CHEMISTRY

ORGANIC CHEMISTRY- DEPTH STUDY ASSESSMENT TASK

ASSESSMENT TASK: 4/5/2020

NESA NUMBER: 34245509

SECTION I- Chemistry of chosen hydrocarbon and procedures required to safely handle and dispose of

organic substancesBenzene C6H6

Discovery Benzene is the simplest organic, aromatic hydrocarbon with the chemical formula C6H6. The word benzene derives historically from gum benzoin, sometimes called ‘Benjamin’. Gum benzoin was known as an aromatic resin. Michael Faraday discovered benzene in 1825 from whale oil. Faraday called this new hydrocarbon “bicarburet of hydrogen”. In 1834 the German chemist Mitscherlich synthesized benzene by heating benzoic acid with calcium oxide (quicklime).

C6H5COOH+CaO→C6H6+CaCO3

August Kekule Von Starndonitz(1829-1896)

StructureKekule proposed in 1856 that benzene had a structure in which six carbon atoms formed a ring with alternating single and double bonds. However, the chemistry of benzene was inconsistent with the structural formula. Since benzene is a cyclic hydrocarbon the carbon atom of benzene is arranged in a six-membered ring bonded to only one hydrogen atom. According to molecular orbital theory, the benzene ring involves formation of three delocalized π – orbitals across all six carbon atoms, while the valence bond theory describes two stable resonance structures for the ring.

Resonance According to the Kekule structure, benzene should undergo the following: -

Addition reactions It gave substitution reaction products rather than addition. All C-C bonds are identical

Experiments show that Kekule structure incorrect An accurate description is given by resonance theory or by orbital

models

The resonance theory of benzene consists of two equivalent Lewis structures, each with three double bonds that alternate with three single bonds. Benzene has a single hybrid structure that combines the characteristics of both resonance forms.

Hence, Kekule structure cannot explain the behaviour of Benzene

Aromaticity Benzene is an aromatic hydrocarbon, as the C-C bonds formed in the ring are not precisely single or double, but they are of intermediate length. Hence, benzene is chemically unreactive compared to alkenes. Aromatic compounds are divided into two groups: benzenoids (containing benzene ring) and non-benzenoids (not containing benzene ring), only if they follow Huckel rule. According to Huckel rule, for a ring to be aromatic it should have the following properties:

Planarity (all atoms should lie in the same plane) Complete delocalization of the π electrons in the ring (4n + 2) π electrons in the ring where n=0 or any +ve integer

Preparation 1) Lab method: By the decarboxylation of sodium benzoate. In this laboratory method sodium benzoate is heated with soda lime to obtain benzene when it gets decarboxylated.

2) From benzene derivatives: By heating phenol with zinc. Benzene is obtained when phenol vapors are passed over heated zinc dust.

3) polymerization of ethyne (acetylene). Benzene is polymerized when ethyne is passed through a red-hot copper tube.

Chemical Properties Due to the presence of p electron clouds above and below the plane electron benzene ring, the ring serves as a source of electrons and is easily attacked by electrophiles. Hence electrophilic substitution reaction are the characteristic reactions of aromatic compounds.

Substitution reactions in benzene are preferred rather than addition is due to the fact that in the former reactions resonance stabilized benzene ring system is retained while the addition reactions lead to the destruction of benzene ring.

Physical Properties Benzene is colorless, mobile, and volatile liquid. It has a boiling point of 80 °Cand freezing point of 5.5 °C .

Benzene being non-polar is immiscible in water but is readily miscible with organic solvents such as alcohol and ether.

Its vapor is highly toxic inhalation over a period of time leads to anemia. It is highly inflammable and burns with sooty flame.

Uses Benzene is found in crude oil and is a major part of gasoline. It is used to make plastics, resins, synthetic fibers, rubber lubricants, dyes, detergents, drugs, and pesticides Benzene is produced naturally by volcanoes and forest fires.

The procedures required to safely handle organic substances Safe handling of any chemical begins with the application of appropriate equipment. In the case of organic substances, Personal Protective Equipment (PPE) is the constitutional gear that must be worn in order to be protected from potential harm. The MSDS (material safety data sheet) should be read and understood for the respective substance(s) that will be used throughout the experiment. The reading of the safety data sheet presents potential hazards to human life, reactivity with other types of substances, environmental threats, and potential combustion. In organic chemistry specifically, in which many substances exist in a gaseous or a

liquid form, the flash point should be paid careful attention; as soon as the temperature deviates upwards from the listed flash point, potentially toxic gas will be produced from the substance. Many organic substances, such as benzene, is an aromatic hydrocarbon; meaning that it will release gases into the atmosphere; and in the case of benzene, will produce toxic gases which potentially can cause: respiratory tract irritation, Central Nervous System (CNS) Depression, and in extreme cases of overexposure, will lead to coma and death. Due to the nature of many organic substances that act to a similar manner to benzene, the use of a fume cupboard is strongly recommended in order to reduce the risk of bodily harm. During an experiment involving organic chemicals, a mistake can occur, such as the contact of organic substances with the skin, eye or can be inhaled. A first-aid kit, fire extinguisher and a fire blanket should be present in the room. Furthermore, it must not be only one person conducting the experiment; meaning, another person must be present in the vicinity.

The procedures required to dispose of organic substances The disposing of organic substances is regulated by laws in most countries, meaning that the regulation is different from each country. In the case of Australian waste-management protocols, all waste must be stored in properly labelled containers. Especially in schools, the science departments should maintain a central, secure waste storage area in which all waste can be stored until a company with the required expertise can remove all the waste in the most effective, environmentally friendly manner possible. The disposing of organic substances through a drain can be considered if the sewer flows to a wastewater treatment plant, and not to a stream or other natural water course. In the case of benzene environment, health and safety must be contacted in dealing with all spills of more than 500ml. Small spills should be immediately cleaned up using an appropriate absorbent. All waste material should be contained and disposed of through the hazardous waste disposal program. Benzene waste must be placed in sealed, intact containers and must be clearly labeled. Benzene must never be poured down the sewer system as it can contaminate the soil and water.

REFERENCES

“Byjus (2000) [online]. Bengaluru: Think and learn private limited. [assessed 25 April 2020]

<<https://byjus.com/chemistry/benzene/>>”

“CAREY, Francis A (2019). <<Benzene chemical compound>> Durham University (Gloria

Lotha) (2019). England.”

“Chemistry explained (2020) [online]. New York: Advameg, Inc. [assessed 24 April 2020]

<<http://www.chemistryexplained.com/Hy-Kr/Kekul-Friedrich-August.html>>”

“CHONG, Minoo (2020) <<Can hydrocarbons be classified based on structure and reactivity>>

Sydney, Australia.”

“Cliff notes (2020) [online]. Houghton Mifflin Harcourt. [assessed on 25 April 2020]

<<https://www.cliffsnotes.com/study-guides/chemistry/organic-chemistry-ii/aromatic-

compounds/benzene>>

“DALAL, Viraf (2018). Dalal ICSE Chemistry series.

Delhi, India: Allied Publishers Pvt. Ltd.”

“DAVIS, Norma (2017). <<Benzene and Aromatic compounds>> 2020 slideplayer.com INC”

“KOTTWITZ, Stefan (2015) [online]. <<Example: Benzene ring>> [assessed 18 April 2020]

<<http://latex-cookbook.net/cookbook/examples/benzene-ring/>>

“Study Adda (2018) [online]. Andra Pradesh: JEE MAIN & Advanced Chemistry Hydrocarbons

Benzene (C6H6 ¿ . [assessed 20 April 2020]

<<https://www.studyadda.com/notes/jee-main-advanced/chemistry/hydrocarbons/benzene-left-

mathbfc_mathbf6mathbfh_mathbf6-right/8956>>”

“THICKETT, Geoffrey (2018). Excel Year 12 Chemistry. [page 128-page 131]

Glebe, NSW: Pascal Press”

“Wisconsin Department of Health Services (2018) [online]. Wisconsin: WDOHS [assessed 5

April 2020]

<<https://www.dhs.wisconsin.gov/chemical/benzene.htm>>”

IMAGES

“Aromatic compounds. Lecture outline aromatic vs aliphatic (2018) [online] Retrieved from

<<https://slideplayer.com/slide/6358543/>>”

“Benzene [C6H6]- Structure (2019) [online] Retrieved from

<<https://byjus.com/chemistry/benzene/>>”

“Benzene- Wikipedia (2020) Retrieved from

<< https://en.wikipedia.org/wiki/Benzene>>”

“How is Benzene prepared from Ethyne- Quora (2018) [online] Retrieved from

<<https://www.quora.com/How-is-benzene-prepared-from-etyne>>”

“Preparation of Benzene (2019) [online] Retrieved from

<<http://www.sureden.com/topics/11-pmt-chemistry-hydrocarbons-preparation-of-benzene-

1059.html>>”

“Prof. Dr. Friedrich August Kekule von Starndonitz (Kekule) (2018) [online] Retrieved from

<<https://www.geni.com/people/Friedrich-August-Kekul%C3%A9-von-Stradonitz/

6000000026601838883>>”

“Reduction of Phenol (2017) [online] Retrieved from

<<https://www.zigya.com/study/book?

class=11&board=pseb&subject=Chemistry&book=Chemistry+Part+II&chapter=Hydrocarbons&

q_type=&q_topic=other&q_category=&question_id=CHEN11094527>>”

SECTION II- Question and hypothesis for scientific investigation

“The use of hydrocarbon fuels has created an economic boon and allowed for readily available electricity and transport. However, they also lead to health issues and are the main cause of modern

climate change.”- [Rawat “et al”., 2016]

In relation to the above statement assess the problems your chosen hydrocarbon can potentially cause to the health of society

and the health of the environment.

Benzene is widely distributed in the environment due to which exposure and low-level inhalation over long periods is a cause of concern. Benzene is highly volatile meaning it generally prefers to be in its vapor form. This means it can easily evaporate into the air from solid materials such as paints or solvents. Benzene’s volatility leads to increased concentrations in indoor air which is often poorly circulated. This can increase personal exposure or exposure dose by inhalation, indigestion or dermal absorption and increases the chance of a cancer-causing event occurring. The most important source of benzene’s toxicity are the many toxic metabolites it can form. For example, benzene is first metabolized primarily in the liver by CYP2E1 (cytochrome enzyme). The metabolites are then transported to the bone marrow using blood proteins which can get into the stem cells. This can cause mutations and chromosomal abnormalities such as ROS (reactive oxygen species), DNA abducts and Topo II inhibition. People working in industries that make or use benzene may be exposed to the highest levels of it. Therefore, benzene is tightly regulated in workplaces in most developed countries due to its higher links of blood disorders and cancers.

The general levels of benzene from automobile exhausts, paints and dyes does not pose a threat to the environment. However, the pollution caused due contamination of waterbodies, soil and air will have an adverse effect on the flora and fauna and aquatic organisms. Benzene reacts quickly in the air with other chemicals to form smog which is broken down within a few days. Before it is broken down the benzene present in the air is removed by chemical reactions or rain, a process which leads to surface and ground water contamination. When aquatic life in rivers, lakes and oceans are

https://www.semanticscholar.org/paper/Advances-in- >> .>..understanding- benzene-health-effects-Smith/9350cafebe4e7ab2b1f4e515548e56d1e86b74ef/figure/1

exposed to benzene they undergo alterations to their behavior, changes in their appearance and their lives are shortened. It also shows adverse effects on the fetus of aquatic animals which affects their ability to reproduce. In animals exposure to food or water which are contaminated with benzene can damage the blood and immune system and cause cancer. They produce the same effects as seen in human beings. Animals have shown neurological, immunological and hematological effects from inhalation and oral exposure to benzene. It inhibits the growth of plants in the soil which leads to their death.

RECCOMENDATIONSBenzene is a highly toxic established environmental carcinogen and chronic exposures can affect bone marrow and cause leukemia. Therefore, the following measures should be taken to reduce the risk of exposure to benzene: -

Since no specific antidote is available for benzene poisoning. It is important that victims seek medical treatment as soon as possible.

If benzene is released into the air, moving to an area with fresh air is important to reduce the risk of death from benzene exposure.

Minimizing emissions from vehicle exhausts by improved design and regular monitoring of engine settings.

By prohibiting smoking inside buildings Developing and implementing policies and legislations to remove

benzene from consumer products such as glues and paints. Public awareness must be risen regarding sources of exposure to

benzene and risk mitigation measures.

In conclusion benzene is among the most widely used chemicals in the world. It is an important source for manufacturing a range of chemicals and plastics. However, exposure to benzene by humans is associated with a variety of acute and long-term adverse health effects due to it being an established carcinogen. Exposure can occur occupationally and domestically due to the use of petroleum products such as motor fuels and solvents. Therefore, public health actions are needed to reduce the exposure of both workers and the general population to benzene.

REFERENCES

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<<https://www.atsdr.cdc.gov/phs/phs.asp?id=37&tid=14>>”

“ChemicalSafetyFacts.org (2020) [online]. United States: Benzene. [assessed on 25

April 2020]

<<https://www.chemicalsafetyfacts.org/benzene/ >>”

“Facts about benzene (2020) [online]. United States: Benzene. [assessed on 20

April 2020]

<<https://emergency.cdc.gov/agent/benzene/basics/facts.asp>>”

“National pollutant inventory (2005) [online]. Australia: Benzene. [assessed on 24

April 2020]

<<https://www.chemicalsafetyfacts.org/benzene/>>”

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<< https://www.petro-online.com/news/safety/15/breaking-news/what-are-the-

effects-of-benzene-on-the-environment/33958>>”

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<< https://www.who.int/ipcs/assessment/public_health/benzene/en/>>”