Dithiocarbamate Preparation as an Instructional Tool for Science Students

A Research

Presented to

The Faculty of College of Science & Technology

Texas Southern University

In Partial Fulfillment of the Requirement for Basic Research

Chem. 451 & 531 Inorganic Chemistry

Submitted by:

Students

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School Year 1999 – 2000

Submitted to:

Mr. Ambrose Okpokpo

ABSTRACT

Dithiocarbamate (DTC) are made of important classes of chemicals which are derived from amines and carbon disulfide. These compounds posses the common functionality called carbamates which are derivatives of dithiocarbamic acid.

The carbamates group of substances are widely used in rubber manufacturing technology and as agricultural fungicides. Dithiocarbamates are divided into three categories: dithiocarbamates salts, neutral dithiocarbamate esters and thiuram disulfides.

A 20% aqueous stock solution of 1.00 mole of the dibutylamine was prepared. From the stock solution of dibutylamine, a 10% in concentration or below 10% concentration by solution was prepared. Using the 10% concentrated solution of dibutylamine, slowly adding 1.05 mole of carbon disulfide followed by the slow addition of 1.00 mole of sodium hydroxide of about 10% in concentration by solution. The resulting product was then allowed to warm to room temperature. The aqueous solution was decanted from the excess carbon disulfide and rinsed with water several times.

The final product evolved from a starting color of transparent as it was formed during the reaction to yellowish color and finally ending at a light greenish color. There was also some gases evolving during the reaction. Final verification and confirmation of the product “Dithiocarbamate” was done with Nuclear Magnetic Resonance Spectroscopy (NMR).

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TABLE OF CONTENT

LIST OF

FIGURES…………………………………………………………………………………………………………………………………………………………………..........iii

ACKNOWLEDGEMENTS……………………………………………………………………………………………………………………………………………………………….iv

CHAPTER

1. ABSTRACT…………………………………………………………………………………………………………………………………………………………………………..i

2. INTRODUCTION…………………………………………………………………………………………………………………………………………………………........1

3. MATERIALS………………………………………………………………………………………………………………………………………………………………………..1

4. PURPOSE…………………………………………………………………………………………………………………………………………………………………………..2

5. EXPERIMENTAL DESIGN…………………………………………………………………………………………………………………………………………………….2

6. RESULTS…………………………………………………………………………………………………………………………………………………………………………….2

7. CONCLUSION…………………………………………………………………………………………………………………………………………………………………….4

Calculations…………………………………………………………………………………………………………………………………………………………………4

8. MISCELLANOUS AND PRECAUTION……………………………………………………………………………………………………………………………………7

9. REFERENCES………………………………………………………………………………………………………………………………………………………………………8

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LIST OF FIGUES

Figure 1………………………………………………………………………………………………………………………………………………………………………………………3

Figure 2………………………………………………………………………………………………………………………………………………………………………………………4

Figure 3………………………………………………………………………………………………………………………………………………………………………………………4

Figure 4………………………………………………………………………………………………………………………………………………………………………………………5

Figure 5………………………………………………………………………………………………………………………………………………………………………………………7

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ACKNOWLEDGEMENTS

Special acknowledgement and thanks to my Advisor, and each of my committee members. I extend my thanks to

my department Secretary, and the my school chairs and their secretaries for making this research possible. I give

special acknowledgement and thanks to Mr. Ambrose Okpokpo for technical and laboratory assistance at Texas

Southern University.

I thank Texas Southern University faculties and staffs for providing me with the opportunity to complete a

research training in science. I thank my mom and dad as well as the rest of my family for

their prayers, encouragement, and support throughout my studies. I give my greatest thanks to God for giving me

the desire, the mind, and the strength to fulfill my ambition in gaining valuable knowledge in science leading to my

completion and fulfillment of the degree requirement for the Bachelor’s or Master’s of Science in Chemistry

degree.

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Introduction

The product of amines and carbon disulfides are a commercially important class of substances called “Dithiocarbamtes.” They possess the functionality which is a common functional group that are formally the derivatives of dithiocarbamic acid, . Based on the commercial importance of dithiocarbamates, they are classified into three categories which are dithiocarbamate salts, neutral dithiocarbarmate esters and thiram disulfides.

Dithiocarbamate salts Dithiocarbamate esters Thiram disulfides

Since these three compounds came from a group of compounds called carbamates , they are widely used as agricultural fungicides, as analytical chemicals, and in rubber manufacturing technologies. Dithiocarbamates salts are also used in the preparation of thiuram disulfides and dithiocarbamate esters.

Carbamates contributes to the mechanism of the enzyme ribulose 1,5-biphosphate carboxylase which has significant role in agriculture and biomass production. Carbamate is formed through the reaction of carbon dioxide with an uncharged amine. The features in the formation of carbamates reinforce the Rubisco mechanism by functioning as bridging ligand between two divalent metal ions. In the process, an aci-carbamate, which is coordinated moderately to a metal ion, retains a negative charge on other noncoordinated oxygen atom that acts as the general base. (Wallace et al., 1998)

William et. al., (1998) performed tests to show that alpha-alkoxy carbamate anions, as opposed to alpha-alkoxy amines, are configurationally stable under certain conditions. Due to the nature of the axial carbamate anion,the efficiency of the acylation was very highlighted and the anions function as a base.

Achilles et. al., (1998) determined ethylenediamine in dithiocarbamate residue by a calorimetric measurement of it’s copper complex at 550 nanometer (nm). Dithiocarbamates was known to consume two equivalents of acid in going to the amine salt. (Edward et. al., 1998) Moreover, using a simple method of assay, the water-soluble dithiocarbamates decomposes in the presence of a known excess of acid followed by back titration with a base.

Disodium ethylenebisdithiocarbamate and it’s air oxidation products,ethylenethiuram and ethylenethiourea, have been separated by Wa-Hung et. al. (1997) on Whatman No. 1. Paper using butanol-ethanol-water as the developing solvent. Some simple dithiocarbamates and thiuram sulfides have been separated by Leung (1997) using Whatman No. 2. Paper impregnated with 2% acrylonitrile-butadiene copolymer in 2:1 benzene-acetone as stationary phase.

Materials

Stand, 2 clamps, large beakers, ice, magnetic stirrer, seperatory funnel, hudd/ventilation, digital scale,

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carbon disulfide, dibutylamine, filter papers, and other relevant materials for the experimention process.

Purpose

The purpose of this research is to detect and determine a particular dithiocarbamate salt that we have produced in the laboratory by instrumental analysis; to enhance enhance our industrial chemical and manufacturing skills through experience in a college laboratory and through hands on training on instrumentation used for solving problems of unknown and known chemicals, toxicants, and pollutants, in the laboratory and in the environment. This research gives students training in the preparation, characterization, evaluation, measurement, and the reactions of dithiocarbamates. Students’ interpretation of Nuclear Magnetic Resonance result was a critical tool in solving problems for these students who have chosen to study science.

EXPERIMENTAL DETAILS

A 20% aqueous stock solution of 1.00 mole of the dibutylamine was prepared. From the stock solution of dibutylamine, a 10% in concentration or below 10% concentration by solution was prepared. Using the 10% concentrated solution of dibutylamine, slowly adding 1.05 mole of carbon disulfide followed by the slow addition of 1.00 mole of sodium hydroxide of about 10% in concentration by solution. The resulting product was then allowed to warm to room temperature. The aqueous solution was decanted from the excess carbon disulfide and rinsed with water several times.

RESULTS The resultant product started revealing its presence by slowly crystallizing, followed by a foul smell which was the release of sulfur, and a gradual change in color starting from transparent form to yellowish and then light greenish color for the end product. At the end, the crystal was very distinct in appearance. Other observations such as the two phases during the reaction revealed that the liquids, dibutylamine and the water were immiscible.

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CONCLUSION

In conclusion, carbon disulfide reacts with amine to give the product called thiocabamates. Subsequent findings were verified using Nuclear Magnetic Resonance to verify that the product was Dithiocarbamate.

Calculations

Figure 2. Scheme of the Preparation of Thiocarbamic Acid

Thiocarbamic acid reacts with amine (diamine) sharing a mechanism that uses the intermediate shown below in figure

Figure 3. Transition State or Intermediate State of Reaction for figure 1

Dibutylamine Dibutylamine 129g/mol 129 g/mole +

Carbon Disulfide

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Dibutyldithiocarbamic Acid Sodium Hydroxide 1 mole Finding: Given in the research, 1.05 mole CS2.

Formula weight of Carbon Disulfide

C = 12g x 1 = 12g S = 32g x 2 = 64 g Total = 76g

Using % Solution = part x 100 Whole 20% Solution = 129g X 100 or [ 129g/645g x 100 = 20% Solution]of Dibutylamine Whole(X)

X = 645g Water addition = 645g – 129g = 516g weighed on a weight measuring balance.

Figure 4. Beaker containing a solution of Dibutylamine

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0.25 moles Carbon disulfide Dibutylamine Dibutyldithiocarbamic acid Sodium Hydroxide or

Carbon Disulfide Diethylamine Diethyldithiocarbamic Acid Sodium Hydroxide

0.25 moles 0.25 moles Ethyldithiocarbamate Metal Complex Metal Chloride Sodium dithiocarbamate or Salt

Moles = grams Formula Weight

= 9.99g (where 9.99g is the weight of the product formed). 129g

= 0.077 moles for the product

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The 9.99g product formed showed that some of the product that made up the 0.25 moles of the original product as shown in the theoretical calculation of the equation above had been lost during the handling process from reaction to product collection.

Due to the result of 0.077 moles of the product produced from the reaction, the following was used to increase product yield: add a mixture of 30ml of H20 and 10ml of Methanol to the products in solution; again, add another mixture of 30ml H20 and 20ml Methanol, and add one more mixture of 30ml H20 and 30ml Methanol to the product in solution….to make the product solution to bring out the maximum product yeiled. This kind of addition of water and methanol mixture is in the form of an arithmetic progression (M milliliters of H20 (N+10) milliliters of Methanol) where M is constant and N is, 0, 10, 20,… and ‘c. The final product generated after all the extractions done on the reactants solution with water and methanol was 0.7744 moles of product. Using the formula: moles = grams/Formula Weight.

0.07744 moles x 237.71g = grams of NiCl2·6 H20 to be added to the solution 18.41g = grams of NiCl2·6 H20 to be added to the solution

Observation: To distinguish the product from any chemical of similar appearance, we familiarize ourselve with the following chemicals: CoCl2 is purple; NiCl2 is dark green and they are covalent. After washing the yellow product with isopropyl ether, the precipitate dissolved in the isopropyl ether. Now the mixture was placed in a rotavapor to crystallize because the crystals was dissolved in Nickel Chloride which gave it it’s green color.

Miscellaneous & Precautions

129g/mole Dibutylamine 40g/mole Sodium Hydroxide 114g/mole Iso-Butane(CH3CH2CHCH3) 4 4 4 The equivalents as shown above was used to calculate the equivalent amount of Sodium Hydroxide required for solution preparation for the 0.25 moles or ¼ moles for the reactant that was to be used to produce the equivalent of 0.25 moles or ¼ moles of products. Therefore, the amount of Sodium Hydroxide required for the reaction is 10g/mole for every (129g/mole)/4 or 32.25g dibutylamine.

Dibutyldithiocarbamic Acid Sodium Hydroxide Sodium Dithiocarbamate Complex

Figure 5. The Reaction of Dibutyldithiocarbamic Acid to produce Sodium Dithiocarbamate Complex

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Observation: Dibutylamine in water has two phases which showed that the liquid is immiscible. The Carbon Disulfide addition resulted in the formation of an acid crystal.

Special precaution was taken when dissolving the compounds because the heavy metal salts are sparingly soluble in water as shown above in the reaction equation. The heavy metal salts are more soluble in organic solvents such as ethyl ether as a result of which some of the original product was lost and the calculation revealed it with some decrease in quantity.

REFERENCES

Achille, Inesi., Vittoria, M., and Leucio, R. (1998). Methodology for the Synthesis of Carbamate esters from Amines. J. of Org. Chem. V63, n4: p1337(2).

Edwardo, H. E., Debacher, N. A.; Sierra, M. M. de S.; Franco. J. D.; and Schutz. A. (1998). Mechanism of Akyl Decomposition of Dithiocarbamates. J. of Org. Chem. V63, n5: p1598(6).

Karl, R. and Ram, R. S. (1996). A facile Preparation of Enecarbamates. J. of Org. Chem. V61, n12: p4180(50).

Marlik. M. A.; Motevalli. M.; O’Brien. P.; Walsh. J. R. Coordination Mode in a Bis(diakyldithiocarbamate)zinc(II) adduct with N,N,N’,N’-tetraethyllenediamine. Inorg. Chem. v36, n6: p1263(2).

Wallace C. W.; John. A. T.; Guterridge. S. ; Hartman. F. C.; and Lorimer. G. H. (1998). Mechanism of Rubisco: the carbamate as general base. Chem. Rev. v98, n2: p549(13).

William R. and Lance. A. (1998). Stereoselective Reactions of Alpha-alkoxy carbamates. J. of Org. Chem. v63, n7: p2062(2).

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