Figure 2.1.1: The products of reaction between (1) diazonium ion and
phenol (2) diazonium ion and 2- naphthol 6
Table 2.1.2: Structures of Azo Dye and Its Properties 6
Figure 2.2.1: Tartrazine 7
Figure 2.2.2: Brilliant Black 7
Table 3.1.1: Use of Azo Dyes in Different Industries 8
Figure 3.1.2: Azo dyes are present in cosmetics and candies 9
Table 3.2: Types of Azo Dyes and Their Related Health Effects 10
Table 4: Countries and the Azo Dyes Banned 11
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Introduction
Azo dyes are compounds that give bright and high intensity colours. It is known as azo dyes because it contains an azo group. Approximately 60-70% of dyes used in the dyes’ industries are azo dyes, such as textiles, printing and food industries. Theoretically, azo dyes can supply any colour by combining different chemical together. However, in reality, yellow and red are the most common colours used. (http://www.food-info.net/uk/colour/azo.htm)
In this 21st century, people consume a lot of processed food everyday. People nowadays usually consumed a larger amount of food additives which comes with the processed food compared to the recommended average intake. This is especially true for children, as they contain lots of food additives, such as azo dyes, that meant to attract them. Besides, food colouring are not only available in food, but are used in medicinal drugs too. These azo dyes sometimes caused patient to suffer from side effects, such as from medicinal syrup for children which contains food colouring. These problems had further led my interest to the topic related to azo dyes.
1.1 History of Azo Dyes
(Moeckly 1998)
Figure 1: The History Development of Azo Dye
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Chemistry Part of the Topic
2.1 Coupling Reaction
Azo dyes can be formed by coupling reaction, in which two reactants join together. In this reaction, a diazonium salt and phenol react in alkaline solution to form azo dyes by the electrophilic aromatic substitution mechanisms (Tan 2004).
The chemical equation below shows the coupling reaction and their products between diazonium ion and phenol or naphthol.
(Keusch 2003)
- (2)
Figure 2.1.1: The products of reaction between (1) diazonium ion and phenol (2) diazonium ion and 2- naphthol
(Page, C, Fennen, J n.d.)
Table 2.1.2: Structures of Azo Dye and Its Properties
Azo dyes can produce any colour on demand. Besides, both of the organic compounds required to form azo dyes are cheap and the energy requirements for the reaction are low which is at or below room temperature. Furthermore, this reaction is environmental friendly as it is carried out in water (http://www.chm.bris.ac.uk/
webprojects2002/price/azo.htm). All these make azo dyes a popular colouring substance.
2.2 The Molecular Structure of Azo Dyes
Azo dyes have an N=N group which links two aromatic rings together is responsible for the colour property of azo dyes. It can absorb visible frequencies of light which will provide a certain colour of high intensity for a certain azo dye.
(http://www.food-info.net/uk/colour/azo.htm)
Figure 2.2.1: Tartrazine
(http://www.food-info.net/uk/colour/azo.htm)
Figure 2.2.2: Brilliant Black
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Advantages and Disadvantages of Azo Dye
3.1 The Application of Azo Dye
The usage of azo dyes is prevalent in many fields due to their intense colour such as in food processing, textile, printing, medical treatment, pharmaceutical and cosmetic industries.
Azo dyes are much more stable than most of the natural food dyes. Azo dyes are heat stable, stable in the whole pH range of foods and do not fade when exposed to light or oxygen. This makes azo dyes applicable in nearly all foods. (http://www.food-info.net/uk/colour/azo.htm)
(http://www.chm.bris.ac.uk/webprojects2001/anderson/colourings.htm)
(http://www.mbm.net.au/health/100-181.htm)
Table 3.1.1: Use of Azo Dyes in Different Industries
Of all the industries, azo dyes are used most prevalently in food industry its safety. This is because direct toxic levels of azo dyes will never be reached by consuming azo dye coloured food. A lethal dose for an average adult is 100kg of azo coloured food in a single day. Reason behind this is because azo dyes are highly water soluble, they do not accumulate in body, but metabolised in liver and excreted in urine (http://www.food-info.net/uk/colour/azo.htm).
Figure 3.1.2: Azo dyes are present in cosmetics and candies
- The Downside of Azo Dyes
Azo dyes are useful in many ways, but its side effects cannot be neglected especially in a long term period. They are known for some serious health complications such as allergy (Hill, 1992).
Tartrazine can cause cancer and aggravate asthma. Besides, it also leads to the alteration of perception and behaviour, uncontrolled hyper agitation and confusion and wakefulness, particularly in young children. Tartrazine also affects zinc metabolism and digestive system.
(http://www.lactose.co.uk/milkallergy/foodadditives100.html)
(http://www.lactose.co.uk/milkallergy/foodadditives100.html)
Table 3.2: Types of Azo Dyes and Their Related Health Effects
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Current development of azo dye around the world
4.1 Food Act 1983 (Act 281) & Regulations in Malaysia
Ministry of Health of Malaysia has introduced Food Act 1983 & Food Regulations 1985 to restrict the type and quantity of food additives used in the food products. In these regulations, the definition of “colouring substance” is “any substance that, when added to food is capable of imparting colour to that food and includes colouring preparation.” (Food Act 1983 (Act 281) & Regulations 2003).
The colouring substances which are allowed are listed in Table I and Table II of the seventh schedule (Food Act 1983 (Act 281) & Regulations 2003). There are 14 synthetic azo dyes that are permitted to be added in food (Appendix I).
- Types of banned azo dyes in major industrialised countries
Each country has her own criteria in setting the list of approved azo dyes. Here are some of the azo dyes that are banned in major industrialised countries around the world:
(http://www.lactose.co.uk/milkallergy/foodadditives100.html)
(http://www.mbm.net.au/health/100-181.htm)
Table 4: Countries and the Azo Dyes Banned
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Conclusion
Azo dye is essential to mankind as it is used in a variety of industries. Despite the drawbacks of azo dyes, such as it is carcinogenic and act as an allergen, people still continue to use it as it is cheap and easy to produce.
In order to minimise the negative effects of azo dyes, manufacturers are urged to reduce the amount of azo dyes use to produce food especially. Consumers must be more careful in the selection of food product by identify the content of the food before purchasing. This will help to reduce the effect of azo dyes until an alternative product is introduced.
(799 words)
Bibliography
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Hill, JW 1992, Chemistry for Changing Times, Macmillan, New York.
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Food Act 1983 (Act 281) & Regulations 2003, International Law Book Services, Kuala Lumpur.
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Tan, YT 2004, Organic Chemistry for STPM, Fajar Bakti, Selangor.
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Lee, FA 1983, Basic Food Chemistry Second Edition, AVI Publishing, USA.
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Page, C, Fennen, J n.d., What are leather dyes today? The relationship between the dye structure and its performance properties, TFL, USA.
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Wageningen University n.d., Azo dyes, viewed 04 February 2007, <http://www.food-info.net/uk/colour/azo.htm>.
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Moeckly, S 1998, The History of the Dye Industry, viewed 04 February 2007, <http://www.jergym.hiedu.cz/~canovm/mechanic/pravid12/gries/g.htm>.
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Keusch, P n.d., Azo Coupling, viewed 13 January 2007, <http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/D-azo-e.htm>.
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Azo Dyes, viewed 13 January 2007, <http://www.chm.bris.ac.uk/webprojects2002/price/azo.htm>.
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Food Additives, viewed 04 February 2007, <http://www.lactose.co.uk/milkallergy/foodadditives100.html>.
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Colours, MBM, Australia, viewed 04 February 2007, <http://www.mbm.net.au/health/100-181.htm>
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Colourings, viewed 04 February 2007, <http://www.chm.bris.ac.uk/webprojects2001/anderson/colourings.htm>
Appendix I