[Beatle]

The role of using azeotropic distillation, i find interesting, because in short, often what gets eliminated in reactions, are species that reverse the initial reaction to begin with, and one common eliminated specie, is H2O.

This is classically known, for the difficulties in synthesising, or simply attempting to distill absolute ethanol. What appears to occur, when ethanol is distilled, a point is reached when the liquid contains 95% ethanol, in conjunction with 5% water, as well as the vapour phase containing this exact ratio, hence with simple distillation of ethanol, the purest one could obtain is the 95% concentration.
 
Then in the history of chemistry, a history, I am new at learning about, came fourth the inclusion of a third specie, and in the case of ethanol:water, in came benzene, and benzene via intermolecular forces, created what is coined an azeotrope, that is a mixture of set amounts of benzene and water, that has a boiling point, lower than ethanol, as well as water, and along came Dean Stark traps, that result in the lowest boiling point specie, or mixture, as an azeotrope is, will enter an upward projected condenser, and when the vapour of this mixture is condensed to its more typical state, and temperature, a downward funnel was designed that when the azeotrope separated, the denser specie of the azeotrope, sinks to the bottom of a trap, that usually includes a tap, so that the water in the described case, is not only separated, but removed, and the top layer of this trap, the less dense specie will fill up, and end up reentering the refluxing flask, to potentially continue the process of removing the eliminated water.

Now learning about this, I wondered, if for an example, acetic acid was in a system of refluxing, being acid catalysed, thus forming one acetic acid to have its carbonyl group protonated, turning it into a more appealing electrophile, for another acetic acid, to act with its OH group of the COOH group to attack, via a 1,2 addition, hence behaving as a nucleophile, so the reaction I believe is the 1,2 - addition, followed by a 1,2-elimination, and what is eliminated is H2O, that if left in check would no doubt hydrolyse the formed anhydride specie, which led me to wonder if toluene, was added, and it still being acid catalysed, would an azeotrope form of a ratio of water and toluene, behaving like benzene and water, for the removal of water for anhydride preparations.

There seems to be an issue of so much reagents compared to products, that suggesting this elsewhere, the potential for products like an alkanoic anhydride as well as water, and toluene, being associated, till the trap, that if there was enough protons in the mix, maybe there would be enough acetic acid molecules reacting as described, and slowly shifting the equilibrium to the right. 

I was advised that acids and water also apparently form azeotropes, and that the water would not form the required union with toluene, due to the hold the acid and water have, but in a refluxing system, as well as learning that, protons can also be included in an azeotropic mixture, I felt that in time, the many dynamics associated with this potential, could even out, and actually be shown to be fruitful.

I am asking this, with a basic grasp of these concepts. Acetyl halides, and alkanoic anhydrides are useful to acetylate molecules, as, for an e.g. acetyl chloride, has its carbonyl attacked by nucleophilic addition reactions, where chlorine acts as a good leaving molecule, which is the same for anhydrides equally good, as they eliminate a resonantly stabilised leaving group.

Acetyl chlorides are usually produced with acetic acid and reagents like SOCl2, or PCl3, PCl5, etc, and using toluene, with a simple Dean Stark trap, seemed appealing to at least explore its potential role in producing anhydrides.

This of course is not limited to acetic acid, but there are all the longer chained alkanoic acids, and even benzoic acid, potentially being a player.

Thanks in advance to helping me grasp these concepts, if so done, and I appreciate being able to ask such questions, in a forum that appears to understand, we are likely to be at different levels of our understanding of chemistry as a practising art.

[pgk]

Dear Beatle,
1). Please, just ask a question in the most laconic way, you can because nobody reads long texts with pleasure.
2). The order of water removing yield by azeotropy is: xylene (30% w/w), toluene (20% w/w), benzene (9% w/w). Furthermore, benzene is highly toxic and carcinogenic.
3). You do not need to add toluene because chlorinated agents are usually liquids that are added in excess and thus, adequate solvents.
4). Besides, there is no formation of water during acyl chlorides preparation with the described reagents.
5). The byproducts of acyl chlorides preparation are usually removed by distillation with the help of a Claisen still head that is connected with flask’s condenser. Instead, you can use a Dean Stark apparatus but this needs enough experience.
6). I fully apologize if not having precisely answered and if not having well understood your questions but I didn’t read you text, in detail because it is too long.
Sincerely yours
pgk 

[Beatle]

Points noted, and will reduce such writing to prevents readers eyes rolling over like a cheap glazed donut. Apologies, but its a learning curb.

One point I will make is, I wasnt implying DS conditions for the formation of acetyl halides, just made mention of them, as they are the usual route, I believe, to the formation of alkanoic anhydrides.

I will revise, and present questions that are more direct, and thanks for the heads up.