Acetic anhydride, as solvent

Perfluoroalkylation can be accomplished via direct reaction of peifluoroalkyl halides and copper with aromatic substrates [232, 233, 234, 235, 236] Thus, perfluoroalkyl iodides or bromides react with functionalized benzenes m DMSO m the presence of copper bronze to give the corresponding perfluoroalkylated products directly in moderate to good yields [233] (equation 157) Mixtures of ortho, meta, and para isomers are obtained [232, 233], The use of acetic anhydride as solvent gives similar results [234, 235], Similarly, the direct reaction of perfluoroalkyl iodides and pyrroles with copper metal regiospecifically gives the 2-perfluoroalkylpyrroles [236] (equation 158). 

Bis[4-methoxyphenyl] Tellurium Diacetate (Acetic Anhydride as Solvent)1 A mixture of 3.84 g (11 mmol) of bis[4-methoxyphenyl] tellurium oxide and 10.8 g (10 ml 106 mmol) of acetic anhydride is heated under reflux for 30 min. The mixture is then allowed to cool and is poured into 100 m/ of water. The aqueous mixture is heated until excess acetic anhydride has been decomposed, cooled, and the deposited crystals are filtered off, and recrystallized from chloroform/petroleum ether yield 3.8 g (73%) m.p. 139°. 

We shall begin by a consideration of some semiquantitative observations for nitration. We have already mentioned that Melander has shown that this reaction, at least in a mixture of nitric and sulfuric acids, follows mechanism 2a. Dewar31 has measured the ratios k /k of the rates of reaction for the nitration of several aromatic hydrocarbons. Unfortunately Dewar s experimental conditions are not the same as those of Melander. He used acetic anhydride as solvent and nitrated with pure nitric acid in the presence of an excess of hydrocarbon in order to obtain only the mononitro derivative. It is not certain that Melander s conclusions would be valid in this particular way of carrying out the nitration. Still it is interesting to see if the constants k do vary in the same way as the free valence. 

Early work utilised acetic anhydride as solvent with the incorporation of an oxidising agent, often iron(ni) chloride (though it is beheved that the acylium cation is the hydride acceptor) latterly the incorporation of 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, 2,6-dimethylpyrylium or, most often, the triphenyhnethyl cation have proved efhcient. In some cases the AH-pyxm is isolated then oxidised in a separate step. ... 

Formaldehyde undergoes thermal ene reactions with reactive 1,1-disubstituted and trisubstituted alk-enes at 180-220 °C. 3-Pinene, a particularly reactive ene component, reacts with formaldehyde at 180 C to give nopol in 95% yield (equation 5). Methylenecyclohexane reacts similarly. Blomquist extended the scope of these reactions by using acetic acid-acetic anhydride as solvent at 180-190 °C. °... 

When potassium permanganate is used as oxidizing agent the alkali concentration that builds up in the mixture as reaction proceeds is often a hindrance it can be avoided by buffering with salts or by use of, e.g., acetic anhydride as solvent. 

The authors have also investigated the preparation of the 2-thioxo-5-imidazolidin-4-ones 17 from thiohydantoin 16 in the presence of potassium acetate, with acetic anhydride as solvent, using both methods. Here, the effect of microwave irradiation was reduction of reaction times and a small increase in the yields. 

Suppose we consider some very weakly basic compounds, such as ketimines, phosphines, and oxiranes. A very interesting method of dealing with oxiranes was developed by Durbetaki. The oxirane was reacted with hydro-bromic acid to form the bromohydrln. This type of reaction has long been known using hydrochloric acid, but in that medium the reaction takes approximately three hours. In glacial acetic acid, the reaction is enough to allow you to titrate directly at normal speed. You can get an end point potentiometrically or with an indicator. In fact, if you have a mixture of amine and oxirane, you can get two potentlometric breaks, the first for the amine and the second for the oxirane. Amides, phosphene oxides, triphenyl methanol, and amine oxides are very weak bases and cannot be titrated in glacial acetic acid under ordinary conditions. However, they can be titrated if one uses acetic anhydride as solvent, or if one uses a solvent that is mixed with acetic anhydride. Why does acetic anhydride work There are two reasons. First, it removes the last trace of water from the solution secondly, perchloric acid in the presence of acetic anhydride forms the ion CHsCO". Since this is an extremely reactive substance, one can titrate very weak bases. 

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