preparation of aquabis oxovanadium

Title: Experiment 2, Bioinorganic Chemistry: Preparation Of Aquabis (Acetylacetonato) Oxovanadium(IV), [VO(acac)2(H2O)]

Objective: To prepare aquabis(acetylacetonato)oxovanadium (IV), [VO(acac)2(H2O)] Introduction:

Vanadium form various mononuclear and polynuclear oxovanadium complexes.

Numerous mononuclear oxovanadium complexes have been reported to be insulinmimetic and as such have the potential to replace animal or synthetic insulin in the treatment of diabetes.

Vanadium coordination compounds are stable in a range of oxidation states (−1 to +5).

Vanadium (IV) is of considerable interest since it is the most stable, with the metal in a d1 configuration. Acetylacetonate (acac) is a common monovalent, bidentate ligand derived from the monodeprotonation of acetylacetone (2,4-pentanedione). The binding of this ligand to a transition metal ion can be thought of as consisting of a covalent bond through one oxygen and a dative bond through the other oxygen (bond order 1.5). The product was known as bis(acetylacetonato)oxovanadium(IV).

Apparatus and Materials: 250 mL conical flask, 250 mL beaker, 10 mL measuring cylinder, glass rod,

hot-plate stirrer, magnetic bar, round bottom flask with vertical condenser, sintered funnel, pH paper,

FTIR spectrometer, Vanadium(V) oxide, absolute ethanol, industrial ethanol, acetylacetone, 16 % w/v of sodium carbonate, methylated spirit (for washing), dichloromethane, diethyl ether, concentrated sulphuric acid (in beaker with pipette dropper in fume cupboard). Procedures:

1. 1 g of vanadium(V) oxide, V2O5 was weighed into a 250 cm3 conical flask.

2. A mixture of 5 cm3 distilled water, 4 cm3 concentrated sulphuric acid and10 cm3 absolute ethanol was obtained and was added to the above oxide.

3. The mixture was heated to boiling in a water-bath with constant stirring until a dark blue

solution is obtained. The deep blue solution contains the VO2+ ions. [Alternatively, a magnetic bar and a hot-plate stirrer are to be used in heating the oxide-sulphuric-ethanol mixture;

heating under reflux). The reduction of the vanadium (V) to vanadium (IV) was complete in about one hour.

4. The solution was filtered.

5. The filtrate was transferred to a 250 cm3 beaker. 5 cm3 acetylacetone and 16 % w/v of sodium carbonate (sodium carbonate solid used is anhydrous) were added.

6. The solution was neutralized slowly with constant stirring to avoid too much frothing. 7. The precipitated bis(acetylacetonato)oxovanadium(IV) was filtered.

8. The precipitate was wash with cold ethanol (industrial grade or denatured) dried using suction filtration.

9. The yield (g and %) was reported.

10. Half of the product was recrystallized.

11. It was dissolved in minimum volume of chloroform.

12. The impurities were filtered and diethyl ether was added until precipitation occurs. 13. The product was filtered, washed and dried. Result:

1. Mass of Vanadium (V) oxide used: 1.0064 g

2. Mass of precipitated Vanadium (V) oxide: 10.9252 g 3. Mass of recrystallize Vanadium (V) oxide: 1.9869 g

Calculation: 1.

V2O5 + 2 H+ ↔ 2 VO2 + + H2O

10 H2O + 2 VO2 + + CH3CH2OH ↔ 2[VO(H2O)5] 2++ CH3COH + 2 H2O [VO(H2O)5] 2+ + 2[C5H7O2] - ↔ VO(C5H7O2)2 + 5 H2O

From the equation, 1 mole of V2O5 produce 2 mole of [VO(H2O)5] 2+. Thus, the mole of [VO(H2O)5] 2+:

= (1.0064 g / 181.88 g mol-1) = 0.00553 mole × 2 = 0.01106 mole.

2. Theoritical mass of bis(acetylacetonato)oxovanadium (IV): = 0.0111 mole × 283.177 g mol-1 = 3.1433 g

3. Percentage yield:

= (1.9869 g / 3.1433 g) × 100 % = 63.21 %

Discussion:

In this experiment, aquabis(acetylacetonato)oxovanadium (IV) was synthesized from a mixture

of vanadium (V) oxide, sulphuric acid and ethanol. Ethanol serves as a reducing agent, which oxidise the vanadium (V) to vanadium (IV). The mixture turned blue indicated that the vanadium had been

reduced. Acetyl acetone that will act as ligand was introduced into the mixture. In this experiment, the

acetyl acetone is polydentate. This is because chelation occurred, which is a condition when a positively charged metal is bound to a ligand by multiple bonds, forming a ring. Chelate rings are more stable

than others complex containing monodentate ligands while this stability is known as the chelate effect. The acetyl acetone, which is a chelate ligands, experience resonance hybridization which results in

greater stability of the complex. Sodium carbonate was added to neutralized the solution for the aim to induce precipitation of the crude product. This precipitate was then filtered with cold ethanol and recrystallized with the use of chloroform.

The final product was known as aquabis(acetylacetonato)oxovanadium (IV). The product is

known to adopt octahedral geometry, with the vanadium slightly displaced from the plane of the

chelate ligands. This is because the excess strains on the chelate ligands prevent the forming of trigonal bipyramidal geometry.

The yield for this experiment is 63.21 %. Most loss was assumed resulted from we failed to

collect some residual product from filter paper, containers and so on, especially after the filtration.

The product was in turquoise in colour, this may be due to unreacted vanadium oxide, which is yellow, remaining in the final product.

The FTIR spectrum of the product and the sample were shown as the figures below. The

experimental values quite match the literature values for the significant stretches. For example, the literature peak value for V=O is 998 cm-1 while the experimental peak value was 997 cm-1, the

literature peak value for carbonyl C=O is 1560 cm-1 while the experimental value was 1558 cm-1. There are several safety precaution steps and improvement steps that can be carry out during

the experiment. First precaution step is students must be take care when taking the vanadium pentoxide because it is toxic. Second precaution step is when carry out the reflux, be sure not too close to the apparatus so that not inhale the toxic gaseous. For the improvement step, the experiment can be

improved by allowing the crystals to forms slowly over time, which would likely improve overall quality.

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1558 1529

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3200

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400.0

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The figure on the top is the experimental IR spectrum while the figure below is the sample experimental IR spectrum.

Conclusion:

In this experiment, bis(acetylacetonato)oxovanadium (IV) was successfully prepared. The yield

was 63.21 %. The significant peak value of IR spectrum of the product was matched well with the

sample. The experiment can be improved by allowing the crystals to forms slowly over time, which would likely improve overall quality. Questions:

1. Obtain FTIR spectrum of the complex. Answer:

In the discussion part. 2. Draw the structure of this complex by using suitable software. Answer:

3. Search the literature for oxovanadium complexs which are insulins – mimetic, nucleolytic and anticancer. Write brief notes on them. Answers:

The main abnormality in insulin – dependent diabetes mellitus (IDDM) is

hyperglycemia due to deficiency of insulin, but there are many serious secondary complications, such as cardiac abnormality, diabetic retinopathy ocular disorders and others. At present severe diabetes can be controlled only by daily injections of insulin, so the development of compounds

that cause insulin replacement or insulin mimetics on oral administration would be very useful. The finding in 1980 that vanadate (+5 oxidation state of vanadium) has an insulin – like

effect stimulated research on insulin – mimetic vanadium compounds. The blood glucose level

of rats with streptozotocin (STZ) – induced diabetes (STZ – rats) was found to be normalized by addition of sodium orthovanadate to their drinking water. Later, vanadium ions and vanadium complexes that are effective on oral administration to diabetis rats have been reported. Now,

many researchers trying to develop new insulin – like vanadyl (+4 oxidation state) complexes that are less toxic than vanadate.

Cytotoxic and antitumor activities of the biligand vanadyl derivative of L - malic acid, (bis - (L -

malato)oxovanadium(IV) (VO(mal)2), the inorganic vanadium(IV) compound, vanadyl sulfate (VOSO4), the oxovanadium monocomplex with L - malic acid (VO(mal)), and the vanadyl biscomplex with acetylacetonate were investigated using several tumor cell lines: mouse fibrosarcoma (L929), rat

pheochromocytoma (PC12), human liver carcinoma (HepG2), mouse embryonic fibroblasts (NIH/3T3),

and also normal human skin fibroblasts. The results showed that VO(mal)2 effectively inhibited growth of cancer cell cultures without any toxic effect on normal human skin fibroblasts. The cytotoxic anticancer effect of vanadium complexes depended in concentration of the compounds studied,

incubation time, types of cell cultures, and nature of ligands surrounding the central group of the complex (VO2+). These studies provide evidence that VO(mal)2 may be considered as a potential anticancer agent due to its low toxicity for non_tumor cells and significant anticancer activity. References:

1. Vanadium. Vanadium’s oxidation state. [online]. Retrieved date: 17/2/2015

Available from: http://www.chemguide.co.uk/inorganic/transition/vanadium.html

2. Journal of Medical Chemistry. A new orally active insulin – mimetic vanadyl complex:

bis(pyrrolidine – N – carbodithioato) oxovanadium (IV). [online]. Retrieved date: 25/2/2015 Available from: http://pubs.acs.org/doi/abs/10.1021/jm00033a002

3. Oliver Chemistry. Crystallization of Oxobis (2,4 – pentanediono)vanadium (IV) via Reduction of Vanadium (V) Oxide. [online]. Retrieved date: 17/2/2015

Available from: http://oliver.chemistry.ucsc.edu/151L/GoodReport3.pdf 4. BioChms. Anticancer Activity of Oxovanadium Compounds.[online]. Retrieved date: 25/2/2015 Available from:

http://www.researchgate.net/profile/N_Belyaeva/publication/233732355_Anticancer_Activity_ of_Oxovanadium_Compounds/links/0fcfd50adfd625fb90000000.pdf