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Hindawi Bioinorganic Chemistry and Applications Volume 2019, Article ID 8260496, 15 pages https://doi.org/10.1155/2019/8260496 Review Article Dithiocarbamates: Challenges, Control, and Approaches to Excellent Yield, Characterization, and Their Biological Applications Ayodele T. Odularu 1 and Peter A. Ajibade 2 1Department of Chemistry, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa 2School of Chemistry and Physics, University of KwaZulu-Natal, Pietermaritzburg Campus, Scottsville 3209, South Africa Correspondence should be addressed to Ayodele T. Odularu; [email protected] Received 16 September 2018; Accepted 26 November 2018; Published 6 February 2019 Academic Editor: Claudio Pettinari Copyright © 2019 Ayodele T. Odularu and Peter A. Ajibade. ,is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Progresses made in previous researches on syntheses of dithiocarbamates led to increase in further researches. ,is paper reviews concisely the challenges experienced during the synthesis of dithiocarbamate and mechanisms to overcome them in order to obtain accurate results. Aspects of its precursor’s uses to synthesize adducts, nanoparticles, and nanocomposites are reported. Some common characterization techniques used for the synthesized products were assessed. Biological applications are also reported. 1. Introduction [7]. ,e basic medium can either be a weak base (ammonia solution) or strong bases (sodium hydroxide and potassium 1.1. Dithiocarbamates. Dithiocarbamates (dtcs) are orga- hydroxide). Bases are incorporated to conserve the amines nosulfur ligands which form stable complexes with metals [8]. General method of preparation is called one-pot syn- [1]. ,e two types of dithiocarbamates are mono- and thesis, where the synthesis reactions can be seen in equations dialkyl-dithiocarbamates. ,e two are formed depending on (1) and (2) [9]. ,e two approaches to synthesis are the the nature of amines used during the synthesis of the insertion reaction approach and replacement (substitution) compound [2]. reaction approach [10–12]. ,e better of the two approaches Chemistry of dithiocarbamates could be dated to start in is replacement because it gives dithiocarbamates compounds the early twentieth century [3], precisely, in 1930 [1]. of high purity [10]. Recently, Aly et al. reported the synthesis Commercial application was used as a fungicide for the first of dithiocarbamate at room temperature against the usual time during World War II [4]. Other wide applications can cold less than four degrees Celsius temperature [13]: be seen in the fields of accelerating vulcanization, acting as RNH + CS + BOH ⟶ RHNCS B + H O flotation agents, agriculture (pesticide), biology, materials 2(l/aq) 2(l) (aq) 2 (l/s) 2 (l) + science, medicine, organic synthesis, photo-stabilizing B: NH4 ; Na; or K� polymers, and protecting radiators [5, 6]. (1) 1.2. Synthesis of Dithiocarbamates. Dithiocarbamates are R2NH(l/aq) + CS2(l) + BOH(aq) ⟶ R2NCS2B(l/s) + H2O(l) compounds formed from the reaction of either a primary B: NH +; Na; or K� (equation (1)) or secondary amines (equation (2)) with cold 4 carbon(IV) sulfide in basic media [2] or alcoholic solution (2) 2 Bioinorganic Chemistry and Applications 2. Challenges Encountered during the Synthesis solution is formed. For the liquid state, the solution is fil- and How to Overcome Them tered. ,e filtrate in a clean labelled vessel is either put in the fume cupboard for slow evaporation to generate crystals or First of all, synthesis must always be done in a tidy envi- refrigerated depending on the condition which suits the ronment. Dithiocarbamates are easy to prepare and at the growth. Another form of liquid in which a product of di- same time need caution during their syntheses. All glassware thiocarbamate can exist is in the form of viscous oil. to be used for the syntheses must be very clean by washing Characterization techniques can be performed directly on with dilute trioxonitrate(V) acid if very dirty or soapy solution viscous dithiocarbamate. ,e other state is the solid form, if less dirty. ,ey are washed with tap water, rinsed with known as precipitate. Precipitate can be washed, dried, and acetone, washed with tap water again, and finally rinsed with a weighed for further applications, such as coordination lot of distilled water before properly dried in the oven. If compounds’ preparation and materials chemistry. Crystals glassware is not clean, there might be possibility of delay in the can be grown from both states of dithiocarbamates. growth of crystals of the compound and might lead to error in result of elemental analysis. When the materials are ready, the experiment is set up, with a magnetic stirrer, magnetic bar 3. Washing, Drying, and Packing of Synthesized stirrer, a reaction vessel, and a clean dried Erlenmeyer flask, all Product of Dithiocarbamate in the fume cupboard. ,e magnetic bar must be cleaned using acetone solvent before use, if possible should be soaked 3.1. Washing of Synthesized Product of Dithiocarbamate. in the solvent overnight prior to the day of synthesis. Once it is Solid samples usually undergo washing by filtration. ,e removed, it should be rinsed with distilled water, wiped different forms of filtrations are the paper filtration and carefully with a paper towel, and put in an Erlenmeyer flask. filtration by suction. ,e better option is the filtration by ,e Erlenmeyer flask containing the magnetic bar stirrer is suction where the precipitate is washed thoroughly by placed in the reaction vessel, where ice blocks or ice chips are solvent. Both forms of filtration demand filter papers. In put to fill the reaction vessel to the brim (ice bath), since the most cases, diethyl ether or cold ethanol are common sol- reaction in most cases takes place at a cold temperature. ,is vents used for washing. ,e aim of washing is to remove temperature helps in the precipitation of the dithiocarbamate impurities (unreacted reactants and by-products) from the to give solid products. ,e magnetic stirrer, where the re- desired product. ,e colour of the washed product is either action vessel is placed on, is plugged to a switch and turned white or cream on the filter paper. on. ,e amine of choice is put first in the Erlenmeyer flask, followed by the base, and finally, the refrigerated carbon(IV) sulfide is added after a while. ,e solution is made to stir for a 3.2. Drying of Synthesized Product of Dithiocarbamate and specific duration based on the colour formed. Colours as- Overcoming Challenge of Air- and Temperature-Sensitive sociated with complete synthesis are pink, yellow, yellowish- Ammonium Dithiocarbamate. Dried dithiocarbamate can red, and white. either be stored in the refrigerator for the nonstable air- and moisture-sensitive dithiocarbamate at room temperature or in the desiccator for the stable dithiocarbamate. Another 2.1. Order of Addition of Reagents for Synthesis of approach is the use of infrared lamp. Dithiocarbamates. Reactants for the synthesis of di- thiocarbamates are amines, base, and carbon(IV) sulfide. ,e order of addition of reagent has no influence on the 3.2.1. Air- and Moisture-Sensitive Dithiocarbamate at Room product formed, provided, they are stoichiometrically right. Temperature Stored in Refrigerator. ,e nonstable air- and Researchers like Ayyavoo et al., Ramos et al., Ramos- temperature-sensitive dithiocarbamates are ammonium Espinosa et al., Sha et al., and Tarique added the amine to dithiocarbamates. ,e nonstability might be due to strength the Erlenmeyer flask as the first reagent, secondly the base, of ammonia solution used as a weak base. In order to and thirdly the carbon disulfide [2, 3, 7, 9, 13], while Al- overcome the challenge of air- and temperature-sensitive Mukhtar and Aghwan added the base first, followed by the ammonium dithiocarbamate, the washed dithiocarbamate is amine, and lastly the carbon disulfide [14]. All reagents are left in a clean vessel stored in a refrigerator and removed added dropwise to prevent oligomerization, unwanted side when needed for characterization. products, vigorous reaction and to control the temperature, as well as, increase selectivity. In the case of the amines, solid 3.2.2. Stable Dithiocarbamates. Strong bases such as sodium amine first undergoes solubility test to determine the right hydroxide and potassium hydroxide form stable products of solvent which dissolves the solid. A solution of this will be sodium salt of dithiocarbamate and potassium salt of di- used during synthesis. On the contrary, the liquid amine can thiocarbamate, respectively. Dithiocarbamate is dried be used directly. mostly in a desiccator containing silica gel. Other desiccants are calcium hydroxide, calcium trioxocarbonate, and so- 2.2. States of Product. ,ere are two states which are gen- dium hydroxide, but silica gel is preferred better so as to erally formed for dithiocarbamates. ,ey are either in the prevent contamination with the product (dithiocarbamate). liquid state or solid state. In other words, in situations where ,e silica gel must be blue to indicate its active and useful solid products are not formed, a free solution or viscous states before pouring in the desiccator. Black silica gel shows Bioinorganic Chemistry and Applications 3 that the silica gel can no longer be used and can be discarded, 4.1. Anomalous Nature of Dithiocarbamates. while red silica gel signifies requirement for it to be charged by Dithiocarbamates are termed anomalous because under heating in an oven. Dithiocarbamate remains inside the mild conditions, crystals of thiourea could be formed by self- desiccator to use at appropriate period. Caution is to be condensation [17]. In this case, the two sulfur atoms are exercised in the use of filter paper by ensuring proper drying reduced to one sulfur atom: of sample in the desiccator so as not to scratch the paper when ammonium dithiocarbamate + heat condition ⟶ thiourea packing. Scratching introduces more carbon into the sample, and the percentage composition of the carbon in the result for (3) elemental analysis becomes higher than the expected value.

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