CHAPTER Chemical synthesis Proofs - Pearson

In this course you have learnt about a range of chemicals and their structures and properties. The chemicals you have studied include metals, pharmaceuticals, polymers, soaps, acids and fuels. These are important raw materials or products that our society relies upon. Most of these chemicals do not occur naturally; they have to be manufactured. This is the job of the chemical industry.

In this chapter you will see an overview of the Australian chemical industry and investigate how the theory you have learnt throughout your chemistry course is vital to the safe manufacture of chemicals in a competitive global environment.

Content

INQUIRY QUESTION

What are the implications for society of chemical synthesis and design?By the end of this chapter, you will be able to:

• evaluate the factors that need to be considered when designing a chemical synthesis process, including but not limited to:

- availability of reagents

- reaction conditions (ACSCH133)

- yield and purity (ACSCH134)

- industrial uses (e.g. pharmaceutical, cosmetics, cleaning products, fuels) (ACSCH131)

- environmental, social and economic issues

Chemistry Stage 6 Syllabus © NSW Education Standards Authority for and on behalf of the Crown in right of the State of NSW, 2017.

Chemical synthesis and design

CHAPTER

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MODULE 8 | APPLYING CHEMICAL IDEAS518

17.1 Chemical synthesis and design

CHEMISTRY INQUIRY CCT

Is baking just a chemical reaction?COLLECT THIS …

• 125 g butter

• 4 eggs

• 2 cups milk

• 1 cup sugar

• 1 cup desiccated coconut

• ½ cup plain flour

• 2 teaspoons vanilla essence

• baking dish

• balance

• blender, electric beater or wooden spoon

• cream (optional)

DO THIS …

1 Weigh the baking dish.

2 Add all the ingredients, mixing well.

3 Reweigh the baking dish containing the ingredients.

4 Bake in a moderate oven (180°C) for 1 hour or until brown on top.

5 Reweigh once cooled.

6 Enjoy with cream!

7 Weigh the empty dish.

RECORD THIS …

Record all mass measurements.

Describe any waste you have created.

REFLECT ON THIS …

1 If the initial and final masses are different, why could this be?

2 What waste have you created, and how should it be disposed of?

3 What would have happened if you had cooked the mixture at 260°C?

4 Where did your raw materials come from?

SNAPSHOT OF THE AUSTRALIAN CHEMICAL INDUSTRYThe chemical industry is one of the most diverse and broad in its reach across Australian society, environment and industry. The sector can be broadly divided into three categories based on what is produced:• basic chemicals: industrial gases, fertilisers, synthetic resins, organic chemicals,

inorganic chemicals• speciality chemicals: explosives, paints, polymers, foam products, adhesives,

inks, glues, surface cleaners• consumer chemicals: cosmetics and toiletries, soaps and detergents, pesticides,

pharmaceuticals, food.Figure 17.1.1 shows a crop of poppies being grown in Tasmania. The pain-

relieving drug morphine can be extracted from poppy seed oil. The Keep Out signs reflect the fact that opium can also be converted to heroin.

Chemistry Australia, which represents the Australian chemistry industry, provides the following snapshot of the importance to Australia of our chemical industry:• It employs over 60 000 skilled workers and is the leading employer of Australia’s

science, technology, engineering and mathematics capability.• It includes over 5500 small to large businesses.• It is our second largest manufacturing sector.• It delivers over $11.6 billion dollars to Australia’s GDP.

Australian chemical industries can be divided into three categories: basic chemicals, specialty chemicals and consumer chemicals.

FIGURE 17.1.1 An opium poppy crop growing in Tasmania. The poppies are used for the synthesis of the pain relieving drug morphine.

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519CHAPTER 17 | CHEMICAL SYNTHESIS AND DESIGN

About 80% of the industry’s output is inputs for other sectors. An example is polymers produced by our chemical industry. Many of these are then used to manufacture components for the construction industry. Every job in the chemical sector creates approximately five more jobs in sectors farther along the supply chain.

Figure 17.1.2 provides a visual representation of the flow-on effect of the chemical industry.

automotive

mining andresources

Australianchemistryindustry

paints andsurfacecoatings

adhesives,glues andsealants

cosmetics,soaps andcleaners

building,construction

andinfrastructure

pipes andsheetingaerospace

defense

food

public healthand watertreatment

furniture andtextiles

medicalware

pulp andpaper

agriculture

packaging educationand IT

pharmaceuticals

consumerappliances

environmentalconservation

FIGURE 17.1.2 The flow-on effect of the chemical industry on other Australian industries.

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Table 17.1.1 is a list of some of Australia’s large chemical companies. Many of these companies will be familiar to you. They are listed in alphabetical order because it would be difficult to rank them in order of profit or production levels, which can vary significantly each year. It is also difficult to discern what proportion of production occurs in Australia, because many of these companies are global organisations.

TABLE 17.1.1 Examples of companies that operate in Australia involved in the chemical industry

Company Examples of products

Alcoa aluminium, alumina

BHP smelted metals

Bluescope Steel steel products

Boral building materials, cement, plaster

Caltex fuels, lubricants

CSL biopharmaceuticals

CSR building materials

Dulux group paints, chemicals

Lion-Nathan beverages, dairy products, juices

NuFarm pesticides, herbicides, fungicides

Orica chemicals, explosives, PVC

Rio Tinto aluminium, smelted metals

Rosella sauces, processed foods

SPC Ardmona (Coca-Cola Amatil) processed food

Tasmanian Alkaloids pharmaceuticals

Unilever soaps and detergents, personal care, food, drinks

The top ten chemicals produced in Australia from petrochemicals are shown in Figure 17.1.3. Australia also produces large volumes of metals such as steel and aluminium, and inorganic chemicals such as sulfuric acid and fertilisers. Production levels can vary significantly with global market prices.

200 000

100 000

0

300 000

500 000

600 000

700 000

800 000

400 000

ammonialD

PE

vinyl

chlorid

eHDPE

polystyr

ene

methanol

ethanol

Annual production of chemicals frompetrochemicals in Australia

Tonn

es p

er a

nnum

ethene

propene

polypro

pene

FIGURE 17.1.3 The top 10 chemicals in terms of volume (tonnes per annum) produced in Australia from petrochemicals

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Case study: QenosThere are many considerations in building a chemical plant. The major considerations are:• location• source of raw materials• product uses• reaction conditions• energy supply• water supply• transport infrastructure• commodity price and market• safety• emissions and disposal of wastes• labour force• ethical considerations.

The infrastructure required can cost over a billion dollars, and the markets are very competitive. Globalisation of industries over recent decades has led to the closure of many plants that were once viable. For example, Australia once had more than five large tyre manufacturing factories and several car manufacturing plants; now there are none. The following case study highlights some of the factors to be considered in planning a viable chemical plant.

Qenos produces ethene, polyethene and other polymers at its production facilities at Botany in NSW and Altona in Victoria (Figure 17.1.4). The company employs over 700 people in these plants. Qenos shares the majority of the Botany Industrial Park (BIP) with two other large companies, Orica Australia and Huntsman Corporation Australia. It is common for chemical manufacturers to form a complex. This allows for sharing of expertise, transport infrastructure, disposal facilities and raw materials. It is also considered more desirable to locate several hazardous industries together rather than to place them at different locations in populated areas.

Qenos uses ethane as a raw material. The ethane is tapped from the Cooper Basin in outback South Australia and piped nearly 1400 km to Botany. The ethane is passed through what is known as a cracker, where it is converted to ethene. This is a one-step process but is not simple. To obtain a viable yield, the following conditions are essential:• temperatures up to 900°C• a very short reaction time• low hydrocarbon concentrations• rapid cooling of products to prevent their decomposition.

The conditions chosen are not random; they are the result of an understanding of principles of reaction rates and equilibrium systems.

The ethene is purified from other products using fractional distillation. It is then polymerised to various forms of polyethene (Figure 17.1.5).

C

H

C

H nH

CH H

H

H

C

H

C

H

C

H

H

H

H H

ethane cracker

LDPE

HDPE

otherpolymers

ethene

FIGURE 17.1.5 Qenos converts ethane to ethene, then polymerises ethene to polyethene.

FIGURE 17.1.4 A section of the large Qenos plant required to produce ethene from ethane

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Many items that are used in the home, such as clingwrap, drink bottles, micro-irrigation pipes, moulded plastics and telecommunication conduits are made from polymers produced by Qenos. Ethene is also sold to other industries that use it to make other products.

Ethene is a volatile gas stored under high pressure. Qenos has to meet high safety standards to conduct an industry such as this in the vicinity of a major city. Waste needs to be minimised and emissions must be controlled. Many regulations are also in place to ensure a safe environment for the workers on this site.

CHEMICAL SYNTHESIS FACTORS

Location and availability of reagentsEthane gas is easily transported through pipes. To produce polyethene in NSW, a pipe had to be built from the natural gas fields in South Australia. Qenos was then free to choose a location like Botany because of its access to a port, energy and water supply. For other industries the location of the raw materials determines the location of the plant. Figure 17.1.6 shows equipment used by Cassegrain Kalara Tea Tree Oil to extract tea-tree oil from native plants. This plant is located on the northern coast of NSW as the climate there suits the growing of tea-tree plantations. It would not be viable to transport trees with such a low oil content to a processing plant in a distant location. It is more practical to extract the oil close to where the trees grow and then transport the extracted oil.

Other examples where the raw material dictates the plant location are:• Mining at Broken Hill. The concentrations of metals such as lead and zinc are as

low as 2–3%. It is not viable to transport the ore to another region if 97–98% of the transported material will end up as waste.

• Dairy and cheese industry factories. Bega and Tilba (Figure 17.1.7) are in the heart of a fertile dairy farming district in south-eastern NSW. It is practical to process the milk close to the source.

• Biofuel plants. These plants use waste agricultural products from sugar and wheat processing plants to produce biodiesel or bioethanol. Plants such as the Manildra facility near Nowra shown in Figure 17.1.8 are located in the cropping districts.

• Coal-fired power stations. These are located near the coal deposits to eliminate transport costs.The location of raw materials is not the only determinant of plant location. Some

other factors that might influence the choice of location are:• Specialised technology or expertise. The University of Sydney lists companies

such as Rio Tinto, Qantas, Elastagen and Sirtex Medical as research partners. It is convenient for the University and for industry to combine on high-tech projects. One of the common areas of combined research is in medical and pharmaceutical research (Figure 17.1.9).

• Port facilities. The steel industry has used Newcastle and Port Kembla for chemical plants as they can ship in high volumes of raw materials and ship out high volumes of exports.

• Remoteness. Lead smelters produce significant emissions, including toxic gases such as SO2. Tailings from the smelter can also lead to high lead content in local soils. It can be an advantage for plants such as this to be in remote areas where fewer people are impacted.

• Water supply. Facilities such as coal-fired power stations need to be close to an adequate water supply (Figure 17.1.10).

• Where the product is sold. Many of Australia’s petrol refineries are located near capital cities because it means overall shorter distances for tranporting the fuel.

FIGURE 17.1.8 A tanker loads bioethanol at Manildra. The plant is located near the wheat processing facility.

FIGURE 17.1.6 Extraction of tea-tree oil by Cassegrain Kalara Tea-tree Oil on the NSW northern coast.

FIGURE 17.1.7 The dairy industry usually processes milk near the fertile areas of each state.

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FIGURE 17.1.9 Pharmaceutical manufacturing is a high-tech industry in which research in often shared with tertiary institutions.

REACTION CONDITIONSThe chemical industry is highly competitive, so chemical companies do not leave the efficiency of their manufacturing plants to chance. They thoroughly research the optimum conditions for reactions that will lead to the highest conversion rates with the lowest production costs.

Earlier in this chapter you learnt that Qenos converts ethane into ethene. This is a reversible endothermic reaction:

C2H6(g) C2H4(g) + H2(g)This process does not work at normal temperatures and pressures because the

system is at or close to equilibrium. Applying equilibrium principles suggests that the yield will be improved under the following conditions:• High temperatures (around 900°C) are used. For an endothermic reaction, the

value of the equilibrium constant Keq increases with temperature.• Low pressures are used. The ratio of reactant particles to product particles is

1 : 2, so low pressure favours the forward reaction.• A catalyst is used. Although the catalyst does not change the yield it does increase

the reaction rate.• The temperature of the products is cooled rapidly. This prevents further

decomposition of the ethene to ethyne or carbon (Figure 17.1.11).

C

H

H

CH HHH

H

H

C

H

C

H

H

H

ethane

increase temperature,Keq increases, forwardreaction favoured

ethene

+

+⇌

⇌

low pressure, forwardreaction favours moreparticles

products cooledrapidly to preventfurther reactions

catalyst used, rateof reaction faster

H2

C

H

H

CH HHH

H

H

C

H

C

H

H

H

ethane

increase temperature,Keq increases, forwardreaction favoured

ethene

+

+⇌

⇌

low pressure, forwardreaction favours moreparticles

products cooledrapidly to preventfurther reactions

catalyst used, rateof reaction faster

H2

FIGURE 17.1.11 Controlling the conditions in a manufacturing process can have a marked impact on the success of the process.

FIGURE 17.1.10 Coal-fired power stations need to be located close to a significant water supply.

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Similar research is conducted into the optimal production conditions for other chemicals, including foods. For example, cocoa beans are roasted at 130°C for several hours to successfully extract, but not decompose, the cocoa. Chocolate produced from the cocoa has a narrow optimum temperature range; at around 50°C it will flow but not coagulate.

The food chemists in the dairy industry are responsible for the careful control of many processes, ranging from the action of rennin on milk to form cheese to the action of bacteria to form yoghurt. All of these processes need to run at specific temperatures and pH values for optimum production.

Another example of the importance of controlling reaction conditions is the production of ammonia from nitrogen and hydrogen gases:

N2(g) + 3H2(g) 2NH3(g)

The graphs in Figure 17.1.12 show the variation of yield with temperature and pressure. The graphs illustrate that high pressure will improve the yield of ammonia but high temperature will limit the yield. Chemists use conditions that are a compromise between yield and the cost of production.

100

200°C300°C

400°C

500°C

600°C

80

60

40

20

Frac

tion

of a

mm

onia

inth

e eq

uilib

rium

mix

ture

(%)

200 400 600Pressure (atm)

800 1000

FIGURE 17.1.12 The percentage of ammonia present when a mixture of nitrogen and hydrogen has reached equilibrium

YIELD AND THE CHEMICAL INDUSTRYMany industrial processes involve a number of steps in order to make the final product. At each step the conversion from reactants to products is usually less than complete. At every step in a reaction pathway the amount of product diminishes. Industrial chemists must consider the efficiency of a reaction pathway and the wastes that are produced (Figure 17.1.13).

In this section, you will learn to perform calculations that can be used to determine the efficiency of processes that involve chemical reactions and help in the development of strategies to minimise waste.

YieldTheoretical and actual yieldsThe mass of product that can be formed if all reactants react to produce products according to the reaction equation is known as the theoretical yield. The theoretical yield is calculated using the mole ratios of the equation and assumes 100% conversion of the reactants. However, as you learnt in Chapter 8, when reactants are mixed together in the correct mole ratio, the amount of products will not always be exactly as predicted from stoichiometric calculations.

GO TO ➤ Chapter 4 page XXX

FIGURE 17.1.13 Most chemical reactions carried out in industrial processes are not 100% efficient and so waste chemicals are produced. The reduction or elimination of waste chemicals is a major concern for industrial chemists.

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A number of factors can influence the amount of product that will be produced for a given reaction.• When a reaction reaches equilibrium rather than continuing on to completion,

the actual yield will be less than the theoretical yield.• If the reaction rate is slow, the reaction may not proceed to completion in the time

available. This will reduce the actual yield so that the theoretical yield is not obtained.• Loss of reactants and products during transfers between reaction vessels, and

in separation and purification stages such as filtration, will result in less product than expected.

Percentage yieldThe percentage yield compares the actual yield to the theoretical yield. It is a measure of the efficiency of a production process, for the particular conditions and method used for the synthesis. The higher the value of the percentage yield, the greater the degree of conversion from reactants to products for the reaction.

Percentage yield can be calculated using the formula:

= ×percentage yield actual yieldtheoretical yield

1001

Worked example 17.1.1

CALCULATING THE PERCENTAGE YIELD OF A REACTION

30.0 g of propan-2-ol was oxidised to propanone using an acidified solution of K2Cr2O7. The propanone that was distilled from the reaction mixture had a mass of 20.0 g. Calculate the percentage yield of this oxidation reaction.

Thinking Working

Write an equation for the reaction. →+ −

CH CHOHCH CH COCH3 3H /Cr O

3 32 7

2

In this case it is not necessary to write a full equation. Because a molecule of the organic product has the same number of carbon atoms as the organic reactant, the number of moles of the product is equal to the number of moles of the reactant.

Use the formula =n mM

to determine the amount of reactant.

=n(CH CHOHCH ) mM3 3

= 30.060.10

= 0.499 mol

Use the mole ratio for the reaction to determine the amount, in mol, of the product that would be made if all of the reactant reacted.

= =Mole ratio coefficient of CH COCHcoefficient of CH CHOHCH

11

3 3

3 3

=n n(CH COCH ) (CH CHOHCH )3 3 3 3

= 0.499 mol

Use the formula m = n × M to determine the mass of the product if all of the reactant reacts. This is the theoretical yield of the product.

m(CH3COCH3) = n × M

= 0.499 × 58.08

= 29.0 g

Calculate the percentage yield for this reaction from the formula:

= ×percentage yield actual yieldtheoretical yield

1001

= ×percentage yield 20.029.0

1001

= 69.0%

GO TO ➤ Section 8.1 page 000

Theoretical yield is the maximum amount of product that can be formed based on stoichiometric calculations using the limiting reactant, and assumes 100% conversion.

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Worked example: Try yourself 17.1.1

CALCULATING THE PERCENTAGE YIELD OF A REACTION

80.0 g of propan-1-ol was oxidised to propanoic acid using an acidified solution of K2Cr2O7. The propanoic acid obtained at the end of the reaction had a mass of 55.0 g. Calculate the percentage yield of this oxidation reaction.

Percentage yields in multistep synthesesWhen a reaction proceeds by a number of steps, the overall percentage yield is reduced at each step. The yield for each step has an effect on the overall yield. A low yield in one of the intermediate reactions can have a significant effect on the amount of final product obtained.

A comparison of the overall percentage yields for different pathways to the same product can be used to determine whether a particular synthetic pathway is the best way to produce an organic compound. Finding the most efficient pathway for the production of a desired chemical is critical, because wasting valuable reactants is poor economic and environmental practice.


CALCULATING THE PERCENTAGE YIELD OF A MULTISTEP SYNTHESIS

Calculate the overall percentage yield for the preparation of C from A if it proceeds by a two-step synthesis:

A → B followed by B → C

The yield of A → B is 80% and the yield of B → C is 70%.

Thinking Working

Calculate the overall yield of C by multiplying the percentage yields together and expressing as a percentage (multiplying by 100).

The overall yield of C is:

× ×80100

70100

1001

= 56%


CALCULATING THE PERCENTAGE YIELD OF A MULTISTEP SYNTHESIS

Calculate the overall percentage yield for the preparation of D from A if it proceeds by a three-step synthesis:

A → B followed by B → C followed by C → D

The yield of A → B is 90%, the yield of B → C is 80% and the yield of C → D is 60%.

Atom economyAn important objective for an industrial chemist who is developing a reaction pathway is to use a sequence of chemical reactions that minimises energy consumption, reduces waste and has a low impact on the environment.

One consideration when planning reaction pathways is to maximise atom economy.

The atom economy for a chemical reaction is a measure of the percentage of the atoms in the reactants end up in the desired product.

As you can see in Figure 17.1.14, if the atom economy of a reaction is high, then there are few, if any, waste products.

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high atom economy

lower atom economy

reactants

reactants

desired product

desired product waste

+

+ +

FIGURE 17.1.14 The different symbols represent different atoms or groups of atoms. In a high-atom economy reaction, all or most of the atoms in the reactant molecules end up in the desired product molecule.

Calculating the atom economy of a reaction provides a method of accounting for the use of materials in a manufacturing process. It tracks all the atoms in a reaction and calculates the mass of the atoms of reactants actually used to form products as a percentage of the total mass of reactants. From this, the mass of reactant atoms that end up as waste can also be calculated.

Once the balanced equation for a reaction is known, the atom economy can be calculated using the formula:

= ×atom economy 100molar mass of desired productmolar mass of all rectants

Because the total mass of products is equal to the total mass of reactants, the following formula can also be used:

= ×atom economy 100mass of desired productmass of all rectants

Use Worked example 17.1.3 to help you with calculations of atom economy.


CALCULATING ATOM ECONOMY

Calculate the atom economy in the production of ethanol from chloroethane. In this process, chloroethane is heated with a solution of sodium hydroxide. The equation for the reaction is:

C2H5Cl(aq) + NaOH(aq) → C2H5OH(aq) + NaCl(aq)

Thinking Working

Calculate the total molar mass of the reactants. M(C2H5Cl) + M(NaOH)

= [(2 × 12.01) + (5 × 1.008) + 35.45] + [22.99 + 16.00 + 1.008]

= 104.51 g mol−1

Calculate the molar mass of the required product. M(C2H5OH) = (2 × 12.01) + (6 × 1.008) + 16.00

= 46.07 g mol−1

Calculate the atom economy for the reaction using the formula:

= ×atom economy 100molar mass of desired productmolar mass of all reactants

= ×

=

Atom economy 100

44.08%

46.07104.51

In this process 44.08% of the starting materials are converted to the desired product.

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CALCULATING ATOM ECONOMY

Calculate the percentage atom economy in the formation of 1-iodopropane (CH3CH2CH2I) from propan-1-ol. The equation for the reaction is:

CH3CH2CH2OH(aq) + NaI(aq) + H2SO4(aq) → CH3CH2CH2I(aq) + NaHSO4(aq) + H2O(l)

PURITY AND QUALITY CONTROLAnother important aspect of chemical manufacture is quality control. Consumers need to be confident that the product they are purchasing is pure enough to perform as expected. This is easier to explain with some examples.• Food products. The labels on foods tell you about the nutritional properties

of the food. If you are allergic to a particular preservative you need to be confident that the label will accurately tell you what preservatives are in the food (Figure 17.1.15).

• Petrol. Drivers need to be confident the level of impurities in petrol is very low to prevent damage to the vehicle.

• Laboratory reagents. Some reagents are very dangerous to handle if concentrated. Laboratory workers need to be aware of the hazards involved in handling these reagents.Qenos needs to test the quality of the raw materials it uses as well as the products

it manufactures. Natural gas arriving by pipe is tested for ethane content as well as sulfur content and other impurities. The ethene Qenos sells is tested to ensure that other chemicals produced in this reaction have been successfully removed.

CHEMFILE EU

PAN pharmaceuticalsIn 2003 supermarket and chemist shoppers were surprised to see many health foods and alternative medicines taken off the shelves. The Therapeutic Goods Administration issued a recall of 219 products manufactured and supplied by PAN Pharmaceuticals because of poor quality control (Figure 17.1.16). Several items were found to have grossly misleading labelling, leading to the possibility of severe health issues in consumers. The company collapsed as a result of the controversy.

FIGURE 17.1.16 Pharmaceutical products being cleared from shop shelves after the 2003 recall.

FIGURE 17.1.15 Most chemical industries have a quality control department, responsible for ensuring the purity of a product is high and that any labelling of ingredients is accurate.

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ECONOMIC CONSIDERATIONSLike all industries, chemical companies need to make a profit. To do this, companies seek to minimise expenses and maximise revenue from sales. In a global market it is not always easy to control either of these factors. Figure 17.1.17 shows the severe drops in the world price of iron ore in 2015. Given the high volume of Australian exports of iron ore, this trend was disastrous and almost single-handedly placed Australia in recession. Our agricultural industries face the same fluctuations in export markets as drought or floods strike different competitor’s crops.

55

50

45

60

65

75

Price of iron ore in 2015

$US

per

tonn

e

70

Jan Feb AprMar

FIGURE 17.1.17 The world price of iron dropped markedly in 2015, causing a similar drop in profits and taxes paid. Global chemical markets are very competitive.

The demise of the car industry in Australia is another example of the competitive nature of manufacturing markets. Since 2012, Ford, Holden and Toyota have all ceased assembling cars in Australia. Their closures had a flow-on effect to associated industries supplying components such as brake pads, upholstery and specialty polymers to the car makers (Figure 17.1.18).

ENVIRONMENTAL AND SOCIAL CONSIDERATIONSChemical industries take in raw materials and convert them to new substances. During this process, waste is often produced. The disposal of waste can be a major problem, especially if it involves toxic materials or gaseous emissions. Chemical industries have a responsibility to minimise the impact of their business on the environment, but they also have to make a profit.

CHEMFILE EU

Union Carbide, BhopalAn accident at the Union Carbide chemical plant in Bhopal, India, serves as a reminder to the world of the dangers associated with chemical processes. In 1984 the pesticide plant accidently released over 30 tonnes of the toxic gas methyl isocyanate. Over 600 000 people were exposed to the gas, and estimates place the death toll between 3800 and 16 000. Toxic material remains at the site to this day (Figure 17.1.19) and the area is still classed as contaminated.

Legal proceedings and compensation case issues have continued in the 30 years since this disaster. Regulations and procedures of chemical plants all over the world were tightened and reviewed after the event. FIGURE 17.1.19 Over thirty years after the Union Carbide disaster, the

site remains in a dilapidated and contaminated state.

FIGURE 17.1.18 Workers assembling a car at a Toyota plant in Altona, Victoria. Many industries supplying speciality parts for the cars were impacted by the Toyota closure.

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Energy industryOpen cut or underground coal mines both leave large holes in the ground that need to be dealt with. When the coal is burnt, the main reaction releasing energy is

C(s) + O2(g) → CO2(g)CO2 is a problem greenhouse gas, especially in the volumes produced by a power station (Figure 17.1.20). As well as CO2, the combustion of coal also produces particulates such as SO2, NO and NO2, which are all problem emissions. State governments are aware that any plans to open new coal-fired power stations will be met with significant opposition.

FrackingThe USA has boosted its energy supplies substantially through the use of fracking, a process in which sand, steam or chemicals are used to shake gas free from rock or coal. Significant lobbying groups exist in most Australian states opposing the opening of fracking sites because of concerns they will contaminate watertables (Figure 17.1.21).

Nuclear industryAustralia could make a profit from the sale of uranium to any bidder on the world market. Uranium can be used in nuclear power plants. However, there is potential for the uranium to be used in weapons, so ethical considerations need to be taken into account. Australia sells uranium to countries that have signed the Nuclear Non-Proliferation Treaty, but controversially agreed to sell uranium to India, a non-signatory country, in 2016.

Mining industryFigure 17.1.22 shows one of the mines at Broken Hill. It is obvious that a mine will have an impact upon the local environment and that the company has a responsibility to restore the area as it progresses. Most companies are aware of this responsibility and direct resources to minimise their impact. As well as a hole in or under the ground, mining companies also have to manage waste and emissions. Figure 17.1.23 shows a laboratory worker testing effluent from a mine.

Zinc and lead ores are often sulfide compounds such as ZnS and PbS. During smelting, the sulfur is converted to SO2 gas. This is a toxic gas and emissions need to be managed (Figure 17.1.24).

GREEN CHEMISTRYThe laws and treaties that were enacted to reduce global pollution were often aimed at dealing with wastes after they had been generated, and did not address methods to reduce the production of waste.

Green chemistry outlines a set of principles that can be used as a framework to evaluate the environmental impact of a chemical process. It focuses on methods that reduce or eliminate hazardous waste. The green approach is that the best way to minimise waste is not to produce it in the first place. Its ultimate goal is to implement energy-efficient, hazard-free, waste-free, efficient chemical processes without sacrificing their effectiveness. Ideally:• goods needed by society should be produced by methods that are not harmful

to the environment• fossil fuels, and other non-renewable resources, should be replaced by

renewable ones• goods produced by society, should either be recyclable or biodegradable• the processes used to manufacture the product should either produce no wastes

or wastes that are recyclable or biodegradable.

FIGURE 17.1.20 Emissions from coal-fired power stations are fairly obvious. Water from cooling towers is relatively harmless but many other greenhouse gases are emitted in large volumes.

FIGURE 17.1.21 An anti-fracking sign from the Northern Territory. Many people in Australia oppose the use of fracking technology.

FIGURE 17.1.22 One of the mines at Broken HillPage

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Principles of green chemistryIn their book Green Chemistry: Theory and Practice, Paul Anastas and John Warner developed 12 principles of green chemistry to help assess how environmentally benign a chemical reaction or process is. These are listed in Table 17.1.2.

TABLE 17.1.2 The 12 principles of green chemistry

1 Prevent waste It is better to design chemical processes to prevent waste than to treat waste or clean it up after it is formed.

2 Design safer chemicals and products

Design chemical products to be fully effective, yet have little or no toxicity.

3 Design less hazardous chemical syntheses

Methods should be designed that use and generate substances with little or no toxicity to humans and the environment.

4 Use renewable raw materials Use starting materials that are derived from renewable resources such as plant material rather than those such as from fossil fuels that will eventually run out.

5 Use catalysts, not stoichiometric reagents

Minimise waste by using catalysts in small amounts that can carry out a single reaction many times. They are preferable to stoichiometric reagents, which are used in excess and work only once.

6 Avoid chemical derivatives Avoid using blocking or protecting groups or any temporary modifications if possible. Derivatives use additional reagents and generate waste.

7 Maximise atom economy Design syntheses so that the final product contains the maximum proportion of the starting materials. There should be few, if any, wasted atoms.

8 Use safer solvents and reaction conditions

Avoid using toxic solvents to dissolve reactants or extract products.

9 Increase energy efficiency Energy requirements should be minimised. Run chemical reactions at room temperature and pressure whenever possible.

10 Design for degradation Chemical products should be designed to break down into harmless substances after use so that they do not accumulate in the environment.

11 Analyse in real time to prevent pollution

Include continuous monitoring and control during process to minimise or eliminate the formation of by-products.

12 Minimise the potential for accidents

Design chemicals and their forms (solid, liquid or gas) to minimise the potential for chemical accidents including explosions, fires and releases to the environment.

Green chemistry practices have major long-term cost benefits to businesses and reduce long-term damage to the environment.

By switching to renewable energy sources, biomaterials and manufacturing chemicals that degrade into harmless substances, green chemistry can protect the planet from long-term deterioration.

Industry can benefit too from green chemistry considerations, since greater efficiency leads to reduced costs and improved profits. As discussed earlier in this chapter, the atom economy approach is a method of accounting for the use of materials in a manufacturing process.

FIGURE 17.1.23 Liquid and solid waste from mining operations is referred to as tailings. Companies have to contain and manage this waste.

FIGURE 17.1.24 The Mount Isa smelter in North Queensland smelts both copper and lead. The high chimneys help to disperse emissions away from the city itself.

Green chemistry methods have been described as ‘preventative medicine for the environment.’

Two commonly used slogans for green chemistry are ‘Benign (or harmless in this context) by design’ and ‘Preventing pollution, sustaining the Earth’.

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Green chemistry in actionMany innovative methods are being implemented by industry to conform to green principles. Two examples are described briefly here.• Petroleum is the raw material for the manufacture of polystyrene. Polystyrene

foam (or expanded polystyrene) is an excellent heat insulator and shock absorber, so it is commonly used in food containers and packaging (Figure 17.1.25a). In the past, polystyrene foam containers used in the takeaway food industry were expanded with chloroflurocarbons (CFCs), which damage the ozone layer. These CFCs have been replaced by pentane as the expanding gas, and much polystyrene foam has been replaced with cardboard containers. Small puffed pellets made of cornstarch, a renewable resource, can also be used as a replacement for the expanded polystyrene pellets used in packaging (Figure 17.1.25b).

• Adipic acid is a compound used in large quantities to make nylon and other useful products. The usual way to make adipic acid is from benzene, a known carcinogen. Scientists have found a way, using genetically altered bacteria as catalysts, to make adipic acid from glucose. Glucose, found naturally in plants, is a harmless substance and can be obtained from waste plant material such as stems, corn husks and even fallen leaves.

(b)

(a)

FIGURE 17.1.25 (a) Polystyrene foam pellets. (b) Biodegradable foam pellets made from cornstarch.

17.1 Review

SUMMARY

• The Australian chemical sector is large, employing thousands of skilled workers and producing goods that contribute significantly to the economy. Much of the output from the chemical industry serves as input to other industries.

• Chemical industries can be categorised as producing basic chemicals, speciality chemicals, or consumer chemicals.

• Chemical industries are large and expensive to build, and they operate in very competitive markets. Intensive research needs to be invested in the design and operation of these plants so that they operate safely and remain viable.

• Key considerations for the chemical industry are:

- source of raw materials

- location

- product uses

- reaction conditions

- energy supply

- water supply

- transport infrastructure

- commodity price and market

- safety

- emissions and disposal

- labour force

- ethical considerations.

• The theoretical yield of a chemical reaction is the mass of the product that would be formed if the limiting reactant reacted completely.

• When a reaction proceeds by a number of steps, the overall percentage yield is reduced at each step.

• The overall yield of the product of a multistep reaction is found by multiplying the percentage yields of each step together and expressing as a percentage.

• Green chemistry aims to reduce waste in a chemical process, rather than having to deal with the wastes produced.

• Waste reduction methods include maximising atom economy, using small amounts of effective catalyst, avoiding high temperatures and pressures, and designing products that degrade.

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17.1 Review

SUMMARY

• The Australian chemical sector is large, employing thousands of skilled workers and producing goods that contribute significantly to the economy. Much of the output from the chemical industry serves as input to other industries.

• Chemical industries can be categorised as producing basic chemicals, speciality chemicals, or consumer chemicals.

• Chemical industries are large and expensive to build, and they operate in very competitive markets. Intensive research needs to be invested in the design and operation of these plants so that they operate safely and remain viable.

• Key considerations for the chemical industry are:

- source of raw materials

- location

- product uses

- reaction conditions

- energy supply

- water supply

- transport infrastructure

- commodity price and market

- safety

- emissions and disposal

- labour force

- ethical considerations.

• The theoretical yield of a chemical reaction is the mass of the product that would be formed if the limiting reactant reacted completely.

• When a reaction proceeds by a number of steps, the overall percentage yield is reduced at each step.

• The overall yield of the product of a multistep reaction is found by multiplying the percentage yields of each step together and expressing as a percentage.

• Green chemistry aims to reduce waste in a chemical process, rather than having to deal with the wastes produced.

• Waste reduction methods include maximising atom economy, using small amounts of effective catalyst, avoiding high temperatures and pressures, and designing products that degrade.

KEY QUESTIONS

1 Last century Australia had several factories such as Nicholas Aspro where pharmaceuticals were manufactured. Aspirin, like many common pharmaceuticals, is no longer made in Australia. Discuss reasons for this change.

2 A company purchases land in Port Kembla to manufacture sulfuric acid, a chemical used in the refining of iron ore. Sulfuric acid can be made from sulfur dioxide gas (SO2). The SO2 is converted to sulfur trioxide (SO3) and then to sulfuric acid.a Suggest three reasons that might lead a company to

choose Port Kembla for this plant.b Discuss the precautions the company might have to

consider.

3 Bioethanol is made at Manildra near Nowra from waste products of the wheat industry.a Give three reasons why this plant is located at Manildra

rather than Broken Hill.b The production of bioethanol uses waste from the

wheat industry. There are limitations however to the volume of ethanol that can be produced at this plant. What are some of those limitations?

4 Chloroethane can be produced from the reaction between ethane and chlorine gas. The equation is

C2H6(g) + Cl2(g) → C2H5Cl(g) + HCl(g)a Calculate the atom economy for the production of

chloroethane.b If the mass of chloroethane produced from 4.00 g of

ethane is 5.40 g, calculate the percentage yield.

5 Hydrogen gas can be produced from methane in a process known as steam reforming. The equation for the process is:

CH4(g) + H2O(g) CO(g) + 3H2(g)

This is an endothermic reaction that is conducted at low pressures and temperatures of over 1000°C. The catalyst used is nickel metal. The hydrogen gas produced can be used as a fuel or in industries such as ammonia production. The conditions for this reaction are chosen carefully to maximise the yield and efficiency of the reaction. List three of the conditions chosen and explain briefly how the choices are designed to improve the yield.

6 Two different methods produce a particular compound. The first method is much less economical in terms of atom economy. The second method uses a hazardous starting material. List some of the factors you would need to take into account when deciding which method of production should be used.Pa

ge Pr

oofs


Chapter review

KEY TERMS

actual yieldatom economycrackerequilibrium constant

frackinggreen chemistrypercentage yieldquality control

renewable energy sourcesrenewable resourcesmeltertheoretical yield

90%

100%

110%

120%

130%

150%

Feb-15 May-15 Aug-15

NSW - wholesale electricity prices(percentage change)

Nov-15 Feb-16 May-16

140%

a What conclusion can you draw from this graph?b Suggest two reasons for the trend evident in the

graph.c Explain how the trend shown in this graph impacts

upon the Australian chemical industry.d Will the impact be the same upon each industry?

Explain your answer.

REVIEW QUESTIONS

1 Which of the following industries is least likely to be located at the source of its raw materials?A multivitamin manufacturerB ethanol from sugar cane industryC copper smelterD cheese factory

2 Secondary schools are consumers of chemicals.a List five chemicals you have used in your

experimental program this year.b List one chemical that you have used at school that

is also commonly used in your home.c List one chemical that you have used that had to be

handled with caution.d List one example of an experiment where different

procedures were required for the disposal of the chemicals used.

3 Many industries install heat exchangers into their plants. As the name suggests, a heat exchanger transfers energy from one section of the plant to another.a Explain why heat exchange systems are likely to

play an important role in manufacturing.b Is a heat exchanger more useful for an exothermic

process or an endothermic process? Explain your answer.

4 Australia has been gradually closing its oil refineries despite the fact that we use large volumes of petrol. Give three reasons for these closures.

5 Chemistry Australia states that most products made by the chemical industry are used by other industries. Give two examples of chemicals that are inputs to other sectors of the Australian economy.

6 The graph below shows the price of electricity in NSW during 2015.

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7 Proponents of the coal industry suggest that the adoption of ‘green-coal’ technology will ensure coal remains an important fuel in Australia.a What aspects of the use of coal is green technology

attempting to address?b How does green-coal technology work?

8 The production of sulfuric acid involves the exothermic reversible reaction between SO2 and O2. The equation is

2SO2(g) + O2(g)�2SO3(g)

What does equilibrium theory suggests about each of the following variables in this process?a the temperature usedb the pressure usedc the ratio of each reactant usedd the use of a catalyst.

9 Copper smelters produce SO2 emissions. Chemical plants that produce sulfuric acid are often placed near metal smelters. Explain why this can be a mutually beneficial arrangement.

10 Ethanol can be produced by two different pathways.Pathway A: C2H4(g) + H2O(l) → C2H5OH(aq)Pathway B: CH3CH2Cl(g) + KOH(g) →

C2H5OH(aq) + KCl(aq)a Which of the two pathways offers the higher atom

economy? Explain your answer.b These two reactions belong to different categories of

organic reactions. What are the two categories?

11 Calculate the percentage yield for the reaction in which 20.0 g of ethanol is oxidised to produce 21.5 g of ethanoic acid according to the equation:

→+ −

C H OH CH COOH2 5H /Cr O

32 7

2

12 Compound D can be synthesised by a reaction pathway that involves a number of intermediate steps. The yield for each step is shown:

→ → →A B C D70% 50% 90%

a Determine the overall yield for the preparation of compound D from compound A.

b How would the overall yield be affected if the yield for B → C was only 10%?

13 Oxirane (also called ethylene oxide) has been manufactured in the past by what was known as the chlorohydrin route, as shown in the figure below.

2O

H2C CH2

+ CaCl2 + 2HCl

oxirane

CH2 + 2Cl2 + Ca(OH)22CH2

Oxirane is now produced using a catalytic method according to the pathway shown in the figure below.

O

H2C CH2

CH2 +1– 2 O2

catalystCH2

Calculate the atom economy for the preparation of oxirane by both of these reactions.

14 An old method for the manufacture of phenol (C6H5OH) from benzene (C6H6) used sulfuric acid and sodium hydroxide in several steps. The overall equation is:

C6H6(I) + H2SO4(aq) + 2NaOH(aq) →

C6H5OH(aq) + Na2SO3(aq) + 2H2O(I)

Calculate the atom economy of this process when phenol is the desired product.

15 When ethanamide is produced by the reaction of ethanoic acid and ammonia, the atom economy is 76.7%. Calculate the total mass of reactants, in kilograms, required to make 2.00 kg of ethanamide.

16 Aspirin can be synthesised by an esterification reaction according to the pathway shown the figure below.

A student reacted a 2.50 g sample of salicylic acid (M = 138.12 g mol−1) with an excess of ethanoic anhydride, using sulfuric acid as a catalyst. After purification a mass of 2.35 g of pure aspirin (M = 180.15 g mol−1) was obtained.a Calculate the theoretical yield of aspirin for the

reaction.b Calculate the percentage yield of aspirin for the

reaction.

C

O

C

O

O2-hydroxybenzoicacid (salicylic acid)

ethanoic anhydride

2-acetyloxybenzoicacid (aspirin)

ethanoic acidCH3

CH3

CH3 CH3

C

C

O

O OH

OH C

O OHOH

O C

O

+ +Page

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17 Imagine that an aluminium refinery is proposed for NSW. The plant will receive concentrated Al2O3 from Queensland and use electricity to produce aluminium metal.

If this industry is to be located in NSW, several factors would need to be considered when choosing an exact location. For each variable below, comment on the importance of that variable for this proposed industry.a transport b energyc emissions d tailingse work force f economicsg safety.

18 Ammonia and the fertiliser ammonium nitrate (NH4NO3) are both manufactured on a very large scale at the Orica plant at Kooragang Island near Newcastle. The plant uses methane gas to produce hydrogen gas. This is then reacted with nitrogen from the air to produce ammonia. The reaction is:

N2(g) + 3H2(g) 2NH3(g)

This is an exothermic reaction. A different part of the plant produces nitric acid from ammonia, and a third part combines the nitric acid with the ammonia to form ammonium nitrate.a Sulfur is scrubbed from the incoming methane gas

before the methane is reacted. Explain why.b Explain what conditions are likely to be used to

maximise the yield of the production of ammonia from nitrogen and hydrogen.

c What is ammonium nitrate used for?d The source of raw materials for this site was not a

significant factor. Explain why.e Give three reasons why Kooragang Island might

have been chosen for the location of this plant.f Calculate the atom economy for the production of

ammonia from nitrogen and hydrogen.

19 In each of the following cases, explain which of the key ideas of green chemistry is being considered when selecting between the chemical processes:a a process that uses hexane (C6H14) as a solvent, one

that uses water as a solvent, or one that uses no solvent

b a process that needs to be carried out at 400°C, or one that proceeds at an acceptable rate at 25°C in the presence of a catalyst

c a process that forms a product that needs to be purified, or one in which the product requires no purification

d a process that uses a starting material produced from petroleum, or one that uses ethanol from the fermentation of sugars.

20 Reflect on the Inquiry activity on page 000. Describe how the cooking process is an example and analogy for chemical synthesis.

CHAPTER REVIEW CONTINUED

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CHAPTER Chemical synthesis Proofs - Pearson

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