DE10050880B4 - pyridine derivatives - Google Patents

Abstract

Pyridine derivatives of the formulas Ia1 and Ia2worin Ra1 and Ra2 are H or alkyl having 1 to 6 C atoms, Rb1 is H, tert-butyl or tert-pentyl, Rb2 is H or tert-butyl.

Description

worin
R^a1 und R^a2 H oder Alkyl mit 1 bis 6 C-Atomen,
R^b1 H, tert.-Butyl oder tert.-Pentyl,
R^b2 H oder tert.-Butyl,
bedeuten.The present invention relates to pyridine derivatives Formulas Ia1 and Ia2

wherein
R ^a1 and R ^{a2 are} H or alkyl having 1 to 6 C atoms,
R ^{b1 is} H, tert-butyl or tert-pentyl,
R ^{b2 is} H or tert-butyl,
mean.

worin
R^a, R^b und R^c jeweils unabhängig voneinander H, einen unsubstituierten oder mit CN oder mit mindestens einem Halogen substituierten Alkyl- oder Alkenylrest mit bis zu 12 C-Atomen, worin ein oder mehrere nicht benachbarte CH₂-Gruppen durch einen Rest ausgewählt aus der Gruppe -O-, -S-, -CO-, -O-CO-, -CO-O- und -C≡C- ersetzt sein können, und
m und n jeweils unabhängig voneinander 0, 1 oder 2,
bedeuten.Another object of the invention are liquid crystal mixtures containing compounds of general formula I.

wherein
R ^a , R ^b and R ^{c are} each independently H, an unsubstituted or substituted by CN or at least one halogen alkyl or alkenyl radical having up to 12 carbon atoms, wherein one or more non-adjacent CH ₂ groups selected by a radical from the group -O-, -S-, -CO-, -O-CO-, -CO-O- and -C≡C- may be replaced, and
m and n are each independently 0, 1 or 2,
mean.

The stabilization of acid labile liquid crystals or liquid crystalline mixtures containing acid labile components is often a problem.

The stabilizers for the purposes mentioned must not be toxic, should exhibit high efficacy at low concentrations, do not cause changes in taste, odor and color, even during prolonged storage or heating, they should be readily soluble or easily dispersible in the substrate , have no adverse effect on the substance to be protected, have a low volatility and can be detected as quantitatively as possible analytically.

Furthermore, the stabilizers should be easy and inexpensive to produce and easy to handle and incorporate.

Object of the present invention was therefore to find inexpensive stabilizers that meet all the conditions mentioned.

Surprisingly, it has now been found that pyridine derivatives of the formula I have a high activity as a stabilizer even at low concentrations, without exerting an adverse effect on the substance to be protected. Furthermore, the partially sterically hindered pyridines according to the invention are distinguished by their temperature resistance, their low viscosity and their volatility.

The invention therefore provides pyridine derivatives of the formulas Ia1 and Ia2. The invention further relates to liquid-crystal mixtures which contain pyridine derivatives of the formula I. Pyridine derivatives of the formula I are distinguished as stabilizers of liquid crystals or liquid-crystalline mixtures because of their basic properties and their structure. By virtue of the substituent in the 4-position, it is possible to achieve liquid-crystalline properties of the stabilizer itself. Simple 4-alkyl or alkoxy-substituted derivatives of pyridine such. B. 4-Octylpyridine are described in the literature, for example in Kaszynski, P .; Huang, J .; Jenkins, G.S. Bairamov, K.A .; Lipiak, D, Molecular Crystals and Liquid Crystals Science and Technology, Section A: Molecular Crystals and Liquid Crystals (1995), 260, 315-32 for the synthesis of liquid crystalline boron clusters.

Due to their structure, these materials have a particularly low vapor pressure and can therefore be used even at high temperatures. They are as well as their reaction products, colorless and thus do not lead to any discoloration of the materials to be stabilized.

In a preferred embodiment of the present invention, the liquid-crystal mixtures comprise compounds of the formula I selected from the compounds of the formula I1, I2 and I3

Most preferably, the liquid-crystal mixtures contain compounds of the formula I selected from the compounds of the abovementioned formula Ia1 and Ia2.

In the compounds of the formula I, the sum of n + m is preferably 0, 1, 2 or 3. In the case n ≠ 0, m is preferably 1. R ^b and R ^c are preferably H, primary, secondary or tertiary alkyl or alkenyl radicals.

If R ^a , R ^a1 , R ^a2 , R ^b and / or R ^{c is} an alkyl radical and / or an alkoxy radical, this may be straight-chain or branched. Preferably, R ^{a is} a straight-chain alkyl radical, and R ^b and R ^c are preferably tertiary alkyl radicals. The radicals have 1, 2, 3, 4, 5, 6 or 7 carbon atoms and accordingly preferably denote methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy.

Oxaalkyl is preferably straight-chain 2-oxapropyl (= methoxymethyl), 2 - (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5- Oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxo-octyl, 2-, 3-, 4-, 5-, 6 -, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If R ^a , R ^b and / or R ^{c is} an alkyl radical in which one CH ₂ group has been replaced by -CH = CH-, this may be straight-chain or branched. It is preferably straight-chain and has 2 to 10 C atoms. It therefore means especially vinyl, prop-1, or prop-2-enyl, but-1, 2- or but-3-enyl, pent-1, 2-, 3- or pent-4-enyl, hex 1-, 2-, 3-, 4- or hex-5-enyl, hept-1, 2-, 3-, 4-, 5- or hept-6-enyl, Oct-1, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, Dec-1 -, 2-, 3-, 4-, 5-, 6-, 7-, 8- or dec-9-enyl.

If R ^a , R ^b and / or R ^{c is} an alkyl radical in which one CH ₂ group has been replaced by -O- and one by -CO-, these are preferably adjacent. Thus, they include an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. Preferably, these are straight-chain and have 2 to 6 carbon atoms.

They therefore particularly mean acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, Propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxycarbonyl) ethyl, 3- (methoxycarbonyl) propyl, 3- (ethoxycarbonyl) propyl, 4 - (methoxycarbonyl) butyl.

If R ^a , R ^b and / or R ^{c is} an alkyl radical in which a CH ₂ group is replaced by unsubstituted or substituted -CH = CH- and an adjacent CH ₂ group by CO or CO-O or O-CO , it may be straight-chain or branched. Preferably, it is straight-chain and has 4 to 13 carbon atoms. It therefore particularly means acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxyethyl, 3 Methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl, 9-methacryloyloxynonyl.

If R ^a , R ^b and / or R ^{c is} an alkyl or alkenyl radical which is at least monosubstituted by halogen, this radical is preferably straight-chain and halogen is preferably F or Cl. In the case of multiple substitution, halogen is preferably F. The resulting radicals also include perfluorinated radicals. For single substitution, the fluoro or chloro substituent may be in any position, but preferably in the ω position.

Branched radicals R ^a , R ^b and / or R ^c usually contain no more than two chain branches. Preferred branched radicals R ^a , R ^b and / or R ^c are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 1-methylheptoxy, t -butyl or t-pentyl.

If R ^a , R ^b and / or R ^{c is} an alkyl radical in which two or more CH ₂ groups have been replaced by -O- and / or -CO-O-, this may be straight-chain or branched. Preferably, it is branched and has 3 to 12 carbon atoms. It therefore particularly denotes bis-carboxy-methyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl, 4,4-bis-carboxy-butyl, 5,5-bis-carboxy-pentyl, 6,6-bis-carboxy-hexyl, 7,7-bis-carboxy-heptyl, 8,8-bis-carboxy-octyl, 9,9-bis-carboxy-nonyl, 10,10-bis-carboxy-decyl, Bis (methoxycarbonyl) methyl, 2,2-bis (methoxycarbonyl) ethyl, 3,3-bis (methoxycarbonyl) propyl, 4,4-bis (methoxycarbonyl) butyl, 5,5-bis (methoxycarbonyl) pentyl, 6,6-bis (methoxycarbonyl) hexyl, 7,7-bis (methoxycarbonyl) heptyl, 8,8-bis (methoxycarbonyl) octyl, bis (ethoxycarbonyl) methyl, 2,2-bis (ethoxycarbonyl) ethyl, 3,3-bis (ethoxycarbonyl) propyl, 4,4-bis (ethoxycarbonyl) butyl, 5,5-bis (ethoxycarbonyl) hexyl.

In formula I as well as in the preferred sub-formulas, R ^{a is} preferably straight-chain alkyl, alkoxy, alkenyl having up to 6 C atoms. The radicals R ^b and / or R ^{c are} in particular H, tert-butyl or tert-pentyl. Especially preferred are compounds wherein R ^b = R ^c .

Particular preference is given to the compounds of the formulas I1, I2 and I3 in which R ^a and R ^b denote secondary or tertiary alkyl radicals.

The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg Thieme Verlag, Stuttgart) under reaction conditions, which are known and suitable for the said reactions. One can also make use of known per se, not mentioned here variants.

The compounds of the invention may, for. B. be prepared according to Scheme 1: Scheme 1

The compounds of the formula I have a wide range of applications. They can easily be used as stabilizers in the food industry and in technical products.

The invention also provides the use of the compounds according to the invention as an additive to liquid-crystal mixtures, liquid-crystalline individual components, lubricants, heat carriers, fuels, pharmaceutical products, vitamin preparations, cosmetics, foods, dyes, paints, polymers, elastomers, detergents, solvents, paper and pesticides.

The compounds of the formula I are added in concentrations of from 0.01 to 5% by weight, preferably 0.01 to 2% by weight, and in particular 0.01 to 1% by weight, to the substance to be stabilized.

Due to the rod-shaped structure, the compounds of the formula I are particularly suitable as stabilizers of liquid-crystalline individual components and liquid-crystal mixtures, since they disturb the liquid-crystalline properties far less than the stabilizers of the prior art.

Since the compounds according to the invention have a particularly low vapor pressure, they can also be used at high temperatures. They have similar properties as liquid crystals and do not lead to discoloration in the liquid-crystal mixtures. In contrast to known stabilizers, they do not have a negative effect on the clearing point of the liquid-crystalline individual components.

The stabilization of the liquid crystals or liquid crystal mixtures is carried out in a conventional manner. In general, all components are dissolved together, preferably at elevated temperature.

The stabilizers according to the invention are preferably used in liquid-crystal mixtures for active-matrix displays, since they do not lead to any appreciable impairment of the voltage holding ratio.

In particular, the stabilizers according to the invention are suitable for increasing the thermal stability of compounds which have the following structural units:

The invention therefore also provides a liquid-crystalline medium which contains at least two liquid-crystalline compounds and additionally a pyridine of the formula I.

The liquid-crystalline medium according to the invention generally consists of 2 to 25, preferably 3 to 15 liquid crystal components and a stabilizer of formula I. However, in individual cases, more than 25 components may be components of a phase according to the invention, for. B. up to 50 components and more. The other constituents are preferably selected from the nematic or nematogenic substances, in particular the known substances, from the classes of azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, cyclohexane-carboxylic acid phenyl or cyclohexyl esters, phenylcyclohexanes, cyclohexylbiphenyls, cyclohexylcyclohexanes, cyclohexylnaphthalenes , Decahydronaphthalenes, 1,4-biscyclohexylbenzenes, 4,4'-biscyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyldithiane, 1,2-bisphenylethanes, 1,2-bis-cyclohexylethanes, 1-phenyl-2-cyclohexylethanes , optionally halogenated stilbenes, benzylphenyl ethers, tolans and substituted cinnamic acids.

The most important compounds which can be used as constituents of liquid-crystalline phases according to the invention can be characterized by the formula II, R ^{1 *} -LGER ^{2 *} II in which L and E are each a carbo- or heterocyclic ring system composed of 1,4-disubstituted benzene and cyclohexane rings, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro- 1,4-phenylene, 4,4'-disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexane systems, 2,5-disubstituted pyrimidine and 1,3-dioxane rings, 2,6-disubstituted naphthalene, di- and tetrahydronaphthalene, quinazoline and tetrahydroquinazoline formed Group, G -CH = CH- -N (O) = N- -CH = CY- -CH = N (O) - -C≡C- -CH ₂ -CH ₂ - -CO-O- -CH ₂ -O- -CO-S- -CH ₂ -S- -CH = N- -COO-Phe-COO- or a CC single bond, Y is halogen, preferably fluorine or chlorine, or -CN, and R ¹ and R ^{2 are} unsubstituted or substituted by one or more fluorine atoms alkyl, alkoxy, alkanoyloxy or alkoxycarbonyloxy having up to 18, preferably up to 8 carbon atoms, or one of these radicals is also CN, NO ₂ , CF ₃ , F, Cl or Br.

In most of these compounds R ^{1 *} and R ^{2 *} are different from each other, one of these radicals is usually an alkyl or alkoxy group and the other alkyl, alkenyl, alkoxy, CN, F, Cl, OCF ₃ , OCHF ₂ , OCH ₂ CF ₃ , OCHFCF ₃ , OCF ₂ CHFCF ₃ , OCH = CF ₂ , OCF = CF ₂ or CH = CF ₂ . But other variants of the proposed substituents are in use. Many such substances or mixtures thereof are commercially available. All these substances can be prepared by methods known from the literature or in analogy thereto.

In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms, wherein the transformation into chemical formulas according to following Tables A and B takes place. All radicals C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl radicals with n or m C atoms. The coding according to Table B is self-evident. In Table A, only the acronym for the main body is given. In the individual case, a code for the substituents R ¹ , R ² , L ¹ and L ² follows separately from the acronym for the main body with a dash: Code for R ¹ , R ² , L ¹ , L ² R ¹ R ² L ¹ L ² nm C _n H _{2n + 1} C _m H _{2m + 1} H H n Om C _n H _{2n + 1} OC _m H _{2m + 1} H H nO.m OC _n H _{2n + 1} C _m H _{2m + 1} H H n C _n H _{2n + 1} CN H H nN.F C _n H _{2n + 1} CN H F nF C _n H _{2n + 1} F H H nOF OC _n H _{2n + 1} F H H n Cl C _n H _{2n + 1} Cl H H nF.F C _n H _{2n + 1} F H F nF.FF C _n H _{2n + 1} F F F nCF ₃ C _n H _{2n + 1} CF ₃ H H nOCF ₃ C _n H _{2n + 1} OCF ₃ H H nOCF ₂ C _n H _{2n + 1} OCHF ₂ H H nS C _n H _{2n + 1} NCS H H RVSN C _r H _{2r + 1} -CH = CH-C _s H _2s - CN H H rESn C _r H _{2r + 1} -OC ₂ H _2s - CN H H nAm C _n H _{2n + 1} COOC _m H _{2m + 1} H H nOCCF ₂ .FF C _n H _{2n + 1} OCH ₂ CF ₂ H F F

Tabelle B:

Preferred mixture components are given in Tables A and B: TABLE A

Table B:

The following examples are intended to illustrate the invention without limiting it. "Working up" means adding water, extracting with dichloromethane, separating, drying the organic phase, evaporating and purifying the product by crystallization and / or chromatography. Above and below mean percentages by weight. All temperatures are in degrees Celsius. Mp. Means melting point and Kp. = Clearing point. Furthermore, K = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The data between these symbols represent the transition temperatures. Δn means optical anisotropy (589 nm, 20 ° C). The viscosity (mm ² / sec) was determined at 20 ° C.

BuLi

Butyllithium

DAST

Diethylaminoschwefeltrifluorid

DCC

Dicyclohexylcarbodiimid

DIBALH

Diisobutylaluminiumhydrid

DMAP

2-Dimethylaminopyridin

DDQ

Dichlordicyanobenzochinon

KOT

Kalium-tertiär-butanolat

NH₄Cl

Ammoniumchlorid

THF

Tetrahydrofuran

TMEDA

Tetramethylethylendiamin

pTsOH

p-Toluolsulfonsäure

The following abbreviations are used:

BuLi

butyllithium

DAST

diethylaminosulfur

DCC

dicyclohexylcarbodiimide

DIBALH

diisobutylaluminum

DMAP

2-dimethylaminopyridine

DDQ

dichlorodicyanobenzoquinone

KOT

Potassium tert-butoxide

NH ₄ Cl

ammonium chloride

THF

tetrahydrofuran

TMEDA

tetramethylethylenediamine

pTsOH

p-toluenesulfonic acid

I. Examples

example 1

900 ml of THF are cooled to 0 ° C. and, with stirring, 0.388 mol of lithium diisopropylamide, 0.800 mol of 1,3-dimethyl-2-imidazolidinone dissolved in 100 ml of THF and 0.399 mol of 4-methylpyridine dissolved in 100 ml of THF are added. After stirring for 2 h at 0 ° C., 0.400 mol A dissolved in 400 ml THF are slowly added dropwise to the reaction mixture. The mixture is allowed to warm slowly to 20 ° C, diluted with water, neutralized with dil. HCl, and worked up as usual.
K 79 N (77.6) I, Δ∈ = +4.5, Δn = + 0.060

hergestellt: R^a n m R^b R^c C₆H₁₃ 0 0 t-Bu t-Bu C₇H₁₅ 0 0 t-Bu t-Bu C₈H₁₇ 0 0 t-Bu t-Bu C₉H₁₉ 0 0 t-Bu t-Bu C₁₀H₂₁ 0 0 t-Bu t-Bu C₆H₁₃ 0 0 t-Pen t-Pent C₇H₁₅ 0 0 t-Pen t-Pent C₈H₁₇ 0 0 t-Pen t-Pent C₉H₁₉ 0 0 t-Pen t-Pent C₁₀H₂₁ 0 0 t-Pen t-Pent H 1 1 H H CH₃ 1 1 H H C₂H₅ 1 1 H H n-C₃H₇ 1 1 H H n-C₄H₉ 1 1 H H n-C₃H₇ 1 1 H H K 2 I n-C₅H₁₁ 1 1 H H n-C₆H₁₃ 1 1 H H H 1 1 t-Bu t-Bu CH₃ 1 1 t-Bu t-Bu C₂H₅ 1 1 t-Bu t-Bu n-C₃H₇ 1 1 t-Bu t-Bu n-C₄H₉ 1 1 t-Bu t-Bu n-C₅H₁₁ 1 1 t-Bu t-Bu n-C₆H₁₃ 1 1 t-Bu t-Bu H 1 1 t-Pen t-Pen CH₃ 1 1 t-Pen t-Pen C₂H₅ 1 1 t-Pen t-Pen n-C₃H₇ 1 1 t-Pen t-Pen n-C₄H₉ 1 1 t-Pen t-Pen n-C₅H₁₁ 1 1 t-Pen t-Pen n-C₆H₁₃ 1 1 t-Pen t-Pen H 2 1 H H CH₃ 2 1 H H C₂H₅ 2 1 H H n-C₄H₉ 2 1 H H n-C₅H₁₁ 2 1 H H n-C₆H₁₃ 2 1 H H H 2 1 t-Bu t-Bu CH₃ 2 1 t-Bu t-Bu C₂H₅ 2 1 t-Bu t-Bu n-C₃H₇- 2 1 t-Bu t-Bu n-C₄H₉ 2 1 t-Bu t-Bu n-C₅H₁₁ 2 1 t-Bu t-Bu n-C₆H₁₃ 2 1 t-Bu t-Bu Analogously, the following pyridines of the formula

produced: R ^a n m R ^b R ^c C ₆ H ₁₃ 0 0 t-Bu t-Bu C ₇ H ₁₅ 0 0 t-Bu t-Bu C ₈ H ₁₇ 0 0 t-Bu t-Bu C ₉ H ₁₉ 0 0 t-Bu t-Bu C ₁₀ H ₂₁ 0 0 t-Bu t-Bu C ₆ H ₁₃ 0 0 t-Pen t-Pent C ₇ H ₁₅ 0 0 t-Pen t-Pent C ₈ H ₁₇ 0 0 t-Pen t-Pent C ₉ H ₁₉ 0 0 t-Pen t-Pent C ₁₀ H ₂₁ 0 0 t-Pen t-Pent H 1 1 H H CH ₃ 1 1 H H C ₂ H ₅ 1 1 H H nC ₃ H ₇ 1 1 H H nC ₄ H ₉ 1 1 H H nC ₃ H ₇ 1 1 H HK 2 I nc ₅ H ₁₁ 1 1 H H nc ₆ H ₁₃ 1 1 H H H 1 1 t-Bu t-Bu CH ₃ 1 1 t-Bu t-Bu C ₂ H ₅ 1 1 t-Bu t-Bu nC ₃ H ₇ 1 1 t-Bu t-Bu nC ₄ H ₉ 1 1 t-Bu t-Bu nc ₅ H ₁₁ 1 1 t-Bu t-Bu nc ₆ H ₁₃ 1 1 t-Bu t-Bu H 1 1 t-Pen t-Pen CH ₃ 1 1 t-Pen t-Pen C ₂ H ₅ 1 1 t-Pen t-Pen nC ₃ H ₇ 1 1 t-Pen t-Pen nC ₄ H ₉ 1 1 t-Pen t-Pen nc ₅ H ₁₁ 1 1 t-Pen t-Pen nc ₆ H ₁₃ 1 1 t-Pen t-Pen H 2 1 H H CH ₃ 2 1 H H C ₂ H ₅ 2 1 H H nC ₄ H ₉ 2 1 H H nc ₅ H ₁₁ 2 1 H H nc ₆ H ₁₃ 2 1 H H H 2 1 t-Bu t-Bu CH ₃ 2 1 t-Bu t-Bu C ₂ H ₅ 2 1 t-Bu t-Bu nC ₃ H ₇ - 2 1 t-Bu t-Bu nC ₄ H ₉ 2 1 t-Bu t-Bu nc ₅ H ₁₁ 2 1 t-Bu t-Bu nc ₆ H ₁₃ 2 1 t-Bu t-Bu

II. Stability Studies / Influence of Various Stabilizers

Nr. Flüssigkristall Host Stabilisator Ergebnis 1 XIX-3-3 Pentylbenzol - > 125°C stürmische Zers. 2 XIX-3-3 Pentylbenzol 0,1% Pyridin Langsame Zers. > 175°C 3 XIX-3-3 Pentylbenzol 0,5% Pyridin Langsame Zers. bei 205°C 4 XIX-3-3 Pentylbenzol > 0,5% Pyridin Keine Zers. bei 205°C 5 XIX-3-3 Pentylbenzol 0,1% D Sehr langs. Zers. > 135°C 6 XIX-3-3 Pentylbenzol 0,5% D Sehr langs. Zers. > 145°C 7 XIX-3-3 Pentylbenzol 1,0% D Sehr langs. Zers. > 150°C 8 XIX-3-3 Pentylbenzol 2,0% D Sehr langs. Zers. > 155°C 9 XICU-3-F Pentylbenzol 1,0% D Sehr langs. Zers. > 150°C 10 XIX-3-3 Pentylbenzol 0,1% B Sehr langs. Zers. > 150°C 11 XIX-3-3 Pentylbenzol 0,5% B Sehr langs. Zers. > 150°C 12 XIX-3-3 Pentylbenzol 1,0% B Sehr langs. Zers. > 150°C 13 XIX-3-3 Pentylbenzol 0,5% A Sehr langs. Zers. > 140°C 14 XIX-3-3 Pentylbenzol 1,0% A Sehr langs. Zers. 150–170°C 15 XIX-3-3 Pentylbenzol 0,5% C Sehr langs. Zers. > 140°C 16 XIX-3-3 Pentylbenzol 1,0% C Sehr langs. Zers. 150–170°C The addition of 0.1-1% pyridine derivatives increases the thermal capacity of z. B. axially fluorinated cyclohexane derivatives (1) and 2,2-difluoro-1,3-dioxane (2). The temperature from which the decomposition occurs depends also on the host used. For the stability tests, a solution of 10% w / w XIK-3-3 or XICU-3-F was heated in the presence of various stabilizers in the course of 30 minutes in the air. Under exclusion of air, the decomposition of the axial fluorine derivatives only begins at about 50 ° C higher temperature.

No. liquid crystal host stabilizer Result 1 XIX-3-3 pentylbenzene - > 125 ° C stormy Zers. 2 XIX-3-3 pentylbenzene 0.1% pyridine Slow Zers. > 175 ° C 3 XIX-3-3 pentylbenzene 0.5% pyridine Slow Zers. at 205 ° C 4 XIX-3-3 pentylbenzene > 0.5% pyridine No shattering. at 205 ° C 5 XIX-3-3 pentylbenzene 0.1% D Very slow. Dec. > 135 ° C 6 XIX-3-3 pentylbenzene 0.5% D Very slow. Dec. > 145 ° C 7 XIX-3-3 pentylbenzene 1.0% D Very slow. Dec. > 150 ° C 8th XIX-3-3 pentylbenzene 2.0% D Very slow. Dec. > 155 ° C 9 Xicu-3-F pentylbenzene 1.0% D Very slow. Dec. > 150 ° C 10 XIX-3-3 pentylbenzene 0.1% B Very slow. Dec. > 150 ° C 11 XIX-3-3 pentylbenzene 0.5% B Very slow. Dec. > 150 ° C 12 XIX-3-3 pentylbenzene 1.0% B Very slow. Dec. > 150 ° C 13 XIX-3-3 pentylbenzene 0.5% A Very slow. Dec. > 140 ° C 14 XIX-3-3 pentylbenzene 1.0% A Very slow. Dec. 150-170 ° C 15 XIX-3-3 pentylbenzene 0.5% C Very slow. Dec. > 140 ° C 16 XIX-3-3 pentylbenzene 1.0% C Very slow. Dec. 150-170 ° C

The 2,6-bis (t-butyl) pyridines A and C have the same stabilizing effect as the 4-unsubstituted body. The effectiveness of the 2,6-bis (t-butyl) pyridines and the unsubstituted pyridines is roughly comparable. However, especially for TFT applications, the unsubstituted pyridines from a concentration of about 0.1% lead to a significant reduction in the holding ratio. This effect occurs for the sterically shielded 2,6-bis (t-butyl) pyridines only at concentrations> 0.5-1%. This is a decisive advantage over the prior art. III. liquid crystal mixtures D 0.90% Clearing point (N, I): 79 ° C PCH-302 8.93% Δε [1 kHz, 20 ° C]: -1.6 CCH 301 29.48% CBC-53F 4.47% CBC 33 4.47% CBC 53 5.36% PCH-301 8.93% CBC-55F 4.47% CBC-33F 4.47% CCN-55 8.93% CCN-47 9.83% XEX V 2V 9.75%

Claims (12)

Pyridine derivatives of the formulas Ia1 and Ia2

wherein R ^a1 and R ^{a2 are} H or alkyl having 1 to 6 C atoms, R ^{b1 is} H, tert-butyl or tert-pentyl, R ^{b2 is} H or tert-butyl. Pyridine derivatives of formula Ia2 according to claim 1 wherein the radical R ^{b2 is} tert-butyl. Liquid-crystalline medium containing at least two liquid-crystalline compounds, characterized in that it has a nematic phase and that it contains at least one pyridine derivative of the formula I.

wherein R ^a , R ^b and R ^{c are} each independently H, an alkyl or alkenyl radical having up to 12 C atoms which is unsubstituted or substituted by CN or by at least one halogen, in which one or more non-adjacent CH ₂ groups are substituted by a radical may be replaced from the group -O-, -S-, -CO-, -O-CO-, -CO-O- and -C≡C-, and m and n are each independently 0, 1 or 2, mean. Liquid-crystalline medium according to Claim 3, characterized in that the pyridine derivatives are selected from sub-formulas I1, I2 and I3

wherein the parameters have the meaning given in claim 3. Liquid-crystalline medium according to Claim 3, characterized in that the pyridine derivatives are selected from the compounds of the formulas Ia1 and Ia2 according to Claim 1. Liquid-crystalline medium according to one or more of Claims 3 to 5, characterized in that it contains 0.01 to 5% by weight of at least one pyridine derivative according to one or more of Claims 1 to 5. Liquid-crystalline medium according to one or more of Claims 3 to 6, characterized in that one or more of the components contains one or more structural elements selected from the following structural elements

Liquid-crystalline medium according to one or more of Claims 3 to 7, characterized in that it contains one or more compounds of the formula II, R ^{1 *} -LGER ^{2 *} II wherein L and E are independently a carbo- or heterocyclic ring system of the 1,4-disubstituted benzene and cyclohexane rings, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro 1,4-phenylene, 4,4'-disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexane systems, 2,5-disubstituted pyrimidine and 1,3-dioxane rings, 2,6-disubstituted naphthalene, di- and tetrahydronaphthalene, quinazoline and tetrahydroquinazoline formed group, G is -CH = CH-, -N (O) = N-, -CH = CY-, -CH = N (O) -, -C≡C-, -CH ₂ -CH ₂ -, -CO -O-, -CH ₂ -O-, -CO-S-, -CH ₂ -S-, -CH = N-, -COO-Phe-COO-, or a CC single bond, Y is halogen or -CN, and R ^{1 *} and R ^{2 * are} unsubstituted or substituted by one or more fluorine atoms alkyl, alkoxy, alkanoyloxy or alkoxycarbonyloxy having up to 18 carbon atoms, or one of these radicals also CN, NO ₂ , CF ₃ , F, Cl or Br. Liquid-crystalline medium according to Claim 8, characterized in that one of the radicals R ^{1 *} and R ^{2 * is} an alkyl or alkoxy group having up to 18 C atoms and the other of the radicals R ^{1 *} and R ^{2 * is} alkyl, alkenyl, alkoxy each with up to 18 C-atoms, CN, F, Cl, OCF ₃ , OCHF ₂ , OCH ₂ CF ₃ , OCHFCF ₃ , OCF ₂ CHFCF ₃ , OCH = CF ₂ , OCF = CF ₂ or CH = CF ₂ . Liquid-crystalline medium according to Claim 8 or 9, characterized in that it contains one or more compounds of the general formula R ^{1 *} -LER ^{2 *} in which L is 1,4-cyclohexanediyl, E is 1,4-phenylene or 1,4-cyclohexanediyl, R ^{1 *} n-alkyl having up to 8 carbon atoms and R ^{2 *} n-alkoxy having up to 8 carbon atoms mean. Liquid-crystalline medium according to Claim 10, characterized in that it contains one or more compounds selected from the compounds of the formulas R ^{1 *} -Cyc-Phe-OCH ₃ and R ^{1 *} -Cyc-Cyc-OCH ₃ in which Cyc 1,4-cyclohexanediyl, Phe 1,4-phenylene and R ^{1 *} n-alkyl having up to 8 carbon atoms. Electro-optical display containing a liquid-crystalline medium according to one or more of claims 3 to 11.