Experimental on anhydrous tetrahydrofuran

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Chapter Three Experimental

3 Experimental

Anhydrous tetrahydrofuran (Aldrich, 99%) was refluxed with sodium metal and distilled. Dimethyl Formamide (Aldrich, 99%) was made anhydrous using activated molecular sieves. 2, 3 dimercapto-1-propanol (Fluka), Sodium methoxide (sodium metal was reacted with methanol), sodium metal (99%, Riedel-de-Haën), methanol (distilled), Ethylene glycol (99%, BDH), triethylenetetramine (Aldrich, 97%), Silver nitrate (Aldrich, 95%), Copper sulphate (Aldrich, 97%), p-toluene sulphonyl chloride was recrystallised with tetrahydrofuran since it had impurities and moisture (Aldrich) and ammonia (Aldrich, 25%).

3.1 SYNTHESIS OF PER-6-IODO β-CYCLODEXTRIN

3.1.1 Synthesis of per-6-iodo β-Cyclodextrin

To three-necked round bottom flask (250ml) triphenyl phosphine (7.02g, 26.6mmol) and iodine (7.04g, 26.4mmol) were added and dissolved in anhydrous dimethyl formamide (150ml) with continuous flushing of nitrogen gas and stirring at room temperature for 15

mins. Cyclodextrin (2g, 1.8mmol) was then added and the reaction was heated overnight (18 hours) under nitrogen atmosphere at 70°C in an oil bath. The reaction mixture was cooled to 0°C and sodium methoxide (8ml) was added drop wise. The mixture was then poured in cold methanol (500ml). The precipitate formed was filtered under vacuum in a burchner funnel. A yellow powder was obtained (2.54g, 1.5mmol)

% yield: 73.9

1H-NMR: (DMSO) δ (ppm): 1.1005 (t, 1H), 2.409 (s, 1H), 2.800 (s, 1H), 3.07 (q, 1H), 3.516 (m, 54H), 5.873 (s, 4H)

3.1.2 Synthesis of per-6-Ethylenediamine β-Cyclodextrin

In a double-necked round bottom flask (100ml)per-6-Ethylenediamine β-Cyclodextrin (2g, 1.05mmol) and ethylene diamine were reacted under nitrogen atmosphere and continuous stirring. The reaction flask was heated under reflux in an oil bath at 50°C for 72 hours. The solvent was reduced to half its volume and DMF (150ml) was added. A white precipitate (4.15g, 2.7mmol) was obtained.

% yield: 44.6

1H-NMR (D2O) δ (ppm): 2.10 (s, 2H), 2.91 (t, 49H), 3.575 (d, 23H), 3.880 (s, 25H), 5.04 (s, 13H)

Prior to synthesis of per-6-ethylene diamine β-cyclodextrin, copper (II) ions were chelated with ethylene diamine and the complexation was monitored under UV/Visible spectrophotometer.

3.2.1 Introductory studies on complexation of copper (II) ions and ethylenediamine as ligand.

Ethylene diamine being immiscible in water was diluted in THF. Copper (II) sulphate was diluted in distilled water. In the titration cell, 3cm3 of the ligand (blank) was pipetted and absorbance was measured over a range of 400 to 900 nm. Then with a micropipette (10 - 100 µL), 10µL, (1 equivalence of the ligand), of the copper sulphate solution was added followed by stirring with a magnetic stirred. The absorbance was measured after addition and stirring of each 10µL copper sulphate solution in the cell. This experiment was carried out with different concentration of the ligand and copper (II) sulphate solution.

Table below shows the different concentration used:

Concentration

of ligand (mol dm-3)

Concentration

of Cu2+ (mol dm-3)

Volume of Cu2+(µL)

added each time

0.01

0.4

10

0.4

0.01

10

After the synthesis of per-6-ethylene diamine β-cyclodextrin, the cyclodextrin based ligand was complexed with copper (II) ions using UV/Visible spectrophotometer to monitor the titration and binding.

3.2.2 Chelation of per-6-ethylene diamine β-cyclodextrin with copper (II) ions

Per-6-ethylene diamine β-cyclodextrin (0.0714g) placed in a volumetric flask (5ml) was diluted with distilled water to give a solution (0.004M). Copper (II) sulphate (1.2g) was diluted in a similar way to give a solution (1.5 M). The ligand (3 cm3) was pipetted in a titration cell (blank) and absorbance was measured over a range of 400 to 900 nm. The ligand was then titrated each time with copper (II) sulphate solution using a micropipette (10 - 100 µL) and maximum absorbance was recorded after addition of each 10µL of Cu2+ ions. Titration was continued until complexation was completed.

3.3 SYNTHESIS OF 2, 3 DIMERCAPTO-IODO-PROPANE

3.3.1 Synthesis of 2, 3 Dimercapto- iodo- propane

To a three-necked round bottom flask (250ml), nitrogen gas was flushed followed by the addition of iodine (10.155g, 0.2mmol) and triphenyl phosphine (10.507g, 0.2mmol). Anhydrous THF (100ml) was added and the mixture was stirred for 15mins prior to addition of 2, 3 dimercapto-1- propanol (2ml, 0.10mmol). The reaction mixture was stirred and refluxed overnight at 70°C in an oil bath. Then maximum volume of the solvent was removed through rotary evaporator. The product was purified using column chromatography technique. Silica was the stationary phase and a mixture of THF and Ether in a ratio of 1:1 was used as the eluent. The purification was successful and the solvent was again removed via rotary evaporator to yield the product (1.895g).

% yield: 76.5

1H-NMR (DMSO) δ (ppm): 0.624 (s, 2H), 1.832 (s, 3H), 2.479 (s, 1H)

3.3.2 Synthesis of calix-4-arene based ligand

In a two-necked round bottom flask (100ml) continuously flushed with nitrogen gas, sodium hydride (0.7075g, 2.95mmol), anhydrous THF (5ml), calix-4-arene (0.125g, 0.295mmol) were added and stirred for 15mins. The 2, 3 dimercapto-1-propanol (1.035g, 2.12mmol) was added and the mixture was stirred at room temperature for 16 hours. The mixture was then cooled to 0°C and methanol (1.5ml) was added. After 10mins, the reaction mixture was poured in a separating funnel (100ml) followed by the addition of water (12.5ml) and ether (12.5ml). The organic layer was washed with water (3 × 6.5ml). The combined organic extracts were dried over sodium sulphate anhydrous. The solution was then filtered and solvent was removed via rotary evaporator.

1HNMR DMSO δ (ppm): 1.16 (d, 1H), 1.236 (s, 1H), 2.494 (s, 2H), 3.370 (s, 3H), 7.621 (m, 1H)

3.3.3 Complexation of Copper (II) ions and ligands

Complexation reaction of the ligands with copper (II) ions was carried out to show the binding of copper (II) ions with the ligands and also the substitution of these ligands by water molecules of addition of certain equivalence of copper (II) ions.

3.2.3.1 Conductimetric titration of Copper (II) sulphate with 2, 3 dimercapto-1-propanol.

Copper (II) sulphate (0.0156g, 2.0 × 10-6 mmol) was prepared in a volumetric flask (100 ml) and diluted with distilled water. 2, 3 dimercapto-1-propanol (0.01ml, 2.0 × 10-6 m mol) was prepared in THF. The metal was titrated with the ligand keeping the volume of the reaction mixture constant at 10ml. Different volume of ligand and copper (II) sulphate were used but the total volume was always 10ml. Each time the conductance was measured and noted in each solution.

Solution

number

Volume of 0.002M,

Cu 2+ ions in ml

Volume of 0.002M,

2,3 dimercapto-1-propanol

in ml

1

9

1

2

8

2

3

7

3

4

6

4

5

5

5

6

4

6

7

3

7

8

2

8

9

1

9

3.4 Stoichiometric determination of silver complexes

3.4.1Silver complexation with ethylene diamine

Silver nitrate (3.40g, 0.2M) was diluted with distilled water in a volumetric flask (100ml) while ethylene diamine (13.5ml, 2.0M) was diluted with THF. Silver nitrate solution (50ml) was placed in a beaker (100ml) well wrapped with aluminium foil to prevent photolysis. Also, a silver electrode and a calomel electrode (connected to an ion analyzer) were placed in the beaker. Ethylene diamine was placed in a burette and activity of silver ions was noted after addition of each 0.2ml of the ligand.

The above experiment was carried out with ammonia as ligand prior to ethylene diamine.

3.4.2 Silver complexation with ammonia

Silver nitrate (0.170g, 2.0M) was diluted with distilled water in a volumetric flask (100ml) and ammonia (14.97 ml, 0.01M) was diluted with distilled water in a volumetric flask (100ml). The silver nitrate solution (50 ml) was placed in a beaker (100ml) well wrapped with aluminium foil to prevent interaction with light. Also, a calomel electrode and a silver electrode (connected to an ion analyzer) were placed in a beaker. Ammonia solution was placed in a burette (50ml) and after addition of each 0.1ml of ammonia with continuous stirring. The ion activity was noted.

3.4.3 Silver complexation with 2, 3 dimercapto-1-propanol

Silver nitrate solution (1.698, 0.01M) was prepared in a volumetric flask (100 ml) with distilled water while 2, 3 dimercapto-1-propanol (0.31 ml, 0.03 M) was prepared in tetrahydrofuran using a volumetric flask (100 ml). The silver nitrate solution was (50ml) was placed in a beaker (100ml) wrapped with aluminium foil. Calomel and silver electrodes were placed in the beaker. The ligand (2, 3 dimercapto-1-propanol) was placed in a burette (50ml) and after addition of each 1.0 ml of ligand (with continuous stirring), the ion activity was measured.

3.5 SYNTHESIS OF CYCLEN

3.5.1 Synthesis of 1, 2 bis ( p-toluenesulfonato) ethane

Sodium hydroxide (8g, 0.2mmol) were dissolved in distilled water (40ml) and ethylene glycol (7.4ml, 0.07mmol) in THF (40ml) were placed in a flask and the mixture was cooled in an ice bath with magnetic stirring and drop wise addition of p-toluene sulfonyl chloride (24.3g, 0.13mmol) in THF (40ml) for over 4 hours. The solution was then poured into ice-water (100ml) and organic layer was extracted with dichloromethane (2 × 15ml). The combined organic extract was then washed twice with water (15ml) and once with saturated sodium chloride solution. The extract was then dried over Magnesium sulphate. The mixture was filtered and upon evaporation, white shiny crystals (2.32g, mmol) appeared.

Mp: 124-127°C

% yield: 65

1H-NMR in CDCl3 δ(ppm): 1.67 (s, 2H), 2.18 (d, 2H), 7.36 (M, 5H)

3.4.2 Synthesis of acyclic tetratosylamide

A double-necked round bottom flask (100ml) was charged with potassium carbonate (1.46g, 30.8mmol), triethylene tetramine (1g, 6.84mmol) and water (40ml). The mixture was refluxed at 80°C in an oil bath with continuous and vigorous stirring. Para-toluenesulfonyl chloride was added in small portions as solid over a period of 4 hours. The mixture was refluxed and stirred overnight and then allowed to cool until a colorless precipitate was evident. The mixture was filtered on a sintered filter funnel and washed in turn with water (3 × 5ml), methanol (3 × 5ml) and finally with diethyl ether (3 × 5ml). The solid was dried under high vacuum to yield acyclic tetratosylamide (2.58g)

Mp: 263°C

% yield: 56.6

1H-NMR in CDCl3, δ(ppm): 3.128 (s, 5H), 3.336(t, 2H), 4.309 (s, 4H), 4.113 (s, 4H), 8.867 (s, 1H), 8.513 (t, 5H)

3.4.3 Synthesis of cyclic tetratosylamide

To a double-necked round bottom flask (100ml), nitrogen gas was flushed followed by addition of anhydrous potassium carbonate (0.835g, 6.05mmol) and acyclic tetratosylamide (2.22g, 2.91mmol) dissolved in THF anhydrous (35ml). Also a solution of 1,2 bis(p-toluenesulfonato)ethane (1.09g, 2.965mmol) in THF (5ml) was prepared in a pressure equalizing addition funnel. The mixture was stirred vigorously at room temperature. The content of the addition funnel was slowly added over a period of 3-4 hours. The final mixture was stirred vigorously overnight. The mixture was then heated at 70°C in an oil bath for 3 hours and the THF was distilled off via a rotary evaporator. The residue was taken up in dichloromethane (5ml) and water (5ml) and transferred into a separating funnel (50ml). The organic layer was extracted with dichloromethane (2× 25ml). The organic extract was dried over potassium carbonate. The mixture was filtered and solvent removed on rotary evaporator. The residue was recrystallised in hot toluene (15ml). On cooling, a white precipitate was deposited. The solid was collected on a sintered filter funnel. Cyclic tetratosylamide (1.39g) was obtained.

Mp: < 263°C

% yield: 61

1H-NMR in CDCl3 δ (ppm): 1.395 (d, 1H), 2.47 (s, 3H), 7.20 (M, 2H), 7.763 (d, 2H)

3.4.4 Synthesis of Cyclen

A dry single-necked round bottom flask (50ml) was charged with the cyclic tetratosylamide (0.78g, 0.99mmol) and concentrated sulphuric acid (2ml). The mixture was heated under nitrogen for 40 hours at 110°C. The mixture was poured in a conical flask and cooled in ice-bath. Slowly water (20ml) was added followed by addition of potassium hydroxide pellets, while swirling the flask. Sufficient pellets were added to make the pH greater than 13. Ethanol was added (7.5ml) and mixture was filtered under reduced pressure in a sintered filter funnel. The residue was washed with ethanol (3ml) and the yellow solid obtained was taken up in hydrochloric acid (0.1 M, 5ml). The solution was transferred in a separating funnel and washed with dichloromethane (2×3ml). The aqueous layer was separated and washed twice more with dichloromethane (2×30ml). The pH is again raised to 13 by addition of more potassium hydroxide pellets. The aqueous layer was extracted with chloroform (5 × 2ml). The organic extracts was combined and dried over anhydrous potassium carbonate. The mixture was filtered and solvent removed on rotary evaporator to yield a colourless solid (0.121g).

Mp: 113-114°C

% yield: 70.5

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