GB1578168A

GB1578168A - Pyridyl alkylsulphonic acid derivatives and their use in electroplating baths

Info

Publication number: GB1578168A
Application number: GB931877A
Authority: GB
Original assignee: Cilag Chemie Ltd
Current assignee: Cilag Chemie Ltd
Priority date: 1976-03-12
Filing date: 1977-03-04
Publication date: 1980-11-05
Also published as: CH630355A5; AT361266B; JPS52116475A; BR7701506A; SU791230A3; IT1083723B; CA1072098A; FR2343729A1; DE2710721A1; ATA166477A; ES456723A1; FR2343729B1; NL7702673A

Abstract

The novel pyridylalkylsulphonic acid betaines of the general formula I <IMAGE> in which the substituents are as defined in Claim 1, are obtained by reacting a 2- or 4-pyridylalkylsulphonic acid or an alkali metal salt thereof with a suitable quaternising agent which is capable of introducing the substituent R on the ring nitrogen atom of the pyridyl group. The compounds of the formula (I) usually give an extremely uniform and flat nickel coating of outstanding ductility, when it is used as additive for conventional nickel electroplating baths. The compounds can be used in the nickel baths either alone or in combination with other additives which promote brightness or levelling.

Description

(54) NOVEL PYRIDYL ALKYLSULPHONIC ACID DERIVATIVES AND THEIR USE IN ELECTROPLATING BATHS (71) We, CILAG CHEMIE A.G., a Swiss Body Corporate, of Hochstrasse 209, Schaffhausen, Switzerland, 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: The present invention relates to certain novel pyridyl alkyl sulfonic acid betaines useful as additives to nickel electroplating baths.

Pyridyl sulfonic acids or pyridyl alkyl sulfonic acids as additives to nickel plating baths have been reported. United States Patent No 2,839,456, describes the use of 4-pyridyl ethane sulfonic acid, in combination with other additives, as a brightener. Although 2- and 4-pyridine ethane sulfonic acids do improve the luster of deposited nickel layers, they do not influence their levelling. United States Patent No 3,444,056 mentions certain quaternary compounds of pyridine-3-sulfonic acid as levellers and brighteners. The N-methyl-pyridine-3-sulfonic acid betaine and N-allyl-pyridine-3-sulfonic acid betaine mentioned in this patent are, however, not fully satisfactory. The nickel deposits turn lusterless and brittle with a too low ampere hour load per liter of nickel bath. This behavior of the bath cannot be prevented by any of the regeneration methods employed in electroplating. The compounds of the present invention produce a highly levelled nickel deposit of excellent ductility in a far more constant bath.

The present invention provides pyridyl alkyl sulfonic acid betaines of the general formula:

in which the substituent -(CH2)nSO3e' is in the 2- or 4-position of the pyridyl ring; n is the integer 1 or 2; and R is a methyl; methallyl; CH2COOH; sodium 2-hydroxypropylsulfonate; sodium 2-hydroxybutylsulfonate; sodium 3-hydroxybutylsulfonate; halobenzyl; loweralkylbenzyl or benzyl group substituted with the group:

wherein the substituent -(CH2)nSO8 is in the 2- or 4-position of the pyridyl ring and n is the integer 1 or 2.

For the purposes of nomenclature, the aforementioned groups: sodium 2hydroxypropylsulfonate; sodium 2-hydroxybutylsulfonate and sodium 3hydroxybutylsulfonate may also be denoted as 3-Na-sulfo-2-hydroxypropyl, 4-Na-sulfo-2 hydroxybutyl and 4-Na-sulfo-3-hydroxybutyl, respectively.

By the term "loweralkyl" as used herein is meant an aliphatic hydrocarbon with from 1 to 4 carbon atoms; and by the term "halo" is meant fluorine, chlorine and bromine, that is, those halogens with an atomic weight of less than 80.

The pyridyl alkyl sulfonic acid betaines (I) of the present invention are conveniently prepared by quaternization of an appropriate 2- or 4-pyridyl alkyl sulfonic acid (II-a) or its alkali metal salt (II-b), preferably the sodium salt:

wherein the substituent -(CH2)nSO3(H,Z) is in the 2- or 4-position of the pyridyl ring and n is 1 or 2. Quaternization is accomplished by using an appropriate quaternizing agent suitable for introducing the aforementioned R-substituent on the ring nitrogen of the pyridyl group, such as, dimethyl sulfate, methallyl chloride, sodium chloroacetate, an appropriate benzyl halide or an appropriately substituted haloloweralkyl, as more fully described and exemplified hereinafter. The compounds of formulae (II-a) and (II-b) are obtained from known procedures in the art, for example, by reaction between 2- or 4-vinylpyridine and sodium bisulfite according to J. Am. Chem. Soc., 69, 2465 (1947) for the preparation of the ethyl sulfonic acids or by reaction between appropriate haloalkyl pyridines and sodium sulfite.

To prepare the formula (I) compounds in which R is methyl, the precursor (II-a) or (II-b) is reacted with dimethyl sulfate as the quaternizing agent, generally utilizing a slight stoichiometric excess of the latter. Elevated temperatures may be employed to enhance the rate of reaction. Since dimethyl sulfate is a liquid at ambient temperatures, the use of an additional organic solvent for the quaternization reaction is normally unnecessary. The reaction may be illustrated as follows:

To prepare the formula (I) compounds in which R is CH2COOH, approximately equimolar amounts of the precursor (II-b) and haloacetic acid in the form of an alkali metal salt, for example, sodium (III) in an aqueous solvent are reacted, preferably under reflux conditions. The reaction mixture containing the so-formed alkali metal salt is then cooled and treated with a suitable mineral acid, e.g., hydrochloric acid, to convert the salt (IV) to its corresponding acid form (V). The foregoing reaction may be illustrated as follows:

The compounds of formula (I) wherein R is halobenzyl or loweralkylbenzyl are prepared in similar fashion. The precursor (II-b) is reacted with an appropriate benzyl halide (VI), e.g., halobenzyl chloride or loweralkylbenzyl chloride, in water, preferably under reflux conditions. After cooling and treatment with mineral acid, the desired N-benzyl substituted Droduct (VII is ohtained.

R' =H, halo, loweralkyl The compounds of formula (I) wherein R is methylallyl may be similarly quaternized, as described above for R as a benzyl group, except that methallyl chloride is used as the quaternizing agent.

The compounds of formula (I) wherein R is sodium 2-hydroxypropylsulfonate, sodium 2-hydroxybutylsulfonate or sodium 3-hydroxybutylsulfonate are obtained by quaternizing (II-b) with an appropriate halo-hydroxyalkyl sulfonic acid in sodium salt form, as illustrated below by sodium 2-hydroxypropylsulfonate (X).

To prepare the compounds of formula (I) wherein R is benzyl substituted with the group:

a,a'-dichloroxylol (o-, m- or p-form) is reacted with at least two stoichiometric equivalents of the precursor (II-b) in an aqueous solvent. Elevated temperatures are advantageously employed to enhance the rate of reaction. Upon completion of the reaction and subsequent cooling of the reaction mixture, followed by treatment with mineral acid, the desired products are obtained through conventional recovery techniques. The foregoing quaternization can be illustrated with a,a'-dichloro-p-xylene as follows:

The compounds of formula (I) produce a highly levelled nickel deposit of excellent ductility when used as additives for the electro-deposition of nickel coatings in conventional galvanic nickel baths. These compounds are suitable for use in galvanic nickel baths either alone or in combination with other luster-promoting or levelling additives. For example, an optimum luster is obtained in combination with such generally known brighteners as saccharin, diarylsulfonimides, naphthalene trisulfonic acids or sulfonates or acetylenic compounds, such as propargyl alcohol. The latter compound is especially useful in enhancing the levelling effect of the compounds of the invention. Furthermore, the compounds of the invention may be used in conjunction with conventional wetting agents such as, for example, sodium lauryl sulfate or with other ionized or non-ionized agents that decrease surface tension. The galvanic baths may also contain conventional buffering agents, such as boric acid or tartrates.

The galvanic bath comprises an acidic solution of a nickel salt, preferably nickel sulfate, nickel sulfamate, nickel fluoborate, nickel chloride or nickel acetate. Mixtures of such salts are also suitable. Typical of the nickel galvanic baths in which the compounds (I) of the invention may be employed are those described in United States Patent No 3,444,056. The compounds of the invention may be advantageously used in concentrations ranging from 0.05 gram per liter (g/l) to 2.0 g/l of bath, although from 0.1 to 0.5 g/l is preferred. Other preferred parameters are a bath temperature of about 50 to 60"C, a pH of about 3.5 to 5.0 most preferably 4.5, and a current density ranging from 1 to 10 amp/dm2. The bath may be mechanically or air stirred. If it is air stirred, the use of a non-foamy agent is recommended.

The present invention also provides an electroplating bath for electro-depositing levelled and lustrous nickel comprising an electroplating bath which comprises an aqueous acidic solution of at least one nickel salt and at least one additive which is a compound of the formula:

in which the substituent -(CH2),S030 is in the 2- or 4-position of the pyridyl ring; n is the integer 1 or 2, and R is a methyl; methallyl; CH2COOH; CH2(CH2)CH2SO3Na wherein x is the integer 1 or 2; sodium 2-hydroxypropyl-sulfonate; sodium 2-hydroxybutylsulfonate; sodium 3-hydroxybutylsulfonate; benzyl; halobenzyl; loweralkylbenzyl; or benzyl group substituted with the group;

wherein the substituent -(CH2)nSO8 is in the 2- or 4-position of the pyridyl ring and n is the integer 1 or 2, in a concentration of from 0.05 to 2.0 grams per liter, and preferably, from 0.1 to 0.5 grams per liter. The preferred additives of formula (I) are those wherein R is either benzyl or a benzyl group substituted with the previously described group:

including but not limited to 2-[N-benzylpyridyl-(2)1-ethane sulfonic acid betaine and 1 ,2-bis[2-(2-sulfoethyl)-pyridinium-(1)-methyljbenzene.

The following Examples are intended to illustrate, but not to limit, the scope of the present invention. Example IV, Example V (first two compounds) and Example VI relate to the preparation of certain pyridyl alkyl sulfonic acid betaines which may be used in the electroplating baths of the present invention.

EXAMPLE I

A. 2-[N-carboxymethyl-pyridyl- (2)]-ethanesulfonic acid betaine: 23.3 Grams (0.2 mol) of chloroacetic acid sodium salt, 41.8 g (0.2 mol) of 2-pyridyl ethane sulfonic acid sodium salt and 50 g of water are refluxed for five hours Following cooling down to 20"C, the reaction mixture is treated with 250 g of concentrated hydrochloric acid.

The crystallized sodium chloride is filtered off by suction and the solution is concentrated to dryness under vacuum. The residue is mixed with 350 ml of methanol. The product, 27.5 g of 2-[N-carboxymethyl-pyridyl-(2)]-ethane-sulfonic acid betaine, which crystallizes at room temperature is filtered off by suction and vacuum dried at 1100C; decomposition point: 214"C.

B. 2-[N-carboxymethyl-pyridyl- (4)]-ethane sulfonic acid betaine is obtained in the same way, by employing an equivalent quantity each of 4-pyridyl ethane sulfonic acid sodium salt and chloroacetic acid sodium salt as reactants; decomposition point: 234"C.

C. [N-carboxymethyl-pyridyl-(4)]-methanesulfonic acid betaine is obtained in the same way, by employing an equivalent quantity each of 4-pyridyl methane sulfonic acid sodium salt and chloroacetic acid sodium salt as reactants; decomposition point: 290"C.

EXAMPLE II

A. 2-[N-methyl-pyridyl-(2)]-ethane sulfonic acid betaine: 55 Grams (0.29 mol) of 2-pyridyl ethane sulfonic acid and 40.7 g (0.32 mol) of dimethyl sulfate are heated to 150-155"C. Two hours later the reaction mixture is allowed to cool down to 20"C and a mixture of 40 ml of ethanol and 40 ml of isopropanol are added. After standing for 24 hours, the precipitated crude product is filtered off by suction. After double recrystallization from methanol, the white crystals are vacuum dried at 80"C. The final yield is 16.8 g of 2-[N-methyl-pyridyl-(2)j-ethane sulfonic acid betaine; decomposition point: 2090C.

B. 2-[N-methyl-pyridyl-(4)/-ethane sulfonic acid betaine is prepared in the same manner from equivalent amounts of 4-pyridyl ethane sulfonic acid and dimethyl sulfate.

EXAMPLE 111

A. 2-[N-(2-methylbenzyl)-pyridyl-(2)]-ethane sulfonic acid betaine: 41.8 Grams (0.2 mol) of 2-pyridyl ethane sulfonic acid sodium salt, 28.1 g (0.2 mol) of o-methylbenzyl chloride and 20 g of water and refluxed for 5 hours. The reaction mixture is then allowed to cool down to 2UOC and 250 g of concentrated hydrochloric acid are added.

The precipitated sodium chloride is filtered off by suction and the filtrate concentrated to dryness under vacuum. The residue is mixed with 200 ml of ethanol and the precipitated white crystal mass is filtered off by suction and vacuum dried at 1100C to yield 32 g of 2-[N-(2-methylbenzyl)-pyridyl-(2)]-ethane sulfonic acid betaine; decomposition point: 223 C.

B. 2-[N-(2-methylbenzyl)-pyridyl-(4)]-ethane sulfonic acid betaine is obtained in the same way, by using an equivalent quantity each of 4-pyridyl ethane sulfonic acid sodium salt and o-methylbenzylchloride as reactants; decomposition point: 241"C.

EXAMPLE IV

[N-benzyl-pyridyl-(2)]methane sulfonic acid betaine: 17.3 Grams (0.1 mol) of 2-pyridyl methanesulfonic acid sodium salt, 12.7 g (0.1 mol) of benzylchloride and 13 g of water are refluxed for 2 hours at 100-1050C. The reaction mixture is allowed to cool down to 200C and 100 ml of concentrated hydrochloric acid are added. The precipitated sodium chloride is filtered off and the solution concentrated to dryness. The residue is mixed with 100 ml of ethanol. The precipitated white crystals are filtered off and vacuum dried at 1100C to yield 13.7 g of N-benzyl-pyridyl-(2) methane sulfonic acid betaine; decomposition point: 230"C.

EXAMPLE V By following the procedures of Examples III and IV, except that equivalent quantities of appropriate reactants are employed, the following respective products are obtained: 2-[N-benzylpyridyl-(2)] ethane sulfonic acid betaine; decomposition point: 198 C.

2-[N-benzylpyridyl-(4)-ethane sulfonic acid betaine; decomposition point: 234 C.

2-[N-(2-chlorobenzyl)-pyridyl-(2)]-ethane sulfonic acid betaine; decomposition point: 2380C.

2-[N-(4-chlorobenzyl)-pyridyl-(2)]-ethane sulfonic acid betaine; decomposition point: 201 C 2-[N-(2-chlorobenzyl)-pyridyl-(4)]-ethane sulfonic acid betaine; decomposition point: 237 C.

EXAMPLE VI

A. 2-[N-(3-Na-sulfopropyl)-pyridyl-(2)]-ethane sulfonic "acid betaine: 4i.8 Grams (0.2 mol) of 2-pyridyl ethane sulfonic acid sodium salt, 30.5 g (0.25 mol) of propansultone, 200 g of methanol and 15 g of water are heated to 65 C for 7 hours. The reaction mixture is then concentrated under vacuum and the residue is mixed with 200 ml of concentrated hydrochloric acid. The precipitated sodium chloride is filtered off and the mother liquor concentrated to dryness. The oily residue is! dissolved in 200 my of methanol and allowed to stand for 2 days. Some 2-pyridyl ethane sulfonic acid, whicE'precipitates within this time, is filtered off and'the filtrate is neutralized with 30% sodium methylate solution (in methanol). A white salt precipitates which is filtered off and vacuum dried at 110 C to yield 17 g of 2-[N-(3-Na-sulfopropyl)-pyridyl-(2)]-ethane sulfonic acid betaine; decomposition point: 228 C B. The procedure of Example VI-A is repeated except that an equivalent amount of butansultone is substituted for the propansultone used therein to yield the corresponding product, 2-[N-(4-Na-sulfobutyl)-pyridyl-(2)]-ethane sulfonic acid betaine.

C. By following the procedure of Example VI-A, except that equivalent amounts of appropriate starting materials are employed as reactant, there are obtained as respective products: [N-(3-Na-sulfopropyl)-pyridyl-(4)]-methane sulfonic acid betaine; and 2-[N-(4-Na-sulfobutyl)-pyridyl-(4)]-ethane sulfonic arid betaine.

EXAMPLE VII

A. 2-[N-(3-Na-sulfo-2-hydroxypropyl)-pyridyl-(2)]-ethane sulfonic acid betaine: 20.9 Grams (0.1 mol) of 2-pyridyl ethane sulfonic acid sodium salt, 19.7 g (0.1 mol) of 3-chloro-2-hydroxypropyl sulfonic acid-'(1)-sodium salt and 20 ml of water are heated at 95 C for 6 hours. The reaction mixture is then concentrated under vacuum and the residue is mixed with 100 ml of concentrated hydrochloric acid. The insoluble sodium chloride is filtered off and the mother liquor concentrated to dryness. The oily residue is dissolved in 100 ml of methanol and allowed to stand for 2 days. Some 2-pyridyl ethane sulfonic acid, which precipitates within this time, is filtered off and the filtrate is neutralized with 30% sodium methylate solution (in methanol). The precipitated white salt is filtered off and vacuum dried at 110 C to yield 11 g of 2-[n-(3-Na-sulfo-2-hydroxypropyl)-pyridyl-(2)]- ethane sulfonic acid betaine; decomposition point: 183 C.

B. The procedure of Example VlI-A is followed, except that equivalent amounts of appropriate starting materials are employed as reactants, to yield the following respective products: 2-[N-(4-Na-sulfo-2-hydroxybutyl)-pyridyl-(2) -'ethane sulfonic acid betaine; 2-[N-(4-Na-sulfo-3-hydroxybutyl)pyridyl-(4)]-ethane sulfonic acid betaine; and [N-(3-Na-sulfo-2-hydroxypropyl)-pyridyl-(4)]-methane sulfonic acid betaine.

EXAMPLE VIII

A. 1, 4-Bis-[2- (2-sulfoethyl)-pyridinium- (1) -methyl7-benzene: 62.8 Grams (0.3 mol) of 2-pyridyl ethane sulfonic acid sodium salt, 17.5 g (0.1 mol) of α,α'-dichloro-p-xylene and 50 g of water are heated to 100-105 C for 4 hours. The reaction mixture is then cooled and 200 g of concentrated hydrochloric acid are added. The precipitated sodium chloride is filtered off and, the filtrate concentrated under vacuum to dryness. 200 Ml of methanol are added to the residue. The precipitated impure crystals are filtered off, dissolved in 120 ml of water at 200C, and again precipitated by adding 480 ml of ethanol. The white crystal mass is filtered off and vacuum dried at 110 C to yield 26 g of 1,4-bis-[2-(2-sulfoethyl)-pyridinium-(1)-methyl]-benzene; decomposition point: > 350 C.

B. In the same manner, except that equivalent amounts of appropriate reactants are employed, there are obtained as respective products: 1,2-bis-[2-(2-sulfoethyl)-pyridinium-(1)-methyl]-benzene; decomposition point: 248 C.

1,3-bis-[2-(2-sulfoethyl)-pyridinium-(1)-methyl]-benzene; decomposition point: 251 C.

1,4-bis-[4-(2-sulfoethyl)-pyridinium-(1)-methyl]-benzene; decomposition point: 258 C.

EXAMPLE IX The following illustrate typical galvanic nickel baths in which the subject compounds of formula (I) may be employed. It is understood that the hereinmentioned subject compounds are not listed for the purpose of limiting the scope of the invention thereto but to exemplify the usefulness of all compounds within formula (I).

A Nickel sulfate . 7H2O .. ...g/l .. 310 Nickel chloride . 6H2O ...g/l .. 50 Boric Acid . .. . . . ...g/l .. 40 Lauryl sulfate . ...g/l .. 0.2 Saccharin .. .................. ...... . ..g/l .. 2.0 2-[N-benzylpyridyl-(2)]-ethanesulfonic acid betaine ..g/l .. 0.3 pH . .... . . ........ .. 4.6.

Temperatur . . ... C .......... .. 50-60 Current density . ..amp/dm2.. 1-7 B Nickel sulfate . 7H2O .. ...g/l .. 310 Nickel chloride . 6H2O ...g/l .. 50 Boric Acid . . ..g/l . 40 Lauryl sulfate ...g/l . 0.2 Saccharin sodium . ...... ..... ..... . ...g/l . 1.0 1,3,6-naphthalene trisulfonic acid sodium salt .... .................. ...... . ...g/l . 1.0 2-[N-benzylpyridyl-(4)]-ethanesulfonic acid betaine ..g/l .. 0.3 pH .... . ......... .. 4.6 Temperature .. . ... C........... ..50-60 Current density . . . ampldm- 1-7 C Nickel sulfate . 7H2O ... ...g/l.. 280 Nickel chloride . 6H2O . . . g/l.. 40 Boric Acid .. . . ...g/l .. 40 Lauryl sulfate ...... . ...g/l.. 0.2 Dibenzylsulfonimide . ...g/l.. . 8.0 Propargyl alcohol ....... ..... ....... . ...g/l .. . 0.04 1,2-bis-[2-(2-sulfoethyl)-pyridinium(1) methyl]-benzene . . . . .g/l . 0.15 pH ..... . . ......... .. 4.6 Temperature . . C .. 50-60 Current density . ...amp/dm2.. 1-7 EXAMPLE X A. The procedure of Example III-A is followed except that 18 g (0.2 mole) of methallyl chloride is substituted for the o-methylbenzyl chloride used therein to yield, as the final product, 2-[N-(2-methylpropen-2-yl)-pyridyl-(2)]-ethane sulfonic acid betaine, also known as 2-[N-methallyl-pyridyl-(2)]-ethane sulfonic acid betaine, decomposition point: 196 C.

B. 2-[N(2-methylpropen-2-yl)-pyridyl-(4)]-ethane sulfonic acid betaine, also known as 2-[N-methallyl-pyridyl-(4)1-ethane sulfonic acid betaine, decomposition point: 208 C, is obtained in similar fashion by using an equivalent quantity each of 4-pyridyl ethane sulfonic acid sodium salt and methallyl chloride as reactants.

Claims

WHAT WE CLAIM IS:

1. A pyridyl alkyl sulfonic acid betaine having the general formula:

in which the substituent - (Cll2)nSO30 is in the 2- or 4-position of the pyridyl ring; n is the integer 1 or 2; and R is a methyl; methallyl; CH2COOH; sodium 2-hydroxypropylsulfonate; sodium 2-hydroxybutylsulfonate; sodium 3-hydroxybutylsulfonate; halobenzyl; loweralkylbenzyl; or benzyl group substituted with the group:

wherein the substituent -(CH2)nSO38 is in the 2- or 4-position of the pyridyl ring and n is the integer 1 or 2.

2. 2-[N-Carboxymethyl-pyridyl-(2)]-ethanesulfonic acid betaine.

3. 2-[N-Carboxymethyl-pyridyl-(4)]-ethanesulfonic acid betaine.

4. [N-Carboxymethyl-pyridyl-(4)]-methanesulfonic acid betaine.

5. 2-[N-Methyl-pyridyl-(2)]-ethanesulfonic acid betaine.

6. 2-[N-(2-Methylbenzyl)-pyridyl-(2)]-ethanesulfonic acid betaine.

7. 2- N-(2-Methylbenzyl)-pyridyl-(4) -ethanesulfonic acid betaine.

8. 2- N-(2-Chlorobenzyl)-pyridyl-(2) ethanesulfonic acid betaine.

9. 2- N-(4-Chlorobenzyl)-pyridyl-2) -ethanesulfonic acid betaine.

10. 2'- N- 2-Chlorobenzyl)-pyndyl-(4) -ethanesulfonic acid betaine.

11. 2-[N-(3-Na-Sulfo-2-hydroxypropyl)-pyridyl-(2)]-ethanesulfonic acid betaine.

12. 1,4-bis-[2-(2-Sulfoethyl)-pyridinium-(1)-methyl]-benzene.

13. 1,2-bis-[2-(2-Sulfoethyl)-pyridinium-(1)-methyl]-benzene.

14. 1,3-bis-[2-(2-Sulfoethyl)-pyridinium-(1)-methyl]-benzene.

15. 1,4-bis-[4-(2-Sulfoethyl)-pyridinium-(1)-methyl]-benzene.

16. 2-[N-Methallyl-pyridyl-(2)]-ethanesulfonic acid betaine.

17. 2-[N-Methallyl-pyridyl-(4)]-ethanesulfonic acid betaine.

18. A process for preparing a pyridyl alkyl sulfonic acid betaine having the formula:

in which the substituent groups are as defined in claim 1 which process comprises quaternizing, by methods known per se, an appropriate 2- or 4-pyridyl alkyl sulfonic acid

or its alkali metal salt

wherein Z is an alkali metal and the substituent -(CH2)nSO 3(H,Z) is in the 2- or 4-position of the pyridyl ring, and ii is 1 or 2 with an appropriate quaternizing agent to introduce the above defined R substituent onto the ring nitrogen of the pyridyl group.

19. A process for preparing 1,2-bis-[2-(2-sulfoethyl)-pyridinium-(1)-methyl]-benzene, which comprises reacting 2-pyridyl ethanesulfonic acid sodium salt with α,α'-dichloro-o- xylol.

20. A process as claimed in claim 18 substantially as hereinbefore described with reference to any one of Examples I to VI.

21. A pyridyl alkyl sulfonic acid betaine as claimed in claim 1 whenever prepared by a process as claimed in any one of claims 18 to 20.

22. An electroplating bath which comprises an aqueous acidic solution of at least one nickel salt and at least one additive which is a compound of the formula:

in which the substituent -CH)nSO3 is in the 2- or 4-position of the pyridyl ring; n is the integer 1 or 2; and R is a methyl; methallyl; CH2COOH; CH2(CH2)xCH2SO3Na wherein x is the integer 1 or 2; sddium 2-hydroxypropylsulfonate; sodium 2-hydroxybutylsulfonate; sodium 3-hydroxybutylsulfonate; benzyl; halobenzyl; loweralkylbenzyl, or benzyl group substituted with the group:

wherein the substituent -(CH2)nSO3 is in the 2- or 4-position of the pyridyl ring and n is the integer 1 or 2, in a concentration of from 0.05 to 2.0 grams per liter.

23. An electroplating bath as claimed in claim 22 wherein the additive is 1,2-bis-[2-(2sulfoethyl)-pyridinium- (l)-methyl]-benzene which is contained in the bath in a concentration of from 0.1 to 0.5 grams per liter.

24. An electroplating bath as claimed in claim 22 substantially as hereinbefore described with reference to Example IX.

25. An article whenever having a coating of nickel electro-deposited thereon from an electroplating bath as claimed in any one of claims 22 to 24.