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@@ -127,6 +127,62 @@ The heterogeneous mixture was subsequently clarified via filtration through a ce
\end{table}
\subsection{\ce{H2SO4} Catalyzed Tandem Hydrolysis--Esterification}
The conversion of ASA to methyl salicylate proceeds via a one-pot tandem sequence (Scheme~\ref{sch:mechanism}). Concentrated \ce{H2SO4} serves as a Brønsted acid catalyst, activating the carbonyl groups toward nucleophilic attack by methanol, and as a dehydrating agent to shift the equilibrium.
\begin{scheme}[H]
\centering
\small
\setchemfig{atom sep=2.0em, compound sep=5em, nodesep=2pt}
% Wrapper to ensure vertical alignment of the three main components
\begin{tabular}{ccc}
\chemname{
\chemfig{*6(-=-(-O-[:-30](=[:-90]O)-[:+30]CH_3)=([:60]-[:90](=[:150]O)-[:30]OH)-=)}
}{\footnotesize Acetylsalicylic Acid}
&
\parbox{2.5cm}{\centering $\xrightarrow[\Delta]{\ce{CH3OH, H2SO4}}$}
&
\chemname{
\chemfig{*6(-=-(-OH)=([:60]-[:90](=[:150]O)-[:30]O-[:+90]CH_3)-=)}
}{\footnotesize Methyl Salicylate}
\end{tabular}
\vspace{1.5em}
\caption{Tandem deacetylation and Fischer esterification sequence.}
\label{sch:mechanism}
\end{scheme}
The transformation encompasses two concurrent equilibrium-driven processes:
\begin{enumerate}
\item \textbf{Acid-Catalyzed Solvolysis:} The acetoxy group undergoes transesterification with methanol to yield salicylic acid and methyl acetate (Eq~\ref{eq:solvolysis}).
\item \textbf{Fischer Esterification:} The carboxylic acid is esterified by the methanol solvent (Eq~\ref{eq:fischer}).
\end{enumerate}
\begin{equation}
\ce{R-OCOCH3 + CH3OH <=>[H+] R-OH + CH3COOCH3}
\label{eq:solvolysis}
\end{equation}
\begin{equation}
\ce{Ar-COOH + CH3OH <=>[H+] Ar-COOCH3 + H2O}
\label{eq:fischer}
\end{equation}
To drive the reaction toward the methyl salicylate product, a substantial stoichiometric excess of methanol was employed, utilizing Le Chatelier's principle to overcome the reversible nature of the esterification.
\subsection{Work-up and Purification}
Following reflux, the reaction was quenched in ice-cold distilled water. Methyl salicylate ($\rho \approx 1.17$ g/mL) was isolated as the organic phase via liquid--liquid extraction. Residual acidic species (\ce{H2SO4}, \ce{CH3COOH}) were neutralized using saturated \ce{NaHCO3}:
\begin{equation}
\ce{H2SO4(aq) + 2NaHCO3(aq) -> Na2SO4(aq) + 2CO2(g) + 2H2O(l)}
\end{equation}
The organic extract was dried over anhydrous \ce{MgSO4} and filtered to yield the pure essential oil.
\subsection{Outline}
The document layout should follow the style of the journal concerned. Where