Metal complexes of Saccharin Synthesis & Characterization

Objectives:

1. To synthesize tetraaqua-bis(o-sulfobenzoimido)copper(II) and tetraaqua-bis(o-sulfobenzoimido)cobalt(II)

2. To characterize tetraaqua-bis(o-sulfobenzoimido)copper(II) and tetraaqua-bis(o-sulfobenzoimido)cobalt(II)

 

Introduction:

Saccharin (C₇H₅NO₃S), also known as 1,2-benzisothiazol-3(2H)-one is discovered by Remsen and Fahlberg in 1879 (as cited in Jovanovski, G., 2000). Saccharin and aspartame are artificial sweeteners which were developed over the years in order to eliminate the caloric intake in the diet associated with carbohydrate sugars. Saccharin is about 500 times sweeter than sugar. Its water soluble sodium salt is widely used as synthetic sweetener for diabetics as well as addictive in dietetic products.

The saccharin was intensively investigated due to its suspected carcinogenic nature. In the studies of Price and his co-workers, it has been shown that it causes urinary bladder carcinomas in mice when implanted in the bladders of mice (as cited in Jovanovski, G., 2000). Since that time, extensive work was carried out to investigate the effect of saccharin on human metabolism. As a result, saccharin has been categorized into the list of potential human carcinogens.

Saccharin contains three functional groups (carbonyl, imino and sulfonyl) connected to each other in a five-membered ring which is condensed to a relatively stiff benzene ring as shown in Figure 1. Saccharin has a high degree of hapticity. It acts as monodentate ligand by using nitrogen atom, carbonyl oxygen atom or sulfonyl oxygen atom and as bidentate ligand via either two atoms. It also acts as a neutral ligand donor. The following figure shows the structures of saccharin and saccharinate anion.

Figure 1 Structure of saccharin and saccharinate anion

From the Günzler, H. & Gremlich, H. ‘s studies of saccharin (as cited in Teleb, S.M, 2004), the spectrum of free saccharin (Hsac) exhibits a weak band at 3215 cm^-1 due to the v(N-H) vibration. Based on spectral investigations for a series of metal saccarinates (Teleb, S.M., 2004), the wavenumber of v(CO) mode can be used to make certain predictions on the type of metal-saccharinate bonding (bonding between metal and nitrogen). Teleb also found that the lowering in v(CO) wavenumber is more pronounced in ionic bond between metal and saccharinate anion. The v(CO) stretch of free saccharin can be observed at the wavenumber of 1725cm^-1 (Jovanovski, G., Soptrajanov, B., & Kamenar, B., 1990, as cited in Teleb, S.M., 2004) and at 1675cm^-1 in the spectrum of sodium saccharinate (Jovanovski, G. et al., 1988, as cited in Teleb, S.M., 2004). Besides, the wavenumbers of sulphonyl stretching, v(SO₂) in free saccharin is observed at 1360cm^-1 and 1180cm^-1 (Jovanovski, G., Tanceva S., & Soptrajanov, B., 1995) for asymmetric and symmetric modes respectively.

In this experiment, cobalt(II) and copper(II) complexes of saccharin are synthesized in order to identify their spectral characterisations. Other metal complexes, such as iron(II), nickel(II), zinc(II) complexes of saccharin may be prepared by using the same method.

 

Materials:

Sodium saccharinate dihydrate, copper(II) sulfate pentahydrate, cobalt(II) chloride hexahydrate

 

Apparatus:

Magnetic stirring hotplate, magnetic stirring bar, beakers, Hirsch funnel, sand bath

 

Instruments:

FT-IR spectrophotometer, UV-Vis Spectrophotometer

 

Procedures:

Part A: Preparation of tetraaqua-bis(o-sulfobenzoimido)copper(II)

1. Copper(II) sulfate pentahydrate was placed in a beaker.

2. Sodium saccharin dihydrate and water were added into the beaker.

3. The mixture was stirred until dissolution occurs with warming on hotplate.

4. Light blue solution was warmed on a sand bath with stirring in order to concentrate the solution.

5. Allowed the contents to cool down slowly to room temperature.

6. The beaker was further cooled down in ice bath for 30 minutes and the crystal was collected by suction filtration.

7. The crystal was washed with minimum ice cold water and dried over silica gel in a dessicator.

 

Part B: Preparation of tetraaqua-bis(o-sulfobenzoimido)cobalt(II)

1. This compound was prepared by using the same procedures in part A. Cobalt(II) chloride hexahydrate, sodium saccharin dihydrate were dissolved in 6ml of water.

 

Part C: Characterization of metal complexes

1. The yield and colour of metal complexes were recorded.

2. IR spectra of the complexes were obtained.

3. UV-Vis spectra of complexes were obtained by using DMF as solvent. λ_max was determined.

 

Results and calculations:

 

Table 1.1: Significant peaks of starting materials in IR spectrum

Starting materials	Sodium saccharinate dihydrate, Na(sac).2H2O	Copper(II) sulphate pentahydrate, CuSO4.5H2O
O-H stretch	3364 cm-1	3339 cm-1
C=O stretch	1648 cm-1	-
SO stretch	1335 cm-1 (asym.), 1143 cm-1 (sym.)	-

 

Table 1.2: Significant peaks of tetraaqua-bis(o-sulfobenzoimido)copper(II) in IR spectrum

Vibrational mode	Wavenumber (cm-1)
O-H stretch	3567, 3503, 3414
C=O stretch	1618
SO stretch	1353(asym.), 1164(sym.)

 

Table 1.3: Significant peaks of tetraaqua-bis(o-sulfobenzoimido)copper(II) in IR spectrum

Vibrational mode	Wavenumber (cm-1)
O-H stretch	3567, 3503, 3414
C=O stretch	1618
SO stretch	1353(asym.), 1164(sym.)

 

References:

1. International Associates. (1985). Inorganic Syntheses. Canada: John Wiley & Sons, Inc.

2. Jovanovski G. (2000). Metal Sccharinates and Their Complexes with N-donor Ligands. Metodij University, Macedonia 73(3), 843-868.

3. Teleb, S.M. (2004). Spectral and Thermal Studies of Saccharinato Complexes. Journal of the Argentine Chemical Society, 92(4), 31-40.