12.1: Side Reactions

Last updated
Save as PDF

Page ID: 213761

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

1. The reaction between NaBr and H₂SO₄ is an acid-base reaction. Bromide ion, which results from dissociation of NaBr in water, reacts with sulfuric acid to capture one of its acidic protons. Equilibrium in acid-base reactions favors formation of the weaker acid (HBr) and the weaker base (bisulfate ion).

The first inorganic salt that forms as a byproduct is therefore NaHSO₄. Remember, sodium is a expectator ion and serves as a counterion for any negative charges present in the medium.

2. Bromide can react with bisulfate ion in another acid base reaction to yield sulfate ion as another byproduct. Therefore Na₂SO₄ is the second inorganic salt that forms.

3. The total number of inorganic salts that can be present in the system is therefore three, namely NaBr, NaHSO₄, and Na₂SO₄. Although they are soluble in water at room temperature, they may be less soluble in ice water and form crystalline precipitates.

4. In part A (preparation of n-butyl bromide), another Sn2 side reaction leading to the formation of n-butyl ether is possible if the alcohol acts as the nucleophile.

5. Finally, a less probable side reaction -an E2 reaction- can happen with water acting as a weak base. This reaction is less probable because E2 reactions normally require strong bases. However the reaction is still possible.