Produce cyclohexene through the acid catalyzed elimination of water from cyclohexanol

  

Objectives:

1. To produce cyclohexene through the acid catalyzed elimination of water from cyclohexanol

2. To understand mechanism involved in the reaction

3. To learn the technique of distillation

Introduction:

Dehydration is defined as a process of removing water from a substance. The loss of water from a molecule is called dehydration which is exactly opposite with the process of hydrolysis. Dehydration is an elimination reaction of an alcohol involves the loss of an OH from one carbon and an H from an adjacent carbon. Overall, this amounts to the elimination of a molecule of water, resulting in a pi-bond formation of an alkene or alkyne. In most of the dehydration of alcohol, heat and catalyze are needed in the reaction. Sulphuric acid (H₂SO₄) and phosphoric acid (H₃PO₄) are the most commonly used acid catalysts.

The dehydration process can be carried out by in two ways. The first way is heating a mixture of alcohol and dehydrating agent in a distilling flask and collecting the olefin (also known as alkene) from the mixture. The second way is passing the alcohol vapour through a heated tube packed with the dehydrating agent at 350°C. The collecting the olefin as it emerges from the tube. The chemical equation for dehydration of alcohol to form alkene and water is shown as below diagram:

For the dehydration of alcohol, the alkene is formed in the reaction. At the same time, the side products are produced from the reaction such as dicyclohexyl ether, polymer, mono and dicyclohexyl sulphate abd degradation products (carbon and carbon dioxide). In many cases, the phosphoric acid is used in the dehydration of alcohol instead of using sulphuric acid due to two reasons. The one of the reason is the lost of organic compound can be minimize through oxidation of phosphoric acid. In addition, the product is being produced without contamination with volatile decomposition products such as sulphurous acid.

Apparatus: Round-bottomed flask(50ml), take off distillation adapter, condenser, thermometer, electric flask heater

Materials: boiling chips, cyclohexanol, cyclohexene, 85% conc. Phosphoric acid, anhydrous magnesium sulpahte

Procedure:

1. Cyclohexanol and conc.(85%) phosphoric acid are added in a round bottomed flask and is mixed together by swirling.

2. Several boiling chips are added, the flask is clamped to a ring stand at electric flask heater height attached with a take off distillation adapter, a thermometer, a condenser and a small receiving flask as shown in the diagram below.

3. The mixture is heated and distillate boiling in the range 85°C-90°Cis obtained.

4. When the distillate is exhausted, the heat is increased gradually. Using the same receiver, the distillate boiling in the range of 90°C - 100°C is collected.

5. The two layers in the receiving flask are tested by adding the distilled water. With the aid of a 9-disposable pipette, the aqueous layer is drawn off and is being discarded.

6. The organic layer is dried up with anhydrous magnesium sulphate.

7. The drying agent is removed by filtering the mixture through a cotton wool plug wedged into the constricted part of a small funnel.

8. The filtrate is collected round bottom flask or small distilling flask. Boiling chip is added to the dried product and distil it through a take off distillation adapter packed with a few small wads of coarse steel wool.

9. The product boiling is collected in the range 3 below and 2 above the boiling point of cyclohexene (83°C) in a tarred bottle.

10. The yield in grams is calculated and the product is submitted to instructor.

Result and calculation:

Weight of cyclohexanol = 10.0060g

Weight of dry conical flask = 51.2460g

Weight of dry conical flask + weight of cyclohexene = 56.2281g

Experimental weight of cyclohexene = 4.9821g

Number of mole of C₆H₁₁OH =

= 0.09996 mole

1 mole of C₆H₁₁OH produces 1 mole of C₆H₁₂

0.09996 mole of C₆H₁₁OH produces 0.09996 mole of C₆H₁₂

Theoretical weight of C₆H₁₂ = 0.09996 mole X 84.096 g/mol

= 8.4066g

Yield percentage =

 

= 59.26%

Discussion:

In this experiment, the cyclohexanol solution is being used in the dehydration process. The cyclohexanol is a six carbon aromatic hydrocarbon which one of the hydrogen atoms, H is substituted by one hydroxyl group, OH^-. Due to the low melting point, the cyclohexanol appear in liquid form at room temperature. The dehydration process of alcohol will convert cyclohexanol which the hydroxyl group, OH^- will be removed to become cyclohexene. Cyclohexene is a six carbon aromatic hydrocarbon with a single double bond in the molecule.

The solution is added with concentrated phosphoric acid in a round bottomed flask and is mixed together by swirling. The phosphoric acid is added as catalyze as such increase the rate of reaction in dehydration without affects the particular chemical reaction. The boiling chips are added into the solution in order to prevent over boiling of the solution. The boiling chips are small, insoluble, and porous stones made of calcium carbonate or silicon carbide. There are a lot of pores inside the boiling chips which provide cavities both to trap air and to provide spaces to allow bubbles of solvent can be form. When boiling chips are heated, it will release tiny bubbles which can prevent boiling over. Boiling over of solvent will cause lost of solution which may lead to inaccurate result to be obtained.

The heating of mixture is carried out in a fractional distillation apparatus. As the mixture is heated, the alkene and water are produced as the products in the reaction. Besides, the side product and impurities of the reaction will be produced at the same time. The temperature of mixture when heating is fluctuated. During the temperature 80°C, the temperature of mixture drops suddenly by 2°C and the temperature remained at 78°C constantly for few seconds. This is because some impurities or side products are being produced in the mixture which may have the boiling point of 78°C. The temperature of mixture drops suddenly because the heat being is absorbed which used to break down the bonding of the side products. When the boiling point is reached, then temperature of mixture remains constant as the state of the side products are converted from liquid form to gaseous form. The temperature of mixture is increases until 107°C after all the side products are being converted.

The temperature of mixture is reached to maximum at 107°C. This temperature is known as the activation temperature which the cyclohexanol start to be dehydrated. The temperature of mixture drops to 83°C and remains constant. This phenomenon takes place because the cyclohexene with lowest boiling point will tends to be distilled first before the higher one. The temperature remains unchanged because the heat is being absorbed to break down the bond between cyclohexene molecules. In all the distillation process, some of the product will be lost since it is hold up in the apparatus which reduce the product yield. In order to maximize the yield, the mixture is continued to be heated at higher temperature range which more than the boiling point of cyclohexene. When the mixture is heated at 90°C-100°C, the water in the mixture will push over the products into the receiving flask along the condenser. The products produced are collected in the same receiving flask.

Then, the receiving flask containing cyclohexene, water and small amount of the impurities. Two layers liquid are present in the receiving flask, one drop of distilled water is added into flask in order to determine the location of aqueous layer. Since the water droplet mix with the lower layer, so the upper layer is determined as cloudy solution while the lower layer is aqueous layer. The upper cloudy layer is cyclohexene with some impurities and water inside. The lower aqueous layer is removed and discarded. But, that is not easy to remove all the water in the receiving flask. So, anhydrous magnesium sulphate is being added. The purpose of adding of anhydrous magnesium sulphate is used to remove residual water in the organic solvent. The magnesium sulphate in the granular form will be preferable. It is known as drying agent in the organic solvent which are not dissolves in the solvent but drying the solvent. The magnesium sulpahte clump together with the water droplets as it solidified them. In another words, it is reacts with water to form hydrates which is their preferred form when water is available. An excess drying agent should be used to ensure that all the water in solvent is removed. If the water remains in the materials collected, it could interfere with the analysis.

Water has been successfully removed from the organic compound mixture, so it is very important to not reintroduce water into the mixture. The final distillation of unpurified cyclohexene must be done very carefully in order to obtain purified products. The temperature of mixture is heated until approximate 85.5°C since this temperature is the boiling point of cyclohexene and hence the pure cyclohexene could be obtained rapidly. The weight of the cyclohenexe is 4.23g.

Error of source includes the condenser and Liebig tubes are not rinsed with a little of distilled water, a little of ethanol and acetone to speed up drying process. So that, the water in the desired products would not presents. This is because some of the water droplets is hold up and stick on the wall of condenser and the second distillation will produce the contaminated cyclohexene.

 

Flickr Tags: dehydration of an alcohol,cyclohexanol and cyclohexene,acid catalyzed elimination of alcohol

Dissolved oxygen (DO)

What is dissolved oxygen (DO)? 

Dissolved oxygen refers to the amount of oxygen level that present in the water or liquid sample. Dissolved oxygen level is very important to the aquatic life in a healthy ecosystem. Too much of oxygen may create algae bloom provided the high nutrient load present in the water, however too low of oxygen amount that present in water will make the fishes suffocating and eventually die. 

How do we measure DO in the water?

METHOD 1: Winkler titration method - conventional method

We can use Winkler titration to measure DO amount in the water sample that has been took and prepared manually from the site into water bottle. The Winkler titration method measures the DO amount in the water sample precisely, this is a method developed by Hungarian analytical chemist named Lajos Winkler in 1888. This method adding chemicals to the water sample to form an acidic solution by creating reaction with the oxygen that present in the water. Then we will add in the neutralizing agent to perform neutralization with titration and the amount of neutralizing agent required indicate the amount of the oxygen level in the water sample. Below is the diagram to show the Winkler titration in step by step. 

Although Winkler titration can deliver highly accurate result, but this method is laborious, time-consuming and highly susceptible to the interference. 

METHOD 2: Using in-situ DO meter

Alternatively, we can use DO meter that can provide instant result instead. A lot of researchers they prefer to use in-situ DO meter because the amount of oxygen in water sample may fluctuate across the time. The amount of oxygen may varies at different water level. The deeper the water level, the lesser the oxygen amount that present. The creation of in-situ DO meter ease the life of a chemist as winkler titration is a tedious procedure to perform DO measurement of water sample. Nowadays, the in-situ DO meter could deliver and perform almost similar result of DO as compared to Winkler titration and hence in-situ DO meter is the first choice of researchers. 

In in-situ DO meter, we do found two major types of technology that present in the market. The first type is called polarographic (aka Clark electrode) method. This is a method invented by Dr Leland Clark in 1956. In 1965, the first biological oxygen monitor is invented and this is a breakthrough technology in medical field. This technology enabled physicians to carry out open-heart surgery for the first time as the real blood oxygen measurements could be recorded during the operation! 

After years of study, another advanced technology called optical or luminescent technology in DO meter has took over the place of polarographic technology. Some researches has chose the DO meter with optical technology due to the easier maintenance and faster warm up time. You may see the differences in between polarographic electrode and optical technology as below. 

Comparison	DO meter with electrode	DO meter with optical
Technology	Polarization technology (old method)	Optical technology (advanced method)
Calibration frequency	Daily	Weekly
Warm up time	10 – 15mins	NO warm up time
Flow dependent	Flow dependent; need to stir manually while using the meter to get actual reading	Flow independent; no need to stir manually while using
Consumables	Membrane cap, filling solution	Membrane cap only
Maintenance	-change the membrance cap -refill the solution in cap -check the solution in cap from time to time -polish the electrode from time to time	- change the membrane cap once the coating of cap wear off; usually can last long up to 12 months or more, depends on usage
Measurement rate	Faster than optical method Estimated 8-25 seconds per sample, but subject to the sample condition	Slower than electrode method Estimated 40 seconds per sample, subject to the sample condition

What is pH?

pH value is a figure to indicate acid, neutral or alkaline. pH value being measured from 0-14, in which it does not have any unit for it. The pH is also being defined as the concentration of hydrogen ion, H+ ion in the aqueous solution. The higher the concentration of H+ in the aqueous solution, the more acidic the aqueous sample is. The pH value will tend to be lower than pH 7 and getting lower and lower and close to pH 0.

Normally, pH is being measured/taken by using the following method:
1. litmus paper
2. Color comparator
3. pH meter

The accuracy of pH reading

pH meter > Color comparator > Litmus paper

What is Water Quality Index?

Water Quality Index (WQI)

Water quality index (WQI) indicates the quality of water based on classification. The WQI will be classified based on the 6 parameters as below:

1. pH

2. Dissolved oxygen (DO)

3. Suspended solid

4. Ammonia nitrogen

5. Chemical oxygen demand (COD)

6. Biochemical oxygen demand (BOD)

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

 

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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