EXP2.docx

Name: Kavisha a/p Sundraraj ID: 1205675 Partner: Chong Yan Jie Practical group: P (3) Experiment details: 

Number: 2

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Title: BIOINORGANIC CHEMISTRY:PREPARATION OF BIS(ACETYLACETONATO)OXOVANADIUM(IV), [VO(acac)2] AND ITS PYRIDINE ADDUCT [VO(acac)2Py]

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Date: 2 FEBRUARY 2017

Submission date: 7 APRIL 2017 Lecturer: DR.OOI MEI LEE

Title: Bioinorganic Chemistry: Preparation of Bis(acetylacetonato)oxovanadium(IV), [VO(acac)2] and its Pyridine adduct, [VO(acac)2Py] Objective: (i) To prepare [VO(acac)2] and its pyridine adduct of [VO(acac)2Py]. (ii) Characterisation of the oxovanadium(IV) complexes with IR spectroscopy Introduction: Vanadium is a transition element with partially filled d-shell. The formation of compounds of vanadium complexes whose colour is due to d-d electronic transitions; such as; [V(H2O)6]+2 (purple), [V(H2O)6]+3 (green), [VO(H2O)5]+2 (blue) and [VO(H2O)5]+3 (yellow). The formation of compounds in many oxidation states due to the relatively low reactivity of the d unpaired electrons; example: V2+, V3+, V4+, and V5+. The formation of paramagnetic complexes is due to the presence of unpaired d electrons. However, the most stable oxidation state for vanadium is +4. Vanadium(V) oxide is with the formula V2O5. Commonly known as vanadium pentoxide, it is a brownish yellow solid, but when freshly precipitated from aqueous solution, its colour is deep orange. Due to its high oxidation state, it is both an amphoteric oxide and an oxidizing agent. Acetylacetone (2,4-pentanedione) is a -diketone. The carbon atom of the CH2 group in between the 2 carbonyl group is α-carbon and the hydrogens attached to it are acidic. This is due to the presence of 2 electron withdrawing carbonyl groups. The α-hydrogen may be easily lost to water to produce an anion stablised by resonance:

The acetylacetonate anion can then act as a ligand towards the oxovanadium cation to produce VO(acac)2. This ligand bonds to the metal ion through both its oxygen atoms and, hence, a six membered, weakly aromatic ring is produced:

Refluxing with pyridine causes further metal-ligand coordination and produces VO(acac)2Py. IR spectroscopy is useful then in distinguishing between the vibrational energies of the dark blue-green VO(acac)2 and greyish VO(acac)2Py.

Apparatus: 

250 ml conical flask

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250 ml beaker

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10 ml measuring cylinder

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Glass rod

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Heating mantle

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Round-bottom flask with vertical condenser

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Buchner funnel

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FTIR spectrometer

Materials: 

Vanadium(V) oxide

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Absolute ethanol

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Acetylacetone

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Anhydrous sodium carbonate

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Dichloromethane

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Diethyl ether

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Concentrated sulphuric acid

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Toluene

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Pyridine

Procedure: Part I: Preparation of Bis(acetylacetonato)oxovanadium(IV), VO(acac)2 1. 1.0 g of vanadium(V) oxide was weighed into 250 ml round-bottom flask. 2. 5 ml of distilled water was added together with 3 ml of concentrated sulphuric acid and 10cm3 absolute ethanol. 3. The mixture was refluxed by using heating mantle. The mixture was swirled while heating to avoid any precipitate formed at the wall of the round bottom flask. 4. After an hour, the colour of mixture turned from green and blue.

5. A little ethanol was added to make the dark solution less viscous. The solution was filtered through a cotton wool. 6. The filtrate was transferred to 250 ml beaker and was added with 3.5 ml acetylacetone. 7. The solution was neutralised by adding slowly and stirring a solution of 10 g anhydrous sodium carbonate in 60 ml of distilled. 8. The product was filtered and dried in air. 9. The product was recrystallized. The product was dissolved in minimum warm chloroform. 10. The impurities were filtered and the filtrate was cooled in an ice bath. 11. About 10-20 ml diethyl ether was added until precipitate occurs. 12. The product was filtered, washed with cold ether and air dried. The yield was recorded. Part II: Preparation of Pyridine Adduct, [VO(acac)2Py] 1. The half of the product from Part 1 was dissolved in about 20 ml toluene and was refluxed for 30 minutes with a large excess (6 ml) of pyridine. 2. The resultant solution was concentrated to a smaller volume by distilling off the toluene and pyridine. 3. The solution was cooled down and crystals were formed in ice bath. 4. A small amount of ether was added. 5. The final product was filter and dried in desiccator. 6. The yield of final product was recorded.

Results:

Part 1:

Mass of V2O5 Mass of petri dish Mass of VO(acac)2 with petri dish Mass of VO(acac)2

1.0019 g 33.2020 g 34.7790 g 1.5770 g

Part 2: Mass of VO(acac)2 Mass of plastic bag Mass of VO(acac)2Py and plastic bag

1.5770 g 1.2273 g 1.9067 g

Mass of VO(acac)2Py

0.6794 g

Calculations: Part 1: V2O5 + C2H5OH + 2H2SO4  2VOSO4 + CH3CHO + 3H2O ---- (1) VOSO4 + 2C5H8O  VO(C5H7O)2 + H2SO4 ----- (2) Equation (1) and (2) are multiply with 2; 1V2O5 + 4(C5H7O-)  2VO(acac)2 Molar mass of V2O5 = 181.88 g/mol Mole of V2O5 = =

mass molar mass 1.0019 g 181.88 g/mol

= 5.509 x 10-3 mol

Since, 1 mole of V2O5 = 2 mole of VO(acac)2 Thus, the mole of VO(acac)2 = 5.509 x 10-3 mol * 2 = 0.011 mol Molar mass of VO(acac)2 = 265.157 g/mol Theoretical mass = molar mass * mole

= 265.157 g/mol * 0.011 mol = 2.92 g Percentage yield = =

actual mass theoretical mass 1.5770 g 2.92 g

* 100%

* 100%

= 54.0 %

Part 2: 1VO(acac)2 + Py  1VO(acac)2Py Mole of VO(acac)2 = mole of VO(acac)2Py =

1.5770 g 265.157 g /mol

= 5.947 x 10-3 mol Theoretical mass = 344.26 g/mol * 5.947x 10-3 mol = 2.047 g Percentage yield =

0.6794 g 2.047 g

* 100%

= 33.19 %

Discussion: In the first part of the experiment, Vanadium pentoxide, V2O5 was refluxed with concentrated H2SO4, water and ethanol for an hour, reduces V2O5 to (VO)2+. Orange V2O5 dissolves in the colourless solvents to form a dark green (VO)2+ solution. V2O5 + 4H+  2(VO)2+ + 2H2O +

1 O2 2

The vanadium (II) ion, VO2+ was chelated with 2 acac– anions to form blue-green [VO(acac)2]. The mass recovered from recrystallization is 1.5770g with percentage yield of 54.0 %. This dark blue-green complex has a square-based pyramidal geometry and is able to accommodate one more ligand as shown below:

bis(acetylacetonato)oxovanadium(IV)

(VO)2+ + 2 acacH  2H+ + VO (acac)2 Sodium carbonate, Na2CO3 was added in order to remove the excess H+ from the ionisation of acacH and concentrated H2SO4 so as to drive the reaction to completion. By Le Chatelier’s principle, with the removal of H+ ions, the equilibrium of the reaction is shifted to favour the formation of the VO(acac)2 complex.

Pyridine adduct

In the second part, pyridine and the complex was mixed with toluene as the pyridine is miscible in organic solvent. Pyridine has a lone pair of electrons on the N atom which can be used to bind with the central vanadium ion to form a 6-coordinated complex. The overall structure of the grey complex, VO(acac)2Py, is an octahedral. The mass of the complex recovered after recrystallization is 0.6794 g with percentage yield of 33.19%. V2O5, VO(acac)2 and VO(acac)2Py are coloured compounds because they absorb light in the visible region. The energy of the absorbed photon corresponds to the energy gap between vanadium ion’s d-orbitals. The colour of the compound observed is complementary to that of the absorbed light. The percentage yield for VO(acac)2 was 54%. This amount of yield is above 50 % and considered to be moderate.. Theoretically, more time is required to leave the mixture to stand in an ice bath for crystallisation after Na2CO3 is added in order to produce a higher yield of VO(acac)2. More amount of base may be added to favour the formation of the desired product as well. As the reagents may be toxic, gloves were worn to protect the hands. This is especially important when handling corrosive reagents such as concentrated sulphuric acid. The experiment was carried out in the fume hood to prevent any inhalation of harmful

organic vapours. The flammable reagents such as pyridine, toluene and acetylacetone were also placed away from naked flames. The most significant precaution in the entire experiment is that men are to be cautious during handling the pyridine as it can cause infertility and chronic exposure can cause harm. Boiling chips were added during reflux to avoid bubbling. Lastly, a magnetic stirrer should be added to the round bottom flask to further ensure homogenous mixing of the reagents, thereby speeding up the reaction. From the IR spectra, it was observed that the V=O stretching mode of VO(acac)2 was at 997 cm-1 while that of VO(acac)2Py, 937 cm-1. The addition of pyridine into the square geometric VO(acac)2 complex caused the vibration frequency of V=O stretching to decrease by 60 cm-1. When the pyridine forms coordinate bond with the VO(acac)2, it introduces a lone pair of electrons from nitrogen into the d-orbital of the oxovanadium ion. This increases the electron density around the vanadium ion and thus, results in electron-electron repulsion between the V=O bond. V=O bond lengthens and weakens in order to minimise the repulsion. Therefore, the band shifts to a lower wavenumber. The difference between these two spectra is that in the pyridine adduct spectrum has more addition peaks compared to VO(acac)2 complex. This may be attributed to the presence of pyridine which affects the absorption peaks due to the distortion of the adjacent bonds. However, the 997 cm-1 peak still appeared in the pyridine adduct spectrum which means that the pyridine adduct is not pure and the reaction was not totally completed. In general, the two spectra are fairly similar for the two complexes having similar structures.

Exercise: 1. FTIR spectrum of the complex.

Significant peaks in [VO(acac)2], cm-1 2967 1531 1373 1019-997 937 799

Species -OH -CH3 C-O V=O C-C C-H

2. Structure of aquabis(acetonato)oxovanadium(IV).

Conclusion: The 1.5770 g dark blue-green complex formed in Part 1 is bis(acetylacetonato)oxovanadium(IV) with the percentage yield of 54.0%. The complex is a square-pyrimidal structured with 5th coordination number. The pyridine adduct is a greycoloured octahedral complex with mass of 0.6794 g and its percentage yield is 33.19 %. The stretching mode of V=O and its pyridine adduct obtained are 997 cm-1 and 937 cm-1 respectively. However, the pyridine adduct complex is found to be impure. Therefore, bis(acetylacetonato)oxovanadium(IV) and its pyridine adduct were prepared. The oxovanadium complexes were characterized with IR spectroscopy.

Reference: 

2017. Bioorganic Chemistry: Preparation of bis(acteylacetonato)oxovanadium(IV) and its Pyridine adduct. UDEC2114 Transition Elements and Coordination Chemistry. Kampar. Universiti Tunku Abdul Rahman. [27 March 2017].

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Chemical Safety Data: Pyridine. 2017. Chemical Safety Data: Pyridine. [ONLINE] Available at:http://www.edu.upmc.fr/chimie/chiminorga/MSDS/Pyridine.htm. [Accessed 27 March 2017].

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Vanadyl acetylacetonate - Wikipedia, the free encyclopedia. 2017. Vanadyl acetylacetonate - Wikipedia, the free encyclopedia. [ONLINE] Available at:https://en.wikipedia.org/wiki/Vanadyl_acetylacetonate. [Accessed 27 March 2017].

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Vanadium(V) oxide - Wikipedia, the free encyclopedia. 2017. Vanadium(V) oxide Wikipedia, the free encyclopedia. [ONLINE] Available at: https://en.wikipedia.org/wiki/Vanadium(V)_oxide. [Accessed 27 March 2017].

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Pyridine - Wikipedia, the free encyclopedia. 2017. Pyridine - Wikipedia, the free encyclopedia. [ONLINE] Available at: https://en.wikipedia.org/wiki/Pyridine. [Accessed 27 March 2017].