prov:value
| - C., but preferably at the boiling temperature of the reaction mixture, optionally in the presence of a condensing agent such as phosphorus oxychloride, thionyl chloride, sulphuryl chloride, sulphuric acid, p-toluenesulphonic acid, methanesulphonic acid,hydrochloric acid, phosphoric acid, polyphosphoric acid, acetic acid, acetic anhydride, N,N-dicyclohexyl-carbodiimide or optionally also in the pre
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