4: Extraction
- Page ID
- 549323
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The Purpose of this Experiment is to:
- Separate a three‑component organic mixture (benzoic acid, 3‑nitroaniline, and naphthalene) using sequential acid–base extractions in a separatory funnel.
- Characterize purity by measuring the melting temperature ranges of the isolated solids with a melting‑point apparatus
INTRODUCTION
Liquid–liquid extraction exploits differences in solubility between immiscible liquids to transfer a solute from one phase to another. In organic chemistry, acid–base extractions convert acids or bases into water‑soluble ionic forms, enabling phase separation from neutral organics. For example, carboxylic acids react with base to form carboxylate salts that partition preferentially to aqueous solution, and amines react with acid to form ammonium salts that do the same.
In this experiment, a mixture of benzoic acid (carboxylic acid), 3‑nitroaniline (amine), and naphthalene (neutral aromatic) is dissolved in an organic solvent immiscible with water (diethyl ether). Selective extractions with dilute HCl (to protonate the amine) and dilute NaOH (to deprotonate the carboxylic acid) shuttle the ionic species into the aqueous phase while leaving the neutral compound in the organic phase. Subsequent back‑neutralization regenerates each neutral compound as a precipitate for isolation and analysis.
Key acid–base transformations:
Carboxylic Acid De-protonation:
\(\mathrm{RCO_2H\ (solv) + OH^{-}\ (aq)\ \rightarrow\ RCO_2^{-}\ (aq) + H_2O\ (l)}\)
Re‑protonation to recover the acid:
\(\mathrm{RCO_2^{-}\ (aq) + H^{+}\ (aq)\ \rightarrow\ RCO_2H\ (s)}\)
Amine protonation:
\(\mathrm{RNH_2\ (solv) + H^{+}\ (aq)\ \rightarrow\ RNH_3^{+}\ (aq)}\)
Basification to recover the free amine:
\(\mathrm{RNH_3^{+}\ (aq) + OH^{-}\ (aq) \rightarrow\ RNH_2\ (s) + H_2O\ (l)}\)
As a purity check, you will determine the melting temperature ranges of the isolated solids. Pure crystalline organics melt over a narrow range; impurities broaden and depress the melting range.