Carboxylic amides, reactivity

The rearrangement of oximes 1 under the influence of acidic reagents to yield A -substituted carboxylic amides 2, is called the Beckmann rearrangement. The reaction is usually applied to ketoximes aldoximes often are less reactive. 

Oxidation by ultra-hot-air treatment for polyolefins exposition to a blast of hot air (roughly 500°C) for a short time to oxidize the surface and create reactive sites such as hydroxyl, carbonyl, carboxyl, amides... Rather similar to flame treatment, it is particularly used for polyethylene and polypropylene. 

Two derivatives of nicotinamide (pyridine-3-carboxylic amide), one of the B2 vitamins, nicotinamide adenine dinucleotide (NAD ) and nicotinamide adenine dinucleotide phosphate (NADP ), serve as redox coenzymes. Of the three heterocyclic ring systems found in these coenzymes, i.e. those of purine, ribose and pyridine, it is the pyridine portion that is reactive in redox reactions. Biologically, two oxidation states are important the oxidized form, NAD(P)+, and the 1,4-dihydro isomer of the two-electron reduced form, NAD(P)H (Scheme 1). Nicotinamide coenzymes interconvert between these two oxidation states in... 

A number of 1,2-dithiolecarboxylic acid derivatives are known. These appear to have typical carboxylic acid reactivity and form acid halides, esters, amides, etc. (67ZC275,72BSF1840), and undergo internal Friedel-Crafts acylation with aromatic substituents (72BSF1840,73BSF721). 

The N-phosphonium salts of pyridines given by the oxidation of phosphorous acid and its esters are very reactive to nucleophiles, activating carboxy, amino, or hydroxy compounds to yield the corresponding carboxylic amides and esters in high yields on further aminolysis, alcoholysis, and acidolysis2 ... 

Azetidin-2-ones are more reactive than y- and <5-lactams because of ring strain. This is true for the alkaline fission to give salts of / amino carboxylic acids, as well as for the acid-catalysed hydrolysis to fi-carboxyethylammonium salts. Starting from alkenes and chlorosulfonyl isocyanate, a stereocontrolled synthesis of / -amino carboxylic acids can be realized. Ammonia and amines react with azetidin-2-ones, also with ring-opening, to produce / -amino carboxylic amides. Hence they are acylated by azetidin-2-ones ... 

Selective reduction of aldehydes in the presence of ketones can be effected with tetra-n-butylammonium triacetoxyborohydride and other reagents. Although lithium aluminium hydride is used most commonly for the reduction of carboxylic esters, sodium borohydride can provide some useful selectivity and its reactivity is enhanced in the presence of metal salts. For example, reduction of carboxylic esters in the presence of carboxylic amides is possible using sodium borohydride and calcium chloride. 

Zinc neutralized, ethylene-methacrylic acid copolymer ionomer Zinc carboxylate Low reactivity with amine but good polar interaction of Zn with amide and amine groups (interfacial complexation) Tg not low cmough, limits low temp, toughness Good solvent resistanee... 

The neutral and acid-catalyzed hydrolyses of a series of phosphoric carboxylic imides X2P(0)NRC(0)R (28) (X = EtO, MeO, Et R = H, Me R = Me, Ph) have been compared with the behavior of related carboxylic acid and phosphoric amides, particularly in acidic conditions where the latter two systems differ greatly. In acid the carboxylic amides react slowly by attack of solvent on the oxygen-protonated form of the substrate and the phosphoric amide reacts rapidly by direct Sjv2(P) displacement via an N-protonated substrate. The acid hydrolysis of (28) lies between these two extremes with the protonation of carbonyl oxygen stabilizing the resonance structure which renders the phosphorus atom more electrophilic and the P-N bond less labile with the consequence that the reactivity of the P-N and C-N linkages become comparable. ... 

The chemistry of the carbonyl group is probably the single most important aspect of organic chemical reactivity Classes of compounds that contain the carbonyl group include many derived from carboxylic acids (acyl chlorides acid anhydrides esters and amides) as well as the two related classes discussed m this chapter aldehydes and ketones... 

Amines are convert ed to amides on reaction with acyl chlorides Other acylating agents such as carboxylic acid anhydrides and esters may also be used but are less reactive... 

As with polyesters, the amidation reaction of acid chlorides may be carried out in solution because of the enhanced reactivity of acid chlorides compared with carboxylic acids. A technique known as interfacial polymerization has been employed for the formation of polyamides and other step-growth polymers, including polyesters, polyurethanes, and polycarbonates. In this method the polymerization is carried out at the interface between two immiscible solutions, one of which contains one of the dissolved reactants, while the second monomer is dissolved in the other. Figure 5.7 shows a polyamide film forming at the interface between an aqueous solution of a diamine layered on a solution of a diacid chloride in an organic solvent. In this form interfacial polymerization is part of the standard repertoire of chemical demonstrations. It is sometimes called the nylon rope trick because of the filament of nylon produced by withdrawing the collapsed film. 

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). 

Chemical Properties. The chemical reactivity of nylon is a function of the amide groups and the amine and carboxyl ends. The aHphatic segment of the chain is relatively stable. 

Much of protein engineering concerns attempts to explore the relationship between protein stmcture and function. Proteins are polymers of amino acids (qv), which have general stmcture +H3N—CHR—COO , where R, the amino acid side chain, determines the unique identity and hence the stmcture and reactivity of the amino acid (Fig. 1, Table 1). Formation of a polypeptide or protein from the constituent amino acids involves the condensation of the amino-nitrogen of one residue to the carboxylate-carbon of another residue to form an amide, also called peptide, bond and water. The linear order in which amino acids are linked in the protein is called the primary stmcture of the protein or, more commonly, the amino acid sequence. Only 20 amino acid stmctures are used commonly in the cellular biosynthesis of proteins (qv). 

Some amides and hydrazides that have been prepared to protect carboxyl groups are included in Reactivity Chart 6. 

In the case of esters, carboxylate anions, amides, and acid chlorides, the tetrahedral adduct may undergo elimination. The elimination forms a ketone, permitting a second addition step to occur. The rate at which breakdown of the tetrahedral adduct occurs is a function of the reactivity of the heteroatom substituent as a leaving group. The order of stability of the... 

There are large differences in reactivity among the various carboxylic acid derivatives, such as amides, esters, and acyl chlorides. One important factor is the resonance stabilization provided by the heteroatom. This decreases in the order N > O > Cl. Electron donation reduces the electrophilicity of the carbonyl group, and the corresponding stabilization is lost in the tetrahedral intermediate. 

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 ... 

Nickel peroxide is a solid, insoluble oxidant prepared by reaction of nickel (II) salts with hypochlorite or ozone in aqueous alkaline solution. This reagent when used in nonpolar medium is similar to, but more reactive than, activated manganese dioxide in selectively oxidizing allylic or acetylenic alcohols. It also reacts rapidly with amines, phenols, hydrazones and sulfides so that selective oxidation of allylic alcohols in the presence of these functionalities may not be possible. In basic media the oxidizing power of nickel peroxide is increased and saturated primary alcohols can be oxidized directly to carboxylic acids. In the presence of ammonia at —20°, primary allylic alcohols give amides while at elevated temperatures nitriles are formed. At elevated temperatures efficient cleavage of a-glycols, a-ketols... 

FIGURE 20.1 Structure, reactivity, and carbonyl-group stabilization in carboxylic acid derivatives. Acyl chlorides are the most reactive, amides the least reactive. Acyl chlorides have the least stabilized carbonyl group, amides the most. Conversion of one class of compounds to another is feasible only in the direction that leads to a more stabilized carbonyl group that is, from more reactive to less reactive. 

Amides are the least reactive carboxylic acid derivative, and the only nucleophilic acyl substitution reaction they undergo is hydrolysis. Amides are fairly stable in water, but the amide bond is cleaved on heating in the presence of strong acids or bases. Nominally, this cleavage produces an amine and a car boxylic acid. 

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