Thiadiazole derivatives, process for their preparation, and their use as precursors for the production of liquid crystals

A 1,3,4-thiadiazole of the formula (I)

• X-B-A.sup.1 -(M.sup.1 -A.sup.2 -).sub.m (M.sup.2 -A.sup.3).sub.n -R.sup.1(I )
• in which the symbols and indices have the following meanings:
• X is Cl, Br or I;
• B is 1,3,4-thiadiazole-2,5-diyl;
• A.sup.1, A.sup.2 and A.sup.3 are identical or different and are 1,4-phenylene, in which one or more H atoms may be replaced by F, Cl and/or CN, pyrazine-2,5-diyl, in which one or two H atoms may be replaced by F, Cl and/or CN, pyridazine-3,6-diyl, in which one or two H atoms may be replaced by F, Cl and/or CN, pyridine-2,5-diyl, in which one or more H atoms may be replaced by F, Cl and/or CN, pyrimidine-2,5-diyl, in which one or two H atoms may be replaced by F, Cl and/or CN, trans-1,4-cyclohexylene, in which one or two H atoms may be replaced by CN and/or CH.sub.3, 1,3,4-thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl, 1,3-dithiane-2,5-diyl, 1,3-thiazole-2,4-diyl, in which one H atom may be replaced by F, Cl and/or CN, 1,3-thiazole-2,5-diyl, in which one H atom may be replaced by F, Cl and/or CN, thiophene-2,4-diyl, in which one H atom may be replaced by F, Cl and/or CN, thiophene-2,5-diyl, in which one or two H atoms may be replaced by F, Cl and/or CN, piperazine-1,4-diyl, piperazine-2,5-diyl, naphthalene-2,6-diyl, in which one or more H atoms may be replaced by F, Cl and/or CN, bicyclo›2.2.2!-octane-1,4-diyl, in which one- or more H atoms may be replaced by F, Cl and/or CN, or 1,3-dioxaborinane-2,5-diyl;
• M.sup.1 and M.sup.2 are identical or different and are --CO--O--, --O--CO--, --O--CO--O--, --O--CS--O--, --CH.sub.2 --O--, --O--CH.sub.2 --, --CH.dbd.CH--, --C.tbd.C-- or a single bond;
• R.sup.1 is --O-benzyl;
• m and n are 0 or 1.