GB2137621A - Preparation of 1-naphthol-4-sulphonic acid - Google Patents

Abstract

A method for producing 1-naphthol-4-sulphonic acid in free acid form and contaminated with less than 2% by weight of the isomeric 1-naphthol-2-sulphonic acid, by sulphonating 1- naphthol in a solvent which is substantially inert towards the sulphonating agent and in which 1-naphthol-4-sulphonic acid has a solubility at >50 DEG C of from 0.01 to 5.0 % weight, comprises the step of separating the 1-naphthol-4-sulphonic acid from the reaction mixture by filtration at >50 DEG C directly after completion of the sulphonation.

Description

SPECIFICATION Improvements in or relating to organic compounds The present invention relates to a method for producing 1 - naphthol - 4 - sulphonic acid, known as Nevile-Wintheracid (NW acid), with a low content of the isomeric 1 - naphthol - 2 - sulphonic acid.

It is known that sulphonation of 1 - naphthol with sulphuric acid, oleum, sulphurtrioxide orchlorosul- phonic acid leads to mixtures of sulphonic acids, namely 1 - naphthol - 4 - sulphonic acid, 1 - naphthol - 2 -sulphonic acid, 1 - naphthol - 2,4- disulphonic acid and 1 - naphthol - 2,4,7 -trisulphonic acid. To improve the yield of the monosulphonicacids, it has been proposed to carry out the sulphonation under condi- tions such that part ofthe starting 1 - naphthol remains unsulphonated.

Alternatively polysulphonation of 1 - naphthol can be significantly reduced or practically avoided by using solvents which are inert under the reaction conditions, e.g. acetic acid, tetrachloroethane, benzene, nitrobenzene and other nitrated or halogenated organic solvents. Although the use of some of these solvents enables all the initial 1 - naphthol to be sulphonated, the resulting sulphonation product is a mixture of isomeric monosulphonic acids.

The Nevile-Winther acid is a useful product, widely employed fororganic synthesis. It is particularly used as a coupling componentforthe production of a great number of azo dyes. Therefore it is highly desirable to produce 1 - naphthol - 4- sulphonic acid as free as possible from the isomeric 1 - naphthol - 2 - sulphonic acid obtained as by-product in the sulphonation of 1 naphthol,andalsofreefrom unsulphonated 1 naphthol, since both products also react as coupling components. Contamination with 1 - naphthol - di and-tri-sulphonicacids is lessseriousforthis application, asthey do not couple with diazonium salts.

Various attempts to improve the yield of 1 - naphthol - 4- sulphonic acid over 1 - naphthol - 2 - sulphonic acid have been made, particularly by varying the reaction conditions, especially by operating attemperatures above 50"C.

However contamination of the 4-isomer bythe 2-isomer is still too high and further purification steps are needed. The usual procedure to separate the 2-isomerfrom the 4-isomer is fractional salting out of an aqueous solution of the isomeric sulphonic acid mixture, based on the factthatthe alkali or alkaline earth metal salts ofthe 2-isomerare less water-soluble than those ofthe 4-isomer. However, not only does the 2-isomer contamination in the finally purified 4 isomerstill amountto 5to 10% by weight but also the yield ofthe4-isomersaltissignificantly reduced by the elaborate purification steps. Furthermore, the salting out process requires high quantities of salt, thus polluting the waste waterto an undesirable extent.

It has now been found that 1 - naphthol - 4 sulphonic acid in the free acid form having a very low content of 1 - naphthol - 2 - sulphonic acid can be obtained directly without elaborate purification steps.

Accordingly, there is provided a method for produc ing 1 - naphthol - 4 - sulphonic acid in free acid form contaminated with less than 2% by weight of 1 naphthol - 2 - sulphonic acid, by sulphonating 1 naphthol in a solvent which is substantially inert towards the sulphonating agent and in which 1 naphthol - 4 - sulphonic acid has a solubility at a temperature > 50 C offrom 5.0% by weight, which method comprises the step of separating the 1 naphthol - 4- sulphonic acid from the reaction mixture by filtration at a temperature > 50 C directly after completion ofthe sulphonation.

Suitablesolventsforthesulphonation include aromatic monocyclic hydrocarbons which may be further nitrated orhalogenated, e.g. benzene, toluene, xylene, nitrobenzene, nitrotoluene, mono-, di-ortri- chlorobenzenes, or halogenated aliphatic hydrocarbons, e.g. chloroform, trichloroethylene, 1,1,1 - or 1,1,2 - trichloroethane, tetrachloroethylene or 1,1,2,2 tetrachloroethane. Depending on the sulphonating conditions and on the sulphonating agent, some aromatic monocyclic hydrocarbons are notfully inert and may be partially sulphonated, e.g. an aromatic monocyclic hydrocarbon such as benzene,toluene or xylene. Preferred solvents are those which are fully inerttowardsthesulphonating agent.

The amount of solvent which may be used according to the invention, isgenerallyfrom2to20times, preferably from 5 to 10 times the amount of 1 naphthol.

By a solubility of 0.01 to 5.0% by weight is meant that 0.01 to 5.0 g of 1 - naphthol - 4 - sulphonic acid are soluble in 100 g solventatatemperature > 50 C, i.e.

from 50 Cto the boiling point ofthe solvent.

Suitable sulphonating agents include sulphuric acid, oleum, sulphurtrioxide and chlorosulphonic acid. Chlorosulphonic acid is the most preferred sulphonating agent. It can be fully consumed in the reaction, even if a slight excess is originally present (e.g. by formation ofdisulphonic acids or reaction with the solvent) and the only by-product is hydrogen chloride, which is evolved as a gas. Chlorosulphonic acid givessuperioryields and puritiesthan other sulphonating agents.

Chlorosulphonic acid is generally used in an excess up to 20% by weight ofthe stoichiometric amount.

When a solvent inerttowardsthe sulphonating agent is used, e.g. halogenated or nitrated hydrocarbons as indicatedabove,thesulphonation iscarriedoutwith the stoichiometric amount or a light excess, e.g. up to 5% by weight of chlorosulphonic acid. When a solvent partially sensitive to the sulphonating conditions is used as a reaction medium, chlorosulphonic acid is added in an excess from 5 to 20% by weight to achieve complete sulphonation of 1 - naphthol.

Sulphonation with chlorosulphonic acid is conve niently performed by adding it slowly, e.g. dropwise, to the dissolved 1 -naphthol,advantageouslyata temperaturefrom - 20"C to 120'C.Whena partially sensitive solvent is used for the reaction medium, the addition of the sulphonating agent is preferably effected at the lower end ofthistemperature range, e.g. from -20"C to +20"C. If a fully inert solvent is used, the sulphonating agent is preferably added at a highertemperature, i.e. > 20 C depending on the boiling point of the solvent used.When addition ofthe chlorosulphonic acid is complete, the reaction mixture is further heated at a temperature > 50 C, preferably at a temperature from 60 to 1 OO"C, for 1 to 12 hours. If a solventwith a boiling point belowthe temperature ranges indicated above is used, the heating may be carried out under pressure.

Filtration ofthe reaction mixture is then carried out at a temperature > 50 C, advantageously atthe same temperature as the reaction temperature, preferably from 60to 100 C, depending on the boiling point of the solvent. The resulting filter cake is preferably washed with pure solvent, preferably at a temperature close to the filtration temperature. Alternativelyorin addition a washing step may be carried out with a solvent of lower boiling point, but in which the solubility ofthe product is similar to that in the reaction medium.

The resulting filter cake contains 1 - naphthol - 4 sulphonic acid in the free acid form, contaminated by a very low content of the undesired 2-isomer and of further organic impurities. The content of 1 - naphthol - 2 - sulphonic acid in the final product is lowerthan 2% by weight, and can be as low as 0.5% by weight or even lower, based on the weight ci - naphthol - 4sulphonic acid. Further organic impurities which may be present are 1 - naphthol in an amount of 0.5% by weight or even less and 1 - naphthol - 2,4- disulphonic acid in an amount from 1 to 3% by weight, all based on the weight of the NW acid.

Afterfiltration and removal of the mother liquor by washing,the resulting filter cake may be dried, conveniently at a temperature below 1 200C, optionally undervacuum.

Before drying, the filter cake may be further washed or stirred with the same solvent as the sulphonation solvent or a different solvent and then filtered atthe sametemperature conditions as indicated above. If anothersolventis used, it may not be fully inert towards the sulphonating agent but it should have solubilising properties similarto those of the sul- phonation solvent. Examples of such solvents are alkyl C1.5-aryl ethers such asanisol orphenetol. The amount of solvent used for this treatment generally ranges from 2to 20 times the volume ofthefilter cake.

Contraryto what has hitherto been believed, the -method of the invention enablesthe production of 1 naphthol - 4 - sulphonic acid in the free acid form by direct separation from the reaction mixture after completion ofsulphonation.

Instead of being dried, the filter cake can be dissolved in water and the organic solvent is removed according to known methods. The resulting aqueous solution of 1 - naphthol -4- sulphonic acid is readyfor use. If desired, the free acid can also be converted into the saltform according to known methods. For example, the sodium sulphonate can be obtained by addition of sodium chloride to the aqueous solution and subsequentwashing of the filter cake with brine.

The resulting sodium 1 - naphthol - 4- sulphonate is practically in the pure form.

The following Examples, in which all temperatures are in degrees Centigrade, illustrate the invention.

Example 1 73 g 1 - Naphthol are introduced in 500 ml chlorobenzene at 30 .60 g Chlorosulphonic acid are then added dropwise and the reaction is continued at 800for4 hours. After this period the reaction mixture contains 1 - naphthol -4- sulphonic acid and 5% by weight based on the theoretical yield of 1 - naphthol - 2 -sulphonicacid.

The reaction mixture is filtered and the filter cake is rinsed with 400 ml I hot chloro benzene to removethe remaining mother liquor. After drying undervacuum, the resulting filter cake contains 1 - naphthol -4sulphonic acid in a yield of 92% oftheory and < 0.5% 1 - naphthol - 2 - sulphonic acid and 3% of 1 - naphthol 2,4- disulphonic acid based on the weight off naphthol -4-sulphonicacid.

The chlorobenzene wet filter cake can be introduced in 200 ml water witch stirring. After elimination ofthe solvent, there is obtained an aqueous solution which after clarification is ready for use.

According to another alternative, 60 g sodium chloride can be added to the resulting aqueous solution. The precipitated sodium 1 - naphthol - 4 sulphonate is filtered and washed with brine. Sodium 1 - naphthol - 4- sulphonate substantially free from organic impurities is thus obtained in a theoretical yield of 88%.

Example 2 Byfollowingthe reaction procedure of Example 1 but using 1,2 - dichlorobenzene instead of chlomben- zene, a reaction mixture containing 4% ofthetheoretical yield of 1 - naphthol - 2 - sulphonic acid is obtained.

By treating the reaction mixture as disclosed in Example 1 free 1 - naphthol - 4 - sulphonic acid is obtained in a theoretical yield of 93%. Itcontains 140.5% 1 -naphthol-2-sulphonicacid and 2% 1 naphthol - 2,4- disulphonic acid based on its weight.

Example 3 73 g 1 - Naphthol and 60 g chlorosulphonic acid are reacted in 500 ml of a mixtureoftrichlorobenzene isomers according to the procedure of Example 1. The resulting reaction mixture contains 2% ofthetheoretical yield of 1 - naphthol - 2 - sulphonic acid. After filtration and rinsing with 400 m I ml hottrichlorobenzene, the filtrate is taken up in 300 ml water and the solvent is removed. The resulting aqueous solution contains 1 - naphthol - 4 - sulphonic acid in a theoretical yield of 93%, and 0.5% 1 - naphthol - 2 - sulphonic acid and 3% 1 - naphthol - 2,4- disulphonic acid based on the weight of the NW acid.

Example4 The procedure of Example 3 is repeated except that the filter cake is rinsed with 400 ml hot chloroform instead ofthe trichlorobenzene to remove the mother liquorfrom the filter cake.

After drying, a filter cake is obtained which contains free 1 - naphthol - 4 - sulphonic acid with atheoretical yield of 92% and < 0.5% 1 - naphthol - 2 - sulphonic acid and 1 % 1 - naphthol - 2,4- disulphonic acid based on theweight of the 4- sulphonic acid.

Example 5 73 g 1 - Naphthol are reacted atO in 700 ml toluene with 61 g chlorosulphonicacidaddeddropwise.The sulphonation reaction is then continued at 800 for4 hours. The resulting reaction mixture contains 5% of the theoretical yield of 1 - naphthol - 2 - sulphonic acid.

The reaction mixture is then filtered and the mother liquor is removed from the filter cake by rinsing with 500 ml hottoluene.

By treating the filter cake as disclosed in Example 1, free 1 - naphthol - 4 - sulphonic acid is obtained in a theoretical yield of 88% and containing 0.5% 1 naphthol - 2 - sulphonic acid and 1 - naphthol and 2% 1 - naphthol - 2,4 - disulphonic acid based on the weight ofthe NW acid. After conversion into the saltform as disclosed in Example 1, sodium 1 - naphthol -4sulphonate substantially free from organic impurities is obtained in a 85% theoretical yield.

Example 6 73 g 1 - Naphthol and 60 g chlorosulphonic acid are reacted in 700 ml benzene according to the procedure of Example 5. The resulting reaction mixture contains 7% 1 - naphthol - 2 - sulphonic acid.

Bytreating the reaction mixture as disclosed in Example 1, free 1 - naphthol - 4- sulphonic acid containing 1% 1 - naphthol - 2 - sulphonic acid and 3% 1 - naphthol - 2,4 - disulphonic acid based on its weight is obtained in a 87% yield.

Example 7 73 g 1 - Naphthol and 65 g chlorosulphonic acid are reacted in 700 ml isomericxylene mixture according to the procedure of Example 5. The resulting reaction mixture contains 2% 1 - naphthol - 2 - sulphonic acid.

By treating the reaction mixture as disclosed in Example 1, free 1 - naphthol - 4 - sulphonic acid is obtained in 80% yield. It contains < 0.5% 1 - naphthol 2 - sulphonic acid and 0.5%1 - naphthol - 2,4 disulphonic acid based on the weight ofthe NW acid.

Examples 73g 1 - Naphthol are reacted at 50" in 300 ml 1,1,2 trichloroethanewith 60g chlorosulphonicacid added dropwise. The sulphonation reaction is continued at 800 for a further 4 hour period. The resulting mixture contains 7% 1 - naphthol - 2 - sulphonic acid. After filtration of the reaction mixture, the filter cake is rinsed with 300 ml 1,1,2 -trichloroethaneto remove the mother liquorfrom the filter cake.

After drying,free 1 - naphthol -4 - sulphonic acid is obtained in 80% yield. It contains 1% 1 - naphthol -2- sulphonic acid and 1 % 1 - naphthol - 2,4- disulphonic acid based on theweightofthe NW acid.

Example 9 73 g 1 - Naphthol and 60 g chlorosulphonic acid are reacted at 50 in 800 ml 1,1,2,2 -tetrachloroethane and the reaction is continued at 80"for4 hours. The resulting reaction mixture contains 4% of thetheoretical yield of 1 - naphthol - 2 - sulphonic acid. After filtration ofthe reaction mixture, the filter cake is rinsed with 500 ml 1,1,2,2 -tetrachloroethane to remove the mother liquorfrom the filter cake.

After drying,free 1 - naphthol - 4 - sulphonic acid with a content of < 0.5% 1 - naphthol - 2 - sulphonic acid and 2% 1 - naphthol - 2,4 - disulphonic acid, is obtained in a theoretical yield of 90%.

Example 10 73 g 1 - Naphthol and 65 g chlorosulphonic acid are reacted at 600 at the boil in 600 ml chloroform, and further stirred at 600 for 10 hoursto give a mixture containing 10% 1 -naphthol-2-sulphonicacid.

The resulting reaction mixture is filtered and the filter cake is rinsed with 500 ml chloroform to be freed from the mother liquor. After drying, a filter cake containing free 1 - naphthol - 4 - sulphonic acid in 80% yield, 0.5% 1 - naphthol -2-sulphonicacid and < 0.5% 1 - naphthol - 2,4 - disulphonic acid (based on the NW acid weight) is obtained.

Example ii 73 g 1 - Naphthol and 60 g chlorosulphonic acid are reacted at the boil in 500 ml trichloroethylene and are further stirred atthe boilfor2 hours, giving a product containing 3% 1 - naphthol - 2 - sulphonic acid. After filtration ofthe reaction mixture, the filter cake is washed with 300 ml trichloroethylene to be freed from the mother liquor. The content of 1 - naphthol - 2 - sulphonic acid in the filter cake is approx. 2% ofthe theoretical yield.

The filter cake is further purified by a treatment at the boil in 500 ml trichloroethylene followed by filtration. After drying, free 1 - naphthol - 4 - sulphonic acid is obtained in a yield of 90%. It contains 1 % 1 naphthol - 2 - sulphonic acid and 3% 1 - naphthol - 2,4 disulphonic acid (based on the NW acid weight).

Example 12 The procedure of Example 11 is repeated butthe filter cake is further purified by a treatment with anisol followed byfiltration.Afterdrying,free 1 - naphthol 4- sulphonic acid is obtained in a yield of 89%. It contains < 0.5% 1 - naphthol - 2 - sulphonic acid and 3% 1 - naphthol - 2,4 - disulphonic acid (based on the NW acid weight).

Claims (17)

1. Amethodforproducing 1 -naphthol-4- sulphonic acid in free acid form contaminated with less than 2% by weight of 1 - naphthol - 2 - sulphonic acid, by sulphonating 1 - naphthol in a solvent which is substantially inerttowards the sulphonating agent and in which 1 - naphthol - 4 - sulphonic acid has a solubility at a temperature > 50 C of from 0.01 to 5.0% by weight, which comprises the step of separating the 1 - naphthol -4 - sulphonic acid from the reaction mixture by filtration at a temperature > 50 C directly after completion of the sulphonation.

2. A method according to Claim 1, in which the solvent is selected from halogenated aliphatic hydrocarbons and aromatic monocyclic hydrocarbons which are optionally nitrated or halogenated.

3. A method according to Claim 2, in which the solvent is selected from benzene, toluene, xylene, nitrobenzene, nitrotoluene, monochlorobenzene, dich lorobenzenes, trichlorobenzenes, chloroform, trichloroethylene, 1,1,1-or 1,1,2 - trichloroethane, tetrachloroethylene or 1,1,2,2 -tetrachloroethane.

4. A method according to any one of the preceding claims in which the solvent is used in an amount from 2 to 20 times the amount of 1 - naphthol.

5. A method according to Claim 4, in which the solvent is used in an amount from 5 times to 10 times the amount of 1 - naphthol.

6. A method according to any one ofthe preced ing claims, in which the sulphonating agent is chlorosulphonic acid.

7. A method according to any one of the preceding claims, in which chlorosulphonic acid is present in an excess from 5 to 20% by weight when the solvent is an aromatic monocyclic hydrocarbon.

8. A method according to Claim 7, in which ch lorosu Iphonic acid is added at a temperature from -20 to +20"C.

9. A method according to Claim 5, in which chlorosulphonicacid is present in a stoichiometric amount or in an excess up to 5% by weight when the solvent is an halogenated or nitrated hydrocarbon.

10. A method according to Claim 9, in which chlorosulphonic acid is added at a temperature > 20 C.

11. A method according to any one of the preceding claims, in which the reaction mixture is heated at a temperature > 50 C after addition of chlorosulphonic acid.

12. Amethodaccordingto Claim 11, in which the reaction mixture is heated at a temperature from 60 to 100"C.

13. A method according to any one of the preceding claims, in which filtration ofthe reaction mixture is carried out at the sametemperature as the reaction.

14. A method accordingto Claim 13, in which filtration is carried out at a temperature from 60to 100"C.

15. A method according to any one of the preceding claims, in which the content of 1 - naphthol - 2 - sulphonic acid in the final product is up to 0.5% by weight based on the weight of 1 - naphthol - 4 sulphonicacid.

16. A method for producing 1 - naphthol - 4- sulphonic acid in free acid form substantially as hereinbefore described with reference to Examples 1 to12.

17. 1 - Naphthol - 4 - sulphonic acid in free acid form whenever produced by a method according to any one of Claims 1 to 16.