Why should care be exercised in handling concentrated acids such as H_2SO_4 and

Question

Why should care be exercised in handling concentrated acids such as H_2SO_4 and HBr? Why do primary alkyl halides typically undergo S_N2 substitution reactions more rapidly than do secondary or tertiary alkyl halides? Why should reflux of the microscale reaction mixture be gentle, with the condensation ring remaining close to the surface of the liquid in the test tube? By observing the reaction mixture, what visual evidence can be gained to indicate that 1-butanol is being converted to 1-bromobutane? What is the function of anhydrous CaCl_2 in this experiment?

Explanation / Answer

1. The concentrated acids should be handled with care because they are very corrosive. They should not be inhaled and they burn the skin when comes in contact. So, they should not be inhaled and handled with gloves and goggles.

2. Primary alkyl halides undergo faster SN2 reaction as compared to secondary and tertiary alkyl halides because the mechanism involves the attack of nucleophile from back of the alkyl halide. There is more steric hindrance in secondary and tertiary alkyl halides, So, the attack is not favorable. But in primary alkyl halides, there is less steric hindrance, thus it proceeds through SN2 mechanism.

3. The reflux should be gentle, otherwise the reaction mixture will bump out of the test tube and may lead to lab accidents.

4. 1- bromobutane and 1-butanol: on comparing the physical properties, they both have different solubility. 1-butanol is soluble in water and 1-bromobutane is insoluble. So, they both will form two layers, being immiscible. Thus, this is the visual evidence that the reaction has happened.

5. The anhydrous CaCl2 is used to absorb the moisture. To keep the reaction mixture away from atmosphetic moisture, the anhydrous CaCl2 is filled in a tube and put on the condensor. it does not allow air moisture to enter the reaction mixture.

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