Chapter 17: Problem 1

You are to carry out the experiment to convert cyclohexene into 1,2-dibromo- cyclohexane by the dropwise addition of liquid bromine to cyclohexene at room temperature followed by heating to \(100^{\circ} \mathrm{C}\) for 30 minutes. Do a Hazard Assessment of the materials involved in the reaction and decide on the apparatus you will use for the synthesis.

Short Answer

Expert verified

To carry out this experiment, a chemist should use a round-bottom flask, dropping funnel, condenser and a heat source for the required temperature. Protective gear is needed due to hazards associated with both bromine and cyclohexene. The experiment involves dropwise addition of bromine to cyclohexene at room temperature, followed by heating the mixture to \(100^{\circ} \mathrm{C}\) for 30 minutes.

Step by step solution

Understanding Reaction

The reaction here is the addition of bromine across the double bond of the cyclohexene to form 1,2-dibromocyclohexane. The chemist should first ensure understanding of the reaction itself and its requirements for execution.

Hazard Assessment

Bromine is highly reactive and dangerous to eyes, respiratory system and skin. So, protective gear such as gloves, lab coats and safety glasses are absolutely necessary. The reaction should be carried out in a well-ventilated area, preferably under a fume hood. Cyclohexene is flammable and its vapors can be harmful, so take precautions to avoid fire ignition sources and ensure adequate ventilation.

Choice of Apparatus

A setup consisting of a round-bottom flask, a dropping funnel for the controlled addition of liquid bromine, a condenser to ensure the reaction mixture does not evaporate, and a heat source for the required temperature.

Execution of experiment

Cyclohexene should be placed in the round bottom flask. Dropwise addition of bromine should be carried out in the flask under room temperature, this should be done slowly and with caution. After the addition of bromine is completed, the mixture should be heated to \(100^{\circ} \mathrm{C}\) for 30 minutes to complete the reaction.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Hazard Assessment in Chemistry Labs

Safety in a chemistry lab is paramount, especially when working with highly reactive and hazardous materials. Hazard assessment is the process of evaluating potential risks associated with chemicals and processes used in experiments. It includes recognizing chemical hazards, understanding their potential impacts, and implementing measures to minimize risks.

Chemical Properties: Every chemical has specific properties that define its hazards. For instance, bromine is corrosive and poses significant risks to eyes, skin, and the respiratory tract.
Material Safety Data Sheets (MSDS): These sheets provide detailed information on handling, storage, and disposal of chemicals. They are a critical part of hazard assessment.
Personal Protective Equipment (PPE): This includes items like gloves, lab coats, and safety glasses, which are essential safety barriers between the chemist and the chemicals.
Engineering Controls: Fume hoods and proper ventilation systems help to keep the exposure to harmful vapors at bay.
Emergency Procedures: Knowledge of first aid measures and the location of safety equipment such as eyewash stations and fire extinguishers is crucial.

By thoroughly assessing hazards and implementing the right safety protocols, chemists can significantly reduce the risk of accidents in the lab.

Synthesis of 1,2-Dibromocyclohexane

The synthesis of 1,2-dibromocyclohexane is a classic example of an addition reaction in organic chemistry, where bromine is added across the double bond of cyclohexene. Understanding the reaction mechanism is key to successful experimentation.

The process involves:

Formation of a bromonium ion intermediate as bromine reacts with the double bond.
The second bromide ion attacking the more substituted carbon, leading to the dibrominated product.

However, due to the reactive nature of the materials, precision during the dropwise addition of bromine is vital. This allows for better control of the reaction and minimizes the risk of rapid, exothermic reactions that can lead to spills or splatters. Also, gently heating the mixture to the correct temperature of (100^{circ} C) is a crucial step for ensuring the reaction reaches completion without decomposing the product.

Handling and Use of Bromine in Chemistry

Bromine is a dark, reddish-brown liquid at room temperature, renowned for its strong and suffocating odor. As a highly reactive halogen, special care must be taken to safely handle and store it.

Storage: Bromine should be stored in a cool, dark place in a container made of material resistant to its corrosive nature, such as glass or certain plastics.
Handling: When handling bromine, PPE should be worn at all times to prevent exposure. Use a fume hood to contain any vapors released during the transfer and reaction processes.
Disposal: Bromine waste must be disposed of in accordance with hazardous waste regulations. Use secondary containment to prevent environmental contamination in case of spills.

When using bromine in experiments such as the synthesis of 1,2-dibromocyclohexane, a calibrated dropping funnel helps in the precise addition, mitigating the risks associated with splashing. Emergency procedures such as immediate flushing with water in case of skin contact and the removal from exposure if fumes are inhaled should be clear to anyone involved in its handling.

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Short Answer

Step by step solution

Understanding Reaction

Hazard Assessment

Choice of Apparatus

Execution of experiment

Key Concepts

Hazard Assessment in Chemistry Labs

Synthesis of 1,2-Dibromocyclohexane

Handling and Use of Bromine in Chemistry

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