Dichloroacetic anhydride

Figure 11. Acylation reactions of ethylenethiourea (ETU) with dichloroacetic anhydride (DCAA) and dichloroacetyl chloride (DCACl)...

A more general and effective modification of the reagent is the system (RC00)Re03/(RC0)20, particularly the (dichloroacetyl)perrhenate with excess dichloroacetic anhydride, which is suitable for iyn-oxidative cyclization of acid-sensitive substrates (in the same reaction as described above). 

Water added during 5 min. to 2 moles trichloroacetyl chloride, and heated 1 hr. at 80-90° tridiloroacetic anhydride. Y 99%. Also dichloroacetic anhydride s. G. I. Kovalenko and B. G. Yasnitskii, Metody Poluch. Khim. Reaktiv. Prep. 1970, No. 21, 111 C. A. 76, 85329. 

The hydroxyl groups in polyesters are determined hy acetylation with an excess of dichloroacetic anhydride in dichloroacetic acid, and measurement of the amount of acetylation by chlorine determination. Owing to the low concentration of hydroxyl groups (especially in high relative molecular weight materials), determination of the excess is inaccurate, so determination of the amount of reagent incorporate is much more attractive. 

The derivatisation of the polyester is carried out in a 10% mmol solution of dichloroacetic anhydride in dichloroacetic acid at 60 °C. A reaction time of 1 hour suffices. After the reaction, the solution is poured into water and the precipitated polymer washed out. To remove the last traces of solvent and acetylation agent, reprecipitation of the derivatised polymer from a hexafluoroisopropanol solution into water is carried out. For polymers with low hydroxyl content (<100 mmol/kg), reprecipitation is carried out from a solution in nitrobenzene into cold light petroleum to obtain more reproducible results. 

The hydroxyl groups in these products are determined by acetylation with an excess of dichloroacetic anhydride in dichloroacetic acid at 60 C and measurement of the amoimt of acetylation by a chlorine determination either by potentiometric titration with silver ions after combustion or by X-ray fluorescence spectroscopy of a compressed disc of the polymer. The suitability of this method for a number of samples is demonstrated in Table 1.12. The standard deviation of the method for high relative molecular weight polymers is 0.7 mmol kg whereas for the low relative molecular weight materials, it is about 10 mmol kg ... 

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