Carboxylic acids, esters and anhydrides

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

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

Acyl iodides.1 This reagent converts acyl chlorides into acyl iodides at 25°. In combination with iodine (1 1) it also converts carboxylic acids, esters, and anhydrides into acyl iodides in generally high yield. This reaction in combination with an alcohol is a useful method for transesterification of hindered alcohols. 

At a first glance it may appear eccentric to show interest in the basicities of carboxylic acids. However, this is not as curious as it seems, since protonated carboxylic acids and their derivatives play the role as important intermediates during acid-catalysed reactions of these compounds. As a matter of fact, Scheele showed as early as in 1782 that addition of sulphuric acid to a mixture of acetic acid and ethanol accelerated esterification [192]. In this respect it is a key point that carboxylic acids, esters and anhydrides possess two oxygens which are po-... 

Reactions of the [Co(NH3)sOH] or [Co(NH3)50H2] ion with a range of species including NO+ 8 NCO, COj, SO2, carboxylic acid esters and anhydrides,acetyl-acetone, HSeOs , Mo04 , H2As04"/HAs04 and HIO3 take place at... 

Table 11.1-23. Lipase-catalyzed enantiomer- and enantiotopos-differentiating alcoholysis of carboxylic acid esters and anhydrides, alcoholysis or hydrolysis of oxazolin-2-ones, and esterification of carboxylic acids (PPL pig pancreas lipase, PCL Pseudomonas cepacia lipase, ANL Aspergillus niger lipase, CSL Candida sp. lipase, Candida cylindracea lipase, CAL-B Candida antarctica B lipase, CRL Candida rugosa lipase).

BF3 OEt2 followed by Diisobutylaluminum Hydride is used for the 1,2-reduction of y-amino-a,p-unsaturated esters to give unsaturated amino alcohols, which are chiral building blocks for a-amino acids. a,p-Unsaturated nitroalkenes can be reduced to hydroxylamines by Sodium Borohydride and BF3-OEt2 in THF extended reaction times result in the reduction of the hydroxylamines to alkylamines. Diphenylamine-borane is prepared from sodium borohydride, BF3-OEt2, and diphenylamine in THF at 0°C. This solid is more stable in air than BF3-THF and is almost as reactive in the reduction of aldehydes, ketones, carboxylic acids, esters, and anhydrides, as well as in the hydrob-oration of alkenes. 

Conversions of acid anhydrides to other carboxylic acid derivatives are illustrated m Table 20 2 Because a more highly stabilized carbonyl group must result m order for nucleophilic acyl substitution to be effective acid anhydrides are readily converted to carboxylic acids esters and amides but not to acyl chlorides... 

Carboxylic acid hydiazides are prepared from aqueous hydrazine and tfie carboxylic acid, ester, amide, anhydride, or halide. The reaction usually goes poody with the free acid. Esters are generally satisfactory. Acyl halides are particularly reactive, even at room temperature, and form the diacyl derivatives (22), which easily undergo thermal dehydration to 1,3,4-oxadiazoles (23). Diesters give dihydtazides (24) and polyesters such as polyacrylates yield a polyhydrazide (25). The chemistry of carboxyhc hydrazides has been reviewed (83,84). 

The most common O- and N-acylation procedures use acylating agents that are more reactive than caiboxylic acids or their esters. Carboxylic acid chlorides and anhydrides react rapidly with most unhindered hydroxy and amino groups to give esters and amides, respectively ... 

A number of other methods exist for the a halogenation of carboxylic acids or their derivatives.134 The acids or their chlorides or anhydrides can be a chlorinated by treatment with CuCl in polar inert solvents (e.g., sulfolane).135 Acyl halides can be a brominated or chlorinated by use of N-bromo- or N-chlorosuccinimide and HBr or HC1.136 The latter is an ionic, not a free-radical halogenation (see 4-2). Direct iodination of carboxylic acids has been achieved with L-Cu(II) acetate in HO Ac.137 Acyl chlorides can be a iodinated with L and a trace of HI.138 Carboxylic esters can be a halogenated by conversion to their enolate ions with lithium N-isopropylcyclohexylamide in THF and treatment of this solution at - 78° with I2138 or with a carbon tetrahalide.139 Carboxylic acids, esters, and amides have been a fluorinated at -78°C with F2 diluted in Ni.,4°... 

Hydrolysis of enol esters 0-83 Reduction of acyl halides 0-84 Reduction of carboxylic acids, esters, or anhydrides 0-85 Reduction of amides 0-95 Alkylation and hydrolysis of imines, alkylation of aldehydes 0-97 Alkylation and hydrolysis of dithi-anes... 

Monocationic acyl ions are readily prepared as persistent species in solutions of low nucleophile strength.68 These acyl ions have been thoroughly characterized by IR and NMR spectroscopy, and several acyl ion salts have been characterized by X-ray crystallography. The monocationic acyl ions are often prepared in situ from carboxylic acids, esters, or anhydrides, by the action of a strong Brpnsted acid, or the ions can be prepared from ionization of an appropriate acid halide with a strong Lewis acid. Both methods have been used to prepare acyl-centered dications, some of which can be considered distonic superelectrophiles. As described previously, dicarboxylic acids cleave to the bis-acyl ions in superacid (FSChH-SbFs) provided that the acyl cations are separated by at least three methylene units (eq 54).55 The first bis-acyl dications were reported by Olah and Comisarow, being prepared by the reactions of dicarboxylic acid fluorides with superacidic SbFs (eq 72).69... 

Carboxylic Acids, Esters, Chlorides, Anhydrides, Amides, and Nitriles The C=0... 

Food, flavors consist of numerous compounds, none of which alone is characteristic of specific food. Classes of compounds which emcompass food flavors are - hydrocarbons (aliphatic, ali-cyclic, aromatic) carbonyls (aldehydes, ketones) carboxylic acids, esters, imides, anhydrides alcohols, phenols, ethers alkylamines, alkylimines aliphatic sulfur compounds (thiols, mono-, di- and tri-sulfides) nitrogen heterocyclics (pyrroles, pyrazines, pyridines) sulfur heterocylics (thiophenes, thiazoles, trithiolane, thialidine) and oxygen-heterocyclics (lactone, pyrone, furan). Discussion will be limited to striking developments in heterocyclics. 

B-allyl-9-BBN reacts vigorously with acid chlorides and acid anhydrides slowly with carboxylic acid esters and N,N-dimethylbenzamide (Eq. 47)98). 

Carboxylic Acids, Ester, Chlorides Anhydrides, Amides and Nitriles ... 

Asymmetric Alkylation. 4-Pseudoephedrine ([IS, 2S]-(+)) is a commodity chemical employed in over-the-counter medications with annual worldwide production in excess of 300 metric tons. The enantiomer, /-pseudoephedrine, is also readily available in bulk and is inexpensive. Pseudoephedrine has been shown to be highly effective as a chiral auxiliary in asymmetric alkylation reactions. Treatment of either enantiomer of pseudoephedrine with carboxylic acid chlorides and anhydrides leads to efficient and selective iV-acylation to form the corresponding tertiary amide derivatives (Table 1). Typically, the only by-product in the acylation reactions is a small amount (<5%) of the A,0-diacylated product, which is easily removed by crystallization or flash column chromatography. Because intramolecular 0- -N acyl transfer within pseudoephedrine 3-amino esters occurs rapidly, and because the A-acyl form is strongly favored under neutral or basic conditions, products arising from (mono)acylation on oxygen rather than nitrogen are not observed. 

These reactions are used to make anhydrides, carboxylic acids, esters, and amides, but not acid chlorides, from other acyl compounds. Acid chlorides are the most reactive acyl compounds (they have the best leaving group), so they are not easily formed as a product of nucleophilic substitution reactions. They can only be prepared from carboxylic acids using special reagents, as discussed in Section 22.10A. 

Adducts (6) and (7) from amides and chlorophosphoric acid aiyl esters or dichlorophosphoric acid aryl esters respectively are well known. - The adducts are formed in a 1 1 ratio. They have been applied to the synthesis of mixed anhydrides from diarylphosphoric acids and carboxylic acids, as well as mixed substituted esters of pyrophosphoric acid. The adduct formation between primary or secondary carboxamides and dichlorophosphates has been used to prepare nitriles and isonitriles respectively. The adduct from DMF and phenyldichlorophosphate is a useful reagent for the preparation of carboxylic acid esters from the corresponding acids and alcohols, 3-lactams from imines and carboxylic acids," carboxylic acid anhydrides, carboxylic acid esters and thiol esters. Adducts of amides with ester amides or diamides of chlorophosphoric acid have been studied. ... 

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