CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present patent application has subject matter related to the disclosure of patent application S. N.

(CEL-88-115) , f led ; and patent application S. N. (CEL-89-72) , filed

BACKGROUND OF THE INVENTION Polymers with a comb structure of pendant side chains are a new class of organic materials which exhibit interesting optical properties.

In United States Patent Numbers 4,694,066;

4,755,574; and 4,762,912 liquid crystalline polymers are described which have pendant side chains which exhibit nonlinear optical susceptibility, in addition to mesogenic properties.

U. S. 4,792,208 discloses nonlinear optically responsive organic compounds and side chain polymers in which the molecular dipoles have an electron donor moiety linked through a conjugated TΓ bonding system to an electron acceptor sulfonyl moiety.

U. S. 4,808,332 and U. S. 4,810,338 disclose polymers with pendant side chains in which a εtilbene- type structure or a diphenylbutadiene-type structure is in conjugation with an electron-donating group and an electron-withdrawing group. These extended conjugated dipolar electronic systems exhibit an exceptionally high level of second order nonlinear optical susceptibility β.

Thin films of organic or polymeric materials with large second order nonlinearities in combination with silicon-based electronic circuitry have potential as systems for laser modulation and deflection, information control in optical circuitry, and the li e.

Of specific interest with respect to the present invention are publication such as U.S. 3,678,082 and U.S.

4,540,743 which described the esterification of alcohols in the presence of an aminopyridine catalyst. Because of the important applications of nonlinear optically responsive organic compounds and polymerizable monomers, there is increasing research effort to develop new and improved methods for synthesizing the conjugated dipolar electronic structures which provide the desirable optical properties.

Accordingly, it is an object of this invention to provide a novel method for the synthesis of organic compounds and polymerizable monomers which exhibit a high level of nonlinear optical response. It is a further object of this invention to provide an improved multistep process for the production of acrylate monomers having a chemical structure characterized by an electron-donating group which is linked through a conjugated electronic system to an electron-withdrawing group.

Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.

DESCRIPTION OF THE INVENTION

One or more objects of the present invention are accomplished by the provision of a process for the preparation of an ester which comprises (1) forming a carboxylate intermediate having the formula:

by reacting the following compounds in an organic solvent mediu :

where X is hydrogen or an electron-withdrawing substituent; Y is an electron-withdrawing substituent; Z is -NR-, -S- or -0-; n is an integer with a value of 1-6; R is hydrogen or a Cj-C ₄ alkyl substituent; and R ¹ is a aliphatic, alicyclic or aromatic radical containing between about 1-12 carbon atoms; (2) heating the carboxylate intermediate of step(l) in an organic solvent medium under acidic conditions at a temperature between about 40°-i50°C to form a stilbene alcohol intermediate

having the formula:

(3) forming an ester having the formula:

by reacting the stilbene alcohol of step(2) with an anhydride having the formula:

0

2 ii

R -C

\

C

/

R ² -C

in an organic solvent medium in contact with a catalyst having the formula:

where X, Y, Z and n are as previously defined; R ² is an aliphatic, alicyclic or aromatic substituent containing between about 1-9 carbon atoms; and M is hydrogen or a tertiary amine substituent containing between about 2-6 carbon atoms.

In another embodiment this invention provides a process for the preparation of an ester which comprises (1) forming a carboxylate intermediate having the formula:

by reacting the following compounds in an organic solvent medium:

where X is hydrogen or an electron-withdrawing substituent; Y is an electron-withdrawing substituent; Z is -NR-, -S- or -0-; n is an integer with a value of 1-6; R is hydrogen or a Cι-C alkyl substituent; and R ¹ is an aliphatic, alicyclic or aromatic radical containing between about 1-12 carbon atoms; (2) heating the carboxylate intermediate of step(l) in an organic solvent medium under acidic conditions at a temperature between 40°-150°C to form a diphenylbutadiene alcohol intermediate having the formula:

(3) forming an ester having the formula:

by reacting the diphenylbutadiene alcohol of step(2) with an anhydride having the formula:

in an organic medium in contact with a catalyst having the formula:

where X, Y, Z and n are as previously defined; R ² is an aliphatic, alicyclic or aromatic substituent containing between about 1-8 carbon atoms; and M is hydrogen or a tertiary amine substituent containing between about 2-6 carbon atoms. In the above represented process embodiments, the X and Y substituents in the organic structures are illustrated by electron-withdrawing groups which include nitro, cyano, trifluoromethyl acyl, carboxy, alkanoyloxy, aroyloxy, carboxamido, alkoxysulfonyl, aryloxyεulfony, tricyanovinyl, triflate, and the like.

The R ¹ substituent in the organic structures is illustrated by aliphatic, alicyclic and aromatic radicals which include methyl, propyl, allyl, methoxyethy1, 3- hexenyl, octyl, decyl, cyclopentyl, cyclohexyl, phenyl, 4-fluorophenyl, 4-methoxyphenyl, tolyl, 4-pyridyl, and the like.

The R ² substituent in the organic structures is illustrated by aliphatic, alicyclic and aromatic radicals which include methyl, propyl, 3-methoxypropyl, hexyl, heptyl, vinyl 2-propenyl, phenyl, 4-methoxyphenyl, 4- ethoxycarbonylphenyl, and the like.

The step(l) reaction to form the carboxylate intermediate is conducted at a temperature between about 15°-110°C for a period of about 0.5-24 hours as necessary for completion of the reaction. The εtep(l) reaction is conducted in an organic medium of one or more solvents such as hexane, benzene, toluene, nitrobenzene, dibutyl ether, dioxane, tetrahydrofuran, dimethylfor amide, carbon disulfide, dimethylsulfoxide, acetone, acetonitrile, pyridine, carbon tetrachloride, and the like.

The step(2) reaction to form the stilbene alcohol or diphenylbutadiene alcohol is conducted for a period of about 0.2-24 hours as necessary to complete the reaction. The step(2) reaction medium is an organic solvent medium of the type described about for step(l). The acidic conditions in step(2) preferably are provided by an organic acid such as formic acid, acetic acid, methacrylic acid, trifluoroacetic acid, benzenesulfonic acid, benzoic acid, and the like.

The step(3) esterification reaction is conducted at a temperature between about 20°-120°C for a period of about 0.5-24 hours as necessary to complete the reaction. The step(3) reaction medium is an organic solvent medium

of the type described above for εtep(l). A preferred solvent medium for step(3) is an organic tertiary amine εuch as pyridine, either alone or in admixture with another organic solvent. An important aspect of the step(3) esterification reaction is the presence of a pyridine or 4-tertiaryamine substituted pyridine catalyst. Illustrative of tertiarya ine substituted pyridine catalysts are 4- dimethylaminopyridine,4-(1-pyrrolidino)pyridine, 4-(l- piperidino)pyridine, 4-(1-hexahydroazepino)pyridine, 4- (4-morpholino)pyridine, 4- (4-methyl-l- piperidinyl)pyridine, and the like.

Preparation Of Schiff Base Starting Material

The other reactants utilized in the invention process embodiments are commercially available or can be prepared by εyntheεiε procedures described in the chemical literature. For example, 2,4,6- trinitrophenylacetic acid can be prepared by the reaction of l-chloro-2,4, ^' 6-trinitrobenzene and ethyl malonate in the presence of metallic sodium.

The following examples are further illustrative of the present invention. The components and specific ingredients are presented as being typical, and various modifications can be derived in view of the foregoing disclosure within the εcope of the invention.

EXAMPLE I This Example illustrates the preparation of 4-[N- (methacroyloxyethyl)-N-methylamino]-4' -nitrostilbene monomer.

A. Aminobenzaldehyde Starting Material

Following the procedure deεcribed in U.S. 4,808,332, a reactor is charged with 2- (methylamino)ethanol (134 g, 1.8 moles), 4- fluorobenzaldehyde (74.4 g, 0.6 mole), potassium carbonate (82.8 g, 0.6 mole) and dimethylsulfoxide (750 ml), and the mixture is heated at 95°C for 72 hours. The product mixture is cooled and poured into three liters of ice water. The yellow solid that precipitates is filtered, washed with water, and dried in a vacuum oven, mp 72°C. The 4-[N-(2-hydroxyethyl)-N- methylamino]benzaldehyde product is recrystallized from water as needle-like crystals.

B. Schiff Base

4-[N-(2-hydroxyethyl)-N-methylamino]benzaldehyde (179 g, 1.0 mole) and toluene (1.2 liters) are charged to a reaction flask, and the reactor is purged with argon.

The reaction medium is heated to reflux under argon, and water is removed with a Dean-Stark trap.

Methanesulfonic acid (0.2 ml) is added to the refluxing solution, and then aniline (102 g, 1.1 moles) is added dropwise, and the heating is continued until about 18 ml of water is removed. A yellow precipitate forms on cooling, and is separated by filtration and dried, p 111.9°C.

C. Stilbene Alcohol

A reactor is charged with 4-nitrophenylacetic acid (163 g; 0.9 mole) and two liters of toluene. The mixture is heated at reflux, and water iε removed with a Dean- Stark trap.

Schiff base (190 g; 0.75 mole) aε prepared above and methacrylic acid (128 ml; 1.5 moles) are added to the reactor contents, and the mixture is heated at 110°C for two hours. The reaction mixture is cooled to room temperature, and the precipitated product (172 g) is separated by filtration.

The crude product (100 g) is recrystallized from 1.5 liters of acetonitrile to yield magenta cryεtals, mp

D. Acrylate Monomer

A reactor is charged with εtilbene alcohol (29.8 g; 0.1 mole) aε prepared above, pyridine (300 ml) and dimethyla inopyridine catalyεt (2.44 g; 0.02 mole). The reactor contentε are heated to 75°C, and methacrylic anhydride (40.1 g; 0.26 mole) is added, and the reaction is conducted at 75°C for 20 hours.

The product mixture is cooled, and poured into a liter of water. The resultant crystalline precipitated iε recovered by filtration, and washed with water and with ether.

The crude product iε recryεtallized from ethyl

acetate to yield orange crystals, mp 152°C.

The corresponding 4-Fluoro and 4-trifluoromethyl acrylates are prepared by substituting 4- Fluorophenylaceticacidand4-trifluoromethylphenylacetic acid, respectively, for the 4-nitrophenylacetic acid reactant in the stilbene alcohol preparation described above.

EXAMPLE II This Example illustrates the preparation of 4-[N-(2- methacroyloxyethyl)-N-methylamino]-2 ',4 ' -dinitrostilbene monomer.

A. Stilbene Alcohol

A reactor iε charged with 2,4-dinitrophenylacetic acid (45.23 g, 0.2 mole; Aldirch) , toluene (360 ml), and Schiff base (50.9 g, 0.2 mole) as prepared in Example I. The reaction mixture is stirred at room temperature for one hour, then methacrylic acid (34.4 g, 0.4 mole) is added dropwise, and the reactor contents are heated at 75°C for three hours and at 110°C for two hours.

On cooling, the product separates as cryεtalε ^' , mp

B. Acrylate Monomer

A reactor iε charged with stilbene alcohol (24 g, 0.07 mole) aε prepared above, pyridine (240 ml) and dimethylaminopyridine catalyεt (1.71 g, 0.014 mole). The reactor contentε are heated to 75°C, and methacrylic anhydride (29 ml, 0.195 mole) iε added, and the reaction is conducted at 75°C for 20 hours.

The product mixture is cooled, and poured into 750 ml of water. The resultant black crystalline precipitate

iε recovered by filtration and dried at 50°C in a vacuum oven, mp 122°-125°C. The chemical εtructure of the product is consistent with a NMR spectral analysis.

Recrystallization of the product from ethyl acetate/ethanol (3.2/1) yields shiny black crystals, mp

125°-126°C.

The corresponding oxy-substituted and thio- substituted acrylates are prepared by using ethylene glycol and 2-mercaptoethanol, respectively, in place of the 2-(methylamino)ethanol reactant in the Schiff baεe preparation deεcribed in Example I.

EXAMPLE III Thiε Example illustrates the preparation of 4-[N-(4- methacroyloxybutyl)-N-ethylamino]-2',4'6 '-trinitrostil- bene.

A. Aminobenz ldehyde Starting Material Following the procedure of Example I, 2- (ethylamino)ethanol iε reacted with 4-fluorobenzaldehyde to provide 4-[N-ethyl-N-(2-hydroxyethyl)amino]benεal- dehyde starting material.

B. Schiff Base Following the procedure of Example I, aminobenzal- dehyde starting material as prepared above is reacted with aniline to form a correεponding Schiff baεe intermediate product.

C. Stilbene Alcohol

2,4,6-Trinitrophenylacetic acid (mp 159°-160°C) iε prepared for l-chloro-2,4,6-trinitrobenzene and ethyl malonate in the preεence of metallic εodium in accordance with a procedure by M. Kimura in J. Pharm. Soc. Jpn. ,

22,1216 (1953).

Following the procedure of Example I, a Schiff baεe as prepared above iε reacted with 2,4,6- trinitrophenylacetic acid to provide a correεponding εtilbene alcohol product.

D. Acrylate Monomer

Following the procedure of Example I, stilbene alcohol as prepared above is esterified with methacrylic anhydride to provide a corresponding acrylate monomer product.

The corresponding acetate and benzoate esterε are prepared by substituting acetic anhydride and benzoic anhydride, respectively, for the methacrylic anhydride reactant in the esterification procedure.

EXAMPLE IV This Example illustrates the preparation of 4-[N-2- (methacroyloxyethyl)-N-ethylamino]-4'-nitro-1,3-butadiene monomer.

A. Diphenylbutadiene Alcohol A reactor fitted with a mechanical εtirrer, thermometer. Dean Stark trap with a condenεer, and an argon bubbler iε charged with 360 ml of toluene. The solvent iε heated to reflux to remove any water and then cooled to room temperature. To the toluene iε added 4- (N-2-hydroxyethyl-N-ethylamino)cinnamaldehyde, (43.86 g, 0.2 mole) with methaneεulfonic acid (0.2 mole %, 0.19 g) . The reaction mixture iε heated to reflux, and aniline (0.2 mole, 18.6 g) iε added dropwiεe with azeotropic removal of water (3.6 ml), for 18 hourε. After cooling to room temperature, 4-nitrophenylacetic acid (43.48 g, 1.238 mole) is added followed by a dropwise addition of methacrylic acid (34.4 g, 0.4 mole). The reaction mixture is stirred at room temperature for 12 hours, heated to 75°C for 3 hours and then refluxed at 110°C for 2 hours. The reaction mixture is cooled to room temperature, and the solid diphenylbutadine alcohol precipitates from εolution. The crude product iε recovered by filtration, and recryεtallized from ethanol.

B. Acrylate Monomer A reactor fitted with a mechanical stirrer, thermometer and temperature controller is charged with 4- (N-2-hydroxyethyl-N-ethylamino)-4' -nitro-1,4-diphenyl- 1,3-butadine (33.85 g, 0.1 mole), dry pyridine (250 ml) and 4-N,N-dimethylaminopyridine (1.71 g, 0.014 mole). The reaction mixture iε heated to 75°C before beginning the dropwise addition of freεhly diεtilled methacrylic anhydride (29 ml, 0.195 mole). The reaction iε maintained at 75°C for twenty hourε, cooled to room temperature, and poured into 750 ml of diεtilled water. The solid product separates as a precipitate. The precipitate is isolated by filtration, and then dried at 50°C in a vacuum oven. ¹ The crude product iε purified by recrystallization from ethanol.