Available on line at Association of the Chemical Engineers of Serbia AChE www.ache.org.rs/CICEQ Chemical Industry & Chemical Engineering Quarterly 18 (1) 7381 (2012) CI&CEQ MILUTIN M. MILOSAVLJEVIĆ1 SYNTHESIS OF TETRAALKYLTHIURAM ALEKSANDAR D. 2 DISULFIDES USING DIFFERENT OXIDANTS MARINKOVIĆ IN RECYCLING SOLVENT MIXTURE JELENA M. MARKOVIĆ2 2 DANIJELA V. BRKOVIĆ A new optimized laboratory synthesis of tetraalkylthiuram disulfides, starting 2 MILAN M. MILOSAVLJEVIĆ from dialkyl amines and carbon disulfide in presence of three oxidants (hyd- 1Faculty of Technical Science, rogen peroxide, potassium peroxodisulfate and sodium hypochlorite) and ap- University of Priština, Kosovska propriate reaction media (two mixtures of isopropyl alcohol–water used in two Mitrovica, Serbia consecutive syntheses) was presented in this work. The first synthesis was 2Faculty of Technology and performed in a recycled azeotropic mixture of isopropyl alcohol–water 87.7%- Metallurgy, University of Belgrade, –12.3%, and second in a filtrate obtained after first synthesis, which was a mix- Belgrade, Serbia ture of isopropyl alcohol–water 70.4%-29.6%. After the second synthesis and filtration, recycled azeotropic mixture isopropyl alcohol–water 87.7%-12.3% SCIENTIFIC PAPER was regenerated from the filtrate by rectification. Considering this, the techno- UDC 547.057 logy for beneficial use of recycling isopropyl alcohol–water mixture as a reac- tion medium for tetraalkylthiuram disulfides synthesis was developed. This DOI 10.2298/CICEQ110726048M concept could contribute to extraordinary economical benefit of implemented optimal laboratory synthesis at semi-industrial level. High yields of tetraalkyl- thiuram disulfides were obtained at both laboratory and semi-industrial level. Structure and purity of synthesized compounds were confirmed by elemental analysis, as well as FTIR, 1H- and 13C-NMR, and MS spectral data. Keywords: tetraalkylthiuram disulfide; optimization; reaction medium, oxidants. Studies of the syntheses and properties of tet- fungicide active compound for corn and wheat treat- raalkylthiuram disulfides have been attractive to the ment [4]. Synthesis of higher alkyl analogues of tetra- scientists in the past and also nowadays due to the alkylthiuram disulfide is described in this work, which broad area of their application: vulcanization accele- also could be used for rubber production and plant rator of natural rubber [1], fungicides [2] and additives treatment, as well as protection of the seed during [3]. The simplest compound in this series tetramethyl storage in a warehouse [4]. thiuram disulfide (TMTD) has the following formula: Synthesis of tetralkylthiuram disulfide can be performed in a two-stage processes. In the first phase, S H3C reaction between carbon disulfide and corresponding S N CH3 secondary amine takes place. In the second step, oxi- (1) dation of the obtained dialkyl ammonium salt of dithio- H C N S 3 carbamic acid by the use of an oxidative agent pro- CH3 S duces tetralkylthiuram disulfide. Many of thiuram di- sulfides were synthesized starting from secondary al- TMTD is widely used as a vulcanization accele- kyl- and arylamines, carbon disulfide and sodium hyd- rator of natural and styrene-butadiene caoutchouc, a roxide [5], or ammonium hydroxide [6] using different oxidative agents in the presence of catalyst and diffe- Correspondening author: M.M. Milosavljević, Faculty of Tech- rent organic solvents. The synthesis of the dialkyl am- nical Science, University of Priština, Knjaza Miloša 7, 38220 monium salt of dithiocarbamic acid takes place ac- Kosovska Mitrovica, Serbia. cording to reaction (2) [6]: E-mail: [email protected] Paper received: 26 July, 2011 Paper revised: 2 October, 2011 Paper accepted: 10 October, 2011 73 M.M. MILOSAVLJEVIĆ et al.: SYNTHESIS OF TETRAALKYLTHIURAM DISULFIDES… CI&CEQ 18 (1) 7381 (2012) S aryl amine, carbon disulfide in presence of triethyl- amine or ammonia, and oxidation performed by oxy- C (2) gen in presence of metal catalyst at temperature 0- 2R2NH + CS2 R2N S R2NH2 –200 C, is presented. Optimal synthesis conditions were defined at 1.7 bar and at temperature of 50 C. In the presence of an oxidative agent, the dialkyl Metal catalyst based on copper, molybdenum, man- ammonium salt of dithiocarbamic acid has been trans- ganese, cesium and cobalt at ratio of 0.01 to 5.00 formed to thiuram [7]. Diethyl dithiocarbamic acid so- mmol of catalyst per mol of secondary amine could be dium salt (DEDTC) is a well known immunopotentia- a potential deleterious agent during vulcanization (re- tor and it was found to be potential medicament for tardation caused by metal contamination) [17,18]. clinical treatment of HIV infections [8]. On the other Among other methods, it is worth mentioning tetraal- hand, sodium hydroxide produces the sodium salt of kylthiuram disulfide synthesis in presence of ammo- dialkyl dithiocarbamic acid presented by reaction (3) nium lignosulfonate catalyst [19], reaction of metal [9]: R2N R2N C SNa + R NH + H O C SR2NH2 +NaOH 2 2 (3) S S The sodium salt of dialkyl dithiocarbamic acid chloride with sodium salt of dithiocarbamic acid [20], can be transformed to tetraalkylthiuram disulfide by and from the salt of dithiocarbamic acid [2,21]. introducing phosgene to the reaction mixture [10,11]: S R R2N S N R 2 C SNa + COCl2 ++COS 2NaCl (4) R N S S R S Moreover, synthesis of tetraalkylthiuram disul- The above-mentioned methods do not describe fide starting from dimethylamine and carbon disulfide tetraalkylthiuram disulfides synthesis by reaction be- in water in the presence of sodium hydroxide was tween secondary alkyl amine, carbon disulfide and described. In the first step, a sodium salt of dimethyl oxidative agent (hydrogen peroxide - H2O2, potassium dithiocarbamic acid was obtained, and in the subse- peroxodisulfate - K2S2O8 and sodium hypochlorite - quent oxidation step of the obtained salt by the use of NaOCl) in a reaction medium recycled azeotropic hydrogen peroxide in presence of sulfuric acid or ga- mixture of isopropyl alcohol–water 87.7%-12.3%. Also, seous chlorine produced TMTD [12]. Also, a well-known there are no literature data dealing about prolonged method for TMTD synthesis is starting with dimethyl- uses of such reaction medium after first synthesis, amine, carbon disulfide and hydrogen peroxide in pre- and recycling of depleted solvent mixture by rectifi- sence of sulfur at room temperature [13]. Laboratory cation after second synthesis. By doing this, extraor- methods for syntheses of tetraalkylthiuram disulfides dinary economical benefit of overall cycles of tetra- by reaction between secondary amines, carbon disul- alkylthiuram disulfides synthesis was achieved at fide and oxidative agents (chlorine, ozone, hydrogen semi-industrial level of their production. The structure peroxide, bromine, iodine, sodium hypochlorite, car- and purity of the synthesized compounds (tetrame- bon sulfochloride, potassium perborate) in presence thylthiuram disulfide (TMTD), tetraethylthiuram disul- of manganese(II) acetate and cesium(III) nitrate, were fide (TETD), tetrapropylthiuram disulfide (TPTD), tet- also published [14,15]. Alternatively, sulfur could be raisopropylthiuram disulfide (TiPTD), tetrabutylthiu- used in reaction with a secondary amine and carbon ram disulfide (TBTD) and tetraisobutylthiuram disul- disulfide in appropriate solvent at temperature 0-150 fide (TiBTD)) were confirmed by results of elemental C, and in presence of a tertiary amine, metal catalyst analysis, FTIR, 1H- and 13C-NMR, as well as MS and oxygen or gaseous mixture containing oxygen spectral data. [16]. A method for synthesis of tetraalkyl or tetraaryl- thiuram disulfides, starting from secondary alkyl and 74 M.M. MILOSAVLJEVIĆ et al.: SYNTHESIS OF TETRAALKYLTHIURAM DISULFIDES… CI&CEQ 18 (1) 7381 (2012) EXPERIMENTAL carbon disulfide in potassium hydroxide – alcohol so- lution [24]. Synthesis of TMTD by using hydrogen peroxide Synthesis of TMTD at different reactant molar ratio oxidant (method A) Influences of reactant molar ratio of dimethyl 1540 cm3 of azeotropic mixture of isopropyl al- amine:carbon disulfide:hydrogen peroxide on yield cohol–water 87.7%-12.3% and 437.4 cm3 (4.16 mol) and purity of TMTD were studied by performing des- of 50.0 % dimethyl amine solution, which increases cribed experiments, and results of syntheses are the solution pH to 9.5, was added into a three-necked given in Table 1. flask of 5000 cm3 equipped with a reflux condenser, dropping funnel, thermometer, cooling jacket and me- Synthesis of TMTD at different concentration of chanical stirrer. After starting the stirrer, 256.4 cm3 suspension (4.16 mol) of 98.0% carbon disulfide was added from Analogously to given example, a synthesis of the dropping funnel for 0.5 h while maintaining the TMTD at different quantity of initial recycled azeotro- temperature in the range 28-35 C, provided by circu- pic mixture of isopropyl alcohol-water 87.7%-12.3% lating cooling water. Upon completion of the reaction was performed to study the effects of dilution or con- the pH of the reaction mixture was 6.5. At this point, centration of reaction mixture. Concentration of sus- 536.2 cm3 of 13.2% hydrogen peroxide solution, pre- pension was calculated on the basis of obtained pro- pared by dilution of 178.6 cm3 (2.08 mol) 35.0% hyd- duct and total reaction volume: 1690 cm3 - 18% sus- rogen peroxide with 406.5 cm3 of azeotropic mixture pension, example 8; 1771 cm3 - 17% suspension, ex- isopropyl alcohol–water 87.7%-12.3%, was added from ample 9; 1840 cm3 - 16% suspension, example 10; the dropping funnel for 0.5 h at 35-40 C. As soon as 1920 cm3 - 15% suspension, example 11, 1380 cm3 - reaction took place, the reaction mixture became 22% suspension, example 12; 1309 cm3 - 23 % sus- yellowish because of suspended TMTD particles. The pension, example 13; 1230 cm3 - 24% suspension, end of the reaction was tested by sampling the re- example 14; 1150 cm3 - 25% suspension, example action mixture, filtration and by adding a few drops of 15. Yield, purity and melting point of the product syn- copper(II) sulfate solution into the filtrate.