Preparation of polyamide by condensation polymerization

Objective:

1. To study and understand the formation of polyamide (nylon) through condensation polymerization between surface technique

2. To observe the effect of external factors on molecular weight and polymer yield

 

Introduction:

Polymerization is a process of forming long and repeating organic polymer chains. Polymerization is categorized into different systems based on the mechanism and structure of polymer. Both structure and mechanism are usually required in order to clearly classify a polymer. Polymers were originally classified by Carothers (1992) into addition and condensation polymerization. However, the more recent terminology further classifies polymerization into step-growth, chain-growth and ring opening polymerization.

 

Condensation polymers are refers to the polymers that were formed from polyfunctional monomers by various condensation reactions with the elimination of some small molecules such as water. The type of end product resulting from the condensation polymerization is depends on the type of functional end group which can react. For example, the formation of polyester between a dicarboxylic acid and a diol in which two monomers are linked together and a water molecule has been produced.

Figure 1 Condensation polymerization between a dicarboxylic acid and a diol

This process can continue adding alternatively one molecule and then the other, building the polymeric chain of hydrocarbon units that joined by ester bond. This is molecule formed from the condensation polymerization is called polyester.

 

In order for a condensation polymerization to occur continuously, the small molecules need to be removed from the system either by heating or through vacuum. However, heating would cause degradation or breaking of polymer molecules from bigger size of polymers to smaller size of polymer molecules. As a result, this will cause the formation of low molecular weight polymer. In order to overcome this problem, polymerization should be carried out at low temperature either by using the method of polymerization in solvent or polymerization between two surfaces of solution (interfacial polymerization). Many polymers can be produced at lower temperature (instead of high temperature) by using Schotten-Baumann reaction of acid chlorides.

 

Interfacial polymerization is refers to the condensation polymerization between two reactants is carried out at the interface of two immiscible solvents in which each containing one of the reactants. Interfacial polymerization is important because it produces the polymer with high molecular weight in a short period of time which under normal conditions of temperature and pressure. This type of polymerization could be carried out at room temperature and the types of polymers that could be formed using this technique are polyurethane, polyamide and polyurea. Thus, the formation of nylon 6,10 which is a type of polyamide that can be produced by using this method of reaction between two surfaces of immiscible solvents. This technique is extremely useful to the reactants which are not stable under the polymerization conditions by other techniques. Among the techniques of condensation polymerization, interfacial polymerization has some added advantages over the other techniques.

 

Nylon 6,10 is produced from the two monomers named sebacoyl chloride (ClOC(CH­₂)₈COCl) and 1,6-diaminohexane (also known as hexamethylenediamine, H₂N(CH₂)NH₂). Sebacoyl chloride is a 10-carbon acid chloride with a –COCl group as functional group at each end. The other monomer is a 6-carbon chain with two amino groups, -NH₂ at each end. Nylon 6,10 is named based on the carbon number of two monomers, in which the first number come from amine monomer while the latter one from acid chloride monomer. These two compounds are polymerized via condensation with the loss of a molecule of hydrogen chloride, as shown in the equation below:

 

Nylon is a term to represent synthetic polyamides. Different nylons are described by a numbering system that shows the number of carbon atoms in the monomer chains. Nylons from diamines and dicarboxylic acids are designated by two numbers in which the first representing the diamine whereas the second representing the dicarboxylic acid. In order to generate a long chain polymer and to expedite the rate of kinetic reaction, the polymerization system should be stirred vigorously to make sure that a new surface of polymer is always produced in the system. This ensures that the polymers produced would give a high percentage of yields. Both hexamethylenediamine and sebacoyl chloride are not solvents in the polymerization process between the interface of solutions. In the stirring technique, the non equilibrium system that occurs eliminates the weakness that might occur in polycondensation process such as:

1. The necessity of high temperature

2. Longer time of reaction

3. Accurate stoichiometric balance of equivalent

Physical properties of nylon 6,10:

1. Bright yellow in colour

2. Less transparent

3. Melting point of 220 °C

4. Moderate crystallinity

5. High impact strength

6. Electrical insulating ability

 

Apparatus:

100ml beaker, 10ml graduated cylinder, glass rod, thin stick

 

Materials:

60% w/v hexamethylenediamine, sebacoyl chloride, sodium laurel sulphate (soap powder)

 

Procedures:

1. 3ml sebacoyl chloride solution and 100ml of hexane (solution B) were added into a 100ml beaker.

2. 0.01g of soap powder was added into the mixture (solution A) of 3ml of hexamethylenediamine, 50ml of water and 2 drops of phenolphthalein.

3. Solution A was added carefully into solution B so as not to disturb the interface between two solutions.

4. A layer of polymer was formed between solution A and solution B. The strand of polymer (nylon) was wrapped around the glass rod and nylon strand was winded onto the rod with a steady pace.

5. The polymer formed was rinsed with water.

6. Let it dry in the oven.

7. The weight of polymer was measured.

8. The steps above were repeated with 5ml of solution B and 3ml of solution A. The solutions were stirred.

9. The polymers formed were characterized and compared.

 

Results and calculations:

Table 1 Observation on polymers that made with different methods

Observations on polymers formed with different methods
Wrapping on glass rod	White, long and weak elasticity nylon was formed.
Stirring	A clump of nylon was formed.

Table 2 Weight of polymer obtained by wrapping on glass rod

Weight of empty watch glass	20.4850 g
Weight of (empty watch glass + polymer, Nylon 6,10)	20.9122 g
Weight of polymer (nylon 6,10)	0.4272 g

Table 3 Weight of polymer obtained by stirring

Weight of filter paper	0.4836 g
Weight of (filter paper + polymer, Nylon 6,10)	0.9099 g
Weight of polymer (nylon 6,10)	0.4263 g

 

Calculate percentage yield

Unstirred interfacial polymerization

Types of monomer	hexamethylenediamine	Sebacoyl chloride
Density (g cm-3)	0.84	1.121
Volume used (cm3)	3.00	3.00
Molecular weight (g mol-1)	116.00	239.00

 

Mass of hexamethylenediamine = 0.84 g/cm³ x 3cm³ x 60% = 1.512g

Theoretical number of mole of hexamethylenediamine = 1.512g / 116 g mol^-1

= 0.013 mol

Mass of sebacoyl chloride = 1.121 g/cm³ x 3cm³ = 3.363g

Theoretical number of mole of sebacoyl chloride = 3.363g / 239 g mol^-1

= 0.014 mol

Thus, limiting agent is hexamethylenediamine.

Molecular weight of repeating unit = 282 g mol^-1

Weight of nylon 6,10 obtained experimentally = 0.4272g

Actual number of mole of repeating unit = 0.4272g / 282 g mol^-1 = 0.0015 mol

Percentage yield = 0.0015 mol / 0.013 mol x 100%

= 11.54%

 

Stirred interfacial polymerization

Types of monomer	hexamethylenediamine	Sebacoyl chloride
Density (g cm-3)	0.84	1.121
Volume used (cm3)	3.00	5.00
Molecular weight (g mol-1)	116.00	239.00

Mass of hexamethylenediamine = 0.84 g/cm³ x 3cm³ x 60% = 1.512g

Theoretical number of mole of hexamethylenediamine = 1.512g / 116 g mol^-1

= 0.013 mol

Mass of sebacoyl chloride = 1.121 g/cm³ x 5cm³ = 5.605g

Theoretical number of mole of sebacoyl chloride = 5.605g / 239 g mol^-1

= 0.023 mol

Thus, limiting agent is hexamethylenediamine.

Molecular weight of repeating unit = 282 g mol^-1

Weight of nylon 6,10 obtained experimentally = 0.4263g

Actual number of mole of repeating unit = 0.4272g / 282 g mol^-1 = 0.0015 mol

Percentage yield = 0.0015 mol / 0.013 mol x 100%

= 11.54%

 

Table 3 Comparisons between two polymers that produced by different methods

Wrapping on the glass rod	Method to produce polymers	Stirring by using glass rod
0.4272g	Mass	0.4263g
11.54%	Percentage yield	11.54%
More elastic	Elasticity	Less elastic
Stronger	Stiffness (Malleability)	Weaker
Stronger	Ability to stick to surface	Weaker

 

Discussion:

In this experiment, the interfacial polymerization technique plays a very important role. This method is primarily used in the case of condensation polymers, in which two reactants have different solubility characteristics. Hexamethylenediamine and sebacoyl chloride were used in this experiment in order to demonstrate the condensation polymerization in the interface between two solutions.

 

Interfacial polymerization is different from the usual condensation polymerization. This is because the monomers (undergo this polymerization) tend to diffuse to the interface and will only react with the polymer chain end formed initially. The diacid chloride and diamine monomer molecules will react with the growing polymer chain end before they penetrate through the polymer film to create the growth of new polymer chains. Therefore, interfacial polymerization creates a high tendency to generate high molecular weight polymer in the polymerization process. In addition, stoichiometry automatically exists at the interface because both monomers diffuse from aqueous phase and organic phase respectively. The stoichiometry at the interface is perfectly controlled by mass transfer controlled rate of diffusion and consumption of each monomer species.

 

Sebacoyl chloride was placed in 100ml of hexane (solution B) while hexamethylenediamine was added with 50ml of water (solution A). The introduction of aqueous layer and organic layer was used to create an interface between two solutions since aqueous layer and organic layer will not mix together. Interfacial polymerization occurs instantly forming a thin film of solid nylon 6,10 at the interface. The thin film at the interface stops further reaction by preventing the monomers to meet each other. During the preparation of solution B, any apparatus used should be rinsed with hexane and thus they do not contain water. If water present, chloride ion, Cl^- of sebacoyl chloride tend to react with the hydroxide, OH^- in water to form sebacic acid as well as two hydrochloric acid molecules.

The reaction between sebacoyl chloride and water is very reactive since chloride ion is a group leaving group.

 

A small amount (0.01g) of sodium laurel sulphate (soap powder) was introduced into the solution B in order to lower the surface tension of solution A and hence hexamethylenediamine will easily solubilize in it. As a result, the condensation polymerization is encouraged to occur in the interface. Since hexamethylenediamine exists its base property in the presence of water, so two drops of phenolphthalein was added as an indicator to show the position of interface between the solutions and to determine the point where hexamethylenediamine has been used up. In alkaline solution, the colour of phenolphthalein is pink while it will be faded if the alkalinity of solution decreases.

 

The interface between solution A and solution B should not be disturbed during transferring the solution A into solution B. This is to make sure both reactants do not form a polymer clump in unstirred interfacial polymerization. The system contains two layers in which solution A with hexamethylenediamine is upper layer whereas solution B with sebacoyl chloride is the lower layer because sebacoyl chloride is denser than hexamethylenediamine. During the transferring process, condensation polymerization between hexamethylenediamine and sebacoyl chloride took place at the interface is shown as the equation below:

At the interface between the solutions, a bigger molecule was formed from the reaction between both monomers and two small molecules hydrochloric acid, HCl were generated. The bigger size molecule formed at the interface could be dimer, trimer, tetramer, oligomer and polymer.

 

In unstirred interfacial polymerization, the colour of phenolphthalein indicator was faded as more nylon was wrapped on the glass rod and finally it was decolourized. This is because the decrease in concentration of hexamethylenediamine in which the diamine was polymerized in the system. In addition, the condensation polymerization produced hydrochloric acid as by-product and it neutralized the acid present in the system. The increase of hydrochloric acid concentration caused the phenolphthalein indicator to be decolourized. In stirred interfacial polymerization, the pink colour of phenolphthalein decolourized immediately once both solutions were stirred. This method produced a polymer clump in the solution. As the time pass, the polymer clump was predicted to become smaller because the hydrochloric acid will hydrolyze the amide bond in the polymer molecule.

 

By comparing both polymers that produced from two methods, the nylon 6,10 in unstirred polymerization results a more elastic and stiffer polymer than the nylon 6,10 in stirred polymerization. Besides, its ability to stick on the wall of beaker and surface is stronger when compared to nylon obtained from the latter method. The molecular weight of nylon obtained in unstirred polymerization is predicted to have higher molecular weight since its mechanical strength is greater than the other one. The weight of nylon 6,10 obtained in the unstirred interfacial polymerization was 0.4272 g while the weight of nylon 6,10 obtained via stirred interfacial polymerization was 0.4263g. Both methods gave the same percentage yield of 11.54%.

 

Reference:

1. Odian, G. (2004). Principles of Polymerization (4^th Ed.). USA: John Wiley & Sons, Inc.

2. Wagh, S.J., & Jadhav K.T. (n.d.) A review on interfacial polycondensation:

types, applications andeffect of various parameters.

3. Ji, J., Childs, R.F., & Mehtra, M. (2001) Mathematical model for encapsulation by interfacial polymerization. 192 (2001), P 55-70.

Determination of chloride ion in natural water

Objectives:

1. To apply Mohr method to the measurement of chloride ion in natural water

2. To determine the chloride concentration in unknown water sample

3. To understand the titration theory of chloride with silver nitrate solution

 

Introduction:

Titration is a common analytical technique in which the concentration of a substance of solution can be determined by adding standard solution that reacts with the unknown. By using the stoichiometry of the reaction and the number of moles of standard solution needed, the concentration of analyte can be determined through titration.

Argentometric titration is a type of titration that based upon silver (I) ion, Ag⁺, for example, Mohr method. In Mohr method, the most important precipitating agent is silver nitrate in which this method determines the chloride concentration of a solution by titration with silver nitrate. In argentometric determination of chloride concentration, potassium chromate is used as an indicator by reacting with silver ions to produce brick-red silver chromate precipitate at the end point.

As the silver nitrate solution is slowly added, the chloride ion will react with silver ion to form silver chloride precipitate.

Ag⁺(aq) + Cl^-(aq) –> AgCl(s) K_sp = 1.70x10^-10

This reaction continues until all the chloride ion in the system has been used up to form precipitate and this approaches the end point of titration. After all the chloride ion has been precipitated, any more silver(I) ion will react with the chromate ion, CrO₄^2- to form a red-brown precipitate of silver chromate as shown in the following equation.

2 Ag⁺(aq) + CrO₄^2-(aq) –> Ag₂CrO₄ (s) K_sp = 9x10^-12

Mohr method can be used to determine the chloride ion concentration of water samples from many sources such as seawater, stream water, river water and estuary water. Two unknown water sample are tested by using the particular method. The Mohr method works well in a slightly acidic condition, hence the pH of the water sample should be adjusted to the range of 6~8 by adding dilute acid or dilute base as needed.

Apparatus:

Conical flask, burette, pipette, measuring cylinder, volumetric flask

Materials:

Deionized water, unknown A water sample, unknown B water sample, 0.075M silver nitrate solution, pH paper, sodium hydroxide solution, calcium carbonate, 0.25M potassium chromate solution

Procedures:

 

Discussion:

In this experiment, the titration of unknown sample was conducted in the pH range of 7 to 8. This is because at pH lower than 7, the chromate ion will be converted to dichromate ion.

CrO₄^2-(aq) –> Cr₂O₇^- (aq)

Eventually, this dichromate ion cannot form a brick red silver chromate precipitate with silver ion and hence end point of the titration cannot be detected. At pH higher than 8, the silver ion will tend to react with the excess hydroxide ion to form brownish silver hydroxide. Formation of silver hydroxide will cover the colour of silver chromate precipitate and hence end point also cannot be seen.

Ag⁺(aq) + OH^-(aq) --> Ag(OH) (s)

Mohr method can only roughly show the concentration of chloride ion in the water sample. This is because excess silver nitrate is needed to produce sufficient silver chromate precipitate to be observed in the solution with heavy white precipitate of silver chloride. Besides, the intense yellow colour of chromate solution causes the brick red silver chromate that formed is hardly to be observed.

 

Precaution steps:

1. All solution mixture that involved silver nitrate solution must be discarded into waste bottle because silver is heavy metal.

2. The burette must be rinsed with silver nitrate solution before titration starts.

3. Wear gloves when handling silver nitrate solution since it will cause skin staining and chemical burn.

4. Chromate solution needs to be used with care as chromate is a known carcinogen.

Flickr Tags: mohr method,chloride ion determination in water sample,titration,silver nitrate solution

Synthesis & characterization of a metal hydride complex

Objectives:

1. To synthesize a cobalt hydride complex

2. To deduce its chemical structure based on the spectral data

 

Introduction:

Metal hydride complexes are very crucial as the intermediates in many catalytic processes such as alkene oligomerization and hydrogenation. Covalently bonded metal hydride complexes are known for all the transition metals. The complexes often contain the metal in a low oxidation state with the ligands of phosphines, carbon monoxide or cyclopentadiene.

 

Isomerization of alkene is always a possibility in any homogenous catalytic reaction that involved alkene. Migratory insertion of alkene into the metal hydrogen (M-H) bond can occur in a Makovnikov addition or anti-Makovnikov manner. Alkene isomerization is a process that involves Makovnikov addition followed by a β-elimination which is shown in the diagram 1 below:

Figure 1: Isomerization of butene by hydride mechanism

In the Figure 1, it shows that the but-2-ene is synthesized from but-1-ene through the hydride mechanism in which metal hydride acts as the intermediate.

One of the well known processes of homogeneous catalytic reaction is hydrogenation of alkene. The metal hydride complex plays a very important intermediate in the hydrogenation of alkene, for example, Wilkinson’s catalyst in the hydrogenation of alkene. The following figure 2 shows how the metal hydride acts as an intermediate in the particular process.

 

Firstly, Wilkinson’s complex will dissociates one phosohine ligand to form a 14 electron complex. This followed by the oxidative addition of hydrogen to form a metal hydride intermediate. In the following step, alkene is added into the metal complex via ligand addition. Migratory insertion of alkene into the M-H bond leads to the formation of alkyl ligand that bonded to rhodium metal. Alkane is formed at the end of the process via reductive elimination between a hydride and an alkyl group. The catalyst is being reused in the hydrogenation process and the process is repeating again.

 

In this experiment, metal hydride complex is being synthesized and characterized by using proton nuclear magnetic resonance (¹H NMR) spectrophotometer in order to determine the number of proton present. IR spectrophotometer is also used in characterizing the metal complex.

 

Materials:

Sodium borohydride, ethanol, cobalt(II) nitrate hydrate, triphenylphoshate, methanol, dichloromethane

 

Instruments:

FT-IR spectrophotometer, NMR spectrophotometer

 

Apparatus:

Melting point apparatus, hotplate stirrer, magnetic stirrer bar, Buchner funnel, beaker, Erlenmeyer flask, Hirsch funnel

 

Procedure:

Part A: Preparation of Metal hydride

Part B: Characterization of Metal hydride

 

Results and calculation:

Table 1: Weight of hydridotetrakis(triphenylphosphito)cobalt(I)

Weight of empty sample vial	12.5925g
Weight of ( sample vial + metal hydride)	19.3553 g
Weight of metal hydride	6.7628 g

Calculating percentage yield of metal complex

One mole of Co²⁺ reacts with one mole of P(C₅H₅)₃.

Mole number of Co²⁺ = 1.5240g / 200.93g mol^-1

= 0.0076 mol

Mole number of P(C₆H₅)₃ = 6.8037g/ 261.97g mol^-1

= 0.026mol

Thus, Co²⁺ is the limiting reagent since P(C₆H₅)₃ is in excess.

Theoretical mass of hydridotetrakis(triphenylphosphito)cobalt(I)

= 0.0076mol x 1107.81g mol^-1

= 8.4194g

Percentage yield = 6.7628 g / 8.4194g x 100%

= 80.32%

 

Table 1: Integration value and number of proton present for each peak in NMR spectrum

Value of integration	= 60	= 1
Ratio	60	1
Number of protons present	60	1

Note: One triphenylphosphate contains 15 H

Since one triphenylphosphate contains 15H, so the presence of 60H indicates that there is four triphenylphosphate ligands binded to the metal hydride complex.

Table 2: Significant peaks of cobalt(II) nitrate hydrate in IR spectrum (Appendix I)

Significant signals	Wavenumber (cm-1)
Expected (from table)	Observed (from spectrum)
O-H stretch	3200-3550	3403
Asymmetric NO2 stretch	1450-1600	1629
Symmetric NO2 stretch	1260-1375	1384

Table 3: Significant peaks of triphenylphosphite in IR spectrum (Appendix II)

Significant signals	Wavenumber (cm-1)
Expected (from table)	Observed (from spectrum)
Aromatic C=C stretch	1400-1600	1481, 1590
=C-H stretch	3010-3100	3062, 3038
C-P stretch	700	absent

Table 4: Significant signals of hydridotetrakis(triphenylphosphito)cobalt(I) in IR spectrum (Appendix III)

Significant signals	Wavenumber (cm-1)
Expected (from table)	Observed (from table)
=C-H stretch	3010-3100	3067
Aromatic C=C stretch	1400-1600	1490, 1591
Co-H stretch	1745-1933	absent
C-P stretch	700	691

Note: The C-P stretch value is obtained from journal. (Kurita et al, 2003)

Electron counting of hydridotetrakis(triphenylphosphito)cobalt(I)

Hydride: donates 2 electrons, each triphenylphosphito donates 2 electrons

Hydride: -1, triphenylphosphosphito: neutral

Oxidation state of cobalt = Co(I), with d⁶

Total electron count = 2 + 4(2) + 6

= 16 electrons

 

Discussion:

The percentage yield of hydridotetrakis(triphenylphosphito)cobalt(I) is 80.32% in which the mass of product obtained experimentally is 6.7628 g.

In this experiment, sodium borohydride (white) was used to provide hydride to metal complex to form a cobalt hydride complex. Ethanol acts as a medium to allow the cobalt complex (greenish brown) can form in the solid state since the cobalt hydride complex is not soluble in ethanol. The product was washed with ethanol, water and methanol is to remove any other unreacted starting materials. This method can reduce the presence of impurities.

From the IR spectrum of triphenylphophate, the significant signals include aromatic C=C (1481cm^-1 and 1590cm^-1) and =C-H (3062cm^-1 and 3038cm^-1). However, the expected C-P stretch at 700cm^-1 did not present. According to the IR spectrum of product, the significant signals that present are =C-H- stretch (3067cm^-1), aromatic C=C (1490cm^-1 and 1591cm^-1) and C-P stretch (691cm^-1). However, there is another expected significant signal did not present in the IR spectrum which is the Co-H stretch (1745-1933cm^-1).

Based on the ¹H NMR spectrum of product, the integration of the first signal (at positive ppm value) shows 66mm while the second signal (at negative ppm value) shows 1.1mm. From the spectrum, number of protons present in the first and second signals is 60 H and 1 H respectively. Hence, the molecular structure of hydridotetrakis(triphenylphosphito)cobalt(I) is deduced as monocapped tetrahedral with the hydride as the face-capping ligand. The figure 3 below shows the structure of hydridotetrakis(triphenylphosphito)cobalt(I).

Figure 3: Molecular structure of hydridotetrakis(triphenylphosphito)cobalt(I)

The fomal oxidation state of cobalt in the metal complex is Co(I). This is because there is only one hydride carrying one negative charge bonded to cobalt while the other four triphenylphosphine ligands are neutral. Based on the electron counting in the calculation and result part, the total electron is 16. The metal complex is stable in 16 electrons because the four sterically bulky triphenylphosphine ligands blocked the vacant site and hence other ligand is not allowed to bind to cobalt. As a result, hydridotetrakis(triphenylphosphito)cobalt(I) has a total number of 16 electrons.

Precaution steps:

1. Make sure the sodium borohydride will never contact with acid or water since it will liberates hydrogen.

2. Dichloromethane is highly volatile and must be used in the fume hood only.

 

 

Flickr Tags: synthesis,characterization,metal hydride,IR,Makovnikov addition,β-elimination,hydridotetrakis(triphenylphosphito)cobalt(I)

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.

Nylon 6,10， Nylon 6,6 and Nylon 11 Synthesis

1. Write the equation involved in the above synthesis, its chemical name and industrial name.

Chemical name: Poly(hexamethylene sebacamide)

Industrial name: Nylon 6,10

 

 

2. Write the equations involved in the synthesis of Nylon-11 and Nylon 6,6.

Synthesis of Nylon 6,6

 

Synthesis of Nylon 11

n [H₂N-(CH₂)₁₀-COOH] –>   -[HN-(CH₂)₁₀-CO-]_n- 

 

Flickr Tags: Poly(hexamethylene sebacamide),Nylon-11,Nylon-6,6

Quantitative analysis by using high performance liquid chromatography

Objective:

1. To determine the concentration of acetophenone in a mixture by reversed phase performance liquid chromatography using standard calibration

 

Introduction:

High performance liquid chromatography (HPLC) is a form of liquid chromatography that used to separate non volatile compounds in a mixture in which they are dissolved in solution. HPLC instruments consist of a reservoir of mobile phase, a high pressure pump, an injector, a separation column, and a detector. HPLC is one of the most widely used analytical techniques in industry. It is used to separate and analyse compounds through the mass-transfer of analyte between stationary phase and mobile phase. The technique of HPLC utilizes a liquid mobile phase to separate the components in a mixture.

First of all, the components themselves are dissolved in a solvent. Then, they (in mobile phase) are forced to flow through a column (stationary phase) under high pressure. The mixture is resolved into its components within the column. Due to the different partitioning behavior of the different components in the mixture, they will pass through the column at different rates and hence separation of compounds can be done based on the individual retention time. The interaction of the solute with mobile phase and stationary phase can be controlled by choosing different mixture of solvent and column.

HPLC mainly categorized into two types: normal phase and reversed phase. For normal phase, polar stationary phase (commonly silica) is used to retain the polar components which will stick at the column for a longer time. Hence, non polar component will pass through the column faster than polar component. The primary difference between reversed-phase chromatography and normal phase chromatography is that its stationary phase utilizes a non-polar or hydrophobic surface (typically long chain hydrocarbon) as opposed to a polar (Si-OH) surface used in normal phase chromatography. In this column, polar component will pass through it faster compared to non polar component.

The principles of high performance liquid chromatography are generally similar with gas chromatography. This analyse is based on a comparison of either peak height or peak area observed. The area under a peak is proportional to the mass or concentration of the compound giving rise to that peak, the formula is shown as below:

A m

A = f m

where f is called the detector response factor for the compound. A plot of peak area versus concentration should be linear in which it can be used as a calibration curve to determine the concentration of compound that present in an unknown solution.

 

Materials:

Stock solution of 1000ppm acetophenone in methanol, mixture M52 containing an unknown amount of acetophenone

 

Apparatus:

Pipette, volumetric flask, beaker

 

Instrument:

High performance liquid chromatography-mass spectrophotometer

 

Procedure:

Result and calculation:

Calculating the volume of 1000ppm acetophenone needed in each standard solution

By applying the forlmula of M₁V₁ = M₂V₂

M₁ = Molarity of stock solution, 1000ppm

V₁ = Volume of stock solution needed

M₂ = Molarity of standard solution

V₂ = Volume of standard solution

(1000ppm)(V₁) = 50ppm (10ml)

V₁ = 0.5ml

Applying the same formula to obtain the volume of stock solution needed to prepare standard solutions with 100, 150, 200, 250 and 300ppm.

Table 1: Concentrations of acetophenone and the peak areas in chromatogram

Volume of 1000ppm acetophenone needed (ml)	Concentration of acetophenone (ppm)	Peak areas in chromatogram	Retention time (min)
0.50	50	2613.34	1.587
1.00	100	3795.08	1.580
1.50	150	4128.18	1.588
2.00	200	5391.71	1.583
2.50	250	7972.67	1.572
3.00	300	9843.05	1.601

Table 2: The peak area of unknown M32 in the chromatogram

Sample	Peak areas in chromatogram	Retention time (min)
Unknown M32	6658.05	1.570

A calibration curve (as shown in Graph 1) has been plotted. The concentration of acetophenone in unknown M32 has been determined by using the calibration curve, which is 205ppm.

Discussion:

The concentration of acetophenone in unknown M32 is determined by using the calibration curve obtained. The peak areas of unknown M32 obtained is 6658.05 with the concentration of acetophenone of 205ppm. Based on the chromatogram obtained, we found that there is only one compound presents in the unknown M32 since the chromatogram showed only one peak. The identity of this compound can be further confirmed by using liquid chromatography mass spectroscopy.

Although we can get the calibration curve, however the calibration is not so accurate. This can be seen at the deviation of the retention time of last two standard solutions which are 250ppm and 300ppm. In order to obtain a better calibration curve, the calibration should be repeated until we obtain the retention time of 1.58min for all the standard solutions. For the sample unknown M32 should be repeated again in order to get the retention time of 1.58min instead of 1.57min. However, we cannot repeat the experiment because we are lack of time.

Precaution steps:

1. Make sure there is no bubble present in the syringe during injection.

2. The syringe used should be washed for few times before use to ensure there is no contamination.

3. Parallax error should be avoided to ensure the concentration of acetophenone is accurate during preparation.

Drying agent

 

Drying agent is a chemical that usually used in absorbing the water present in the organic solvent. This is because the presence of water may cause the ineffective reaction or any other undesirable reactions.

The efficiency of drying agent is measured by capacity and rate. The maximum number of moles of water that the drying agent can absorb is called capacity. The rate of water absorption is another factor that affects the efficiency of drying agent. Some of the examples of drying agents are shown in below.

 

Magnesium Sulfate:

Advantage: Magnesium sulfate is a rapid and efficient drying agent with high capacity.

Disadvantage: Sensitive to epoxide, need to be filtered out due to its fine powder form

 

Sodium Sulfate:

Advantage: less reactive, present in granule form which is easier to be removed, high capacity  

Disadvantage: lower efficiency and lower completeness than magnesium sulfate

 

Calcium Sulfate:

Advantage: High completeness, high efficiency

Disadvantage: low capacity

 

Calcium Chloride:

Advantage: High completeness, high efficiency

Disadvantage: low capacity

 

Potassium Carbonate:

Advantage: moderate capacity, moderate efficiency

Disadvantage: Not sure

 

Technorati Tags: drying agent,advantage and disadvantage,magnesium sulfate,calcium sulfate,capacity,efficiency

Polymer solubility parameter and solubility of polymer

Questions:

1. Calculate the polymer solubility parameter, δ₂ for PVC, LDPE, PS and PMMA by using the equation below, where the molar attraction constant per unit for the functional groups are referring to the appendix 1.

 

 

 

Type of polymers and their repeating unit	Molecular weight, M (g mol-1)	Sum of molar attraction constant, ∑E (J1/2 cm3/2 mol-1)	Density, ρ (g cm-3)	Solubility parameters, δ2 (J1/2 cm-3/2)
-(CH2CHCl)- Poly(vinyl chloride)	62.50	891.00	1.41	20.10
-(CH2CH2)- Low Density Polyethylene	28.00	560.00	0.85	17.00
-CH2CHΦ)- Polystyrene	104.00	1937.00	1.05	19.56
-[CH2CH(COOCH3)]- Poly(methyl methacrylate)	86.00	1352.00	1.17	18.39

 

2. Explain how solubility is affected by polymer chain structure.

When molecular weight of polymer increases, its solubility will decrease. Crosslinked polymers do not dissolve but they only swell when the solvent diffuse into the polymers. Lightly crosslinked polymers swell extensively in solvent in which unvulcanized material would dissolve. When crosslinking degree increases, the solubility decreases. This is because the strong cross-linked polymers will inhibit interaction polymer chains and solvent molecules.

 

Flickr Tags: polymer solubility parameter,PVC,LDPE,PS and PMMA,solubility is affected by polymer chain structure

Synthesis of poly(methyl methacrylate) or poly(methyl methacrylate)-co-poly(butyl acrylate) & characterization of the polymers by infrared spectroscopy (IR)

Objectives:

1. To synthesize poly(methyl methacrylate) and poly(methyl methacrylate)-co-poly(butyl acrylate)

2. To characterize poly(methyl methacrylate) and poly(methyl methacrylate)-co-poly(butyl acrylate) by using infrared spectroscopy (IR) and differential scanning calorimetry (DSC)

Introduction:

Poly(methyl methacrylate), PMMA, is known as Plexiglas in 20^th century, is an amorphous, transparent and colourless thermoplastic. PMMA is hard and stiff but brittle and notch-sensitive, with a glass transition temperature of 105°C. PMMA is a polymer that made up from its basic unit of methyl methacrylate, MMA. Figure 1 show the monomer MMA and its polymer.

Figure 1 PMMA and its monomer unit

PMMA is a polymer that has characteristics of good abrasion and UV resistance and excellent optical clarity but poor low temperature, fatigue and solvent resistance. Besides, it is flammable but has low smoke emission.

PMMA usually behaves in a brittle manner when loaded, thus restricting its application. The solution to overcome is copolymerizes of MMA with other monomers, such as butyl acrylate (BA). Brandrup J. & Immergut E.H.’s study (as cited in Sirapanichart, S., Monvisade P., Siriphannon P., & Nukeaw J., 2011) found that poly(butyl acrylate), PBA is considered as a colourless transparent rubbery polymer at ambient temperature, thus it is commonly used in copolymer systems to alleviate the brittleness of the final product.

PMMA is produced through free radical polymerization from MMA. In this experiment, PMMA is synthesized via bulk polymerization by using free radical that produced by redox initiator. MMA is supplied with a small amount of inhibitors (an organic acid), which is used to prevent polymerization during shipping and storage. By using excess initiator, MMA still can be polymerized in the presence of inhibitors but low yield will be produced. To maximize the yield of polymer, the inhibitors are usually removed prior to use in order to generate long chain polymer at fast rate. The inhibitor can be removed through the process of distillation, chromatography or base extraction. For the copolymerization between MMA and BA, the synthesis is following the same method as polymerization of pure MMA. The figure 2 below shows the possible polymerization between BA and MMA monomers.

 

Figure 2 Polymerization between BA and MMA monomers.

Apparatus:

Pasteur pipette, large test tube, beaker, heater, Buchner funnel, watch glass, boiling tube

Materials:

Methyl methacylate (MMA), butyl acrylate (BA), N,N-dimethylaniline, benzoyl peroxide, boiling chip, methanol, acetone, alumina, 10% sodium hydroxide solution

Instruments:

Infrared spectrophotometer, differentiate scanning calorimeter

Procedures:

Removal of inhibitor by extraction

1. MMA and BA were purified by extraction with 10% sodium hydroxide solution.

Polymerization of monomers

1. 10ml of MMA was added with 1 drop of N,N-dimethylaniline and 0.1g benzoyl peroxide. The mixture was placed in boiling water bath.

2. At 3 minutes interval, 1 drop of aliquot was transferred into a test tube with methanol. Observation was recorded.

3. After 15 minutes, boiling tube was cooled and polymer was dissolved in 10-15ml of acetone.

4. While stirring vigorously, the polymer solution was poured into a beaker containing 80-100ml methanol.

5. Precipitated polymer was collected by vacuum filtration. The percent conversion was determined.

6. Steps 1-5 were repeated by using 65:35 of MMA: BA.

Characterization of polymers

1. 20% w/v solution of PMMA in acetone was prepared and was casted on a glass plate.

2. Clear film was obtained for IR and TGA analysis.

3. Procedures were repeated by using mixture of MMA and BA.

Results and calculation:

Part 1

Table 1.1: Observation of PMMA in methanol

Observations
3rd minute	Aliquots turns solution to cloudy.
6th minute	White precipitate is formed at the bottom and clear solution.
9th minute	White precipitate is formed at the bottom and clear solution.
12th minute	White precipitate is formed at the bottom and clear solution.
15th minute	White precipitate is formed at the bottom and clear solution.

Table 1.2: Weight of PMMA synthesized

Weight of empty petri dish	52.75g
Weight of (petri dish + poly(methyl methacrylate) PMMA)	55.36g
Weight of poly(methyl methacrylate) PMMA	2.61g

Table 1.3: Significant peaks of PMMA in IR spectrum (Appendix I)

Functional groups	Wavenumber, v (cm-1)
C=O stretch	1727
C-O stretch	1152

Part 2

Table 2.1: Observation of co-poly(MMA/BA) in methanol

Observations
3rd minute	Small amount of white precipitate is formed and clear solution.
6th minute	More white precipitate is formed and clear solution.
9th minute	Larger amount of white precipitate is formed and clear solution.
12th minute	More and more white precipitate is formed and clear solution.
15th minute	Largest amount of white precipitate is formed and clear solution.

 

 

 

Technorati Tags: poly(methyl methacrylate),PMMA,poly(methyl methacrylate)-co-poly(butyl acrylate) characterization of the polymers

Resonance structure of acetylacetonate, magnetic moment of Mn(acac)3

Questions:

1. Draw the structures of acetylacetonate and its resonance structure.

 

 

2. Structure of Mn(acac)₃

 

 

3. Find out the magnetic moment of Mn(acac)_3.

Charge of Mn³⁺ = +3

Total number of electron in Mn atom = 25

Number of electron in Mn³⁺ ion = 22

Eletron configuration of Mn³⁺ : [Ar] 3d⁴

μ_s = g √s(s+1)

= 2 √ 2(2+1)

= 4.90μB

 

Technorati Tags: structure of acetylacetonate,Mn(acac)3

Preparation of cis-bis(glycinato)copper(II) monohydrate & tran-bis(glycinato)copper(II) monohydrate

Objectives:

1. To prepare both cis- and trans­ copper glycine complexes

2. To verify the complex is kinetic product or thermodynamic product

3. To characterize both cis- and trans­ copper glycine complexes

Introduction:

Glycine is one of the biologically important compounds in the group of amino acids. Among the twenty one natural amino acids, glycine is the simplest amino aicd. Amino acid has both the functional group of amine (-NH₂) and carboxylic acid (-COOH). They are the basic units of the proteins in which the building block of every single living cell. Proteins are polypeptides or polyamide that formed by joining the –NH₂ group of one amino acid to the –COOH group of another one and therefore a long and complicated peptide chain is formed.

 

Glycine is the simplest model for peptide coordination and its complexes with various metal ions have been thoroughly studied. Elzbieta (2008) claimed that glycine can even forms more essentially stable complex with copper (II) compared to other amino acids. The structure and stability of the complexes are determined by nature of metal, the nature of the ligands and environment. The environment is controlled by the factors such as temperature, the type of solvent, the interaction enthalpies, entropies, and Gibbs energies.

 

The binding modes of glycine ligand can be varied since it has at least two donor atoms. The glycinate ion is able to adopt a η³-coordinated mode via its amino, -NH₂ and carboxylate, -COOH groups to chelate one copper ion and bridge to another copper ion. The variation of glycinate binding modes is shown in the picture below:

Picture 2. Five coordination modes of amino acid. a) η1-coordination mode; b)η2-coordination mode; c) η3-coordination mode with strong Cu-O bond; d)η3-coordination mode with weak Cu-O bond beyond 2.5 Å; e)η4-coordination mode (M is Na+ ion or lanthanide ion)

 

In this experiment, a pair of geometric isomers of copper(II) glycine complex are prepared. Deprotonated glycine, or known as glycinate ion, NH₂CH₂COO^- is capable to form two coordination bonds to copper metal through the lone pair electrons of nitrogen and oxygen atoms. Hence, it functions as a chelating ligand or more specifically it is known as bidentate ligand and favors the formation of bis(glycinato)copper(II) complex. The reaction between copper(II) acetate monohydrate and glycine can produces mixture of both isomers in an equilibrium mixture. However, the cis isomer precipitates much more quickly then trans isomer and hence leading to a shift in equilibrium away from trans with producing only cis isomer. Cis isomer is the kinectically favoured product whereas trans isomer is thermodynamically favoured. In order to produce trans isomer, the cis isomer can be converted into another isomer by supplying heat energy at 180 °C for time of 15 minutes.

Picture 3. a) cis-Cu(gly)2 b) trans-Cu(gly)2

Materials:

Copper(II) acetate monohydrate, glycine, ethanol 95%

Apparatus:

Magnetic stirring hot plate, magnetic stirring bar, Erlenmeyer flask, Hirsch funnel, test tube

Procedure:

Part A: Preparation of cis_-bis(glycinato)copper(II) monohydrate

Part B: Preparation of tran-bis(glycinato)copper(II)

Results and calculations:

Table 1 Amount of reactants used and amount of products obtained

Reactants
Weight of copper(II) acetate monohydrate	0.3007g
Weight of glycine	0.2328g
Products
Weight of filter paper I	0.3233g
Weight of filter paper I + cis-product	0.6061g
Weight of cis-product	0.2828g
Weight of filter paper II	0.3001g
Weight of filter paper II + trans-product	0.3684g
Weight of trans-product	0.0683g

Chemical reaction:

(CH₃COO)₂Cu.H₂O + 2 H₂NCH₂COOH àcis-(H₂NCH₂COO)₂Cu.H₂O + 2 CH₃COOH

Determination of limiting agent

Molecular weight of (CH₃COO)₂Cu.H₂O = 199.55 g mol^-1

Number of mole of (CH₃COO)₂Cu.H₂O = 0.3007g / 199.55 g mol^-1

= 0.0015 mol

Molecular weight of H₂NCH₂COOH = 75.00 g mol^-1

Number of mole of H₂NCH₂COOH = 0.2328g / 75.00 g mol^-1

= 0.0031 mol

Thus, copper(II) acetate monohydrate is the limiting agent in this reaction.

Percentage yield calculation

Molecular weight of (H₂NCH₂COO)₂Cu.H₂O = 229.55 g mol^-1

Theoretical weight of cis-(H₂NCH₂COO)₂Cu.H₂O = 0.0015 mol x 229.55 g mol^-1

= 0.3443 g

Percentage yield of cis-(H₂NCH₂COO)₂Cu.H₂O = 0.2828g / 0.3443g x 100%

= 82.14%

Theoretical weight of trans-(H₂NCH₂COO)₂Cu. = 70 mg

Percentage yield of tran-(H₂NCH₂COO)₂Cu = 0.0683g / 0.070 g x 100%

= 97.57%

Discussion:

From this experiment, the weights of both isomer cis-Cu(gly)₂.H₂O and trans-Cu(gly)₂ obtained are 0.3443g and 0.0683g respectively. Each isomer contributed the percentage yield of 82.14% for cis-Cu(gly)₂.H₂O and 97.57% for trans-Cu(gly)₂ respectively.

 

The dissociation of glycine molecule produces a glycinate anion, NH₂CH₂COO^- in which it replaces the position of acetate ion, CH₃COO^- in the copper complex. The dissociated proton from glycintate ion is accepted by acetate ion and hence acetic acid is produced in the reaction between copper(II) acetate monohydrate and glycine.

(CH₃COO)₂Cu.H₂O + 2 H₂NCH₂COOH à(H₂NCH₂COO)₂Cu.H₂O + 2 CH₃COOH

The reaction was takes place in a hot 95% ethanol. Ethanol did not participate in the reaction but it acts as a medium to allow the copper(II) complex to form at 70°C. When cooled down, the copper(II) complex crystallize out from the ethanol.

The solid cis-monohydrate was heated at 200 °C by using an aluminium block in order to convert cis-monohydrate to trans­-complex. The temperature of aluminium block is approximately measured by using hexane with a thermometer. The dehydration of cis-bis(glycinato) copper(II) monohydrate, cis-Cu(gly)₂.H₂O at sufficiently high temperature (approximately at 200 °C)leads to the formation of mainly anhydrous trans-complex, which is readily to be re-hydrated to give trans-bis(glycinato) copper(II), trans-Cu(gly)₂.H₂O if present in solution.

Precaution steps:

1. Handle copper(II) acetate monohydrate carefully. It is harmful if swallowed, inhaled or absorbed through the skin.

2. Keep a distance from the hot plate when heating aluminium block.

 

Technorati Tags: cis- and trans­ copper glycine complexes,cis-bis(glycinato)copper(II) monohydrate & tran-bis(glycinato)copper(II) monohydrate

Reduction of 1-phenyl-1,2-propanedione to 1-phenyl-1,2-propanediol

Asymmetric Synthesis with Baker’s Yeast:

Objectives:

1. To reduce 1-phenyl-1,2-propanedione to 1-phenyl-1,2-propanediol

2. To monitor the course of reaction by using TLC

3. To characterize the produce by FT-IR spectroscopy and gas chromatography-mass spectroscopy (GC-MS)

Introduction:

Lithium aluminium hydride and sodium borohydride are good reducing agent, in which it can reduce a ketone to an alcohol. However, they are not able to generate a chiral alcohol because they can nucleophilic attack both sides of carbonyl group, hence producing racemic mixture. In order to obtain a chiral alcohol, baker’s yeast is used.

Asymmetric reduction of 1-phenyl-1,2-propanedione by using baker’s yeast in this experiment in order to produce (-)-(1R,2S)-1-phenyl-1,2-propanediol with the enantiomeric excess of 98% or more. The completeness of reaction is determined by using thin layer chromatography (TLC). Pure 1-phenyl-1,2-propanediol is characterized by using infrared (IR) spectroscopy and mass gas chromatography-mass spectroscopy (GC-MS).

Apparatus:

Erlenmeyer flask, hotplate-stirrer, magnetic stirring bar, TLC tank, micropipette, separatory funnel, UV lamp, rotary evaporator

Materials:

1-phenyl-1,2-propanedione, freeze-dried Baker’s yeast, TLC plate, tert­-butyl methyl ether (BME), magnesium sulphate anhydrous, cylohexane

Instruments:

IR spectroscopy, gas chromatography-mass spectrometer

Procedures:

Result and calculations:
Observations on TLC plate:

Descriptions: At 0th minute, two spots present on the TLC plate. Reactant and product present in the reaction mixture. At 20th minute, two spots present on the TLC plate. Reactant and product present in the reaction mixture. At 40th minute, only one spot presents on the TLC plate. Reactants have been used up shows complete reaction. At 60th minute, only one spot present on the TLC plate. Reactants have been used up shows complete reaction.

Table 1: R_f value of each spots on TLC plate

Time (minutes)	0	20	40	60
Distance travelled by each aliquots (cm)	1st spot	2.90	2.90	2.90	2.90
2nd spot	5.20	5.20	-	-
Retardation factor, Rf	1st spot	0.41	0.41	0.41	0.41
2nd spot	0.74	0.74	-	-

*TLC is performed by using a mixture of cyclohexane:BME (3:2)

*solvent front is 7cm.

Table 2: Weight of 1-phenyl-1,2-propanediol

Weight of round bottom flask	97.6703g
Weight of (round bottom flask + 1-phenyl-1,2-propanediol)	97.9018g
Weight of 1-phenyl-1,2-propanediol	0.2315g

Table 3: Significant peaks of starting material and product in IR spectrum

Functional group	Wavenumber of Compound, v (cm-1)
1-phenyl-1,2-propanedione	1-phenyl-1,2-propanediol
C=O stretch	1715, 1676	absent
O-H stretch	absent	3369

Molecular weight of 1-phenyl-1,2,-propanedione = 148 g /mol

Molecular weight of 1-phenyl-1,2-propanediol = 152 g / mol

Density of 1-phenyl-1,2,-propanedione = 1.101 g ml^-1

Mass of 1-phenyl-1,2,-propanedione = density x volume

= 1.101 g ml^-1 x 0.23 ml

= 0.2532g

1 mole of 1-phenyl-1,2,-propanedione produces 1 mole of 1-phenyl-1,2-propanediol

Mole number of 1-phenyl-1,2,-propanedione = 0.2532g / 148 g mol^-1

= 0.0017 mol

Theoretical mass of 1-phenyl-1,2-propanediol = 0.0017 mol x 152 g mol^-1

= 0.2584g

Percentage yield = 0.2315g / 0.2584g x 100%

= 89.59%

Discussion:

In this experiment, 1-phenyl-1,2-propanedione was reduced to 1-phenyl-1,2-propanediol by using baker’s yeast. The mass of 1-phenyl-1,2-propanediol obtained experimentally is 0.2315g and its percentage yield is 89.59%.

Thin layer chromatography was used to monitor the reduction of 1-phenyl-1,2-propanedione in this experiment. Based on the observation of TLC plate, the reaction was completed at 40^th minutes since the TLC plate only shows one spot is present. After the reaction completed, the product was extracted with BME and was dried with drying agent to remove water in the organic layer.

The following mechanism shows that how ketone was reduced into alcohol by yeast.

Firstly, the hydride from baker’s yeast nucleophilic attack to carbonyl carbon (labeled as carbon 2) and caused the reduction of the carbonyl group. Oxygen of the particular carbonyl group was bearing with partial negative charge in which it can abstract a proton from water molecules to form hydroxyl group.

Then, another carbonyl group (labeled as carbon 1) was attacked by hydride from back side and hence produced an alcohol that has two carbons with different chirality. The alcohol obtained is named (1R,2S)- 1-phenyl-1,2-propanediol. However, (1S,2R)- 1-phenyl-1,2-propanediol might present with a very low yield.

From the IR spectrum, 1-phenyl-1,2-propanedione shows the presence of C=O stretch at 1715cm^-1 and 1676cm^-1. Besides, this ketone compound did not show any O-H stretch signal in the IR spectrum. From the alcohol spectrum, there shows a broad O-H stretch signal at 3369cm^-1 and it did not have C=O stretch signal. According to IR spectrum, the ketone compound has been successfully reduced to form an alcohol compound as obtained in the experiment because IR spectrum indicated the presence of O-H group.

Precaution steps:

1. Do not use separatory funnel point to anybody when releasing the vapour.

2. Do not shake the separatory funnel vigorously to avoid emulsion formation.

Technorati Tags: Asymmetric Synthesis with Baker’s Yeast,Reduction of 1-phenyl-1,2-propanedione,IR of 1-phenyl-1