ESTERS AND ANHYDRIDES

Phosphoric acid can form esters with alcohols. It can form monoesters, diesters, and triesters. A general representation of the formation of phosphoesters is given below. R represents the alkyl group. 

At nonnal biological pH range (7.35-7.45), the phosphate esters usually show a double negative charge. This property of the phosphate esters makes them generally water soluble, and thus perfect for the physiological environment in our body. 

Phosphoric acid is an integral part of some of the most important biomolecules in our body. 

Reaction 1 depicts the conversion of phospho-enol pyruvate to pyruvate. 

Phosphate is a part of many high-energy compoimds in biological systems. Examples include ATP (adenosine triphosphate)) and GTP (guanosine triphosphate). 

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It is convenient to consider the indiflferent or neutral oxygen derivatives of the hydrocarbons—(a) aldehydes and kelones, (b) esters and anhydrides, (c) alcohols and ethers—together. All of these, with the exception of the water-soluble members of low molecular weight, are soluble only in concentrated sulphuric acid, i.e., fall into Solubility Group V. The above classes of compounds must be tested for in the order in which they are listed, otherwise erroneous conclusions may be drawn from the reactions for functional groups about to be described. 

When the compound for identification fails to respond to test 4 (aldehyde or ketone), the next class reactions to apply are the hydroxatnic acid teat and saponification, i.e., hydrolysis in alkaline solution. These are the class reactions for esters and anhydrides the rarely-encountered lactones react similarly. 

The production of both an alcohol and the sodium salt of an acid might easily be confused with the hydrolysis products of an ester (in the above instance benzyl benzoate). Such an error would soon be discovered (e.g., by reference to the b.p. and other physical properties), but it would lead to an unnecessary expenditure of time and energy. The above example, however, emphasises the importance of conducting the class reactions of neutral oxygen-containing compounds in the proper order, viz., (1) aldehydes and ketones, (2) esters and anhydrides, (3) alcohols, and (4) ethers. 

If the unknown neutral, oxygen-containing compound does not give the class reactions for aldehydes, ketones, esters and anhydrides, it is probably... 

Nitrogen is a better electron parr donor than oxygen and amides have a more stabilized carbonyl group than esters and anhydrides Chlorine is the poorest electron pair donor and acyl chlorides have the least stabi lized carbonyl group and are the most reactive... 

Just as most other aldehydes do, furfural condenses with compounds possessing active methylene groups such as aUphatic carboxyUc esters and anhydrides, ketones, aldehydes, nitriles, and nitroparaffins. 

Solid Peroxygen Compounds. Hydrogen peroxide reacts with many compounds, such as borates, carbonates, pyrophosphates, sulfates, sihcates, and a variety of organic carboxyHc acids, esters, and anhydrides to give peroxy compounds or peroxyhydrates. A number of these compounds are stable sohds that hydrolyze readily to give hydrogen peroxide in solution. 

Under Barbier conditions, trifluoromethyl bromide reacts with electrophiles, such as aldehydes, Orkelo esters, activated esters, and anhydrides in the presence of pyridine to give trifluoromethylated compounds [35, 45 46] (equations 34 37)... 

Stability toward reduction makes hydrogen fluoride a good medium for different hydrogenation processes [1, 2] It is a useful solvent for the hydrogenation of benzene in the presence of Lewis acids [f ] Anhydrous hydrofluonc acid has pronounced catalytic effect on the hydrogenations of various aromatic compounds, aliphatic ketones, acids, esters, and anhydrides in the presence of platinum dioxide [2] (equations 1-3)... 

Comp.ne the ai tion of caustic tdkalis on ethers, esters and anhydrides. 

Phosphate esters and anhydrides dominate the living world. Major areas of synthetic interest include oligonucleotides (polymeric phosphate diesters), phospho-rylated peptides, phospholipids, glycosyl phosphates, and inositol phosphates. ... 

Cationic copolymerization of cyclic ethers, formals, esters and anhydrides has been thoroughly studied in recent years and sufficient information about it is now available. The propagating species involved in the cationic copolymerization of these oxacyclic monomers are believed to be the oxonium ions in most cases, but their detailed nature is dependent on monomer structure. From their copolymerization behavior, these monomers can be arranged in the following order of increasing car-bocationic character of the propagating species ... 

These reactions are most important for the preparation of acyl fluorides. " Acyl chlorides and anhydrides can be converted to acyl fluorides by treatment with polyhydrogen fluoride-pyridine solution" or with liquid HF at — 10°C. Formyl fluoride, which is a stable compound, was prepared by the latter procedure from the mixed anhydride of formic and acetic acids. Acyl fluorides can also be obtained by reaction of acyl chlorides with KF in acetic acid or with DAST. Carboxylic esters and anhydrides can be converted to acyl halides other than fluorides by the inorganic acid halides mentioned in 10-77, as well as with PhsPXa (X = Cl or but this is seldom done. Halide exchange can be carried out in a... 

Reduction of Carboxylic Acids, Esters, and Anhydrides to Aldehydes ... 

The photolysis of carboxylic acids and derivatives as lactones, esters and anhydrides can yield decarboxylated products 253>. This reaction has been utilized in the synthesis of a-lactones from cyclic diacyl peroxides 254) (2.34) and in the synthesis of [2,2]paracyclophane by bis-decarboxylation of a lactone precursor (2.35) 255). This latter product was also obtained by photoinduced desulfurization of the analogous cyclic sulfide in the presence of triethyl phosphite 256). 

Carbodiimides are, in general, useful compounds for effecting certain dehydrative condensations, e.g., in the formation of amides, esters, and anhydrides. These two crystalline water-soluble carbodiimides are especially useful in the synthesis of peptides and in the modification of proteins. The excess of reagent and the co-product (the corresponding urea) are easily separated from products with limited solubility in water. The hydrochloride is best employed in nonaqueous solvents (methylene chloride, acetonitrile, dimethylformamide). The methiodide is relatively stable in neutral aqueous systems, and thus is recommended for those media. 

Attempted simple oxidation of alkyl groups on thianthrenes would also effect 5-oxidation. However, sulfones can be side-chain-oxidized 2,3,6,7-tetramethyl-, 1,2,7,8-tetramethyl-, 1,4,6,9-tetramethyl-, and 1,3,7,9-tetra-methylthianthrene tetroxides gave the tetra-acids with 25% HNO3 at 220°C. These tetra-acids were converted to esters and anhydrides in the usual ways (69USP3410868). 

Copolymers of vinyl chloride with vinyl acetate and maleic anhydride are made more adhesive to metals through hydrolysis of the ester and anhydride units. 

The catalyst components are generally dissolved in methyl acetate which acts as both reactant and solvent. Other solvents may be used and in fact, upon several batch recycles where lower boiling products are distilled off, the solvent is an ethylidene diacetate-acetic acid mixture. Any water introduced in the reaction mixture will be consumed via ester and anhydride hydrolysis, therefore anhydrous conditions are warranted. Typical batch reaction examples are presented in Table 1. There is generally sufficient reactivity when carbon monoxide and hydrogen are present at 200-500 psi. Similar results were obtained from the pilot plant using a continuous stirred tank reactor (CSTR). The reaction can also be run continuously over a supported catalyst with a feed of methyl acetate, methyl iodide, CO, and hydrogen. 

Oxoalkylphosphonic acids can be hydrolyzed in this way (119), as in the enzyme-catalyzed hydrolysis of phosphonoacetaldehyde (73, 69-71), but with much more difficulty. The lability of 2-oxoalkylarsonic acids presumably reflects the ease with which water can more easily enter the coordination shell of arsenic than that of phosphorus, because of the larger size of the atom, i.e., the same feature expressed in the lability of esters and anhydrides of arsenate. 

Synthesis of esters and anhydrides from carboxylic acids. 

A chemist s description of the unique suitability of phosphate esters and anhydrides for metabolic transformations. 

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