Hydrolysis of halogenalkanes.

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Hydrolysis of halogenalkanes


Aim and background reading

The aim of this experiment is to show how the rate of reaction of the halogenoalkanes changes in respect to the C-X bond, where the C is the carbon and the X is the halogen. This will occur through a nucleophilic attack. The halogenoalkanes undergo hydrolysis according to the following equation:

CnHn+1X   +   OH¯   à   CnHn+1OH   +   X¯

Nucleophilic attacks are a predominant type of chemical attack. It is a type of substitution reaction where a nucleophile breaks the bond between the carbon and in this case the halogen and removes the halogen to get a halide ion. There are 3 main types of nucleophilic reaction; one involves hydrolysis, which is the one being used in this experiment and involves an OH molecule, cyanide ions, which is not being used due to cyanide being extremely dangerous and the final nucleophilic reaction involves ammonia ions. This one is not used because it will just keep substituting the chemicals and you will end up with a huge range of compounds, most, if not all of which will not be needed. These products are called amines and an example of one would be CH3CH2NH2, which is ethylamine.

The three elements that will be used for this investigation are chlorine, bromine and iodine. Chlorine is a greenish yellow gas, which combines directly with nearly all elements. Chlorine is a respiratory irritant. The gas irritates the mucous membranes and the liquid burns the skin.

Bromine is the only liquid nonmetallic element. It is a member of the halogen group. It is a heavy, volatile, mobile, dangerous reddish-brown liquid. The red vapour has a strong disagreeable odour, resembling chlorine, and is irritating effect to the eyes and throat. It has a bleaching action. When spilled on the skin it produces painful sores. It is a serious health hazard, and maximum safety precautions should be taken when handling it.

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Iodine is a bluish-black, lustrous solid. It volatilises at ambient temperatures into a pretty blue-violet gas with an irritating odour.

          The bond enthalpies of the 4 most reactive halogens is as follows

From the above table you can see that bond enthalpy decreases going down the group. This means that the weaker bonds will be more reactive with a nucleophile, and the C-Cl bond will be the hardest to break out of the bonds being tested as it has a higher value compared to the others. Halogenalkanes are classified as tertiary, secondary and primary. This depends upon the number ...

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