Condensation of 2-chloropyridinium chloride with thiourea: Structure of the resulting product and its use as a brightener in nickel plating electrolytes

The protonated form, 2-chloropyridinium chloride, was synthesized and characterized spectroscopically for the first time to eliminate the influence of the basic nitrogen center in pyridine on the stability of the resulting isothiuronium salt. This compound readily condensed with thiourea to form the corresponding isothiuronium salt. Nuclear magnetic resonance (NMR) spectroscopy (¹H and ¹³C) revealed that the salt exists as two stable conformers differing in the orientation around the C2–SC(NH₂)₂ bond. These conformers are most clearly distinguished in the ¹³C NMR spectra by the chemical shift of the C4 signal in the pyridine ring relative to its position in neutral 2-chloropyridine. The presence of two stable conformers, determined by an additional basic center in the α-position, may represent a general pattern for this class of compounds. The synthesized pyridinium isothiuronium chloride was investigated as a brightener in a nickel plating electrolyte. Preliminary tests using a Hull cell identified an effective concentration range of 0.10–0.45 g/L and operational current densities of 3–20 A/dm². The addition of the agent at 0.40–0.45 g/L to a sulfate nickel plating electrolyte produced bright nickel coatings with high current efficiency, low porosity, and increased hardness. The microhardness of the coating was found to increase with the additive concentration.

1. Lukevits É. Pyridine derivatives in the drug arsenal (150 years of pyridine chemistry). Chemistry of Heterocyclic Compounds. 1995;31:639-650. DOI: 10.1007/BF01169065.

2. Abbas H.-A.S., El Sayed W.A., Fathy N.M. Synthesis and antitumor activity of new dihydropyridine thioglycosides and their corresponding dehydrogenated forms. European Journal of Medicinal Chemistry. 2010;45(3):973-982. DOI: 10.1016/j.ejmech.2009.11.039.

3. Dyadyuchenko L.V., Dotsenko V.V. Synthesis of isoxazolo[5,4-b]pyridine derivatives (microreview). Chemistry of Heterocyclic Compounds. 2021;57:627-629. DOI: 10.1007/s10593-021-02959-7.

4. Leontyev T.N., Lebedeva A.Yu., Fedorova O.A. Synthesis and study of the spectral properties of styryl dyes based on benzothiazole and pyridine. Uspekhi v khimii i khimicheskoi tekhnologii. 2015;29(7):114-116. (In Russian). EDN: ULVPPR.

5. Brown C.M., Kitt M.J., Xu Z., Hean D., Ezhova M.B., Wolf M.O. Tunable emission of iridium(III) complexes bearing sulfur-bridged dipyridyl ligands. Inorganic Chemistry. 2017;56(24):15110-15118. DOI: 10.1021/acs.inorgchem.7b02439.

6. Shi S., Lei P., Szostak M. Pd-PEPPSI: a general Pd-NHC precatalyst for Suzuki–Miyaura cross-coupling of esters by C–O cleavage. Organometallics. 2017;36(19):3784-3789. DOI: 10.1021/acs.organomet.7b00565.

7. Kokina T.E., Glinskaya L.A., Piryazev D.A., Eremina Y.A., Naumov D.Y., Larionov S.V., et al. Synthesis and structures of Cui,II complexes with a 2,2´-bipyridine derivative bearing a (+)-3-carene moiety. Russian Chemical Bulletin. 2018;67:1251-1260. DOI: 10.1007/s11172-018-2209-1.

8. Lebedeva O.V., Chesnokova A.N., Badlueva T.V., Sipkina E.I., Rzhechitskii A.E., Pozhidaev Yu.N. Hybrid ion-exchange membranes based on heteroaromatic sulfonic acid derivatives. Petroleum Chemistry. 2015;55:333-338. DOI: 10.1134/S0965544115040040.

9. Lebedeva O.V., Sipkina E.I., Pozhidaev Yu.N. Adsorption of platinum(IV) by a composite based on silicon dioxide and copolymer of 4-vinylpyridine and 2-hydroxyethylmethacrylate. Protection of Metals and Physical Chemistry of Surfaces. 2017;53:80-84. DOI: 10.1134/S2070205117010130.

10. Sipkina E.I., Lebedeva O.V., Pozhidaev Y.N., Oborina E.N. Adsorption of platinum(IV) onto composites based on silicon dioxide and vinyl acetate/1-vinylimidazole and vinyl acetate/4-vinylpyridine copolymers. Protection of Metals and Physical Chemistry of Surfaces. 2017;53:657-662. DOI: 10.1134/S2070205117040207.

11. Sosnovskaya N.G., Istomina N.V., Bogdanova I.N., Rozenzweig I.B., Tyurin M.D., Korchevin N.A. Influence of process conditions and organic additives structure on the formation and properties of coatings during electrochemical nickel plating. Fizikokhimiya poverkhnosti i zashchita materialov. 2024;60(6):629-653. (In Russian). DOI: 10.31857/S0044185624060064.

12. Szeptycka B. Effects of organic compounds on the electrocrystallization of nickel. Elektrokhimiya. 2001;37(7):805-810. (In Russian). EDN: IYPVHM.

13. Ushakov I.A., Nikonova V.S., Polynskii I.V., Knyazeva L.G., Polynskaya M.M., Antsiferov E.A. Study on efficiency of corrosion inhibitors based on derivatives of isothiuronic salts. Proceedings of Universities. Applied Chemistry and Biotechnology. 2021;11(2):326-332. (In Russian). DOI: 10.21285/2227-2925-2021-11-2-326-332. EDN: VBVSIX.

14. Polynsky I.V., Knyazeva L.G. Study of the possibility of using isothiuronium salts as corrosion inhibitors. Uspekhi v khimii i khimicheskoi tekhnologii. 2021;35(5):89-91. (In Russian). EDN: WPWBCC.

15. Ivanova A.O., Sosnovskaya N.G., Nikonova V.S., Levanova E.P., Popov S.I. The use of isothiuronic salts as brightening additives in the technology of bright nickel electrochemical plating. Proceedings of Universities. Applied Chemistry and Biotechnology. 2017;7(4):136-141. (In Russian). DOI: 10.21285/227-2925-2017-7-4-136-141. EDN: YMQFTF.

16. Sosnovskaya N.G., Istomina N.V., Sinegovskaya L.M., Rosenzweig I.B., Korchevin N.A. Electrodeposition of bright nickel coatings from sulfate electrolyte in the presence of isothiyronium salts. Electroplating & Surface Treatment. 2019;27(4):4-11. (In Russian). DOI: 10.47188/0869-5326_2019_27_4_4. EDN: MHXVSI.

17. Grabelnykh V.A., Bogdanova I.N., Sosnovskaya N.G., Istomina N.V., Russavskaya N.V., Kondrashov E.V., et al. Characteristics of 2-chloropyridine and thiourea condensation. Structure of the as-formed products and their effect on coating properties during electrochemical nickel plating. Proceedings of Universities. Applied Chemistry and Biotechnology. 2022;12(4):498-505. (In Russian). DOI: 10.21285/2227-2925-2022-12-4-498-505. EDN: NSNWDX.

18. Levanova E.P., Grabel’nykh V.A., Vakhrina V.S., Russavskaya N.V., Albanov A.I., Korchevin N.A., et al. Synthesis of new 2-(alkenylsulfanyl)pyrimidine derivatives. Russian Journal of Organic Chemistry. 2014;50:429-433. DOI: 10.1134/S1070428014030221.

19. Cossar B.C., Fournier J.O., Fields D.L., Reynoids D.D. Preparation of thiols. The Journal of Organic Chemistry. 1962;27(1):93-95. DOI: 10.1021/jo01048a024.

20. Kandalintseva N.V., Prosenko A.E., Dobchenko O.I., Stoyanov E.S. Synthesis of S-alkylisothiuronium halides by reaction of thiourea with ω-(4-hydroxyaryl)alkyl halides. Zhurnal organicheskoi khimii. 2001;37(9):1317-1320. (In Russian).