By definition, a table of contents is a listing of the contents of the
document in the order in which those contents occur. A sorted list of the
document's contents is an index. Word has better ways to create an index
than using the TOC functions.
But if you really must: create the TOC as normal. Select it all. Press
Ctrl-Shift-F9 to unlink the field contents. Use Table > Sort. Note that the
page numbers will no longer update automatically. If you change the document
contents you'll need to re-do the whole process. (Which is why this is a
lousy way to create an index.)
