Ammonium acetate mixture

Kim and Salem (1986) developed a technique for rapid and detailed molecular species analysis of PL with use of reversed-phase HPLC with on-line TS/MS. In conjunction with a hexane/methanol/0.2 m ammonium acetate mixture as mobile phase, the technique was generalized for natural mixtures of PC and PE. The positive ion spectra of PC gave fragments similar to those of ammonia Cl, but the TS produced much simpler spectra, with extremely low background. As an example, 16 0/18 1 GPC gave the DG ion at m/z 578, the result of a loss of the phosphocholine group. The ions derived from phosphocholine were detected at m/z 142 and 184, with the peak at m/z 142 usually more intense than that of m/z 184. The molecular ion was present as a protonated form at m/z 761. The m/z 142 ion was monitored for the detection of PC. Coupling of reversed-phase HPLC with MS detection allowed an extensive separation of the molecular species of egg yolk PC. The DG ion peaks, which are predominant in the TS spectra of PC, allowed an easy reconstruction of the 10 major molecular species of PC. 

Sample preparation Homogenize (Ultra-Turrax ION head) tissue with 4 vol of ice-cold pH 7.4 phosphate-buffered saline at 0° twice for 30 s each time, let stand at 4°C for 30 min, centrifuge at 2000 g for 10 min, add to a C8 SPE cartridge (Varian), wash and elute using MeCN/50 mM pH 4.0 ammonium acetate mixtures (unspecified). Evaporate the eluate to dryness under a stream of nitrogen at 40°, reconstitute the residue with MeOH 50 mM pH 4.0 ammonium acetate 50 50, inject a 75 p-L aliquot. 

The formation of ethyl isopropylidene cyanoacetate is an example of the Knoevenagel reaction (see Discussion before Section IV,123). With higher ketones a mixture of ammonium acetate and acetic acid is an effective catalyst the water formed is removed by azeotropic distillation with benzene. The essential step in the reaction with aqueous potassium cyanide is the addition of the cyanide ion to the p-end of the ap-double bond ... 

Isolation of dry, normal ammonium acetate, prepared by neutralizing acetic acid with anhydrous ammonia or ammonium carbonate, is difficult because of ammonia loss during evaporation of water. Consequendy, commercial grades of ammonium acetate are often mixtures of the neutral and acid salts, or are suppHed as ammonium acetate solution [8013-61-4]. 

A mixture of 105.6 g. (1.1 moles) of freshly distilled furfural, 87.0 g. (1.0 mole) of 98% cyanoacetic acid (Note 1), 3.0 g. of ammonium acetate, 200 ml. of toluene, and 110 ml. of pyridine is placed in a 1-1. round-bottomed flask equipped with a Stark and Dean water trap and reflux condenser. The mixture is boiled under reflux for 2 days. The theoretical quantity of water is collected in the trap within 1 hour. Upon completion of the reflux period, the solvent is removed under reduced pressure by heating on a water bath. The residue, distilled through a 15-cm. Vigreux column at 11 mm. pressure, yields 88.6-93.3 g. (74.5-78%) of colorless liquid boiling at 95-97°, 1.5823-1.5825. 

Cyanoamidines such as (10) are converted into the more useful 2-formyl-A-norsteroids (11) by reduction with lithium in methylamine (buffered with ammonium acetate) followed by hydrolysis on hydrated alumina. This yields a mixture containing approximately 5 parts of the 2j5-aldehyde and 3 parts of the 2a-aldehyde (11). Both aldehydes are smoothly dehydrogenated by 2,3-dichloro-5,6-dicyanobenzoquinone in the presence of acid to the 2-formyl--A-iiorsteroids (12). ... 

A green chemistry variation makes use of solventless conditions to minimize the waste stream from reactions of this type. To a mortar are added aldehyde 67, ketone 68 and solid sodium hydroxide. The mixture is ground and within 5 minutes aldol product 69 is produced. Addition of the second ketone and further grinding affords the 1,5-diketone 70, which can be isolated and cyclized to pyridine 71 with ammonium acetate. The authors report that this method can substantially reduce the solid waste (by over 29 times) and is about 600% more cost effective than previously published procedures. 

The o-aminophenylpropiolic acid 4 (20 g) in water (60 mL) and aqueous ammonia (9 mL, d = 0.88) was added with shaking during 15 minutes to a mixture prepared from ferrous sulfate (220 g), water (440 mL), and aqueous ammonia (110 mL, d = 0.88). After 45 minutes, with occasional shaking but no external cooling, the suspension was filtered. The residue was washed with water, and the combined filtrates were treated with ammonium acetate (60 g) and made weakly acidic with acetic acid. The solution was then cooled to 0°C by addition of crushed ice, and then made acidic to Congo-red with concentrated hydrochloric acid (70-80 mL). Additional hydrochloric acid (20 mL, 2 N) was immediately added, and the turbid solution which resulted was diazotized with 20% aqueous sodium nitrite, after which the mixture was kept at 70°C. The cinnoline acid 6 was separated over 45 minutes as a dark brown, granular solid (12.5 g), m.p. 260-265°C. ... 

Direct bromination readily yields the 6-bromo derivative (111), just as with uracil. Analogous chlorination and iodination requires the presence of alkalies and even then proceeds in low yield. The 6-chloro derivative (113) was also obtained by partial hydrolysis of the postulated 3,5,6-trichloro-l,2,4-triazine (e.g.. Section II,B,6). The 6-bromo derivative (5-bromo-6-azauracil) served as the starting substance for several other derivatives. It was converted to the amino derivative (114) by ammonium acetate which, by means of sodium nitrite in hydrochloric acid, yielded a mixture of 6-chloro and 6-hydroxy derivatives. A modified Schiemann reaction was not suitable for preparing the 6-fluoro derivative. The 6-hydroxy derivative (115) (an isomer of cyanuric acid and the most acidic substance of this group, pKa — 2.95) was more conveniently prepared by alkaline hydrolysis of the 6-amino derivative. Further the bromo derivative was reacted with ethanolamine to prepare the 6-(2-hydroxyethyl) derivative however, this could not be converted to the corresponding 2-chloroethyl derivative. Similarly, the dimethylamino, morpholino, and hydrazino derivatives were prepared from the 6-bromo com-pound. ... 

Extension of this work by studying the reaction of 3-methyl-5-nitro-pyrimidin-4(3//)-one with -X-arylketones in the presence of ammonium acetate surprisingly revealed the formation of a mixture of 4-arylpyrimidines and 6-arylpyridin-2(l//)-ones (00JCS(P1)27). The ratio between pyridine and pyrimidine formation is dependent on the substituent X. With electron-donating substituents the formation of the pyridin-2(l//)-ones is favored, with electron-attracting substituents the formation of the pyrimidine derivatives (Scheme 21) In the formation of the 6-arylpyridin-2(l//)-ones the C-4- C-5-C-6 part of the pyrimidone-4 is the building block in the construction of the pyridine ring. Therefore, the pyrimidone can be considered as an activated o -nitroformylacetic acid (Scheme 21). 

For most free amino acids and small peptides, a mixture of alcohol with water is a typical mobile phase composition in the reversed-phase mode for glycopeptide CSPs. For some bifunctional amino acids and most other compounds, however, aqueous buffer is usually necessary to enhance resolution. The types of buffers dictate the retention, efficiency and - to a lesser effect - selectivity of analytes. Tri-ethylammonium acetate and ammonium nitrate are the most effective buffer systems, while sodium citrate is also effective for the separation of profens on vancomycin CSP, and ammonium acetate is the most appropriate for LC/MS applications. 

Hence, water, ammonia, hydrogen fluoride and carbon dioxide separate from the mixture into the gaseous phase. However, despite the possibility of a solid-state interaction, the application of ammonium acetate solutions for washing of... 

The synthesis of imidazoles is another reaction where the assistance of microwaves has been intensely investigated. Apart from the first synthesis described since 1995 [40-42], recently a combinatorial synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles has been described on inorganic solid support imder solvent-free conditions [43]. Different aldehydes and 1,2 dicarbonyl compounds 42 (mainly benzil and analogues) were reacted in the presence of ammonium acetate to give the trisubstituted ring 43. When a primary amine was added to the mixture, the tetrasubstituted imidazoles were obtained (Scheme 13). The reaction was done by adsorption of the reagent on a solid support, such as silica gel, alumina, montmorillonite KIO, bentonite or alumina followed by microwave irradiation for 20 min in an open vial (multimode reactor). The authors observed that when a non-acid support was used, addition of acetic acid was necessary to obtain good yields of the products. 

In an off-line configuration, a complex peptide mixture from a proteomic sample is loaded onto a SCX column and fractions collected (Fig. 11.1). After the collection of fractions, they are then loaded into an autosampler and analyzed via the traditional RP/ MS/MS approach. Using this system, a variety of buffers and elution conditions may be used (Table 11.1). For example, one may use a volatile salt such as ammonium formate (Adkins et al., 2002 Blonder et al., 2004 Fujii et al., 2004 Yu et al., 2004 Qian et al., 2005a and b) or ammonium acetate (Cutillas et al., 2003 Coldham and Woodward, 2004), collect SCX fractions, lyophilize, resuspend in low acetonitrile and acid, and then directly analyze via RP/MS/MS. In most of the cases, when ammonium acetate or ammonium formate are used, a 20-minute wash period is used to remove the ammonium acetate or ammonium formate prior to the reversed-phase gradient (Table 11.1). However, because fractions are collected and can be buffer exchanged,... 

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