2-fluorobenzonitrile derivatives and their use in optical displa

Details 2-fluorobenzonitrile derivatives and their use in optical displa 2-fluorobenzonitrile derivatives and their use in optical displa

1986-10-14

1988-11-15

Lee, Mary C.

Organic compounds -- part of the class 532-570 series

Organic compounds

Nitriles

558425, G02F 113, C07C12152

Patent

active

047844710

DESCRIPTION:

BRIEF SUMMARY
The invention relates to new fluorobenzene derivatives of the formula I ##STR2## wherein m is 0, 1 or 2 and to reactive derivatives thereof which are particularly suitable for use as intermediate products for the preparation of liquid-crystal compounds, and to the preparation thereof.
The use of liquid-crystal materials for achieving electrooptical effects in display devices, such as, for instance, digital calculators or clocks, is generally known nowadays. One of the parameters of liquid-crystal materials which is important for the operation of electrooptical displays is the dielectric anisotropy (.DELTA..epsilon.) of the material. This is to be understood as meaning, for a given frequency and temperature, the difference between the average dielectric constant (.epsilon..sub.II) measured parallel to the longitudinal axis of the molecules of the material, for example at a common orientation, and the average dielectric constant (.epsilon..sub.I) measured perpendicular to the longitudinal axis of the molecules.
The algebraic sign and the amount of the dielectric anisotropy of a given liquid-crystal material constitute one of the most important parameters which define the nature of electrooptical devices in which appropriate materials can be used.
Liquid-crystal materials having a high positive dielectric anisotropy, described in brief as "strongly positive" materials in the following text, can, for example, be used in known twisted-nematic devices. For example, mixtures of 4-alkylcyanobiphenyls, p-4-alkylcyclohexylbenzonitriles and 4-cyano-4'-(4-alkylcyclohexyl)-biphenyls have been introduced for applications of this type to an extent which is of economic importance.
Liquid-crystal materials having a small positive dielectric anisotropy, described in brief as "weakly positive" materials in the following text, can be mixed either with strongly positive materials or with strongly negative materials in order to modify the dielectric anisotropy.
The compounds of the formula I can be used like similar, not laterally fluorinated compounds, for example, like the compounds listed in German Offenlegungsschrift No. 2,944,905, as intermediates products for the synthesis of liquid-crystal materials of high or low positive dielectric anisotropy.
The invention was based on the object of indicating fluorobenzene derivatives, and the preparation thereof, which are suitable for the particularly simple synthesis of liquid-crystal compounds having a weakly positive or strongly positive dielectric anisotropy.
It has now been found that the compounds of the formula I are excellently suitable for the one-stage synthesis of a large number of target products.
In addition, the provision of the compounds of the formula I considerably widens, in a very general manner, the range of intermediate products suitable from various aspects for the preparation of liquid crystals.
The invention relates, therefore, to the fluorobenzene derivatives of the formula I ##STR3## wherein m is 0, 1 or 2, to reactive derivatives thereof and to a process for their preparation, characterised in that, in order to prepare cyclohexanecarbaldehdyes of the formula I (m=1 or 2), a compound of the formula II ##STR4## is reacted, in the presence of a base, with a triphenylalkoxymethylphosphonium halide, and the resulting alkoxymethylene compound is treated with an acid, or, in order to prepare benzaldehydes of the formula I (m=0), a compound of the formula III ##STR5## wherein R.sup.1 is halogen or OH, or reactive derivatives thereof, is oxidised, or a compound of the formula IV ##STR6## wherein X.sup.1 and X.sup.2 are each halogen or X.sup.1 and X.sup.2 together are .dbd.NOH ##STR7## wherein X is halogen, a monovalent metal or a corresponding equivalent is formylated, ##STR8## wherein Q.sup.1 and Q.sup.2 independently of one another are H, alkyl or unsubstituted or substituted aryl or aralkyl is treated
The invention also relates to the use of fluorobenzene derivatives of the formula I, according to claim 1, as intermediate products in the preparation of liquid-c

REFERENCES:
patent: 4664840 (1987-05-01), Osman

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