Carboxylates, ammonium

Many of these salts melt or sublime before or during decomposition and reaction temperatures generally increase with molar mass. Thermal analyses for a selection of ammonium carboxylates have been given by Erdey et al. [915] who conclude that the base strength of the anion increases with temperature until it reaches that of NH3. Decompositions of ammonium acetate ( 333 K) and ammonium oxalate ( 473 K) proceed through amide formation. Ammonium benzoate and ammonium salicylate sublime ( 373 K) without decomposition but ammonium citrate decomposes ( 423 K) to yield some residual carbon. 

Hajek et al. [173] have reported a detailed kinetic study of the solid phase decomposition of the ammonium salts of terephthalic and iso-phthalic acids in an inert-gas fluidized bed (373—473 K). Simultaneous release of both NH3 molecules occurred in the diammonium salts, without dehydration or amide formation. Reactant crystallites maintained their external shape and size during decomposition, the rate obeying the contracting volume equation [eqn. (7), n = 3]. For reaction at 423 K of material having particle sizes 0.25—0.40 mm, the rate coefficients for decompositions of diammonium terephthalate, monoammonium tere-phthalate and diammonium isophthalate were in the ratio 7.4 1.0 134 and values of E (in the same sequence) were 87,108 and 99 kJ mole-1. 

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Amides are sometimes prepared directly from carboxylic acids and amines by a two step process The first step is an acid-base reaction m which the acid and the amine combine to form an ammonium carboxylate salt On heating the ammonium carboxy late salt loses water to form an amide... 

Low surface energy substrates, such as polyethylene or polypropylene, are generally difficult to bond with adhesives. However, cyanoacrylate-based adhesives can be effectively utilized to bond polyolefins with the use of the proper primer/activa-tor on the surface. Primer materials include tertiary aliphatic and aromatic amines, trialkyl ammonium carboxylate salts, tetraalkyl ammonium salts, phosphines, and organometallic compounds, which are initiators for alkyl cyanoacrylate polymerization [33-36]. The primer is applied as a dilute solution to the polyolefin surface, solvent is allowed to evaporate, and the specimens are assembled with a small amount of the adhesive. With the use of primers, adhesive strength can be so strong that substrate failure occurs during the course of the shear tests, as shown in Fig. 11. 

It is thought that these trialkonolamine borates may enhance the reactivity of the rhodium carbonyl anions by minimizing their tendency to form contact ion pairs in solution under the reaction conditions employed. The same patent discloses that ammonium salts and salts of Groups I and II, especially cesium and ammonium carboxylate salts, function as promoters (63). 

Rh complexes with ChiraPhos, PyrPhos, or ferrocenyl phosphines lacking amino alkyl side chains (such as BPPFA) are much less active toward tetrasubstituted olefins. Table 6-1 shows that in asymmetric hydrogenations catalyzed by 5a-d, the coordinated Rh complex exerts high selectivity on various substrates. It is postulated that the terminal amino group in the ligand forms an ammonium carboxylate with the olefinic substrates and attracts the substrate to the coordination site of the catalyst to facilitate the hydrogenation. 

Fig. 9.1 Yields and ee values for ring-opened products prepared using [Rh(PPF-P Bu2)l] catalyst in the presence of activated amines, malonates, or ammonium carboxylates.

The isomerization from 10 to 11 in the crystalUne state requires not only the movements of atoms but also a change in the crystal symmetry and the reconstruction of the hydrogen bond network pattern. In the crystals of these primary ammonium carboxylates, ID ladder-type hydrogen bonds are observed. The isomerization from the ZZ to EE form is associated with the rotation of carbonyl groups and the change in the hydrogen bond structure in this case. The quantitative transformation of 10 to 11 in the crystalUne state suggests that the molecular motion in the crystals occurred cooperatively with the minimum movement of atoms in the crystals via a phase transition from the crystal of 10... 

In addition to transacylation reactions and the heating of ammonium carboxylates (Section 16.3), unsubstituted amides may be prepared by careful partial hydrolysis of nitriles ... 

Similar effects of relative permitivity D on the cyclotrimerization were also observed in the case of substituted ammonium carboxylate catalysts. It was also observed that, besides relative permitivity, the specific solvation of reactants by aprotic dipolar solvents had a considerable effect on the rate constant of cyclotrimerization of isocyanates (see Table II). 

By adjusting the exposure time, quantitative conversion of carboxylic acid groups (followed near 1710 cm 1) can be obtained (fig. 5). Typical bands at 1836, 1796 and 1555 cm 1 correspond to acid fluorides, acid chlorides and ammonium carboxylates groups respectively. In the case of EMA (Ethylene-Methacrylic acid) some sodium carboxylate groups were initially present. FTIR analysis showed that these functions (1559 cm 1) were also converted into acid fluorides ... 

The mechanism of carbodiimide-mediated amide formation is outlined in Figure 13.4. The first intermediate formed during the reaction of a carbodiimide with a carboxylic acid (or an ammonium carboxylate [56]) is an O-acylisourea [1]. Under acidic conditions [57,58], this intermediate reacts with acids to yield anhydrides, and with alcohols, phenols, HOBt, or other compounds containing hydroxyl groups, to yield the corresponding esters. The carbodiimide is thereby transformed into a urea. 

Initiation takes place by rapid reaction of an ammonium salt with the anhydride (Eq. (46)) whereby ammonium carboxylate is formed. In the propagation step, the carboxylate anion opens an epoxy ring and forms an ammonium alcoholate (Eq. (47)). The latter reacts with the anhydride to yield another ester bond, and ammonium carboxylate is recovered (Eq. (48)). Termination occurs through decomposition of the ammonium counter ion, the alkoxide anion abstracting a proton from the quaternary nitrogen with the formation of a deactivated tertiary amine. 

Other groups [99, 100] investigated the possibility of carrying out a surfactant-assisted polymerization of VDF in scC02, using diethyl peroxydicarbonate (DEPDC) as a free radical initiator, with the aim of testing several perfluoropolyether compounds synthesized by Solvay Solexis as stabilizers. When ammonium carboxylate derivatives were used, an effective stabilization of the polymer particles was obtained, and the polymer was collected from the reactor with yields of up to 63%. This corresponded to a solid content in the reactor of 220 g I in the form... 

Figure 5. N—H bond lengths in N—H O hydrogen bonding systems. The phenomenon of N—H bond stretching is only weakly represented (if at all), probably because there are only few nearly matched systems that have been characterized by neutron diffraction. Neutron diffraction data are from the CSD. From top to bottom all N—ammonium-carboxylate, ApKa 5 neutral heterocycle-...

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