The object of this invention is an agent, i.e. an organosi- licon compound for imparting lipophilic properties to a hydrophilic surface, such as that of glass, quartz, oxidiz¬ ed silicon, metal-metal oxide or of a plastic containing OH-and/or NH-groups. By means of the invention the physico- chemical characteristics, especially the adsorption charac¬ teristics of such a surface may be selectively modified and/or improved. According to one mode of the invention, the agent according to the invention may be polymerized, optionally using further, per se known silicon compounds, to form a silicon polymer, which may be applied by adsorp¬ tion to a surface which advantageously has been pretreated according to the invention. An important field of use of the compounds in question is in chromatography, both gas and liquid chromatography, especially gas chromatography, and in electronics.

It is known to treat surfaces of e.g. glass with organo- silicon compounds or polymers in order to modify their hydrophilic characteristics, such as for chromatographic purposes, cf DE 834 002, DE 29 30 516, Advances in Chemist¬ ry Series, vol. 87 (1968), Bascom .D. and GB 1,354,357. However, in these known methods, primarily aliphatic sila- nes have been used. In instances where aromatic silanes have been used, the phenyl substituent has either been un- substituted or substituted with groups or atoms, notably halogen atoms, which do not, however, provide the desired selectivity according to the invention. It is also known to form surface films containing more complicated substituted aromatic groups. However, rather than using the film-form¬ ing compound as such to make the film, the film is formed by building the desired molecule from smaller molecular moieties, starting from the substrate surface and proceed-

ing therefrom in an outward direction by consecutively add¬ ing the required molecular moieties (Journal of American Chemical Society, vol. 102 (1980) no 12, p. 4029 to 4030).

It is an object of the invention to provide new organo- substituted silanes, containing as a substituent a phenyl group which is further substituted, so as to provide com¬ pounds by means of which the properties of the treated surface may be tailor-made in a highly selective manner. This object is achieved by selectively choosing such subs¬ tituents on the phenyl group(s) in the silane, which are able to actively participate in inter olecular forces, such as in the formation of charge-transfer complexes.

The organo-substituated silane according to the invention is represented by the general formula

Z ¹ - Si - Z ² (I)

I R2

wherein Z^ and Z ² independently is chlorine, fluorine, bromine, alkoxy with not more than 6 carbon atoms, NH, - H2 i -NR2 - wherein R' is alkyl with 1 to 3 carbon atoms, -SH, -CN, - N3 or hydrogen, and R ¹ is

wherein each S-substituent, which can be the same or diffe¬ rent, is hydrogen, whereby the phenyl ring may contain at the most four hydrogen substituents, alkyl with 2 to 4 car¬ bon atoms, or methyl or methoxy, in which case there may be at the most three hydrogen substituents in the phenyl ring, cyano, ethoxy, or two adjacent S-substituents form with the phenyl nucleus a naphtalene or anthracene group, or three adjacent S-substituents form together with the phenyl nuc¬ leus a pyrene group, and X is the group -(CH2)n~' wherein n is 0 to 20, preferably 10 to 16, or the group

wherein i is 0 to 10 and k is 1 to 5, whereby, when n is not 0, i.e. X is a spacer group, the S-substituents, espe¬ cially S3, can also be phenoxy or biphenyl, and R ² is equal to Z^ or R! , or is lower alkyl, lower alkenyl, phenyl, or phenyl substituted with lower alkyl or lower alkoxy.

The term "lower" in connection with groups of* compounds contain from 1 to 7 , preferably from 1 to 4 carbon atoms.

Especially advantageous compounds according to the inven¬ tion are obtained when R^ is one of the following groups

which groups ϊl-~ are attached directly to the silicon atom or

wh

The compounds according to the invention are thus silanes containing at least one group Z, which can form a chemical bond with a hydrophilic group of the surface to be treated, and one or two selectively substituted phenyl groups.

According to the invention, the adsorption characteristics of the surface thus treated may be modified and/or impro¬ ved. Especially the surface may be modified in a selective manner by using the specific substituents on the phenyl group as defined above. Surfaces are thus obtained which are well suited to a variety of purposes, such as for chro-

matographic purposes, or which have specific electrical properties and suitable for use in electronical applicat¬ ions, and/or which may be further treated, for example by adsorbing thereon a further layer, e.g. obtained by polyme¬ rizing the compounds (I).

The most important forces prevailing between non-ionic molecules stem from hydrogen bonds and dipole-dipole-inter- actions. In certain instances the formation of charge- transfer complexes is prevalent. Compared to these forces the Van der Waals forces are weak. However, in certain instances the only forces between molecules are the Van der Waals forces.

As mentioned above, surfaces have previously been coated for chromatographic purposes with compounds such as methyl-, octadecyl- and phenylsiloxanes, the interaction of which with the compounds to be fractionated is weak. An essential characteristic of the invention is that the relationship between these different forces can be selectively regulated as compared to the use of plain alkyl or phenyl groups. The manner of regulating according to the invention is illust¬ rated in the following.

Hydrogen bonding acceptor properties are enhanced by the introduction into the phenyl group of e.g. methoxy or cyano groups. In the case of two methoxy groups the following isomers are formed

In these compounds the mutual distances between the oxygen

atoms are 2,8 A, 4,8 A and 5,6 A. Thus if a compound which is to interact with a surface treated with a dimethoxy- phenyl-compound contains two active hydrogen atoms at a pre¬ determined mutual distance, the one dimethoxy-phenyl-isomer is chosen for surface treatment in which the distance bet¬ ween the dimethoxy groups is suitable, i.e. best corres¬ ponds to that between the hydrogen atoms, resulting in an strong interaction.

Also dipole-dipole-interactions may be enhanced by the use of methoxy and cyano groups. As the dipole moments of structural isomers vary considerably, the chromatographic separation of isomers can be facilitated.

Charge-transfer donor characteristics are enhanced by the use of alkyl or alkoxy groups, especially methyl and metho¬ xy groups. On the other hand, charge-transfer acceptor cha¬ racteristics are enhanced by the use of cyano groups. Poly- cyclic aromatic hydrocarbons being charge-transfer donors form together with cyano substituted aromatic groups charge- transfer complexes. By varying the number and position of the cyano groups, the stability of the complexes may be varied, which fact finds applicability for example in chro¬ matography as well as in electronics.

Especially in connection with gas chromatography the ther¬ mal stability of the surface layer is important. The bond between an aromatic group and the silicon atom is strong. On the other hand, it is occasionally of advantage that the active group is not close to the substrate surface. Both these objects may be achieved by using a compound according to the invention which as a spacer group comprises a p-phe- nylen-methyl- or a poly-p-phenylen group as follows

The poly-p-phenylen structure is of importance also in electronical applications, especially in cases where the substrate is a metal-metal oxide as it allows for easy electron transfer between the metal surface e.g. to a se¬ cond film adsorbed onto the treated surface. As a specific example may be mentioned treating an indium-tin oxide co¬ vered glass surface with a poly-p-phenylene silane compound containing in the terminal phenyl ring a cyano group, onto which treated surface a pyrene group containing phosphogly- cerol film may be adsorbed, the cyano group and the pyrene group forming a charge-transfer-complex, as stated above.

As mentioned above, according to one mode of the invention, in order to enhance or modify the adsorption characteris¬ tics of a surface especially useful for gas chromatography purposes onto a surface optionally treated with a silane according to the invention may be adsorbed a polymerized film of the same or of a similar silane compound containing the active phenyl groups defined in the formula I, the po¬ lymerized silane having the formula

wherein R-- and R ² have the meanings defined above, R^ to R^ are independently lower alkyl, lower alkenyl, phenyl or lower alkyl-phenyl, and p > 1, q and r ^ 0. The groups R! and R ² may be the same as or different from the correspond¬ ing groups used in the surface treatment step. The groups R in the polymer are naturally chosen according to the end use of the surface in question. The preparation of the po¬ lymers is conventional, and known to a person skilled in the art.

As also mentioned above, another important field of use of the invention is in electronics, especially in applications where surfaces treated according to the invention are used together with films of Langmuir-Blodgett type, for example in photo or sun cells, micro circuits etc. Thus for example silane compounds with substituents having electron acceptor characteristics, for example cyano groups, may be used for treating a surface. Onto such a surface exhibiting electron acceptor characteristics a film containing donor groups, for example alkyl or alkoxy groups, of Langmuir-Blodgett type may be applied. Electron transfer between these layers may be initiated with external means, for example using a

voltage potential or light. The donor groups may naturally be included in the surface treatment agent, whereby on the treated surface a layer exhibiting acceptor characteristics is applied.

The silane compounds according to the invention are novel and they may be prepared using processes equivalent to pro¬ cesses known in the art. A suitable method for preparing these compounds is the Grignard reaction, whereby one mole of a Grignard reagent R^— Mg Br, prepared in a manner known, is reacted with one mole of a compound having the formula R Si (Z^)2 Z ² , in which formulas the symbols have the above meaning. An alternative mode of preparing the compounds of the invention, wherein X is p-phenylene con¬ taining spacer group, comprises, forming in a first step in a manner described above the corresponding p-Br-substitut- ed silane compound, ^" Br-X-(R ² ) Si Z^-Z ² wherein the Z-subs- tituents have the above meaning, but may not be halogen, and thereafter forming its zinc derivative Br-Zn-X-(R ² ) Si Z^Z ² which in the presence of a suitable Pt- catalyst to¬ gether with the compound

Br

gives the desired compound.

The following examples illustrate the invention,

Example I

117 g (0.63 moles) of 5-bromo-l,3-dimethyl-benzene was dissolved in anhydrous tetrahydrofuran. This solution was slowly added to a reaction flask wherein 17,0 g (0,70 mo¬ les) of magnesium shavings were stirred in anhydrous tet¬ rahydrofuran. Nitrogen gas was used as a protective gas in the flask. After the addition the solution was boiled for a further half hour. The cooled solution was slowly added to a vigorously stirred solution containing 250 ml (2.13 moles) of methyl-trichlorosilane in anhydrous tetrahydrofu¬ ran. During the addition the temperature was kept at 0 to 10° C. After the addition the solution was stirred for a further 2 hours at 20°C.

From the reaction mixture a major part of the solvent and unreacted methyl-trichlorosilane was removed under reduced pressure. From the pulpy residue the product was extracted with n-hexane.

The n-hexane extract was concentrated and the product iso¬ lated by vacuum distillation.

The product, (3,5-dimethyl-phenyl)-methyl-dichlorosilane, exhibited a boiling point of 67°C/0,12 mbar. Its NMR- spectrum confirmed its structure. Its purity was determi¬ ned using gas chromatography.

Example II

202 g (0.93 moles) of 4-bromo-l,2-dimethoxy-benzene was dissolved in anhydrous tetrahydrofuran. This solution was slowly added to a flask wherein 24,3 g (1.00 moles) of magnesium was stirred in anhydrous tetrahydrofuran. Nitro¬ gen was used a protective gas in the flask. After the ad-

dition, the solution was stirred for a further half hour. The cooled reaction mixture was slowly added to a vigo¬ rously stirred solution containing 370 ml (3.14 moles) of methyl-trichlorosilane in anhydrous tetrahydrofuran. Du¬ ring the addition the temperature was kept at 0 to 10°C. After the addition the solution was stirred for 2 hours at 20°C.

From the reaction mixture a major part of the solvent and unreacted methyl-trichlorosilane was removed. The product was extracted from the pulpy residue with a mixture of n- hexane and anhydrous ethylether.

The extract was concentrated and thereto was added 390 g (3.7 moles) of trimethylortoformate. After about a week the mixture was distilled under reduced pressure. The cru¬ de product was distilled under vacuum.

The product, (3,4-dimethoxyphenyl)-methyl-dimethoxy-silane boiled at 113°C/0.4 mbars. Its NMR-spectrum confirmed its structure. Its purity was determined using gas chroma¬ tography.

In the same way as described in the Examples I and II the following compounds may be prepared.

3-(3,5-dimethoxyphenyl)-propyl-trichloro-silane,

6-(l-pyrenyl)-hexyl-methyl-dimethoxy-silane,

16-(2,5-dimethoxyphenyl)-hexadecyl-trimethoxy-silane,

4-quaterphenyl-trimethoxy-silane, and

4-/4*-(phenoxy)-phenoxy/-phenyl-methyl-dichloro-silane.

Example III

141 g (0.67 moles) of 4-bromo-2,6-dimethyl-benzonitrile was dissolved in a mixture of anhydrous tetrahydrofuran and methyldimethoxychlorosilane. This solution was slowly ad¬ ded to a flask wherein 36.5 g (1.5 moles) of magnesium was stirred in anhydrous tetrahydrofuran. In the flask nitro¬ gen was used as a protective gas and the reaction tempera¬ ture was 10 to 35°C. After about 20 hours a major part of the solvent and unreacted methyldimethoxychlorosilane was removed from the reaction mixture under reduced pressure. The product was extracted from the pulpy residue with a mixture of n-hexane and anhydrous ethylether.

The extract was concentrated and the product isolated by vacuum distillation. The crude product was purified by me¬ ans of vacuum distillation.

The product, (3,5-dimethyl-4-cyano-phenyl)-methyl- dimethoxysilane boiled at 120°C/0.4 mbars. Its structure was confirmed with NMR and its purity determined with gas chromatography.

The purity of the products according to Examples I, II and III was over 95%.

In the same way as described in the Example III, the follo¬ wing compounds may be prepared.

(3,5-dicyano-phenyl)-phenyl-dimethoxy-silane, and

(3' ,5 ^• -dicyano-biphenyl)-methyl-dimethoxy-silane.

Example IV

A silicon polymer containing 10% of 3,5-dimethylphenyl groups was prepared in the following manner.

In a flask using nitrogen as a protective gas, at 0°C 3.000 g (0.01369 moles) of (3,5-dimethyl-phenyl)- methyl-dichlorosilane, 7.022 g (0.05446 moles) of dimethyl- dichlorosilane and 0.0897 g (0.0006 moles) of methyltrich- lorosilane was mixed and to this flask was slowly added a 6N ammonia solution. The product was extracted into ethyl- ether, the ether extract washed.with water and dried with anhydrous calcium sulfate.

The polymerization was carried out by evaporating the et- hylether and to the residue 0.1% of tetra-methylammonium- hydroxide was added. The mixture was stirred under nitroge.n gas at 100-120°C and the viscous product for a further 20 minutes at 140°C to destroy the catalyst. The silanol groups in the product were capped by treatment with hexa- methyldisilazane for 8 hours at 80 to 100°C.

The low molecular compounds were removed by dissolving the product in ethylether and precipitating the polymer by the addition of methanol or a water-methanol-mixture. The steps of dissolution and precipitation were repeated several times. The solvent residues were removed in an nit¬ rogen stream at 120°C.

From the product a silica capillary column was prepared, using as a substrate a commercial fused silica capillary, onto the inside surface of which after treatment according to the invention, a film of the polymerized silicon com¬ pound was adsorbed. The characteristics of the column were tested using a Grob-test mixture.

Example V

A silicon polymer containing 25% of 3,4-dimethoxyphenyl groups was prepared in the following manner.

In a flask under a nitrogen atmosphere, at 20°C 4.846 g (0.020 moles) of

(3,4-dimethoxyphenyl)-methyl-dimethoxysilane, 2.188 g (0.0182 moles) of dimethyl-dimethoxysilane, 0.0545 g (0.00040 moles) of methyl-trimethoxysilane and 0.138 g (0.00053 moles) of l,3,5-trivinyl-l,3,5-trimethyl-cyclotrisiloxan are mixed for 50 hours with 7 ml of acetonitrile and 7 ml of water. To the reaction mixture water was added and the product extracted with dichloromethane.

The .product was polymerized and tested as in Example IV.

Example VI

A silicon polymer containing 5.5 % of

3,5-dimethyl-4-cyano-phenyl groups was prepared in the following manner.

In a flask 2.350 g (0.010 moles) of (3,5-dimethyl-4-cyano- phenyD-methyldimethoxy-silane and 9.620 g (0.080 moles) of dimethyldimethoxysilane were mixed with 7 ml of acetonitri¬ le and 7 ml of water at 20°C for 50 hours. To the reaction mixture water was added and the product was extracted with dichloromethane.

The product was polymerized and tested as in Example IV.

In the following Table the retention times for the polymers of Examples IV, V and VI with respect to certain listed

test compounds are given. For comparison purposes a commer¬ cial column SE-54 was used.

From the results obtained it can be seen that for a number of test compounds the retention times are greatly increa¬ sed as compared to those of the standard column, which na¬ turally is of advantage in certain applications. More im¬ portant, however, is the fact that by using different acti¬ ve groups on the phenyl nucleus, the retention time for any specific compound may be varied, thus allowing for the tailor-making of columns for e.g. gas chromatography for specific applications.

TABLE

Retention times (RT) and relative retention time (RRT) in mi

Stationary phase composition Phase layer Column I.D. Leng

SE-54 phenyl 5%, vinyl 1% 0,25 um 0,20 mm 25

Ex. IV 3,5-dimethyl phenyl 10% 0,25 um 0,20 irm 25

Ex. V 3 ,4-di-methoxy phenyl 25%, vinyl 2% 0,20 um 0,20 mm 25

Ex. VI 3,5-dimethyl-4-cyanophenyl 5,5% 0,20/um 0,20 πm 25