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CHMI-2427 lab...

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Experiment 8: Properties of Alkyl Halides Lab Report Form

Observations/Results: Table 1: Identification of unknown alkyl halides n-Butyl Bromide

sec-Butyl bromide (2bromo butane)

t-Butyl bromide (2-bromo-2methylpropane)

Unknown

- Initial flame is

- Initial flame is a

- Initial flame is a

- Large initial

fast, large and normal (orangeyellow) colour ! - Blue-green little flame ! - Flame is wider than sec-butyl bromide

normal (orangeyellow) colour ! - Blue flame ! - Flame is taller than 1st ! - Very slim flame

Alcoholic silver nitrate AgCl = white! AgBr= off-white ppt! AgI=bright yellow

- No reaction

- Whiteish ppt

15% sodium iodide in acetone

- Yellow

Beilstein Positive = bluegreen colour

when added ! - Clear and transparent ! - Becomes slightly white and cloudy

-

normal (orangeyellow) colour ! Blue flame ! Flame is taller than 1st ! Wider than 2nd ! Flame seemed to have gone out faster

normal (orangeyellow) coloured flame ! - Blue flame! - Short and wide

- Whiteish ppt forms right away forms right but only at the when added to bottom of test test tube (all of tube! it)! - White ! - Ppt is off white! - Nitric acid - Nitric acid added ! added ! - Becomes cloudy - Forms bright and white yellow ppt

forms right when added to test tube! - Ppt is off white! - Nitric acid added! - Forms bright yellow ppt

- Clear ! - Remained clear

- Clear ! - Yellow

- Clear ! - Yellow

- Whiteish ppt

The identity of the class of alkyl halide for the unknown is a t-butyl bromide

Discussion: 1. Discuss your observation for each test and for each of the non alkyl halides. Draw the reaction mechanism for each chemical reaction 2. From the chemical tests, can you distinguish the type of alkyl halide for the unknown? Explain.

The first test performed was the Beilstein test, a blue-green coloured flame is indicative of the presence of a halogen within the compound of interest. All four of the compounds being tested within this experiment yielded the blue-green flame. The test consisted of a copper wire in

the precedes of oxygen HCl and heat, the reaction which gives the desired coloured flame is as follows,

All three of the known alkyl halides along with the unknown gave the desired blue-green flame, therefore, it can be deduced that all of the compounds being tested contain a halogen, bromide. The second test was the alcoholic silver nitrate test, which preceded in an SN2 fashion. The reaction between an alkyl halide and silver nitrate will result in an alkyl nitrate and a silver halide, silver bromide, precipitate (ppt). The reaction rate is dependent on the structure of the alkyl and the halide (in this experiment the halide is bromide for all), tertiary alkyls being the fast, secondary alkyl and primary alkyl being the slowest. As seen within the experiment, the primary alkyl bromide, n-butyl bromide, did not initially and was the slowest, it reaction can be depicted as,

The secondary alkyl bromide, sec-butyl bromide (2-bromobutane), reacted when it was initially added to the test tube. However, it did not react with the flu volume within the test tube, a reactions was observed solely at the bottom of the test tube. It reaction can be displayed as,

The tertiary alkyl bromide, t-butyl bromide (2-bromo-2-butylpropane), as expected reacted very quickly with the entire volume within the test tube. The reaction is as follows,

The unknown reacted in the same way as the tertiary, as it was initially added to the test tube, it reacted with the entire volume. It produced the same ppt and reacted at similar rates to tbutyl bromide. The last test performed was sodium iodide in acetone, which also follows an Sn2 reaction. Its reaction rate is depended on the structure, the primary alkali halides will react the fasted, followed by secondary and tertiary being the slowest. It was seen in the experiment, as the n-butyl bromide reacted the fasted to give the yellow colour. N-butyl bromide reacted in the following mechanistic way,

The secondary, tertiary and unknown did not initially react as they needed to be submerged into a heat bath in order to catalyze their reactions. The secondary alkyl bromide failed to react and the solution remained clear. However, the tertiary and unknown produced the yellow colour after being submerged in the bath in the following way,

The unknown alkyl halide used in the following experiment can be identified as a tertiary alkyl bromide. In the first test, it confirmed the precise of a halogen. The second test, it reacted in the same way as the tertiary known alkyl bromide. In the third test, the tertiary and unknown reacts again in the same way and under the same conditions. Therefore, we can deduce the unknown alkyl halide is tertiary....