GB2200912A

GB2200912A - Terphenyl derivatives and liquid crystal materials containing them

Info

Publication number: GB2200912A
Application number: GB08802902A
Authority: GB
Inventors: George William Gray; Kenneth Johnson Toyne; David Lacey; Richard Michael Scrunston; Lawrence Kam Ming Chan
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1987-02-11
Filing date: 1988-02-09
Publication date: 1988-08-17
Anticipated expiration: 2008-02-09
Also published as: GB8703103D0; GB2200912B; GB8802902D0

Abstract

Terphenyls having a general formula I: <IMAGE> where R<1> contains from 1 to 12 carbon atoms and is selected from R, OR, ROCO and RCOO where R is alkyl, each of A, B, C, D, E and G is independently selected from hydrogen, fluorine or chlorine, one or two of A, B, C, D and G being fluorine and/or chlorine, and X is selected from <IMAGE> where R<2> is alkyl. These terphenyls are suitable for use as components of ferro-electric smectic liquid crystal materials.

Description

TERPHENYL DERIVATIVES AND LIQUID CRYSTAL MATERIALS CONTAINING THEM This invention relates to movel terphenyl compounds, to liquid crystal materials containing them and to electro-optical devices which use such materials. In particular the invention concerns terphenyl compounds which may be used as components of ferroelectric smectic liquid crystal materials.

Ferroelectric smectic liquid crystal materials are increasingly being used in electro-optical display devices as they allow the possibility of very high switching speeds and bistable characteristics. Such materials necessarily exhibit a chiral smectic phase eg the chiral smectic C, F, G, H, I, J and K phases, designated herein S* etc. Generally the S*C phase is preferred1 as this is the most fluid.

Desirable characteristics in a ferroelectric smectic liquid crystal material include low viscosity, a wide temperature range over which the S* phase is present, an 5A phase at a temperature above which the S* phase is present, and a high spontaneous polarisation coefficient Ps (measured in nC cm Generally ferroelectric smectic liquid crystal materials consist of a mixture of compounds which together show a smectic phase, especially smectic C. If an optically active compound is included in such a mixture the smectic phase shown by the mixture is induced to be chiral.

It is an object of the invention to provide novel terphenyls which may be included in ferroelectric smectic liquid crystal materials.

According to the present invention a novel terphenyl has a formula:

Formula I 2 wherein R1 contains from 1 to 12 carbon atoms and is selected from R, OR, ROCO and RCOO where R is alkyl, each of A, B, C, D, E and Gris independently selected from hydrogen, fluorine or chlorine1 one or two of A, B, C, D, E and GF being fluorine and/or chlorine, wherein X is a group selected from:

2 wherein R is alkyl containig from 1 to 12 carbon atoms.

The group X may be in an optically active (+) or (-) form, or may be a racemic mixture of its optical enantirmers.

Compounds of formula I may be used as components of ferroelectric smectic liquid crystal materials, and according to the present invention there is provided a ferroelectric smectic liquid crystal material which is a mixture of compounds, at least one of which is a compound of formula I. Usefulness as a component of a ferroelectric smectic liquid crystal material is one of the factors determining the structural preferences discussed below.

R1 is preferably C3 to C10 n-alkyl or n-alkoxy.

The terphenyl "core" of the compound of formula I preferably has a structure selected from 1.1 to 1.6 below, especially 1. 2 1.3 or 1.5:

R2 is preferably n-alkyl.

R2 R preferably contains 1 to 6 carbon atoms, and preferred structures for the group X are those listed below:

Compounds of formula I may be prepared by Routes A, 3 and C as shown in Figs 1, 2, 130f the accompanying drawings. The individual steps of these routes are known, but the overall route is in each case novel. These routes may be used for the preparation of both optically active and racemic compounds of formula I. These routes are outlined below.

Route A Step Al. The starting biphenyl is commercially available.

Grignard reaction using magnesium, sodium-dried ether.

4-n-R- cyclohexanone. Acid-hydrolysis to the cyclohexanol.

Step A2. Sodium-dried benzene solvent, P2 05 Step A3. Sodim-dried toluene solvent, 2,3-dichloro-5,6dicyanobenzoquinone.

Step A4. Friedel-Crafts reaction using AlCl3 and RCOCl.

sieve-dried nitrobenzene solvent.

Step A5. Baeyer-Villiger oxidation using m-chloroperoxybenzoic acid, dry dichloromethane solvent, followed by hydrolysis.

Step A6 (i) Reaction of appropriate R-lactate ester with toluene-4sulphonyl chloride to form:

in pyridine solvent.

(ii) Reaction of product of (i) with the terphenyl from step A5 in acetonitrile plus K2CO3.

Route A is a general route for the preparation of compounds of formula I where X is

and is suitable for optically active and racemic compounds.

Route B 2 Step B1. R I, silver oxide , DMF.

Step B2. KOH, water/methanol.

Step B3. Dicyclohexylcarbodi-imide (DCC) method using the terphenyl:

Although illustrated for a terpehnyl with the fluorosubstituent on the central ring, route B is suitable for all fluoro-substitution patterns and may be used to prepare both optically active and racemic compounds.

Route B is generally suitable for compounds of formula I where X is:

Route C Compounds where X is

SteP Cl Friedel Crafts reaction using AlCl3 and CH3COCl, sieve dried nitrobenzene solvent.

Step C2 Bromoform reaction.

Step C3 Dicyclohexylcarbodiimide esterification using

Step C4 Cross coupling using n-Bubi, ether, -35 C 20 min., ZnCl2, THF, N2.

SteP C5 Pd(Phf )2C12, di-isobutylaluminium hydride, THF, N2.

This route is suitable for the preparation of both optically active and racemic compounds.

Racemic and/or optically active compounds of formula I may be used as components of ferroelectric smectic liquid crystal mixtures. Such mixtures must contain at least one optically active compound to induce the appearance of an S*, preferably SC* phase. It is preferred to include at least one optically active compound of formula I in the mixture, as many optically active compounds of formula I have been found to induce the appearance of SC* phases having a high Ps.

Such a ferroelectric smectic liquid crystal mixture will also normally contain one or more other compounds which either separately or when mixed together show a smectic liquid crystal phase, preferably Sc, over a useful temperature range. Such compounds or mixtures thereof are generally termed "smectic hosts".

A wide range of smectic hosts is known, but two particularly preferred types of host are: (a) The compounds disclosed in PCT/GB86/0040, eg having a formula:

where RA is n-alkyl or n-alkoxy and R is alkyl, or mixtures B thereof, especially eutectic mixtures.

(b) The terphenyls disclosed in EPA 84304894-3 eg having a formula:

where RA and RB are independently selected from n-alkyl and n-alkoxy, or mixtures thereof, especially eutectic mixtures.

Other known examples of smectic hosts include compounds of the following general formulae:

(racemic) where RA and RB are independently selected from n-alkyl and n-alkoxy and RC is n-alkyl. In these host compounds, RA and R3 are preferably C3 - C12 RC is preferably ethyl.

In a ferroelectric smectic liquid crystal material of this invention, it is particularly preferred to use one or more optically active terphenyls of formula I together with one or more optically active compounds which induce an S* phase, ideally of high Ps. Such a mixture may optionally additionally include one or more host compounds, and optionally additionally one or more additives.

Preferably in such a case the sense of the helical twist induced in the material by the terphenyl(s) of formula I is opposite to that induced by the other optically active compound(s) which induce a high Ps.

In this way the length of the helical pitch of the 5c phase of the mixture may be controlled by altering the relative proportions of the terphenyl of formula I and the other optically active compound.

Preferred other optically active compounds include the compounds disclosed in EP-A-0110299, eg:

and particularly the compounds containing a in PCT/GB 87/00441, eg:

CN -COOCH-alkyl group disclosed

where RA is C3-C12 n-alkyl or alkoxy, and R3 is C1-C12 alkyl, preferably h being methyl or a C1 - C6 branched alkyl.

It is desirable that each optically active compound in the mixture induces the same sense of Ps in the mixture.

The mixture may also contain other known additives to improve the properties, eg Ps, Sc phase breadth, viscosity etc or to induce the appearance of an SA phase of a temperature above the SC* to assist alignment. An example of a class of compounds which may be used to broaden the Sc phase is:

Another useful class of additives are compounds of formula:

wherein RA is n-alkyl or n-alkoxy, and RB is n-alkyl. Preferably RA and RB independently contain 3-12 carbon atoms.

Other additives will be apparrent to those skilled in the art.

Typically but not exclusively a ferroelectric smectic liquid crystal mixture of the invention will have the following composition: One of more smectic ) ) 30 - 99 weight % host compounds ) Optically active ) 1 - 20 weight % compound(s) of formula I Other optically active 0 0 - 20 weight % compound(s) Additives if present.

) O - 20 weight % Racemic compound(s) of formula I ) O - 20 weight % The total being 100 weight%. The nature and relative proportions of the various components of a liquid crystal material of the invention will depend upon the use for which the material is intended, and some experimentation may be necessary to suit a particular requirement, but the basic principles of mixing and assessment of such materials are well known in the field.

The liquid crystal materials of the invention may be used in any of the known types of ferroelectric smectic liquid crystal display device, eg the "Clark-Lagerwall Device" described in Appl.

Phys Lett (1980), 36 899 and in Recent Developments in Condensed Matter Physics (1981), 4,309. The physics of this type of device and the method of constructing it are well known. and are described for example in PCT/GB85/00512, and PCT/GB86/0040.

In practice such a device usually consists of two substrates, at least one of which is optically transparent, electrodes on the inner surfaces of the substrates by which a voltage may be applied and a layer of the liquid crystal materials sandwiched between the substrates. It is desirable that the helical pitch length of the Sc* phase is comparable to the thickness of the material, which is why long pitch mixtures are useful. The materials of the invention may be used in both the birefringence type display mode and the guest-host type display mode of the Clark-Lagerwall device g The device may for example be in the form of a clock, calculator or video screen display, and methods of making the device in this form will be well known to those skilled in the art.

The invention will now be described by way of example only with reference to Figs 1, 2,13 which show preparative routes A, B and C for compounds of Formula I, and Figs 3 - 12 which show various properties of ferroelectric smectic liquid crystal mixtures containing them.

The following abbreviations are used: S = smectic liquid crystal phase.

I = isotropic liquid.

Ch = cholesteric liquid crystal phase.

C = solid crystal.

All temperatures are in OC.

Ps expressed in nCcm H1 is a smectic host having the composition:

F C3H17COOCH1 H17 I\ 9-11 1:1:1 CgHl?0COOFCSHll 1:1:1 by weight.

E7 is a nematic liquid crystal mixture having the composition:

H2 is a smectic host having the eutectic composition:

The following compounds were prepared: Reference Prep. Route Formula CK 621 A CK 622 A CK 627 C CK 629 C CK 633 B

Table 1 below lists properties of these compounds.

Table 2 below lists properties of ferroelectric smectic liquid crystal mixtures containing these compounds.

Additional properties of ferroelectric smectic liquid crystal mixtures containing these compounds are illustrated in Figs 3 - 12 and are discussed briefly below.

CK 621 Graphs of Ps and tilt angle of the smectic phase against temperature in the host H1 are shown in Figs 3 and 4 respectively.

Table 1 Properties of Compounds

Compound LC transition temps. ( C) optical Rotation ( ) Ch pitch ( m) Sense of Ch CK 621 C 72.5 I (53 Ch 51 SA, 49 C)a + 28.7 0.195 D CK 622 C 73.5 I (64 SA, 49 SB 32 C)a + 26.3 0.241 D CK 627 C 52 SA 80 I + 37.6 0.101 CK 629 C 57 S? 61 SC 79.5 SA 111 I + 26.3 0.113 CK 633 C1 53.5 C2 56 SB 98 SA 145 I - 0.281 D Note: (a) bracketed liquid crystal transitions are monotropic, ie observed on supercooling.

(b) Ch pitch measured at room temp in E7. a large Ch pitch suggests the possibility of a large Sc* pitch.

Table 2 Properties of Ferroelectric Mixtures

Comp Solventa LC transition temperatures Psc(nC cm-2) Tilt ( )c Ps sense Cell thickness CK 621 H1 SC*78.2 SA93.2 Ch 37(10) 162(2) 10(10) 17(20) + 6 m CK 622 H1 S? 26.3 SC*91.8 SA 105.6 135(30) 42(10) 33.5(30) 19.5(10) + 5.1 m Ch 139.5 I 100(50) CK 629 FTPb SB? 71 SC* 83 A 139 Ch 20(10) - 147 I CK 633 H1 S? 32.8 SC* 92.3 SA 111.2 2(10) - 6 m Note: (a) 10 wt% solutions were used (b) FTP is the compound

(c) The figure in brackets is the temperature below the SC-SA transition. ( C) CK622. Graphs of Ps and tilt angle of the smectic phase against temperature in the host H1 are shown in Figs 5 and 6 respectively.

CK629. Fig 7 shows a graph of Ps against temperature for a 10 wt % solution of CK629 in FTP (as defined in Table 2).

CK633. Fig 8 shows a graph of Ps against temperature for a 10 wt % solution of CK633 in H1.

Further properties of ferroelectric smectic liquid crystal mixtures containing compounds of formula I were investigated as below.

Mixture A. This consisted of 85 wt % of H2 plus 15 wt % of a mixture consisting of:

(the senses of optical activity of these two compounds being opposite.

A graph of Ps against temperature of this mixture is shown in Fig 9.

Mixture B. (ref 17) This consisted of 77 wt t of H2 plu= the following:

(of optical activity opposite to the terphenyl, to extend St pitch and to induce SA phase) The mixture had the transition temperatures (0c) C 5(?) SB(?) 15 SC* 65.5 SA 82 Ch 129 I Graphs of Ps and tilt angle of the SC* phase against temperature for mixture B are shown in figs 10 and 11 respectively. A 6um cell having polyimide alignment films was used. Fig 12 shows the variation of response time with peak-to-peak vol-tage of a liquid crystal cell using mixture B as its working medium.Response time at two temperatures 30 and 40 C, and for two levels of contrast change 0-100% and 10-90% are shown.

These results demonstrate the usefulness of mixture B and of the compounds and mixtures of the invention.

Mixture C.

The two optically active compounds in this aixture had configurations that induced the appearence of chiral smectic phases of opposite helical twist sense. The mixture had phase transitions ( C) I 145 N 114 5A 59.7 SC*10 S? The following preparative examples illustrate the use of Routes-A and C to prepare compounds of Formula I.

PrePazative Example 1: Route A Compounds of formula: Step Al.

cis-/trans-4-n-Alkyl-1-(2'-fluorobiphenyl-4'-yl)-cyclohexanols About a third of a solution of 4-bromo-2-fluorobiphenyl (25.1 g, 0.10 mol) in sodium-dried ether (60 cm3) was added, under anhydrous conditions, to magnesium turnings (2.40 g, 0.10 g atom).

The reaction was initiated by the addition of a crystal of iodine and gentle warming. The remaining solution of 4-bromo-2-fluorobiphenyl was added dropwise so that the reaction mixture gently boiled. After the addition, the reaction mixture was gently heated under reflux for 30 min. On being cooled, a solution of the appropriate 4-n-alkylcyclohexanone (0.10 mol) in sodium-dried ether (50 cm3) was added dropwise over a period of 30 min, and the resulting reaction mixture was then heated under reflux for a further 30 min. The cooled solution was then carefully poured onto a vigorously stirred mixture of concentrated sulphuric acid (25 cm ) and crushed ice (300 g).The product was extracted into ether (3 x 200 cm3) and the combined ethereal extracts were washed with water (200 cmS) and dried (MgSO4). The residual alcohol was crystallised from hexane to give compound (1) as a mixture of cis-/tr:s-isomers (approximately in the ratio 50:50 by glc). The yields were found to be in the range of 65 to 75z. Step A2.

4-n-Alkyl-1-(2'-fluorobiphenyl-4'-yl)cyclohexenes (2) A solution of an isomeric mixture of compounds ( 1) (0.058 mol) in sodium-dried benzene (100 cm3) was added dropwise to a vigorously stirred mixture of phosphorus pentoxide (21.3 g, 0.15 mol) and sodium-dried benzene (200 cm3) over a period of 30 min, under anhydrous conditions. The resulting mixture was stirred for 3 h at room temperature. On being cooled to OOC, ice-water (300 cm3) was added carefully. The product was extracted into benzene (2 x 150 cm3) and the combined organic extracts were washed successively with 5X w/v sodium carbonate solution (100 cm3) and water (100 cm3) and then dried (tIgS04). After removal of the solvent, the residue was recrystallised from ethanol.Yields of the compounds ( 2) were in the range 90-95% and the purities by HPLC were all > 98 %.

Step A3.

4"-n-Alkyl-2'-fluoro-1,1':4',1"-terphenyls (3) A solution of the appropriate compound ( 2) (0.050 mol) in sodium-dried toluene (100 cmS) was added slowly to a vigorously stirred mixture of 2,3-dichloro-5,6-dicyanobenzoquinone (25.0 g, 0.11 mol) in sodium-dried toluene (200 cm3) over a period of 30 min. The reaction mixture was then heated at 1100C for 3 h.

On being cooled to room temperature, the dark precipitate of the quinol was filtered off, and the filtrate was washed successively with 15% w/v sodium metabisulphite solution (150 cm3) and water (100 cm3) and finally dried (tIgS04). After removal of the solvent, the dark residue was sublimed under reduced pressure (120-140 C/0.01 mm Hg) and the white solid obtained was crystallised from ethanol. Yields of compounds (3) were in the range 65 - 75 %, the purities by hplc were 95 %.

Step A4.

4-n-acetyl-4"-n-alkyl-2'-fluoro-1,1':4',1"-terphenyl (4) To a cooled, stirred mixture of finely powdered anhydrous aluminium chloride (0.11 mol) and compound (3) (0.010 mol) in sieve - dried nitrobenzene (90 ml), a solution of acetyl chloride (0.11 mol) in dry nitrobenzene. (40 cm3) was added dropwise over a period of about 15 min, keeping the temperature below 50C. The reaction mixture was then stirred at room temperature under anhydrous conditions for 16 11. The mixture was then poured onto a mixture of ice (60 g), water (10 cm3), and concentrated hydrochloric acid (10 cm3), and the resultant mixture was vigorously stirred for 30 min. The separated organic layer was washed with water (50 cm3), and the solvent removed by steam distillation.

The crude product was purified by column chromatography on silica gel using chloroform : petroleum fraction (bp 60-800C) (1 : 1) as eluent.

Step A5.

4"-n-alkyl-2'-fluoro-4-hydroxy-1,1':4',1"-terphenyls. (5) A solution of m-chloroperoxybenzoic acid (0.030 mol) in sieve-dried dichloromethane (35 cm3) was added dropwise to a stirred solution of the appropriate compound (4) (0.020 mol) in sieve-dried dichloromethane (20 cm3), keeping the temperature below 50C. The reaction.mixture was stirred for 5 days at room temperature. The precipitated m-chlorobenzoic acid was filtered off and washed with dichloro methane. The filtrate and washings were then treated successively with'saturated sodium bicarbonate solution (20 cm3) and water (20 cm3), and finally dried (tIgS0X). After removal of the solvent, the residue was crystallised from toluene:ethanol (5:95) and used directly in the hydrolysis below.

The residue from the above reaction (0.015 mol) was added to a solution of potassium hydroxide (0.050 mol) in water (20 cm3) and ethanol (60 cm ), and the mixture was then heated under reflux for 3 h. On being cooled, the ethanol was removed by distillation under reduced pressure. Water (20 cm3) was added to the residue and the resulting solution was acidified with cold 18X w/v hydrochloric acid. The product was then extracted into ether (3 x 50 cm3) and the combined ethereal extracts were washed with water (50 cm3) and dried (MgS04). After removal of the solvent, the residue was crystallised from toluene:hexane (2:1). The yields for these products were in the range 65 - 75 %.

Step A6.

To a mixture of compound (5) (0.0090 mol) and anhydrous potassium carbonate (c0.039 mol) in sieve-dried butanone (45 cm3), the bromocarboxylic acid R2 (0.0144 mol) OCOCH(CH3)3r was added slowly with stirring, and the resulting mixture heated under reflux overnight, under anhydrous conditions. When the mixture was cold, the salts were filtered off and the solvent was removed from the filtrate by distillation under reduced pressure. The residue was purified by column chromatography on silica gel, using chloroform:petroleum fraction (bp 40-600C) (1:2) as eluent. The appropriate fractions were concentrated and the residue was crystallised from 90% aqueous ethanol to give compound (6).

Preparative Example 2: Route C Compounds of formula:

Step C1 Step Cl was performed using a procedure similar to that of Step A4 described above.

Step C2 This step used a method similar to that of "Vogei's Textbook of Practical Organic Chemistry" (4th edn.), longman, p 825.

Step C3 Step C1 was performed musing a procedure similar to that of A.Hassner and R.Siminoff, "Tetrahedron Lett.", (1978), p 4475.

Step C4 Two alternatives were used for step C4. Where R1 was alkoxy a method similar to that of step A6 was used, with the appropriate alkyl bromide R 4 r and 4-bromophenol. Where R1 was alkyl the alternative below was used.

To a cooled, stirred mixture of finely powdered anhydrous aluminium chloride (0.11 mol) and an excess of bromobenzene (30 cm3) was added dropwise the appropriate n-alkanoyl chloride (0.10 mol), keeping the temperature below 50C. The reaction mixture was then stirred at 700C for 2 h. When cooled, the mixture was poured onto a mixture of ice (60 g), water (10 cm3), and concentrated hydrochloric acid (10 cm3); the resultant mixture was vigorously stirred for 30 min. The product was extracted into chloroform (2 x 50 cm3) and the combined organic extracts were washed with water (50 cm3). After the removal of the solvent, the excess of bromobenzene was removed by steam distillation.The product was extracted into chloroform (2 x 50 cm3) and dried (MgS04). After removal of the solvent, the residue was distilled in vacua to give the compounds

(where R is alkyl). Yields were in the range So - 60 %.

This compound, with an appropriate R, (0.007 mol) was added to a stirred mixture of diethylene glycol (50 cm3), hydrazine hydrate (0.035 mol) and potassium hydroxide cm.0175 mol).

The reaction mixture was then heated at 1300C for 2 h. The excess of hydrazine hydrate and water formed in the reaction was distilled off and the temperature of the reaction mixture was raised and then maintained at 1800C for 4 h. On being cooled to room temperature, the mixture was poured into water (100 cm3) and the product was extracted into ether (3 x 100 cm3). The combined ethereal extracts were washed with water (100 cm3) and dried (MgS04). After removal of the solvent, the residue was purified by distillation under reduced pressure to yield the 4bromoalkyl phenyl as colourless liquids.

Step C5.

This was carried out using a procedure similar to that of K.Tamao et al Bull. Chem. Soc. Japan, (1976) 49 1958.

Claims

1. A terphenyl of formula:

where R1 contains from 1 to 12 carbon atoms and is selected from R, OR, ROCO and RCOO where R is alkyl, each of A, B, C, D, E and G is independently selected from hydrogen, fluorine or chlorine, one or two of A, B, C, D, E or G being fluorine and/or chlorine, wherein X is a group selected from:

wherein R2 is alkyl.

2. A terphenyl according to claim 1 wherein R1 is C3 to C10 n-alkyl or n-alkoxy.

3. A terphenyl according to claim 2, wherein X is

and R2 is C1-C6 n-alkyl.

4. A terphenyl according to claim 3, wherein R2 is methyl.

5. A terphenyl according to claim 2, wherein X is

and R2 is C1-C6 n-alkyl.

6. A terphenyl according to claim 5, wherein R2 is ethyl.

7. A terphenyl according to claim 2, wherein X is

and R2 is C1-C6 n-alkyl.

8. A terphenyl according to claim 7, wherein R2 is C6H13.

9. A terphenyl according to any one of the preceding claims, wherein any one of B, C, D or G is fluorine and the remaining substituents A, B, C, D, E or G are hydrogen.

10. A terphenyl according to any one of claims 2 to 9 having a strucutre:

11. A terphenyl according to any one of claims 2 to 9 having a structure

12. A ferroelectric smectic liquid crystal material which is a mixture of compounds, at least one being a terphenyl as claimed in any one of claims 2 to 11.

13. A liquid crystal material according to a claim 12, containing in addition at least one compound of formula:

wherein RA is n-alkyl or n-alkoxy, and RB is n-alkyl.

14. A liquid crystal material according to claim 12, containing in addition one or more terphenyls of formula:

where RA and RB are independently selected from n-alkyl and n-alkoxy.

15. A liquid crystal material according to any one of claims 12 to 14, and containing in addition one or more other optically active compounds which induce an Sc* phase in the material, the sense of the helical twist induced by the tenphenyl(s) of formula I being opposite to that induced by the other optically active compound(s).

16. A liquid crystal material according to claim 15 wherein at least one of the other optically active compounds is a compound of formula

where RA is C3-C12 n-alkyl or n-alkoxy and RB is C1-C12 alkyl.