Acid Route

The preparation of amides via the free acid, diamine and catalysts, is also referred to as the Yamazaki reaction. Organic phosphor containing compounds, such as triphenyl phosphite are used as catalysts. In addition, in NMP/pyridine solvents, salts such as LiCl and CaCl2 are dissolved that favor polymerization. 

The reaction has to be conducted at elevated temperatures in order to achieve high-molecular-weight polymers. Isophthalic acid gives somewhat higher molecular weight polymers than terephthalic acid. Nevertheless, for certain types of PAs, products with only low molecular weights are obtained. The acid route is used rather for the preparation of specialized types of polyamides. 

---

Structurally the difference between PEN and PET is in the double (naphthenic) ring of the former compared to the single (benzene) ring of the latter. This leads to a stiffer chain so that both and are higher for PEN than for PET (Tg is 124°C for PEN, 75°C for PET is 270-273°C for PEN and 256-265°C for PET). Although PEN crystallises at a slower rate than PET, crystallization is (as with PET) enhanced by biaxial orientation and the barrier properties are much superior to PET with up to a fivefold enhancement in some cases. (As with many crystalline polymers the maximum rate of crystallisation occurs at temperatures about midway between Tg and in the case of both PEN and PET). At the present time PEN is significantly more expensive than PET partly due to the economies of scale and partly due to the fact that the transesterification route used with PEN is inherently more expensive than the direct acid routes now used with PET. This has led to the availability of copolymers and of blends which have intermediate properties. 

Nitrophosphate fertilizer is made by digesting phosphate rock with nitric acid. This is the nitrophosphate route leading to NPK fertilizers as in the mixed-acid route, potassium and other salts are added during the process. The resulting solution is cooled to precipitate calcium nitrate, which is removed by filtration methods. The filtrate is neutralized with ammonia, and the solution is evaporated to reduce the water content. The process of prilling may follow. The calcium nitrate filter cake can be further treated to produce a calcium nitrate fertilizer, pure calcium nitrate, or ammonium nitrate and calcium carbonate. 

European Fertilizer Manufacturers Association. 1995a. "Production of NPK Fertilizers by the Nitrophosphate Route." Booklet 7 of 8. Brussels, and 1995b. "Production of NPK Fertilizers by the Mixed Acid Route." Booklet 8 of 8. Brussels. 

SYNTHESIS OF MIXED OXIDES USING POLYBASIC CARBOXYLIC HYDROXY-AND AMINO-ACID ROUTES PROBLEMS AND PROSPECTS... 

In this paper we have tried to present a brief overview of state-of-the-art of the synthetic chemistry of oxide materials based on polybasic carboxylic hydroxy (amino) acid routes. It has been shown that, in spite of enormous number of papers on the subject (we have mentioned just a few latest references, significant efforts should be undertaken in order to... 

Alternatively, an acid route has also been reported [26], where the leaching is accomplished using a mixture of HNO3 and HF, and separation and recovery of the nickel and cadmium is performed with solvent extraction. First, in the cadmium circuit the leaching solution is adjusted to pH 3 prior to... 

As indicated by XRD patterns, there exist just 2-3 broad peaks in the calcined acid-made materials (Fig. 3A). Moreover, the N2 adsorption/desorption isotherm shown in Fig. 3B, the calcined acid-made mesoporous silica indeed possesses a broad capillary condensation at the partial pressure p/p0 of ca. 0.2-0.4, indicating a broad pore size distribution with a FWHM ca. 1.0 nm calculated from the BJH method. This is attributed to the occurrence of partial collapse of the mesostructure during the high temperature calcination. The hexagonal structure completely collapsed when subjected to further hydrothermal treatment in water at 100 °C for 3 h. Mesoporous silica materials synthesized from the acid route are commonly believed to be less stable than those from the alkaline route [6,7]. 

Scheme 9 Tetramic Acid Route to y-Amino-p-hydroxy Acids153 57 ...

Consideration of the tetrahydroiso-a-acids depends on their precursors. They are manufactured commercially from, ultimately, either a- or /3-acids. The chromatogram of those from the a-acid route demonstrate a chromatographic profile similar in detail to conventional iso-a-acids, with similar ratios of stereoisomers. Those derived from /3-acids look quite different. Because the /3-acids are racemic, there is a random distribution of orientations about the two adjacent chiral centers, which in practice results in the two peaks of about equal area for each of the... 

Whereas the importance of the exchange mechanism via route (i) is rapidly decreasing with decreasing acidity, route (ii) is facilitated by the increasing basicity of the superacid counterion. 

Figure 14.1 The precipitated calcium carbonate (PCC) production process A schematic representation, according to the acetic acid route [21, 51].

When it is required to prepare an a-bromo acid from a carboxylic acid which is not particularly readily available commercially, but which can be synthesised by the malonic acid route (Section 5.11.6, p. 680), advantage may be taken of the ease of bromination in the a-position of the intermediate alkylmalonic acid. The substituted bromomalonic acid undergoes ready decarboxylation on heating to yield the a-bromo acid (e.g. 2-bromo-3-methylpentanoic acid, Expt 5.166). 

Pogozelski WK, Tullius TD (1998) Oxidative strand scission of nucleic acids Routes initiated by hydrogen abstraction from the sugar moiety. Chem Rev 98 1089-1107 Poole JS, Eladad CM, Platz MJ, Fredin ZP, Pickard L, Guerrero EL, Kesser M, Chowdhury G, Kotande-niya D, Gates KS (2002) Photochemical electron transfer reactions of tirapazamine. Photochem Photobiol 75 339-345... 

L.M. Marzo, Nitric Acid Route Recovers More Heat From Tailgas , Chemical Engineering, 26 November, pp.36-37 (1973). 

Pogozelski WK, Thomas DT. Oxidative strand scission of nucleic acids routes initiated by hydrogen abstraction from sugar moiety. Chem Rev 1998 98 1089-107. 

---