Chiral compounds

Details Chiral compounds Chiral compounds

1998-09-18

2000-08-08

Kelly, C. H.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

2522992, 549430, C09K 1934, C09K 1958, C07D30700

Patent

active

060997516

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to chiral compounds of the formula I ##STR2## where R.sup.1,R.sup.2,R.sup.3 and R.sup.4 are hydrogen or aromatic, aliphatic or araliphatic radicals having 1 to 40 carbon atoms, having 1 to 20 carbon atoms, contains a polymerizable group.
The invention furthermore relates to the use of chiral compounds of the formula Ia ##STR3## where R.sup.1,R.sup.2,R.sup.3 and R.sup.4 are hydrogen or aromatic, aliphatic or araliphatic radicals having 1 to 40 carbon atoms, having 1 to 20 carbon atoms, use of these liquid-crystalline compositions for coating substrates and for the preparation of interference pigments, and to the use of the interference pigments in printing inks and surface coatings.
Chiral compounds of formula Ia where R.sup.3 and R.sup.4 are hydrogen, and R.sup.5 and R.sup.6 are aryl has been known for some time under the name TADDOLs (.alpha.,.alpha.,.alpha.',.alpha.'-tetraaryl-1,3-dioxolane-4,5-dimethanols ) and are used, for example, as catalysts for enantioselective syntheses. (cf. Dahinden et al. in "Encyclopedia of Reagents for Organic Synthesis", Paquette, L. A., Ed.; John Wiley & Sons, Chichester, 1995).
Liquid-crystalline phases containing chiral compounds frequently have remarkable properties. Thus, cholesteric phases, in which the molecule of the liquid-crystalline compound has a helical arrangement, can be formed, for example, by doping a nematic liquid-crystalline phase with a chiral compound. Such cholesteric phases frequently exhibit colored interference effects through selective reflection of light of a certain wavelength at the helical liquid-crystal structure. These colored cholesteric phases can be frozen, for example by cooling to below the glass transition temperature or by incorporation into polymeric networks, enabling their use in colored coatings or as interference pigments.
Numerous compounds have been disclosed as chiral dopes for liquid-crystalline phases (for example in DE-A 4342280). Suitable dopes should have a high twisting power, so that small amounts of the dope are sufficient to induce the helical structure. In addition, the chiral dopes should have good compatibility with the liquid-crystalline compounds, enabling effective interaction between these components. Many of the known chiral dopes are unsatisfactory with respect to these properties. In addition, many chiral compounds are of only limited suitability for polymeric cholesteric liquid-crystal systems, since they cannot be incorporated covalently into polymeric networks.
It is an object of the present invention to provide chiral compounds which are highly suitable as dopes for liquid crystals owing to their compatibility with liquid-crystalline compounds and their twisting power.
We have found that this object is achieved by the chiral compounds of the formulae I and Ia mentioned at the outset.
In the formulae I and Ia, the radicals R.sup.5, R.sup.6, R.sup.7 and R.sup.8 are aromatic or aliphatic radicals having 1 to 20 carbon atoms. These radicals are preferably sterically hindered radicals, since their size has a particular effect on the twisting power of the compounds. First, at least one of the radicals in the pairs R.sup.5 /R.sup.6 and R.sup.7 /R.sup.8 is preferably a branched or cyclic aliphatic radical having 6-20 carbon atoms. The volume of the substituents is more important here than the chemical composition. Thus, besides pure hydrocarbon radicals, alkyl or cycloalkyl groups which are interrupted by oxygen, sulfur, imino or C.sub.1 -C.sub.4 -alkylimino groups are also suitable. Examples of hydrocarbon radicals which may be mentioned are methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, and preferably branched hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, hexadecyl, octadecyl and eicosyl. Cycloaliphatic radicals, such as cyclopentyl, cyclohexyl, cycloheptyl and decahydronaphthyl, are also suitable.
R.sup.5, R.sup.6, R.sup.7 and R.sup.8 are particularly preferably aromatic radi

REFERENCES:
patent: 5047557 (1991-09-01), Hafner et al.
patent: 5498367 (1996-03-01), Buchecker et al.
Helvetica Chimica ACTA, vol. 79, 9, Sep. 18, 1996.
Journal of the American Chemical Society, vol. 114, No. 7, Mar. 25, 1992, DC US, pp. 2321-2336.
Encyclopedia of Regents for Organic Synthesis, Paquette, L.A., Ed., John Wiley & Sons, Chichester, 1995, Dahinder, et al.
The Journal of Organic Chemistry, vol. 60, Mar. 24, 1995, No. 6, 1788-1799, Dahinden et al.
Berichte der Bunsen-Gesellschaft Fur Physikalische Chemie, phys. Chem. 78, (1974), 869.

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