\documentclass[german=false,thesistype=master, nolistoffigures,
nolistoftables]{tubsthesis}
\usepackage{booktabs}
\usepackage{colortbl}
\usepackage[nottoc]{tocbibind}
\usepackage{enumitem}
\usepackage[english]{babel}
\usepackage{graphicx}
\usepackage{subfigure}
\usepackage{chemmacros,environ}
% in older versions there is no \IfChemCompatibilityT
\providecommand\IfChemCompatibilityT[3]{}
% load the `reactions' module in newer versions:
\IfChemCompatibilityT{>=}{5.0}{
\usechemmodule{reactions}
}
% redefine the environments:
\RenewEnviron{reaction}
{\begin{equation}\expandafter\ch\expandafter{\BODY}\end{equation}}
\RenewEnviron{reaction*}
{\begin{equation*}\expandafter\ch\expandafter{\BODY}\end{equation*}}
\RenewEnviron{reactions}
{\begin{align}\expandafter\ch\expandafter{\BODY}\end{align}}
\RenewEnviron{reactions*}
{\begin{align*}\expandafter\ch\expandafter{\BODY}\end{align*}}
%\usechemmodule{reactions}
%\usepackage{cleveref}
\chemsetup{modules={all}}
\usepackage{longtable}
\usepackage{tabu}
\usepackage{siunitx}
%%%%%%%%%%% Mathemodus
\usepackage{amssymb}
\usepackage{amsmath}
\numberwithin{equation}{section}
\usepackage[parfill]{parskip}
\usepackage{romannum}
\usepackage{ragged2e,array,longtable}
\usepackage{hyperref}
\usepackage[%
nonumberlist, % keine Seitenzahlen anzeigen
automake,%
xindy={language=german-din},% Sortiert Einträge im Verzeichnis
acronym, % Abkürzungsverzeichnis erstellen
nomain, % kein Glossar
translate=babel,%
nogroupskip,% Vertikaler Spalt
toc,% Verlinkung im Inhaltsverzeichnis
section=chapter,%
]{glossaries}
% Code were error occurs
\underline{\parbox{\linewidth}{\textbf{Overall redox reaction}}}
\begin{reactions}
16 Li + S8 &<=> 8 Li2S\label{reac:Overall}
\intertext{\underline{\parbox{\linewidth}{\textbf{Anode reaction}}}}
Li &<=> Li+ + e-\label{reac:Li}
\end{reactions}
\underline{\parbox{\linewidth}{\textbf{Cathode reactions}}} \begin{minipage}[t]{0.4\textwidth}
\begin{center}
\textit{Electrochemical reactions}\\
\end{center}
\begin{reactions}
S8 + 2 e- &<=> S8^{2-} \label{reac:S82}
%
S8^{2-} + 2 e- &<=> 2 S4^{2-} \label{reac:S42} \\
S42^{2-} + 2 e- &<=> 2 S2^{2-} \label{reac:S22} \\
S22^{2-} + 2 e- &<=> 2 S2^{2-}\label{reac:S2}
\end{reactions}
\end{minipage}%
\begin{minipage}[t]{0.6\textwidth}
\begin{center}
\textit{Precipitation/dissolution reactions}\\
\end{center}
\begin{reactions}
S8 \lqd &<=> S8 \sld \label{reac:S8s} \\
2 Li+ + S2^{2-} \lqd &<=> Li2S2 \sld \label{reac:Li2S2} \\
2 Li+ + S2- \lqd &<=> Li2S \sld \label{reac:Li2S} \\
Li2S2 \sld + 2 Li+ + 2 e- \lqd &<=> 2 Li2S \sld \label{reac:2_Li2S}
\end{reactions}
\end{minipage} \\
...
不幸的是，小页面中的标签在编译时会出现错误：
'! Undefined control sequence.
<argument> reac:S\chemformula
_subscript:n {8}\chemformula _subscript:n {2}
l.144 ...ral working principle}{equation.2.1.3}{}}'
我希望这足以说明我的问题（这是我在 Stack Exchange 上提出的第一个问题）当我注释掉 minipages 中的标签并仅保留前两个标签时，一切正常。即使不更改参考编号，问题也会出现。
答案1
您的代码可以简化为以下更短的示例，但在编译时仍会产生错误消息：
\documentclass{report}
\usepackage{chemmacros}
\chemsetup{modules={all}}
\begin{document}
\begin{reactions}
S8 + 2 e- &<=> S8^{2-} \label{reac:S82}
\end{reactions}
\end{document}
为了修复这个问题，\label用一组包围" ... "：
\documentclass{report}
\usepackage{chemmacros}
\chemsetup{modules={all}}
\begin{document}
\begin{reactions}
S8 + 2 e- &<=> S8^{2-} "\label{reac:S82}"
\end{reactions}
\end{document}
另请参阅：手册的“8.转义输入”一节chemformula。
将其应用到您的示例中，我们最终得到以下 MWE，它应该编译时不会出现错误消息：
\documentclass{report}
\usepackage{chemmacros}
\chemsetup{modules={all}}
\begin{document}
\noindent\underline{\parbox{\linewidth}{\textbf{Overall redox reaction}}}
\begin{reactions}
16 Li + S8 &<=> 8 Li2S \label{reac:Overall}
\intertext{\underline{\parbox{\linewidth}{\textbf{Anode reaction}}}}
Li &<=> Li+ + e- \label{reac:Li}
\end{reactions}
\underline{\parbox{\linewidth}{\textbf{Cathode reactions}}}
\begin{minipage}[t]{0.4\textwidth}
\centering
\textit{Electrochemical reactions}
\begin{reactions}
S8 + 2 e- &<=> S8^{2-} "\label{reac:S82}"\\
S8^{2-} + 2 e- &<=> 2 S4^{2-} "\label{reac:S42}" \\
S42^{2-} + 2 e- &<=> 2 S2^{2-} "\label{reac:S22}" \\
S22^{2-} + 2 e- &<=> 2 S2^{2-} "\label{reac:S2}"
\end{reactions}
\end{minipage}%
\begin{minipage}[t]{0.6\textwidth}
\centering
\textit{Precipitation/dissolution reactions}
\begin{reactions}
S8 \lqd &<=> S8 \sld{} "\label{reac:S8s}" \\
2 Li+ + S2^{2-} \lqd &<=> Li2S2 \sld{} "\label{reac:Li2S2}" \\
2 Li+ + S2- \lqd &<=> Li2S \sld{} "\label{reac:Li2S}" \\
Li2S2 \sld{} + 2 Li+ + 2 e- \lqd &<=> 2 Li2S \sld{} "\label{reac:2_Li2S}"
\end{reactions}
\end{minipage}
\end{document}