2-Fluoropyridines, their preparation and their use in liquid crystal mixtures

A ferroelectric liquid crystal mixture, which comprises at least two components, which liquid crystal mixture contains, as one component, a compound of the formula I ##STR79## in which the symbols have the following meaning:

• R.sup.1, R.sup.2, independently of one another, are H, or straight-chain or branched (with or without the inclusion of an asymmetric carbon atom) alkyl having 1 to 16 carbon atoms, it also being possible for one or two non-adjacent --CH.sub.2 -- groups to be replaced by --O--, --CO--, --CO--O--, --O--CO--, --O--CO--O--, --CH.dbd.CH--, --C.tbd.C--, or --Si(CH.sub.3).sub.2 --, and it also being possible for one or more hydrogen atoms of the alkyl radical to be substituted by F, or are one of the following chiral groups:
• ##STR80## A.sup.1, A.sup.2, A.sup.3, A.sup.4, identical or different, are 1,4-phenylene, pyridazine-3,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl, it being possible for one or two hydrogen atoms to be replaced by F, trans-1,4-cyclohexylene, in which one or two hydrogen atoms can be replaced by CN, 1,3,4-thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl, naphthalene-2,6-diyl, or 1,3-dioxaborinane-2,5-diyl;
• M.sup.1, M.sup.2, M.sup.3, M.sup.4, identical or different, are --CO--O--, --O--CO--, --CH.sub.2 --O--, --O--CH.sub.2 --, --CH.sub.2 --CH.sub.2 --, or --C.tbd.C--;
• R.sup.3, R.sup.4, R.sup.6, R.sup.7, independently of one another, are H or straight-chain or branched alkyl having 1 to 16 carbon atoms or R.sup.3 and R.sup.4 together are also --(CH.sub.2).sub.4 --, or --(CH.sub.2).sub.5 -- if bound as substituents to a dioxolane system,
• M.sup.5 is --CH.sub.2 --O--, --CO--O--, --O--CH.sub.2 --, --O--CO--,
• k, l, m, n, o, p, q, r are zero or one, with the proviso that the sum of k+m+p+r is less than 4 and greater than zero,
• and with the proviso that either
• a) R.sup.1 or R.sup.2 is H or a straight-chain or branched alkyl (with or without the inclusion of an asymmetric carbon atom) having 1 to 16 carbon atoms, in which one or two non-adjacent CH.sub.2 -groups are replaced by --C.tbd.C--, or Si(CH.sub.3).sub.2, or one of the following chiral groups:
• ##STR81## b) or at least one of A.sup.1, A.sup.2, A.sup.3, A.sup.4 is 1,3,4-thiadiazole-2,5-diyl or 1,3-dioxaborinane-2,5-diyl.

A fluoropyridine compound of the formula I ##STR85## in which the symbols have the following meaning:

• R.sup.1, R.sup.2, independently of one another, are H, or straight-chain or branched (with or without the inclusion of an asymmetric carbon atom) alkyl having 1 to 16 carbon atoms, it also being possible for one or two non-adjacent --CH.sub.2 -- groups to be replaced by --O--, --S--, --CO--, --CO--O--, --O--CO--, --O--CO--O--, --CH.dbd.CH--, --C.tbd.C--, --Si(CH.sub.3).sub.2 --, and it also being possible for one or more hydrogen atoms of the alkyl radical to be substituted by F, Cl, Br or CN, or are one of the following chiral groups:
• ##STR86## A.sup.1, A.sup.2, A.sup.3, A.sup.4, identical or different, are 1,4-phenylene, pyridazine-3,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl, it being possible for one or two hydrogen atoms to be replaced by F, trans-1,4-cyclohexylene, in which one or two hydrogen atoms can be replaced by CN, 1,3,4-thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl, naphthalene-2,6-diyl, or 1,3-dioxaborinane-2,5-diyl;
• M.sup.1, M.sup.2, M.sup.3, M.sup.4, identical or different, are --CO--O--, --O--CO--, --CH.sub.2 --O--, --O--CH.sub.2 --, --CH.sub.2 --CH.sub.2 --, or --C.tbd.C--;
• R.sup.3, R.sup.4, R.sup.6, R.sup.7, independently of one another, are H or straight-chain or branched alkyl having 1 to 16 carbon atoms or R.sup.3 and R.sup.4 together are also --(CH.sub.2).sub.4 --, or --(CH.sub.2).sub.5 -- if bound as substituents to a dioxolane system,
• M.sup.5 is --CH.sub.2 --O--, --CO--O--, --O--CH.sub.2 --, --O--CO--,
• k, l, m, n, o, p, q, r are zero or one, with the proviso that the sum of k+m+p+r is less than 4 and greater than zero,
• and with the proviso that either
• a) R.sup.1 or R.sup.2 is H or a straight-chain or branched alkyl (with or without the inclusion of an asymmetric carbon atom) having 1 to 16 carbon atoms, in which one or two non-adjacent CH.sub.2 -groups are replaced by --C.tbd.C--, or Si(CH.sub.3).sub.2, or one of the following chiral groups:
• ##STR87## b) or at least one of A.sup.1, A.sup.2, A.sup.3, A.sup.4 is 1,3,4-thiadiazole-2,5-diyl or 1,3-dioxaborinane-2,5-diyl.

A ferroelectric liquid crystal mixture, which comprises at least two components, which liquid crystal mixture contains, as one component, a compound of the formula I ##STR91## in which the symbols have the following meaning:

• R.sup.1, R.sup.2, independently of one another, are H, or straight-chain or branched (with or without the inclusion of an asymmetric carbon atom) alkyl having 1 to 16 carbon atoms, it also being possible for one or two non-adjacent --CH.sub.2 -- groups to be replaced by --O--, --CO--, --CO--O--, --O--CO--, --O--CO--O--, --CH.dbd.CH--, --C.tbd.C--, or --Si(CH.sub.3).sub.2 --, and it also being possible for one or more hydrogen atoms of the alkyl radical to be substituted by F, or are one of the following chiral groups:
• ##STR92## A.sup.1, A.sup.2, A.sup.3, A.sup.4, identical or different, are 1,4-phenylene, pyridazine-3,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl, it being possible for one or two hydrogen atoms to be replaced by F, trans-1,4-cyclohexylene, in which one or two hydrogen atoms can be replaced by CN, 1,3,4-thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl, naphthalene-2,6-diyl, or 1,3-dioxaborinane-2,5-diyl;
• M.sup.1, M.sup.2, M.sup.3, M.sup.4, identical or different, are --CO--O--, --O--CO--, --CH.sub.2 --O--, --O--CH.sub.2 --, --CH.sub.2 --CH.sub.2 --, or --C.tbd.C--;
• R.sup.3, R.sup.4, R.sup.6, R.sup.7, independently of one another, are H or straight-chain or branched alkyl having 1 to 16 carbon atoms or R.sup.3 and R.sup.4 together are also --(CH.sub.2).sub.4 --, or --(CH.sub.2).sub.5 -- if bound as substituents to a dioxolane system,
• M.sup.5 is --CH.sub.2 --O--, --CO--O--, --O--CH.sub.2, --O--CO--,
• k, l, m, n, o, p, q, r are zero or one, with the proviso that the sum of k+m+p+r is less than 4 and greater than zero,
• and with the proviso that either
• a) R.sup.1 or R.sup.2 is H or a straight-chain or branched alkyl (with or without the inclusion of an asymmetric carbon atom) having 1 to 16 carbon atoms, in which one or two non-adjacent CH.sub.2 -groups are replaced by --C.tbd.C--, or Si(CH.sub.3).sub.2, or one of the following chiral groups:
• ##STR93## b) or at least one of A.sup.1, A.sup.2, A.sup.3, A.sup.4 is 1,3,4-thiadiazole-2,5-diyl or 1,3-dioxaborinane-2,5-diyl.