 655 and Athens Conference on Coatings 2001, 411-418 , reported is not storage stable. For a technical application, the compounds are therefore not suitable. In the US 3338859 Furthermore, a compound is described in which the amino group is connected via a Cyclohexyloxyrest with the silicon of the organosilicon compound. A disadvantage of this compound is that it is present as a mixture of diastereomers, which have different chemical properties. Subsequent reactions at the amino group may therefore be uneven.

The invention relates to aminoalkyl-functional organosilicon compounds in which the aminoalkyl groups are connected via an oxygen atom with the silicon of the organosilicon compounds, wherein the carbon atom adjacent to the oxygen atom of the aminoalkyl carries one or two further hydrocarbon radicals, wherein the number of carbon atoms of the two further hydrocarbon radicals together at least is two.

It has surprisingly been found that amine-functional organosilicon compounds in which the aminoalkyl group is connected via an oxygen atom with the silicon of the organosilicon compound, wherein the carbon atom adjacent to the oxygen atom carries one or two further hydrocarbon radicals, wherein the number of carbon atoms of the one or both further radicals together is at least two, storage stable compounds.

Preferably, the number of carbon atoms of the one or more further hydrocarbon radicals at the carbon atom adjacent to the oxygen atom of the aminoalkyl group is two, three or four.

The invention relates in particular to amine-functional organosilicon compounds consisting of at least one unit of general formula I and none or at least one unit of general formula II R ² _b [OC (R ³ R ⁴ ) -R ⁵ -N (R ⁶ R ⁷ )] _c SiO _{(4- (b + c) 3/2} (I), R ¹ _a SiO _{(4-a) / 2} (II), in which
R ^{x is} hydrogen or a C ₁ -C ₁₀ -hydrocarbon radical which is unsubstituted or substituted by substituents selected from -CN and halogen,
R ¹ and R ² independently of one another are hydrogen atoms or unsubstituted or with substituents which are selected from -CN, NR ^x ₂ , COOH, COOR ^x , -halo, -acryl, -epoxy, -SH, -OH and -CONR ^x ₂ substituted C ₁ -C ₂₀ hydrocarbon radicals or C ₁ -C ₁₅ -hydrocarbonoxy radicals in which in each case one or more methylene units which are not adjacent to one another can be replaced by groups -O-, -CO-, -COO-, -OCO- or -OCOO-, -S- or NR ^x ,
R ³ and R ⁴ independently of one another denote hydrogen or C ₁ -C ₂₀ -hydrocarbon radicals in which in each case one or more, non-adjacent methylene units are represented by -O-, -CO-, -COO-, -OCO- or -OCOO-, groups -S-, or NR ^x can be replaced, with the proviso that the number of carbon atoms of the two radicals is at least two,
R ⁵ C ₁ -C ₂₀ -hydrocarbon radical, in each of which one or more, non-adjacent methylene units represented by groups -O-, -CO-, -COO-, -OCO- or -OCOO-, -S-, or NR ^x can be replaced
R ⁶ and R ^{7 are} hydrogen or unbranched, branched or cyclic saturated or unsaturated alkyl group having 1 to 12 C atoms or aryl group or aralkyl group, wherein individual non-adjacent methylene units may be replaced by nitrogen atoms or oxygen atoms,
a is 0, 1, 2 or 3,
b the values 0, 1 or 2,
c the values 1, 2 or 3 and
b + c is 1, 2, 3 or 4.

R ¹ and R ² preferably have 1 to 12 atoms, in particular 1 to 6 atoms, preferably only carbon atoms or an alkoxy oxygen atom and otherwise only carbon atoms. Preferably, R ¹ and R ^{2 are} straight-chain, branched or cyclic C ₁ -C ₆ -alkyl or alkoxy radicals. Particularly preferred are the radicals methyl, ethyl, phenyl, vinyl, trifluoropropyl, methoxy, ethoxy and i-propoxy. The radicals R ¹ and R ² may be the same or different on the same silicon atom.

R ³ and R ⁴ preferably have 1 to 12 atoms, in particular 1 to 6 atoms, preferably only carbon atoms or an alkoxy oxygen atom and otherwise only carbon atoms. When R ³ is a hydrogen atom, then R ⁴ must have and when R ⁴ is a hydrogen atom, then R ³ must be at least two carbon atoms contain at least two carbon atoms. Preferably, R ³ and R ^{4 are} straight-chain, branched or cyclic C ₁ -C ₆ -alkyl radicals or aryl radicals, particularly preferably the radicals methyl, ethyl and propyl.

The radical R ⁵ is preferably a C-bonded C ₁ -C ₆ -hydrocarbon radical in each of which one or more non-adjacent methylene units can be replaced by groups -O-, -S- or -NR ^x -. Preferably, R ^{5 is} a straight-chain or branched alkyl radical. More preferably, the alkylene radicals are methylene, ethylene, propylene, butylene, CH ₂ -NH-CH ₂ -CH ₂ , CH ₂ -NH-CH ₂ -CH ₂ -CH ₂ , CH ₂ -CH ₂ -NH-CH ₂ -CH ₂ -CH ₂ , CH ₂ -CH ₂ -NH-CH ₂ -CH ₂ and CH ₂ -CH ₂ -NH-CH ₂ .

R ⁶ and R ⁷ are preferably independently of one another hydrogen or unbranched, branched or cyclic saturated or unsaturated alkyl group having 1 to 6 C atoms or aryl groups, non-adjacent methylene units being able to be replaced by nitrogen atoms or oxygen atoms.

More preferably, R ⁶ and R ^{7 are} independently hydrogen or C ₁ -C ₅ alkyl group, wherein individual non-adjacent methylene groups may be replaced by nitrogen atoms, in particular the radicals methyl, ethyl and propyl. Most preferably, R ⁶ and R ^{7 are} hydrogen.

The amino-functional organosiloxanes of units of the general formulas I and II can be linear, branched, cyclic, bicyclic, tricyclic or polycyclic.

The amino-functional organosiloxanes of units of the general formulas I and II preferably contain 1 to 20, in particular 2 to 10 units of the general formula I. The amino-functional organosiloxanes preferably contain 1 to 500, particularly preferably 4 to 200, in particular 10 to 100 units of the general formula II.

Preferably, at least 90%, in particular at least 95% of the units of the general formula II a is 2.

For the amine-functional organosilicon compounds according to the invention, no technically suitable simple production process existed hitherto.

The US 6482912 and WO 02/060972 describe the preparation of non-inventive polysiloxanes having aminoalkyl groups linked to the silicon via an oxygen atom by dehydrogenating linkage of an H-siloxane and an aminoalcohol using a rhodium compound as a catalyst. Although this route is hydrosilylation-free, it does not represent any improvement over hydrosilylation since a noble metal catalyst, in this case even the extremely expensive rhodium, and an H-functional siloxane are also required. In addition, the formation of hydrogen during the reaction also poses high safety requirements. In addition, the reaction is necessary to achieve high yields reaction complex: to avoid autocatalysis by free amino groups, the reaction solution from the frozen state can be heated very quickly to 80 ° C, at this temperature, the desired reaction takes place. These conditions can not be realized on an industrial scale.

There was therefore also a need for a simple and inexpensive access route to the amine-functional organosilicon compounds according to the invention.

Tacke describes in Liebigs Ann Chem. 1982, 1706-1711 the reaction of 1,3-dichloro-1,1,3,3-tetramethyldisiloxane with a tertiary amine, the N, N-dimethylaminoethanol, to give the compound N, N '- (4,4,6,6-tetramethyl-3 , 5,7-trioxa-4,6-disilanonamethylen) bis (dimethylamine,) wherein it uses five times the molar amount of a tertiary amine as the base. However, the use of bases, especially organic bases such as tertiary amines, in high excess is uneconomical for a technical process. According to the Tacke protocol, the amine hydrochloride formed in the reaction is also separated off as a solid by filtration. However, solid filtrations are complex in technical processes and therefore make the entire process considerably more expensive.

It has now surprisingly been found that the amine-functional organosilicon compounds according to the invention can be prepared in a simple manner by reacting halogen-functional organosilicon compounds and amino alcohols without the additional use of amine bases in high yields.

The invention therefore also provides a process for the preparation of the compounds from at least one unit of the general formula I. R ² _b [OC (R ³ R ⁴ ) -R ₅ -N (R ⁶ R ⁷ )] _c SiO _{(4- (b + c)] / 2} (I), and none or at least one unit of the general formula II in which halogen-functional organosilicon compounds consisting of at least one unit of the general formula III and none or at least one unit of the general formula II R ¹ _a SiO _{(4-a) / 2} (II), R ² _b X _c SiO _{[4- (b + c)] / 2} (III), with amino alcohols of the general formula IV HO-C (R ³ R ⁴ ) -R ⁵ -N (R ⁶ R ⁷ ) (IV) be reacted, wherein the radicals R, R ¹ to R ⁷ , a, b and c have the abovementioned meanings, and
X is halogen, preferably Cl.

Chloro-functional siloxanes are produced on an industrial scale, they arise in the incomplete hydrolysis of chlorosilanes with water or in the reaction of hydroxysiloxanes with chlorosilanes.

The amino alcohols used are in a simple manner, for example by reaction of ammonia or amines with epoxides, eg. As 1,1-dimethylethylene oxide or n-butylene oxide in good yields available.

The aminoalcohol of the general formula IV is preferably used in proportions of from 0.1 to 2 equivalents, more preferably in proportions of from 0.5 to 1.5 equivalents, based on the molar amount of Si-bonded chlorine in the units of the general formula III. When using a molar deficit of amino alcohol remain Si-Cl groups in the reaction mixture, which can then optionally be converted in the presence of water or alcohols into other alkoxysilane or Siloxangruppierungen.

The reaction is preferably carried out at temperatures between 0 and 180 ° C., more preferably between 20 and 150 ° C., and pressures preferably between 100 mbar and 10 bar, more preferably between 1 and 5 bar. The reaction times are preferably 1 minute to 8 hours, more preferably 10 minutes to 4 hours.

The reaction can be carried out in batch mode or in semi-batch mode or continuously. Preference is given to one of the two reactants, preferably the halogen-functional organosilicon compound, and then the second component, preferably the amino alcohol added. After the reaction of the aminosilane with the halogen-functional organosilicon compound to remove hydrochloric acid are preferably alkali metal or alkaline earth metal hydroxides, oxides or carbonates, preferably of sodium, potassium, calcium or magnesium, more preferably of sodium and potassium, preferably in amounts of 0.9 to 1.4 equivalents, more preferably in amounts of 0.95 to 1.1 equivalents, each based on the molar amount of chloride present. Unreacted Si-Cl groups react to form the corresponding Si-OH or Si-O-Si groups. The bases are preferably used as aqueous solutions. The salts formed in the reaction of the hydrohalic acid with the base can then be separated off in a simple manner with the aqueous phase. In the reaction or in the work-up, it is possible to use further components, for example solvents, in amounts of at least 1% and at most 200%, preferably at least 10% and at most 100%, based on the total reaction mass be used. Examples of solvents are aprotic solvents, preferably linear or cyclic, saturated or unsaturated hydrocarbons, eg. As pentane, cyclohexane, toluene, ethers such as methyl tert-butyl ether, anisole, tetrahydrofuran or dioxane, halogenated hydrocarbons such as dichloromethane, 1,2-dichloroethane or chlorobenzene, nitriles such as acetonitrile or propionitrile, or DMSO.

Following the process of the invention, equilibration reactions may be carried out to achieve the desired molecular weight of the amine-functional organosilicon compound. The equilibration reactions may be carried out in the manner known to those skilled in the art. As a rule, linear or branched hydroxy-containing polysiloxanes or cyclic siloxanes or mixtures of these are used in the presence of suitable catalysts known to the person skilled in the art.

All the above symbols of the above formulas each have their meanings independently of each other. In all formulas, the silicon atom is tetravalent.

In the following examples, unless otherwise indicated, all amounts and percentages are by weight, all pressures are 0.10 MPa (abs.) And all temperatures are 20 ° C.

Example 1 (not according to the invention), preparation of the amino alcohols, formula IV

80.5 g (1.12 mol) of 1,1-dimethyl ethylene oxide are reacted with 381 g (22.4 g) of ammonia in 151 g of water in an autoclave for 1 hour at 80 ° C. It is then fractionally distilled. This gives 79.4 g (80%) of 1-amino-2-methyl-propan-2-ol (IV with R ³ = R ⁴ = methyl, R ⁵ = CH ₂ , R ⁶ = R ⁷ = H) with Sdp 59 ° C / 20 mbar.

In an analogous manner, 1-aminobutan-2-ol (IV with R ³ = ethyl, R ⁴ = H, R ⁵ = CH ₂ , R ⁶ = R ⁷ = H) is prepared from 1-butylene oxide. 1- (N- (2-amino) ethyl) -aminobutan-2-ol (IV with R ³ = R ⁴ = methyl, R ⁵ = CH _2, R ⁶ = H, R ⁷ = CH ₂ -CH ₂ -NH ₂ ) with bp 100 ° C / 10 mbar is obtained by reacting 1,1-dimethyl ethylene oxide with 5 equivalents of ethylenediamine at room temperature and subsequent fractional distillation in 79% yield.

Example 2

9.8 g of α, ω-chlorine-terminated linear polydimethylsiloxane having a M _n of 1210 g / mol, determined by ¹ H-NMR spectroscopy, corresponding to 16.3 mmol of Si-Cl groups, are heated to 80 ° C. under argon heated and with stirring with 1.59 g (17.9 mmol) of 1-amino-2-methyl-propan-2-ol (IV with R ³ = R ⁴ = methyl, R ⁵ = CH ₂ , R ⁶ = R ⁷ = H). The temperature rises briefly up to about 100 ° C. The mixture is stirred for 2 hrs. At 80 ° C on, then cooled to 60 ° C and then with vigorous stirring 1 N NaOH until the pH is about 10 to 10.5. This requires about 16.2 ml of NaOH solution. The phases are separated, the siloxane phase is washed with 10 ml of saline solution and volatilized under reduced pressure at 110 ° C./20 mbar. 10.3 g of amine-functionalized oil are obtained.
¹ H-NMR (D ₆ -benzene): δ = 0.046 m (SiMe ₂ ) _n 0.061 s (SiMe ₂ ), 0.076 (s, SiMe ₂ ), 1.22 (s, CMe ₂ ), 2.52 (s , -CH ₂ -).
²⁹ Si NMR (CDCl ₃ ): δ = -22.65, -22.37, -22.07, -19.17 (OSiMe ₂ -O-CMe ₂ )

Example 3

50.1 g of α, ω-chlorine-terminated linear polydimethylsiloxane having a M _n of 2723 g / mol, determined by ¹ H-NMR spectroscopy, corresponding to 18.4 mmol of Si-Cl groups, are heated to 80 ° C. under argon heated with stirring and 4.10 g (46.0 mmol) of 1-amino-2-methyl-propan-2-ol (IV with R ³ = R ⁴ = methyl, R ⁵ = CH ₂ , R ⁶ = R ⁷ = H). The temperature rises briefly up to about 90 ° C. The mixture is stirred for 2 hrs. At 100 ° C on, then cooled to 80 ° C, diluted with 150 ml of toluene, transferred to a separatory funnel, add 37 ml of 1 N NaOH and shake the mixture. The aqueous phase is separated and the organic phase washed twice with water and then evaporated on a rotary evaporator under reduced pressure. This gives 44 g of amine-functionalized oil.
¹ H-NMR (D ₆ -benzene): δ = 0.046 m (SiMe ₂ ) _n , 0.061 s (SiMe ₂ ), 0.076 (s, SiMe ₂ ), 1.22 (s, CMe ₂ ), 2.52 ( s, -CH ₂ -).
²⁹ Si NMR (CDCl ₃ ): δ = -22.65, -22.37, -22.07, -19.17 (OSiMe ₂ -O-CMe ₂ )

After storage for 6 months at room temperature, no change in the ¹ H NMR spectrum occurred.

Example 4

50.0 g of α, ω-chlorine-terminated linear polydimethylsiloxane having a M _n of 2494 g / mol, determined by ¹ H-NMR spectroscopy, corresponding to 20.1 mmol of Si-Cl groups, under argon to 80 ° C. heated and with stirring within 7 min with 3.93 g (44.1 mmol) of 1-aminobutan-2-ol (IV with R ³ = ethyl, R ⁴ = H, R ⁵ = CH ₂ , R ⁶ = R ⁷ = H). The temperature rises briefly up to about 103 ° C. The mixture is stirred for a further 1 h at 100 ° C, treated with 150 ml of toluene, then cooled to room temperature, mixed with 28.5 ml of 1 N NaOH and the mixture is shaken out. The aqueous phase is separated and the organic phase is extracted twice with water washed and then evaporated on a rotary evaporator under reduced pressure. The residue obtained is the amine-functionalized oil.
¹ H-NMR (CDCl ₃ ): δ = 0.050 m (SiMe ₂ ) _n , 0.104 s (SiMe ₂ ), 0.874 (t, CH ₃ ), 1.09 (broad, NH ₂ ), 1.47 (m, -CH ₂ -), 2.60 and 2.70 (AB, CH ₂ -N).

Example 5

25.0 g of α, ω-chlorine-terminated linear polydimethylsiloxane having a M _n of 2723 g / mol, determined by ¹ H-NMR spectroscopy, corresponding to 18.4 mmol of Si-Cl groups, are heated to 80 ° C. under argon heated with stirring in about 6 min with 3.03 g (23.0 mmol) of 1- (N- (2-amino) ethyl) -aminobutan-2-ol (IV with R ³ = R ⁴ methyl, R ⁵ = CH ₂ -NH-CH ₂ -CH ₂ , R ⁶ = H, R ⁷ = H). The temperature rises briefly up to about 84 ° C. It is diluted with 10 ml of toluene and stirred for 2 h at 100 ° C, then cooled to 55 ° C, further diluted with 30 ml of toluene and added in a separating funnel in portions with 1 N NaOH, being shaken in between until the pH Value is about 10 to 10.5. It will require about 18 ml of NaOH solution. The phases are separated, the toluene phase is washed twice with 10 ml of water and distilled toluene on a rotary evaporator in vacuo. This gives 21.7 g of amine-functionalized oil and volatilized under reduced pressure at 110 ° C / 20 mbar. 20.3 g of amine-functionalized oil are obtained.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The 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

• US 6482912 [0005, 0019]
• US 3338859 [0005, 0005]
• WO 02/060972 [0019]

Cited non-patent literature

• Macromol. Rapid Commun. 2001, 22, 655 and Athens Conference on Coatings 2001, 411-418 [0005]
• Liebigs Ann Chem. 1982, 1706-1711 [0021]

Claims (7)

Aminoalkyl-functional organosilicon compounds in which the aminoalkyl groups are connected via an oxygen atom with the silicon of the organosilicon compounds, wherein the carbon atom of the aminoalkyl group adjacent to the oxygen atom carries one or two further hydrocarbon radicals, the number of carbon atoms of the two other hydrocarbon radicals together being at least two. Amine-functional organosilicon compounds according to claim 1, consisting of at least one unit of general formula I and none or at least one unit of general formula II R ² _b [OC (R ³ R ⁴ ) -R ⁵ -N (R ⁶ R ⁷ )] _c SiO _{[4- (b + c)] / 2} (I) R ¹ _a SiO _{(4-a) / 2} (II) where R ^{x is} hydrogen or a C ₁ -C ₁₀ -hydrocarbon radical which is unsubstituted or substituted by substituents selected from -CN and halogen, R ¹ and R ² independently of one another are hydrogen atoms or unsubstituted or having substituents which are selected from -CN, NR ^x ₂ , COOH, COOR ^x , -halo, -acryl, -epoxy, -SH, -OH and -CONR ^x ₂ substituted C ₁ -C ₂₀ hydrocarbon radicals or C ₁ -C ₁₅ -hydrocarbonoxy radicals, in each of which one or a plurality of non-adjacent methylene units may be replaced by groups -O-, -CO-, -COO-, -OCO-, -OCOO-, -S-, or NR ^x , R ³ and R ⁴ independently of one another are hydrogen or C ₁ -C ₂₀ -hydrocarbon radicals in each of which one or more non-adjacent methylene units can be replaced by groups -O-, -CO-, -COO-, -OCO- or -OCO-, -S- or NR ^x , with the proviso that the number of carbon atoms of the two radicals is at least two, R ^{5 is} C ₁ -C ₂₀ Hydrocarbon radical in which in each case one or more, non-adjacent methylene units can be replaced by groups -O-, -CO-, -COO-, -OCO- or -OCOO-, -S- or NR ^x , R ⁶ and R ^{7 is} hydrogen or straight, branched or cyclic saturated or unsaturated alkyl group having 1 to 12 C atoms or aryl group or aralkyl group, wherein individual non-adjacent methylene units may be replaced by nitrogen atoms or oxygen atoms, a is the values 0, 1, 2 or 3, b the values 0, 1 or 2, c the values 1, 2 or 3 and b + c 1, 2, 3 or 4 mean. Amine-functional organosilicon compounds according to Claim 2, in which R ¹ and R ^{2 are} straight-chain, branched or cyclic C ₁ -C ₆ -alkyl or alkoxy radicals, or phenyl or vinyl radicals. Amine-functional organosilicon compounds according to Claim 2 or 3, in which R ³ and R ^{4 are} straight-chain, branched or cyclic C ₁ -C ₆ -alkyl radicals or aryl radicals. Amine-functional organosilicon compounds according to claim 2 or 3, which contain 1 to 6 units of the general formula I and 1 to 200 units of the general formula II. A process for the preparation of the compounds according to claim 2 from at least one unit of general formula I. R ² _b [OC (R ³ R ⁴ ) -R ⁵ -N (R ⁶ R ⁷ )] _c SiO _{[4- (b + c)] / 2} (I), and none or at least one unit of the general formula II in which halogen-functional organosilicon compounds consisting of at least one unit of the general formula III and none or at least one unit of the general formula II R ¹ _a SiO _{(4-a) / 2} (II), R ² _b X _c SiO _{(4- (b + c)] / 2} (III), with amino alcohols of the general formula IV HO-C (R ³ R ⁴ ) -R ⁵ -N (R ⁶ R ⁷ ) (IV), are reacted, wherein the radicals R, R ¹ to R ⁷ , a, b and c have the meanings mentioned in claim 2, and X is halogen. Process according to claim 6, wherein the reaction is carried out between 20 and 150 ° C.