GB1582713A - Benzoaxazole derivatives process for their preparation and their use as optical brighteners - Google Patents

Description

(54) NOVEL BENZOXAZOLE DERIVATIVES, PROCESS FOR THEIR PREPARATION AND THEIR USE AS OPTICAL BRIGHTENERS (71) We, HOECHST AKTIENGES ELLSCHAFT a body corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Postfach 80 03 20, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to benzoxazole derivatives and to a process for their preparation.

It has been proposed to use 1,4-bis-[benzoxazolyl-2']-naphthalenes (cf. German Patent No. 1 282 592, German Offenlegungsschrift No. 1 745 622 and German Offenlegungsschrift No. 2 237 874) and 2,6-bis [benzoxazolyl-2']-naphthalenes (cf. German Patent No. 1 719 353) as optical brighteners.

The present invention is based on the observation that certain 1,7-bis-[benzoxazolyl2']-naphthalenes, which are colorless or slightly yellow, and have a pronounced violet to reddish-blue fluorescence in solution, possess excellent optical brightening properties and confer upon substrates containing them a reddish-white coloration.

The present invention provides compounds of the formia

in which each of R1 to R4, which may be the same or different, is a hydrogen atom or a non-chromophoric substituent, and R5 is a hydrogen atom, an alkyl group, a holagen atom, preferably a chlorine or bromine atom, a carboxy or sulfo group or a functionally modified carboxy or sulfo group.

Suitable non-chromophoric substituents are especially straight chain and branched alkyl groups having up to 18, preferably up to 12, especially from 1 to 4, carbon atoms which may be substituted by a carboxy group or a functionally modified carboxy group, alkenyl groups preferably having from 2 to 4 carbon atoms, aryl groups, preferably phenyl groups, aralkyl groups, preferably phenyl-lower alkyl groups, for example benzyl and phenethyl groups, acyl groups, carboxy and sulfo groups, functionally modified carboxy and sulfo groups, arylamino groups, sulfonyl groups and halogen atoms, preferably chlorine atoms.

By the term "functionally modified carboxy group" there is to be understood a carboxylic acid derivative, that is to say a compound having a carbon atom three valencies of which are occupied by hetero atoms, especially oxygen, nitrogen or sulfur atoms. More especially there is to be understood by this term salts with colorless cations, preferably alkali metal or ammonium salts, the cyano group, carboxylic acid ester groups, carboxylic acid amide groups and carboxylic acid hydrazides and the analogous thioderivatives. Preferred carboxylic acid ester groups are those of the formula COOQ1, in which Q1 is a phenyl group or an optionally branched lower alkyl group, each of which may carry one or more substituents, preferably lower dialkylamino, lower trialkylammonium, hydroxy or lower alkoxy groups. Preferred carboxylic acid amide groups are those of the formula CONQ2Q3, in which each of Q2 and Q3 is a hydrogen atom or a lower optionally substituted, alkyl group, or in which Q2 and Q3 form together with the nitrogen atom a hydro-aromatic ring.

By the term "functionally modified sulfo group" there is to be understood a sulfo group which is bound to a hetero atom, that is to say salts with colorless cations, preferably alkali metal or ammonium salts, sulfonic acid ester groups and sufonamide groups. Preferred sulfonic acid ester groups are those of the formula SO,OQ1, in which Q1 has the meaning given above, and preferred sulfonamide groups are those of the formula SO2NQ2QS, in which Q2 and Q3 have the meanings given above.

By the term "acyl group" there is to be understood a group of the formula COQ4 in which Q4 is an optionally substituted, preferably lower alkyl group or phenyl group, especially an unsubstituted lower alkanoyl group or the benzoyl group.

By the term "sulfonyl group" there is to be understood a group of the formula SO2Q4, in which Q4 is a lower alkyl or phenyl group which may be substituted by a lower dialkylamino, a lower trialkylammonium, an acylamino or a sulfo group.

Preferred compounds of the formula (1) are those in which each of R1 to R4, which may be the same or different, is a hydrogen atom, an alkyl group having from 1 to 18 carbon atoms which may be substituted by one or more non-chromophoric substituents, an alkenyl group having from 2 to 4 carbon atoms, an aryl, aralkyl or carboxy group, a group of the formula -COOR10 or -SO2R10 in which R10 is a straight chain or branched alkyl group from 1 to 18 carbon atoms, a hydroxyalkyl or alkoxyalkyl group, a dialkylaminoalkyl group, a trialkylammoniumalkyl group or an aralkyl group, or in which two adjacent substituents R1 to R4, together with the carbon atoms to which they are attached, form a fused hydroaromatic or aromatic ring, and R5 is a hydrogen atom, an alkyl group having from 1 to 4 carbon atoms, a chlorine atom, a cyano group or a group of the formula -COOR11 or -SO2R11 in which R11 is a hydrogen atom, an alkyl group having from 1 to 4 carbon atoms or an aryl or aralkyl group.

Especially preferred compounds in accordance with the present invention are those of the formula

in which each of R1 and R2 is a hydrogen atom, an alkyl group having from 1 to 18 carbon atoms which may be substituted by one or more non-chromophoric groups, an aralkyl or carboxy group, a group of the formula -COOR6 or -SO2R6 in which R6 is a straight ohain or branched alkyl group, having from 1 to 18 carbon atoms, a hydroxyalkyl, alkoxyalkyl, dialkylaminoalkyl, trialkylammoniumalkyl, or aralkyl group, or in which R1 and R2, on adjacent carbon atoms form, rogerher with those carbon atoms, a fused hydroaromatic or aromatic ring.

Other especially preferred compounds as those of the formula

in which each of R2 and R3 is a hydrogen atom, a (C,) alkyl or a (ICl) alkoxy group, a chlorine or bromine atom, a phenyl, carboxy, alkoxycarbonyl, dimethylaminoalkoxycarbonyl or hydroxyalkylsulfonyl group or R2 and R3, together with the carbon atoms to which they are attached, form a fused benzene ring, and R1 is a hydrogen atom or R1 and R2, together with the carbon atoms to which they are attached, form a fused benzene ring.

The compounds accotd'ing ro the present invention can be synthesize in various ways.

Two preferred methods are as follows: (a) The dichloride of naphthalene-1, 7dicarboxylic acid is condensed with 2 moles of an o-aminophendl of the formula

preferably in rhe presence of an acid acceptor, and the resulting bis-acylamino compound of the formula

is heated, suitably in an inert gas atmosphere, preferably under n'itrogen, in a high-boiling solvent, preferably in 1 ,2,4-trichlorobenzene, a mixture of trichlorobenzenes or methyl benzoate, at a temperature of from 180 to 250 C, preferably of from 190 to 220 C, optionally in the presence of a catalyst such as zinc chloride or p-toluene-sulfonic aid.

(b) The compounds of the formulae (1), (2) and (3) can be synthesized in a single step process using as starting compounds 1 mole of naphthalene-1, 7-dicarboxylic acid or a deri native thereof, for example the dinitrile, and at least 2 moles of an o-amino-phenol of the formula (4), by heating these compounds to a higher temperature, suitably of from 150 to 300 C, suitably in an inert gas, preferably under nitrogen. This reaction is carried out in the presence of a dehydrating agent.

Examples of dehydrating agents or of catalysts acting as dehydrating agents are boric acid, boric anhydride, zinc chloride, aluminium chloride, polyphosphoric acid, and pyrophos phoric acid. It may be advantageous to use a high-boiling solvent, for example dichloro benzene, trichlorobenzene, α-chloronaph- thalene, tetralin or an aliphatic, optionally etherified, hydroxy compound, for example ethylene glycol monomethyl ether, diethylene glycol diethyl ether and triethylene glycol di methyl ether, preferably polyphosphoric acid, 1,2,4-trichlorobenzene or a mixture of trichlorobenzenes.

The compounds of the formulae (2) and (3) can be obtained by reacting naphthalene-1, 7-dicarboxylic acid with the appropriate aminophenols of the formulae (7) and

These processes and other processes suitable for the preparation of such compounds are described in the patent literature mentioned above.

The o-aminophenols of the formulae (4), (7) and (9) are either known from the literature (cf. Beilsteins Handbuch der organischen Chemie, 4th edition, volume XIII) or may. be prepared according to known methods. The substituents R1 to R4 may also be introduced into the products obtained by known pro cesses, for example by halogenation, chloro methylation and sulfochlorination, or by pro cesses starting from chlorosulfonated or carboxy-containing compounds to give com pounds having functionally modified sulfo- or carboxy groups or by converting these groups into other groups of this kind or into the free acids, for example by transesterification or hydrolysis.

Suitable o-aminophenols are, for example: o - aminophenol, 3 - amino - 4 - hydroxy - 1 methylbenzene, 3 - amino - 2 - hydroxyl methylbenzene, 4 - amino - 3 - hydroxy - 1 methylbenzene, 5 - amino - 4 - hydroxy - 1,2 dimethyl - benzene, 5 - amino - 4 - hydroxy 1,3 - dimethylbenzene, 3 - amino - 4 hydroxy - 1 - tert. - butylbenzene, 5,6,7,8 tetrahydro - 1 - amino - 2 - naphthol, 5,6,7,8 tetrahydro - 3 - amino - 2 - naphthol, 5 amino - 6 - hydroxy - hydrindene, 3 - amino 4 - hydroxy - diphenyl, 6 - chloro - 4 - amino- 3 - hydroxy - 1 - methyl - benzene, 4 - chloro- 2 - aminophenol, 5 - chloro - 2 - aminophenol, 4,6 - dichloro - 2 - aminophenol, and 3 amino - 4 - hydroxy - 1 - - hydroxyethyl sulfonyl - benzene, moreover 2 - amino - 3 oxybenzoic acid methyl ester, 3 - amino - 2 oxybenzoic acid methyl ester, 3 - amino - 4 hydroxy - benzoic acid methyl ester and 4 amino - 3 - hydroxybenzoic acid methyl ester.

Instead of methyl esters the following esters of the above aminohydroxybenzoic acids may also be used: the ethyl, propyl, isopropyl, n - butyl, isobutyl, tert. - butyl, n - amyl, n - hexyl, n - heptyl, n - octyl, n - nonyl, n - decyl, n - undecyl, n - dodecyl and lauryl esters.

Suitable alcoholic compounds for the trans esterifications are, for example: tert. - butanol, n - amyl alcohol, 2 - ethylbutanol - (1), octanol, cetyl alcohol, lauryl alcohol, cyclo hexanol, 2-, 3- and 4 - methylcyclohexanols, glycol, propianediol - (1,2), n - butanediols (1,3) and - (1,4), 2 - methyl - n - butanediol (1,3), n - hexanediol - (2,5), glycerin, penta erythritol, diethylene glycol, triethylene glycol, glycol monomethyl ether and monoethyl ether and - mono - a - butyl ether, 3 - methoxy n - buranol - (1), glycide, benzyl alcohol, 2 phenyl - ethanol - (1), 4 - isopropylbenzyl alcohol, 2 - dimethylaminoethanol - (1), 2 diethylaminoethanol - (1), 2 - di - n - butyl aminoethanol - (1) and 1 - dimethylamino propanol - (2).

Substrates which can be brightened with the compounds of the present invention are, for example: lacquers, synthetic fibers, for example those consisting of or containing acetylcellulose, polyamides, polyoefins, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile and especially polyesters, as well as sheers, films, ribbons and ether shaped articles of such materials.

The compounds which are insoluble in water may be used as solutions in organic solvents or as aqueous dispersions, preferably with the use of a dispersing agent. Suitable dispersing agents are, for example soaps, polyglycol ethers derived from fatty alcohols, fatty amines, or alkyl phenols, cellulose sulfite waste liquors or condensation products of optionally alkylated naphthalene-sulfonic acids with formaldehyde.

The fibrous material can be brightened with the aqueous or organic liquor either by an exhaustion processes, at a temperature preferably of from about 20 to 150 C, or under thermosoling conditions, the latter method involving impregnating or spraying the textile material for example with the brightener solution or dispersion and squeezing it off, for example, between rollers to a liquor take-up of from about 50 to about 120%. The textile material is then submitted for a period of from about 10 to 300 seconds to a heat treatment, preferably by dry heat, at a temperature of from about 120 to 240 C.

This thermosoling process can alternatively be combined with further finishing operations, for example finishing with artificial resins in order to impart easy care properties, the materials optionally being condensed after impregnation and drying at 100 to 150 C, for a period of from 5 to 20 minutes at a tem perature of from 150 to 200 C for the purpose of cross-linking.

The compounds according to the present invention may also be added to washing detergents. These washing detergents may contain the usual fillers and auxiliaries, for example alkali metal silicates, alkali metal phosphates or condensed phosphates, alkali metal borates, alkali metal salts of the carboxy-methylcelluloses, foam stabilizers, for example alkanolamides of higher fatty acids or complex forming agents, for example soluble salts of the ethylene-diamine-tetraacetic acid or diethylene-triamine-pentaacetic acid, as well as chemical bleaching agents, for example perborates or percarbonates, perborate activators of the polyacetic acid amide type, which lead to splitting off of peracetic acid when used with the percompounds, and disinfection agents.

The compounds according to the present invention may also be added to high molecular weight organic materials prior to or during shaping. They may be added, for example, during the preparation of fibers, films, sheets, ribbons, plates or other shaped articles to plastics powders, thermoplastic compositions melts, polymer solutions or dispersions; for example they may be dissolved in spinning solutions prior to spinning. Suitable com pounds may also be added to the low mele- cular weight starting materials prior to polycondensation or polymerization, for example in the case of polyamlide-6, polyamide-6,6 or linear polyesters of the polyethylene tereph thalate type.

It is especially significant that those compounds according to the present invention which are substituted by two carboxy or alkoxycarbonyl groups may be incorporated into linear polyesters and synthetic polyamides by ester or amide bonds, if they are added to these materials or preferably to their starting compounds under appropriate conditions.

Brighteners which are incorporated into a substrate by a chemical bond in this manner are distinguished by extremely high sublimation and solvent-fastness properties.

In the above field of application, preferably in the brighteneing of fibrous materials by the exhaustion process or under thermosoling conditions, the compounds according to the present invention may be used in admixture with brighteners of other classes of compounds, preferably with brighteners the formula

in which R1 and R2 have the meanings given above. The use df compounds of the present invention in admixture with the compound of the above formula in which R1 and R2 are both hydrogen atoms is especially advantageous for textile applications. In this manner, very good degrees of whiteness from neutral to reddish white shades may be obtained.

The shade of the optically brightened substrates may be influenced by varying the ratio of the brilghtening compounds according to the present invention and the compounds of the above formula.

The quantity df rhe compounds according to the present invention to be used for brightening may vary within wide limits, depending on the application purpose and on the desired effect. It can be easily determined by simple preliininary tests and is generally from about 0.01 to about 2%, preferably from 0.02 to 011%, based on the material to be brightened.

The following Examples illustrate the invention. The percentages are by weight, un less otherwise stated.

EXAMPLE 1: 21.6 parts by weight of naphthaRene-1,7- dicarboxylic acid and 22.9 parts by weight of o-aminophenol were heated for about 4 hours to about 210 C with the addition of 1.5 parts by weight of boric acid in 100 parts by volume of 1,2,4-trichlorobenzene. About 30 parts by volume of trichlorobenzene and water distilled off. The reaction mixture was cooled to about 80 to 900'C, about 80 parts by volume of ethanol were added and cooling was continued until room temperature was reached.

The precipitated 1,7-bis[benzoxazolyl-2']naphthalene (compund 101) was suctionfiltered, washed with ethanol and dried. 30 parts by weight of the above compound were obtained, which had a melting point of from 182 to 183 C. A sample which was recrystallized from toluene melted at from 187 to 188 C (slightly yellow crystals).

EXAMPLE 2: 21.6 parts by weight of naphthalene-1,7dicarboxylic acid and 28.8 parts by weight of 5-amino-4-hydroxy-1,2-xylol were heated while stirring with 150 parts by weight of polyphosphoric acid (85% P2O5) to 180 C over a period of one hour and stirred for another 3 hours at 1800C. A homogeneous mass was formed, which was allowed to cool to about 100 C, about 200 parts by volume of hot water (from 80 to 90 C) were then added dropwise, and a precipitate formed. The sus pension obtained was further diluted with 500 parts by volume of cold water and cooled to room temperature and the precipitated product was suction-filtered off. The resulting product was washed until neutral with water and, after drying, about 35 parts by weight of 1,7 - bis(5,6 - dimethyl - benzoxazolyl - z) naphthalene (compound 104) were obtained.

A sample which was recrystallized from toulene had a melting point from 228 to 2300'C (yellowish crystals).

EXAMPLE 3: 21.6 parts by weight of naphthalene-1,7 dicarboxylic acid were heated in 100 parts by volume of toluene with 27.8 parts by weight of thionyl chloride for a period of about 3 hours, from an initial temperature of 70 C to 110 C. Thereafter about 70 parts by volume of solvent were distilled off under a nitrogen atmosphere at a temperature of from about 105 to 110 C and the distilled solvent was replaced by fresh toluene. The acid chloride solution thus obtained was added, at a temperature of from 70 to 75 C, over a period of 15 minutes, to a mixture of 33.4 parts by weight of methyl 3-amino-4-hydroxy benzoate in 200 parts by volume of toluene, optionally with the addition of 26 parts by weight of dimethylaniline and the resulting mixture was refluxed for 3 hours. Toluene was then steam-distilled off, the aqueous phase was decanted from the precipitated greasy product and the latter was heated with 400 parts by volume of acetone. The turbid solution which formed was clarified and the acylamino compound formed was precipitated by adding 600 parts by volume of water. The resulting mixture was suction-filtered and washed with water and after dry ing, 44.0 parts by weight of a beige powder were obtained which had a melting point of from 230 to 240 C.

The acylamino compound obtained was cyclized by heating for about 4 hours under nitrogen in 500 parts by volume of methyl benzoate in the presence of about 2 parts by weight of toluene-sulfonic acid, at a tempera ture of from about 180 to 190 C. After clari fication with about 4 parts by weight of char coal, about 300 parts by volume of methyl benzoate were distilled off and after cooling to room temperature, the precipitated 1,7bis(5 - methoxycarbonylbenzoxazolyl - 2)naphthalene (compound 108) was suctionfiltered off. The resulting product was washed with methanol and, after drying, there were obtained 32 parts by weight of a yellowish crystalline powder, which could be further purified by recrystallization from methyl benzoate. This product had a melting point of from 259 to 2610C.

EXAMPLE 4: 47.8 parts of 1,7-bis(5-methanycarbonylbenzoxazolyl-2)-naphthalene were suspended in 800 parts by volume of isopropanol and 25 parts by weight of potassium hydroxide dissolved in 50 parts by volume of water were added. The reaction mixture was refluxed for 2 hours, 90 parts by volume of water were added and the mixture was again refluxed for 2 hours. The addition of 90 parts by volume of water repeated, and the reaction mixture was kept at the boil for 3 hours. 50 parts by volume of concentrated hydrochloric acid in 300 parts Iby volume of water were added, the mixture was digested for about 1 hour at a temperature of from 70 to 800C, suction-filtered at room temperature, washed neutral with water and dried. Thus 43 parts by weight of a brownish crude product were obtained, which could be further purified by recrystallization from dimethylformamide.

The pure 1,7-bis(5-carboxybenzoxazolyl-2)naphthalene (compound 109) melted at a ternperature of from 391 to 3940C and precipitated as light yellow crystals.

EXAMPLE 5: 45 parts by weight of 1,7 - bis(5 - carboxybenzoxazolyl - 2) - naphthalene were heated in 500 parts by volume of o - dichlorobenzene with 50 parts by weight of thionyl chloride for a period of about 5 hours, from an initial temperature of 70 C, up to 100 C. Thereafter about 250 parts by volume of o - dich iorbbenzene were distilled off and after coal ing, the precipitated acid chloride was suctionfiltered off and washed with cyclohexane.

The acid chloride which was still moist with the solvent was taken up in 300 parts by volume of dioxane and 15 parts by weight of dimethylaminoethanol were added. The reaction mixture was heated for 2 hours to 80 C, while stirring, then diluted with 500 parts by volume of water and clarified with 5 parts by weight of kieselgur. The pH of the filtered product was adjusted at a value of from 8 to 9 and the reaction product was salted out with sodium chloride. It was suction-filtered off and washed with water. After drying, there were obtained 38 parts by weight of a yellowish orude product. By recrystallization from acetic ester pure 1,7 - bis [5 - ( - dimethylaminoethoxycarbonyl)benzoxazolyl - 2] - naphthalene (compound 110) was obtained as yellowish crystals, which had a melting point of from 115 to 117 C.

The compounds listed in the following Table, as far as they have not be mentioned in the Examples 1-5, may be prepared in an analogous manner. TABLE

Absorption measured in dimethyl formamide No. R M.P. Xmax.[nm]

101 aNf 187-188 342 24.5 102 of 189~190 334 25.2 103 %I70N 168-170 355 24.9 C/f5 cH3 N 104 228-230 358 23.7 CH3 c6 105 CtCNS 239-241 358 25.7 C/f3 CH3 N 106 172-173 17 2~175 338 24.0 Cll3ooC C.

107 182-184 337 27.2 108 < > 259-261 339 25.2 TABLE (Continued)

Absorption measured in dimethyl formamide No. R M.P. # max. [nm] #. 10-3

109 Atoox 391-394 - 110 N (CA/39Z uoS 115-117 355 25.3 111 CtfsOoC 270-272 346 29.3 C3ooc 112 NOTCH2 CH2 5 2 < 212-222 338 24.1 113 tNX 271-275 363 27.1 114 271-273 354 34.0 EXAMPLE 7: A fabric of polyethylene terephthalate sralple fibers was treated ar a goods-to-liquor ratio of 1:20 with a 0.2% aqueous dispersion of the compound 104 which had been prepared with the addition of a dispersing agent (calculated on the weight of the goods), for 1 hour, at 1200C in a high temperature dye ing apparatus. The fabric sample bad a high degree of whiteness of a reddish shade, after rinsing and drying, in comparision with an untreated sample.

EXAMPLE 8: A fabric of polyethylene terephthalate staple fibers was treated for one hour, at 1200C in a high temperature dyeing apparatus at a goods - to - liquor - ratio of 1:20 with a 0.08% aqueous dispersion of a mixture consisting d from 50 to 80 parts of 1,4 - bis- (benzoxazolyl - 2) - naphthalene and of from 20 to 50 parts of the compound 102 which had been prepared with the addition of a dispersing agent (1 g/l calculated on the weight of the fabric). The sample had a con siderably Imlproved degree of whiteness of a neutral to reddish shade, after rinsing and drying, in comparison with unbrightened material.

EXAMPLE 9: A fabric of triacetate was treated for one at at 120 C in a high temperature dyeing apparatus at a good - to - liquor - ratio of 1:20, with the addition d 2 g/l of sodium chlorite and !1 g/l of an activator, with a 0.08% aqueous distension of a mixture consisting of from 50 to 80 parts of 1,4 - bis (benzoxazolyl -'2) - naphthalene and of from 20 to 50 parts of the compound 101. The sample had a very high degree of whiteness after rinsing and drying, in comparison with a material which had not been brightened.

EXAMPLE 10: A fabric of polyethylene terephthalate staple fibers was impregnated with a liquor containing 7.5 g/l of a 7% aqueous dispersion of a mixture consisting of from 50 to 80 parts of 1,4-bis-(benzoxazolyl-2)-naphthalene and of from 20 to 50 'parts of the compound 101.

The fabric was squeezed off between two rubber rollers, until the Liquor take up was 80% of tihe weight of the fabric. The fabric was then dried on a pin stenter at 1900C for 45 seconds and fixed. Very good degrees of whiteness of a neutral to reddish shade were obtained.

Claims (1)

1. WHAT WE CLAIM IS:

   1. A compound of the formula

   in which each of R1, K2, R3 and R4, which may be the same or different, is a hydrogen atom or a non-chromophoric substituent and R5 is a hydrogen atom, an alkyl group, a halogen atom, a carboxy group, a sulfo group or a functionally modified carboxy or sulfo group.

   2. A compound as claimed in claim 1, in which each of R1 to R4 which may be the same or different, is a hydrogen atom, an alkyl group having from I to 18 carbon atoms which may be substituted by one or more non-chromophoric groups, an alkenyl group having from 2 to 4 carbon atoms, an aryl, aralkyl or carboxy group, a group of the formula -COOR10 or -SO2R10 in which R10 is a straight chain or branched alkyl group having ifrom 1 to 18 carbon atoms, a hydroxyalkyl or alkoxyalkyl group, a dialkylamino alkyl group, a trialkylammoniumalkyl group or an aralkyl group, or in which two adjacent groups substituents R1 to R4, together with the carbon atoms to which they are attached, form a fused hydroaromatic or aromaric ring, and R5 is a hydrogen atom, an alkyl group having from 1 to 4 carbon atoms, a chlorine atom, a cyano group or a group olf the formula -COOR11 or -SO2OR11, in which R11 is a hydrogen atom, an alkyl group having from 1 to 4 carbon atoms or an aryl or aralkyl group.

   3. A compound as claimed in claim 1 having the formula

   In which each of R1 and R2 is a hydrogen atom, an alkyl group having from I to 18 carbon atoms which may be substituted by one or more non-chromophoric groups, an aralkyl or carboxy group, a group of the formula -COOR6 or -SO2R6 in which R6 is a straight chain or branched alkyl group having from 1 to 18 carbon atoms, a hydroxyalkyl, alkoxyalkyl, dialkylaminoalkyl, trialkylammoniumalkyl, or aralkyl group, or in which R1 and R2 on adjacent carbon atoms form, together with those carbon atoms, a fused hydroaromatic or aromatic ring.

   4. A compound as claimed in claim 1 having the formula

   fin which each of R2 and R3 is a hydrogen atom, a (C1-C4) alkyl group, a (C1-4) alkoxy goup, a chlorine or bromine atom, a phenyl, carboxy, alkoxycarbonyl, dimethylaminoalkoxycarbonyl or hydroxyalkylsulfonyl group or R2 and R3, together with rhe carbon atoms to which they are attached, form a fused benzene ring and R1 is a hydrogen atom or R1 and R2, together with the carbon atoms ro which they are attached, form a fused benzene ring.

   5. Process for the preparation of a compound as claimed in claim 1, which comprises reacting 1 mol of the dichloride of the naph- thalene-l, 7-dicarboxylic acid with at least 2 mols of an o-aminophenol of the formula

   and cyclizing the resulting di-N,N'-acyl compound of the formula

   at a temperature of from 180 to 2500C.

   16. A process as claimed 'in claim 5, wherein the reaction is carried out in an inert gas atmosphere.

   7. A process as claimed in claim 5 or claim 6, wherein the reaction is carried out in a high-boiling solvent.

   8. A process as claimed in in claim 7, wherein the solvent is methyl bezoate, 1,2,4-trichlorobenzene or a mixture of trichlorobenzenes.

   9. A process as claimed in any one of claims '5 to 8, wherein cyclization is carried out in the presence of a catalyst.

   10. lA process as claimed In claim 9, wherein the catalyst is zinc chloride or p-toluenesul- tonic acid.

   11. Process for the preparation of a compound as claimed in claim 1, which comprises reacting 1 mol of naphthalene-1,7-dicarboxylic acid with at least 2 mols of an o-aminophenol as specified in claim 5, in the presence of a dehydrating agent at a temperature of from 150 to 300 C.

   12. A process as claimed in claim 11, wherein the dehydrating agent is boric acid.

   13. A process as claimed in claim 11 or claim '12, wherein the reaction is carried out in a high-boiling solvent.

   14. A process as claimed in claim 13, wherein the highJboiling solvent is polyphos- phoric acid, 1,2,4-trichlorobenzene or a mixture of trichlorobenzenes.

   15. A process for the preparation of a compound as claimed in claim 1, carried out substantially as described in any one of the Examples herein.

   16. A compound as claimed in claim 1 whenever prepared by a process as claimed in any one of claims 5 to 15.

   17. An article or composition which contains a compound as claimed in claim 1 as an optical brightener.

   18. An article or composition as claimed in claim '17, which also contains a compound of the formula

   in which R1 and R2 have the meanings specified in claim 1.