Formation anhydride

The reason for using an excess of,sny, 1 mol of thionyl chloride is to avoid anhydride formation ... 

Anhydride Formation. The carboxyl group ia A/-protected amino acids is converted iato the symmetrical anhydride on treatment with the carbodiimide (84). 

The reaction is not suitable for hindered carboxylic acids, since considerable symmetrical anhydride formation (52% with pivalic acid) results. Symmetrical anhydride formation can sometimes be suppressed by the use of stoichiometric quantities of DMAP. 

Acetic anhydride formation has been observed under such conditions. ... 

Salts are sometimes added to drilling muds to obtain certain desired mud characteristics. They can also enter the drilling fluid through contamination by addition of makeup water, formation-fluid inflow, and drilled formations such as salt domes, gypsum or anhydride formations. In freshwater systems, if salt contamination reaches undesirable levels, the following methods should be considered for control. 

Et3N, EtaO, -78 -> 0 °C (mixed anhydride formation then... 

The reaction is highly exothermic with a AH of -170 kJ/gmol. Due to the slow second reaction aging is required to convert the formed pyrosulfonic acid with alkylate to the desired end product LAS (Table 2). There are two main side reactions anhydride formation and sulfone formation. 

The phosphinic isocyanates (116) and isothiocyanates (117) react with oxygen, nitrogen, and phosphorus nucleophiles by attack at carbon rather than phosphorus. Phenyl phosphonodichloridate has been recommended as a useful reagent for the activation (presumably by mixed anhydride formation) of carboxylic acids for conversion to amides and hydrazides. ... 

Citraconic anhydride formation from pyruvic acid by oxidative decarboxy-condensation has not been known prior to these studies. Therefore, in this paper, we attempted to get more insight into the new reaction. 

The results shown in Figure 4 indicate that the oxygen dependency of the acetic acid formation is higher than that of the citraconic anhydride formation. Therefore, use of a low oxygen concentration is beneficial to the selectivity to citraconic anhydride, though it is disadvantageous to the reaction rate. 

As may be seen in Figures 5 and 6, when iron phosphate is used as the catalyst, the selectivity is dependent largely on the reaction temperature. Therefore, the activation energy for the citraconic anhydride formation is considered to be much lower than that for the acetic acid formation. Indeed, the selectivity to acetic acid decreases steadily with a decrease in the temperature. However, the selectivity to citraconic anhydride shows a maximum at about 200 C. Possibly, the vaporization of pyruvic acid may become difficult at temperatures below 200°C. 

Drivers for Performing Maieic Anhydride Formation in Micro Reactors... 

Beneficial Micro Reactor Properties for Maleic Anhydride Formation... 

The equilibrium in this first step favors tlie shift to anhydride formation if the second mole of carboxylic acid in the second step with forms imidazole to form a salt that is insoluble in the solvent used (ether, tetrahydrofuran, benzene). 

Intermediate anhydride formation by means of TV-trifluoroacetylimidazole has been employed in the preparation of /7-nitrophenylesters of TV-protected amino acids, which are important in peptide synthesis. 31... 

One further point. In all the cases of anhydride formation discussed, the displacing ion has been anionoid oxygen derived from a hydroxyl... 

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