Anhydride, mixed

With higher aliphatic acids, RCOOH, keten yields first a mixed anhydride CH3COOCOR, which can be distilled under reduced pressure by slow distillation at atmospheric pressure the mixed anhydride undergoes rearrangement into the anhydride of the higher fatty acid and acetic acid, for example ... 

The preparation of a-phenylclnnamlc acid from benzaldehyde, phenylacetic acid, acetic anhydride and triethylamine is described. Presumably equilibria are set up between phenylacetic acid and acetic anhydride to form phenylacetic anhydride, a mixed anhydride or both ... 

The desired pyridylamine was obtained in 69 % overall yield by monomethylation of 2-(aminomethyl)pyridine following a literature procedure (Scheme 4.14). First amine 4.48 was converted into formamide 4.49, through reaction with the in situ prepared mixed anhydride of acetic acid and formic acid. Reduction of 4.49 with borane dimethyl sulfide complex produced diamine 4.50. This compound could be used successfully in the Mannich reaction with 4.39, affording crude 4.51 in 92 % yield (Scheme 4.15). Analogous to 4.44, 4.51 also coordinates to copper(II) in water, as indicated by a shift of the UV-absorption maximum from 296 nm to 308 nm. 

Solutions of dinitrogen tetroxide (the mixed anhydride of nitric and nitrous acids) in sulphuric acid are nitrating agents ( 4.3.2), and there is no doubt that the effective reagent is the nitronium ion. Its formation has been demonstrated by Raman spectroscopy and by cryoscopy ... 

APA may be either obtained directly from special Penicillium strains or by hydrolysis of penicillin Q with the aid of amidase enzymes. A major problem in the synthesis of different amides from 6-APA is the acid- and base-sensitivity of its -lactam ring which is usually very unstable outside of the pH range from 3 to 6. One synthesis of ampidllin applies the condensation of 6-APA with a mixed anhydride of N-protected phenylglydne. Catalytic hydrogenation removes the N-protecting group. Yields are low (2 30%) (without scheme). 

The decarbonylation-dehydration of the fatty acid 887 catalyzed by PdCl2(Ph3P)2 fO.Ol mol%) was carried out by heating its mixture with acetic-anhydride at 250 C to afford the terminal alkene 888 with high selectivity and high catalyst turnover number (12 370). The reaction may proceed by the oxidative addition of Pd to the mixed anhydride[755]. 

The product is a mixed anhydride Acetic acid acts as a nucleophile and substi tutes for chloride on the benzoyl group... 

Loss of a proton and of chloride ion from the tetrahedral intermediate yields the mixed anhydride... 

This procedure is applicable to the preparation of both symmetrical anhydrides (R and R the same) and mixed anhydrides (R and R different)... 

The 7 glutamyl phosphate formed m this step is a mixed anhydride of glutamic acid and phosphoric acid It is activated toward nucleophilic acyl substitution and gives glutamine when attacked by ammonia... 

Acid Anhydrides. Symmetrical anhydrides of monocarboxylic acids, when unsubstituted, are named by replacing the word acid by anhydride. Anhydrides of substituted monocarboxylic acids, if symmetrically substituted, are named by prefixing bis- to the name of the acid and replacing the word acid by anhydride. Mixed anhydrides are named by giving in alphabetical order the first part of the names of the two acids followed by the word anhydride, e.g., acetic propionic anhydride or acetic propanoic anhydride. Cyclic anhydrides of polycarboxylic acids, although possessing a... 

Fluorosulfuric acid [7789-21-17, HSO F, is a colodess-to-light yellow liquid that fumes strongly in moist air and has a sharp odor. It may be regarded as a mixed anhydride of sulfuric and hydrofluoric acids. Fluorosulfuric acid was first identified and characterized in 1892 (1). It is a strong acid and is employed as a catalyst and chemical reagent in a number of chemical processes, such as alkylation (qv), acylation, polymerization, sulfonation, isomerization, and production of organic fluorosulfates (see Friedel-CRAFTSreactions). 

The anhydride of formic acid has not been isolated, but mixed anhydrides are known, and, with acetic acid, the latter have utifity as formylating agents (22). The only known formyl haUde is the fluoride, which has a boiling poiat of —29° C. 

The rearrangement is self-cataly2ed by the organosulfonic acid that is already present or acid from hydrolysis of the mixed anhydride product. If the... 

AijAT-dicyclohexylcarhodiimide (DCC) also leads to essentially quantitative conversion of amic acids to isoimides, rather than imides (30,31). Combinations of trifluoroacetic anhydride—triethjlarnine and ethyl chi oroform a te—triethyl amine also result in high yields of isoimides (30). A kinetic study on model compounds has revealed that isoimides and imides are formed via a mixed anhydride intermediate (12) that is formed by the acylation of the carboxylic group of amic acid (8). 

Fig. 2. Cyclization of amic acid to imides or isoimides via (12). Formation of the mixed anhydride intermediate (12) is shown in text.

Benzoyl chloride and sodium isopropyl xanthate gave a mixed anhydride that was stable to pyridine catalyst, but a 2-year-old sample had turned to isopropyl ben2oate (16). 

Anhydride of chloric acid, Cl20, is unknown. Oxides with even number of oxygen atoms are mixed anhydrides. Other chlorine oxides such as the radicals CIO, CIO, and CIO are known. Chlorine monoxide [14989-30-17, CIO, plays a key role in depletion of the o2one layer. 

The chlorine oxides are anhydrides or mixed anhydrides of the chlorine oxo-acids oxides with an odd number of oxygens are simple anhydrides whereas those with an even number are mixed anhydrides. 

The use of dehydrating agents such as sulfuric or phosphoric acid on (555 X = OH) was also successful, and these closures may proceed via mixed anhydrides 67AHC(8)277, 75MIP41600). Carbonyldiimidazole effected the conversion of hydroxamic acid (557) into a 3-hydroxy-1,2-benzisoxazole derivative (79JHC1277). The mixed anhydride (558) where... 

The aziridinecarboxylate (177) undergoes ring expansion in good yield, possibly via a mixed anhydride, on treatment with thionyl or oxalyl chlorides in benzene (69JA4590). 

At Smith Kline French a general approach to cephalosporin and penicillin nuclear analogs was developed that utilizes a monocyclic /3-lactam (59) with the correct cis stereochemistry as a key intermediate. This is prepared by reaction of the mixed anhydride of azidoacetic acid and trifluoroacetic acid with imine (58) followed by oxidative removal of the dimethoxybenzyl group. This product could be further elaborated to intermediate (60) which, on reaction with a -bromoketones, provides isocephalosporins (61). These nuclear analogs displayed antibacterial properties similar to cephalosporins (b-79MI51000). 

Decaitxjxylallon of a mixed anhydride (Ihlohydtoxamlc-cartwxylic) and interception of radicals as a sulfide, selenide or bromo denvative. 

Carboxylic acids react with trifluoroacetic anhydride to give mixed anhydrides that are especially useful for the acylation of hindered alcohols and phenols ... 

The active acylating agent may be the protonated mixed anhydride, or, alternatively, the anhydride m dissociate to the acylium and trifluoroacetate ions ... 

Mechanism I was ruled out by an isotopic labeling experiment. The mixed anhydride of salicylic acid and acetic acid is an intermediate if nucleophilic catalysis occurs by mechanism 1. This molecule is known to hydrolyze in water with about 25% incorporation of solvent water into the salicylic acid. 

Sodium acetate reacts with /p-nitrophenyl benzoates to give mixed anhydrides if the reaction is conducted in a polar aprotic solvent in the presence of a crown ether. The reaction is strongly accelerated by quartemary nitrogen groups substituted at the orthc position. Explain the basis for the enhanced reactivity of these compounds. 

These authors suggest that the reaction may proceed through the formation of their mixed anhydrides , and illustrate a metal ion templated, mixed carboxylic-sulfonic anhydride. 

Mixed anhydrides of a carboxylic acid and trifluoroacetic or triflic acids... 

Selectivity and reactivity of mixed anhydrides toward primary and secondary aliphatic and aromatic amines has been studied in details [42, 43] (equation 22) Fluorocarboxyhc acids and then denvahves are used as building blocks m condensa non reactions widi dmucleophihc species for the synthesis of fluoroalkyl-subshtuted lieteroaromahc systems [S 9, 40, 44, 45, 46, 47 4S] (equations 20 21, and 23)... 

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